Adding reverb to a 5F6-A or marshall type cirquit

[tore_t]

Hi !

From time to time I get asked to add reverb to a Fender tweed Bassman or "classic" Marshall amp.
Of course, as little coloration of the dry signal as possible is wanted.

Lately, I've been working and experimenting a little on this subject.
I thought maybe my conclusions would be of interest...!

I've tried foldback reverbs, but I think that it's good to have a little more reverb on hand than you can get with this method.
I've also tried the cirquit found in Doug's library pages ("Adding reverb to a Western Electric cirquit"), but I wanted both a little more dwell and reverb level than what I got... plus that I think that the drive offered by a 12AX7 half sounds rather thin...
Of course, it would sound better if you used a full 12AT7 like on the stout reverb, but as mentioned, i wanted the possibility for more dwell and to be able to have the reverb louder in the mix....

After a bit of experimenting, I've ended up with this cirquit:

http://www.triple-t.no/tore/gmf/t-add-reverb.jpg

This cirquiet needs the addition of two extra tubes and a reverb driver transformer, but you get a reverb that colors the
dry sound of the amp very little, and you have reverbs from subltle to beyond dick dale levels on tap...
The cirquit also adds very little noise to the amp. It was no trouble finding space for the cirquit in a standard Marshall Smallbox - type chassis. I built the cirquit on phenolic component strips. I placed the tubes and tranny on the rear face of the chassis... This will place them hanging like in a Fender, as the chassis goes into a bluesbreaker type cab.

I can take tome photos an post them if anybody's interested...

[GroundhogKen]

Thank you, Tore.

That looks very good.  Does the reverb sound good with the send coming before the tone controls?

That style of circuit may be useful for making a fancy buffered effects loop, too---maybe change the dwell and mix controls into equalization and mix controls.


Ken

[tore_t]

Thank you, Tore.

That looks very good.  Does the reverb sound good with the send coming before the tone controls?

That style of circuit may be useful for making a fancy buffered effects loop, too---maybe change the dwell and mix controls into equalization and mix controls.


Ken

Hello Ken !

I was also worrying a little about this (no tonecontrols before or after the reverb), but to me, it sounds just like I hoped...!
Of course, you can easily add a Fender Standalone style tone control for the reverb if you like.... That would make it even more flexible...

FX loop.. Why not ?
A trick here (If you want both reverb and a FX loop) could be taking the FX send form the cathode of the reverb driver... This would give a nice, buffered low impedance signal of about the right level, I think....

The return could go via a resistor or pot to the grid of the second gainstage of the reverb recovery... Guess that could work..... Dang, now i know what to do tonight... ;-)
 
BR,

Tore T

[pzung]

hey thanks,
i'm havng some issues trying to get my reverb to sound right. this looks like one more good refference.
allthough the circuit i'm using has no cathode follower... see "reverb problem driving me nuts".

[tbeck]

Hey Tore, if the FX loop works that way, could you add it to the schematic for us?

[pzung]

could you post what voltage ranges you expect to see in this circuit?

thank you.

[tore_t]

Hi !!

I tested and spice'd a little last night on the possibility for adding a FX-loop to this cirquit.
The send part works perfectly, but I need to work a little more on the return...
Putting the return back between the two reverb recovery stages gives the right amount of
return gain, but the phase is opposite...
Putting the return via a voltage divider attenuator on the first recovery stage cures this, but
I think the reverb will suffer from this... hmm...

Anyhow, here's my take on a FX loop design by Dan Torres that i have installed in some
Marshalls and 5F5-A's with good results....
http://www.triple-t.no/tore/gmf/t-loop.jpg

This loop also works as a boost stage/ mastervolume when nothing is plugged into it..!

Heres my voltages for the Reverb-cirquit as is in the first schematic (top of post):

Input voltage (Choke output:) 420V

12AT7 anode voltage (no signal): 415V
12AT7 cathode voltage: 8,5V

Voltage at + side of 16uF cap: 368V

1st recoverystage:
Anode: 248V
Cathode: 1,9V

2nd recoverystage:
Anode: 305V
cathode: 3,0V


Best wishes from Norway,
Tore T

[Bp-Plickner]

Tore T

Can you post some pics?

Thanks
BP

[tore_t]

Hi all, here are some pics, showing the installation.

As mentioned, the chassis is going into a bluesbreaker style cab, and the thought is to make a cutout in the rear panel for the reverb controls.

http://www.triple-t.no/tore/gmf/t-rev-1.JPG

http://www.triple-t.no/tore/gmf/t-rev-2.JPG

http://www.triple-t.no/tore/gmf/t-rev-3.JPG

http://www.triple-t.no/tore/gmf/t-rev-4.JPG

http://www.triple-t.no/tore/gmf/t-rev-5.JPG

As you see, the reverb-cirquit is built on phenolic strips, and it looks a bit messy,
as space was tight.. but it actually turned out to give VERY LITTLE noise... as close
to "dead quiet" as any tube reverb I've heard...

Tore T

[tore_t]

Here are some pics & clips of the finished amp if anyone's interested..!








Some clips.. made with 50s style strat plugged directly into amp.

http://www.triple-t.no/tore/gmf/normal.mp3
http://www.triple-t.no/tore/gmf/surf.mp3
http://www.triple-t.no/tore/gmf/torr.mp3
http://www.triple-t.no/tore/gmf/crunch.mp3
http://www.triple-t.no/tore/gmf/max.mp3

BR,

Tore T

[BriteLite]

Nice job Tore T. I like the color with the gold plate. Knobs are cool also. The vent is a great idea. I have been thinking about adding reverb to one of my older dust gatherers as a project. Your project and Doug's library will make great guides.

Peace