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In Reply to: RE: Cathode bypass cap value 300B SET question posted by beto1 on August 09, 2015 at 14:15:54
"so the design of my amp (AN Kit One) use this high and not common value to elevate the damping factor and maybe and give a way to manage and tighten the bass response on wider kind of speakers. "
That value (220uf) might not be common in practice but the formula says it will bypass the cathode to 2Hz.
This keeps that filter from shifting the phase of 20Hz.
That's probably not needed but might have been part of their thinking for using that value cap.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Follow Ups:
For what it's worth, the WE Model 91 used 16uF or 25uF at different times.
"The data sheet on the 91 claims a useable range of 50 to 8000 cycles...."Making some assumptions, a 16uf cap would give a -3db point of 25Hz. A little lower if the output transformer impedance is higher than 2500 ohms. Most of the lost amplitude is restored in one octave.
How low did theater speakers (or film sound tracks) go back in the day?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 08/09/15 08/10/15
Thanks Tre,
very helpful comments.
What is your opinion about using other kind of capacitors, non electrolytic?
Regards
I would use a film capacitor whenever possible.
It's easy for me because I don't play bass through my SET amplifiers.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
"It's easy for me because I don't play bass through my SET amplifiers."
what do you mean? you use 2 or 3 amplifiers, one for each speaker driver?
and you you mean that film caps has an issue with bass response?
I don't get it
No, that's not what I meant.There's no reason to bypass the cathode lower than the lowest frequency the amplifier is going to have pass through it.
I bi-amp. I use a 200Hz low pass filter (1/2 of a electronic crossover) between my preamp and a SS amp that drives my JBL 15" woofers.
I use my SET amplifier from 200Hz on up. It has a cap in series with the input that creates a 6db per octave high pass filter at 200Hz so the output tube and the output transformer doesn't play much really low frequencies.
I therefore don't need to bypass the cathode of the output tube all the way down to the lowest frequencies the way I would have to if the amplifier was being used full range.
BTW IMO, film caps are better at all frequencies.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 08/09/15
TRE, I like the idea of using tuned amps for biamping. I've done this with a pair of Tympani 1D's at 6db/oct with very good results. Why did you choose to use an electronic xover for low pass? Was it for level adjustability?
I wanted a steeper slope.
My midrange speakers fall off all by themselves fairly rapidly below 200Hz but my woofers would play quite well above 200Hz.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
With the recent posts on musical loadlines I would almost think you would want a steeper slope on the midrange. A first order slope is only 18db down at 25hz. Is that enough? I'm speaking from the SET amp view, not the driver.
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Big speakers and little amps blew my mind!
You have a point but the cure might be worse than the illness.I don't want to go active on the high pass and I don't know where to get a really good 250Hy small signal filter choke (or any 250Hy small signal filter choke).
FYI, I use a 330k grid resistor on the input stage of my SET amp. (the value is large because I see no reason to "load down" what's driving it)
I have a small cap in series that creates the 6db high pass filter.
To make that a 12db high pass filter I would need a very large value choke.
Do you know of an easier way to do this passively?
Since I'm doing this at the input and it is a cap coupled 2 stage SET amp I guess I could create another 6db high pass filter by using the coupling cap.
Truth is, I intend to try this but just adding the 6db filter helped a lot. If there's more improvement to be had, I think I'll save it and savor it later. I'm enjoying what I have right now.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 08/12/15
Tre,
Wouldn't having R/C filters in series increase the slope without using a choke/inductor?
Yes. I have one at the input to the power amp and I could lower the value of the coupling cap between the driver stage and the output stage to create another.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Please do enjoy your system. It's just a question that's been in the back of my mind.
Phil Marchand uses a ferrite core (ferrite pot core/pot ferrite core?) coil in his PPXLOs that many of the knowledgeable guys at diyAudio swoon over, and would die to know where he sources them from. I don't think he sells them individually. His PPXLOs are second order, and they would be easier for me. Are they passive enough for you?
Why don't you want to use an active high pass? Just because it's active doesn't mean it has to add gain.
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Big speakers and little amps blew my mind!
I can't find anything on line about the PPXLO.
The XM46 looks good by the impedance is too low (1k).
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Oh, and it says typical impedance is 1K. If you find it interesting, then you should send an inquiry to Mr. M. who says he can build anything you want. He is an extremely nice man.
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Big speakers and little amps blew my mind!
I'm sure he's a great guy but the higher the impedance the larger the inductors need to be and I think that will lead to higher and higher winding capacitance causing other problems.
LCR RIAA filters are available in 600 ohm and 10k but everyone seems to say the 600ohm sounds better.
But 10k is a lot easier to drive.
Every step of the way is a compromise of one form or another.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
> "Every step of the way is a compromise of one form or another."
You got that right. That's why there are 10,000 paths in this hobby.
Mr. M is a great guy. An old school Frenchman, and willing to talk to somebody on the phone for five minutes. You could ask him yourself tomorrow if you so choose.
Is this all an issue because you use a TVC or AVC? I think an active crossover would take care of that problem. Yet another compromise.
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Big speakers and little amps blew my mind!
"Is this all an issue because you use a TVC or AVC?"No, not at all. The AVC is a step down autoformer (unless you have it wide open) so the output impedance is lower than that of the source.
I'm just OCD and like to keep my load lines as horizontal as I can. Decreases the HD, ya know!
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 08/12/15
Just exploring the possibilities.Have a good one.
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Big speakers and little amps blew my mind!
Edits: 08/12/15
.
Have Fun and Enjoy the Music
"Still Working the Problem"
My mistake. It's been a long time since I looked at his site.
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Big speakers and little amps blew my mind!
"I therefore don't need to bypass the cathode of the output tube all the way down to the lowest frequencies..."
And as a result, you can use smaller value caps, which makes film caps practical. [I think this might be the point that wasn't clear to the OP.]
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Buy Chinese. Bury freedom.
nt
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Have Fun and Enjoy the Music
"Still Working the Problem"
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