John Curl's Blowtorch preamplifier part II - Page 3259 - diyAudio
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Old 13th January 2013, 01:00 AM   #32581
fas42 is online now fas42  Australia
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Originally Posted by Esperado View Post
About pots, what did-you think about PGA23XX ? With no contact noise, no wear, and a HD+n of ~0.0002%, i think we can consider those as "quality" parts despite the low price ?
A tick from me, I haven't used them seriously in a project yet, but assembled a test setup with the "poorer" performing version, and was completely happy with the results. My main concern was that I didn't have a high speed clock around spitting out RF garbage, so I did this using completely discrete logic, and up, down push buttons to change levels. So that once the level changed there was no digital pollution in the picture ...

Frank
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Old 13th January 2013, 01:16 AM   #32582
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Originally Posted by simon7000 View Post

As this took me 4 hours I am not inclined to do much more.

ES
ED,

Nice work its amazing to see such low readings being made.

Still I dont understand how the effect can produce a second?

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Old 13th January 2013, 02:08 AM   #32583
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First, I still prefer an Alps pot to ANY electronic volume control. I hope to stand corrected on this, one day.

Second, I can't teach a course in connector/relay design. IF you want to understand the differences in switches, then study up, yourself. Everybody and his brother knows that I PREFER Shallco silver switches, then sealed relays with gold on gold contacts.
However, cheap switches made of tin or zinc alloys, etc, may actually not sound too good after a while due to internal tarnishing, etc. But they may be perfectly good for an off-on switch or a relay control.
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Old 13th January 2013, 02:26 AM   #32584
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First part of a good article on contacts:
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File Type: jpg contact2.jpg (753.5 KB, 204 views)
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Old 13th January 2013, 02:36 AM   #32585
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Originally Posted by fas42 View Post
A tick from me, I haven't used them seriously in a project yet, but assembled a test setup with the "poorer" performing version, and was completely happy with the results. My main concern was that I didn't have a high speed clock around spitting out RF garbage, so I did this using completely discrete logic, and up, down push buttons to change levels. So that once the level changed there was no digital pollution in the picture ...

Frank
my concern about them is no matter what care you may have gone to beforehand, the output is channeled through the internal opamp with a fair serve of feedback. i'm not anti-opamps (or anti feedback), I dont always use them but have had excellent results with well executed designs.

the thing is, if your pot has them inside, why bother with any analogue stage, you have just put everything through the lens of the opamps in the volume control. may as well just put one directly after a voltage output dac and be done with it.

seems a bit boring to me, at that point I may as well buy commercial.
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Old 13th January 2013, 05:21 AM   #32586
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the thing is, if your pot has them inside, why bother with any analogue stage, you have just put everything through the lens of the opamps in the volume control. may as well just put one directly after a voltage output dac and be done with it.

seems a bit boring to me, at that point I may as well buy commercial.
My goal is optimum quality, the path to getting that is all that matters, boring or otherwise. It may be a single chip, but everything that's relevant to getting discrete circuitry to behave itself is also important here: power supplies, grounding, protection from interference. Get that wrong, and you might as well not have bothered trying the exercise ...

There are never, ever, ever magic solutions to getting sound to jump cleanly through the hoop; only by being obsessive about each and every detail does it all come together ...

Frank

Last edited by fas42; 13th January 2013 at 05:23 AM.
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Old 13th January 2013, 08:20 AM   #32587
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For the record.
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File Type: png scott_noise.PNG (62.5 KB, 174 views)
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Last edited by PMA; 13th January 2013 at 08:25 AM.
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Old 13th January 2013, 08:36 AM   #32588
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Quote:
Originally Posted by qusp View Post
seems a bit boring to me, at that point I may as well buy commercial.

Quote:
Originally Posted by john curl View Post
First, I still prefer an Alps pot to ANY electronic volume control.
I suppose at this level of noise/distortion that no difference can be shown on measurements between the two. So it is a subjective preference ?
However, can-you define the differences you feel (hear) and if you made blind tests between the two with consistent results (I know Alps is hype and you are kind a fashion victim/executioner) ?

On my side, with the simplicity they provide, the low cost, the precision of levels between channels, the reliability and the ease of remote, i think that it is currently the best solution on the shelf .
I use 3 of them for my active system: One for bass (left channel) treble(right hannel) of each stereo active enclosures, one for the sub. This allow the remote to be in the preamp, and the signal to be send full level to each enclosures, reducing signal/noises induced in the links between preamps and amps.
All in one, the result is better that any other solution i had tried.

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Last edited by Esperado; 13th January 2013 at 09:06 AM.
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Old 13th January 2013, 11:30 AM   #32589
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Quote:
Originally Posted by john curl View Post
First, I still prefer an Alps pot to ANY electronic volume control. I hope to stand corrected on this, one day..
I moved from Alps to TVC, from TVC to LDRs, and later from LDRs to 32 bit Digital. ( I use mostly digital sources )

For me, every analogue type I tried had a signature but LDRs - with very carefully made PSU arrangement - was the cleanest sounding I had heard.

The 32 bit digital control does not seem to have a signature - at least not one that I can hear - so I've stopped thinking about volume controls.

Last edited by mikelm; 13th January 2013 at 11:38 AM.
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Old 13th January 2013, 11:45 AM   #32590
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Default Maybe a picture helps

Does anyone not see that the input resistance at DC is 10 Ohms times A? (tiny errors due to op-amp bias current can be ignored). I call this bootstrapping, sorry if folks use another term for this.
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