Pass DIY Addict
Joined 2000
Paid Member
Felipe,
My recommendation is very similar to what Joris has indicated. What you have not specified, though, is the load presented by your speakers. If you want 50w into an 8ohm load, this is somewhat "easier" (less bias, less heat, smaller heatsink, smaller chassis, more light weight chassis, etc) than building an amp that will deliver 50w into a 4 ohm load.
Or, you could design the amp to provide approx 50w into both an 8ohm and 4 ohm load. A design like this would have rail voltage of about 17v, bias of 5.0A (easily adjustable with the trim pots), AC Current gain to 50%, use 2 fets per quadrant (8 output fets total), and total heatsinking of 0.15c/w per channel. This design would utilize a 500VA transformer with something like 14vac or 15vac secondaries. Basically any transformer that you need would have to be a custom build for you, its unlikely that you would find an "off the shelf" ready made transformer to suit your needs.
If you optimize for an 8 ohm load at 50w, you might be able to get away with only 4 fets total per channel, but still need 0.15c/w worth of heat sinks. This design would consume approx 150w out of the wall socket and run slightly cooler in temperature than the version above (though keep the heat sinking the same).
Optimizing for a 4 ohm load at 50w, you should use 8 fets total per channel due to the higher bias setting. This design would consume approx 200w of power from the wall outlet and keep the final heat sink temperature somewhere in the 45-50c range.
Hope this helps a little...
My recommendation is very similar to what Joris has indicated. What you have not specified, though, is the load presented by your speakers. If you want 50w into an 8ohm load, this is somewhat "easier" (less bias, less heat, smaller heatsink, smaller chassis, more light weight chassis, etc) than building an amp that will deliver 50w into a 4 ohm load.
Or, you could design the amp to provide approx 50w into both an 8ohm and 4 ohm load. A design like this would have rail voltage of about 17v, bias of 5.0A (easily adjustable with the trim pots), AC Current gain to 50%, use 2 fets per quadrant (8 output fets total), and total heatsinking of 0.15c/w per channel. This design would utilize a 500VA transformer with something like 14vac or 15vac secondaries. Basically any transformer that you need would have to be a custom build for you, its unlikely that you would find an "off the shelf" ready made transformer to suit your needs.
If you optimize for an 8 ohm load at 50w, you might be able to get away with only 4 fets total per channel, but still need 0.15c/w worth of heat sinks. This design would consume approx 150w out of the wall socket and run slightly cooler in temperature than the version above (though keep the heat sinking the same).
Optimizing for a 4 ohm load at 50w, you should use 8 fets total per channel due to the higher bias setting. This design would consume approx 200w of power from the wall outlet and keep the final heat sink temperature somewhere in the 45-50c range.
Hope this helps a little...
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I joined this forum about 4 months ago in what started out as a project to repair an A75 I built about 15 years ago. Great amp I might add...but a little finnicky. I had gotten away from this hobby at the behest of my wife...
(I'm sure a few of you here know what I'm referreing to). Anyway, this repair project has reminded me how much I enjoy building audio gear...and listening to your work. After everything I've read on this thread about the AX I need to build one. Does Peter still have PCBs available and how would I go about contacting him? I'm still new here and trying to find my way around. What it would take in terms of number of frontend and PSB boards to do a couple 100w monoblocks?
Dan
(I'm sure a few of you here know what I'm referreing to). Anyway, this repair project has reminded me how much I enjoy building audio gear...and listening to your work. After everything I've read on this thread about the AX I need to build one. Does Peter still have PCBs available and how would I go about contacting him? I'm still new here and trying to find my way around. What it would take in terms of number of frontend and PSB boards to do a couple 100w monoblocks?Dan
Pass DIY Addict
Joined 2000
Paid Member
A good, cheap heatsink is a junkyard motorcycle engine. The heads an be used for "small" heatsinks, the engine block is an excellent large heatsink. Alternatively, look for any aircooled car or airplane engine. VV bug comes to mind. Plenty of thermal mass and lots of fins. Should be very cheap, too. Late Bob Pease had such a heatsink in a photo somewhere, that's what inspired me to look for one. If that's not enough, then simply get an aluminum head from any watercooled car, and use water cooling
A bit late but....
I finally got to fire up my aleph-X today.
It is the "standard" 45w version running 15v rails with 10k macmillan resistors.
After warming up & adjustment of V1, V2, V3 the relative offset measures just a few millivolts, same for absolute DC offset from either speaker terminal to ground.
The problem is that the nominal 0.5 volts I started with across the source resistors is now scewed so that I have 4.6v across one and 5.4v across the other. Is this actually a problem (if so any advice gratefully received) or can I just ignore it?
I finally got to fire up my aleph-X today.
It is the "standard" 45w version running 15v rails with 10k macmillan resistors.
After warming up & adjustment of V1, V2, V3 the relative offset measures just a few millivolts, same for absolute DC offset from either speaker terminal to ground.
The problem is that the nominal 0.5 volts I started with across the source resistors is now scewed so that I have 4.6v across one and 5.4v across the other. Is this actually a problem (if so any advice gratefully received) or can I just ignore it?
Oops...
"4.6v across one and 5.4v across the other" - Sorry, those values are of course 10 x too big - should be 0.46v and 0.54v across the source resistors.
If I even out the voltages over the source resistors to 0.5v each then the relative offset increases to 0.054v - should I just leave it like that?
What are acceptable offset values?
"4.6v across one and 5.4v across the other" - Sorry, those values are of course 10 x too big - should be 0.46v and 0.54v across the source resistors.
If I even out the voltages over the source resistors to 0.5v each then the relative offset increases to 0.054v - should I just leave it like that?
What are acceptable offset values?
Pass DIY Addict
Joined 2000
Paid Member
Playing music
Thank you for your prompt replies.
I have reset the voltage across the source resistors back to 0.5v, relative offset is running at 56mv.
I plugged in some speakers and as expected there is nothing but silence at the speaker cone (I've built this amplifier with a regulated power supply).
I used a cheap portable radio/cd player as a signal source for now and played a CD through the amplifier - all works as expected
I still need to check a few things out with a scope before i'm completely happy but things are looking good so far.
And Eric - Thankyou for your informative web site!
Just 3 more to test now.....
Thank you for your prompt replies.
I have reset the voltage across the source resistors back to 0.5v, relative offset is running at 56mv.
I plugged in some speakers and as expected there is nothing but silence at the speaker cone (I've built this amplifier with a regulated power supply).
I used a cheap portable radio/cd player as a signal source for now and played a CD through the amplifier - all works as expected
I still need to check a few things out with a scope before i'm completely happy but things are looking good so far.
And Eric - Thankyou for your informative web site!
Just 3 more to test now.....
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Clipping
I have connected the amplifier to a signal generator and have noticed a couple of problems;
With just over 3 volts input the output starts to clip - the bottom half of a sine wave is clipping first (but i'm probably swinging 26 volts pk-pk, just 4 volts shy of the rail voltages) is this about right or should it clip symetrically?
I don't have 3v coming out of my preamp - 0.5v is all i have, so i'm not going to be able to drive the amplifier properly without changing the gain (or introducing another gain stage somewhere). Which resistor values can be changed and what is the penalty for doing so (i'm not sure what can be changed without affecting the balance of things).
I have connected the amplifier to a signal generator and have noticed a couple of problems;
With just over 3 volts input the output starts to clip - the bottom half of a sine wave is clipping first (but i'm probably swinging 26 volts pk-pk, just 4 volts shy of the rail voltages) is this about right or should it clip symetrically?
I don't have 3v coming out of my preamp - 0.5v is all i have, so i'm not going to be able to drive the amplifier properly without changing the gain (or introducing another gain stage somewhere). Which resistor values can be changed and what is the penalty for doing so (i'm not sure what can be changed without affecting the balance of things).
Pass DIY Addict
Joined 2000
Paid Member
Hi Jason,
The problem you are experiencing with input clipping is not really a "problem" per se. I have a short write up about this on my web page in the Power Bandwidth and Input Sensitivity sub-section of Output Testing. In order to get greater input sensitivity, try doubling R16 and R30. Doing this gave me 5dB more output for the same input level, but it comes at the cost of reducing the power bandwidth. I have a small hum at the speaker that I think is coming from my power supply, but I haven't spent the time to track it down. Increasing my input sensitivity increased the amount of hum I was experiencing at the speaker, so I think I ended up changing it back soon after. My speakers are not very sensitive, so this hasn't really been an issue for me.
I have also noticed my clipping does not occur quite symmetrically. One side clips a little bit before the other side, though not by much. Input levels before clipping occurs are also on my web page.
Hope this helps a little...
Eric
The problem you are experiencing with input clipping is not really a "problem" per se. I have a short write up about this on my web page in the Power Bandwidth and Input Sensitivity sub-section of Output Testing. In order to get greater input sensitivity, try doubling R16 and R30. Doing this gave me 5dB more output for the same input level, but it comes at the cost of reducing the power bandwidth. I have a small hum at the speaker that I think is coming from my power supply, but I haven't spent the time to track it down. Increasing my input sensitivity increased the amount of hum I was experiencing at the speaker, so I think I ended up changing it back soon after. My speakers are not very sensitive, so this hasn't really been an issue for me.
I have also noticed my clipping does not occur quite symmetrically. One side clips a little bit before the other side, though not by much. Input levels before clipping occurs are also on my web page.
Hope this helps a little...
Eric
Newbie With Some Questions
Been into audio equipment for a long while (got cables older than some of the builders here, and am just considering DIY for the first time. A few weeks ago I heard a friend's Pass Labs Int-30A sounding really beautiful. I'd been thinking about saving up $1.5-3K for a used Spectral amp, but was pretty knocked out after researching the Pass Labs equipment to find that Nelson has so many designs available to DIYers willing to put in some time, thought, and effort. That seems like a really good bargain to me.
- I loved the sound of the Int-30A, so whatever DIY amp has the closest "family resemblance" to that is what I'd like to point toward. Am I correct in supposing the Aleph-X is the closest available DIY design to the Pass XA series? (I'm aware this isn't normally what one would consider a starter project, but I'm prepared to take things slowly and carefully, do lots of research, and ask what are hopefully very occasional, appropriate questions.)
- In order to keep costs and numbers of boxes and power cords down, I'd prefer to build a stereo design rather than two monoboxes. Speakers are a pair of Vandersteen 2Ces, early 90s vintage. Dimensions of the bay in a wooden cabinet in which a stereo amp would sit (open front, 2" high opening cut across the lower back for cable and power connections) are 22" wide, 23" deep, 8" high. Current amp is a late-80s PSE Studio IV, 100wpc into 8 ohms, nearly double that into 4 ohms. Do I have a prayer of building a stereo amp with reasonable power output for the Vandersteens that would fit into the available space and have room for sufficient heat dissipation? If such a stereo amp is possible, what sort of wpc output range should I look at?
Otherwise, guess I'll be looking at a couple of mono amps.
Thanks very much in advance for your thoughts and advice.
Been into audio equipment for a long while (got cables older than some of the builders here
, and am just considering DIY for the first time. A few weeks ago I heard a friend's Pass Labs Int-30A sounding really beautiful. I'd been thinking about saving up $1.5-3K for a used Spectral amp, but was pretty knocked out after researching the Pass Labs equipment to find that Nelson has so many designs available to DIYers willing to put in some time, thought, and effort. That seems like a really good bargain to me.- I loved the sound of the Int-30A, so whatever DIY amp has the closest "family resemblance" to that is what I'd like to point toward. Am I correct in supposing the Aleph-X is the closest available DIY design to the Pass XA series? (I'm aware this isn't normally what one would consider a starter project, but I'm prepared to take things slowly and carefully, do lots of research, and ask what are hopefully very occasional, appropriate questions.)
- In order to keep costs and numbers of boxes and power cords down, I'd prefer to build a stereo design rather than two monoboxes. Speakers are a pair of Vandersteen 2Ces, early 90s vintage. Dimensions of the bay in a wooden cabinet in which a stereo amp would sit (open front, 2" high opening cut across the lower back for cable and power connections) are 22" wide, 23" deep, 8" high. Current amp is a late-80s PSE Studio IV, 100wpc into 8 ohms, nearly double that into 4 ohms. Do I have a prayer of building a stereo amp with reasonable power output for the Vandersteens that would fit into the available space and have room for sufficient heat dissipation? If such a stereo amp is possible, what sort of wpc output range should I look at?
Otherwise, guess I'll be looking at a couple of mono amps.
Thanks very much in advance for your thoughts and advice.