Upupa, you made me go in and censor you manually. That took work. I hate work. It makes me grumpy.
Peter, the TKD mono pot (stepped attenuator) that we use in the CTC costs $169.00 each. Please look at the latest catalog. We just bought one last week. There is a cheaper TKD, which we are designing into the Parasound JC-2 in order to REPLACE the Alps pot used previously, and it costs about $60.00
Folks, I might say something about pots.
Back in the '60's we usually used Allen-Bradley baked carbon pots. We used them exclusively at Ampex and for virtually every pro audio application. When I met with Mark Levinson in 1973, he was using a very expensive dual pot (for the time) $20.00, because it TRACKED better than any other dual pot, at the time. To improve tracking further, Mark used a linear taper pot (100K) with a 50K load resistor as a load to make it into a sort of log taper. This idea was given to him by Dick Burwen (sp), and it worked very well.
I got my Levinson JC-2 in 1974 and I put it into our professional sound system that we were developing at our lab in Switzerland. At one point, in one listening test, my associate, John Meyer and my other associate Bob Minor, (his father used to be my audio mentor) both told me that something was wrong with the sound of my JC-2 preamp.
WHAT? My preamp is virtually perfect! I exclaimed, but they were insistent about it
So, I said "Don't touch anything!" and I carefully took the preamp to my test bench, WITHOUT changing the controls. Well, guess what I found? DISTORTION! and lots of it. It was in the POT, but only at certain positions on the pot. Full on, or over most of the range of the pot was OK.
Flying back to the States, I tried to tell Mark Levinson about my finding. He was very resistant, so I rubbed his nose in it by taking a pot off his assembly line and measured it with his test equipment in front of him. Mark was converted.
I started to measure all kinds of different pots, and I found that many of the Allen-Bradley pots that I had stocked my lab with, failed! They had significant distortion at certain positions of the pot. I also tried some Bourns pots, that looked almost exactly like the A-B pots and they were OK. What is going on here?
Later, Alps pots became available and they measured great! Yet, over the years, I found that they did not sound right, for my best efforts. Still, they are practical, track OK, and have very low distortion. Personally, I think that it is the substrate that they use that makes the difference, for some reason. I have much more experience about this, but you should understand that something can even measure OK and still not sound exactly right. Go figure!
Back in the '60's we usually used Allen-Bradley baked carbon pots. We used them exclusively at Ampex and for virtually every pro audio application. When I met with Mark Levinson in 1973, he was using a very expensive dual pot (for the time) $20.00, because it TRACKED better than any other dual pot, at the time. To improve tracking further, Mark used a linear taper pot (100K) with a 50K load resistor as a load to make it into a sort of log taper. This idea was given to him by Dick Burwen (sp), and it worked very well.
I got my Levinson JC-2 in 1974 and I put it into our professional sound system that we were developing at our lab in Switzerland. At one point, in one listening test, my associate, John Meyer and my other associate Bob Minor, (his father used to be my audio mentor) both told me that something was wrong with the sound of my JC-2 preamp.
WHAT? My preamp is virtually perfect! I exclaimed, but they were insistent about it
So, I said "Don't touch anything!" and I carefully took the preamp to my test bench, WITHOUT changing the controls. Well, guess what I found? DISTORTION! and lots of it. It was in the POT, but only at certain positions on the pot. Full on, or over most of the range of the pot was OK.
Flying back to the States, I tried to tell Mark Levinson about my finding. He was very resistant, so I rubbed his nose in it by taking a pot off his assembly line and measured it with his test equipment in front of him. Mark was converted.
I started to measure all kinds of different pots, and I found that many of the Allen-Bradley pots that I had stocked my lab with, failed! They had significant distortion at certain positions of the pot. I also tried some Bourns pots, that looked almost exactly like the A-B pots and they were OK. What is going on here?
Later, Alps pots became available and they measured great! Yet, over the years, I found that they did not sound right, for my best efforts. Still, they are practical, track OK, and have very low distortion. Personally, I think that it is the substrate that they use that makes the difference, for some reason. I have much more experience about this, but you should understand that something can even measure OK and still not sound exactly right. Go figure!
john curl said:
Indeed, mono pots are still available, I was refering to stereo, as I find them more practical. Although my setup for an attenuator was even less practical: http://www.diyaudio.com/forums/showthread.php?postid=863703#post863703
Presently I'm using S&B TX102 line stage with very good results.
john curl said:
Very interesting John.
I have never measured pots ans honestly thought that their
distortion would be -way- down, even though they all sound slightly
different. WRT Alps, I agree, I believe a good switched attenuator,
especially separately switching in pairs of R's, with something
like rohpoint non inductive WW R's is definately more transparent
sounding.
Anyone tried bulk foil R's in a switched attenuator?
Cheers,
Terry
Hi Terry,
I have tried (and presently use) Vishay bulk-foils, together with 2 Shallco switches in a dual mono arrangement which is coupled together with some gears. The result, sonically, is unbelievably better compared with any pot I have ever tried, and channel-matching is effectively perfect.
These include all the usual 'suspects' like Sfernice, Noble, Alps and Penny & Giles etc.
In my view, the cost and trouble is well worthwhile, and the only downside is that they are manual, as opposed to being able to be used with a remote.
I have considered motorising this switched attenuator, but even with weaker detent springs which I have also tried, the torque necessary would be beyond the means of any usual motor's abilities, regrettably.
Regards,
I have tried (and presently use) Vishay bulk-foils, together with 2 Shallco switches in a dual mono arrangement which is coupled together with some gears. The result, sonically, is unbelievably better compared with any pot I have ever tried, and channel-matching is effectively perfect.
These include all the usual 'suspects' like Sfernice, Noble, Alps and Penny & Giles etc.
In my view, the cost and trouble is well worthwhile, and the only downside is that they are manual, as opposed to being able to be used with a remote.
I have considered motorising this switched attenuator, but even with weaker detent springs which I have also tried, the torque necessary would be beyond the means of any usual motor's abilities, regrettably.
Regards,
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