Looking for a 4-output Amp switcher

[mnordbye]

Basically, i'm in need of a Amp switcher with 1 input for the guitar (or any instrument) and 4 outputs to amps. A switch for each output too. Anyone who has any suggestions for me? I also want it too be as quiet as possible. Also, i DI out would be cool.

I've looked at the AMP switcher projects over at Geofex: http://www.geofex.com/fxprojex.htm Does anyone have any experience with such a amp switcher?

Thanks,

[mnordbye]

Thought id BUMB this one.

[Auke Haarsma]

I've built the Humfree ABY several times with good results. I think you can expand it to get 4 outputs.

[mnordbye]

I'll check out that one then. Thanks!

Also, i forgot i've built one of these for a friend. http://www.generalguitargadgets.com/index.php?option=com_content&task=view&id=16&Itemid=26 I haven't looked at it too much lately, but would it be possible to modify this to my needs? 4 outputs and a on/off switch for each that is. Maybe use 2 of these boards?

[R.G.]

The GGG project is the same as the DIY article at GEO, just with a PCB laid out for it.

The GEO project can be expanded to four outputs easily enough. Just replicate the transformer circuits again. The simplest thing to do for the switching is to replace them with a rotary switch.

In retrospect, it occurs to me that one might get better hum performance in some situations if the non-used outputs had their inputs grounded. I may have to dig out the prototype and mess with that. A few people have reported some situations where there was still a bit of hum. It is remarkably difficult to allow for all possible hum situations. But maybe this can be improved. I'll look at it.

If you insist on doing the selection by stomping a switch, either the same one potentially several times, or one of four stomp switches to go directly to the other amp, the switching setup becomes a CMOS logic circuit. It's doable, but some people are afraid of that.

[mnordbye]

Ye, i don't want to go the CMOS way, which is way too close to digital for me! 

Really, i wanna do this as simple as possible. And since this is going to be used in a studio, the rotary switch suggestion seems perfect for my needs. I don't think i'm gonna be playing through several amplifiers at the same time, but if so, not more than 2 at a time.

How should a go about this then? I can think i need 2 of those PCBs and a rotary switch, i guess. Do i have to change anything from the layout too? The switching must be modified at least, i guess.

Thanks!

[R.G.]

Hmmm. If you have time to flip the switches and may need more than one at a time, just put a switch on each one. If you use a DPDT toggle switch, it can both select the signal and turn on an indicator LED for each output.

Here's how to wire it. First, think in blocks. I suggest that you print the schemo and circle the blocks, then maybe cut them out and paste them on another sheet of paper in paper-dolly fashion to show the new schematic. Software works for this too.

The blocks are (1) the input opamp section up to the output pin of the opamp at point A, (2) the output transformer block, that being the part from the output jack back through the transformer to the primary pins, (3) The resistor/capacitor network from point A to just before the switching stuff consisting of the 100 ohm, the 100uF and the 0.1film caps, and (4) a new block - just an opamp follower, with input at the + input pin and its output tied to the inverting input.

In the new arrangement, the input section stays the same. This provides a high input impedance and a tiny amount of voltage gain to make up for some losses in the transformers.

You will make up four (or more!) output sections. Each output section consists of a cascade of one of the new Block 4 followers, a Block 3 resistor/cap network on the output, and a Block 2 transformer block. This gives you an output section that only needs a signal in at the + input of the opamp to provide an output on the isolated output for that section.

Now we hook them together. From the input section, take a 10K resistor to the input of each output section. Also, connect a 1M from the + input of each of the output sections to ground. As this sits now, all four output sections are active all the time, and you have a four- (or more) way splitter, but no muting of any of them.

Now, for each output section, hook up a toggle switch to mute the output and to indicate when it's active. You can use a SPDT toggle. Hook the pole (center contact) of the switch to ground. Hook one outside throw to the + input of an output section, right where the 10K and 1M meet at the + input pin. Hook a resistor/LED indicator to the other throw of the switch. When the switch is switched one direction, it ties the input of the output section to ground, muting it, and opens the LED so it is dark. Flipped the other way, it releases the output section to pass signal, and at the same time ties the LED/resistor to ground so it indicates that the channel is on.

Make one toggle switch setup for each output section you like. Flip toggles on/off to enable/disable the channel.

Note that I have assumed a bipolar power supply here. For a studio box, I recommend you power the opamps with a real bipolar power supply of about +/-12 to +/-15, and bias them all at ground, as I've shown the +/-9V supplies in the diagram.

[aziltz]

maybe look at the Voodoo Lab Amp Switcher's features.  it uses relays to do off/on or exclusive switching.  4 outs plus tuner.

[mnordbye]

Thanks R.G.! I'll try out what you suggested.

[sevenisthenumber]

Hmmm. If you have time to flip the switches and may need more than one at a time, just put a switch on each one. If you use a DPDT toggle switch, it can both select the signal and turn on an indicator LED for each output.

Here's how to wire it. First, think in blocks. I suggest that you print the schemo and circle the blocks, then maybe cut them out and paste them on another sheet of paper in paper-dolly fashion to show the new schematic. Software works for this too.

The blocks are (1) the input opamp section up to the output pin of the opamp at point A, (2) the output transformer block, that being the part from the output jack back through the transformer to the primary pins, (3) The resistor/capacitor network from point A to just before the switching stuff consisting of the 100 ohm, the 100uF and the 0.1film caps, and (4) a new block - just an opamp follower, with input at the + input pin and its output tied to the inverting input.

In the new arrangement, the input section stays the same. This provides a high input impedance and a tiny amount of voltage gain to make up for some losses in the transformers.

You will make up four (or more!) output sections. Each output section consists of a cascade of one of the new Block 4 followers, a Block 3 resistor/cap network on the output, and a Block 2 transformer block. This gives you an output section that only needs a signal in at the + input of the opamp to provide an output on the isolated output for that section.

Now we hook them together. From the input section, take a 10K resistor to the input of each output section. Also, connect a 1M from the + input of each of the output sections to ground. As this sits now, all four output sections are active all the time, and you have a four- (or more) way splitter, but no muting of any of them.

Now, for each output section, hook up a toggle switch to mute the output and to indicate when it's active. You can use a SPDT toggle. Hook the pole (center contact) of the switch to ground. Hook one outside throw to the + input of an output section, right where the 10K and 1M meet at the + input pin. Hook a resistor/LED indicator to the other throw of the switch. When the switch is switched one direction, it ties the input of the output section to ground, muting it, and opens the LED so it is dark. Flipped the other way, it releases the output section to pass signal, and at the same time ties the LED/resistor to ground so it indicates that the channel is on.

Make one toggle switch setup for each output section you like. Flip toggles on/off to enable/disable the channel.

Note that I have assumed a bipolar power supply here. For a studio box, I recommend you power the opamps with a real bipolar power supply of about +/-12 to +/-15, and bias them all at ground, as I've shown the +/-9V supplies in the diagram.

Anyone tried this?