1 guitar - 2 amps - 1 speakercab

[carrejans]

I want to switch between two tube heads, using the same speakercab.
How can this be done? Is it doable for a DIY project, without digital electronics?


Here is a commercial one: http://www.tonebone.com/tb-headbone-vt.htm
Do you know of any other?

[therecordingart]

I want to switch between two tube heads, using the same speakercab.
How can this be done? Is it doable for a DIY project, without digital electronics?


Here is a commercial one: http://www.tonebone.com/tb-headbone-vt.htm
Do you know of any other?

My guess is that you'll need a dummy load and a make before break type of switch. I could be wrong though.

[R.G.]

Doing this is not complicated. You just have to go through what's needed for each piece step by step.

The front end has all the problems of a one-guitar-two-amps AB box. The back end has all the problems of a two-amps-one-speaker box, and both of them are flipped at the same time.


For the front end, you have to worry about switching the signal to the correct amp and probably muting the amp input that is not in use. For the back end, you have to worry about switching the speaker signal wire to the correct amp, plus putting a dummy load on the amp which is not being used because tube amps don't like to be unloaded.

You *may* have to worry about ground noise and AC leakage in the speaker common circuit. I'd have to think some more.

None of these are insurmountable, but you'll need a lot of switch contacts for the actual switching, more for the ground switching if that's needed, and it will be hard finding a manual switch that has that many contacts. Relays would be great for it, but then you need to power the relay coils, and the speaker relays need to handle significant current, so you need signal relays for the input and power relays for the output.

I'd have to draw it out to try to minimize the number of contacts.

[MetalGuy]

I've built a 2 amp/ 2 cab switcher and it worked but it had some grounding issues at the input because my signal splitter was not isolated from ground I suppose.
I used relays and uCUs for the switching introducing some minor delays in order to keep the amps connected to a load at all times.When not working one amp is muted but I got some pops from the relays. The whole thing consisted of a pedal (on stage) and a switching unit (near the amps and cabs). It was powered by a 12 VDC regulated wallwart.
R.G.: Concerning the splitter I was wondering if those transformers listed in your article are OK. Is 300Hz to 3kHz enough for guitar use or we should go for a full band transformer?

[R.G.]

R.G.: Concerning the splitter I was wondering if those transformers listed in your article are OK. Is 300Hz to 3kHz enough for guitar use or we should go for a full band transformer?

One of the points of the article was that you can get full guitar range out of a $2.00 transformer rated by the maker for 300-3K. What the manufacturer really meant was that "it'll go at least down to 300Hz and at least up to 3kHz. Anything else is just gravy, but don't count on it.".

In actual fact, the measured response of the 300-3K transformer in that circuit was 60Hz to 22Khz. The 22KHz came from the raw transformer being much better at high frequencies than it had to be, and the low end came from driving the primary with a bunch of current at the low end.

If you build a 300-3K filter (as I did, in the Lo-Fi project) it sounds distinctly "old time telephone-y". It's not enough for full range guitar. But the cheapo transfomrers I mentioned actually work better than they say.

There are some much better transformers available now. They're $10-$12 each instead of the $50 you used to have to pay for full audio response. So those can be used. But the $2 ones work fine as long as you use my circuit or something similar to extend the bass response.

[carrejans]

Thanks to Geert Jacobs, I found a schematic on the web:
http://web.archive.org/web/20030812220539/www.aikenamps.com/HeadSwitch.pdf

Doesn't make use of a PIC to control the relays, like the ToneBone one does.

Doesn't seem too complicated to fabricate; so I think I will try to make it.

Just still two questions though.
- Do you think there will be a hearable silence between the switching? (because I want to switch during a song; not in between songs)
- Will this work hum-free, you think?

[R.G.]

I looked it over. It looks pretty good. Randall doesn't design junk. Be sure to follow the directions for isolated phone jacks, ground wiring, isolation between input and output, and relay selection.

About the only issue this doesn't address fully is the issue of input hum from two amp inputs. Actually, it does address it, with the ground lift switch. That ought to work in most cases. But hum is very devious, and comes from many sources. Chances are this will work for the vast majority of cases.

[MetalGuy]

In actual fact, the measured response of the 300-3K transformer in that circuit was 60Hz to 22Khz. The 22KHz came from the raw transformer being much better at high frequencies than it had to be, and the low end came from driving the primary with a bunch of current at the low end.

Thanks for making that clear.

About the only issue this doesn't address fully is the issue of input hum from two amp inputs.

I think that's exactly where my problem was but I hope your isolated output splitter will take care of that.
Maybe a delay circuit without uCUs for the switching can be used as well like those in Engl E530 or Mesa DR.

Do you think there will be a hearable silence between the switching? (because I want to switch during a song; not in between songs)

Without delay circuit there should be no silence except for the time needed for the realy to switch and bounce which is in the range of 10-15 msec depending on the relay.

[Ronsonic]

I'm the aerial view, trees / forest guy. I got that way from finding myself buried in pine needles too often. Not a criticism of the idea, just another perspective.

Can I suggest that as a practical matter, hauling another speaker cab is simpler, more reliable, no more expensive, uses few cables, is easier to portage and set up and is just plain more rock and roll.

I'll shut up now.

[liquids]

Sorry I'm late...

https://taweber.powweb.com/store/2head.htm

[carrejans]

Sorry I'm late...

https://taweber.powweb.com/store/2head.htm

The 2 Head Amp Switcher DOES NOT switch your guitar input from amp to amp.

[G. Hoffman]

Sorry I'm late...

https://taweber.powweb.com/store/2head.htm

The 2 Head Amp Switcher DOES NOT switch your guitar input from amp to amp.

No, but it would be a trivial job to make a footswitch to do both the A/B switching and to switch the amp switcher.


I've made something similar to switch between my normal amp speaker and my "Leslie/Vibrotone" cabinet.  The only differences are no front end switching, and I had to design it to swtich between the 4 ohm and 8 ohm outputs so I could have a sort of "A/B/Y" set up and get both speakers at once some of the time.  On the other hand, I'm thinking of doing exactly this when I get my new amp finished, so please let us know how yours goes.


Gabriel

[liquids]

I thought a simple buffered dual output, one for each amp, would be fine...then all you need to do is switch amps.  This a diystompboxes forum right?