Bypassing Signal Coupling Caps

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simon
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#16

Post by simon »

The LCRs are available in a few different voltage ratings, but it's the 1500V ones that seem.to be recommended. Whether they're any better than other ratings I've no idea.
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#17

Post by Neal »

I would avoid the Maplin metallised Polys, go for the Metal Film versions IE: http://uk.rs-online.com/web/p/polypropy ... s/3847751/
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Mike H
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#18

Post by Mike H »

SteveTheShadow wrote:Cheers chaps,
I'll order some polystyrene caps. Not too expensive, can't break anything and not a big financial hit if they don't deliver the goods.
Be careful with Voltage rating.
 
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#19

Post by Mike H »

SteveTheShadow wrote:Hmm..
Had a go with my pair of 10,000pF Russian, silvered mica caps across the greenies on one channel and it's good that I did.
The difference was clearly audible, even though only the one channel was affected, and it wasn't good.
A layer of God knows what, was added to the affected channel, resulting in a shrill quality to everything from the upper midrange onwards....fooking horrible.
Much like ceramic, and for the same reasons, mica don't actually make very good audio caps, despite how much they may cost. So not surprised they sound harsh, as ceramics will.
 
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Mike H
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#20

Post by Mike H »

simon wrote:
The LCRs are available in a few different voltage ratings, but it's the 1500V ones that seem.to be recommended. Whether they're any better than other ratings I've no idea.
This is more like a step in the right direction IMHO, although personally I thought the ICW ClarityCaps (HFC) have a slight edge over the Maplin LCR's.

YMMV

:D
 
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#21

Post by IslandPink »

Two things ( going back a step ) -
I think the trouble from combining caps is that if they have substantially different DCR's, there are slight phase shifts that occur towards the top of the frequency range that are akin to the sort of things we found on the filament supplies, in the feedback loop experiments .
I was also able to show some small but abrupt changes to the Z-out of the shunt power supply (T-Rex) , in LTSpice, when using an electrolytic combined with a film cap, on the cathode of the KT88 ; this seemed to be linked to the poor performance at the top-end , when tried in real-life.
This is mainly a big problem combining electros with film caps.
Supporting this , I have had more success with combining metallised polyprop with a small film/foil polyprop . Eg. using a GE poly/oil ( 97F-code) with an Audyn KP-SN film/foil , or an Arcotronics KP-1.72 film/foil seemd to work very well to get a biggish power-supply cap - I felt that this was very close in sound and transparency to a Black Gate WKZ .

2. I find all metallised film caps I've tried so far to be lacking in midrange tone compared to film & foil caps . The best of them ( eg. Mundorf silver/gold ) can have a very clean and resolved top-end, but the mids remain uninteresting . I haven't tried dynamicaps, but I've given up buying any more metallised ones myself now after having various ones recommended to me, that turned-out disappointing.
That's why I mainly recommend the Mundorf Zn tin/polyprop nowadays .

I also really like the Copper Jensens , if the signal level and current are high enough , eg. power amps.
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izzy wizzy
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#22

Post by izzy wizzy »

I used to bypass caps all over the place. I now don't bypass any.

I think it's like seasoning. Sure the judicious placement of one or maybe two in some critical position, maybe (I still don't do even this) but too much and it overloads the senses and takes away the flavour of the music.

I like to get one thing to do one thing well. Two things to do one thing rarely works IMHO and IME. There's something nice about one capacitor that adding another takes away almost every thime I try it now. Sure it adds a bit of pizazz and wow but there's always something that goes away. A sense of people being involved; it always makes it more HiFi.

And I dislike metallised film for the same reason. Film and foil all the way. I'd even take a not so good film and foil over a superdoo metallised jobby. There's that zing to almost every metallised film I've tried.

anyhoo, just my 2p.

cheers,

Stephen
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#23

Post by thomas »

Hmmm interesting.....
A few years ago when I first started putting valve amps together I put multiple 'snubbers' in everywhere, from the p/s to coupling stages. After a while I started paring them back and by and large I think things sound better without them now (less 'muddy', better soundstage)... (But one of my phonostages still has a russian green thing and teflon jobbie combined for the output....just sounds... nicer...)
A couple of weeks ago as a birthday pressie (as well as my Jeff Beck tickets!) I bought a capacitance and esr reader and had a happy hour measuring all the caps I could find. I was wondering if I could equate the 'sound' I heard with their esr (I couldn't, really, unless the capacitor was really bad. I binned a suspect 50uf cerafine as its esr was >8r, though...)
As a comparison an LCR 1uf measured 0.31r whilst an asc oil 50uf 0.02r . Vintage dubillier 8uf 0.06r, and russian KBG 8uf 0.14r. Most electrolytics were under 0.5r. Unfortunately my meter won't measure less than a microfarad, and some of the measurements were erratic...
My 2d's worth , there.... :)
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Mike H
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#24

Post by Mike H »

Sudden light bulb going on in the dark cobwebbed recesses of my bwain - if ESR is in some way variable with operating conditions, could you put a low value resistor in series to damp the effect? E.g. variable with frequency (say) so put a 1 Ohm resistor in series (say) equalises the freq response and nullifies the effect.

Just a random thought.
 
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#25

Post by IslandPink »

It's worth a try , though I suspect adding a resistor would make it tough to get the gains in transparency you'd want from using the quality cap . I'd do it with one of those BI-Industries planar resistors if so .
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izzy wizzy
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#26

Post by izzy wizzy »

Mike H wrote:Sudden light bulb going on in the dark cobwebbed recesses of my bwain - if ESR is in some way variable with operating conditions, could you put a low value resistor in series to damp the effect? E.g. variable with frequency (say) so put a 1 Ohm resistor in series (say) equalises the freq response and nullifies the effect.

Just a random thought.
I did just that when I needed a big coupling cap to a TVC to push the resonant freq out of the bass range. I used a 22u BG with 1k series resistor and a 1u film foil in parallel. It was named lossy parafeed http://www.audioasylum.com/forums/bottl ... 72908.html

This whole bypassing thing is passed off a science by some. Bypass to be 10% or some such and then another 10% of that. In reality it's a gamble with no known outcome as caps aren't perfect in the real world. They area bunch of non ideal leakage, inductance, capacitance and resistance. Now bung that lot in parallel with another like that and at best, you might get your desired result by complete fluke or you might get the usual result which is a horrible resonant mess.

cheers,

Stephen
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andrew Ivimey
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#27

Post by andrew Ivimey »

That was very well expressed Stephen. I couldn't agree more!

'''''''In reality it's a gamble with no known outcome as caps aren't perfect in the real world. They area bunch of non ideal leakage, inductance, capacitance and resistance. Now bung that lot in parallel with another like that and at best, you might get your desired result by complete fluke or you might get the usual result which is a horrible resonant mess. ''''''
Philosophers have only interpreted the world - the point, however, is to change it. No it isn't ... maybe we should leave it alone for a while.
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