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Old 18th October 2013, 09:23 PM   #11
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ESP was where I found the variable load balance control. I didn't really like it. I only have one ganged pot on hand, my reason to use a smaller pot each channel in series with the volume pot to get a balance adjustment.

My AV receiver can balance it but my DIY TDA7294 no, and why I was looking at options.
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Old 19th October 2013, 06:16 AM   #12
Mooly is online now Mooly  United Kingdom
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Or just use two pots in all, one for each channel and wired as a volume control for each.
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Old 19th October 2013, 11:09 AM   #13
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Then I'd have to fiddle with both for volume changes. I did look at linking two pots with gears. Pull put for balance, disengages gears, adjust and push back in. Detent problems, looked at a pulley system, but they can slip. Very old stuff. I think a gear linked pot might work if the shafts were conical and spring loaded on the end.

Stupidly complex mechanical stuff but worth a look.
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Old 19th October 2013, 11:13 AM   #14
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Location: Scottish Borders - Kelso; on the famous Tweed River!
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Or just use two pots in all, one for each channel and wired as a volume control for each.
Common sense speaks!

Why complicate things with more joints, pots etc than is necessary?
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Old 19th October 2013, 11:13 AM   #15
Mooly is online now Mooly  United Kingdom
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O rings and a belt to link to pots. I've seen it done before. If the knobs are professionally turned it can look really good too.
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Old 22nd October 2013, 12:49 PM   #16
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I didn't see anything at all the LM4562 would be in my application. Some sort of dream opamp with no faults.
One funny application I saw was a 600v ESL headphone amp. I guess it's safe, but I wouldn't be cozy with 600v buzzing around my head like an electroshock brain treatment system.

Last edited by Wavewhipper; 22nd October 2013 at 01:07 PM.
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Old 26th October 2013, 08:43 PM   #17
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The dual 100kA pot and TL802 did a great job. I configured it as a non inverting follower with the wiper straight to the non inverting end, output to inverting input wire connection and straight to the TDA7294. No electrical noise and distortion undetectable. There was a little noise when turning the new Radio Shack pot, then it worked in.

Too busy yesterday, will test the equalizer today. When flat, as per application note build, this amp sounds a lot like a 1990's Onkyo amp. Very clean but a bit light on the bass.

Later I may try digital pots
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Old 26th October 2013, 10:17 PM   #18
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Near the bottom of this page link is a graph that shows perceptible distortion begins around 0.4%. I can get by with a single TL082 buffer but in order to be sure I get the best transient response and to keep distortions from added accessory devices I have some LME49860NA chips on order. LME49720 was not in stock so the best substitute I could find were the LME49860's. I can't see much difference except that the LME49860 has a slightly higher Vmax of +-22v vs +-17 of the LME49720.

I can chain quite a few of those and not worry about adding up distortion. The TL082's turn yuk with a much lower number of them. The LME chips look a lot better for an equalizer circuit.

I say it ain't no good unless it's 10x better than the error effects level.

http://www.r-type.org/articles/art-143.htm

Last edited by Wavewhipper; 26th October 2013 at 10:22 PM.
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Old 27th October 2013, 02:31 PM   #19
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DF96 wins the configuration award. It would need a quad op amp but with the new low price low distortion amps, no problem. Last I looked them, amps in the LMEXXXX league were 5-$10 each.
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Old 1st November 2013, 01:42 AM   #20
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You were right jean-paul. After some listening, I started noticing the TL082 shapes the sound to what the DJ's here in the USA make old songs sound like, The Blast From the Past sound. A nervous sort of feel to it.

Due to stock on hand, I chose an LME49860NA/NOPB to hear if it would help. Now it's like silk. I really hear an improvement, especially on cymbals. And the nervous blast from the past sound is gone.

Thanks for the advice.

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Never ever use TL082 in a device that must sound good. There are so many better choices. OPA2604, LM4562 (bipolar) etc.
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