| MEGA-amp |
I just recently received my aleph 2 PCBs from Kristijan.
Going over his parts list I have a few questions:
The R values for the main board are listed, is there a general wattage rating for the resistors i'm looking for, for the main PCB components? I saw somewhere that all resistors are rated at 25W unless otherwise noted.
per Kristijan's schematic:
1. R1=4,75 K?
is this 4 watts 75,000 ohms? 4.75 K? his notation is confusing me
2. D1-D5= zener 9,1 V
9.1 V? wattage?
3. What voltage is recommended for the caps on the main PCB?
C1=1 nf
C2-C4=220 uf
C5=10 pf
C6=1 nf
4. what will yield the best sound? Bulk Metal Foil, Thin Film, Metal Film. Or is the type non-important?
5. Do any resistors require tolerances of 1%?
Thanks in advance
John |
|
|
| elizard |
| quote: | Originally posted by MEGA-amp
Going over his parts list I have a few questions:
The R values for the main board are listed, is there a general wattage rating for the resistors i'm looking for, for the main PCB components? I saw somewhere that all resistors are rated at 25W unless otherwise noted.
|
that's 0.25W (1/4Watt) .. 25watt is a slight overkill :)
| quote: | Originally posted by MEGA-amp
per Kristijan's schematic:
1. R1=4,75 K?
is this 4 watts 75,000 ohms? 4.75 K? his notation is confusing me
|
That's 4.75Kohms
the ',' in europe is used as a '.' in US/Canada is generally
| quote: | Originally posted by MEGA-amp
2. D1-D5= zener 9,1 V
9.1 V? wattage?
|
this is my guess only, but i'm guessing its just a standard zener diode, so whatever wattage they are
The rest of the questions I don't have an answer to, except one last one.
I don't think any resistors REQUIRE a 1% tolerance, however if you can afford 1% resistors i think you'll be graced with a (possibly ever so) slightly better amp.
edit: you can refer to http://www.passlabs.com/pdf/aleph/a2srv0.pdf for more info of course
another edit: the only resitor's wattage you need be concerned about are the 0.47ohm and the 1ohm ones, those i believe are 5watt wirewounds if i'm not mistaken. |
|
|
| BobEllis |
| quote: | Originally posted by elizard
the only resitor's wattage you need be concerned about are the 0.47ohm and the 1ohm ones, those i believe are 5watt wirewounds if i'm not mistaken. |
THE RESISTOR POLICE ARE COMING TO GET YOU, ELIZARD! BAR THE DOORS! :D
Some say that you should use thick film resistors here, but I plan to use cement wirewounds. Maybe when I have silly money I'll try something exotic, but for now I'll worry about choosing the best sounding transistors.
As for capacitor voltage ratings, I'd go slightly above the rail to rail voltage for the 220uf (eg. 25 volt rails, rating > 50 V) for teh others the dc potential across them is small, so virtually anything will do. |
|
|
| moe29 |
the lowest values you'll be able to find for the small caps will be
well within tolerences (1nf, 10pf) The 220uf cap = 50v (Digikey part# P5572-ND)
Zeners = 1watt (Digikey part# 1N4739ACT-ND)
NTC (for power supply inrush limiting) KC006L-ND
10PF cap 399-1806-1-ND
.001uF P4785-ND
(i'm sure there are better sounding parts that could be substitued
for the above, but you can get all these at one place, and they work!)
m. |
|
|
| moe29 |
:) as for the resistors:
3 watt parts, use the Panasonics from Digikey
.47ohm P0.47W-3BK-ND
1ohm P1.0W-3BK-ND
1/4 watt parts Yageo 1% Metal Films will do fine, Digikey also |
|
|
| jewilson |
The 220uf cap should be a Black Gate
The resistors should be RN60D Dale/Vishay metal flim. www.mouser.com
Panasonics from Digikey have ferrous metal lead, So don't use any resistors that can be picked up with a magnet.
The 10pf cap should be a Mica type. |
|
|
| moe29 |
the only Black Gate cap i see on Percy Audio that fits would be a
220uF 160V NH for 29.95 USD a piece. Times 6 for stereo Aleph 2
would be $180.00 ..... YIKES!!! :bigeyes:
or are you just talking their Standard Polarized line, which would
be 220uF 50V for $6.95 USD for $42.00 total.
You can get 10 of the Panasonics i posted for $4.10 USD.
I'd try them first and see how things sound.
Pass Labs uses the same Panasonic resistors in their Amps, they
can't be that bad.
the above caps and resistros sound great in my Aleph 2's.
...go figure. |
|
|
| trigon |
I have used BlackGate FK 220uF 25V for my Aleph 4 and with 50V rail voltage I have measured 16V on bootstrap and the others are not that critical they can be 6.3 if you want, but I have used all 220uf 25V FK BlackGate
Hope this help
Trigon |
|
|
| jewilson |
Seeing how that this cap on the inverting balanced input, I would not use just any old cap there Moe. However, the 220uf for the bias could be a Panasonic, it’s not that important since it not in the signal path. If the PCB had room I would use and Black Gate and parallel with a Polypropylene 2uf on the input only.
I just hate to use parts that know I will remove later, just cost more time and money. |
|
|
| moe29 |
Jim,
C5 is the cap you are saying should be Black Gate right?
what you're saying makes since - and i'm not saying that Black Gates
don't make any difference sound wise... Just hard to reccomend
them for a first time build. (i'm assuming this, becuase of the
questions from the original post)
I guess i'm just always for getting the circuit built first, and then
doing upgrades later. |
|
|
| Magura |
True, but in the end i understand the question being that he dosnt want to spend un-nessecery money, not that he dont want the best possible....maybe im wrong.
In the end of the day its terribly expensive to upgrade half of the amp by buying better parts (that could have been bought in the first place) within the first 2 weeks.
Magura |
|
|
| tomchaoda |
I can not find the thermostatic switch rated at 75 degrees C used in Aleph 2 and 5 in either Digi-key or Mouser! Does anyone has the part number to order?
Also, I like to use the copper plate to connect the large filter cap. Local Home Improvement store does not have it. Anyone knows where I can find them (in US)? (like a 2mm thickness used in the photo)
Thanks
Thomas |
|
|
| Magura |
| quote: | Originally posted by tomchaoda
Also, I like to use the copper plate to connect the large filter cap. Local Home Improvement store does not have it. Anyone knows where I can find them (in US)? (like a 2mm thickness used in the photo)
Thanks
Thomas |
Check your mail.
:) Magura |
|
|
| moe29 |
The point i'm trying to make is you do not need to build
an Aleph 2 with exotic and expensive parts for it to sound good.
The Aleph series was Class A pretty much across the board - no
matter who was reviewing.
My Aleph 2 sounds great and compares nicely to my production Aleph 3...
sans exotic parts.
First time builders shouldn't be lead to believe that their amp
will be second rate if they don't use exotic parts. And where's the
fun of experimenting if you use exotics right off the bat? You have
nothing to compare to. Someone certainly isn't going to take out
Black Gates to see if it sounds better with Panasonics! ;)
(sorry if i'm going on and on) |
|
|
| Alain Dupont |
Tomchaoda,
Look at DigiKey : #317-1000-ND
Thermostat 70 C NC with leads
I will use two to protect the final stages
of my A75 and cut the power supply in case of overheat...
Alain. |
|
|
| tomchaoda |
Alain,
Thanks for the info. It is very useful.
Thomas |
|
|
| tomchaoda |
:knight:
Thanks for all info regarding parts question I posted earlier. I also find them and would like to share with you.
For the 75C Thermostatic switch, I find one I like in Digi-Key.
Digi-Key: #317-1001-ND
Mouser has Vishay Thermal switch rated at 70C or 80C, but not 75C. However, they do not have them in stock!
For the copper flat sheet:
for 1 mm (~0.04"), they have it in Thompson Emanel, link here:
http://www.thompsonenamel.com/produ...erflatsheet.htm
For 2 mm (~0.09"), I found it on eBay, but it is not cheap! But I like 2 mm for better conductance.
FYI
Thomas |
|
|
| Magura |
| quote: | Originally posted by tomchaoda
:
For the copper flat sheet:
for 1 mm (~0.04"), they have it in Thompson Emanel, link here:
http://www.thompsonenamel.com/produ...erflatsheet.htm
For 2 mm (~0.09"), I found it on eBay, but it is not cheap! But I like 2 mm for better conductance.
FYI
Thomas |
You should rather use 2 * 1mm than 2mm for better conductance....wich is though irrellevant in this case, since 1mm * 25mm copper bar is more than overkill already :D
Magura |
|
|
| tomchaoda |
One more common question, does Q1 ~ Q3 IRFP9610 need to add the mica insulator at all?
From the schematic, it seems no; but I saw a few saying it must, or the bias will be hard to adjust! Are they right or not?
Thanks,
Thomas |
|
|
| Brian Donaldson |
All three mosfets must be electrically insulated from each other. thermal coupleing makes no difference in bias. Thermally coupleing the diff pair will make the dc offset more stable, but most people don't bother. Most people don't even use sinks.
I bought 2 bars of copper 3/16" x 2" x 36" on Ebay for something like $18.00. Made nice busses |
|
|
| SI |
| Hi, I'm thinking about using 4 x 27,000 micro F at 63 Volts for +- 45 volt rails. It's for my very first Aleph project. Question is if this is enogh per channel. |
|
|
| Brian Donaldson |
| It'll do but more would be better. Also make it a CRC to get the most smoothing possible from the ufs you have. |
|
|
| SI |
If I do a CRC layout, Do i have to change the secondary voltage of the Transformer ? What would the Resistence value and power rating be? Should I keep the same voltage and up the capacitance?
Thanks.
SAAD//:confused: |
|
|
| GRollins |
This is why people recommend L instead of R...it doesn't change (much) the voltage coming through. With resistance, it's a balancing act. The more resistance you use, the better your filtering will be. The flip side of the equation is that the more R you use the more voltage drop and heat you'll have to deal with.
Inductors are superior but cost more, and are bulkier & heavier. Bulk and weight aren't a problem to DIY folks, but cost is a nuisance to those whose wallet has been on a diet. (Hint: Wind your own.) If you go with resistors, you can calculate the heat (I squared R), and voltage drop (E over I) easily enough, just plan ahead and you'll be okay. Unless you want to get really nutso, stay under 5 ohms; don't be ashamed to go under 1 ohm.
Don't get confused when you read the specs on an inductor and see that it has, say, one-tenth of an ohm resistance. It's apples and oranges. It's the inductance, not the resistance, that makes an inductor worthwhile. Inductors have the added benefit of increasing filtering as the frequency increases. Resistors have a flat response. This translates as inductors being better at taming incoming RF and such.
Grey |
|
|
| Mark A. Gulbrandsen |
We have a Metal Supermarket here in SLC. I love those guys over there...not the cheapest to buy from but they also do any shearing or cutting for free while many metal vendors charge anywhere from 2.00 to 30.00 per cut. They also will order in anything you might need that they don't normally stock and you only have to buy what you want of it.
Mark |
|
|
| Brian Donaldson |
| Also beware with the CLC. The inductor is not able to dissapate more than about 8 watts or so without getting hot enough to melt the insulation in the center of the coil. My first try was around 2 ohm, 2.5 mh. the extra resistance made the PSU sim look great, but at 6A the inductor dissapates 18 watts and gets too hot for comfort. I'm resorting to mounting a big *** pair of 3 ohm 100 watt wire wound vitreous ceramic type resistor on the outside of the amp in back because I need to dump a few volts. |
|
|
| SI |
I think I'm going to try both CLC and CRC filters.
Mr, Rollins
What would the inductor value be if I'm trying to shed couple of volts. The Tranformer I'm looking at has a 35v+35v secondary and If I 'm looking to get +- 45v at the rails, according to Mr.pass my Transformer secondary should be 33v+33v.
Mr, Donaldson,
I was wondering if the total bias current is my "I" and voltage I want to drop is my "E" when I'm calculating for the resistor.
All the help is greatly appreciated.
Regards.
SAAD// |
|
|
| GRollins |
SI,
If you're wanting to drop voltage, it's generally better to use resistors. One of the reasons to use an inductor is that it keeps voltage losses to a minimum.
As for a resistor, one or two ohms should do the trick. Make sure the resistor has sufficient wattage capability.
Of course, you could also use both inductors and resistors.
On the other hand, the Aleph 2 would be perfectly happy with that extra couple of volts.
Grey |
|
|
| trigon |
One more time these are in my Aleph 4 monoblocks and everything is ok. :)
Trigon |
|
|
| moe29 |
actually, you may come up a little short of 45V rails with 35V secondaries.
I used a VM 1000VA with 37V secondaries and i'm right at, or a
1/2 volt under 45 Volt rails.
It all just depends on how you build your power supply. I used a
Thermistor for inrush current suppression on the AC mains, and
a CLC arrangement (2 mH inductors). You loose a volt here and
there... but being off a couple shouldn't matter that much.
Go for the 35/35, i'm sure it'll be fine for you! |
|
|
| SI |
One more question : If I deceide to add more output devices(4 IRFP240) per channel what are the changes do I have to make to the circuit to acomodate those extra devices ?
The problem is that I build the 2nd set of cabinets a little too big and was wondering if I could use up the space, and I got very inefficiant speakers and a very dead room sonicly.
Regards.
SAAD// |
|
|
| Brian Donaldson |
Everything else being equal, adding more output devices will increase bias and dissapation. At some point, the capacitance of the extra outputs will lower the high frequency roll off. Your power output is limited by rail voltage and current. If your speakers are 4 ohm or less, the extra current will increase power out. I think current starving becomes an issue below 6 ohms with the stock Aleph 2.
If you dig up my old thread, I ran 8 devices per side and decreased the source resistance to almost double the bias. |
|
|
| Mark A. Gulbrandsen |
Hey Brian,
You forgot to mention the extra 50 tons of air conditioning you also installed to keep the house cool in the summer;)
Mark |
|
|
| Brian Donaldson |
| They do raise the room temp by 8 degrees |
|
|
| sippo |
Hello,
i´m new to this forum and first of all i want to thank everybody for the great information i got here.
Since this thread is about Aleph 2 i think you can help me on my problem with an Aleph 4.
I built up a prototype and it worked fine, 20mV DC out right from the start. After putting together the final version the output voltage raised to -21 VDC !
I´ve checked everything several times, replaced to zenerdiodes that where damaged, but still no success.
The measurements are:
Z9-> 9,2 V
Q3-> 3,4 V
R3-> 5,6 V
R24-> 86 mV
Sourceresistors 1,5 Ohm-> 66 V on currentsource
Sourceresistors 1,5 Ohm-> 24,3 V on outputstage
PSU+- 45,5 V
I´ve no idea what the problem could be, maybe you have an answer to this.
Thanks in advance
Frank |
|
|
| tomchaoda |
According to the schematics, R24 should be 4 to 5 V. Check your Q1A1, Q1A2 and R24 again! This may be the problem.
Thomas |
|
|
| SI |
I read some where that the zeners are there just to save the Mosfets since they are very sensitive to static electricity. The Mosfet's should not be handled unless you are properly grounded.;) Check and see if your Diff pair still alive and working properley.
Regards.
SAAD// |
|
|
| sippo |
I´ve checked the Fets and R 24 and they are OK. Put them back in the circuit and voila, the voltage dropped to -17 VDC ???!!!!
If i change parts enough or just take out and put them back in the circuit for the next few days i might reach 0 VDC !!!!:D :D
Frank :confused: |
|
|
| sippo |
Hello everybody,
after further detective work on the PCB i thought i´ve found a short circuit. Having fixed it i turn on the amp again and immediately R 3 melt.
This gets more and more frustating to me (having in mind the amp allready worked a few days before).
Does anybody have an idea what´s wrong ?
Regards
Frank |
|
|
| SI |
Hi, Can anybody help me with the part# for TH1(thermistor) in a ALEPH 2 ?
I wonder if it's the same as TH2, which is CL-60.
Regards.
SAAD// |
|
|
| moe29 |
| Digikey = KC006L-ND |
|
|
| SI |
| quote: | Originally posted by SI
I wonder if it's the same as TH2, which is CL-60.
|
So, TH1 and TH2 are same part, if I understand correctly.
Regards.
SAAD// |
|
|
| moe29 |
Yes they are. From the Service Manual:
TH1 is a power thermistor used to connect the circuit and chassis ground to the AC outlet
ground. It will normally operate at 5 ohms, suppressing ground loops in the system, but will
drop to a low impedance if significant current is passed through it.
TH2 is a power thermistor (Keystone CL-60) which is used to suppress inrush current. |
|
|
| SI |
Hi, I was wondering any body wants to trade 8 caps of higher voltage to 16 of these brand new caps. I found out it's not a good idea to run caps at their 95% voltage rating. I know I can't afford any more caps, and I bought a case of these.:bawling:
So, please help.:xfingers:
Regards.
SAAD// |
|
|
| moe29 |
i run those same caps in my Aleph 2, with no problem.
that rating has to be + or - 10% or so, so just be positive ;) |
|
|
| Netlist |
| quote: | Originally posted by moe29
that rating has to be + or - 10% or so, so just be positive ;) |
Another angel for Jam ;) |
|
|
| moe29 |
there's no way running 45 volt rails on those caps is any danger!!
:att'n: Fearless DIYer:att'n: |
|
|
| Magura |
Those are cheap caps of good quality. Give it a shot, if one should blow, simply replace it. As i remember it, those caps are 6 USD a pop (pun not intended).
Magura:) |
|
|
| moe29 |
| Netlist... i just saw that other post under Tradin Post re: Angels :) |
|
|
| jewilson |
| Normally capacitors or under rated by about 10%. These should ok at 90% of their voltage other wise the vendor would rate them lower. |
|
|
| GRollins |
If the caps are old, they may blow due to age. Otherwise, there shouldn't be a problem.
You're sure that you didn't hook the cap up with the wrong polarity...right?
Grey |
|
|
| SI |
I am very new at this DIY game, at least the Audio side. In the industrial set up we allways worked with WV (Working Voltage) rating, But when I raised the question about these caps being part of a A2 power supply, Some one in the forum mentioned that it was not adviseable to use caps at so close to their WV. Now I think I'm going to finish building the amp.
BTW, Is there any thing about having too many caps? I'm throwing 8 caps per channel. They were cheap.;)
Let me just thank you guys once again, I'm sure there's gonna be many more to follow.
Regards.
SAAD// |
|
|
| GRollins |
Have you seen the movie Finding Nemo?
You know how Marlin (the father Clown fish) is showing Nemo how to leave the anemone and he goes out, and back in, then out, then back in...
There are people in the world who are...shall we say...overly cautious. Boldness challenged. Lacking the true pioneer spirit.
They probably wake up in the morning and check for rattlesnakes in their shoes before putting them on...whilst living on the 35th floor of an apartment building in Manhattan.
As long as the caps aren't really, really old, they're good for it. If they are old, they're going to **** out anyway no matter what, so you might as well pump 'em full of electrons. If you hook them up backwards, all bets are off.
Too many caps? We are DIY. We laugh at the very thought of too much of anything (except heat--take heat seriously).
Just watch the inrush current when you turn the thing on. If it gets too extreme, you could start the filter with an inductor, which will knock down the initial spike a bit. If that doesn't do the trick, then consider a slow start circuit.
Once upon a time, I raided a pile of defunct mainframe computer gear and got a bunch of caps. What to do? Hmmm. Before all was said and done, I had laced a quarter-Farad or so to one of my Threshold S-500s. Whoa! Popped fuses on turn-on. Whipped up a simple RC timer/comparator/driver transistor/relay to switch a resistor in and out of each rail at turn-on. Worked like a charm. Sounded great.
My rule of thumb is this: Watch your neighbor's lights when you turn on your amplifier. If his lights dim, then you're doing okay. Don't bother watching your own--any DIY worth his salt can dim his own lights.
Grey |
|
|
| tomchaoda |
| quote: | | Hi, I was wondering any body wants to trade 8 caps of higher voltage to 16 of these brand new caps. I found out it's not a good idea to run caps at their 95% voltage rating. I know I can't afford any more caps, and I bought a case of these. |
If I remembered correctly, the commercial Aleph 2 also use the 50V rating!
Thomas |
|
|
| SI |
Mr Rollins, Point well made and taken.
Off topic: I really have to watch what I say in these posts. One might conceive it a wrong way and harass the people I'm trying to show humble gratitude to. I also find these people funny, Because they are also looking at the threads, but offering little or no help.
On a different note: Mr Rollins, I read a lot of your posts and I was wondering have you ever thaught about taking a crack at writing. For people who's thinking that he writes everyday; I meant writing books. Anyway, I think I saw some where that you mentioned that you might be working on a book or did I completely take it out of context. How ever, you should go for it.
I was also wondering if you can post a picture or two of your water-cooled Alephs.
Regards.
SAAD// |
|
|
| uli |
| quote: | Originally posted by GRollins
.
My rule of thumb is this: Watch your neighbor's lights when you turn on your amplifier. If his lights dim, then you're doing okay. Don't bother watching your own--any DIY worth his salt can dim his own lights.
Grey |
Mmmmuuhahahahahahahahah
great picture Grey!!!
Uli
:nod: :nod: :nod: |
|
|
| arold19 |
I want to know the power rating for some resistor in the Aleph 2
1-For the 0,47 Ohm output resistor ????? maybe 5w ???
2-For the 1 Ohm resistor near the output mosfet ?? 5w ??
All the other resistor are 1/4 watt ???? |
|
|
| SI |
| quote: | Originally posted by arold19
I want to know the power rating for some resistor in the Aleph 2
1-For the 0,47 Ohm output resistor ????? maybe 5w ???
2-For the 1 Ohm resistor near the output mosfet ?? 5w ??
All the other resistor are 1/4 watt ???? |
You are in the right ball park. The heavy hiters thinks, keeping 0.47 and 1 ohm resistors at 3-5 watts so that you can paly with the bias current without letting all the pretty smoke out of these resistors.;) The rest could be 1/4 watt.
Regards.
SAAD// |
|
|
| GRollins |
SI,
I'm already a writer. Been one for fifteen years or so. If you read science fiction, I'll have a Victor & Martin story in the June (I think) issue of Analog...and a story which uses electronics as a plot device, no less. www.analogsf.com
Books require a tremendous commitment of time. No gots. I've been trying to pull together a fixup of my Darwin's Children series for several years now, but it's a battle to get large blocks of uninterrupted time. Incidentally, do not confuse my title Darwin's Children with a recent book by an author whom I shall not name. I asked him not to use that title, but was basically told to take a hike. As far as I can tell I originated the phrase. Since then, it's been used for at least one song, one poem, and the aforementioned book. No, I don't have any legal way to stop them from doing that.
arold19,
The 3W blue Panasonic metal film resistors are ideal for the job. Get 'em at Digikey. As SI says, the rest can be 1/4 or 1/2W, whatever makes you happy.
Oh, and uli...you get bonus points for taking out the entire block...
Grey |
|
|
| SI |
Like the most commoners I never cared much for reading of any kind, even a machine manual puts me to deep coma. These even has pictures. Since I started the DIY amp project I did a book worth of reading and I like it.:cannotbe: Even when pictures are as rare as me reading.
Ironically, In your case "The survival of the fittest" comes to mind or is it "The survival of the one with most expensive lawyers", I don't know. Good luck with the book and keep us informed. For all it's worth, I think you are an asset to this forum.
Thanks,
SAAD// |
|
|
| Mark A. Gulbrandsen |
SI,
Its sad that you hate reading. while I'm not a really good reader...some comprenhension problems and such so I sometimes need to re-read things over a couple of times... I still view reading as a learning experience for the most part. Manuals are a great learning tool and I read and study many...pictures or not.
Mark |
|
|
| GRollins |
SI,
You're probably pulling my leg, but I had a story called Survival of the Fittest back about ten years ago.
Manuals are good, too. Textbooks. Mysteries. Spy novels. Oddly, I don't read much science fiction any more. I don't care for the way the field is going. Strange, but there it is.
Reading is good in a number of ways. I think I heard recently that they've completed a study that indicates that reading (hence keeping your mind active) can reduce your chances of getting Alzheimers (that's probably not how it's spelled, but I'm too tired to look it up). Who knows what the mechanism is. Kinda like audio...there are things that you can observe, but you can't see why they work. Someone will figure it out one of these days.
Grey |
|
|
| SI |
Seems like a weiard coincidence.
One question: How do you measure the bias, and is it true in A2 if one removes the R19 it sounds better, If it so, Do you put a jumper in place or just omit R19.
Brian Donaldson: I was wondering if you can post a schematic for your A2 + ?
Regards.
SAAD// |
|
|
| jewilson |
The Panasonic resistors are not true non-ferrous metal leads or they have some steel or iron in them. These types of resistors should be avoided for audio as the lead came become magnetized, inductive and harder to solder. You can tell if a resistor or capacitor has these types of leads with a magnet, if it attracts then you should not use them.
My recommendation is to use Dales-Vishay resistors use RN55 or RN60. I refer the RN60 and feel they sound just a little better. You can get these resistor at www.mouser.com or from www.newark.com. :) |
|
|
| Brian Donaldson |
SI
I changed the source resistors to .68 ohm and added 2 more fets per side. I also put pots in for R 19 and R 21 so I could vary the Bias and AC current gain. The rest is stock Aleph 2. My goal was 200 W into 4 ohms without running out of current. And by god, they'll heat up a room.
I'm gettin ready to move into my new house with a listening room upstairs. I had the electrician add a 220V 20A circuit for these babys. |
|
|
| SI |
| quote: | Originally posted by Brian Donaldson
SI
My goal was 200 W into 4 ohms without running out of current. |
I think I have the same goal and I was also wondering how do you calculate the bias and current gain.
Thanks Brian.
SAAD// |
|
|
| Brian Donaldson |
Bias is set by the source resistors on the current source (positive half) and adjusted by r 19. lowering resistance lowers bias. Nelson suggested (and I followed) using a pot and listen and measure. If you like, replace with a resistor after you find what you like.
I think the current gain is set by the bank of resistor between the speaker and the output rails. It is adjused buy r21. I don't recall what the relation is. But again, put in a pot and a resistor so you can vary from around 30% to 300% of original value and play with it.
I dropped the source resistors from 6 @ 1 ohm to 8 @ .68 ohm to roughly half the impeadance. So my bias should be double the stock amp (everything else being equal) I also almost halfed the output sense resistance, so the AC gain would remain the same at 4ohms as the stock amp at 8ohm load. I also marked my pots so I knew where the stock resisance was so I could start there and return there if I had doubts or problems.
The pots also serve another purpose. You can see how hot you feel comfortable running the amps and dial in the minimum A/C gain you need to not be current starved. |
|
|
| Brian Donaldson |
| Actually, the Aleph CCS seems to have 2 senses. The 220 uf off the output rails that connects between 4.75K and 1.5K between +rail and bjt modulates based on voltage, and 220 uf through 681 ohm to base of bjt modulates based on current load. Am I understanding this correctly? A while back when I was working on the mods, I thought I understood it, but now I'm unsure. I'll have to study this some more. |
|
|
| Mattyo5 |
Ok, Aleph 2 parts questions. I'm planning on using 16 fets total per channel, 1 ohm mills MRA-5's on each FET, and i was thinking of using for outputs ...instead of 8 of the .47 ohms in parallel for the output, how about 3 of the .33 ohm MRA-12's. I'm trying to save a few bucks and just wondering if doing this would be ok. Later!
-Matthew K. Olson |
|
|
| Mattyo5 |
anyone have any idea on how to use fewer higher power resistor on aleph 2 outputs rather than like 7 or 8 .47 ohm 3 watts?
since i'm using 16 FETs per channel, could I drop the emmitter resistors to .75 ohm mills mra-5's and use perhaps 3 of the .22ohm mra-12's as output resistors? thanks guys!
other options? i'm ordering from percyaudio.com soon i hope
-Matthew K. Olson |
|
|
| Brian Donaldson |
Using the 3 .33 ohm output resistors (I think) will increase AC current gain by almost 2X. 3 .22 ohms will increas by +- 1.5X
Decreasing source resistors from 1 ohm to .75 will up bias as will adding 2 fets per rail. Doing both will increase idle current around 2X. Should make a really spunky Aleph, with enough heatsinks. Almost able to push 2ohm loads to 400 W (these are all best case guesses of course) |
|
|
| Mattyo5 |
Ok, lets assume I don't want to change ac current gain or bias, i'll stick w/ 1 ohm resistors for source resistors, for all 16 devices, now, since I don't want to use 8 resistors for output resistors, how many mills MRA-12 and what value should I use (to save $$). I'll have a variable resistor for the bias setting (i've actually got a pot in mind and possibly a lighted meter for the back panel to indicate bias :-D). I've got some big sinks, no doubt, but i don't know if it'll be that spunky an aleph :)
-Matthew K. Olson |
|
|
| Brian Donaldson |
| The 2 extra devices will up the bias by a factor of 8/6, but that can be undone by your pot. For the output sense resistors, use whatever combination gives you .06 ohms. Very little voltage will cross these resistors, so 1 watt should be fine. Use ohms law to check dissapation. |
|
|
| Mattyo5 |
Ok, then 16 1 ohm source resistors, and 3 paralleled .22ohm mills MRA-12's ... it'll give me .073 ohms. That'd work i hope. Thanks!
-Matthew K. Olson |
|
|
| Billc |
| As devices are added the bias will increase, but that may not be a problem. I would not worry too much about the resistors on the output since you will be adjusting the AC current gain anyway. Bill :D |
|
|
| Mattyo5 |
ok, time to email percy then !
-Matthew K. Olson |
|
|
|
