Everyone raves about the Alps Blue Velvet, which you can pretty much only buy from one source in any given location for around $16. But, I've also heard some bad things about it's tracking and such. Other people rave about these $20-60 pots... but who wants to pay that kind of money?
I am wanting to build a passive preamp with a good pot in it. I've considered stepped attenuators, and really just don't want to build one. Plus, they're pricey as well. I've been looking for Bourns 82 series cermet pots, which seem to be fairly good on paper, but haven't been having any luck.
Does anyone here know of a good stereo pot (or pair of mono pots) that would have good channel matching, excellent tracking, extremely low noise, great sound, and high reliability without breaking the bank? Let's try to keep this under $20. I am really hoping for something that can de-throne the Alps Blue (RK27).
Thanks all
I am wanting to build a passive preamp with a good pot in it. I've considered stepped attenuators, and really just don't want to build one. Plus, they're pricey as well. I've been looking for Bourns 82 series cermet pots, which seem to be fairly good on paper, but haven't been having any luck.
Does anyone here know of a good stereo pot (or pair of mono pots) that would have good channel matching, excellent tracking, extremely low noise, great sound, and high reliability without breaking the bank? Let's try to keep this under $20. I am really hoping for something that can de-throne the Alps Blue (RK27).
Thanks all
Hi,
cermet pots are very difficult to build accurately enough to give good stereo tracking. But the sound is good.
Plastic track pots are quite good sounding but in log law the tracking is again a bit loose. Laser trimming helps here and these are often the source of the "better audio pots".
For good sound and impecable tracking then a stepped attenuator is the only way to go . They are bulky and expensive. The dual stepping version with only one pair of resistors on line at any time are reputed to be the best but are twice as expensive.
Linear law pots are, by far, the more accurate of stereo trackers.
You can convert these to a form of log law with a faking resistor.
Choose a lin about 10times bigger than you want and add a faking resistor about 10% to 15% of the pot value from wiper to ground. Down side is a variable input impedance with wiper position but a low source impedance should not be troubled with this.
Try a lin plastic with faking and tell us what you think.
Some decades ago a British audio journalist did an article on passive attenuator with a cap across some part of it to control (improve) the high frequency pass ability and reported really good and consistent results. Try a search on passives and see if you can find some data.
cermet pots are very difficult to build accurately enough to give good stereo tracking. But the sound is good.
Plastic track pots are quite good sounding but in log law the tracking is again a bit loose. Laser trimming helps here and these are often the source of the "better audio pots".
For good sound and impecable tracking then a stepped attenuator is the only way to go . They are bulky and expensive. The dual stepping version with only one pair of resistors on line at any time are reputed to be the best but are twice as expensive.
Linear law pots are, by far, the more accurate of stereo trackers.
You can convert these to a form of log law with a faking resistor.
Choose a lin about 10times bigger than you want and add a faking resistor about 10% to 15% of the pot value from wiper to ground. Down side is a variable input impedance with wiper position but a low source impedance should not be troubled with this.
Try a lin plastic with faking and tell us what you think.
Some decades ago a British audio journalist did an article on passive attenuator with a cap across some part of it to control (improve) the high frequency pass ability and reported really good and consistent results. Try a search on passives and see if you can find some data.
I was looking at offerings by Bourns- cermet and conductive plastic. Seems no one stocks the useful higher values. They also don't have any dual section ones. Mouser and Digikey can order them in large quantities, but it is a little pricey.
I am hoping to find a good linear pot that I could use the log faking with. I want something, though, that has the absolute best matching between channels. Since many dual section pots have poor channel matching, I thought that a pair of closely matched single pots would do better. I could use a few gears to use one know to control both pots.
I guess by the time I spend all the time and money to find a good pot and implement it effectively, I could have just bought a few stepped attenuators...
I am hoping to find a good linear pot that I could use the log faking with. I want something, though, that has the absolute best matching between channels. Since many dual section pots have poor channel matching, I thought that a pair of closely matched single pots would do better. I could use a few gears to use one know to control both pots.
I guess by the time I spend all the time and money to find a good pot and implement it effectively, I could have just bought a few stepped attenuators...
Another option is 10-turn precision pots, such as Bourns 3540/3541
series and similar from Spectrol, etc. If you do a bit of work with
Excel, you'll find that the bottom couple turns of the total available
rotation provide a reasonable "law" for an audio attenuator. The
remaining 8 turns of rotation only provide a bit more gain, but
in most applications you never work with the volume control
near the top portion of its rotation anyway. I've looked at
log-faking using 10-turns and think it'll do more harm than good.
These pots are available in ganged versions, though I am
vitrually certain they're custom with large minimums.
Richard Marsh used the Spectrol equivalents years ago and just
had two separate single units. I would suppose he'd have used the
little counter/index gizmos to set them the same.
series and similar from Spectrol, etc. If you do a bit of work with
Excel, you'll find that the bottom couple turns of the total available
rotation provide a reasonable "law" for an audio attenuator. The
remaining 8 turns of rotation only provide a bit more gain, but
in most applications you never work with the volume control
near the top portion of its rotation anyway. I've looked at
log-faking using 10-turns and think it'll do more harm than good.
These pots are available in ganged versions, though I am
vitrually certain they're custom with large minimums.
Richard Marsh used the Spectrol equivalents years ago and just
had two separate single units. I would suppose he'd have used the
little counter/index gizmos to set them the same.
http://www.hificollective.co.uk/components/potentiometers.html
They have different pots for sale, among other things...
They have different pots for sale, among other things...
I have had very good results with the Bourns 53-series pots. I have a bjillion 300K linear mono ones that I use everywhere. PM your address to me and I'll mail a couple to you. The datasheet can be found here. The part number is 53AAAB28B40. The '40' at the end of the part number is the code for 300K -- a nonstandard value.
Cheers,
-Casey Walsh
Cheers,
-Casey Walsh
Hi,
these threads are quite interesting and informative:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=73538&perpage=10&pagenumber=1
& 1st link
Have you tried Farnell as a source for Bourns?
these threads are quite interesting and informative:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=73538&perpage=10&pagenumber=1
& 1st link
Have you tried Farnell as a source for Bourns?
You might want to check this out. Doesnt come with mounting hardware, but you can get that real cheap. I ordered 10 packs, and look what I got, one in each.
Pretty good deal I would say. Only problem with that site is it might end up costing you more than $20 to get that pot, because they have so many neat things there that I end up spending far more than I intended to.
Pretty good deal I would say. Only problem with that site is it might end up costing you more than $20 to get that pot, because they have so many neat things there that I end up spending far more than I intended to.
cetoole said:You might want to check this out. Doesnt come with mounting hardware, but you can get that real cheap. I ordered 10 packs, and look what I got, one in each.
Pretty good deal I would say. Only problem with that site is it might end up costing you more than $20 to get that pot, because they have so many neat things there that I end up spending far more than I intended to.
Have you tried the pots yet?
jaudio said:
Not yet, all I have done so far with them is measure the resistance between each channel, which is decent. Near as good as 2 of my black beauties, the two channels are pretty close, 2 that the channels are 80 ohms apart, which is under 1% matching, and the worst is still 3% matching. I tested one of the ones that matches to 1%, and every position I tried (probably a dozen or so), the two channels remained within 1% of each other. These are all 10k pots. Not quite as good as the Black Beauty I have that matches to 0.12%, 60 ohms difference, 50k pot. Pretty good deal for those too at $10 each shipped from JBL, but I think they are out now.
Hi,
-60db is when the output is 1/1000 of the input i.e. 2Vac input and 2mVac output.
Use your DMM set to resistance to set the level eg. track resistance = 10.35k and lower leg set to 10.3ohms. It does not matter if the setting is slightly off, -59db or -61db will do.
-50db is 1/300 and -70db is 1/3000.
Again super accuracy in the mechanical setting is not important. What you are trying to find is the db error between channels at each setting.
Remember to use the actual track resistance for each channel when doing the comparison. Db attenuation = 20 times (lower leg resistance/track resistance) from the example above 10.3/10k35 =.0009951 and log = -3.002 and 20 log = -60.04db.
Low level listening is nearly always down at these levels and medium level listening is often at the -40 to -50db level. I and many others find these are attenuator settings that often get listened to. Serious imbalance is more than annoying particularly if balance controls were thrown out with the tone controls. I have recently bought a new preamp that has given me back a balance for the first time in more than a decade but it's range of adjustment is +-4db.
This defence is pre-empting those that will come back to say -60db is unrealistic.
Do your measurements and then decide if the pots are accurate enough to work effectively at your listening levels. If you NEVER listen at these low levels you can pad up the attenuator by adding a fixed resistor below the pot between track and ground and return the wiper to ground below the fixed resistor. Adding 10r will reduce the MAX attenuation to -60db. For real accuracy each channel will have a slightly different padding resistor to ensure the ratio pad to track is identical.
Now all your adjustments will be above this level. If you now retest your modified pot you will now find that the tracking is improved at the low level setting due to adding the extra resistor and restricting the attenuator range.
-60db is when the output is 1/1000 of the input i.e. 2Vac input and 2mVac output.
Use your DMM set to resistance to set the level eg. track resistance = 10.35k and lower leg set to 10.3ohms. It does not matter if the setting is slightly off, -59db or -61db will do.
-50db is 1/300 and -70db is 1/3000.
Again super accuracy in the mechanical setting is not important. What you are trying to find is the db error between channels at each setting.
Remember to use the actual track resistance for each channel when doing the comparison. Db attenuation = 20 times (lower leg resistance/track resistance) from the example above 10.3/10k35 =.0009951 and log = -3.002 and 20 log = -60.04db.
Low level listening is nearly always down at these levels and medium level listening is often at the -40 to -50db level. I and many others find these are attenuator settings that often get listened to. Serious imbalance is more than annoying particularly if balance controls were thrown out with the tone controls. I have recently bought a new preamp that has given me back a balance for the first time in more than a decade but it's range of adjustment is +-4db.
This defence is pre-empting those that will come back to say -60db is unrealistic.
Do your measurements and then decide if the pots are accurate enough to work effectively at your listening levels. If you NEVER listen at these low levels you can pad up the attenuator by adding a fixed resistor below the pot between track and ground and return the wiper to ground below the fixed resistor. Adding 10r will reduce the MAX attenuation to -60db. For real accuracy each channel will have a slightly different padding resistor to ensure the ratio pad to track is identical.
Now all your adjustments will be above this level. If you now retest your modified pot you will now find that the tracking is improved at the low level setting due to adding the extra resistor and restricting the attenuator range.
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