Valve Wiz Buffer Loop

[drz400]

That schematic is fairly close to the D'lator but for me, since HAD designed the D'lator as a companion buffered loop for his ODS amps, I trust his design to work and sound better than just about any other design.
If you want to build the loop inside an existing amp, shouldn't be a problem as long as you have room for another tube.
Just wire it point to point.
Grab the B+ off of the PI node for the right approximate voltage then drop it down from there.

Problem with the Dumbleator is it isn't the best idea to have a pot as an output level unless it is 10K or less since you don't have a constant output impedance, it is dependent on the setting of the pot.

[Structo]

Not sure what you mean by that.

They work great with ODS amps.

Originally the loop had a 220K fixed resistor on the output, which was replaced with a 250KA pot.

[Tonegeek]

Not sure what you mean by that.

Think of the pot as being in parallel with the input to the following stage. When you adjust the pot the impedance changes as you add in or remove that impedance of the following stage. If the pot is 250k and the next stage has combined impedance (input resistor + tube) of 100k then the variance between 250k (full off) to 71.4k (full on) is 178.6k

If the pot is 20k and the next stage has combined impedance (input resistor + tube) of 100k then the variance between 20k (full off) to 16.7k (full on) is only 3.3k

As you see the impedance will vary more using a large value pot vs a smaller value pot. Bottom line is your tone and possibly touch response of the amp will change slightly when you adjust the large value pot because the impedance will change more as you add in or remove that impedance of the following stage. The impedance is a factor along with any existing capacitance in figuring the frequency passed. Of course everything is a trade off, the smaller value pot will cost you some power but in the follower circuit it is not a problem. In a gain stage going between say a 100k and 250k pot can make a huge difference in tone and response of the amp. An example is the drive pot in the non hrm amps. some like 100k and some like 250k. Big difference. In this case it is most noticed by a change in amplitude, but the tone is affected as well.

[Structo]

Thanks for the explanation.

I made a mistake in my comment, the resistor replaced by a pot was the Return.

All theory aside for a moment, the Dumbleator really enhances the ODS amp while at the same time giving you a buffered loop to have effects such as reverb in.

[Tonegeek]

Thanks for the explanation.

I made a mistake in my comment, the resistor replaced by a pot was the Return.

All theory aside for a moment, the Dumbleator really enhances the ODS amp while at the same time giving you a buffered loop to have effects such as reverb in.

++1 on the dlator. I think I agree with Merlin that the local feedback makes no difference. I have not looked at it on a scope and just done minimal listening tests, but could not hear a difference with it out of circuit.