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Old 11th June 2006, 06:03 AM   #1
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Question Newbie Question

I've not had much experience with amps, but I've had a few oldies (hand me downs) that have worked reasonably well. However, on BOTH of them, I have encountered the same issue and want to know if (1) it is something I can fix and/or (2) is it ME? I apologize in advance if my inepititude has led me to skip a previous answer to this question, but I have not found any such thing.

Both of my amps are two channel. In case I'm not using the right terminology, I mean that I can have an A and a B channel, each consisting of a left and right speaker. In other words, I can have two pairs of speakers connected and choose which pair I want to be directing output to.

However, both of these amps have an issue where both pairs of speakers will not function at the same time. Perhaps I can explain this better:

If Channel A is on and Channel B is off, Channel A plays. (All is good.)
If Channel A is off and Channel B is on, Channel B plays. (Still good.)
If Channel A is on and Channel B is on, only Channel A plays. (But I wanted BOTH!)

Now, here's where the interesting part (to me!) comes in. If I reverse the speaker connections on the amp (e.g., swap Channel A and B), the same speakers will stay on when I turn on both channels. In other words, now when Channel A is on and Channel B is on, only Channel B plays. (Grrrr....)

My reasoning thus far has led me to believe that, in both scenarios, the amp favored the speakers which were the beefest (i.e., more watts). Is this coincidence? Is there a reason for this? Can I get both channels going at the same time?

I would greatly appreciate any advice / information. Thanks in advance!

P.S. If I'm describing this poorly, PLEASE let me know. I want to learn! Thanks again!
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Old 11th June 2006, 06:42 AM   #2
poobah is offline poobah  United States
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Your reasoning seems correct. I would guess that one pair of speakers is 4 ohm and the other is 8 (maybe 16). The 4 ohm speakers will consume twice as much power.

Doubling the power does not directly imply doubling the volume though. One pair of speakers may also be much more efficient... more sound per watt... I would bet the 4 Ohm speakers happen to be more efficient.

Perhaps this partially explains the difference in volume you are hearing.

Weird...
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Old 11th June 2006, 06:48 AM   #3
AndrewT is offline AndrewT  Scotland
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Hi,
I have never heard of your switching arrangement but easily think of a senario to explain it. That is until you said
Quote:
Now, here's where the interesting part (to me!) comes in. If I reverse the speaker connections on the amp (e.g., swap Channel A and B), the same speakers will stay on when I turn on both channels. In other words, now when Channel A is on and Channel B is on, only Channel B plays. (Grrrr....)
I wonder if you have a set of low impedance and high impedance speakers? the low impedance is pulling more current than the high impedance and the high impedance are playing quietly and are drowned out. Are they in the same room?
Alternatively you may have a very sensitive pair of speakers and a much less sensitive pair again leading to a large difference in sound output.

In both of the senarios there will be some output from the quiet speakers, not total silence. I am at a loss to explain why the same set appear to go completely silent, when the switch should be connecting them in series or in parallel.
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Old 11th June 2006, 10:25 AM   #4
djk is offline djk
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There is something wrong in the speaker switching of your amp.

Most amps these days wire the A and B speakers in series.

While this looks good on paper, it is not a good idea in practice (unless the speakers are identical).

Buy another amp to drive the second set of speakers, and parallel the inputs.
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Old 11th June 2006, 05:46 PM   #5
CBS240 is offline CBS240  United States
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I saw a stereo one time that had 4 speaker outputs, with an A/B switch. It could be used to drive side A OR B as you could use two speakers in one room but not another, or vise-versa. This was always kind of puzzling to me but it still only had two amp channels, R & L, and was not quadraphonic. IMO this was a marketing ploy against uninformed customers, or intended for small office use elevator music . It really was a cheaply built P*O*S anyway. I used to have an old Channel Master that someone through out but I fixed it. Some dolt had shorted all the output channels. It was quadraphonic and it had a joystick balance control which I liked quite well, I could adjust the stereo focus anywhere in the room...right on my recliner.
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Old 12th June 2006, 05:55 PM   #6
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Thanks guys. I very much appreciate the advice and info. I'm just trying to get a cheap system together to help out my mother, a school teacher, so she can setup a basic audio and P.A. system in her classroom, which is why I'd like to get a couple more speakers, but it looks like I may not get that luxury.

I am trying to get my hands on some more speakers to determine if it is an issue with them. Poobah, you mentioned that it might be something with the ohms each speaker is designed for. Is there a way to determine this? (I've got my trusty multimeter, but am uninitiated in the interactions of multimeters and audio equipment). Unfortunately, it doesn't look like there's any labeling on the speakers (unless it's on the inside). Any suggestions on how to get more info?

I'd like to stay away from getting a second amp as, again, this is for my mother and the less confusion, the better. :-)

Thanks again!
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Old 12th June 2006, 06:16 PM   #7
poobah is offline poobah  United States
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This is REALLY rough and full of pitfalls... but if you measure the resistance, the impedance of a speaker would usually be 50% higher. So if you measure 5 Ohms... you might GUESS that they are "8 Ohm" speakers.

I'll get torn up on this one for sure though!


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Old 12th June 2006, 08:32 PM   #8
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Quote:
Originally posted by poobah
This is REALLY rough and full of pitfalls... but if you measure the resistance, the impedance of a speaker would usually be 50% higher. So if you measure 5 Ohms... you might GUESS that they are "8 Ohm" speakers.

I'll get torn up on this one for sure though!
Well, at the very least, it sounds like I should be able to tell if there is a significant difference. I'll defend you! I'll let you know what I find.

Thanks again!
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Old 14th June 2006, 04:00 PM   #9
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While I was discussing all of this with a friend, he came up with what I have deemed the most incredible idea ever. :-) He suggested that I simply unplug all speakers then, using only one identical pair of speakers, connect one to Channel A and one to Channel B. If I connect one to the left channel and one to the right, I'm back in the same boat. But if I connect them both to the same channel (i.e. one on Channel A's left and one on Channel B's left), it functions as expected (that is both output at the same time!).

So, for now, I have taken one set of speakers and plugged them into the left channel and one set of speakers and plugged them into the right channel and everything functions as I would expect it to. So, I am not sure if my amp is freaked out or what, but I've got a solution. If I get a chance, I will try this on my old amp (the other one I mentioned at the start of this) to see if it works there too.

Anyway, thanks so much for the help and great ideas!
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