Add reverb to Plexi

[basschops1528]

Hey guys,

I was reading this http://el34world.com/Forum/index.php?topic=14690.msg140334#msg140334 and got an idea to one day add reverb to my newly built plexi down the road. I'm curious how it sounds. I'm planning to add a master volume--ppimv as sluckey and a few others suggested in another thread and I want to be able to do the master volume and get LOTS of gain AND have reverb. I don't want to sacrifice channel two for the reverb so tubeunits schematic seems like a better choice. Is there a way to put the master volume before the reverb so I can still get my "ppimv"esque gain going into a good spring sound like a modern amp without sacrificing the channel? I can accomodate the extra tubes, pots, and components needed for t's mod.

[HotBluePlates]

Doug posted how to add reverb to the "Western Electric circuit" in the Library of Information.

Supposedly, the 5F6-A Bassman was based on a Western Electric circuit, and the first Marshall amps were copies of the Fender Bassman.

This approach puts the reverb circuit between the 1st & 2nd gain stages. You're asking for reverb after the "post-phase inverter master volume;" few reverb circuits are injected that late, although there are some foldback reverb circuits which tap the reverb drive signal from the speaker and re-inject it earlier in the amp. Ultimately, it sounds like you want to add reverb to your distorted signal (and you're generating distortion via a master volume arrangement), rather than distort the reverb'd signal.

That's not usually found in vintage-style amps, though again it's possible in a foldback design. The problem is, sometimes foldback reverb circuits can oscillate (though there are other workarounds). The traditional answer was get your dirt for the reverb sound from a pedal. Modern amps might have their own pedal-like distortion circuits completely inside a single preamp channel so adding reverb over that is no problem. The architecture of those amps is very different from a plexi.

[Ken Moon]

I'm not sure what the advantage is of putting the clipping preamp stages before the reverb.

There are some awesome reverb pedals out there - I use a Mad Professor Silver spring unit, and the TC Hall of fame sounds great too. I'm sure there are several others.

If you're determined to add it into the amp, I'd suggest an ECL86-based circuit right after the input stage with the pentode side as the driver. Or look at the Fender Vibro King, which is essentially a Fender outboard reverb unit as the input stages (EL84 driver IIRC).

edit: Vibro King schematic is here:

http://www.studiosoundelectronics.com/schematics/vibro_king_manual.pdf

[TIMBO]

This will get what you want, easy to add.

[tubenit]

I've done reverb both ways using Hoffman's  "add reverb to a western circuit" and "one tube reverb" approach. 

I prefer the "one tube reverb" approach with the insertion just prior to the LTPI.  It sounded warmer in tone to me and allowed the front end of the amp to be cranked a little more then the "add reverb to a western circuit", IMO. I have tried both ways on the same amp before which was a Plexi 50 that I built into a gutted JCM900 chassis. The owner preferred the "one tube reverb" tone also.

Both sounded fine.  If you want a brighter reverb tone closer to a Fenderish reverb, Doug's is a better approach for a cleaner tone.  Both good, just different.

Double check the PPIMV with fixed biased. Maybe Sluckey will see this and comment whether that piece is drawn correctly?

With respect, Tubenit

[basschops1528]

I really just want reverb and the ability to still have a master volume so u can crank the amp for a van halen acdc type of distortion, the way a Marshall is meant to sound

[TIMBO]

Just add the master volume pot between the treble and the mixer resistor for the reverb. Having both the master and PPIMV work well together.

[sluckey]

Is there a way to put the master volume before the reverb so I can still get my "ppimv"esque gain going into a good spring sound like a modern amp without sacrificing the channel?

My Plexi 6V6 has a master volume just before the PI. The attached pdf shows how I would connect tubenit's one tube reverb circuit into my amp. This is exactly what you asked for. Some people don't care for this type MV, but Marshall used it on his JCM-800 2204 amp (others too). I like it. As Timbo says, you can also do the dual pot PPIMV for even more knobs.

[John]

I have my reverb just before the PI as well, almost exactly like Sluckey's drawing. (MV after the PI using the dual ganged pot). It works great, sounds great!


I have a gain/vol pot just before the reverb too, coming off a small pentode. It's not nearly as interactive with the reverb as I thought it would be, you have to pretty much dime it before you notice a big increase in the amount of reverb. FWIW.

[basschops1528]

Tubeunit, do you have any sound clips of your plexi 50 with master volume both clean reverb and dimed reverb for example?

[tubenit]

Tubeunit, do you have any sound clips of your plexi 50 with master volume both clean reverb and dimed reverb for example?

Wasn't my amp.  It belonged to a friend. I don't have any soundclips.  Sorry.

with respect, Tubenit

[tubenit]

This isn't the Plexi 50 so you may not be interested in it ...................     It was a Tweed OD Lite.  Which is like the Tweed BluezMeister but with only a 5879 in the OD instead of two triodes like the TBM.

However, it does have the "one tube reverb" and the rhythm is played clean and the solo at the end is pretty well cranked.  So, in that sense it may give you some idea of the reverb with a reasonably clean tone and an overdriven tone.

http://www.soundclick.com/player/single_player.cfm?songid=9575220&q=hi&newref=1

with respect, Tubenit