Made the local Feedback Switchable... question:

[JubileeMan 2555]

Well, I made the FB switchable and it was VERY VERY noticable. Quite shocking actually.

But, I think it simply added too much gain since this feedback jumps over 2 gain stages.

I'm going to experiment with higher, 10M, 22M, and 40M resistors to see the sweetspot between smooth, and wild.

Question: In the Dumble designs, he used a .05uf cap in series with his local feedback loop resistor. Was this because HE setup the feedback to enter into the Plate where there is the B+ voltage and needed to stop the direct current from going up stream, or was there at tonal purpose to the cap?

...long question short, would I benifit from using a cap in series even though, in tweed designs, the feedback connects to the cathode of the last gainstage?

[donnyjaguar]

Do you have a schematic(s) of the capacitor(s) in question?
Feedback amplifier design is hard enough for me to articulate already!

[JubileeMan 2555]

Do you have a schematic(s) of the capacitor(s) in question?
Feedback amplifier design is hard enough for me to articulate already!

This is the circuit I have and am modifying:

http://www.tylergrund.com/images/superamp_schematic.jpg

And I couldn't find a schematic, but here is a nice color layout of the LFB in a dumble style amp:

http://www.tylergrund.com/images/dumble_layout.jpg

[RedMan]

Well, I made the FB switchable and it was VERY VERY noticable. Quite shocking actually.

But, I think it simply added too much gain since this feedback jumps over 2 gain stages.

I'm going to experiment with higher, 10M, 22M, and 40M resistors to see the sweetspot between smooth, and wild.

Question: In the Dumble designs, he used a .05uf cap in series with his local feedback loop resistor. Was this because HE setup the feedback to enter into the Plate where there is the B+ voltage and needed to stop the direct current from going up stream, or was there at tonal purpose to the cap?

...long question short, would I benifit from using a cap in series even though, in tweed designs, the feedback connects to the cathode of the last gainstage?

The second stage has a gain of less than one so it's really not a whole lot of gain across those 2 stages. I'd be tempted to use the loop for an active bass flub reduction control.

[xk49w]

The second stage has a gain of less than one so it's really not a whole lot of gain across those 2 stages. I'd be tempted to use the loop for an active bass flub reduction control.My eyes are squinting but to me it looks like a conventional high gain stage with a cathode follower.

[Trout]

The basic Circuit is the same as the 5E7 bandmaster, I have a 10M in that position, though I have read somewhere that going much beyond 22M that it starts to sound very raspy?

[1guitarslinger]

With the resistor removed, try also removing the cathode bypass cap on V2, and see what you think.

This will allow the amp to sound more "open" but keeps the gain from being over the top.

You may, or may not like it, but it's worth giving a try.

This makes the arrangement similar to a 5F6A.http://www.ampwares.com/ffg/schem/bassman_5f6-a_schem.gif

You may also want to back down to a 12AY7 in V1, if you're not already using one, and see how that sounds.

[RedMan]

My eyes are squinting but to me it looks like a conventional high gain stage with a cathode follower.

When I say the second stage I mean within that loop. It is in fact a cathode follower stage with a gain of less than 1 which makes the stages within the loop a whole lot less than if the second stage had some gain going on.