If I were to build a simple 100k audio taper dual pot in front of a stereo opamp inverting buffer (av = 1), would the .03% distortion of the opamps I have on hand, TL082, add to the .003% of my equalizer or multiply it ?
Does distortion get noticeable to keep adding opamps in the signal path ?
I already bought TL082's but I do know there are lower distortion amps out there.
Now also, is there an easy way to add a balance pot and not exaggerate the audio taper of the pot I already bought ? I do not plan any input resistor to ground, but the balance pot may affect the taper of the volume pot if both are at the input.
It looks like I would need to put the balance pot at the input, go through a buffer, feed the volume pot then through another buffer to isolate any interaction of the pots. Then comes my reason for the distortion question. .03 + .03 + .003% = .063% ?
Does distortion get noticeable to keep adding opamps in the signal path ?
I already bought TL082's but I do know there are lower distortion amps out there.
Now also, is there an easy way to add a balance pot and not exaggerate the audio taper of the pot I already bought ? I do not plan any input resistor to ground, but the balance pot may affect the taper of the volume pot if both are at the input.
It looks like I would need to put the balance pot at the input, go through a buffer, feed the volume pot then through another buffer to isolate any interaction of the pots. Then comes my reason for the distortion question. .03 + .03 + .003% = .063% ?
Combining distortions in different stages does not have a simple answer, as they can interact, and of course they are signal-level dependent. However, for low amounts of distortion you can assume that the worst case is that they simply add up.
How best to combine a volume pot and a balance pot depends on how aggressive a balance control you want. If +-3dB is sufficient balance variation then a linear balance pot of the same value as the log volume pot can be wired as a variable resistance in series with the top of the volume pot. At mid position the balance pot will be 50k (in your example) so you lose about 3dB of signal at max volume.
PS this ought to be in the Line Stage forum
How best to combine a volume pot and a balance pot depends on how aggressive a balance control you want. If +-3dB is sufficient balance variation then a linear balance pot of the same value as the log volume pot can be wired as a variable resistance in series with the top of the volume pot. At mid position the balance pot will be 50k (in your example) so you lose about 3dB of signal at max volume.
PS this ought to be in the Line Stage forum
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Can't put a schematic up for now, but here is my hope :
Balance
One 50k linear pot, 1 end to the L channel from CD, opposite end to the R channel from CD, and the wiper to ground.
Volume, one end of 100k log pot to L channel from CD (same point as above) opposite end to gnd. Wiper to inverting input of L channel buffer (AV = 1).
Same for R channel.
I have never found things that simple, so I figure on the balance pot at the input, then from the output of the first balance buffer, feed the top of the 100k volume pot, bottom to gnd, and wiper to a second inverting buffer.
I'll just have to try a single stage. So what, it inverts, the Australians live upside down and they don't notice.
Balance
One 50k linear pot, 1 end to the L channel from CD, opposite end to the R channel from CD, and the wiper to ground.
Volume, one end of 100k log pot to L channel from CD (same point as above) opposite end to gnd. Wiper to inverting input of L channel buffer (AV = 1).
Same for R channel.
I have never found things that simple, so I figure on the balance pot at the input, then from the output of the first balance buffer, feed the top of the 100k volume pot, bottom to gnd, and wiper to a second inverting buffer.
I'll just have to try a single stage. So what, it inverts, the Australians live upside down and they don't notice.
That is not a balance control, but a variable load. You will see almost no effect until the wiper reaches an end-stop; at that point one channel will almost disappear.Wavewhipper said:
Read my post 2 very carefully. Write out a circuit diagram of what you think I described. Think about how it works.
I'm a novice myself, but personally i would use a buffer stage between the volume and balance pots.
There may be a way to skip an intermediate buffer, but as i said, I'm a novice and I don't know of a way.
With devices like LM4562 and LME49710/20/40 i doubt an extra buffer is much of a concern as far as total THD is concerned.
There may be a way to skip an intermediate buffer, but as i said, I'm a novice and I don't know of a way.
With devices like LM4562 and LME49710/20/40 i doubt an extra buffer is much of a concern as far as total THD is concerned.
Ok, I can do it like in post 2, I think that would take 3 pots, 1 ganged volume and two single pots for balance, one each channel. That would be the easy way out of two amps/channel. And it looks like I'll put the TL082's in a socket and find a better direct upgrade on my next order.
I am trying to use what I have for now, packing to move in a few weeks and want to get it started before my stuff gets lost in the boxes.
I am trying to use what I have for now, packing to move in a few weeks and want to get it started before my stuff gets lost in the boxes.
I was going to say look at sound.westhost.com (Rod Elliots site) and search for potentiometers but the site looks down just at this moment.
That shows how to wire the balance control as DF96 suggests (the dual gang pot for balance is the best option, single pots can allow crosstalk due to the small but finite and variable wiper contact resistance)
That shows how to wire the balance control as DF96 suggests (the dual gang pot for balance is the best option, single pots can allow crosstalk due to the small but finite and variable wiper contact resistance)
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.
My AV receiver can balance it but my DIY TDA7294 no, and why I was looking at options.
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.
Stupidly complex mechanical stuff but worth a look.
Common sense speaks!
Why complicate things with more joints, pots etc than is necessary?
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.
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.
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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
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
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
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
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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.
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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