When using a capacitor over the kathode-resistor, some people claiming that an electrolyctic will distort the sound. I've read the http://www.diyaudio.com/forums/show...e=15&highlight=cathode capacitor&pagenumber=1
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 ?
Thanks
björn
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 ?
Thanks
björn
BYPASSED.
Hi,
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.
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,
Hi,
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.
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,
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.
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.
RE:HERESY.
Hi,
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.
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,
Hi,
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.
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,
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...
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...
RE:We will light a torch...
Hi,
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.
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,
Hi,
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.
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,
Hi,
Depending on the time contants, yes.
Not just for an SE amp though, it's the same story allover really.
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,
Depending on the time contants, yes.
Not just for an SE amp though, it's the same story allover really.
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,
Re: RE:We will light a torch...
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?
fdegrove said:
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?
Re:Re: RE:We will light a torch...
Hi,
Oh,yes...absolutely.
I must have expressed that here on the forum at least half a dozen times.
Yup...couldn't agree more.
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.
That, plus other advantages, yes.
Oh, and as you said somewhere else Johnson noise won't get cancelled out by balancing.
Cheers,
Hi,
Oh,yes...absolutely.
I must have expressed that here on the forum at least half a dozen times.
Yup...couldn't agree more.
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.
That, plus other advantages, yes.
Oh, and as you said somewhere else Johnson noise won't get cancelled out by balancing.
Cheers,
I've got to find something for us to disagree about!
Hmmm. It has to be admitted that OPTs are less than perfect at frequency extremes, what with leakage inductance and lack of primary inductance, but they are an extremely elegant solution to the impedance matching problem, and they enhance efficiency, which is not something that could be said of OTLs. I've always felt that it is the mid-range that is most important. Get that right, and then worry about the rest. It seems to be easier to get that right with valves than SS. Conversely, SS can manage good bass.
fdegrove said:
Hmmm. It has to be admitted that OPTs are less than perfect at frequency extremes, what with leakage inductance and lack of primary inductance, but they are an extremely elegant solution to the impedance matching problem, and they enhance efficiency, which is not something that could be said of OTLs. I've always felt that it is the mid-range that is most important. Get that right, and then worry about the rest. It seems to be easier to get that right with valves than SS. Conversely, SS can manage good bass.
RE:I've got to find something for us to disagree about!
Hi,
30 years of audio experience and what do you get?
Well, Class A designs are considered the "nec plus ultra" in traditional designs and are just as inefficient as OTLs give or take a Watt or two.
Given a choice I'd go OTL, all else being equal.
When it comes to ultimate music reproduction I don't mind footing the bill.
Yes, and after you have that spot on with an OPT coupled design, what can you do?
Nothing.
Yes.
Valves can deliver good bass too, you just need a lot of them in // to get low enough Zo and this is where a bi/tri amped setup comes in plus a good valved x-over.
Tight bass with valves running full range is much harder to do.
Matching a SS subwoofer to a valve based full range amp seamlessly may prove just as hard though.
Cheers,
Hi,
30 years of audio experience and what do you get?
Well, Class A designs are considered the "nec plus ultra" in traditional designs and are just as inefficient as OTLs give or take a Watt or two.
Given a choice I'd go OTL, all else being equal.
When it comes to ultimate music reproduction I don't mind footing the bill.
Yes, and after you have that spot on with an OPT coupled design, what can you do?
Nothing.
Yes.
Valves can deliver good bass too, you just need a lot of them in // to get low enough Zo and this is where a bi/tri amped setup comes in plus a good valved x-over.
Tight bass with valves running full range is much harder to do.
Matching a SS subwoofer to a valve based full range amp seamlessly may prove just as hard though.
Cheers,
Re: More than one way to skin a cap.
It doesn't solve the problem completely though. The DC bias you apply has a source impedance, either through the grid-leak resistor, or the bias supply to the bottom end of the driver transformer secondary. If, at the moment of overload, grid current flows:
The high value grid leak resistor will be unable to hold the bias under control
Or,
The cap that decouples the bottom end of the driver TX secondary is called upon to supply stored charge - back to square one!
I have been looking into the second case problem, and believe I've found a solution:
No cap....
Supply the bias point with a low impedance source such as a cathode follower.
Of course that begs the question: Where does the cathode follower get it's supply, but let's not go there
Shifty,
The bottom end response is better with grid bias, as is the power output. It's just more trouble. But in my opinion, worth it
Cheers,
Well, many designs do, but it adds a tweak to the circuit.Circlotron said:
It doesn't solve the problem completely though. The DC bias you apply has a source impedance, either through the grid-leak resistor, or the bias supply to the bottom end of the driver transformer secondary. If, at the moment of overload, grid current flows:
The high value grid leak resistor will be unable to hold the bias under control
Or,
The cap that decouples the bottom end of the driver TX secondary is called upon to supply stored charge - back to square one!
I have been looking into the second case problem, and believe I've found a solution:
No cap....
Supply the bias point with a low impedance source such as a cathode follower.
Of course that begs the question: Where does the cathode follower get it's supply, but let's not go there
Shifty,
The bottom end response is better with grid bias, as is the power output. It's just more trouble. But in my opinion, worth it
Cheers,
Thanks for all the replys.
But if I tell you thats its a guitaramp. Not a quad 505 or something equal....
And expermenting with a Ck makes A LOT difference. (Bass boost)
And that is a thing I can understand. But I wanna know more about the distorsion (if) and why its "only" on electrolytic. (I asume that we must compare the same value i.e. 10uF or what ever.)
cheers, and keep your answers coming. I learn alot.
björn
But if I tell you thats its a guitaramp. Not a quad 505 or something equal....
And expermenting with a Ck makes A LOT difference. (Bass boost)
And that is a thing I can understand. But I wanna know more about the distorsion (if) and why its "only" on electrolytic. (I asume that we must compare the same value i.e. 10uF or what ever.)
cheers, and keep your answers coming. I learn alot.
björn
Gammelmalle,
In basic terms the value of the cathode capacitor cannot "boost" the bass. However, too small a value can cause loss of lower frequencies, as there is more feedback, or degeneration at them.
For the giutar amp application, it's enough to have a sufficiently large value cap to cover the frequency range, but not so large as to cause overload recovery delay.
Cheers,
In basic terms the value of the cathode capacitor cannot "boost" the bass. However, too small a value can cause loss of lower frequencies, as there is more feedback, or degeneration at them.
For the giutar amp application, it's enough to have a sufficiently large value cap to cover the frequency range, but not so large as to cause overload recovery delay.
Cheers,
Instead of running the bottom of the grid resistor to ground, run it to negative whatever volts you want for bias.ShiFtY said:
Also, this next method have been done a googleplex times before, but how would it go to use a zener diode instead of a cathode resistor. Maybe a bypass cap across the zener. The voltage across the zener would not really change with changes in cathode current. Just what you want!
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