Optimal solutions eh? So adding a few capacitors to filter out DC isn't optimal? I'll just go spend a ton of many so that the new piece of gear I buy will already have the caps pre-installed for me, sounds like a genius idea.
Somebody trying to fix their audio equipment on diyaudio.com... this is insanity!!
Appreciated - and it is a good way to learn. The problem is that there is so much bad advice around. A lot of "audiophile" sites are full of people with no real understanding of technology and electronics, who rely on superstition and folklore - and *know* that they are right.
If you want to go for 3 Hz, use a 0.5 uF capacitor. The cutoff point is the -3 dB point, so it's effects on anything above 20 Hz will be pretty much unmeasureable. If you want to play it really safe, even a 1 uF cap is still not physically that large (or expensive).
So, just to verify - neither of the balanced input connections are in any way connected to ground? They just go to pins 2 and 3 on the XLR connector? And they use the hypex-provided mogami shielded twisted pair cable?
Are you using a power inlet with an integrated filter circuit, or just a plain power connector?
Just a plain power connnector. I have not connected the ground of the cabinet to mains ground.
Yes I use the mogami and pin 1 is for 2 and pin 2 to 3 on the XLR. I have done balanced connections for man years.
My apologies for asking obvious questions - just want to make sure I understand your wiring correctly.
Duh - broke a nc400 
So, my turn to screw up. As my source has a very hot output, I wanted to reduce the gain of my nc400's by removing R141 on all of them.
As we know, it is a tiny surface-mount resistor, but despite the fact that neither my eyesight nor my finger dexterity is what it was 30 years ago, I usually manage OK with surface mounted stuff. Well, in this case I did OK with 7 out of 8 amps.
With the last one something went wrong. Looks OK visually (well, it's hard to say what is going on on the underside of the circuit board), but instead of sound I now get a very loud 1 Hz metronome. A big fat kick out of the speaker approximately once a second.
Protection circuit kicking in?
Ideas and suggestions welcome...
So, my turn to screw up. As my source has a very hot output, I wanted to reduce the gain of my nc400's by removing R141 on all of them.
As we know, it is a tiny surface-mount resistor, but despite the fact that neither my eyesight nor my finger dexterity is what it was 30 years ago, I usually manage OK with surface mounted stuff. Well, in this case I did OK with 7 out of 8 amps.
With the last one something went wrong. Looks OK visually (well, it's hard to say what is going on on the underside of the circuit board), but instead of sound I now get a very loud 1 Hz metronome. A big fat kick out of the speaker approximately once a second.
Protection circuit kicking in?
Ideas and suggestions welcome...
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 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...
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.
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I totally understand the frustration. Basically the DAC designed passes the buck to the next step in the chain.
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
Ouch, yes...
You definitely have a point.
For static, even hundreds of K should do it, without affecting the circuit operation and creating ground loops.
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.
Well chicken you are !
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...
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.
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
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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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