Increase Reverb in a One Tube Reverb

[Darkbluemurder]

This weekend I changed the reverb. I used a reverb recovery amp similar to what Matchless used in their Chieftain model. When I used the exact circuit the reverb level was the same as with the one tube reverb. I then added a 25uF cap on both cathode resistors. The reverb then increased significantly. When turned up full it is now OK, and with the reverb on 7 it is as much reverb as before turned up full.

However since this is still nowhere near the reverb level of my Bandmaster I switched tanks - same result. I have tried several different tubes without any effect. I now suspect that the reverb transformer in the Deluxe II is bad. I have a replacement left so hopefully that will do the trick.

I read very little about reverb transformers going south - what is your experience?

[Svempan]

As I understand it you don’t have global negative feedback over the power amp. That opens interesting possibilities to use the phase inverter as a mixer. Using a reverb recovery amp similar to what Matchless used in their Chieftain model is, as I see it, one of them. Is that how you’ve done it?

I haven’t seen, or self been able to design, such a mixer solution with a tong tail pair phase inverter together with conventional global negative feedback. I guess it’s impossible, or does someone have a solution?

Regarding blown reverb transformers. I’ve worked as a tube amp tech for over 20 years and in fact I have never repaired or serviced an amp with a blown reverb transformer. Maybe I’m unusual, I don’t know. I know that one of my tube amps tech friends has had that problem a couple of times, so it does of course exist.

It will be interesting to hear what results your replace transformer makes.

Sven-Johan

[Darkbluemurder]

As I understand it you don’t have global negative feedback over the power amp. That opens interesting possibilities to use the phase inverter as a mixer. Using a reverb recovery amp similar to what Matchless used in their Chieftain model is, as I see it, one of them. Is that how you’ve done it?

I haven’t seen, or self been able to design, such a mixer solution with a tong tail pair phase inverter together with conventional global negative feedback. I guess it’s impossible, or does someone have a solution?
Sven-Johan

I do have global negative feedback. I used the Chieftain circuit but coupled the reverb in through a 470k resistor which meets the 100k coming from the dry side (same as in the one tube reverb). Both join the circuit at the master volume input. The master volume output goes to the PI input cap.

I tried to couple the reverb in the other side of the PI but as you said this is impossible in an amp with global negative feedback since the reverb sound is killed through the shunt element of the feedback circuit (in my case the 470 ohms resistor - didn't have a 390 to exactly match *umble specs).

[FUCHSAUDIO]

The "problem" with the concept of reverb in a guitar amp is the fact you need a circuit loss within the circuit to achieve it. That loss (in a Fender it's 3.3 meg in some cases) kills tone and the feel of the amp. Reducing the resistor value can reduce the negative effect, but eventually, that resistor becomes a feedback loop from the output of the pan, back to the input circuit, making the reverb sound poor. An active mixer (like the Overdrive Reverb), gets rid of some if this problem, but of-course it adds additional circuitry which may change the sound.

Reverb is a juggling act for sure. Too much return gain makes the pan too sensitive to vibration and feedback. The input drive is limited, or the pan will saturate and distort. Fun indeed....

[heisthl]

Yes reverb reduces gain but is not necessarily a "tone sucker" if done right. In my last project "HRM Champ" in the files section I used an add on box for reverb and loop and put front panel switches on the amp to bypass. There is a definite loss when reverb is switched in but you can easily get it back witht the D'lator. In fact, the ideal reverb might be a combination of a preset D'lator type boost circuit that comes on when reverb is switched in, and possibly better yet, automatically switched out when OD is engaged.

[Svempan]

The "problem" with the concept of reverb in a guitar amp is the fact you need a circuit loss within the circuit to achieve it. That loss (in a Fender it's 3.3 meg in some cases) kills tone and the feel of the amp. Reducing the resistor value can reduce the negative effect, but eventually, that resistor becomes a feedback loop from the output of the pan, back to the input circuit, making the reverb sound poor. An active mixer (like the Overdrive Reverb), gets rid of some if this problem, but of-course it adds additional circuitry which may change the sound...

Hrmm... Excuse me that I repeat myself, but look at the schematic of the "LS-Mod on blackface reverb" that I wrote about earlier in this thread.

Of course an added circuit do change the sound more or less, but by choosing tubes from different makers and/or different tubes of the same type I’ve managed to get the dry sound of the Vibrato channel to sound very much like the Normal channel. The wet reverb sound is not changed that much compared to the original circuit.

Compared to the same circuit without reverb, the loss, tone killing and changes in sound is, in my opinion, very small with the LS-Mod Reverb.

If you don't like the reverb sound of the Fender blackface reverb, this is, of course, not the way to go. My personal opinion is that the blackface reverb sound is one of the best spring reverb sounds for electric guitar.

It would be interesting if some people here tried the LS-reverb and then would give comments. I'll start a thread on the technical discussion forum about it to see what happens.

[Darkbluemurder]

[quote="FUCHSAUDIO"]The "problem" with the concept of reverb in a guitar amp is the fact you need a circuit loss within the circuit to achieve it. That loss (in a Fender it's 3.3 meg in some cases) kills tone and the feel of the amp. Reducing the resistor value can reduce the negative effect, but eventually, that resistor becomes a feedback loop from the output of the pan, back to the input circuit, making the reverb sound poor. quote]

I agree to the 3.3 meg situation negatively affecting the dry sound and yes, reducing that resistor to 100k will decrease the reverb. But if I take the common gain stage in the blackface Fender which amplifies the reverb and dry signals and assign that to the reverb signal only then I have a strong reverb and a good dry signal. That is what I did in my modded Bandmaster. The reverb mix resistor in that is 100k. The amp has a super lush wet reverb if I turn up the dwell pot. If I turn down the dwell pot it's as if the dry tone steps forward in the mix.

Since the gain stage arrangement is the same in my DR II it should have roughly the same amount of reverb but it doesn't by far. I still have to turn up the reverb full - that cannot be right. If it's not the tubes, pan or cabling - what else is there to check but the reverb TX?

[Darkbluemurder]

Replaced the reverb TX on Sunday - that was NOT it. Same level of reverb as before. I'll leave it at that - it seems that I cannot any more reverb out of this particular amp.