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Old 11th May 2003, 10:54 PM   #1
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Default electrolytic vs non ellyt

When using a capacitor over the kathode-resistor, some people claiming that an electrolyctic will distort the sound. I've read the Cathode bypass caps?
but I only get more mixed up. Can it help to put another lower value non eletrolytic across the other. Lets say I have a 22uF Ck over a 1,5k ohm resistor. Will an 0,1 uF help ?
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björn
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Old 11th May 2003, 11:15 PM   #2
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Default BYPASSED.

Hi,


Quote:
When using a capacitor over the kathode-resistor, some people claiming that an electrolyctic will distort the sound.
They do and it ain't pretty.

With such a low bypass as 22uF you could envisage using a decent filmcap or composed values to make up the 22uF.
Space permitting of course.

Quote:
Can it help to put another lower value non eletrolytic across the other. Lets say I have a 22uF Ck over a 1,5k ohm resistor. Will an 0,1 uF help ?
I am no big fan of the following technique but the rule of thumb for bypassing electrolytes goes like 1/10 of the original value.
In your case that would be 22uF elco + 2.2uF film + 0.22uF + 0.022uF.

You may have to fiddle a bit to find the tonal balance that suit you and your system best though.

Cheers,
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Old 12th May 2003, 12:03 AM   #3
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Default Heresy

Well, I realise this won't make me popular, but I don't have a problem with electrolytics. Modern ones are far, far better than old ones, and if you choose low ESR types, then I think it's hard to find fault with them.

More to the point, if you don't bypass the cathode, ra rises far faster than feedback acts to correct power supply noise. In other words, you throw power supply noise rejection away. Seems like a bad deal to me, but if we all agreed, we'd all listen to Quad 405s.

I'm just going to put my paws over my ears until the dust settles.
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Old 12th May 2003, 12:23 AM   #4
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Default RE:HERESY.

Hi,

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Well, I realise this won't make me popular, but I don't have a problem with electrolytics. Modern ones are far, far better than old ones, and if you choose low ESR types, then I think it's hard to find fault with them.
LOL...I expected some resistance on this albeit not from you.

Finding out what a cap sounds like isn't all that hard, use it as a coupling cap and tap off the signal at the output.
Listen to the sound with a good headphone set such as the Stax Lambda Pro and be your own judge.

Granted, modern low ESR electrolytes have improved a lot over the past 20 years, they still have a long way to go to reach the "perfect" cap status.

Quote:
More to the point, if you don't bypass the cathode, ra rises far faster than feedback acts to correct power supply noise. In other words, you throw power supply noise rejection away.
Sure, you have got to know what you're doing...one reason I so often emphasise the importance of a good PSU (read very high PSRR) and some circuits are more prone to that than others too.

Cheers,
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Old 12th May 2003, 12:38 AM   #5
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Default We will light a torch...

Ah, well. I don't like to use bypass capacitors, not because they're electrolytic, but because they're capacitors. NiCds, diodes, short-circuit, etc, etc, anything to stop a cathode moving, rather than a capacitor. It's all about what happens when you momentarily overload that stage...
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Old 12th May 2003, 01:00 AM   #6
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Default RE:We will light a torch...

Hi,

Quote:
Ah, well. I don't like to use bypass capacitors, not because they're electrolytic, but because they're capacitors.
Memory effects are the culprit plus the fact that most are just not linear at audio frequencies...
They always seem to slow down transient response, IMO and gobbling up detail, smearing etc.

I tried all kinds of caps for bypassing cathodes, not even the best filmcaps worked satisfactorily.

Quote:
It's all about what happens when you momentarily overload that stage...
Well, a none bypassed cathode resistor will have the valve overload quicker unless you rebias to prevent this.
One should design with this in mind right from the start IMHO.

Quite a lot more can be said about caps and stray capacitance, all of this deserves a thread all to itself, I feel.

Cheers,
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Old 12th May 2003, 01:05 AM   #7
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Some electrolytics really do sound bad- I have some cheap speaker crossover ones that sound great, and some others that sound terrible. I have yet to try expensive film caps.

For a cathode bypass on a SE power tube, isn't the entire AC signal passing through the cap?
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Old 12th May 2003, 01:15 AM   #8
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Hi,

Quote:
For a cathode bypass on a SE power tube, isn't the entire AC signal passing through the cap?
Depending on the time contants, yes.
Not just for an SE amp though, it's the same story allover really.

Quote:
Some electrolytics really do sound bad- I have some cheap speaker crossover ones that sound great, and some others that sound terrible. I have yet to try expensive film caps.
In a multiway x-over, if you change one than best to change the lot.
If you don't you may face a complete tonal imbalance + the fact that you gain in efficiency when swapping to filmcaps.

So caveat emptor,
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Old 12th May 2003, 01:22 AM   #9
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Default Re: RE:We will light a torch...

Quote:
Originally posted by fdegrove
I tried all kinds of caps for bypassing cathodes, not even the best filmcaps worked satisfactorily.
Exactly. So perhaps it's not really the fact that it's an electrolytic, rather, that it's a capacitor?

In theory, we never overload a stage, and we design to avoid overload. In practice, we do overload. I've come to the conclusion that the important point is how quickly the stage recovers from overload. A cathode bypass capacitor extends the time needed for recovery into hundreds of milliseconds, and I suspect that is why you prefer to avoid using them. Balanced audio doesn't need cathode bypasses, perhaps that's why it sounds so clean?
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Old 12th May 2003, 01:41 AM   #10
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Default Re:Re: RE:We will light a torch...

Hi,

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Exactly. So perhaps it's not really the fact that it's an electrolytic, rather, that it's a capacitor?
Oh,yes...absolutely.
I must have expressed that here on the forum at least half a dozen times.

Quote:
In theory, we never overload a stage, and we design to avoid overload. In practice, we do overload. I've come to the conclusion that the important point is how quickly the stage recovers from overload.
Yup...couldn't agree more.

Quote:
A cathode bypass capacitor extends the time needed for recovery into hundreds of milliseconds, and I suspect that is why you prefer to avoid using them.
Indeed, and most OPTs present a similar behaviour to my ears, although much less in the mids, they're wideband phase behaviour buggs me just the same.

A well designed system should have all the virtues of sand devices without their nastiness and conversley well designed valve gear should have all the virtues of sand devices without the valves' shortcomings...valves have a lot less shortcomings and the so called "valve" sound can be attributed mainly to these darned bypass caps IME.

Quote:
Balanced audio doesn't need cathode bypasses, perhaps that's why it sounds so clean?
That, plus other advantages, yes.
Oh, and as you said somewhere else Johnson noise won't get cancelled out by balancing.

Cheers,
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