Real separate channels, how to?

[rootz]

From the start of my amp building 'career' I've been intrigued by channel switching amps. Although I have made designs for microprocessor controlled designs, I never actually built one. It was just way over my head (mostly the programming part didn't suit me well).

Still I'd like to make a design, maybe just for the sake of it. What I'd like is independent gain, tmb, volume, reverb send, reverb return and maybe presence for both channels. Maybe some switching like bright, mid boost and deep. Not against using those on push pull switches.

Who has done this kind of stuff here on the forum? I know Two Rock did the Onyx and Fuchs has the ODS-II. I think I saw a separate channel ODS amp from VVT too? Any specifics about those amps?

Anyway, of course I started tinkering and came up with a design. I have far too many gain pots in the overdrive side of things. I want just one, but which should I ditch? And how does the Onyx just have 5 preamp tubes and do what I want to do? so many questions...

[talbany]

VVT Was my company.Which amp were you referring too. Do you remember?

Tony

[rootz]

Thanks Tony. I kinda remembered VVt was your company. Not clearly though, so thanks for refreshing my memory. The amp is the earthquake 9.1. As far as I can see at least separate tone controls. Are the gain controls still cascading? What can you tell about the topology/building blocks of this amp?

[dbharris]

Maybe check the Mesa Lonestar schematic? https://schematicheaven.net/boogieamps/ ... nestar.pdf

That could be similar to what Two Rock was doing and sharing some tubes. There are some limitations here, you couldn't have high and low plate channels, just one or the other.

I have a Lonestar Special and it works quite well for that hot rodded fender thing. Sometimes I set it up where 1 channel is clean and the other dirty. Or where each channel is on the edge of break up but the eq tuned for different guitars, etc.

-Dan

[JayB]

As a long time lurker, you're going to miss that dumble vibe with that plate driven tone stack design. I turned my old Fender Concert 2 into a two channel dumble low plate classic inspired amp that's very much like the last one you built. I had an extra triode and one tube to use so it was an easy choice. I like that jazzy clean thing at times but that meant compromising with the overdrive. Clean is triode - tone stack - triode - reverb mixer. Over drive is triode - tone stack- triode - triode - triode -reverb mixer. Using the typical dumble inverter power amp set up. I just use two relays to do switching at input and output. One of my favorite amps that'll do jazz, blues to rock.

[rootz]

Maybe check the Mesa Lonestar schematic? https://schematicheaven.net/boogieamps/ ... nestar.pdf

That could be similar to what Two Rock was doing and sharing some tubes. There are some limitations here, you couldn't have high and low plate channels, just one or the other.

I have a Lonestar Special and it works quite well for that hot rodded fender thing. Sometimes I set it up where 1 channel is clean and the other dirty. Or where each channel is on the edge of break up but the eq tuned for different guitars, etc.

-Dan

I did take a look and exactly what you said: no real separate channels there. I like the idea about muting with a J175, although I doubt it is necessary. I got the switching idea from sloclone forum, the 2CGA amp.

The Lonestar is really it's own thing. I'm more or less aiming for a Dumble sans the compromise between clean and OD. Yes, I'm thinking inside instead of outside the box on that part of the design lol...

[rootz]

As a long time lurker, you're going to miss that dumble vibe with that plate driven tone stack design. I turned my old Fender Concert 2 into a two channel dumble low plate classic inspired amp that's very much like the last one you built. I had an extra triode and one tube to use so it was an easy choice. I like that jazzy clean thing at times but that meant compromising with the overdrive. Clean is triode - tone stack - triode - reverb mixer. Over drive is triode - tone stack- triode - triode - triode -reverb mixer. Using the typical dumble inverter power amp set up. I just use two relays to do switching at input and output. One of my favorite amps that'll do jazz, blues to rock.

I'm actually hoping for that Dumble sound with the plate driven tone stack. It is essentially an HRM amp with PAB engaged the way I've drawn it. Pretty much how you'd use it I think. So low plate classic for clean, high plate HRM in PAB mode for the OD. Now if I could lose one of the gain pots in the OD channel that would be great.

I'm curious JayB, how did you do the switching? Have you got a schematic of your amp?

And still curious about how other Dumble based amps like the Onyx, Earthquake and ODS-II do the switching job. How independent are the channels and how's the switching done?

[JayB]

I'm actually hoping for that Dumble sound with the plate driven tone stack. It is essentially an HRM amp with PAB engaged the way I've drawn it. Pretty much how you'd use it I think. So low plate classic for clean, high plate HRM in PAB mode for the OD. Now if I could lose one of the gain pots in the OD channel that would be great.

I'm curious JayB, how did you do the switching? Have you got a schematic of your amp?

And still curious about how other Dumble based amps like the Onyx, Earthquake and ODS-II do the switching job. How independent are the channels and how's the switching done?

My quick thrown together schematic. That last relay is drawn wrong but you should get the idea. 2 missing 100k resistors after C11, C13 and C16. Missing 250pf plate bypass on R15. I just borrowed the existing voltage supply and pedal. Power supply is the exact same as the original concert 2. Preamp triodes sit around 190V. Almost 500V on the 6L6 plates. It's plenty loud.

[talbany]

Thanks Tony. I kinda remembered VVt was your company. Not clearly though, so thanks for refreshing my memory. The amp is the earthquake 9.1. As far as I can see at least separate tone controls. Are the gain controls still cascading? What can you tell about the topology/building blocks of this amp?

Rootz
The 9.1 was basically an HRM with a few tweaks to it. The earlier versions had the HRM stack T,M,B on the front of the amp instead of the inside trimmers. This was an extremely versatile amp however it was a cascading type design and didn't have discrete channels. We did however come up with an amp called the tone blender which did have 2 discrete channels with a clean channel and OD side with relays that combined both channels (hence the word "Tone Blender") this gave more clarity and control to the Overdrive section since you could basically blend in how much of the clean signal with the overdriven one. The OD side IIRC did have the HRM on trimmers inside the amp that we preset for the speaker in the combo. This amp also had reverb blended in at the PI as well as a passive boost (lift the stack on clean channel),although there were a number of different ways you could switch in and out certain stacks for certain boost functions,however the cool function was to be able to blend in both clean and OD signals (in phase) before hitting the PI was the inspiration behind it. Another advantage to this design were the master volumes seemed to work better so you had more control on the overall volume of the amp on both clean and overdrive sides.. These were of course all PCB based designs.

It's a little complex but the topology was basically this. If you think of switching between 2 seperate amps on stage. the 1st amp would be an ODS running clean only Skyliner w/boost,the 2nd amp would be running in HRM overdrive mode. The 3rd function would be if you simulated both amps on at the same time
Add in
Built in Spring Reverb
Built in Buffered loop (optional)

Tony

[rootz]

That second amp you mention Tony, is pretty much what I mean, minus the 3rd mixing of the channels option. Mixing should be doable if I want that. I can imagine it being more difficult if you want to be able to switch independently between all 3 modes. How to switch from clean to blend to od without having to 'untap' the blend mode? It's like switching with 3 discrete channels ala the Soldano X88r. Selecting a channels means the previous selected channel has to be disabled. That requires more logic thinking (and in some cases programming) than I like haha! I'm more an emotions kinda guy

When looking at JayB's schematic (thanks a lot by the way!) and your ideas, I wonder how silent the switching is and how you've done that/implemented the relays. JayB's schematic has no option to shunt the inactive channel to ground at e.g. the grid of the 3rd or 4th OD triode. Many amps do (again, like the X88r or an ODS on clean). It seems to be good practice, but why exactly?

Furthermore, the M-B Lonestar, many (if not all) Engls, some Fenders and probably many other amps mute the signal during switching via one or more j-fets (j111/j113) or p-fets (j175). I keep wondering: how necessary is this muting?

Interesting you mention spring reverb and a loop Tony. Maybe I should add that loop too. I'm working on some new driver ideas for the reverb. Like a mu-follower, a pentode (EL84 ala Vibro King) and a push/pull ECC99. Thinking about a loop with a 12dw7; half ecc83 and half ecc82. The ecc82 side would make a CF capable of driving a 10k send pot, so the high end losses would be minimal. I need to investigate if there are safe ways to bread board some of the ideas.

[JayB]

I use the relay to shunt the input of the unused pre-amp grid to ground. I let the outputs of the preamps fly on the other relay. As long as there is a grid to ground reference, it's noise free. I use a cap and diode for each relay for any fly back pop. Technically the input on my schematic could be done better with each preamp having it's own 1meg ground / grid input resistor. The way it's drawn now it would pop but I threw that together so I wouldn't forget. There is room for improvement on that schematic.

What ever you do, don't steal voltage from the heaters for relays. I've never had any luck with that.

[donvan]

Selecting a channels means the previous selected channel has to be disabled. That requires more logic thinking (and in some cases programming) than I like haha!

I was recently reading about channel switching in Merlin Blencowe's book: Designing Tube Preamps... I highly recommend that book. The concepts of channel switching circuits are covered. But your are correct, more complex switching schemes will require more logic. Most likely you won't need to micro processors and programming though.

[j0k3335]

I'm actually hoping for that Dumble sound with the plate driven tone stack. It is essentially an HRM amp with PAB engaged the way I've drawn it. Pretty much how you'd use it I think. So low plate classic for clean, high plate HRM in PAB mode for the OD. Now if I could lose one of the gain pots in the OD channel that would be great.

I'm curious JayB, how did you do the switching? Have you got a schematic of your amp?

And still curious about how other Dumble based amps like the Onyx, Earthquake and ODS-II do the switching job. How independent are the channels and how's the switching done?

My quick thrown together schematic. That last relay is drawn wrong but you should get the idea. 2 missing 100k resistors after C11, C13 and C16. Missing 250pf plate bypass on R15. I just borrowed the existing voltage supply and pedal. Power supply is the exact same as the original concert 2. Preamp triodes sit around 190V. Almost 500V on the 6L6 plates. It's plenty loud.

... need to solve some health problems ( ) and it will take some time : but no need to say that I will try all these informations and schematic in my own 7ender Concert II

Thanks a lot JayB

[rootz]

I have that book too, from 2009 right? Can't find a chapter or even paragraph about channel switching in it. Are you sure it was Merlin's book?

[JayB]

I'm actually hoping for that Dumble sound with the plate driven tone stack. It is essentially an HRM amp with PAB engaged the way I've drawn it. Pretty much how you'd use it I think. So low plate classic for clean, high plate HRM in PAB mode for the OD. Now if I could lose one of the gain pots in the OD channel that would be great.

I'm curious JayB, how did you do the switching? Have you got a schematic of your amp?

And still curious about how other Dumble based amps like the Onyx, Earthquake and ODS-II do the switching job. How independent are the channels and how's the switching done?

My quick thrown together schematic. That last relay is drawn wrong but you should get the idea. 2 missing 100k resistors after C11, C13 and C16. Missing 250pf plate bypass on R15. I just borrowed the existing voltage supply and pedal. Power supply is the exact same as the original concert 2. Preamp triodes sit around 190V. Almost 500V on the 6L6 plates. It's plenty loud.

... need to solve some health problems ( ) and it will take some time : but no need to say that I will try all these informations and schematic in my own 7ender Concert II

Thanks a lot JayB

The Concert II is wiring nightmare but it's doable if taking the time. The original fiber board went bad in mine over the years of use from humidity. I had it since my late teens.
You're more than welcome Jose. You can message me anytime you want and I wish you the best with the health. That must come first. I had to do the same not long ago and if I didn't I wouldn't be here today.