Relays for 2-channel 2204

[Xander8280]

Keeping the loop after the master volume(s) does change its level depending on the playing level but, the clean and lead channel then have a similar level. If it is before the master(s) the cranked gain channel will hit the loop harder than the clean channel does (shouldn't matter as long as you aren't clipping your pedals in the loop).

Ideally loop send and return level controls would be nice to have but you'd have to tweak it every time you change your volume level for the best SNR. There has to be some compromise for easy plug-and-play rigs.

[ViperDoc]

I realized quickly that designing a channel-switching amp is too advanced for me at the moment. Now, building one is another matter! I'm going to build a 2550X head and learn from that. I have a Metro Loop that I thought would work really well, I just need to study how to add it into the mix either at the original SJ location, or according to the Metro instructions.

[pdf64]

...Tube effects loops I've done that worked nice were a cathode follower with a volume control going to the SEND...

Are you using the cathode follower because it's low impedance output (<2k) is able to drive cable runs without treble loss / hum pick up?
Or because it adds a tonal effect and its low output impedance is immaterial?
If the former, consider that the 250k level control, other than at max or very low settings, is adding significantly to the output impedance of the send signal. eg at the electrical halfway point, the output impedance will be >60k.
I acknowledge that the Dumble fx loop uses a CF and a 250k send level control but from the above we must assume that for reasons unknown he was not concerned about the potential issues, eg his use of bright switches kinda indicates that the loop was not intended to be tonally 'transparent'.

[Xander8280]

...Tube effects loops I've done that worked nice were a cathode follower with a volume control going to the SEND...

Are you using the cathode follower because it's low impedance output (<2k) is able to drive cable runs without treble loss / hum pick up?
Or because it adds a tonal effect and its low output impedance is immaterial?
If the former, consider that the 250k level control, other than at max or very low settings, is adding significantly to the output impedance of the send signal. eg at the electrical halfway point, the output impedance will be >60k.
I acknowledge that the Dumble fx loop uses a CF and a 250k send level control but from the above we must assume that for reasons unknown he was not concerned about the potential issues, eg his use of bright switches kinda indicates that the loop was not intended to be tonally 'transparent'.

I ended up using a static divider on my send jack; 270kOhm/8.2kOhm. I did a follower just for some isolation and buffered (cable driving like you mentioned). I wanted 30dB of attenuation to cancel out my recovery stage and was tired of attempting attenuation networks on the SEND and RETURN. I used coax on all the leads and kept most components local to the tube socket, the character/tone of the amp didn't seem different after adding in the loop.

If the attenuation precedes the CF you could be golden but, maybe a boat strapped deal to totally avoid any Miller effect?

Maybe somebody should do some of those metal can opamps on an eyelet/turret board to keep the vintage vibe and avoid the headaches (opens the door for very exotic options).

[Xander8280]

I realized quickly that designing a channel-switching amp is too advanced for me at the moment. Now, building one is another matter! I'm going to build a 2550X head and learn from that. I have a Metro Loop that I thought would work really well, I just need to study how to add it into the mix either at the original SJ location, or according to the Metro instructions.

Don't give up. I like the idea of having a tone stack for each channel, the effects loop can always added/tweaked later.

[ViperDoc]

I realized quickly that designing a channel-switching amp is too advanced for me at the moment. Now, building one is another matter! I'm going to build a 2550X head and learn from that. I have a Metro Loop that I thought would work really well, I just need to study how to add it into the mix either at the original SJ location, or according to the Metro instructions.

Don't give up. I like the idea of having a tone stack for each channel, the effects loop can always added/tweaked later.

Thanks for the encouragement, Xander. A separate tone stack per channel is definitely a plus, I just have no experience building a multi-channel amp. I'll tell you, one of THE VERY BEST SOUNDING amps I own and have ever heard is the Landry M50V. It's a 40 watt 6v6 2-Channel amp that has one of the most versatile clean-to-crunch channels I've ever heard. The second channel has crunch to super high gain, too. Nice. It has individual tone stacks, too. I've never opened it up, but...maybe I should....

[Ray Barbee]

One thing no one mentioned is your tonestack switch relay is right at you cathode follower, which has a reasonably large dc voltage. If you try to switch there, it will pop like a 44 magnum, and your relay isn't going to be happy with that dc either. You could use a large blocking cap before your relay, Isolate the stacks like diesel does and just switch the outputs, or both.

[ViperDoc]

Thank you, Ray, you are correct! Thanks for noticing that. Colossal has been helping me with that issue. I'm going out of V2B with a 1 uF coupling cap into a relay common and a 10M resistor to ground on a tone stack entry relay and then a 10M resistor to ground on the exit relay common.

[ViperDoc]

One thing no one mentioned is your tonestack switch relay is right at you cathode follower, which has a reasonably large dc voltage. If you try to switch there, it will pop like a 44 magnum, and your relay isn't going to be happy with that dc either. You could use a large blocking cap before your relay, Isolate the stacks like diesel does and just switch the outputs, or both.

I just read an old report of a builder who built a very similar amp to this one based on the same base schematic and he had channel-switch pop with a single relay. My build uses 3 relays for the channel switch and 2 for a diode clipping circuit. Should I consider coupling caps and 10M resistors to ground with each relay?

[Xander8280]

One thing no one mentioned is your tonestack switch relay is right at you cathode follower, which has a reasonably large dc voltage. If you try to switch there, it will pop like a 44 magnum, and your relay isn't going to be happy with that dc either. You could use a large blocking cap before your relay, Isolate the stacks like diesel does and just switch the outputs, or both.

I just read an old report of a builder who built a very similar amp to this one based on the same base schematic and he had channel-switch pop with a single relay. My build uses 3 relays for the channel switch and 2 for a diode clipping circuit. Should I consider coupling caps and 10M resistors to ground with each relay?

The goal is for there to be no DC switching (the pop) when you have a relay switching. From your last schematic shared this is what I'd do.

- The input relay could use a 10M to ground between V1A's 0.022 and the 470k||500pF to keep that node ground referenced (not floating) since the grid input to V1A is ground referenced. It is referenced through the gain pots but, this would be something to try if you are getting some popping at the input switch.

- The CF has some issues with the high DC voltage on the pole but the two throws are AC coupled. You could have the large cap and 10M resistor to the pole with 10M resistors on each throw to ground. This way the relay has only AC on it and all three nodes are referenced to ground (no DC).

- The volume relay could use a 10M resistor on the pole to ground so the pole is ground referenced like each throw is through their volume pots.

[ViperDoc]

Thank you, Xander!