Adding a Solid State Spring Reverb to "Any" Tube Amp

[jonyoungyi]

I just finished the Hoffman Blues Junior Conversion board and it's working swell (aside from my other post about "smoothing" distortion. Haven't tried the suggestions yet). My next endeavor is to add reverb to the amp!

I've an old reverb tank that I'm not using and stumbled across this sold state layout (I've also attached a .png):

https://robrobinette.com/Compact_Reverb.htm#Solid_State_Spring_Reverb

I was curious if it's as simple as splicing between V2 and MASTER Pot, right after the .0022 cap. I've outlined this on the attached schematic.

Is it really that simple? *scratches head*

Any and all help is appreciated! Some of you have already helped me so much, it's really encouraging!

[2deaf]

You would want to straddle R20 (220K) for the reverb send and return.

Did you start with a Blues Jr. that had reverb and converted it to the Hoffman Blues Junior?  If so, you can alter the bias circuit for the split supply, but not the way Rob shows.  Rob starts off with a bias supply that puts out twice the voltage as a Blues Jr.

[tubenit]

On your Blues Jr conversion,  ..................   I would simply add a passive effects loop and put a delay pedal or reverb pedal in the loop.

http://www.ebay.com/itm/NUX-Time-Core-Electric-Guitar-Effect-Pedal-7-Delay-Models-True-Bypass-I9N6-/351806514879?hash=item51e94d66bf:g:ssoAAOSw65FXqvYV

With respect, Tubenit

[2deaf]

If you choose to go with the passive FX loop, delete the 220K resistor and the .033uf capacitor in series with the FX send.  The 220K resistor in conjunction with the capacitance developed by the patch cable forms a high frequency roll-off filter that you don't want.  You could place the 220K resistor from switch to switch on the send and return jacks instead of a piece of wire.  That way the 220K resistor is gone when the loop is in use and it reverts to the original circuit when nothing is plugged in.

The .033uf capacitor serves no useful function that I see.  I can see it blocking a nice low impedance path to ground for any hum that the patch cable picks up, however.  If you just got to have that capacitor, make it a really high value one. 

[jonyoungyi]

Dude, you guys are so rad! I appreciate it so much! The effects loop is what I'll do! I've made some belton brick pedals, so I might just stick that circuit in to the amp and power with a 9v transformer.

Thanks again, I really appreciate the help! Hopefully I can help out in the future!

[Apprentice]

Although this post is a bit old I was hoping for a bit of help. I’ve built the Hoffman BJ and love it. Tried Rob Robinette’s solid state driver for spring reverb and cannot get it to stop buzzing. So I’m ditching that idea and will fit a fx in and fx out via 2 12a jack sockets and get a reverb pedal.
The Hoffman BJ has no 0.033 cap after the 220k which is where fender take their reverb circuit from.
What would be the ideal way of installing the FX loop. I like the 220k on the loop jack socket idea but read previously that you can keep the 220k in circuit (basically in series with effects).
Does anyone have any better ideas or thoughts?

[sluckey]

I would put a passive loop between R20 and C11 of Hoffman's schematic.

[Apprentice]

Hi Sluckey, so if I’m understanding I would keep the 220k and the cap in the fx loop?

[sluckey]

yes

[Apprentice]

Nicely done Sluckey. Took me a few moments to work out the switches on the 12a’s but now working fine. I just want a bit of reverb to give a bit of ambience. I’m not a great pedal board player but it’s nice to have the choice of adding pedals when I want. Thanks again, much appreciated