Aleph-X builder's thread.

DC Servo for the AlephJ-X

Hi,

some people asked for information on the dc-servo I put in my Aleph-X a while ago. I finally managed to write it all up.

The parts values will probably not fit any other amp as they will vary with supply voltage, cooling, McMillan resistor values, JFet or Fet input etc. etc. but it will help getting started.

Main motivation for doing this was the possibility to raise the values of the McMillan resistors above 30k. I think these have quite an influence on sound quality. This would not have been possible otherwise as mains voltage fluctuations are just too big where I live.

I put it all together in a pdf. This made it a lot simpler for me to write down. The pics are a bit small but I can post them separately if needed.

Hope this helps,

William
 

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Aleph X for 2017

Hello
For a member of Pink Fish, I have made the following purchase.
4x Aleph X boards (2 surplus)
3x Soft start boards (1 surplus)
3x discrete regulators (need 1)
5x 1000va transformers, with 18v18 x4 secondaries (3 surplus)
12 x copper bus bars to mount the transistors directly to this with no isolators the copper bar then insulated with Sil-Pad.
4x Heat Sink = 400x150x50
14x capacitors 50v 68000uf
Pack of components for the amp boards and soft start.
All good, however, I need two more power caps to make up the 16 required, they are United Chemi-Con U32D, 68,000uf 50v. Can anyone advise where to purchase these caps, or advise on inserting alternatives (I guess it would require 4 off).
So far, done some top level reading and gathering of information regarding the Aleph X. (Gulp) !. I am beginning to understand that, the Aleph X, is a quite a different amp to the F5 's I have constructed so far, (I hope that I haven't bitten of my than I can chew!).
(I am currently part way through building a stero F5t, with twin power supplies, completed and tested).
The Aleph X will be mono's.
 
William - thank you for the writeup. I've been adjusting my amps every few months to account for the change of season and the accompanying change in ambient temperature in the semi-unfinished portion of my basement where the amps live. It is surprising how much the offset changes - this will remove a seasonal chore!

Esprit - have a look through my Aleph-X web page, it will probably answer most of your questions. I am wondering why you are bothering with copper bus bars for mosfet mounting. If you don't insulate each transistor from the copper bar, then you can only put one transistor on each bar, so you're not likely to be doing much spreading of heat across your sinks and will only be introducing another thermal junction which will decrease your cooling efficiency. Best in this case to just mount the mosfets directly to your sink with an electrical insulator. Finding good caps is always a treasure hunt. I don't have ready made sources for these, you just have to poke around. I advise against using old/surplus parts - go with new parts.
 
William,

If I may offer one tweak to your DC servo circuit, you could use the balanced output of the amp to good advantage by summing the outputs at the input of your DC servo. The music signal sums to nearly zero and wouldn't need to be filtered, leaving only the common mode signal that is mostly the DC you want to use, along with any 50Hz/60Hz power supply noise and harmonics.

Jeremy
 
Zen: I don't have either a PDF or Gerbers. The only thing I have are digital images of the front and back of the bare PCB. Lower resolutions ones are on my website - I can provide higher resolution if you think they'll help.

Edit: Someone here has got to have the original files - I think they were a "design by committee" so there should be multiple sources...
 
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Sneak preview of my upcoming AJXH build...
 

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Target rails are +/-15V DC from a Zen V3 style IRFP240/9240 capacitance multiplier. Raw DC is from a Toroidy 240VA 2*15VAC audio grade transformer hooked up to a single full wave bridge, 12*33000uF (that's like 0.4F) filter capacitance, one reg per rail per channel (four total, C-C-reg-C configuration). Output devices will be curve traced quads of FQP3N30 FETs, biased at 0.5A. It's obscenely overbuilt.
 
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Gents,

I am having issues with both of my AlephX boards. I thought I was careful in placing each part, taking my time measuring each component before soldering it on, but alas - I'm having issues.

R1 and R6 basically burn instantly when I turn the amp on.

This only happens on one amp.

I'm hoping I can resolve one at a time, before I move onto the next.

Thanks in advance :)

-Vlad
 
My first thought is to check your Q2 mosfet(s) and make sure they are COMPLETELY isolated from your heat sink. Use your DMM, there should be no connectivity between any of the legs and the sink. You may need to remove the device from the board first and depending on your implementation, this could be a lot of work.

Also, check out the voltages around your input differential and the output mosfets between the two channels. This might provide some clues about where the errant voltage is appearing.