> I built this circuit during the holidays and couldn't get it to work due to some stupid grounding mistake.......... Now it seems to work OK, here is the schem.......
I've been quiet, hoping that someone else would po> I built this circuit during the holidays and couldn't get it to work due to some stupid grounding mistake.......... Now it seems to work OK, here is the schem.......
I've been quiet, hoping that someone else would point out the obvious:
You are not clear in what you are doing!
What do U1 Q1, U2 Q2, U3 Q3 do for you? Nothing! Take them out, use just a 3K resistor and the big cap, it will work fine. In fact I don't see how it can work as shown, unless reality is not the same as the drawing (would not be a suprise).
Also using G2 as the output of V2 is unusual. It has been done when you need a low-power triode and all you have is a glass pentode. G2 is a fine "Plate", if a little easy to cook. Then the original plate may be grounded, which acts to shield the rest of the tube.
And the unbypassed G2 on V3 is odd. Normally you must bypass G2 it get good gain.
The 10K load on V3's 1Meg variable plate resistor does not look right. Plate resistors are usually smaller than the load. And 10K is a fairly low load for these tubes.
> The 3 tube preamp puts out very modest, 20log 20/0.8 = 27.95 dB
That's stunningly modest. 6SN7 gain-stage, 6BA6 gain-stage, and 6SK7 cathode follower would give voltage gain over 1,000 or 60dB and THD under 1% at 1V out without any feedback or big stability issues. You seem to have over-complicated, got "modest" performance, and at this point nobody understands what that circuit really does.
Start with the 90 year old tube amplifier designs. Don't go sticking Silicon up their butts without knowing what it really does. int out the obvious:
You are not clear in what you are doing!
What do U1 Q1, U2 Q2, U3 Q3 do for you? Nothing! Take them out, use just a 3K resistor and the big cap, it will work fine. In fact I don't see how it can work as shown, unless reality is not the same as the drawing (whould not be a suprise).
Also using G2 as the output of V2 is unusual. It has been done when you need a low-power triode and all you have is a glass pentode. G2 is a fine "Plate", if a little easy to cook. Then the original plate may be grounded, which acts to shield the rest of the tube.
And the unbypassed G2 on V3 is odd. Normally you must bypass G2 it get good gain.
The 10K load on V3's 1Meg variable plate resistor does not look right. Plate resistors are usually smaller than the load. And 10K is a fairly low load for these tubes.
> The 3 tube preamp puts out very modest, 20log 20/0.8 = 27.95 dB
That's stunningly modest. 6SN7 gain-stage, 6BA6 gain-stage, and 6SK7 cathode follower would give voltage gain over 1,000 or 60dB and THD under 1% at 1V out without any feedback or big stability issues. You seem to have over-complicated, got "modest" performance, and at this point nobody understands what that circuit really does.
Start with the 90 year old tube amplifier designs. Don't go sticking Silicon up their butts without knowing what it really does.