Mixing/Grids for Skipped gain stage

[GlideOn]

Edit: Updated Layout to reflect more the Robinette spec "Nakid" due to difficulty sourcing some Soldano Avenger-specific componentry: https://ampgarage.com/forum/download/file.php?id=76829

I have decided to overhaul my amp into a Soldano SLO/Avenger voicing, utilizing an unused V3A triode as a gain stage in my Single Ended (utilized for the Cold Clipping stage after V1A and V1B gain stages).

I'm feeling pretty confident in my layout overall, but I'm wanting to add either a clean channel or an un-cascaded voicing, have as panel switch or foot switch between the two. I do have a JHS AB Mini I can utilize for this.

As some may know, the Avenger does not have the dedicated clean channel/triode that an og SLO has - it's a more streamlined single channel and adds the JCM800 style Low jack as more of an afterthought to plug into for clean-ish tones...just not at the same time of course...

...or can you?

I had thought to attempt to tackle this age-old bear and one of the thoughts was to give it its' own gain pot (technically sharing a shaft on dual gain pot) and own grid resistor into the next gain stage.

Normally this is a simple 470k grid stopper coming in after the gain pot, but potentially summing two signals together I'm curious what the side effects/penalties are.

I wrote up some crude schematic(s) to show the proposed solutions.

My current layout shows the stock single 470 and 10k (minimal value is possible ) for the clean side.

Will any of them work and if so, what are the side effects?

AX84 SEL Soldano 2 maybe.pdf

Soldano Avg SE 1.pdf

Soldano Avg SE alt.pdf

Soldano Avg SE alt2.pdf

[GlideOn]

Anybody? Bueller? Bueller?...

[sluckey]

If you simply want to have a HI/LO option like the JCM800 2204, then just copy the simple Marshall circuit.

But, sounds like you want to play through both inputs at the same time and mix them together. You cannot do this because the two signals are opposite phases at the point you want to mix them back together and this results in phase cancellation which sounds thin. Also, the HI signal will be about 50 times greater than the LO signal. Guess which one is gonna swamp the other.

BTW, a Switchcraft 14B jack looks like the attached. I don't know what your symbol represents.

[GlideOn]

Actually, I don't want to play them at the same time, simply want to switch between one or the other. The JHS Mini AB in question doesn't have the ability to put both on at the same time, it's strictly one or the other.

Also am aware of the significant volume drop, however, if I simply patch in a boost pedal on the other side of the split stereo cable on the switched "B" side that should make up for any volume loss.

Basically I'm seeing if this hair-brained idea is feasible in the first place before I spend all the time and labor implementing it.

[sluckey]

Basically I'm seeing if this hair-brained idea is feasible in the first place before I spend all the time and labor implementing it.

No pain, no gain. You may be on the verge of becoming the next gitamp guru, or not.

[GlideOn]

If you simply want to have a HI/LO option like the JCM800 2204, then just copy the simple Marshall circuit.

But, sounds like you want to play through both inputs at the same time and mix them together. You cannot do this because the two signals are opposite phases at the point you want to mix them back together and this results in phase cancellation which sounds thin. Also, the HI signal will be about 50 times greater than the LO signal. Guess which one is gonna swamp the other.

BTW, a Switchcraft 14B jack looks like the attached. I don't know what your symbol represents.

I'm not quite sure what you mean by "just wire it like the Marshall circuit."

Won't plugging in both essentially short the first gain stage that way?

[GlideOn]

Bump!

Let get some brains to weigh in on this today! I'm rewiring my board as we speak!

Let me know if you need any clarifying.

[Bergheim]

Not sure I understand how the inputs are meant to work. In one post you want to be able to plug into both inputs, then in another they're only supposed to be switchable. Mixing parallel channels is easiest done with a resistive mixer, as in one of your schematics. To use only one channel at a time it's easiest to do it like the JCM800 2204 hi/lo arrangement.

[GlideOn]

Not sure I understand how the inputs are meant to work. In one post you want to be able to plug into both inputs, then in another they're only supposed to be switchable. Mixing parallel channels is easiest done with a resistive mixer, as in one of your schematics. To use only one channel at a time it's easiest to do it like the JCM800 2204 hi/lo arrangement.

The idea I had in mind was to use a type of jack that plugs into both "inputs" at the same time via stereo instrument cable, but strictly an 'either/or' scenario to be sent directly to an JHS AB pedal on the floor to select A or B only, no Y, no paralleling channels. I'd rather not have to unplug/plugin to input each time and as I mentioned, have a solution for the volume drop of the "low" input (clean boost!).

The input is a Switchcraft 14B. It's 2-in-one. Stereo shorting, though technically only one side needs the shorting function for the first stage triode.

It's kind of an ass-backwards (or forwards?) way of using one less cable coming out of the amp for a hopefully more elegant solution for channel switching. It's strictly for utility purposes and to use one less cable.

I have no idea what the schematic symbol is for a 14B so I did my best to illustrate. @sluckey was gracious enough to illustrate the proper symbol for it, so go ahead and sub that in if you can.

Of course, this is all theoretical. I have no idea if/what consequences, side effects (likely) that can be dealt with or mitigated.

I'm pretty sure the two parts need to have mixed resistors to sum their respective into the second gain stage, but I can't fathom what will happen.

So I am kind of at a standstill until I can figure this out.

Schematics are not my strong suit, lol! Am an artist and illustrator at heart and I find it more useful to illustrate especially custom builds where physical component location is integral to locating and mitigating potential noise/oscillation.

[Bergheim]

Sounds like the easiest way would be a single input jack going to both channels. Then a switch that grounds one channel's output at a time, right before the mixing resistors.

[Littlewyan]

What have you got so far to work with? Do you already have the Lo jack for the Avenger circuit? If so you could easily switch to bypass a gain stage. Or if you have an unused triode we have a huge range of possibilites for creating a simple clean channel. A photo of your current build would help.

[GlideOn]

What have you got so far to work with? Do you already have the Lo jack for the Avenger circuit? If so you could easily switch to bypass a gain stage. Or if you have an unused triode we have a huge range of possibilites for creating a simple clean channel. A photo of your current build would help.

Yes, it's currently a standard Switchcraft J12B shorting Mono jack, but I do not have room to add another jack hence the reason to swap with a Stereo Jack.

I have 2x 4PDT switches on the faceplate I've setup as Bright Cap switching and Crunch/Lead, kind of my own design borrowed from other amps I've built with similar switching schemes.

I wouldn't be opposed to substituting one of the 4PDT switches for an extra jack if that's what you're implying. I'm not dead set in having them I just have a penchant to add as much stealth-like versatility as I can to an amp.

Proposed layout is in first post: https://ampgarage.com/forum/download/file.php?id=76829

Sounds like the easiest way would be a single input jack going to both channels. Then a switch that grounds one channel's output at a time, right before the mixing resistors.

That's...what this is. A single physical jack going to both channels, as it were.

I don't want it on a dual-pole switch on the amp's front panel. I want it on a pedal. Hence the reason I posted this question!

[Bergheim]

I don't want it on a dual-pole switch on the amp's front panel. I want it on a pedal. Hence the reason I posted this question!

A SPST switch with ground to the middle lug, and either channel on the outer lugs would suffice. Principally it doesn't matter if the switch is on the amp or in a pedal, but in the latter case I'd do the switching with a relay. That way, the audio signal is kept within the amp and not all the way through the pedal cable where it might pick up unneccessary noise.

[GlideOn]

I don't want it on a dual-pole switch on the amp's front panel. I want it on a pedal. Hence the reason I posted this question!

A SPST switch with ground to the middle lug, and either channel on the outer lugs would suffice. Principally it doesn't matter if the switch is on the amp or in a pedal, but in the latter case I'd do the switching with a relay. That way, the audio signal is kept within the amp and not all the way through the pedal cable where it might pick up unneccessary noise.

Yes, that's be the easy way but again, I'm specifically wanting it to be switched at the pedal board.

Besides, an AB pedal grounds the other side when not in use, no? And an instrument cable is shielded to mitigate RF noises to begin with.

Relay is an option but again - space is limited.

I was looking at the Granger Relay unit which neatly compartmentalizes the jack and board together, but even that is on the larger side and my measurements would have it bumping up against the V1 section.

Chassis is 16x8x2. Not big.

Respectfully, it seems as if my proposal isn't really being considered? Is there something I can help clarify? Humor me for a moment, if you can?

[GlideOn]

All, I've updated the layout to reflect more the Robinette "Nakid" spec as some things are difficult to source (2.2M in 1W rating, variable trim pots, etc) that make the Avenger what it is. There's a lot of alleged tweaks to the circuit and I'm limited to a single schematic of what I can tell is the original/stock config, possibly not reflecting latest revisions.

I think it's easier overall for me to emulate the Robinette designs. I kept the "low" connecting straight the the stock gain pot 1M and left the value alone for clean/low input side, dirty/high side has 1M parallel to ground to reflect a 500k gain pot in Rob's layout