In making my preamp i often find volume pots that have stereo balance issues.
One channel is louder than the other until the pot is turned past almost half of its rotation.
Theyre all log curves and ive even had alps blue velvet with this issue. And its not an excessive gain issue. Ive tuned my whole system against that. (Preamp x3, amp x15)
My question is how do you weed out these pots? Ive put my multimeter to them but cant tell whats going on. Maybe build a test jig?
One channel is louder than the other until the pot is turned past almost half of its rotation.
Theyre all log curves and ive even had alps blue velvet with this issue. And its not an excessive gain issue. Ive tuned my whole system against that. (Preamp x3, amp x15)
My question is how do you weed out these pots? Ive put my multimeter to them but cant tell whats going on. Maybe build a test jig?
Use Bourns...or find mil grade in surplus.
And use a trim pot in series if needed.
Some Philips sets here had L/R volume controls, no balance control.
That works, too...
And use a trim pot in series if needed.
Some Philips sets here had L/R volume controls, no balance control.
That works, too...
I have actually made pots; Audio/log is not really that, not impossible but very cumbersome and low yield, so commercial compromise is to make them out of two linear half tracks in series, on the same Pertinax strip:
0-5 is low value, typically 10% of full scale, and 5-10 is remaining 90%.
To match them, get a bunch, and for each one first set knob to 5 , or 50% rotation, measure wiper to ground and wiper to Hot leg.
Choose those where 0-5 resistance is the same ratio relative to 0-10 value.
Absolute value is not that important but ratio, since this is a voltage attenuator.
Examples:
Pot 1: 10k and 100 k respectively.
Pot 2: 11k and 110k: still fine.
Pot 3: 10k and 110k: unsuitable, even if it shows same 10k as the first one, the ratio is wrong.
IF you had direct access to a Factory, like I had in the old days (70s to early 90s) you could measure the raw tracks, and then assemble matched ones, but since that is impossible after Globalization, second best is measure and choose from a LARGE bag, obviously quite random and inefficient.
Oh well.
I just buy a bunch of cheap pots and sort through them for a good one. Received 5pcs 20k log pots from Ali the other day. One is damn near perfect and the other four are unusable. It was $6 shipped for all of them, so still a decent deal.
Thanks for the tip, gentlemen.
So its basically a $6 chinese pot+ all the work gone into testing them 😅
Milspec seems like the best option atm.
So its basically a $6 chinese pot+ all the work gone into testing them 😅
Milspec seems like the best option atm.
IF it´s real, yes 😉
I don´t want to complicate your life, but many pots can be opened (just twist open 4 retaining tabs) and resistive wafers exchanged, then you match them.
Still needs buying extra, but maybe you can improve yield from , say, 1 to 2 good ones out of 20/25 which is completely random, because factory assembler guy just gets a bucket with 1000 wafers and must assemble 500 pots, he picks them at random, to maybe 5 to 10 good ones out of 25.
Found an excellent tutorial showing what I do:
As you see, it depends on pot brand.
Against what´s expected, here an average pot (CTS) is better to work with than a premium one (Bourns)
Experiment with junkbox/damaged pots to get the knack of it.
I do it all the time because most Musical Instrument amps have non generic but matching shafts and knobs, so I match a new wafr to an old shaft. Say, D shaped.
I don´t want to complicate your life, but many pots can be opened (just twist open 4 retaining tabs) and resistive wafers exchanged, then you match them.
Still needs buying extra, but maybe you can improve yield from , say, 1 to 2 good ones out of 20/25 which is completely random, because factory assembler guy just gets a bucket with 1000 wafers and must assemble 500 pots, he picks them at random, to maybe 5 to 10 good ones out of 25.
Found an excellent tutorial showing what I do:
As you see, it depends on pot brand.
Against what´s expected, here an average pot (CTS) is better to work with than a premium one (Bourns)
Experiment with junkbox/damaged pots to get the knack of it.
I do it all the time because most Musical Instrument amps have non generic but matching shafts and knobs, so I match a new wafr to an old shaft. Say, D shaped.
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Buy ? the Cheap (ish) Chinese Dact Stepped attenuators. (Ebay)
These use SMD resistors rather than badly made resistive tracks..
SMD resistors are FAR harder to Eff up ..even in Chinese manufacture.
These use SMD resistors rather than badly made resistive tracks..
SMD resistors are FAR harder to Eff up ..even in Chinese manufacture.
Two suggestions:
Bournes < Alpha. Cheap Tayda pots have better symmetry. https://www.taydaelectronics.com/potentiometer-variable-resistors.html
RK27 much nicer taper and better tracking. almost 30$ from Mouser, under 10$ from GD-parts or LCSC.. https://www.goodcomponent.com/produ...0ka2x20ka2x50k2x100ka2x250ka2x500ka-1189.html
A third more expensive option is a 1024 step attenuator... Seriously good for the price, too. Arrived in less than 2 weeks. https://www.aliexpress.com/item/4000480828404.html
Bournes < Alpha. Cheap Tayda pots have better symmetry. https://www.taydaelectronics.com/potentiometer-variable-resistors.html
RK27 much nicer taper and better tracking. almost 30$ from Mouser, under 10$ from GD-parts or LCSC.. https://www.goodcomponent.com/produ...0ka2x20ka2x50k2x100ka2x250ka2x500ka-1189.html
A third more expensive option is a 1024 step attenuator... Seriously good for the price, too. Arrived in less than 2 weeks. https://www.aliexpress.com/item/4000480828404.html
Hi, I have recently used the Muses pot supplied by Academy Audio. It used the same chip as Pass does on their $6000 preamp.
It's a bit complicated to install & instructions are not the best. But the supplier does answer emails quite promtly & the sound of the pot may be just about the best available at the present time.
https://www.academyaudio.com/product-page/mcu-m-mini-controller-for-muses
Cheers
It's a bit complicated to install & instructions are not the best. But the supplier does answer emails quite promtly & the sound of the pot may be just about the best available at the present time.
https://www.academyaudio.com/product-page/mcu-m-mini-controller-for-muses
Cheers
Like I said, use single pots for each channel, not stereo, if you worry about variation.
And the best quality would be wire wound industrial or military quality, or multi turn...though knobs for those may have limited variety available.
And the best quality would be wire wound industrial or military quality, or multi turn...though knobs for those may have limited variety available.
Go here: ...
https://www.ebay.ca/itm/13356961901...BiTjhUj4tXozzluVKwrRIy+DoQ==|tkp:BFBM7MWLgJtg
Have a few of these and in process of buying more.
Cheap.. easy.. V good. One can do far worse.. I certainly have in the past
https://www.ebay.ca/itm/13356961901...BiTjhUj4tXozzluVKwrRIy+DoQ==|tkp:BFBM7MWLgJtg
Have a few of these and in process of buying more.
Cheap.. easy.. V good. One can do far worse.. I certainly have in the past