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Old 11th February 2006, 05:44 PM   #11
daly2k is offline daly2k  United States
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Default aleph 100x

GL pretty impressive, did you use the pc board that was part of the x thread? Looks like you did pt. to pt. If you used the board where did you get it? I built the alpeh 1.2's using pt to pt wiring.
Just takes a bit longer. Your pictures are insipiring me to attemp this project. dave
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Old 11th February 2006, 07:59 PM   #12
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Default nice heatsinks

I do a similar approach using ribs and bar-stock for spacers. I like the idea of using sleeves on the treaded rod to create space between the ribs. Great when using a low speed fan...

John
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Old 12th February 2006, 12:30 AM   #13
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Hi John.

How is that new room of yours going.

This is one of the best diy X Aleph implementations I have seen and I propose to update my X Aleph along these lines.


20 IRFP240's is a good number.

I etched a pair of your boards diy style yesterday in anticipation!

(As much as I like my summer (ska) amp, its not nearly as much fun as diy class A SE)

Ian
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Old 12th February 2006, 01:43 AM   #14
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Default Hey Ian!

Long time, no see.

At the risk of hijacking this thread: (sorry)

My media room is rather interesting. I've installed a twelve foot by seven foot Dalite projection screen (3.6 meters x 2.1 meters) and slam it with an anamorphic lens/Infocus X1 (the one with the Farouja process). Great introduction to front projection at a very reasonable price--costs less than a 1.5 meter plasma by at least half. HUGE picture! I've purchased three Hafler amps on Ebay to drive my horns, bass horn included (similar to Nelson's Klein, but front loaded with LAB 12s).

I lost one channel on my Ax (motorboating) so I use the other channel for my center speakers (7.1). I've constructed a couple of twelve foot (3.6 meter) transmission lines using a pair of LAB 12 drivers in each and placed them a meter behind the sofa. BIG first octave!

I have plenty of the original AX pcbs left. If you need a pair, just holler.

I'm gathering materials to construct an Aleph 30 (Peter's pcb and resistors and my unused, massive chassis--I once posted a pic of it. It was for the Aleph 2s.

So, here I am hanging out at the big AX page. Someday, I've got to build me one of these brutes.

Nice chatting,

John
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Old 12th February 2006, 02:18 PM   #15
daly2k is offline daly2k  United States
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Default 100aleph x

John, I am considering building the Aleph X, do you have enough circuit boards for a stereo pair. I of course will build two mono amps? Please advise the cost and how I can acqire them. thanks, dave
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Old 13th February 2006, 03:59 PM   #16
gl is offline gl  United States
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Hi Dave,

Yes this is just simple point-to point wiring on the perf board. The board material is a better grade of phenolic and is made by Vero. I don't have a part number. It came out of the junk box. If I had purchased the material I would have bought one of their FR4 versions instead. It's better material. Mouser and Digikey both carry the Vero products I believe. The layout of the parts on the perf board was my own.

I am glad you were inspired by the pictures. That's why I posted them. I was encouraged by other pople here so I'm very happy to give some of that back.


Hi John,

My original intent was to put a 40mm 12V fan in the middle of the front of the chassis, then seal the chassis, and run the fan at 9V into the resulting plenum. It was a Pabst 612-something which had a noise figure of 16-17dBA. I ended up not using it. The air noise was inaudible but there was still a higher pitched buzz that sounded like commutating noise that I couldn't get rid of. I was going to use the fan control circuit NP published here a short while ago.


Hi Ian,

Thank you for your kind words. Frankly your posts have a significant part of the inspiration for these amps. Did you stick with the your original 4.7K MacMillan resistor values? I am thinking of increasing the value to 10K or even 22K to see what happens. Any thoughts? I recall that you also added input coupling caps to your Aleph-X but never published an updated schematic. How does what you did compare to what I did? Thanks very much.

Cheers to everyone,
Graeme
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Old 13th February 2006, 05:07 PM   #17
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Hi Graeme,

I'll take a pat on the head any day but you got the wrong Ian.

Try sending the other famous "Ian" a message via his profile to answer your questions!

If you search back in the first 50 or so pages of Grey Rollins original thread we tried other values and 4.7 K seems about optimum. The Load resisters (30-100R) also help to stabalise the DC.

Ian Mackenzie (Macka)
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Old 13th February 2006, 05:14 PM   #18
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Hi Ian,

Sorry about that. In fact this may not be the first time I've made this mistake. You're perfectly welcome to keep the pat on the head by the way. Thanks for the reply.

I remember smaller values being tried - e.g. 2.2K and 1K - but I don't recall people trying larger values. And I really don't remember that anyone actually "listened" to other values to see if the sound was affected.

Graeme
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Old 27th February 2006, 10:49 PM   #19
gl is offline gl  United States
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Prompted by Ians comments above, I decided to do more work on finding the optimal value for the MacMillan resistors in my Aleph-X's . Over the years NP has given out factory values for several of the parts on Greys original schematic but the value for the MacMillan resistors isn't one of them. I am going to assume that people reading this post know where these resistors are in the Aleph-X and what they do. My Aleph-X' were built with a value of 4.75K.

I started this quest by reviewing the first 100 pages of the big Aleph-X thread which was a good thing because I found some information I had missed.

My summarized findings are:

1) NP refers to these parts as one of several ways to control absolute DC offset performance. No one way is seen as the best and he appears to recommend a balance of all methods. These include close matching of parts, load resistors from the output nodes to ground, and the MacMillan resistors.

2) The MacMillan resistors are not required. Grey Rollins original circuit did not include them. However, he had to use a fairly low value of 30 ohms for the output load resistors in order to achieve a level of absolute DC offset control he could live with.

3) NP states in a post somewhere around page 58 that the MacMillan resistors could be as low as 5K without things "going to hell". A few members tried 1K and 2K resistors and seemed happy with the results. So what is meant by "goes to hell"? These resistors provide feedback to the diff pair sources and as the value drops the common mode performance of the amplifier suffers. The big question is - does the sound of the amp suffer?

Clearly, the only thing to do was try some differnet values and 1) listen to the amps and 2) measure the absolute DC offset performance. The worst case range range of possible resistor values was infinity at the high end and 5K at the low end. I figured from NP's remark about 5K that 10K would be a more reasonable "lowest" value.

The first value tried was 22K. The relative DC offset performance was fine. The absolute DC offset to a long time to settle - like an hour or more and even then it wandered seemingly with a mind of its own over a range of 1 to 1.5 volts. The sound, however, improved dramatically over the origina 4.75K resistors. A tightness and constriction in the sound disappeared and the music became more dynamic and relaxed. The sense of space improved. And I'm pretty certain the low bass performance below 30Hz improved as well. As a maggie user this last point is a big deal.

I decided that next I would try decreasing the value instead of increasing it - so 10K's went in. Again the relative DC offset performance was fine. Almost all of the improvement in the sound remained. This is a tough call, by the way, because you need to give the amps a long time to heat back up to operating temp before seriously listening. The absolute DC performance was more controlled - starting out at 8 - 9 volts and settling to 5 - 6 volts after 5 minutes. It then took another 45 minutes to settle down to below a volt. Any wandering was small and tolerable. In the end this is where I have decided to leave things for now.


Has anyone else done any similar experiments and listening tests? If so could you please add your findings. I would really appreciate any feedback from anyone. Thank you.

Regards,
Graeme
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Old 28th February 2006, 03:56 AM   #20
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Interesting observations.

I can only think that careful matching of the input pair and both halfs of the negative side would help with offset issues.

30 ohms is not a hell of a lot in the scheme of things anyways.

I plan to re engineer my X Aleph along your lines soon and will post my impressions and measurements.

Ian
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