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-   -   Are huge DC blocking caps on Zen ok? (http://www.diyaudio.com/forums/pass-labs/22055-huge-dc-blocking-caps-zen-ok.html)

Arx 28th October 2003 02:51 AM

Are huge DC blocking caps on Zen ok?
 
Has anyone experimented with the size of capacitors for DC blocking on a Zen V2?

It calls for 10000uF. The most apropriate caps I have available are 4 - 3300uF 40V (2 per channel for 6600uF) or some 68000uF 50v ones.

Is 6600 enough? Is 68000 too much? is there an upper limit on what will work well?

I thought it was kind of cool having my turn on thump down to .5 hz or so ;) but will it hurt anything?

Panelhead 28th October 2003 03:14 AM

Re: Are huge DC blocking caps on Zen ok?
 
Quote:

Originally posted by Arx
Has anyone experimented with the size of capacitors for DC blocking on a Zen V2?

It calls for 10000uF. The most apropriate caps I have available are 4 - 3300uF 40V (2 per channel for 6600uF) or some 68000uF 50v ones.

Is 6600 enough? Is 68000 too much? is there an upper limit on what will work well?

I thought it was kind of cool having my turn on thump down to .5 hz or so ;) but will it hurt anything?

IMHO the minimum value for the caps will be decided by the impedance of your speakers. If you are running 4 ohm speakers the 6600 ufd may not be large enough.
I was using a 4700 ufd Nichicon Muse with a 680 ufd BG NX with my 16 ohm speakers. Worked fine.
Recently switched to a 10,000 ufd Jensen 4 pole cap. The bass did not improve any. But the mids and highs seemed better.
I would be suspect of the quality of the 68,000 ufd cap. Being in a feedback loop the cap is more transparent than you would expect. But a big nasty electrolytic will hurt the sonics.
Do not worry about the 40 volt rating. When first turned on the voltage on the cap comes to around 40 volts for a short time. But quickly drops to the value selected. If you are running 23 - 24 volts on the output the amp will have to swing a bunch to overvoltage the caps.
To go from 24 volts to over 40 would require swinging 32 volts peak to peak. With 5 - 8 ohm speakers the current source should limit the output before overvoltaging the cap.
But the amp is recommended to be built with 50 volt caps here. Mine worked fine with 35 volt rated caps on the output but I did replace them with 63 volt.

George

GRollins 29th October 2003 12:20 AM

If you're worried about the sound of electrolytics, bypass them with film caps, the more, the merrier.
Purely as an abstract figure, 68000uF isn't too much. You'll just get deeper and deeper response, although the Zen will never be what most people would call the ultimate subwoofer amp.
George is correct, the minimum value for the cap will be determined by the impedance of the speaker and how low you want it to go. On the other hand, you could use it as part of the crossover network, in which case you might have to actually decrease the value.

Grey

fdegrove 29th October 2003 12:44 AM

Hi,

I'm no big fan of decoupling electrolytic caps with filmcaps but if you must resort to that, decouple at the consumer end.

As close as physically possible that is.

Cheers,;)

Nelson Pass 29th October 2003 12:53 AM

The typical Zen has two blocking capacitors, one at the input
and one at the output. If the feedback loop output point is
taken outside the output capacitor, and the feedback input point
is taken outside the input capacitor, then its effect is divided
by the feedback, not that there is a lot of that available. In
this case, however, the ratio of the two caps comes into play,
as certain ratios will allow some low frequency (subsonic)
resonance. This is not a big deal, but when you alter the
values of the caps, you might test for some under-damped
subsonics, which you can see by watching the output slowly
vary when a DC event occurs.

This of course is easily simulated, and is one of the cases where
I would tend to trust the simulator. We are simply looking at a
2 pole high-pass with inverting gain where both caps have
significant effect when the circuit passes through unity gain.
Staggering their values sufficiently fixes it, if it's a problem.

Arx 30th October 2003 08:43 PM

Seemed to work last time.
 
Well, that gives me a little more info at the higher end of things. What about the 6600uF (Would fit better into the chassis i'm thinking of using)

As far as sound goes, I used the 68000's in the first test along with the 20% tolerance, etc. and in that case I couldn't hear any change with a variety of film bypass caps.
Maybe quality of the rest of the circuit, or the nasty *** input signal from the sound card i'm feeding it from is just clouding the difference though.
Personally I'm a bit of a sceptic when it comes to magical "Audio Grade" stuff. I got some panasonic polyprop caps though, so i'll probably throw them in just for good measure, and I picked up some 2% resistors that weren't manufactured 50 years ago, and salvaged from broken television sets.
I'm just afraid i'm going to lose that "smooth midrange, and sweet but slightly subdued treble that only raw carbon resistors can give" ;)

Grey: I've got a big bag of .68uF Mylar caps. Maybe I should just stack them all up and see what happens ;)

Btw: What is the consumer end of an electrolytic cap? It shouldn't really matter where i put the bypass, should it?

fdegrove 30th October 2003 10:30 PM

Hi,

Quote:

Btw: What is the consumer end of an electrolytic cap? It shouldn't really matter where i put the bypass, should it?
Sorry, my bad. I should have read the thread title...

I was under the impression you wanted to add PS bypass caps.
From that I'd advise to decouple locally, i.e. at the spot were the current is requested.
E.g. the transistor, Fet, whatever it's feeding.

For a DC blocking cap I'd still recommend to put the bypass as close to the electrolytic as ossible to avoid stray inductance.

Cheers,;)

Arx 31st October 2003 12:27 AM

Gotcha.. That makes more sense. I was actually planning on doing exactly that with the psu caps, depending on what I decide to use for a chassis.

I'm either going to use a computer case, in which case it'll be a pretty conventional layout, or preferably I have a couple of old 10Megabit Stackable Rackmount hubs that i was thinking of gutting, one for preamp/one for amp.

That's why I'm curious about using smaller caps, because there's no pretty way to shoehorn 2 bigass caps into a 1u Chassis. The rest of the components I can make fit quite well, except for the Power suppply, which would get its own case, and of course i would use the film caps close to the board to make up for the wiring impedance and all that crap.

I'm leaning towards the computer case right now though, because it'll give me a place to mount an analogue VU meter :hphones:

GRollins 31st October 2003 01:31 AM

The consumer end of an electrolytic cap is the one with the screws on it.
Ahem...
Okay, where were we?
Oh, smaller caps. Smaller caps mean a higher cutoff for the frequencies going out to the speaker. That was what I was referring to above when talking about the possibility of factoring it into the crossover. Won't hurt anything. The bass will lean out to a greater or lesser degree depending on the Z of the speakers.
A sound card???
If your source is a sound card, I wouldn't drop a lot of money on high-bucks parts; you won't hear the difference. In that context, the money would be better spent elsewhere in your system. The .68uF Mylars will do fine. Later on you can upgrade parts if the mood strikes you and your wallet will allow.

Grey

fdegrove 31st October 2003 01:40 AM

Hi,

Quote:

A sound card???
One of us must have missed something?

Cheers,;)


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