Simple stereo balance metering circuit

premiumplus

Chief Journeyman
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Feb 21, 2013
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612
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Flint, MI
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Stuck in the 70's
#1
Hey guys,
I've wanted a simple way to measure my stereo left/right balance for some time. It's not always easy, at least for my ears/perception to get the balance right. I've got one ear that was injured and this has been a big help for me.
I used the same circuit as drawn below except since I didn't have a 1-0-1 mA null meter handy, I used a vintage VTVM. I set it up to measure dc voltage on the 1.5 volt scale, and centered the meter at mid-scale. I did a quick internet search and found a bunch of meters for under $10 here: https://www.fairradio.com/catalog.php?mode=view&categoryid=3984 . The diodes are 1N4004 (just about any silicone diode will do fine) and the resistors are 1/2 watt non-inductive...again, I don't think this is critical at all, and it's just what I had on hand.
Anyway, it works great and doesn't load the amp in any way that I can tell. If you cranked the amp up and were putting, say 50 volts RMS (312.5 watts RMS with 8 ohm speakers) into the meter circuit, the diodes would conduct and the current drawn by the resistor is only 50 milliamps. Not a big deal when you consider that 8 ohm speakers are pulling 6.25 amps, so they are swamping out the meter. I just use it for setup anyway, and then flip the "Speaker B" switch that it's connected to off. It's cool and simple, and solves a problem that I've had for a long time. If you do your own taping, recording, or use outboard processors you know how fast things can stack up and create an imbalance in stereo image. This lets you see immediately how balanced the system output is. I was surprised how this setup lets me see changes that I can't easily hear.

 

gadget73

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Aug 29, 2014
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#4
My cheater method is to use an analog voltmeter, going from + to + on the amplifier. Set it to AC, and feed a mono signal in to the amp. When the balance is correct, the meter will read 0 volts. If its off in either direction, it reads some amount of voltage. It won't tell you which direction its off, you just have to fool with the balance to figure that out. This also only works on amplifiers that use - as common ground. Thats most things, but if you happen to own something where - is not the same on all channels, it won't work.
 

NavLinear

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#5
Great idea. I now have a use for my neglected Simpson 260.
 

orange

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Broken beyond repair but highly affable
#6
It's sad when you neglect your Simpson, Navo.
 

gadget73

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Aug 29, 2014
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#8
Mine is on the bench next to the VTVM, and gets used often. My digital kind of sucks, so I rely on the 7P for a lot of things. The VTVM is nice, but I usually don't feel like waiting on it to warm up.
 
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