Re: went over my head.....
You gotta be kidding .... 😎
Wilson Audio Watt/Puppy in his +/- 7's incarnation at the moment!
http://www.wilsonaudio.com/products/wattpuppy/index.html
It is one of the most 'talked' about speaker in speakerland as far as my world goes...
Edwin
carpenter said:
You gotta be kidding .... 😎
Wilson Audio Watt/Puppy in his +/- 7's incarnation at the moment!
http://www.wilsonaudio.com/products/wattpuppy/index.html
It is one of the most 'talked' about speaker in speakerland as far as my world goes...
Edwin
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.
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.
How will the 044n sound best ?
...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 ?
...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 ?
Yes.
It is off the topic and it is not really a great speaker and yes Thorsten has put together a kit:
http://www.fortunecity.com/rivendell/xentar/1179/projects/david/david.htm
And now back to the subject...
It is off the topic and it is not really a great speaker and yes Thorsten has put together a kit:
http://www.fortunecity.com/rivendell/xentar/1179/projects/david/david.htm
And now back to the subject...
What do you call "not reeally a great speaker"?Blitz said:
I'm thinking about biolding a pair of proac response 2.5
Are the puppies worse?
so, according to the wanted power, we should always use the less devices possible.MEnsing said:
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".
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".
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
*****
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
Blitz
Blitz,
seems you plan to build some aleph x?
I have just started.
perhaps we could mail about speakers etc. ?
Gruß
Ralf
Blitz said:
Blitz,
seems you plan to build some aleph x?
I have just started.
perhaps we could mail about speakers etc. ?
Gruß
Ralf
Schematics for the high-power version (based on Grey's input)
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
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
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
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
Schematic based on the group's input (from the Aleph-X-Threat)
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
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
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.
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.
Re: How will the 044n sound best ?
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
Blitz said:
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
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
Happy New Year – Jens
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.
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.
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
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
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