| Blitz |
I have read Aleph-X threats now for 8 hours and I have to admit that I am not yet through with everything. But even with extensive usage of the search functionality I have found some comments how to come to a high-power version of an Aleph-X, but I am not sure if they included all information to be considered. Therefore I would like to collect some of your experiences on that topic as I can imagine that there are some more DIYs out there who have planned to go for an Aleph 2, changed now there mind and want the same thing in terms of power, but with advantages of the Aleph-X.
Here now some thoughts / questions:
- Heatsinking: Also when utilizing now IRFP044 under very different voltages, we are in the same ballpark with the Aleph 2, right ?
- Voltages: Instead of 45 VDC, we are looking now for 15 VDC in the schematics I have seen. Will this hold to be true if raising the IRFP044 from 4 pcs/channel to 12/channel ( The Alephs raised voltages with growing number of fets ?)?
- Components to be trippled: When now coming from 4 044 up to 12: Will really only the fets be trippled or all components around them as well ( what my understanding is right now): In Grey's schematic this would be r7, r5, q1, q2, r6, r9. What about the circuit around the mpsa18 which drive q1 ? Will this drive as many IRFs as I put in parallel or has it as well to be trippled ?
- Are there any other issues to be considered, why in some threats is has been stated that the time is not yet there to go for a high-powered version ?
Regarding Components: What would be your recommendation: IRFP240 (which gives me the option to go back to the Aleph 2 if the Aleph-X is not my pair of shoes) or thhe IRFP044N (which cost me the same, but if have read somwhere the the N-Version is not that suitable for audio; the superior 044 VErsion is diffcult to get though).
Regarding separate PSU for the driver-stage: Do the same comments on the Aleph apply here (meaing not possible as part of the concept) or could this be an improvement ?
THanks & Best Regards |
|
|
| Jens |
Blitz,
- Heatsinking: Also when utilizing now IRFP044 under very different voltages, we are in the same ballpark with the Aleph 2, right ?
> Yes <
- Voltages: Instead of 45 VDC, we are looking now for 15 VDC in the schematics I have seen. Will this hold to be true if raising the IRFP044 from 4 pcs/channel to 12/channel ( The Alephs raised voltages with growing number of fets ?)?
> I’ll go for 22 VDC on 12 IRF240 <
- Components to be trippled: When now coming from 4 044 up to 12: Will really only the fets be trippled or all components around them as well ( what my understanding is right now): In Grey's schematic this would be r7, r5, q1, q2, r6, r9. What about the circuit around the mpsa18 which drive q1 ? Will this drive as many IRFs as I put in parallel or has it as well to be trippled ?
> Include r36, r38, r40, r41, q10 and q11. “Only” q1, q2, q10 and q11 are controlled by the circuits around q3, q4, q8 and q9 (MPSA18). <
- Are there any other issues to be considered, why in some threats is has been stated that the time is not yet there to go for a high-powered version ?
> Uplift the current sources, I’ll go for some 7A all-in-all, using 0R39 source resistors <
Jens |
|
|
| Cobra2 |
A high power Aleph-X, Just what I also had in mind... :)
Can someone please post schematics on a few versions of this?
Something around 150W+ would suit me perfectly!
Arne K
NORWAY:) |
|
|
| Variac |
Blitz, you beat me to it! I think there are a lot of people out there with Aleph 2's or that they might want to convert or who just want a more powerful Aleph X.
In my case a have 24 IRF 140's, and 2) 37.5 volts toroids.
Cobra:
Because people will be converting from the Aleph 2 could we agree on 100w. ch for the moment? That extra 50 watts would hardly be noticed maybe?
Everyone: Does the standard Aleph X that you have been discussing have a lower voltage just because it is lower powered? or the the X use lower volts for the same output?
Can I use my toroids?
Thanks all |
|
|
| grataku |
Cobra,
nobody, that I know of, has drawn up the schematic for this yet, actually I did but that's besides the point. If you plan to be successful in your high power Aleph X you got to be ready to study the aleph, Zen4, and AlephX thread in detail and thuroghly understand what you dealing with and be ready to make mods when mods need to be made. Even though all the info you need are pretty much available, nobody besides Pass labs has built anything close to what you want.
Calculate all voltages and currents, size out all the components. If you have SPECIFIC question on points that you don't understand I think members will be happy to help out. |
|
|
| Jens |
Cobra2:
To get 150W on 8 ohm, you need about 28VDC, 4,35 A current, 12 x Power MOSFETs and source resistors of 0R68 – if I’m not wrong on this.
Variac:
Compared to the Aleph, the Aleph-X used 1/2 voltage and double bias.
Jens |
|
|
| Variac |
Thanks Jens, that's the sort of concise reply that is soooo helpful
For me this is just for long term planning. Now I know to use those toriods in another project- unless I want 200w/ ch !!!!!
:devily: |
|
|
| grataku |
Jens, the current you are proposing is really bare bones for 150W,
you are going to be short if your speakers impedance drop to even 6ohms.
Nelson uses 8amps and +-30V for 200W. I would plan for at least 6 amp bias xchn. |
|
|
| Blitz |
Variac,
I have not yet simulated this in PSU-Designer, but I would consider a choke-input-setup, where you have a anyhow a much lower VDC compared to a pi-filter (in theory instead of VDC= VAC*1,414, it would be VDC=VAC*0,9). MArk Levinson has used this in his Cello-Amplifiers as it reduces power-supplier-noise (smoothes the spikes produced by a pi-filter)and gives nice regulation. The trick is to calculate the inductance correct, which is quite small here compared to tube equipment. So, in the case of 28 VDC with 4,350 A it would be 6,5 mH (more is no problem). If you still have to much VDC, have another RC-filter to follow (so you end up with an LCRC-Filter).
Best REgards |
|
|
| Jens |
Mark:
100W on 8 ohm means about 23VDC and 3.55 A bias.
200W on 8 ohm means about 32VDC and 5A bias.
grataku:
I said 8 ohm… you are right
150W on 6 ohm means about 28VDC and 5A bias.
150W on 4 ohm means about 28VDC and 6.12A bias.
Jens |
|
|
| Blitz |
Jens,
I just found a threat around Aleph X-Biasing:
http://www.diyaudio.com/forums/show...ias+calculation
It seems that your cals are right for one side of the Aleph-X, but as we have two (per channel), the current needs to be doubled, so for 150 W into 8 ohms it would have to be 8,66A @ 34,6 V. Sorry, just found these formulas a minute ago. So, let'S do some calcs with them:
8 ohm:
60 Watt: 21,9 V, 5,4 A
100 Watt: 28,3 V, 7,1 A
150 Watt: 34,4 V, 8,6 A
6 Ohm:
60 Watt: 19 V, 6,3 A
100 Watt: 24,5 V, 8,2 A
150 Watt: 30 V, 10 A
4 Ohm:
60 Watt: 15,5 V, 7,7 A
100 Watt: 20 V, 10 A
150 Watt: 24,4 V, 12,2 A
Well, how much Fets should I use now to get the power desired ? From Mr. Pass we learn that he uses his devices at 18 Watt dissipation, 2 Amp each and max 70volts (I wonder from where these 70V should come from). On the other hand he states that he gets 200 Watt from 32 fets. If I get this right now, for 100 Watt we would need not the originally planned 12 fets, but 16. If you want to go for 150 Watt. this would be 24...wow. |
|
|
| Variac |
woohoooo we're off!!
Blitz: Ironically about 6 months ago, after bothering lots of people here, I got the message about the inductor being first in line lowering the voltage. This was to use my 37 volt transformers in a Son of Zen. I had been looking forward to using them in a more conventional pi configuration in an Aleph 2.
But now suddenly now that the Aleph X is the hot ticket, I'm back to the same problem. Oh well, I guess I'l just leave them in the SOZ (stll not hooked up- but verry close) I believe Nelson says even 2 mH does a great job filtering- but for the
LC arrangement you are prob right! Thank you
HAppy holidays |
|
|
| hifiZen |
Just remember that a choke-input filter needs to be loaded with a minimum current at all times, otherwise the output voltage will rise, possibly exceeding the rating of your caps! *kapow!*
That would <i>not</i> be pretty! :o |
|
|
| Cobra2 |
Now we are getting somewhere...:)
I have read almost all of the documentation, but silly me, do not understand more than half... And these treads spreads, and tend to get very long...
So I really appreciate when scaling info is posted, with examples.
And the "X" have hold me back from assembling the "2", witch I otherwise would have asked for help for making into a "1,6" (something inbetween the 2 and 1,2).
Yes, I woud probably be happy with 100W, If I did not know...
ArneK
NORWAY
(With europeean all time high price on el-power coming...) |
|
|
| Blitz |
OK, reading further does not necessarily help to avoid confusions...I am studying not the Aleph-X-Thread and just have found some calcs from GRey which look quite different:
The voltage has to multiplied by 0,8 and the current is only half of the current which was stated in the link above, so Jens would be in the right ballpark again.
Is this now the right formular ? |
|
|
| Blitz |
OK. It does not become clearer when looking into the XA-200 Owner's manual:
http://www.passlabs.com/pdf/xa200man.pdf
There it is stated that the xa-200 powersupply with +-35 Volts at 30 Amps ! This is quite different from the 30 Volts at 5 Amps stated somewhere in the threat. So do we have to double now the current or not ?
BTW: The XA-200 has about 400000uF on board. Wow.
The comment on the choke-input is absolutety correct, that is especially true for tube equipment, if you have not heated the tubes and they don't draw any current yet. Voltages raise and your capacitors can blow, if you have not a bleeder resistor which always draws some current. But with SS ? Should draw current all the time, or ? |
|
|
| Variac |
fortunately with class A especially I think the coils are always loaded. Now if the mosfets blow? then no current then the caps go bang? On my Son of Zen this might be an issue with only 2 Mosfets per channel but balanced, so if one blows, current shuts down! Luckily I used higher voltage caps.
This brings up a point: A huge cap supply is cheaper with the lower voltage X aleph since lower voltage rated caps are a lot cheaper. BUT you wouldn't want to do the coils right after the bridge topography with the lower rated caps- rather you should use the "correct" transformer
As always, p;lease correct me |
|
|
| Blitz |
| Well, with PSU-Designer you can see nicely what the voltage after the choke would be. If you set the inductance higher then needed you have enough headroom, even if one mosfet would blow up. As well it has been reported that the oversizing of the transformer has not to be done like you normally do it: This seem to become very clear when you look at the current spikes generated in a pi-filter. Most Transformer are heavily oversized for normal operation, but the spikes are so huge, that any reserve to handle them is appreciated and improves the sound. With a choke-input you have no spikes. So, you have solved the problem at its root... |
|
|
| diyman |
Based on Blitz, to have an output of 150W at 8 ohms, we need a +/- 34.4V @ 8.6A power supply. At this voltage which is more than double the original +/- 15V supply, do we need to rescale the values of the other resistors in addition to those used for bias adjustment?? If we do, can I use those values of the Aleph 60 that runs at +/- 35V ??
For bias current adjustment, the low value resistors will be calculated to give a total 8.6A as required.
ckt |
|
|
| Blitz |
DIYman,
As stated above, I have read further through the threat's (not should mean now...typo...). Grey stated that the voltage has to be mupliplied by 0,8, so it is not 34,4, but 27,7 for 150 W at 8 ohms.
Still, we have a bit confusion: If I understood Audiofreak right we need 8,6 A (see link above). Grey clearly stated that half of this is enough (in the Aleph-X-Threat). So, let's wait and see if we can receive some feedback from them.
By the way: Grey has as well published a formular to calc the source resistor accordingly: Rs=(0,5/(I/2)) which in this case would lead us to 0,23 ohm for 4,3 or 0,115 ohms for 8,6.
Best Regards |
|
|
| diyman |
Blitz,
Thanx for the info. In fact calculating the value of source resistors as you mentioned should not be a problem as Grey 's formula is very straight forward. In fact, what I'm curious are the values of the OTHER RESISTORS. If you run the circuit at 27.7V(assuming its correct!), it's still more than double the original supply voltage of +/- 12V. If you compare the resistor values of the Aleph 30 which runs at +/- 25V, you will notice that some of the other resistors are slightly different from the original Aleph-X. So if we scale the power supply to +/- 27.7V @ 8.6A, do we just apply the higher voltage with the correct source resistors values only or do we have to scale the other resistors as well?
ckt :confused: |
|
|
| Edwin Dorre |
| quote: | Originally posted by Blitz
I have read Aleph-X threats now for 8 hours and I have to admit that I am not yet through with everything. |
I have lots of the same questions. Perhaps someone with a lot of knowledge of the X design can make a cook book.
As input parameter; X watts at Y ohms, number of fets and a few (or a lot) of calculations for the volts, amps of bias, ohms of resistors, watts per fet etc. comes out (excel sheet?) .
This will save us a lot of reading and like me I can use all the help I can get. The Aleph-X thread is too long and has too much non-aleph-X info in it. For my Aleph 4 I used mark finnish his doc a lot.
Perhaps a volunteer?
Edwin |
|
|
| Blitz |
Edwin,
This would be great, but I guess that is more than we can expect.
That's why I started this threat: Clarify the open upscaling questions and once this is clear, it easy to make the cals like I started it above. In parallel I am now reading through the Aleph-X-Threat (440 Word-pages) and delete everthing which is only noise / raw information, but does not influence the schematic of the amp. ONce I have a consolidated version of this thrat, I am happy to share this with you.
Best REgards |
|
|
| Blitz |
From Mr. Pass:
"The XA200 has a CRCRC (cap/thermistor/cap/thermistor/cap)
filter for the power supply. At about an 8 amp bias, the
remaining ripple is about .02 volts."
Interesting...especially the 8 amps...are these per channel or per side ? I guess per side: If he has 32 mosfets in total, 16 per channel, 8 are current sources, 8 are output devices, 2 sides with 4 outputdevices each, each draws 2 A (most of the data comes from the owner's manual), this would mean 8 A bias for each crcrc-filter, meaning that we have 16 A in one channel, meaning that Grey's calcs on current are wrong, and Audiofreak is right.
Any thoughts ? |
|
|
| Blitz |
Sorry guys, just found this from Mr. Pass on the xa-200:
Posted by Nelson Pass on 09-11-2002 08:00 PM:
"Been covered before. 4 banks of 8 matched devices."
So, a xa-200 has per channel 32 mosfets. Mmmmmh. I hope I understand my mistake now: The output is like a circutron, Therfore the current of the two sides don't add each other...When I have 32 mosfets, it come down to 8 output fets per side...each should than only draw 1 A instead of two. The pass-side says 2 A .. I am getting confused. Any thoughts ? |
|
|
| paulb |
| quote: | Originally posted by Blitz
I am now reading through the Aleph-X-Threat (440 Word-pages) and delete everthing which is only noise / raw information, but does not influence the schematic of the amp. ONce I have a consolidated version of this thrat, I am happy to share this with you.
|
Blitz, good idea. Could you post this on this Wiki? |
|
|
| wuffwaff |
Ok,
I´ll try.
First it is very important not to confuse effective and peak (x2^0.5) values cause this makes things very complicated.
Lets say you want 200 watts in 8 ohms this means 40 volts and 5 Amps both effective values.
This is independent of class a,b,c,d,t or x.
Now you must calculate the peak values voltage = 40x 1.41=56.56
current = 5 x 1.41 = 7.07A
These are the values an amp must be able to deliver into an 8 ohm load.
Now for an Aleph X:
Since the amp is sort of bridged each output has to deliver half the voltage wich in this case is 56,56/2=28,28volt. To allow for losses driving the fets and over the source resistors the supply voltage has to be about 2 to 3 volts higher so + and - 30 to 31 volts.
The current that has to be delivered goes through both amps so it still is 7.07 amps. But since you have two amps total current is 14.14 amps.
Nice thing about the active current source is that it can actually double it´s output so total bias for an Aleph X is 14,14/2 = 7,07 amps.
This amp will dissipate 7,07 x 31 x 2 = 438 Watts for one channel.
More dissipation will be in the transformers, diodes, chokes etc. so 500-550 watts per channel is not unrealistic.
This means the transformer has to be about 1000-1500VA depending on personal taste. The secondary voltage depends a lot on wich diodes and/or chokes are used but won´t be much less than the supply voltage (so 28-31 volts). It is very important to calculate this before ordering!
I think it equally important to read Pass Labs user manuals very carefully and look at all the specs as nice but not neccessarily precise information.:cool:
william |
|
|
| Blitz |
Thanks for this summary. After now going to numerous threats, I know that this is the coreect way to calculate it and you have even made us aware of other variables in the equasion. Thanks a lot.
Before I now calcualte the new, right values for the different setups (for the lazy bones): What would be your recommendation on the number of mosfets ? Let's take your example: 200 Watts in 8 ohms:
Power Dissipation only in the mosfets would be: 28,3*7,1*2= 400 Watt. When using 16 Mosfets (Let's assume 044Ns), we have 25 Watt / device at 28,3 V and 0,88 A, Correct ?
Now, from a power dissipation point of view this seems to be feasable. I read somewhere that the fets sound better the more current we put through them tough. Some put 2 A amps through them. Is it really the current which make them sound better or the power dissipation ?
Theoretically this example should result in the same values the XA-200 has. Well, still the 2 A through each Mosfets is not feasible yet or will the peak current be 0,88A * 2 ( I thought the factor 2 was already inculded in the equation above )?
Best Regards |
|
|
| nobody special |
William,
Nice and concise! It's about time someone posted that...
I have been reading the x thread from the beginning, and it took me a while to sort through the calculations on my own... it's sort of a tricky circuit- with the active current sources and the bridged output stage.
One thing that nobody seems to talk about when considering dissipation is how much it will go up under normal operation when the active current sources "kick in". I assume that most listening will be using around 1-2 watts maximum, and that the peak demands will be very short in duration. Any thoughts on this?
I have calculated my heatsinking to have a 19° C temp rise at idle, but I'm wondering how much heat I will really see in actual operation.
My amp will be a 40 watt/ 8 ohm- 12 output devices / channel... max of about 60W- current limited into lower impedances. Can't wait to see some of the higher powered versions! Unfortunately, my heat sinks just can not handle any more, or I would crank the bias up.
-NS |
|
|
| wuffwaff |
NS,
dissipation in the output fets is at it´s highest when no power is delivered. So actually the amp will cool down when delivering real power (this power is used to heat up your speakers).
With the X the two active current sources will work together in such a way that when one doubles the current, the other one will shut of so total current draw will be constant all of the time independent of input signal and/or load.
william |
|
|
| nobody special |
William,
I did not know that about the current sources! Thanks for the info...
I am tempted to increase the bias now, considering this new information. My speakers have a minimum impedance of about 3.2 ohms, so any increase in bias will help me out. Thankfully, they are about 92.5 db / 1 watt, so I don't need a whole lot of power.
-NS |
|
|
| wuffwaff |
Blitz,
yes, power dissipation per fet is roughly total dissipation/number of fets so in this case about 438/16 = 27.4 watts per fet (the error made here is total bias/(total fets) x (source resistor value).
I don´t think 27 watts per fet is too much but it depends on heatsink temperature and method of mounting the fets. I like to keep dissipation per fet at 20-25 watts. This allows for quite high heatsink temperatures (summer....).
Also the more fets the lower the voltage drop over the source resistors giving a bit higher efficiency and more power into lower impedances.
william |
|
|
| Blitz |
Here I found an alternative way of calculationg the bias, which basically seems to adress the changing impedance with frequency of most speakers, but results in much higher bias as calculated above I guess (Upto 8/3 times higher if you calculate for a 8 ohm speaker with a 3 ohm minimum) to keep full power over the whole frequency band (while we could question that assumption as I guess most speakers have there minimum at the lower end where they need real power):
"Now, if you used 8 ohms as your reference load, then there are a couple of different ways of going about the calculations for lower load impedances, depending on what you want to achieve. They will give different results... let me elaborate:
You have two choices:
1. set up the amp for 8 ohm loads, then calculate what kind of power you will be able to get into a 4 or 2 ohm load.
2. Set up the voltage rails for the desired peak power into 8 ohms, then calculate what current will be required to drive this voltage into a lower impedance load, and set the bias current accordingly.
Method 1 just tells you how much power you can get into a lower load impedance. If you attempt to drive a low value load with an amplifier set up this way, you will not be able to drive peak voltage into the load... your amp will be current limited into loads under 8 ohms.
Method 2 allows you to drive 8 ohms at the desired power level, and ensures that your amp will be voltage-limited into lower loads, down to 4 ohms or whatever you used to calculate the bias current. This method of course results in much higher idle currents, since it will be necessary to drive lower loads to the same voltage (and hence much higher power levels) than an 8 ohm load.
IMHO, method 2 is superior when you will be driving real loudspeakers, since most 8 ohm speakers have impedance dips to 4 or 6 ohms at some frequency range. Since speakers are generally designed for voltage drive, you'll want to be able to give them the full voltage your amp is capable of without being current limited.
So, to continue the design example using method 2:
100W into 8 ohms dictates 22V rails, giving roughly 40V peak into the load. If the loudspeakers have an impedance dip to, say, 4 ohms (you'll have to verify this with your own speakers), then 40V/4R = 10A. This will be the peak current to the load, and each half of the Aleph-X will have to idle at half this current, for a total idle current of 10A.
__________________
Chad.
"
Any thoughts ? How practical is that ? In a real world, the speaker may have his dip in the bass (I know that it is different with some electrostatic speaker though). Additionally we should assume that we need probly real power especially in the bass. So, If I am voltage limited in the Mids/ Highs (let's assume we have there 8 ohms), does it matter ? Will we see distortion or only limited power ( which we anyhow don't need that much in that frequency area ) ? In other words: will it be audible if we stay with or limited voltage calculated for 3 ohms or should we design the voltage for 8 ohm and the current for 3 ohms ? |
|
|
| Jens |
The appended little spreadsheet may helps in the configuration of an Aleph / Aleph-X (see tabs). I hope the file is self-explanatory, simply start with the input on the left side (yellow fields) and thereafter with your input on the right side (blue fields).
May I ask Grey, Chad, Peter… to have a look on the results and let us know if it’s okay or even not. Needless to say, I’m not an EE…
Jens |
|
|
| wuffwaff |
Blitz,
to calculate bias values into lower impedances just change the numbers. The calculation stays as it is.
Problem (as always) is the heat dissipation. You´ll have to decide beforehand wich voltage you can live with and then go for the largest possible bias. For my Thiels I will use 16V rails and 10A of total bias cause they are below 3 Ohms most of the time.
Jens,
I can´t really see what you´ve done cause the formulas are not open for examination ("blattschutz"). One mistake you´ve made is to calculate the ac current by dividing by 1,3 wich in this case is too much.
What do you mean with "bias rms" the bias will always be the peak value so 7,07A for 5A rms
Dissipation won´t be 32x5x2 but 32x7.07x2.
william |
|
|
| Nelson Pass |
| quote: | Originally posted by Blitz
There it is stated that the xa-200 powersupply with +-35 Volts at 30 Amps ! This is quite different from the 30 Volts at 5 Amps stated somewhere in the threat. |
The writer of that was talking about the current rating of
the supply, which he computed from 2KVA / 70 volts. It
is not the draw of the circuit. |
|
|
| wuffwaff |
and another excel-file,
here you can calculate as long as your processor likes:)
william
P.S. only suited for Aleph-X
P.P.S. I´ve got an even better one for calculating heatsinks but that would reduce posts too much:D |
|
|
| Blitz |
William,
This hits the nail on its head. By playing around with it I found my personal favorite BIAS ( I have a speaker with 5,5 Ohm):
voltage 19,5 volts
bias 6,3 amps
ac current gain 50% 50% means half the current by the source
number of fets 8
Peak current 6,3 amps
power 8 Ohms 76,6 watts
power 6 Ohms 102,1 watts
power 5 Ohms 99,2 watts
power 4 Ohms 79,4 watts
power 2 Ohms 39,7 watts
Dissipation 245,7 watts
Dissipation per fet 30,7125 watts
Number of fets is counted without the current fets, right ? So in reality I need double the amount of fets, in my case 16 per channel.
I guess Mr. Pass is somewhere in this ballpark:
voltage 31 volts
bias 8 amps
ac current gain 50% 50% means half the current by the number of fets 16
Peak current 8 amps
power 8 Ohms 210,3 watts
power 6 Ohms 192,0 watts
power 5 Ohms 160,0 watts
power 4 Ohms 128,0 watts
power 2 Ohms 64,0 watts
Dissipation 496 watts
Dissipation per fet 31 watts
Still, the only thing which makes me wonder is that the current and dissipation is still quite different from what is stated in the documentation. Clearly, I don't want ask for secrets of the XA-200 ( I would love to, but would not expect an answer as this is part of the game. On the other side, it is christmas...), but be sure that we have no flaws in the calcs. Any comments, Mr. Pass (thanks for taking the time to be with us)?
May be this is my last post for a few days. In that case: Happy christmas to everybody ! And thanks for the input ! This was more and faster than I have anticipated ! |
|
|
| Variac |
Yes it would be nice to nail down the number of devices needed.
People converting Aleph 2's would have 12 per channel, and it would be a pain to get new ones to match. So I now realize that I'm (and other Aleph 2 folks) am looking for the specs to make an x aleph with 12 Mosfets, whatever power that turns out to have, and biased the same relative amount as the Aleph 2 which Mr. Pass claims sounds most pleasing to him due to the biasing the 2 has. |
|
|
| chris ma |
I can understand that we can all learn from thread like this one, especially for newbie like myself, but after a few posts that I read here all I can think of this is getting very dangerous here. Just a warning guys it is all well for having interaction among a few of us to kick the ball around a bit but we do humblely require the old hands to guide us thru, and any not so experienced DIYERs out there reading this thread should have the patient to wait and see/watch what the other more milage guys stated clearly what is safe and what is not before you act upon. That's why I (I mean I) always try to stay away from the serious chats among experience fellow members when they have something to discuss instead of posting questions that interupted them or basic/newbie questions should be asked when it is appropriate.
We have no dead line to meet, just try to do a good job and enjoy/reward ourselves with a fine product.
From a humble newbie Happy Season,
Chris
I hope I am not stepping onto anybody's toes. |
|
|
| Blitz |
Variac,
I am clearly not understanding the circuit yet really, but looking at the formulars of William, I understand now that the dissipation of 245 Watt must include the current sources (he has doubled the dissipation, so one part for the output mosfet, the other for the current source I guess). If this is true, the values for the aleph 2 obviously could be:
voltage 22 volts
bias 5,8 amps
ac current gain 50%
number of fets 12
Peak current 5,8 amps
power 8 Ohms 100,0 watts
power 6 Ohms 100,9 watts
power 5 Ohms 84,1 watts
power 4 Ohms 67,3 watts
power 2 Ohms 33,6 watts
Dissipation 255,2 watts
Dissipation per fet 21,26666667 watts
Or with minimum dissipation:
voltage 22 volts
bias 5 amps
ac current gain 50%
number of fets 12
Peak current 5 amps
power 8 Ohms 100,0 watts
power 6 Ohms 75,0 watts
power 5 Ohms 62,5 watts
power 4 Ohms 50,0 watts
power 2 Ohms 25,0 watts
Dissipation 220 watts
Dissipation per fet 18,33333333 watts
William ?
Best Regards |
|
|
| GRollins |
Would it help any if I said that building a bridged amp (such as the Aleph-X) is simply a case of building two smaller amps--each with 1/4 the power you require. If you intend to build a 100W amp, you'll end up putting two (heavily biased...which is where most people go wrong) 25W amps back-to-back.
I'm in the middle of writing a story, and thought I'd take a break. Decide on a target wattage (100? 150? 200? Into what load?) and I'll try to get back over here the next time I take a break.
Grey |
|
|
| BrianGT |
| quote: | Originally posted by GRollins
Would it help any if I said that building a bridged amp (such as the Aleph-X) is simply a case of building two smaller amps--each with 1/4 the power you require. If you intend to build a 100W amp, you'll end up putting two (heavily biased...which is where most people go wrong) 25W amps back-to-back.
I'm in the middle of writing a story, and thought I'd take a break. Decide on a target wattage (100? 150? 200? Into what load?) and I'll try to get back over here the next time I take a break.
Grey |
Grey, would would you recommend for aiming for 150W into a steady 4 ohm load?
--
Brian |
|
|
| Blitz |
Chris, no problem. If this is your method of learning, that's OK. Mine is different. I want to ask my questions. If they are stupid, well great ! Than it should be very easy to answer them. When I look at the viewing counter of this threat, it seems that some people share the same interest / questions with us here. If no one starts to ask, why than have a forum ?
BTW I smoked a couple of amps, but that's OK as finally most of them survive these days. I personally come more from the tube fraction, so SS was not my cup of tea, but the Aleph-X seems to interesting...and if I smoke again some things, well...that's part of the learning experience. No risk, no fun.
By the way: Let's not have philosophical discussions / flame wars or any of this stuff in this threat at least. Let's stay with the subject. So, do you have a content question or answer ? |
|
|
| Blitz |
I would agree to Variac: Let's go for an Aleph-X which can be easily generated from an Aleph 2, so the questions is how much can we get out of 12 Mosfets / channel without changing heatsinks etc. If the dissipations calcs above are right, we talk about 100 Watt into 6 ohm with some stability around it (so that power is not cut in half immediately with half of the impedance).
Best Regards & THanks for your help |
|
|
| Variac |
So Grey,(a pleasure to hear from you....) Instead of a target wattage, we have a target of 12 mosfets per ch and Aleph 2 heatsinks!!
With enough bias to make it sound goooood! |
|
|
| fcel |
| Yeah, that is what I want too! |
|
|
| vpharris |
| quote: | Originally posted by Blitz
Number of fets is counted without the current fets, right ? So in reality I need double the amount of fets, in my case 16 per channel. |
No; that's not right. It is pretty much an Aleph output stage, so the current source provides the current to bias the output transistor(s). Therefore, (of course) that current flows through both the current source transistors and the output transistors.
The dissipation is basically the bias current times the voltage across the two transistors, which is pretty much the differential rail voltage (V+ - (V-)).
About how much you can dissipate with X number of transistors, keep in mind that Mr. Pass's "standard" is about 25 watts for his commercial offerings. (Aleph 2 dissipates 300 W. 300/12=25 W per device). But on the Zen amp (Zen 4) they dissipate 40W each. (40V rail and 2A bias; two transistors in series dissipating 80 W total). I think I've seen him comment that he figures about 50Watts as his upper limit for home projects where it's ok if one fails every once in a while.
So maybe that's some help.
Merry Christmas. El Pipo tomorrow! |
|
|
| chris ma |
No problem Blitz,
Glad that you asked those questions that I have in mind too. I do not really care how much power I am going to get for the Aleph-X. What I want to know is ;
1/with using 2 11"X11" heatsink per channel what are the maximum number of output devices I can have, share the load
2/ and I want to limit the heatsink to around 50 degree C max.
3/ with speaker load of nominal 8ohm to 6ohm.
So how do I work this backward to (per channel)
1/ get the suitable current bias per device and hence total Iq ?
2/ what rail voltage requires?
3/ what size/spec transformer is suitable?
4/ when adding more devices, do I have to do anything with R8,R10,R37 and R39 assuming I am going to replicate the devices as Q1a, R7a, R5a and so on...(Grey's schematic).
5/ I know someone has mentioned how to set this up to run unbalanced, but I am confused by the different methods, can a schematic for that part of the circuit post/draw here?
6/ How about the Ian's resistors, can a schematic post here, I am not sure where I should connect them? Oh what value should they be for the above parameters?
7/ regulate PSU or multiplier? or where can I find a tube rectifier schematic to use instead of those $5 35A surplus bridge recticfier, any advantage using tube rectifier?
Any comments is appreciated.
Regards,
Chris:cool: |
|
|
| Blitz |
Chris,
THanks for your questions. Certainly I can't answer them all as I need to learn some more, here some of my comments:
- Heatsinking: I guess more tech. spechs are need of the heat sink you have in mind. William, your heat-sheet would be great ?
- TUbe-rectifying: Great idea, but these in general are made for high voltages and low currents. THerefore, You can have in theory some for the driver stage (Counterpoint did that, but they had a triode (6922) as well in the driver stage). But I believe you can't separate the driver stage-rail from the output stage in an Aleph. There are other ways to get SS-Diodes calm. I have a nice article on how to filter anything out, which I can send you after christmas.
- Choke-Input will help you in two respects: Less noise from the transfomer / diodes and you can come along with a smaller transformer to obtain the same / better sonic results. Quiet common in tube gear, but a good choke costs money, therefore not oftenly seen these days.
- Bias and voltages should be easy to calculate with Williams sheet.
- Transformer secs I would simulated with PSU-Designer to be sure (depends on the diodes and filtering you want to use) (www.duncanamps.com )
- There have been quite a bit of discussion around regulated supplies but with 5 Amps to regulate this might be not very practical (and series regulators are anyhow not good for audio) |
|
|
| Jens |
Even I have in mind to modify my Aleph 2 (actually it’s a 1.6) into a 100W (down to 2 ohms) Aleph-X. I’ll use the new (X) front-ends, the 12 PowerMosFets (IRF240) as already installed, will have new 1,000VA transformers with 2x 18VAC and 6 capacitors of 47,000µF each in a CRCRC configuration. The bias will be some 7A, which means each transistor handles about 27W (1.2A) and the total dissipation will be 320W. To get the expected 0.5V over the source resistors, I’ll change these resistors (Aleph 2 = 1R) into 0R39.
Merry Xmas to all of you - jens |
|
|
| GRollins |
Running behind (what, you're surprised?), so I'm doing this on the fly...
Okay, let's postulate that you want to rebuild a pair of Aleph 2s into an Aleph-X of some reasonable wattage. I'm sure you'd probably like it if the power came out about the same, right?
Looks as though the rails will need to be +-22.7V.
You'll be putting three pairs of devices on each side, for a total of twelve for the entire channel.
(You <i>are</i> building monoblocks, aren't you?)
If you were to assume a purely resistive 8 ohm load, you could use a .82 ohm Source resistor for each MOSFET. We're assuming that the nominal voltage across the Source resistor will be .5V, the way Nelson did it in the Alephs. Remember that any number of other things will influence that number, not least of which being heat.
However...
Since there aren't that many purely resistive 8 ohm speakers out there, let's throw in some more bias by reducing the Source resistor value. This will keep our circuit from current limiting if the impedance drops a little bit. The .82 ohm resistors would give you a bias (again, assuming .5V across the resistor) of a bit over .6A per device. Seeing as how it's Christmas, let's heat the house 'for free.' Let's use .47 ohms for the Source resistor. This will give a bias of about 1A per device. Given that the rails are 22.7V, we'll be looking at around 24 or 25W dissipation per MOSFET (i.e. the same as an Aleph). Dissipation at idle will be just south of 300W per chassis, so plan accordingly. A 500VA transformer would do the job with good ventillation--possibly even a fan--but I'd rather go for a higher VA rating just to be sure. At least 600VA, perhaps even 750 or 1kVA. The power draw will be pretty close to DC, even under load, so you don't need to get as funky with the power supply as you would with a class AB amp. That's not to say that you can't use an elaborate circuit, just that it's not as critical. Power supplies just love delivering DC; it's when you ask a DC supply to deliver AC that it gets twitchy.
Since you're developing the same amount of heat, you can use the same heatsinks you were using for your Aleph 2s.
Whether you can use the same output devices is another question, though. You'll be running half the voltage and twice the current, so you'll be hitting a different point on the SOA chart. Keep your wits about you.
Your nominal output power will still be 100W, which won't hurt your feelings, I'm sure.
There will be other things that need adjusting, but there are two loaves of fresh bread coming out of the oven, and they're calling my name. I'll try to get back with some other values tomorrow.
Grey |
|
|
| carpenter |
Thanks Grey, that's a wonderful post with plenty of meat.
John |
|
|
| Nelson Pass |
I always like some extra bias, but I should point out that
the reactance (phase angle) of the load has nothing to do
with the selection of bias point. As long as the absolute
impedance is the same as a resistive load, then the bias figure
for that resistive load will be adequate.
A point I have always intended as a thread unto itself, it is
a fact that amplifiers usually have less distortion into reactive
loads than resistive loads of the same absolute impedance.
With a resistive load, the amplifier is called upon to deliver
maximum current at the same time as maximum voltage. This
means that the output devices max out for current just as the
voltage across them is at a minimum - a double gain hit on the
gain of the devices.
With a 90 degree reactive load, maximum current occurs when
the voltage across the device is at quiescent ( value of one
supply rail ) and so the gain of the device is higher and more
linear, and the distortion is lower.
It's true that for AB type amps driving a reactive load results
in more dissipation, but were talking DIY here, not some wimpy
plastic and tin commodity. Class A amps? They just laugh at
reactive loads. The worst case for them is idle.
In any case, when I see discourse on reactive loads and how
tough they are, I just smile.
Merry Xmas. |
|
|
| Jens |
| Thanks Grey, this confirms my calculations. Am I right, that I get even 100W on 2 ohms if the bias is ~1,2A each, which means the source resistors should be .42 ohms (.39 next available)? |
|
|
| joke |
Hi oll ... I would like to builld 50W Aleph X...I have 24 IRFP240 so I can use 3 pair of mosfets on ich side ,but I think that my heatsinks could only take 2 pairs on each side( for total of 8 per chanell ) ...
Is it posibile to get 50 W with 2 pairs of mosfet on each side and at what voltage ... do I nead to change some resistors ???
I'am not EE so please give me some advice ...
It would be nice if some one could write some doc about what we have to do if we would like to build 25,50,75,100W Aleph-X version ( what resistors to change,what transformers to use ... )
Thanks
Josip |
|
|
| GRollins |
Jessica Rabbit stared in horror at the stream of yellow-green liquid jetting towards her...
"It's <i>diiip!</i>," she screamed.
(...what I wouldn't give to be stranded on a remote island with that woman, 'toon or not...but I digress...)
Phase rotations don't scare me. Impedance dips do. Nasty, slimy, hungry little things that scuttle around and eat all my precious power.
("<i>Ah, my Precious!</i>" he whispered, caressing the heatsink with his fingers. "<i>We wants it, we needs it...</i>)
If you're Nelson, with speakers that will comb your hair (think the old Maxell ads, hair streaming back) at thirty paces on a single watt, you can afford to feed the dips a stray morsel of power. Don't forget, the man builds thousand watt amps for a living--though if I read the signs aright, the ones he has at home are far, far smaller. Me? I'm running upper eighties for efficiency, resistive (hence a flat impedance curve--okay, okay, the RD-75s have an RCL notch filter, but let's not get picky) from 70Hz up, so I don't have to worry about such things except with the subs. But I prefer to leave some margin for impedance dips, just because.
I've always had this sneaking suspicion that Z-dips are responsible for peoples' assessments that certain amp/speaker combinations 'aren't dynamic.' At low volumes, everything's all right, but turn it up and the poor amp runs out of current because it's all being sucked into this black hole at the (I guess I should specify a relatively broadband problem for clarity's sake...) dip, leaving little for other frequencies when someone does something rude like whack a drum.
(Nelson, you've got more experience at this than I do, and more test equipment to investigate these things. Comments? I'm just running this as one of my philosophical musings, perhaps with insufficient data.)
Is the fault that of the amp designer or the speaker designer?
Yes.
Each should make allowances for the other. Since we're talking amps, here, it's up to us to plan for inconsiderate speaker designers. (Old driver-safety ad: Watch out for the <i>other</i> guy! Probably only makes sense to folks here in the US over <i>mumble</i> years of age. [Actually, I'm 45--not that bad, as these things go--unless you're seventeen, in which case it's worse than the far side of the moon. Inconceivable to live so long.])
Besides, even if the speaker doesn't have a black hole, more bias sounds good.
And it gets chilly down here in the basement in the winter. I'll take all the 'free' heat I can get.
Grey
P.S.: More on parts values later. I've got to find the confounded schematic so I can talk semi-intelligently about what to change. Worse yet, my mind is on other things...namely turning the preamp circuit I've been threatening to post into a universal gain module suitable for other projects. And I had another idea for a story this afternoon, and I haven't even finished the other one yet. Yikes! |
|
|
| Nelson Pass |
| quote: | Originally posted by GRollins
Is the fault that of the amp designer or the speaker designer?
|
Definitely goes both ways.
I used to wonder what all the fuss was about Watt/Puppies
until I hooked up an X600. Then I decided that both Alephs
and Wilsons were at fault. ;) |
|
|
| carpenter |
| What are Watt/puppies? |
|
|
| Edwin Dorre |
| quote: | Originally posted by carpenter
What are Watt/puppies? |
You gotta be kidding .... :cool:
Wilson Audio Watt/Puppy in his +/- 7's incarnation at the moment!
http://www.wilsonaudio.com/products...uppy/index.html
It is one of the most 'talked' about speaker in speakerland as far as my world goes...
Edwin |
|
|
| vuki |
What are Watt/puppies?
very expensive, audiophile-loved, two-parts floorstanders that have real trouble to play music. I listened them few times in various iterations and even with high-powered 600W/8R amps they sounded like small ineficient minimonitors on steroids - clean, sterile and dynamicly flat even at low volumes.:down: |
|
|
| Blitz |
| ...looks like we are off now with Grey's and Nelson's help. I would like to ask one of my earlier questions again: Will a 044n sound better at 1 A / 22 W or 2 A /44 W per piece ? Since we are in DIY, it is not such an issue to exchange them every 5-10 Years when that has a significant impact on sound. I have read Nelson's article in Audio express where he suggests to run a 044 ( which has nearly double of the capacity) with 2 A / 44W. I guess with a reason. Has made any one own listening experiences to share with us ? |
|
|
| Bricolo |
Off topic (but not off forum :D):
Does the Watt puppies exist in DIY? |
|
|
| MEnsing |
Blitz,
This is what Nelson wrote to almost the same question.
| quote: | It has been my experience with Mosfets that the total
bias is the key element to performance. Within reasonable
limits it can be through 1 device or distributed through
parallel devices, but the total remains the prime factor.
Too few devices and you might cook the parts. I like to
stay around 25 watts or less, but I have successfully used
the IRF 150 watt parts up to 50 watts without seeing
many failures.
With more devices, it's easier to get the current up there,
but you reach a limit in the amount of capacitance you
want to try to drive. Practically speaking, for something
like an Aleph circuit, this limit is less than 12 devices in
parallel, and usually I prefer half that.
Within those boundaries, if you want the best performance,
you crank the bias up all you dare. |
|
|
|
| Bricolo |
What do you call "not reeally a great speaker"?
I'm thinking about biolding a pair of proac response 2.5
Are the puppies worse? |
|
|
| Bricolo |
| quote: | Originally posted by MEnsing
Blitz,
This is what Nelson wrote to almost the same question.
|
so, according to the wanted power, we should always use the less devices possible. |
|
|
| Blitz |
On the mosfets: I know the theory through reading through other threats, but in this concrete application: Will we have an even better sounding Aleph X with 100 Watts if we would use only half of the 12 Mosfets ? And how much better ? Any real listening experiences ?
On the speakers: Obviously a question of taste. I heard once a pair on real big Krells and I didn't like them. Harsh trebles, technical sounding and a badly integrated woofer. Clearly the tweeter is not bad for the money (100 $; but listen to a Philips Magnetostat or true ribbon like an expolinear www.expolinear.de ..), the scan-speak-mid-ranger is to slow, but OK ( compare this to an Eton 5" or Focal and you forget this chapter; they are great for bass, but for true imagining in the mids ?) and on bass ...well...listen once to something like an active exponential horn subwoofer (fairly small to put in the corner of a room) or maybe Nelson's new woofer and we talk again about a complete different class. I have nothing against Wilson, but it is an OK speaker for far too much money. By the way: The ceramic enclosure-legend: TAke an MDF-enclosure and stick some ordinary ceramic plates ( like you would use in your bathroom) into it and you have it. A german DIY-Magazine has made the measurements regarding this material mix and it is extremly good. But why paying 40000 $ for it ? If you are interested into this stuff further, let's start a new threat under "speakers". |
|
|
| GRollins |
All right, let me see if I can get all the rest of the changes together...
*****
Disclaimers:
--All references are to the original schematic that I posted on the first page of the Aleph-X thread.
--If you're working off of another schematic that someone else posted, you'll have to double check the part numbers.
--If you've chosen to modify the circuit, then getting the decimal in the right place is your responsibility. I've got enough on my plate trying to check (and recheck...) my own numbers.
--No, I don't have any plans to drawn up a full set of schematics at 25W, 50W, 75W, 100W, 150W, and 200W. Please don't ask for a custom wattage design. I might throw a fit. It wouldn't be a pretty sight.
--These values are for the 100W (22.7V rail) version I posted about the other day.
--Unless you're really, really determined, I would not recommend this as a newbie's first project. There's some fiddle factor involved. Start with a Zen or something. If, in spite of this warning, someone gets in over their head, post. There's a fair possibility that the answer can be found. The problem will be that a newbie might not have the diagnostic experience to figure out what's wrong. Until we know what's wrong, we can't suggest fixes. A meter is essential. A freq. generator and an oscilloscope are a real good idea. It won't hurt to have big load resistors and other odds and ends on hand. Not to mention soldering irons, pliers, and your favorite flavor of ethanol. You know, the usual.
--Don't lose sight of the fact that this circuit is based on Nelson Pass's work at Pass Labs and is covered by active patents. Start trying to make money off of this and his lawyers will slide you down a mile-long rusty razor blade into a vat of salt water filled with mutant sharks (lasers on their heads are optional, but likely).
*****
Uh, okay...now where did I put my notes?
Ah, caught them. The pesky things were trying to sneak off.
1) You'll need to increase the wattage capability of R1, R4, R44, and R45. Should you power up the amp without a load, then present it with a signal, you'll toast the 3W resistors in the original design. The power will go to ground via these resistors. Plan accordingly. Note that they'll also get pretty warm when you're setting the DC offset.
2) Match R2, R3, R42, and R43 in value and quantity to the number of Source resistors in your output stage. For an output stage with three device pairs per side, you should have six resistors per side of the same value as the Source resistors. This is part of the Aleph current source. Unless you've got a very clear idea as to why you want to do this differently, don't change things at random. Read Nelson's Patent first. Understand it. Then you can mess with it...but you probably won't want to any more.
3) Don't forget the 221 ohm resistors at the output MOSFET Gates. All added-on MOSFETs will be in parallel with the ones shown on the schematic, just the way the Alephs were.
4) As in the Alephs, the output current source (the group of components clustered around Q3 and Q8) is hooked <i>only</i> to one MOSFET's Source resistor, not the whole bank in parallel.
5) R14, R15, R31, and R32 will now be 1.5k
6) Increase R17 to something on the order of 3.3k. You've got latitude here. I know people went for pages in the Aleph-X thread talking about current sources. Knock yourself out. Put in a battery for all I care. Just kidding. A battery won't work well for this. The point is to get something on the order of 20mA flowing through the front end differential and to make it variable to the tune of, say, +-10%. If you want to obsess about current sources, be my guest. I'm working on the X-preamp and writing on four different stories. I don't have the time or the inclination to get in a dither about current sources.
Note that I posted an alternate set of values for the adjustment resistors for the front end current source on page 8 of the Aleph-X thread:
R24 332 ohms
R26 562 ohms
V2 still 200 ohms
This gives you somewhat tighter control of the current source at the expense of range. Use either set.
7) Somebody said that Nelson said that lower values for R19 and R29 were a good idea. 20K max? I don't remember. Something like that. Just use the same value on each side and you'll be fine.
8) Inevitably, someone will post wanting to know if the amp will accept a single-ended input. The answer is yes. Just ground the unused input or your gain will drop. This is just like the Alephs. Most anything posted about an Aleph front end is true here. I'm just using the output from both sides of the differential, that's all.
9) I think I remember seeing someone complain about using a 3W resistor for R21. If you want to use a smaller resistor, have at it. If you find yourself in a ground loop situation, feel R21. If it's hot, put in a bigger one. You'd be surprised how much juice you can develop in a ground loop.
10) Don't like pots? That's cool. Put them in anyway. Adjust the circuit until you've got it beat into shape. Pull the pots out, measure them, and plug in fixed resistors. Presto! No pots.
I think that's it. I am--as usual--on the run. If anyone spots something I missed, say so and I'll take a look. This ain't rocket science, but it's certainly more than a biplane. Perhaps something along the lines of a 747. It's doable. Any intermediate to advanced DIY critter can follow this trail of bread crumbs and come up with a functioning amp.
Might even sound good...<i>ahem</i>...
Grey |
|
|
| ralf |
| quote: | Originally posted by Bricolo
Off topic (but not off forum :D):
Does the Watt puppies exist in DIY? |
Bricolo
i made two of them like wilson in oen piece of stone.
Ralf |
|
|
| ralf |
| quote: | Originally posted by Blitz
On the mosfets: I know the theory through reading through other threats, but in this concrete application: Will we have an even better sounding Aleph X with 100 Watts if we would use only half of the 12 Mosfets ? And how much better ? Any real listening experiences ?
On the speakers: Obviously a question of taste. I heard once a pair on real big Krells and I didn't like them. Harsh trebles, technical sounding and a s material mix and it is extremly good. But why paying 40000 $ for it ? If you are interested into this stuff further, let's start a new threat under "speakers". |
Blitz,
seems you plan to build some aleph x?
I have just started.
perhaps we could mail about speakers etc. ?
Gruß
Ralf |
|
|
| Blitz |
Grey, thanks a lot for the input. That helped me to create some schematics based on your original design (see attachment). Please provide feedback if you see any flaws (anybody else please feel invited as well).
Best Regards
Frank |
|
|
| Blitz |
Ralf,
Yes, I want to build the Aleph-X 2, that's why I want to come up with a schematic which represents the current status of development / experience of this group. Let's come together to share what we learn while building it.
In terms of speaker: Currently I am working on a line-source-project with the big Newforms and some Eton-Chassis ( about 40 pcs), 6db-crossover, 6 ohm, >91 DB, two ways. I have once heard the Dali Megaline which was extremly impressive. My speaker will be a bit wife-friendly though.
Best Regards |
|
|
| Blitz |
Besides putting together a design which should work based on Grey's input (see above), I also wanted to put together a schematic for the same amp, but with the design-features which I have understood ( more or less) from discussions in this forum and to wrap up the status of discussion ( I found it at least very difficult to understand where we stand in terms of the different features discussed in 440-MS-Word-pages in the Aleph-X-Threat).
PLease have a view on the schematic and provide feedback on
- any bugs in the schematic
- recommended variations in values and your listening experiences
- comments on reproduceability (does such a word exist? There have been discussion around the new current source)
- your preferred solution (as there are some variances now to Grey's original posting)
I don' want to ask you now to repeat everything which has been discussed in length in the Aleph-X-Threat, but to provide a short comment if that's a version you would go for. I would like to ask especially those who have build it with similar power ratings for their comments.
Harry / Fred / Peter what would be your estimate on the current source resistor values ?
Grey, what are your thoughts on this ? What are the effects of leaving out the zeners in the input section as suggested by ritrion ?
Thanks & Best Regards |
|
|
| Jens |
Blitz:
0R47 source resistors means even 100W on 2R5 speaker impedance with a total dissipation of about 290W on 6.4A bias. Alternatively we can use 0R56 source resistors for 100W down to 3R5 speaker impedance and a total dissipation of about 245W on 5.4A bias. |
|
|
| Faber |
| quote: | Originally posted by Blitz
...looks like we are off now with Grey's and Nelson's help.
...
..I have read Nelson's article in Audio express where he suggests to run a 044 ( which has nearly double of the capacity) with 2 A / 44W. I guess with a reason. Has made any one own listening experiences to share with us ? |
I do not have this article, unfortunately, but I'm also interested to this answer. May anybody explain, please?
Thank you and Happy new year!
BR, Fabrizio |
|
|
| Jens |
Just converted my PowerBoard with 3 transistors each into a PDF-file (actually a set of 4 boards on the sheet) and hope this is useful for some of us.
Happy New Year – Jens |
|
|
| nania |
I'm not convinced that the constituency here has a grasp of the why and wherefore of a buildout/up of the original Aleph-X so I will present what will be the reference post for questions on these matters.
1. How big an amp do you need?
Here you will account for your room characteristics, listening position and your loudspeaker sensitivity. The target dB sp level you should be aiming for is 100dB. This is an ear damaging level if sustained but should be sufficient for most of the members on this forum (even our NY members with 60dB of ambient noise). Your room characteristics and loudspeaker positioning will give a maximum usable (output power) dB level. Highly reflective rooms (rooms with echo) will have a lower usable dB level than rooms with a fully absorbtive character like an anechoic chamber. When I say maximum usable output level I mean that you can play your music louder than this dB level but distortions and compression effects will probably subtract from its reality and to me, the realistic reproduction is all that matters. Lets look at each of the elements in a little more detail.
room characteristics- this is too much to post but in detail but try to reduce the liveliness of your room so that you don't hear your oxford's (or loafers') footfall after you step. Subtract 3dB for each additional meter distance from your loudspeakers (do not measure on a diagonal) output plane.
loudspeaker sensitivity-the sensitivity of your loudspeakers will have a great deal to say about how much amp you need to make music because the more sensitive your speakers, the less power you need to deliver to them. Is there such a thing as too much sensitivity? Well, balance your desire for dynamics with the annoyance factors of electronic background noise, hum and hiss and you will answer your own question. If your music is "black silent" with 108dB 1W/8Ù sensitivity drivers then good for you but that is seldom the reality.
loudspeaker impedence-this is where most people screw up when it comes to making the right amp. You will need to get an impedence profile for your loudspeakers or measure it under different frequency loads and graph it. You will find that many 8Ù loudspeakers will have impedence dips under 4Ù. Why is this important? Your amp will be required to sustain power delivery to this changing impedence in order to continue delivering the music in phase and in the correct amplitude and to the extent that it cannot, the soundstage will waver or collapse and the dynamics will mute. For a more detailed discussion of why this happens, please look in this thread.
How does this all work and what does it mean to me? For example, you are putting 32W through your speakers and they have a 90dB 1W/8Ù sensitivity and your listening position is on a couch 3 meters from the loudspeaker staging plane. You will have about 99dB of spL. Even if you are listening in midtown Manhattan during ruch hour you will still have 39dB of real dynamic range which is almost double the amount available on recorded music. For more details on the dynamic range of recorded music please read this .
If your speakers have 86dB 1W/4Ù sensitivity you may very well need an amp bigger than the original Aleph-X posted by GRollins. Okay, lets get to the nitty gritty, you want a bigger amp?
You have discovered that your speakers above dip to 2.5Ù and they have a piddly 83dB 1W/8Ù sensitivity and your listening position is 2 meters from the speaker plane. I will need about 75W to reach my target output goal and the impedence indicates that the power delivery must increase 320% to maintain its integrity into the lower impedence. So how do we calculate this out?
1. calculate the bias current:
75W/8Ù X 320% = 240W/2.5Ù (Let's round up to 250W)
We know that P=(I^2)R so if we divide the power by the impedence we see that we are left with about (100A^2) or 10A of bias current required to be delivered into each speaker or 10A per channel. This means that each channel requires a source resistor that will bring 10A of bias current, 5A to the output mosfets and 5A to the current source mosfets. A 300mÙ 2W resistor will accomplish this. More on this later.
2. calculate rail voltage:
We know that P=(V^2)/R so if we multiply the power by the impedence we see that we are left with about (600V^2). Once again we round up to (625V^2) to be conservative and find a result of 25V peak voltage (because it was derived from peak power) but we want the RMS figure so we must multiply the 25V peak X 0.707. This would leave us an ideal rail voltage of around 17.5V but since we must account for losses we add the cumulative losses from diodes, silicon et al to this number to come up with around 20V rails.
3. calculate the power dissipation:
Okay, we have 20A of total bias (assuming stereo) with 20V rails so that means our chassis must be able to dissipate 400W (P=VI). This is a significant amount of heat to dissipate but we must ask how many mosfets will be able to carry this power through them. Since Nelson has stated that the fewer mosfets used the better (presumably because of the increasing gate capacitance of the mosfets), we see that 12 mosfets may be able to achieve this IF they can dissipate 33W each. This is alot to ask of some mosfets but if we use IRFP150N's we should be in the clear.
We're almost there guys (and gals) so stay with me. Now that we know how many Watts will need to be burdened by each of the mosfets we can calculate the bias current at the given rails and the source resistors that will generate that bias current. We should note that input mosfets other than the IRF9610 may require a different calculation but the idea is the same. We know that each mosfet must carry 33W and that the rail voltage will be 20V so about 1.66A will be required to flow through each mosfet. We can double check this by dividing the total bias current by the number of mosfets used and we see that we are right. So which source resistor will bring up the bias to 1.66A on each mosfet? Well, because we know the characteristic of the IRF9610 we use 0.5V as its driving voltage so in order to obtain 300mÙ as the source resistor value. Ohm's Law confirms 1.66A x 300mÙ=0.5V.
Now comes the painful PARTs requirement:
In order to build a power supply to feed your new ~75W/channel Aleph-X you will need a transformer capable of 20A. For those of us in the US, that means a 2.4kVA transformer! That is no typo! Or, if you like, you may use 2-1.2kVA or any derivative that will get you those 20A. This will create a big headache for alot of you because of the case size constraint you will run into when fitting the transformer with all the capacitors. Believe me, I know! This should help alot of you and hopefully discourage more of you from trying to build beyond your means. You have been warned. |
|
|
| Blitz |
Nania,
I am not sure what your message / posting is about.
When I calculate with Williams spreadsheet we have at 20 V / 10 A the following result:
voltage 20 volts actual rail voltage at the fets
bias 10 amps total bias for one channel
ac current gain 50%
number of fets 12 total number of fets for one channel
Peak current 10 amps maximum output current
power 8 Ohms 81,0 watts
power 6 Ohms 108,0 watts
power 5 Ohms 129,6 watts
power 4 Ohms 162,0 watts
power 2 Ohms 100,0 watts
Dissipation 400 watts
Dissipation per fet 33,33333333 watts
Transformer secondaries 15,38 volts for 1.3
16,67 volts for 1.2
18,18 volts for 1.1
20,00 volts for 1
Transformer wattage 800 watts for factor 2
1200 watts for factor 3
Source-Resistor 0,30
If you feel there are mistakes in the spreadsheet, than shows us where exactly.
I believe your VA calcs on the transformer are wrong as well: To receive 1200VA you calculated 10 A *120V ! Bare in mind that a transfomer transforms voltage and current, therefore you can't calculate the voltage of the primary with the current of the secondary to get the right VA. If you want to understand the right VA you get the minimum by 10A * 20V * 1,4 (in a pi filter) or 10 A * 20 V (in a choke-input). Wether the transformer gets hot under these conditions or feels perfectly well is a question of its design. My transfomer winder ask me regarding target figures for regulation/ temperatures etc and than makes his decisions(utilizing a simulation program).
If you want to understand the reasonable max., you simulate the PSU with PSU-Designer and look at the current spikes at the bridge rectifier. You take this current multiply it with the voltage and here we go: Your transformer will never be even stressed by the PI-Filter and the huge current-spikes which come with it. You will find out, that it is cheaper to use a choke-input-filtering as the spikes are very small. Everything between min and max is perfectly suitable, but potentially with some downsides on the sonics.
Best Regards |
|
|
| Blitz |
Just to avoid any confusion on the VAC ratings above: I am looking in the example only on the transformer-part (AC), William has made some assumptions on voltage drop through Diodes, filtering, transformer regulation to show how much V AC is needed to get 20 V DC. I personally would simulate this with PSU-Designer, as this is the must accurate and simple way to come up with reasonable AC ratings. And you need as well some (4V*10 A perhaps)additional VAC to incorporate the losses.
Best Regards |
|
|
| Blitz |
...and than multiply the whole rating by two (I forgot the current source), so a 480 VAC-Transformer would be the minimum.
As said earlier my personal favorite is this combination ( I have a 6 ohm speaker):
voltage 19,7 volts actual rail voltage at the fets
bias 6,3 amps total bias for one channel
ac current gain 50%
number of fets 12 total number of fets for one channel
Peak current 6,3 amps maximum output current
power 8 Ohms 78,3 watts
power 6 Ohms 104,4 watts
power 5 Ohms 99,2 watts
power 4 Ohms 79,4 watts
power 2 Ohms 39,7 watts
Dissipation 248,22 watts
Dissipation per fet 20,685 watts
Transformer secondaries 15,15 volts for 1.3
16,42 volts for 1.2
17,91 volts for 1.1
19,70 volts for 1
Transformer wattage 496,44 watts for factor 2
744,66 watts for factor 3
Source-Resistor 0,48
which resuts (per channel)
- for pi-filter:
min. (19,7V+4V)*6,3A*2 = 298 VAC
max. (based on current spikes in normal operation):
(19,7+4V)*25A*2=1185 VAC
- for choke-input:
min. (19,7V+4V)*6,3A*2 = 298 VAC
max. (19,7V+4V)*7,5A*2 = 355 VAC
calculated with 2 chokes (15mH) per channel
Best Regards |
|
|
| Blitz |
OK, guys, I have just realized that the Version 1.0 has been downloaded about 100 times now, but no one has any comments ? Well than let's have a look together at least at the current source. I changed it now to the version hifizen is suggesting in his beta-version 0.9: So, It is basically Fred's version with connection to the negative rail. Clearly, this is nothing new, but should serve me / you as a wrap-up how the circuit would look like. I guess the resistor values need to be adjusted as we have changed the rail voltage quite a bit. Is there anyone out there with a simulator who give us the right values (wold be great to have it for 22,7V and 19,75V)?
THanks & Best REgards |
|
|
| nania |
Blitz| quote: | | If you feel there are mistakes in the spreadsheet, than shows us where exactly. |
The buildout formula I described is an attempt to simplify in a few easily comprehensible steps how to buildout ANY SIZE version of the Aleph-X. I haven't seen the Williams spreadsheet and don't know the formulas used within it so I won't comment on its merit at this time but I suspect there is an error because the power value described under a 2ohm load seems a bit low. There will be some falloff (collapse) as the speaker load falls below the 2.5ohm level but I doubt that it will be as steep as the Williams model presents it. I should remind you that my example was to build out a version that would be stiff to 2.5ohms not 2ohms. It would be interesting to see what the spreadsheet model says the power output would be under a 2.5ohm load which is the example you should have provided if you wanted to highlight a disparity or attempt to invalidate my method.| quote: | | I am not sure what your message / posting is about. |
Well, my post was an attempt at trying to move the elephants before the mice. Many people want to build bigger than what is practical and the result is usually not as good as something planned to a purpose. I tried to provide some useful perspective since once you build your amp, you will have to live with it and pay the electric bill it generates. If others on this forum are like me, they have their amps on for the better part of the day so this is issue is not insignificant IMHO| quote: | | I believe your VA calcs on the transformer are wrong as well |
You are entitled to your opinion. I will tell you that any time the transformer is stressed the possibility of the music signal integrity degenerating increases. I will also tell you that the use of inductance in the power supply is not a panacea and I much prefer a simpler CRC power supply with the capacitance size and quality reducing the ripple but again, this is only my opinion and the readers may form their own as they read through our respective posts. |
|
|
| Ian Macmillan |
Since there seem to be very few comments forthcoming on your high power circuit, I thought I would chip in with something. I suspect that the lack of opinions has more to do with the time of year than any lack of interest.
I've only had a quick look at your circuit but one thing strikes me as indeed it did for Grey's circuit, and that is the inclusion of V1, R11 and V3, R33. I appreciate the need for some form of differential current adjustment but these parts can easily cause more problems than they solve.
Others, including Grey, have mentioned that these parts are not strictly necessary, but I would go further and say they are best removed. If you model this current source in isolation, you will see that the current is not as constant as one would like with variations in voltage across the current source (as opposed to at the intended control point). This has to do with the variation in current in (and hence in the voltage drop across) V1, R11, etc. as the voltage across the entire current source varies. The net effect of this is to make the amplifier more sensitive to DC at the output and hence less easy to trim for zero voltage.
In my own prototype of Grey's circuit, I have also omitted the over current protection parts associated with Q4.
I haven't yet tried a high power version although it is my intention to do so. Hence I cannot yet comment on what really matters other than through simulation.
Ian. |
|
|
| Blitz |
Ian,
Great to have you here and thanks for your comments. Do you see any issues with the current source itself ? HAve you the possibility to simulate the right resistor values for it ?
Nania,
Please don't get me wrong: I appreciate your input, but I truely like to learn from your calcs vs. the calcs other made. You find Williams Spreadsheet in this threat ( page one or two) as an attachment. So, please have a look at it and suggest your corrections.
Your essay on Watts is correct, but it is like someone comes to Mercedes-Dealer and wants a Mercedes, but while being there someone else tells him that in most situations a VW Polo will be equally fast and that he should get a Polo. So, this threat is meant for people who know what they want. Or for all the Aleph 2 Owners / Builders who want a X-Version now. Besides thjis I am with you: I run a triode amp with 25 W SE (VV520V2) and it is awesome ( could have only some more bass control though....).
On the transfomers we are more or less on the same page: If you use a CRC_Filter and don't want any limitations on sonics, go for a 1200VA. Technically less would do so...I missed that comment on your threat. By the way: What issue do you have with choke-input ? With a nice LCRC you have a better ripple rejection than with similar (R)CRC-Filter, need much less VA for the same sonics ( see above), have much less stress ( 7,5 A peaks to 25A peaks) on the diodes etc.
Best Regards |
|
|
| nania |
Blitz| quote: | | ...it is like someone comes to Mercedes-Dealer and wants a Mercedes, but while being there someone else tells him that in most situations a VW Polo will be equally fast and that he should get a Polo. |
I don't know that this is a representative analogy. Saying that building a smaller amp which sounds better than a bigger one is comparing a Polo to Mercedes might be insulting to the Tri-Star if the quality of our aural experience is the goal. You will concede the point that louder is not always better, yes? So why put your resources into a bigger amp if it doesn't help you enjoy the music more? The only reason would be to match it better with a future speaker or listening environment and if you are making that kind of a change, you will most likely improve those parameters rather than worsen them.| quote: | | What issue do you have with choke-input ? |
Outside of the ways it can create more problems than it can solve if implemented poorly (with the wrong value, wrong diameter wire in the coil, etc.) there are the issues related to its physical footprint in the case, its cost and sonically its potential for current limiting/wavering effects and the consequence that has on bass response. To me, these outweigh the 10mV additional noise reduction you may get using a coil. |
|
|
| Cobra2 |
Please go onwards with the calculations,
-but remember that (I think) most of the hundreds of PCB-buyers will use a filterless PSU, atleast for a start,
(and might fine-tune the PSU when everything is in working order/or as a future upgrade/tweak).
What do we then come up with?:confused:
Arne K
NORWAY
(Need hot amps...it's freezing outside...):eek: |
|
|
| Blitz |
OK, Nania I see that we don't come together on choke-input (still I don't get the point with the current though as the delivery should depend creatly on the impedance of your PSU, mainly determined by your last capacitor and real good chokes have not more resistance than the resistor you use anyhow). I guess it won't help that most of the Cellp-Amps by MArk LEvinson use them, and Nelson and many others besides me like chokes as well as stated several times in other threats.
For everybody else interested in this subject, one of the greatest transformer winders building any choke you can think of (his standard are 6 chamber-chokes to avoid resonances, and than he has three even better options on top of that to offer) you will find here:
http://www.ae-europe.nl/ (dutch side, bit very friendly guy talking german and english as well)
For the tube freaks: You will get there OPTs on or surpassing the level of TAngo / Tamura even with amorphous core for a fr | | | |
