Some comments, observations and speculation:
I sympathize with the original p[ost. I've thought about that myself. The selection of dual-ganged pots from catalog sources such as Mouser and Digikey is very limited.
If money is no object you can order up a custom pot of nearly any configuration from www.potentiometers.com as well as some other sources. However, the minimum order regardless of volue is likely to be US$100.
I have some concern that the dual pots that ate easily obtainable may not track each channel as closely as one might like.
On a preamp, the need for control elements on the front panel may conflct with the desire to keep the signal path as close to the inputs and output terminats as one can.
All the above , makes one wish a simple any ineaxpensive IC were available that you could control from a standard off the self pot. As mentioned VCAs are a possability. There are digital volume controls as well. There are optoisolators. It is not clear to me if each of these are not potential noise and distortion sources - the idea of adding another active component in the signal path is unappealing.
Here is an idea for someone who has the time and inclination: how about a pair of LED controlled LDR's? As the control pot wiper moves the voltage and current appled to one of the LEDs moves in the opposite direction from the other. In the simples form this would be very non-linear but perhaps the control voltage could be compensated/manipulated to suffeciently reduce the nonlinearity. I'm assuming that the LDRs are availavle that add no more to the signal than a good quality pot or attenuator.
I've too many thing on my plate to pursue this notion now so it remains in my mental "someday when I got some extra time" file.
I sympathize with the original p[ost. I've thought about that myself. The selection of dual-ganged pots from catalog sources such as Mouser and Digikey is very limited.
If money is no object you can order up a custom pot of nearly any configuration from www.potentiometers.com as well as some other sources. However, the minimum order regardless of volue is likely to be US$100.
I have some concern that the dual pots that ate easily obtainable may not track each channel as closely as one might like.
On a preamp, the need for control elements on the front panel may conflct with the desire to keep the signal path as close to the inputs and output terminats as one can.
All the above , makes one wish a simple any ineaxpensive IC were available that you could control from a standard off the self pot. As mentioned VCAs are a possability. There are digital volume controls as well. There are optoisolators. It is not clear to me if each of these are not potential noise and distortion sources - the idea of adding another active component in the signal path is unappealing.
Here is an idea for someone who has the time and inclination: how about a pair of LED controlled LDR's? As the control pot wiper moves the voltage and current appled to one of the LEDs moves in the opposite direction from the other. In the simples form this would be very non-linear but perhaps the control voltage could be compensated/manipulated to suffeciently reduce the nonlinearity. I'm assuming that the LDRs are availavle that add no more to the signal than a good quality pot or attenuator.
I've too many thing on my plate to pursue this notion now so it remains in my mental "someday when I got some extra time" file.
I suggest two ways. First get a nice quality dual gang pot like the Alps Blue. The best source for these is Tangent's Audio Part. At 15$ a pot they're dirt cheap and do a really good job. Here's the link: http://tangentsoft.net/audio/shop/
The second is a digitally controlled pot. The principle is simple, it uses comparators (LM339) to evaluate the current resistance of the mecanical pot and adjust digital pots over multiple channels accordingly. See the following article: http://www.elecdesign.com/Articles/Index.cfm?ArticleID=2531#
Hope this might be of some help!
The second is a digitally controlled pot. The principle is simple, it uses comparators (LM339) to evaluate the current resistance of the mecanical pot and adjust digital pots over multiple channels accordingly. See the following article: http://www.elecdesign.com/Articles/Index.cfm?ArticleID=2531#
Hope this might be of some help!
Wow, www.potentiameters.com is lots o fun:
click on " "rotary potentiameters " under the Alps logo in the lower
left corner . Then check out the RK 50 model.
Looks pricey, but made for Audiopiles. Carbon Element, gold wipers, tracks +/- 1 dB I'll try to get a price. Any opinions on these?
Also:
how about a group order of a cermet 2 stage with concentric
shaft? Each stage is attached to one shaft. That way you grab both knobs for initial adjustment, then just one to tweak the balance. I've always felt that this is the way to conveniently deal with this problem. Much better than 2 separate knobs!!
1. First, get a model that is great for gainclones
Kwei etc. prefers linear cermet
2. Some people that need balanced controls might want a total of 4 stages- 2 hooked to each shaft.
3. Also some Pass project people might want a 5k model- quite hard to find and used in some of his preamp designs.
If we need a minimum order, our history of successful group buys
should inspire us to get going!
click on " "rotary potentiameters " under the Alps logo in the lower
left corner . Then check out the RK 50 model.
Looks pricey, but made for Audiopiles. Carbon Element, gold wipers, tracks +/- 1 dB I'll try to get a price. Any opinions on these?
Also:
how about a group order of a cermet 2 stage with concentric
shaft? Each stage is attached to one shaft. That way you grab both knobs for initial adjustment, then just one to tweak the balance. I've always felt that this is the way to conveniently deal with this problem. Much better than 2 separate knobs!!
1. First, get a model that is great for gainclones
Kwei etc. prefers linear cermet
2. Some people that need balanced controls might want a total of 4 stages- 2 hooked to each shaft.
3. Also some Pass project people might want a 5k model- quite hard to find and used in some of his preamp designs.
If we need a minimum order, our history of successful group buys
should inspire us to get going!
For an integrated circuit solution, try this part:
MAS9116
http://www.evoxrifa.com/_private/mas_datasheets/da9116.pdf
Or, for a truly passive switched solution, though it not ready yet:
http://www.diyaudio.com/forums/showthread.php?postid=245155#post245155
MAS9116
http://www.evoxrifa.com/_private/mas_datasheets/da9116.pdf
Or, for a truly passive switched solution, though it not ready yet:
http://www.diyaudio.com/forums/showthread.php?postid=245155#post245155
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