Plexi style channel/gain stage relay switching

[burger]

Hi all,

Looking for some suggestions, or confirmation that I'm on the right track, for some proposed mods to a Ceriatone Yeti50.  I assembled it myself from the kit, I'm absolutely loving the driven sound of it - totally awesome - but as a single channel amp I do miss being able to switch to a cleaner tone.

So having just installed a DPDT relay into an 18W 1974x clone to convert that into a channel switcher, I now have plans to mod the Yeti.

Here's a schematic I found for on the Net for the Chupacabra, which other than slightly different voicing is the same as the Yeti.


The idea is to use two DPDT 5V relays to;
- switch out the second gain stage
- use a completely independent volume for the clean voicing, most likely with bright cap to taste.
- second relay to switch the stages into the CF, and bypass the Jose diodes and Master Volume.  Essentially turning the clean voicing into a non master volume channel.

Proposed wiring for gain voicing as stock Yeti:


And switched to clean:



Comments and advice welcome!

[PRR]

Welcome.

Looks OK.

In "clean", if Master happens to be full-up, then the clipping diodes are still in the path. If Master is even down to "9", it probably makes no difference.

[burger]

Ah yes, you are of course right!  Hmm, need to think of another way to get them out of the path without introducing another relay.

I almost never have the diodes switched in anyway, but I'd like to preserve the option without impacting the clean path.

[burger]

Here's an alternative that looks to completely switch out the master vol and clipping diodes, but still limits the mod to using two relays.  Moves the Gain 1 control up before the first relay, essentially this now doubles as Volume for the clean path and Gain1 for dirty.  Slight compromise and assumes I can strike a Gain1 setting that works for both paths, which I think will be ok given the testing I have done .

Gain stage in:


Clean voicing:


Does it work?...pros and cons?

[burger]

Ok, so I finally got around to implementing this.

It's fantastic!  It took a little bit of tweaking to get it switching sweetly but I'm pretty happy with the end result.  The gain sound is unchanged, but now in addition I have a very sparkly usable footswitchable clean tone.

Here's the final schematic, I hope it helps someone out that is thinking of doing something similar.

Clean voicing:


Dirty voicing:


The Gain 1 pot is share for both channels, which is fine for me, however importantly I have a separate master 1M audio pot to allow the two channel volumes to balance.

[burger]

Quick update on this.

I've tweaked it slightly by removing the master volume (relay 2) and also removing the 470k resistor (relay 1) for the clean voicing.  Switched to this voicing it really behaves like a NVM plexi.

Dirty voicing remains as per the Yeti spec.

I've also added a PPIMV for the Yeti as per the hints on this page.  https://ameblo.jp/daily-in-the-clouds/entry-11933591394.html
Works great!