I may add that the (case dependent) source impedance and interconnect capacitance may play a part in the gain equation.
Hence my suggestion for that 'weird looking' servo in this post
cheers
Hence my suggestion for that 'weird looking' servo in this post
cheers
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.
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
Grey
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
Grey
MikeW said:
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
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.
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.
john curl said:
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
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.
