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Old 8th April 2012, 03:57 PM   #3551
robbbby is offline robbbby  Canada
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Quote:
Originally Posted by cab View Post
Cobble to your heart's content. I am sure you will be able to band aid and duct tape something excellent together after spending a few weeks monkeying around with it...
Thanks for reminding me, I almost forgot to order a roll of duct tape.
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Old 8th April 2012, 04:38 PM   #3552
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Quote:
Originally Posted by Julf View Post
Not sure a pair of normal, decent poly caps ($1.50) would compromise the performance.
I was of course exercising my frustration re. the DAC maker, but having built lots of preamps with various coupling caps, I've found real differences. This is in series with the whole signal, so all that ultra-low distortion and noise will rest on the quality of that cap. There is the endless debate of the audibility of various series caps, and there are many examples of builders who will spend a lot on them. My now-defunct company spent hundreds on series caps *per preamp*, though that was for two 200V 4uF array (1/ch) of C0G monolithic ceramics. Hmmm, I bet you can guess why we went under! Anyway, many UcD amps live with input caps bypassed with wire...

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Originally Posted by Julf View Post
Why? Why not just connect + and - inputs together? And definitely don't connect anything to ground. Then just measure the DC on the output.
Yes, that's what I would do too ("You could probably tie them all together, but a little resistance never hurts"), but for other people's gear I think of any possible failure mode. If one input, say noninverting, happens to have blown since the last test and goes open and gathers a static charge, the resistor would protect the inverting input from it when the input is connected. That's almost an impossible situation, but when dishing advice late at night I try to be silly over-cautious.

Re. the ground, again I was thinking of a path for static discharge; there should be a safe resistance for that connection, maybe it should be much higher? Thanks.

Last edited by Sam Lord; 8th April 2012 at 04:44 PM.
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Old 8th April 2012, 06:31 PM   #3553
Julf is online now Julf  Europe
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Quote:
Originally Posted by Sam Lord View Post
I was of course exercising my frustration re. the DAC maker
I totally understand the frustration. Basically the DAC designed passes the buck to the next step in the chain.

Quote:
having built lots of preamps with various coupling caps, I've found real differences
I will not doubt your experiences, but personally I have not found any audible differences between film caps unless using really ancient oil-and-paper caps (and electrolytics are of course a different story). And there is a fair bit of pretty good research out there that shows most "audiophile" cap snobbery to be pure voodoo. Here is a pretty good look at the issues: Elliott Sound Products: Capacitor Characteristics

Quote:
My now-defunct company spent hundreds on series caps *per preamp*, though that was for two 200V 4uF array (1/ch) of C0G monolithic ceramics. Hmmm, I bet you can guess why we went under!
Ouch, yes...

Quote:
That's almost an impossible situation, but when dishing advice late at night I try to be silly over-cautious..
You definitely have a point.

Quote:
Re. the ground, again I was thinking of a path for static discharge; there should be a safe resistance for that connection, maybe it should be much higher? Thanks.
For static, even hundreds of K should do it, without affecting the circuit operation and creating ground loops.
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Old 8th April 2012, 06:33 PM   #3554
Julf is online now Julf  Europe
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Originally Posted by Erlend Sæterdal View Post
I would take the board out and look both underneath and on the upside!
Unfortunately that would require removing several components from their heat sink connection - probably not a good idea!
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Old 8th April 2012, 06:34 PM   #3555
Julf is online now Julf  Europe
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Quote:
Originally Posted by cab View Post
Cobble to your heart's content. I am sure you will be able to band aid and duct tape something excellent together after spending a few weeks monkeying around with it...
I think we all appreciate these helpful and informative comments...
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Old 8th April 2012, 06:55 PM   #3556
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Quote:
Originally Posted by Julf View Post
Unfortunately that would require removing several components from their heat sink connection - probably not a good idea!
Well chicken you are ! I did that with my Coldamps and changed a lot of components.

I am playing on the NC. Well it is fantastic good I must admit.
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Old 8th April 2012, 07:08 PM   #3557
Julf is online now Julf  Europe
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Originally Posted by Erlend Sæterdal View Post
Well chicken you are ! I did that with my Coldamps and changed a lot of components.
Good for you - I think I have done enough hypex-breaking for today. Won't try separating the circuit board from the aluminium base plate until I am sure there is no other way...
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Old 8th April 2012, 07:59 PM   #3558
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Originally Posted by Julf View Post
Good for you - I think I have done enough hypex-breaking for today. Won't try separating the circuit board from the aluminium base plate until I am sure there is no other way...

Ok hope you solves it .
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Old 9th April 2012, 12:09 AM   #3559
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Originally Posted by Julf View Post
...there is a fair bit of pretty good research out there that shows most "audiophile" cap snobbery to be pure voodoo. Elliott Sound Products: Capacitor Characteristics
Ach, tell me about it : ) . I read about the various electrical attributes long ago when it mattered in the business. We kept pretty agnostic, though we came to the very strong conclusion that arrays of middle-quality X7R ceramics, pricey but no insanely so, really sounded fantastic as coupling caps. They weren't equal to our C0G=NP0 arrays, but were 10x cheaper. Their mildly piezoelectric nature added no measurable noise or distortion in that role, and just sounded better (dynamic, transparent, tonally true, etc.) than polypropylene film caps. I never heard a comparison between those arrays compared with polystyrene or teflon caps, but trusted the judgment of my my-experienced partner who felt the arrays beat all but teflon, and had vastly less inductance than any F/F caps of equal value. One source I trust implicitly is Grant Carpenter of Gordon Audio,
Gordon Microphone Preamplifier System
which makes perhaps the best micpres on earth. He uses only big polystyrene caps (REL RTX) in the signal path. I urged him to offer a costlier teflon version, which he did, but then had to withdraw it because of a sudden scarcity of good teflon film. He said he could hear the difference between the tin foil/polystyrene caps and the PTFE caps only during full moons, etc... meaning that he *felt* he could hear it only sometimes. But his insistence on the next-best film caps was based on his listening. He also said that some metallized polypropylene caps sounded better to him than many polyprop F/F caps. Anyway if you record you should consider his gear. The man can design: his single-chassis, single x-former micpre has unmeasurable crosstalk, i.e. <-140dB at 200kHz, the limit of Audio Precision gear... Sorry to bore with all this but I thought you and others might like this quirky perspective.

Quote:
Originally Posted by Julf View Post
For static, even hundreds of K should do it, without affecting the circuit operation and creating ground loops.
Yes, but I felt there was some other advantage to keeping that resistance moderate, i.e. well under the input Z. It had to do with the input tracking the ground voltage fairly closely, but some failure modes would make this worse, some better...but in fact was just thinking aloud and getting nowhere. Thanks Julf for your comments and patience, I have real honesty issues without solid builders like you around. : )

Kudos too to Robbbby and Erlend for persisting in chasing down their unruly charges (heh, charges )

I hope to break a Hypex amp sometime, it has to be a thrill! 8P
Cheers

Last edited by Sam Lord; 9th April 2012 at 12:29 AM.
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Old 9th April 2012, 03:57 AM   #3560
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Quote:
Originally Posted by Julf View Post
Good for you - I think I have done enough hypex-breaking for today. Won't try separating the circuit board from the aluminium base plate until I am sure there is no other way...
its not a problem. just take out the screws and lift off. Just the heat sink compound is all that's holding it at that point.

Alan
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