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Old 5th April 2008, 01:48 AM   #491
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Michael Percey.
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Old 5th April 2008, 02:05 AM   #492
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Mike,
For what it's worth, the RelCap people also make the RTX caps that I'm fond of. Both caps are polystyrene film & foil, but the internal construction differs. No, I haven't compared the two against one another--perhaps John has. In any event, they're good parts.
www.percyaudio.com

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Old 5th April 2008, 02:55 AM   #493
MikeW is offline MikeW  United States
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I had to change the output transistors. NJW 0302, 0281. Slight biasing accident. I can't find the Toshiba's I had. It's tough to get old.
I will give the amp a listen tomorrow. The wife and son are asleep.
The RL cap only go up to 3 uf. from Percyaudio.

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Old 5th April 2008, 03:08 AM   #494
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Quote:
Originally posted by MikeW


Slight biasing accident.

The RL cap only go up to 3 uf. from Percyaudio.


You're not alone. I had a 'slight biasing accident' with the first iteration of my auto-bias circuit. Didn't think things through and had the wrong value of resistor. Nothing like feeling dumb to sharpen your hindsight.
Michael Percy has as good a selection of those caps as anyone, however others do carry the parts. I believe Handmade Electronics does: www.hndme.com although they tend towards the higher voltage parts for tube folks. I think there are others who carry the caps, but can't remember. You might check www.capacitors.com to see if they've got a list of distributors.
If nothing else, parallel the caps.

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Old 5th April 2008, 06:20 AM   #495
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Use .1uf RT for bypassing. Direct couple the amp and add a non-invasive servo, if necessary, using typical servo techniques. Just make sure that it is nor tightly connected to the loop. IF you have to use an input coupling cap then use a Rel PPMF 8uf cap as an input cap. It is best to avoid RTX, because it is very high Q. It is best for switching amps and switching power supplies. Please remember, it is my initial design, and I am only trying to get you out of trouble. You can modify it later with your favorite caps, etc.
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Old 5th April 2008, 08:37 AM   #496
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Hi Patrick re; your question in #454. The answer is 1969. That was the first published article from JLH in what was then "Wireless World". It was a 4 transistor single rail version. Since then a lot has changed with the magazine now called "Electronics World". In between I think it was "Electronics and Wireless World" and in that incarnation, in 1996, John Linsley Hood published an uprated split rail version of 15 watts.
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Old 5th April 2008, 09:06 AM   #497
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Quote:
Originally posted by john curl
No, your caps appear to be lousy in your amp. I think that is your biggest problem.

The input cap and the two large red decoupling caps were supplied by me. All are Wimas. Not top notch high end audio caps but I thought that Mike did not want to use more expensive/exotic ones.

My feeling has been that only "normal quality" components were to be used. If not, I would change all caps and all resistors, too, and use another coil, and also non FR4 PCB.

A more complex power supply would also be needed to raise sonics, IMO.

I would short the input cap and see how that affects the sonical character to begin with. Then move on to change the two larger decoupling caps.

Adding a few 100nF PP or PS caps is another idea I would try.



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Old 5th April 2008, 03:49 PM   #498
MikeW is offline MikeW  United States
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I have taken out the input cap. Increased R 9 to 8k. There was a little hum when it was 4.5K. The amp is sounding better. Give me a couple more days for listening.
The servo will take a board re-spin and another power supply.
I think that would have to be another thread.
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Old 5th April 2008, 05:56 PM   #499
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Sigrud, the Wima caps aren't (bad) it is that we have found the Rel RT caps to be best. That is: Charles Hansen, Bob Crump, and me, independently of each other. There must be something 'right' about them. I am told that you will find Rel in 7 out of 8 of the best sounding amps and preamps in the high end world, today. I am not surprised.
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Old 5th April 2008, 08:10 PM   #500
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Mmm, name another manufacturer of >10nF styrene caps nowadays.
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