Two channel footswitchable

[jeff]

 Anyone suggest a good schematic for an amp with two footswitchable channels. High gain/low gain with seperate tone stacks, gain, and vol. for each.

Thanks
  Jeff

[Shrapnel]

Hi-gain -Marshall
Lo-Gain - Fendery?

OR

Hi-gain - Soldano SLO ?
Lo-gain - Marshall or fender?

Help us know more.

[jeff]

I was thinkin' gain gain/cathodefollower tone stack vol(ala bassman) for one channel the same with one extra gain stage(ala marshall) for the other channel. I'm really interested on how to do this with relays. but really more interested in how it's done so any schematic would be appreciated.

Would you have build two seperate preamps or can you just use the relays to add one stage and swap gain and tone stack/vol. controls? It just seems to me when you step on the pedal the signal would drop out for a split second as the relay swaps.

I was checking out Doug's relay that adds a gain stage but is that a smooth transition between in and out? Is the relay so fast you don't hear it switch in the split second where nothing is connected? http://www.el34world.com/projects/images/18wattstoutReverbSchematic.gif

Curious to see how others have done this.

[jeff]

Let's just say, for the sake of argument, you used a relay and both positions are connected to the same thing. As you switch it there'll be a split second where nothing's connected so wouldn't you hear your signal cut out?

So I'm thinking you need to have two full preamps and have the relay ground out the unused channel. That way for that split second, both are "on" and the transition is more seemless. I get how you could do that but how do you bring them together without the tone/vol of one affecting the other?

If you use two 470K resistors to isolate the two volumes then each channel has a voltage divider of 470K/470+(the other channels vol wiper to ground). One channel would see a 470K/1.47M(~3/4 the signal) voltage divider when the other's volume is full up and a 470K/470K(1/2 the signal) when the other is down. So wouldn't one channels vol would be affecting the other's?

 

[Shrapnel]

Here is one example straight out of Doug's schematic library. It's a fairly simple 2 channel tube amp, that shows one way to do two channels. It should be adaptable to what your thinking of and I think comes close to what you were describing design wise.

http://www.el34world.com/charts/Schematics/files/kitty_hawk/kittyhawk_quatro.pdf


There are others too in the library (link on the bottom of any forum page) that can show off multiple channels too.

[tubenit]

 

Anyone suggest a good schematic for an amp with two footswitchable channels. High gain/low gain with seperate tone stacks, gain, and vol. for each.

Sure, I drew something like that up a few months ago.  Look at the various schematics in this thread ......... Check it out here:
 http://www.el34world.com/Forum/index.php?topic=12712.0

AND Geezer has already built a HoSo56 with relay "pseudo channel switching" & relay "boost" that might accomplish what you are wanting also.  

http://www.el34world.com/Forum/index.php?topic=10999.0

With respect, Tubenit

[The_Gaz]

And just to clarify, there is no pause when switching - it's instant.

[sluckey]

Let's just say, for the sake of argument, you used a relay and both positions are connected to the same thing. As you switch it there'll be a split second where nothing's connected so wouldn't you hear your signal cut out?

Small signal switching relays usually switch in a few milliseconds. Is that a problem? If so, use some fast Vactrols with logic switching.

[jeff]

Thanks for all the schematics. Lots of good ideas I can't wait to try.

And just to clarify, there is no pause when switching - it's instant.

Thanks, that was my main concern, if two preamps were needed or you can just swap out pots. I guess for my first attempt at channel switching I'm going to try simply having two vols. and to gains. and use the relays to switch pots/settings.

[jeff]

Let's just say, for the sake of argument, you used a relay and both positions are connected to the same thing. As you switch it there'll be a split second where nothing's connected so wouldn't you hear your signal cut out?

Small signal switching relays usually switch in a few milliseconds. Is that a problem? If so, use some fast Vactrols with logic switching.

Only if it's noticable.
I'm gonna try something like Geezer's "pseudo switching" for now and see how that works for me. Then on to the more complicated juicy stuff.

[TIMBO]

Hi Jeff,I 've been messing with the Mesa Boogie Dual Rectifier and have found it a bit of a challange  but interesting. I think that you could do something similar.

Depends on the sounds you are looking for but a clean circuit that has relays(throughout the amp) that could be switch at the same time to create a different sound.

[jeff]

Thanks, I'll give that a good lookin at. I think something like that is what I need.
 I love my amp high gain and low gain so I think the answer is just to swap gains and vols for two switckable settings right now. I'll try this out when I get around to my high gain 100/50Wer. Are the cathode cap switches also relay controlled to switch in or out when switching channels, or face mount switches to preset to taste. Lots o' switches! I like it. What's the .005 cap on the supply of the second stage? Is that in parallel with it's filter cap or a typo and instead of to ground bypasses the 100K, Or plate to ground?? Is V1A unused?

 And advice on relays?

[TIMBO]

Hey Jeff, The schem is as original and that cap is to ground and not sure of its purpose, maybe treble bleed, smoothing 
Yes, V1a is unused for the moment and i would like to use it for something, but cause this is a HIGH GAIN amp adding another gain stage would be TOOOO much i would think but it could be fun to try a few things  . I'll get it working first.

[Geezer]

I'm gonna try something like Geezer's "pseudo switching" for now and see how that works for me. Then on to the more complicated juicy stuff.

Here's a simple test before you do anything invasive on the amp:

Set the gain & master (& tone stack) for a good clean sound/tone

Now (without touching the tone stack) can you adjust the gain & master for a good overdrive sound at about the same/equal perceived volume as the clean/tone?

If yes, then the "pseudo switching" will work for you (that amp)

If not, it's useless to do all the work, as it won't work in an acceptable manner (for the circuit).

The idea came about because I noticed I could get good clean and OD tones from the HoSo56 without adding any more gain stages. I have also used another relay to simultainiously switch in an Mid-boost (tone-stack lift resistor) to get a better OD tone, or have it on a separate footswitch to use as a "Boost" for solos.

G

[jeff]

Ok Geezer, thanks for the input. I give that a try before doing any surgery.