AX100 100W Aleph-X Monoblocks

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Hi GL,
I was wondering how your two mono block AlephJ-X's are sounding and did you happen to bring them to the last burning amp festival. I'm still planning to build a pair in the near future. I've just repaired my F5 for the 4th time(wanted to make sure I could keep my first amp alive). This time a did a complete rebuild so I'm fairly confident that it's gonna survive this time.
Once I start on the Mono's I want to go point to point on a blank circuit board as much as possible. Do you think silver plated solid copper 12 or 10awg would be good for the output. Jumper all the transistors kinda like the way you did it. I'm wondering if this would make any difference on the sound.
 
In these larger class A amplifiers it becomes very difficult to picture the small footprint of the output device transferring heat fast enough and with enough efficiency to use up the heat sink area needed for these projects.
In Graeme's nice industrial looking amp he has a plethora of individual aluminum plates sucking up the heat from just 100 watts of class A amplification.
If the cost of ready made commercial heat sinks are a large burden to the budget his approach may be one to look at. Salvaging nice plates of aluminum and cutting to fit works quite well and is also different and unique.
If you look at some of the pictures of DIY amps on this forum and the web you can get some really nice ideas on how to use salvaged materials and save big bucks. The assemble time goes up but in a hobby it is considered free time.


Tad
 
I bought a bunch of of large heatsinks on eBay measuring WxHxL 4 1/4" x 5 1/2" x 2 1/2". I was planning on using 12 of them for each monoblock. They didn't come with specs but I'm thinking (hoping) this will be enough. On the other hand I'm using 3 of these heatsinks for each channel on my F5 and they dissipate at about 114F on the tips. So I'm not sure if it's enough for the 100w monster amps. If not I was thinking of using fans or even second type of heatsink on top of the output transistors. Something similar to GL's heatsinks.
 
I bought a bunch of of large heatsinks on eBay measuring WxHxL 4 1/4" x 5 1/2" x 2 1/2". I was planning on using 12 of them for each monoblock. They didn't come with specs but I'm thinking (hoping) this will be enough.

Have a look at Rod Elliot's heat sink estimating spreadsheet: ESP Download Page. For a 100w monoblock, you'll need somewhere close to 0.06 c/w total. Each of my amps has about 0.07c/w total heatsinks and burns off nearly 400w (22v rails, 9A draw) which results in a thermal rise of about 32-34c.
 
AX100 updates

GR, I hope you are still out there. Well it is winter in middle america and time to do Pass audio projects. I have retired and moved and to get my AX100's here I had to partially disassemble them to get the movers to box them.

Have you done any further updates? My plan is to design some new chassis for them and redo the circuit boards. I could never get the absolute DC levels to drop below 10volts on one amp. I have measured j-fets and matched perfectly outside the circuit but once installed they didn't act as matched. On the amp with the high absolute dc offset I have a pot that I installed and adjusted to get the jfets matched in the front end. I guess this may have an affect on the absolute dc.
Other differences from your last published schematic:

I am not using and input cap--maybe this has something to do with it?
I have 12 outputs vs 10
I am using J-fets for the cascode vs transistors-which I will change. I have used these mono amps with great success but they have been in boxes for about a year as we had to remodel our new home. I am anxious to get going again. thanks and I hope all is well with you--dave
 
I am not using and input cap--maybe this has something to do with it?

This is the first most-likely culprit of your offset. When I originally built my amps, I was able to skip the input caps and "tune" the offset to CD player and I didn't have any problems. As my system neared completion, I added a new preamp and my DC offset went sky-high. Input caps were the solution, have a look at my web page.

Eric
 
Eric, you have given me hope for an easy way out. I really liked your web page and plan to investigate your project for some tips. I too only need about 100 watts/channel so we are about the same for design parameters. GL had gone the XA route but now that is even out of date based on the new pass designs. Thanks again and as I go forward I will let you know what happened--dave
 
Hi Dave,

Congratulations on being retired. I look forward to the day.

I apologize for not seeing your post here sooner but I only log in once a week or so. I've been doing DIY electronic projects in the musical instrument vein more lately.

I too think that your problem lies with the input JFET's. I wasn't able to make my amps play at all without them and I still don't understand why. I didn't spend much time on the problem because the caps fixed everything. I would suspect that your 170's aren't matched as well as you think and I would re-check them. Ian MacKenzie (in OZ) had used matched 170's with great success as you might remember from the beginning of this thread.

I have not modified this design much over the last couple of years. It still works well and sounds superb. By the way I consider the XA with JFET inputs to still be the pre-eminent design on this site.

My most recent project is a direct box based on the F4 circuit. It would also make a first class headphone amp too. I have been meaning to post it here for over a year. Maybe I need to retire...

Graeme
 
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Hi Bluewater,

Sorry for not responding sooner.

Unfortunately I have missed Burning Amp the last two years because of schedule conflicts. The last time I attended I did indeed bring these amps. Alas there were too many other amps there and we didn't get to fire them up. Perhaps this will happen in 2012.

From the information you give on your heat sinks I am unable to advise you on whether or not they would work for the AX100J. If you run the outputs on separate heat sinks like I did then make sure your matching is as good as possible.

Most of the heat generated on my heat sink plates is dissipated within 3" or 4" of the output transistors. I believe that you could cut my heat sink plates down from 8" tall to 7" or even 6.5" and not see much of a net temperature rise. As I've stated before I would place the output transistors at different points on the plates if I had it to do over. Experience is a wonderful thing.

Most of the heat sink interconnect buses are 12ga tinned solid copper wire. Some are 12ga stranded wire that has been stripped of the PVC jacket. I don't think that silver plating would make an audible difference. You'll notice from the photo's that the output connections are very, very short.

I would encourage you to build this circuit. Like I stated in the last post I personally consider this to be one of the top power amp projects on this forum. And 'no' I haven't auditioned many of the others. And 'yes' I'm completely and arbitrarily biased - no pun intended.

Graeme
 
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Bring those "same ole" amps in 2012 and I promise to get them in a system.The 5 listening rooms will help. I really want to hear them! It's Oct. 28th , you can start planning now!

Mark




Hi Bluewater,

Sorry for not responding sooner.

Unfortunately I have missed Burning Amp the last two years because of schedule conflicts. The last time I attended I did indeed bring these amps. Alas there were too many other amps there and we didn't get to fire them up. Perhaps this will happen in 2012.

Graeme
 
I definitly plan on building the Aleph-JX 100w mono amps. In fact I have 99% of the parts. Just earlier on I realized that I was jumping the gun with not enough experience and if I failed, well failure is not an option. I'm feeling more confidant now, especially with Eric's wiki on the subject. Thanks Eric! I only have one amplifier that I've built and that would be the F5. An amazing amplifier, the best sounding I have ever owned. I'm going to build the F2J next and if all goes smoothly I'll start the Aleph-JX monoblocks next. Experience is really what is keeping me from building the monoblocks.
 
Bluewater: I'm happy to hear that you found my web page of some use. I started the same way you did. The first amp I built was the a40 about 10 years ago. At the time, everyone else was here was building the Aleph2 or Aleph4 (very similar designs). I chose the a40 because there was a nice PDF on the PassLabs web site that had everything I needed. I wasn't about to tackle an Aleph design because there were just too many questions that I had.

After building my a40 (and making a few mistakes along the way), I began gathering parts for the newly developed Aleph-X. I still didn't have a great understanding of things and figured that if I spent my time gathering parts and following the thread, by the time I built my Aleph-X there would be plenty of people with enough experience to help me. My timing worked out pretty well, though I almost waited too long since by the time my Aleph-X amps were nearing completion, everyone else had moved on to the F-series of amps...

Have fun!
 
These amps will at at BA 2012 this coming weekend. I have requested that they be put in the Pass room but I have left their use and location up to Mark (Variac).

It has been a few years since the amps or I have been to BA and I am looking forward to renewing friendships and being inspired by the cool things other folks build and bring.

Graeme
 
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