1959/OWM/2203 Switchable(Not Working, Of Course)

[Rp3703]

Does anyone see any issues with this schematic. It will be built on a 1959 SLP reissue PCB and is supposed to allow you to switch from 1959 SL to a One Wire Mod or a 2203. I plan on using a SPTP switch that will switch on one relay for the OWM or three other relays for the 2203. The tone stack and power amp should be standard Marshall with a master volume and probably a PPIMV.

[Rp3703]

Here's a JPG. of it.

[Rp3703]

Since I'm getting zero replies, maybe I need to clarify what I'm asking for. I have never worked with relays before, so I'd like some verification that my switching mechanism will function correctly. Also, if there is some sort of issue with say running cathode signal through relays or popping when switching between preamps, something that I am overlooking, I would appreciate knowing that beforehand. I do not need clarification on the function of the three preamp versions. I'm pretty positive I have that part right. Thanks.

[shooter]

typically if there's no jump out at you issues there probably won't be comments
I didn't see any, but I'm cutting trees and hot 

as to "pop", any time you break or make an active signal, it's a good bet there could be pops, use your fav search tool and read about mitigating switching pops in an audio path, should have everything from basics to MIT engineering 

[pdf64]

These circuits have a fair degree of gain, which makes its layout design critical for a good margin of stability. But all those circuit switching options inevitably compromises layout, so stability may be an issue.

[Rp3703]

So, while trying to figure out the wiring layout for this relay system, I realized that my original schematic is wrong on the One Wire Mod relay. I have attached the corrected schematic.

[Rp3703]

This will all be built onto a 1959 SLP reissue PCB. Out of convenience, I will be attaching the Hoffman relay PCB's to the two PCB mounting screws on the left and I will have to add two new holes for the two relay PCB's in the center. I've attached a layout drawing of what I'm talking about.

[Rp3703]

Took my time wiring this amp up but I finally finished today. It looks crowded because I stuck a 1959 circuit into a JTM45 chassis. If everything goes like my previous amp builds, all that's left to do is fire this up and feel the disappointment of it not working.

[Rp3703]

As was to be expected, my complicated switching guitar amp is not working. The relays work. I can feel them clicking. The PPIMV works. It lowers the volume rather well. The amp passes signal in 1959 mode but has a slight squeal to it but only when strumming the guitar hard and more so on the bright channel than the normal. In One Wire Mod mode it just sounds like crap when strumming the guitar. In 2203, it just hums with no signal coming out. I have tried swapping the OT primary but that only made it worse. Since signal passes, I'm guessing the schematic I drew has errors. So here are my first questions.

1. Does the ground buss bar running on the back of the pots need to have a wired connection to chassis ground or does the connection of the pot through the chassis make an adequate chassis ground connection?
2. In One Wire Mode, the one side of the relay connects the normal volume pot wiper to the grid of V1A. The bright input is also connected to the grid of V1A. Does this create an issue?

[pdf64]

1 Probably but it’s not certain. I fixed a DrZ where every pot lost its chassis connection. Tighten any of their nuts and it would fine - for a bit. Eventually installed a proper high torque, star washer chassis 0V fastener.

2 There would be a problem if using the bright jack and the normal vol was turned down.

[andregarcia57]

This will all be built onto a 1959 SLP reissue PCB. Out of convenience, I will be attaching the Hoffman relay PCB's to the two PCB mounting screws on the left and I will have to add two new holes for the two relay PCB's in the center. I've attached a layout drawing of what I'm talking about.

HELLO EVERYTHING IS FINE? Do you have the measurements of the original PCB?thank you

[nandrewjackson]

Post #8
2) OWM active.


Signal into normal channel and normal volume pot is all ok, except, you now have a low R (34K) to ground because of the bright channel switching jacks.

[nandrewjackson]

Relay logic for 2203 looks ok, check for wiring error.


Do you have signal generator? O-scope?