SI Super-T and speaker AB switch to ONE speaker

[Taperwood]

In short, I need a mono speaker signal. I need to combine the L and R speaker outs to one wire and then go through an AB switch to two speakers, but only one will be playing at a time.

These are single driver speakers (8 ohm) that I am prototyping, and I need to do fast AB switching between the two to test for different design parameters.

Can I safely do this, and what kind of switch would I need? I can solder well enough, but I need this to be absolutely safe for the amp and the speakers, and I don't know enough about electronics to feel confident doing this without advice.

Thanks for any advice you can give.

Doug

[DcibeL]

Would it not make more sense to send the input signal into a SPDT switch and have each "throw" connected to either left or right input of the amp. As it doesn't seem to me that you are trying to increase power output in any way, I don't understand why you would want the switch on the output.

I tried drawing a picture. I should have been an artist . When switch is in position 1, the top speaker plays, when the swtich is in position 2, the bottom speaker plays. Very effective for A/B comparisons of speakers.

[Taperwood]

Thanks DcibeL,

I always thought it was bad to only have one channel of an amp "amplifying." That's why I was thinking via the speaker wires.

So you are saying to run both L and R input cables into a switch and then run one cable each to the L and R input of the amp? (I use RG6 for this setup). In other words, you are saying to combine the L and R input at the switch to make a mono output for the L and R inputs of the amp? Correct?

You are right, I'm not trying to increase power or anything. In fact, I want this as neutral and safe as possible for the equipment.

Thinking out loud here: The L and R input from source goes to the single pole of the switch. Switch setting A sends the combined L and R signal to the R channel input of the amp via one cable. Switch setting B sends the combined L and R signal to the L channel input of the amp via one cable. Correct?

QUESTION: So what type of SPDT switch do I get to switch a 75 ohm RG6 signal? Rotary? Toggle? Wall switch? (This is where I am totally ignorant) I will have to buy four RCA jacks (2 in, 2 out) and wire them to the switch, correct?

Am I making progress?

Thank again,

Doug

[DcibeL]

Originally posted by Taperwood
So you are saying to run both L and R input cables into a switch

That would be L or R signals into the switch, and connect all grounds together.

Originally posted by Taperwood
QUESTION: So what type of SPDT switch do I get to switch a 75 ohm RG6 signal? Rotary? Toggle? Wall switch? (This is where I am totally ignorant) I will have to buy four RCA jacks (2 in, 2 out) and wire them to the switch, correct?

You can use which ever type of switch you like, I would try for a "make before break" type to reduce popping when the signal is switched. If you don't know what that is, your local electronics supply store will. If you were planning on making a switch box for this purpose, all you would need is 3 RCA's. 1 in, 2 out.

[Taperwood]

Originally posted by DcibeL

That would be L or R signals into the switch, and connect all grounds together.

Keeping in mind that, above all, I want to protect the amp and drivers from damage, but I was thinking of taking the two center pins and the two grounds on the L and R inputs and combining each inside the switch since I will have to run wires from the RCA plug to the switch anyway. Would that be safe to do? Or would a RCA stereo to mono patch cord work better?

I really need the signal from both L and R for this to work. It would be hard to test speakers when all you can hear is half the stereo signal

I'm still wondering about having only one amp channel active at a time, though. You are saying this should not affect it at all?

Doug

[dnsey]

I was thinking of taking the two center pins and the two grounds on the L and R inputs and combining each inside the switch since I will have to run wires from the RCA plug to the switch anyway. Would that be safe to do?

Yes, that's fine

I'm still wondering about having only one amp channel active at a time, though. You are saying this should not affect it at all?

No, no problem whatsoever - as far as the amp's concerned, each channel is independent anyway. It would be just the same as a stereo signal panned hard L or R.

[Taperwood]

Wonderful. Thank you DcibeL and dnsey. I will get the parts and make the attempt. If I have another question, I will ask.

(I do have an old throwaway chip amp setup (from computer speakers) that I can test this on first. I think that would be a good idea, given my comprehension of electronics).

Thanks again,

Doug

[DcibeL]

Originally posted by Taperwood
Keeping in mind that, above all, I want to protect the amp and drivers from damage, but I was thinking of taking the two center pins and the two grounds on the L and R inputs and combining each inside the switch since I will have to run wires from the RCA plug to the switch anyway. Would that be safe to do? Or would a RCA stereo to mono patch cord work better?

I'm not sure I quite understand what you are trying to explain here but here it goes. The grounds do not need to be switched. Just connect them together at some point. Don't use a Y-cable to try and mix Left and Right channels together. This will effectively connect the left output of your source to the right output of your source, and the result will be unsatisfactory. This is not the proper use of a Y-cable. Proper use of a Y-cable would be to plug one (either left or right) output from your source into both inputs on the amp. In this case both channels play the exact same thing, but without a switch to turn each side on and off.

I don't understand why you need to mix both left and right channels together. For testing purposes, this shouldn't matter. What would matter is that the same signal is tested on both speakers for an A/B comparison. The only "easy" way to mix both left and right channels together into a mono track that I can think of off the top of my head would be with the use of a computer.

[Pano]

Going back to the top post.
You certainly DON'T want to combine the outputs in any way, the Super-T will not function like that.

If I understand what you are trying to do, the simplest solution woul d be:

Connnect one speaker to left, one to right. Use an RCA Y-cable on the input. Connect the single end of the Y to your source, the split end to the amp. That way you are driving left and right with an identical signal. (As seen in DecibeL's drawing).

Now just plug or unplug the Y-cable to left or right on the amp. If you want to be fancy, you could put a switch in there, but you don't really need it.

[Taperwood]

Thanks, I understand that the ground does not go through the switch. However, I've also read in threads on modding some of these amps in this forum (excuse my ignorance) "never tie the grounds together on the (power something?)" Does this come into play here, or is it strictly related to the power supply?

The reason you need the full stereo signal is becasue of the mixing between the two channels. For instance, the recording engineer might have boosted the drums by 6db over the vocals in the left channel (or something like that). So if you were using the left channel only to AB test, you would not hear what you were supposed to hear. You couldn't properly evaluate the sound of the speaker because the drums would be dominating everything else. You need the signal from both channels to get the proper mix level.

Doug