Adding Reverb to Champ

[Electron Tornado]

I'm looking at building a Champ clone from one of Tino Zottola's books. It looks like a straight forward first step into tube amps. I would like to add a reverb to the amp, and so far, I've only come across a few amp schematics that have reverbs. Does anyone know if there are any sources, web or otherwise, that would have some "how to" info on adding a reverb to a tube amp?

Thanks

[tubeswell]

FWIW I posted a schematic of a 5F2A with reverb (courtesy pyschonoodler) on this link earlier.

http://music-electronics-forum.com/s...ead.php?t=8060

[Bruce / Mission Amps]

FWIW I posted a schematic of a 5F2A with reverb (courtesy pyschonoodler) on this link earlier.

http://music-electronics-forum.com/s...ead.php?t=8060

Have you built this circuit up yet and have it running?
I don't think that will work right or at least not satisfactorily.
At R1, the dwell and volume control are in parallel, so the effective resistance is half of the two 1M pots... that's not really a bad thing yet but since they are in parallel, with the dwell control turned down to near zero, it will also kill all the preamp audio so there will be nothing to amplify with respect to dry signal if you want zero reverb.
You'll need a very small, 500pF input capacitor to the top of the dwell control and I'd consider moving it to after the volume control's wiper so the signal the reverb input sees is controlled by the actual volume level of the amp instead of wide open raw preamp signal.
Also, I have never tried this.... but I suspect your small 10K mixing/isolation resistor at the insertion point will be far too small to allow much dry to wet signal mixing and the tone and volume of the amp will suffer because of the reverb level pot seriously degrading and loading down the grid of the mixer/recovery amplifier stage.
I would think a resistor on top of the pot would help, as maybe using a 250K or 500K pot instead.
Now it could be that the stage's extra amplification is not needed and the 100K will just bring the two mixed signals back to unity.... as I mentioned I have not tried the circuit.

[Tubenit]

Verb O Champ

Haven't built this, .......BUT ....... I have successfully used this type of reverb insertion in a number of amps including the 3 I currently own and play. However, I have not tried it in a single ended amp.

CHECK for errors and that the schematic and layout match. Simply posting this for a critique.

To get it more "Champ-like", just leave the input gain stage non-paralleled and use a 5E3 type vol & tone stack.
The V1-3 cathode switch is a spdt with center off to get a bright/full/fat tone option

With respect, Tubenit

[Tubenit]

Champ O Verb layout

Check that the layout and schematic match.

[Bruce / Mission Amps]

Now that does looks like a circuit that would work!
Three tubes is a bit more work so in order to use only two tubes I would try a small +15dB to 18dB gain, FET preamp for the first stage and V1 would now be the tone recovery and reverb tank driver.... with the mixer amp stage being the other half of the reverb tank recovery tube.
If using three preamp tubes with one unused doesn't matter.. then the way it is drawn should be fine.
I guess you could go full Fender and use a 12AT7 for V2 all by itself, but with both triodes parallel'd to drive the tank.
Have you sent me this schem before?

[tubeswell]

Have you built this circuit up yet and have it running?
I don't think that will work right or at least not satisfactorily.
At R1, the dwell and volume control are in parallel, so the effective resistance is half of the two 1M pots... that's not really a bad thing yet but since they are in parallel, with the dwell control turned down to near zero, it will also kill all the preamp audio so there will be nothing to amplify with respect to dry signal if you want zero reverb.
You'll need a very small, 500pF input capacitor to the top of the dwell control and I'd consider moving it to after the volume control's wiper so the signal the reverb input sees is controlled by the actual volume level of the amp instead of wide open raw preamp signal.
Also, I have never tried this.... but I suspect your small 10K mixing/isolation resistor at the insertion point will be far too small to allow much dry to wet signal mixing and the tone and volume of the amp will suffer because of the reverb level pot seriously degrading and loading down the grid of the mixer/recovery amplifier stage.
I would think a resistor on top of the pot would help, as maybe using a 250K or 500K pot instead.
Now it could be that the stage's extra amplification is not needed and the 100K will just bring the two mixed signals back to unity.... as I mentioned I have not tried the circuit.

Hi Bruce

Thanks for your feedback.

No I haven't built that circuit yet. I uncovered it on my earlier quest for 5F2 with 'verb circuit ideas, and have been investigating the possibility of adding it to a dual 6V6 SE amp (which was the subject of my other post). I have stashed your comments and tubenit's schem and layout away in my next project folder.

[Tubenit]

Verb O Champ FTS

Ok, going with Bruce's idea ....... this is a Verb O Champ using a 12AT7 and I put in a Fender type tone stack with a few changed component values. You can use the Duncan Tone Stack Calculator to see what those would do.

Check for errors, I haven't built this.

Tubenit

[Tubenit]

Verb O Champ FTS layout

Layout. Check for errors and consistency with schematic.

Tubenit

[Tubenit]

Verb O Champ 5F2 tone stack

Another version using a 5F2 tone stack and not parallleling V1. This would have a vol, tone & reverb on the front and the dwell pot on the back of the chassis.

Check for errors.

Tubenit

[Tubenit]

Verb O Champ 5F2 TS layout

Check for errors and that the layout is consistent with the schematic.

Tubenit

[Bruce / Mission Amps]

Another version using a 5F2 tone stack and not parallleling V1. This would have a vol, tone & reverb on the front and the dwell pot on the back of the chassis.

Check for errors.

Tubenit

Still, as I reflect on this, the problem with those dwell controls when used as drawn is that the original stand alone reverb's dwell control did not shut the rest of the dry signal off.
The dry signal was shunted around the reverb section and into the cathode follower mixer stage in stand alone units... so the dwell on those had NOTHING to do with the dry signal.
The way it is in the schem you provided, it will effect the dry signal negatively if the dwell is set to zero, or minimum. As a matter of fact, I suspect it will shut the amp off.... and if you use a 500pF cap in front of the dwell control it will act like a high freq treble cut too.
Maybe just no dwell control or a resistive isolation there to reduce that effect.
And, there needs to be a small value coupling cap to the grid load resistance of the 12AT7.

To be honest, except in stand alone reverb units, I find the dwell control installed in classic BF Fender amps to be about 95% worthless.
If you want less reverb drive, less twangy reverb or less boing etc., etc... tune the drive and recovery section's gain and bandpass freqs rather then less drive to the 12AT7.

[Tubenit]

dwell & tone/vol

Bruce,

Regarding shutting off the dry signal ........... (if I am not understanding what you are saying, please correct me).

EDIT: Bruce was pointing out an error in how I had drawn the dwell pot and the cap going to it. I have redrawn
the last two schematics and layouts. He was correct that the way I had drawn them would have killed the dry signal.
The Verb O Champ II & Verb O Champ III schematic now show how I have this done on my current amps and it works fine.


I have this reverb circuit with dwell on each of my 3 amps. After reading your post, I plugged in and checked out my memory. I can turn the dwell all one way and then all the other way and it has NO impact on tone or volume at any level that I can tell. Obviously, it does change the amount of reverb and can shut the reverb off but not change the volume or tone.

Having said that, I am really using the dwell pot like a trim pot. It is on the back of the chassis of all three amps
(two being a tweed chassis/cab and one a head). I set it at 50/50 on two and 75/25 on the other. It seems to work just fine and I did not care for a straight 1M resistor to ground. I think with more mids being verbed the fixed resistor made it too boingy for me.

Gibson amps had a dwell like I am using (even though you don't typically see that on a Fender):
http://www.schematicheaven.com/gibsonamps/ga17rvt.pdf
http://www.schematicheaven.com/gibso...vt-galaxie.pdf
http://www.schematicheaven.com/gibso...rvt-regent.pdf


With respect, Tubenit

[tubeswell]

Many thanks for your thoughts and scheme ideas tubenit. Can I ask - did you go to the effort of drawing these up for this thread? You are obviously a person of great energy and enthusiasm. Cheers Mate :-)

[Tubenit]

schematic drawing

Yeah, I drew them up for this thread. Having said that, I have over 100 editable SCH schematics and layouts so it's pretty easy to do. I usually can find a schematic I have and alter it in about 10-20 minutes into something else.

Some people work crossword puzzles ........ I draw schematics. What's ironic is that 5 yrs ago, I could NOT read a schematic and even tell what was a resistor or capacitor.

Just a hobbyist and have had zero actual training in electronics. Learned by reading the net and experimenting alot.

with respect, Tubenit