John Curl amp

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#489
No, your caps appear to be lousy in your amp. I think that is your biggest problem. I would try to servo it, if I were you. Then you should probably change your bypass caps to Rel RT, then we can work on reducing the output coil inductance. I can promise this: If I made the amp, it would pass the listening quality test.
 
#493
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.

:angel:
 
#494
MikeW said:


Slight biasing accident.

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


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.

Grey
 
#495
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.
 
#496
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.
 
#497
john curl said:
No, your caps appear to be lousy in your amp. I think that is your biggest problem.
Click to expand...


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.



Sigurd
 
#498
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.:smash:
 
#499
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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