Increase Reverb in a One Tube Reverb

[Darkbluemurder]

I must admit I always thought that the BF reverb was just too much. You had only 2 choices: either off or "fully" on at a knob setting of 2-3, the rest of the knob range being useless to me.

I liked the improvement in the dry sound with the one tube reverb but I now keep the knob always full up, and it still is not enough! Going back to BF is not what I want to do. I have two ideas I would appreciate your comments on:

1. Increase the input cap from 500pf to 1000pf (I believe I read somewhere that this improved the balance of the reverb-to-dry sound ratio).

2. Instead of putting the reverb return after the 470k resistor to the PI input (before the Master Volume) put it in the grounded side of the PI (think Matchless Chieftain). My idea is that since the reverb will pass the Master Volume it goes full volume into the PI, thereby giving me more range with the reverb knob. I believe Smitty does this with the Blueverb amps, too.

As always thanks a lot for your input.
Cheers Stephan

[Normster]

I used a 1-tube reverb in a Vibroverb style amp and it will take the reverb all the way to surf even with a 250kA pot. Rather than try to increase reverb by changing the mix resistor ratio, try increasing the value of the grid load on the reverb return. Maybe try increasing from 220k to 470k and see if that puts it in range for you. (I actually left it off of mine completely with no oscillation.)

[Darkbluemurder]

Thanks Norm. I took the 220k resistor off but it didn't make enough difference.

The problem I noticed with putting the reverb into the other side of the PI is the NFB circuit which puts the reverb to ground through the shunt resistive element. The Matchless Chieftain - being without NFB - does not have this problem.

[Darkbluemurder]

Recently I came across an old thread in this forum where Bob-I discussed the reverb circuit in the 3 channel amp.

I understand that this circuit is basically the 1 tube reverb with an additional gain stage after the recovery stage. I tried this with a 1MA Dwell control in front in my Bandmaster. With the Dwell and Reverb controls set to 5 this is exactly the sound I was looking for - glassy, shimmering and yet the tone is not as far pushed back in the mix as with the traditional Fender circuit.

So it seems that I have the solution to my problem - I just got to make room for the additional gain stage and the Dwell control in the Deluxe Reverb II and I'm there.

Once again thanks to all the guys contributing to this forum.

[Bob-I]

Recently I came across an old thread in this forum where Bob-I discussed the reverb circuit in the 3 channel amp.

I understand that this circuit is basically the 1 tube reverb with an additional gain stage after the recovery stage.

Also a parallel 12AT7 driver. I believe that lowered the impedance, the overall tone was improved more than the amount of reverb.

I tried this with a 1MA Dwell control in front in my Bandmaster. With the Dwell and Reverb controls set to 5 this is exactly the sound I was looking for - glassy, shimmering and yet the tone is not as far pushed back in the mix as with the traditional Fender circuit.

I used a trimmer inside for the dwell and found that with this set at about 75% the reverb control gives me a really nice range.


Lately I've been using an ECL86 as a single tube reverb. Works out really well.

[Icetech]

Thanks for the tips to try:) My ods has a 1 tube reverb, which works ok, but i would like a lusher subtler reverb.. this one is more of a smack of reverb:)

For my money, old ampegs had the best reverb... i need to look at those circuits sometime:)

[Darkbluemurder]

Also a parallel 12AT7 driver. I believe that lowered the impedance, the overall tone was improved more than the amount of reverb.

Lately I've been using an ECL86 as a single tube reverb. Works out really well.

Bob,

I already use a paralleled tube as a driver (a 12AX7 which didn't give more reverb compared to a 12AT7 but I like the tone).

I saw in your schematic that you used the ECL86 as a driver. That made me think of using a pentode as recovery amp instead of using 2 triode stages. Has anybody tried that?

[Bob-I]

Bob,

I already use a paralleled tube as a driver (a 12AX7 which didn't give more reverb compared to a 12AT7 but I like the tone).

Actually a 12AT7 should drive the reverb a tad more. I personally don't like the 12AX7 driver, sounds harsh to me but whatever floats your boat.

I saw in your schematic that you used the ECL86 as a driver. That made me think of using a pentode as recovery amp instead of using 2 triode stages. Has anybody tried that?

It's actually a pentode triode so the entire reverb is with the one tube, pentode driver/triode recovery. It sounds very good to me.

[FUCHSAUDIO]

Thanks for the tips to try:) My ods has a 1 tube reverb, which works ok, but i would like a lusher subtler reverb.. this one is more of a smack of reverb:)

For my money, old ampegs had the best reverb... i need to look at those circuits sometime:)

Check out the old Gemini and VT-22's They used 6FQ7's (heavy duty dual triodes) as drivers, without transformers (they used a capacitor), and sounded amazing. Some of the Traynors used 6BQ5's (EL-84's) as reverb drivers with and without transformers. Pentodes have lots of available gain and the Traynor reverbs sounded excellent too. Remember; The pans are higher input impedance when you don't use a driver transformer. The proper pans are still available.

[Svempan]

I’m rather new on this forum, but have suggestions about the Fender Blackface reverb that you may like. I’m a tube amp tech in Sweden (Scandinavia, Europe) and have many years of experience especially on Fender amps.

The suggestion I give here is not actually a so called one tube reverb, but I do think that it makes the dry sound of the Vibrato channel on blackface and silverface Fenders to sound much like the sound of the Normal channel (if that’s what you’re after).

Many people don't like the sound of the 3.3MOhm/10pF solution in these Fenders and think that the Normal channel sounds better, especially with distortion. I think that modifying the reverb circuit according to the schematic here makes a good improvement (if you think that the Normal channel gives a good sound).

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.

The dry sound gets a little louder with this mod so you have to set the Reverb control a little higher.

This mod uses a ECC832 or 12DW7 tube. Remark that you have to move most of the wires from one of the triode parts to the other.

Take care,

Sven-Johan

PS: I have tweaked the curcuit a bit but I like to give credit to the person who originally gave me the idea and a circuit solution with the ECC832 (12DW7) in the reverb circuit. It's an amp tech friend of mine called Lars Söderqvist of reVintage Amps here in Sweden. Here’s his web site: http://www.revintage.se/

[Darkbluemurder]

Svempan,

Thanks a lot, that looks very interesting! It appears as if this mod is intended to

(a) balance the dry and reverb signal better and
(b) overcome the loss of gain caused by the vibrato.

Indeed, going from the 3M3/10pf plus full gain stage in the BF designs to a one tube reverb reduces the overall gain and volume of the amp quite a bit. Therefore the additional stage using the ECC82 half of the ECC832 makes sense. The loss of gain did not disturb me though as the amps that I did this to were too loud for my tastes anyway.

Last Saturday I first increased the 100k mix resistor to 150k and then to 220k and bypassed it with a 47pf cap. By the same token I reduced the 47pf cap on the master volume to 10pf to keep the amp from being too bright. I have to play the amp a bit first before implementing the next changes and see if that is enough.

Cheers Stephan

[Svempan]

Stephan,

The main goal with this reverb circuit is to make the amp sound a little fuller and not so trebly and scooped in the middle that it is with Fender's original 3M3/10pF solution.

I also think that big series resistances makes the sound less clear, less dynamic and that the guitar tone is camouflaged more. With no or small series resistances I think that the true tone of the guitar and what you make with the strings when you play is more audible and comes thru more.

For what I have tested the 12AU7 part of the ECC832/12DW7 in the mixing circuit, doesn’t distort more easily than in Fenders original circuit. Maybe it even distorts less easily or later or that it has more head room (or what you want to call it).

I have also used this kind of mixing and reverb recovery it in another circuit with a pentode and a bigger transformer in the drive circuit. Se the schematic here (4 pages). The value of the screen grid resistor on the pentode could probably be tweaked a little more, so I will do that. The transformer has 1/32 turn ratio (1/1024 impedance ratio) so with the 10 ohm input impedance of the six spring reverb tank I use it matches the EL85 very good.
This reverb circuit is in one of my own amps that is inspired by Steel String Singer and Dumbleland.
An EL84 would maybe be a better choice because it’s commercially available. In this particular amp I use EL85 because of its low heater current. An EL84 would probably require a transformer with another impedance ratio.

With booth of these reverb circuits I can certainly get enough wet reverb sound...

In fact I haven’t tried the so called one tube reverb yet. It looks interesting so I probably will, but it’s easy to think that most people that have tried it aren’t completely satisfied. Is that true? What do you think?

Take care,

Sven-Johan

[Darkbluemurder]

Sven-Johan,

Thanks for your input. This looks all very interesting.

I believe most folks who went for the one tube reverb (including myself) did it (a) to improve the dry sound of the amp and (b) because the typical BF reverb was too much.

Whereas the one tube reverb completely achieves both goals it does so "too much" on (b) IMHO, i.e. I am back to square one with not enough reverb. I changed the driver tube back to a 12AT7 but it did not make much of a difference. Also the increase of the 100k to a 220k/47pf combination did not do it.

BTW: my cathode combination on the 12AT7 is 820R/5uF (like in the one tube reverb) whereas the BF combination is 2k2/25uF. I suppose that the BF values drive the reverb transformer harder in the low end. But then again the SF cathode is 680pf without a cap which should drive the transformer less. Yet the SF reverb is just as much as the BF reverb. So I am thinking that I will need either two triode stages in the reverb return or one pentode. I'll report back one I decided which way to go.

[glasman]

Maybe adding a simple (gasp he is going to use the T word) single transistor buffer with say a gain of 10 to 20 would do the trick.

4 resistors, 3 caps and 1 2N3904 should add just enough gain and could be driven off of most relay power supplies.

Sorry for mentioning the T word....

Gary

[Johnhenry]

I've been useing the Kalamazoo Reverb 12 circuit in my S/E amp's and it's working great for me, got surf or just a touch, very adjustible, you can check out the Schematic over at Schematic Heaven, you do have to use the Gibson reverb transformer and Gibbs tank though.
Johnhenry