Hi, fdegrove -
Actually, in my later projects, I have (had) been becoming very concerned with microphonics, to the extent where I actually fabricated a couple chassis where I shock mounted small signal tubes encased in a solid block of black anodized aluminum with heat sink fins attached!
I once fabricated a transformerless 3 tube microphone preamp with an unusually low noise factor (something like 4db) and 90db common mode rejection - I've got the schematic somewhere. It was very instructive to check the relative microphonics of different tubes at the input stage. With a 'good' 12ax7 & listening to the output through a headphone amp, I could tap the side of the tube with a pencil and hear maybe a small thunk if I whacked it hard enuf. With a 12at7, it sounded like there was a little spring reverb in there. With a 6dj8, it sounded like a glass chandelier landing on a concrete sidewalk. The related factor appeared to be transconductance/filament power.
Actually, in my later projects, I have (had) been becoming very concerned with microphonics, to the extent where I actually fabricated a couple chassis where I shock mounted small signal tubes encased in a solid block of black anodized aluminum with heat sink fins attached!
I once fabricated a transformerless 3 tube microphone preamp with an unusually low noise factor (something like 4db) and 90db common mode rejection - I've got the schematic somewhere. It was very instructive to check the relative microphonics of different tubes at the input stage. With a 'good' 12ax7 & listening to the output through a headphone amp, I could tap the side of the tube with a pencil and hear maybe a small thunk if I whacked it hard enuf. With a 12at7, it sounded like there was a little spring reverb in there. With a 6dj8, it sounded like a glass chandelier landing on a concrete sidewalk. The related factor appeared to be transconductance/filament power.
Ummm... Why did you ask that?
Re: Re: Re: Thorsten, what film capacitors do you use?
Konnichiwa,
Not quiet, the issues are more complex. With enough AC voltage modulation applied a Capacitor will "sing" like a canary, indicating mechanic resonances excited by the signal (similar to electrostatic speakers). It will also act as pure "receiver".
As other mentioned, materials also play their big roles. In case you are stuck for answers, look for plastic encased cap's that contain no magnetic parts. The dielectric and foil/film vs. metalised construction is less important than that the capacitor may be wound tightly under tension and then enclosed and that no magetic parts be used. Also look for the capacitors slew rate, the more the better....
Sayonara
Konnichiwa,
arnoldc said:
Not quiet, the issues are more complex. With enough AC voltage modulation applied a Capacitor will "sing" like a canary, indicating mechanic resonances excited by the signal (similar to electrostatic speakers). It will also act as pure "receiver".
As other mentioned, materials also play their big roles. In case you are stuck for answers, look for plastic encased cap's that contain no magnetic parts. The dielectric and foil/film vs. metalised construction is less important than that the capacitor may be wound tightly under tension and then enclosed and that no magetic parts be used. Also look for the capacitors slew rate, the more the better....
Sayonara
Hi, Marztv -
If your leads are magnetic, I personally would keep them as short as possible. My experiences with steel leads have not been positive from a SQ viewpoint.
KYW brings up a good point wrt even caps with the best dielectrics using magnetic components. I see those Russian teflons on Ebay, but I force myself to turn away. However I have a stash of 0.22uF 600VDC teflon film and foils custom made by Reliable Capacitors for that extra special project.
I have nothing against oil filled capacitors - in fact I use a number of AC rated 'oil'-filled polypropylenes as power supply filters. Maybe I'm missing something, but my understanding is that the oil is mostly there to prevent corona discharge, not to significantly affect the dielectic properties.
My phono preamp has some air variable capacitors that are used to adjust input capacitive loading, HF phase compensation and crosstalk compensation. My approach with this design was that if I could add a circuit to compensate for something, I would do it as long as I could do so without adding any active stages for the bulk of the signal. This preamp has three stages from phono input to amp output. I actually considered building a stacked plate air capacitor for the RIAA shaping but figured I had to draw the line somewhere.
If your leads are magnetic, I personally would keep them as short as possible. My experiences with steel leads have not been positive from a SQ viewpoint.
KYW brings up a good point wrt even caps with the best dielectrics using magnetic components. I see those Russian teflons on Ebay, but I force myself to turn away. However I have a stash of 0.22uF 600VDC teflon film and foils custom made by Reliable Capacitors for that extra special project.
I have nothing against oil filled capacitors - in fact I use a number of AC rated 'oil'-filled polypropylenes as power supply filters. Maybe I'm missing something, but my understanding is that the oil is mostly there to prevent corona discharge, not to significantly affect the dielectic properties.
My phono preamp has some air variable capacitors that are used to adjust input capacitive loading, HF phase compensation and crosstalk compensation. My approach with this design was that if I could add a circuit to compensate for something, I would do it as long as I could do so without adding any active stages for the bulk of the signal. This preamp has three stages from phono input to amp output. I actually considered building a stacked plate air capacitor for the RIAA shaping but figured I had to draw the line somewhere.
Thanks all who have replied to my posting.
Frank: Sorry for my misunderstanding, I got the impression it was a term for a kind of metal or alloy, like 'mylar' is polyester... But I guess these leads are just steel, because they appear homogenic.
thoriated: I had no idea the leads were magnetic until I just checked it. It never crossed my mind before. I'm not usually worried about wire quality for short runs inside an amp, but I think I'll cut them tighter in future projects, especially after reading this thread.
I have a large collection of old surplus components, so that's what I usually dig out when I'm about to build something. Some of it is really nice, like big oil caps and resistors with silver leads, but other things are... well, old junk. I have maybe 100 of the 0.33uF spragues, so I'll definitely keep using them though
John: Thanks for making things clear. Where did you find that information? Is there a source on the net somewhere? I also have bigger 1uF/600v kinds of Spragues that are also marked with 118P. I take it that they are also metallized polyester then? I usually put those as bypasses for PSU electrolytics, or as a small bank of uF between the rectifier tube and choke, with good sonic results.
Frank: Sorry for my misunderstanding, I got the impression it was a term for a kind of metal or alloy, like 'mylar' is polyester... But I guess these leads are just steel, because they appear homogenic.
thoriated: I had no idea the leads were magnetic until I just checked it. It never crossed my mind before. I'm not usually worried about wire quality for short runs inside an amp, but I think I'll cut them tighter in future projects, especially after reading this thread.
I have a large collection of old surplus components, so that's what I usually dig out when I'm about to build something. Some of it is really nice, like big oil caps and resistors with silver leads, but other things are... well, old junk. I have maybe 100 of the 0.33uF spragues, so I'll definitely keep using them though
John: Thanks for making things clear. Where did you find that information? Is there a source on the net somewhere? I also have bigger 1uF/600v kinds of Spragues that are also marked with 118P. I take it that they are also metallized polyester then? I usually put those as bypasses for PSU electrolytics, or as a small bank of uF between the rectifier tube and choke, with good sonic results.
Take a look at this thread. It shows a little about magnetics influence on a circuit (or the lack of).
http://www.diyaudio.com/forums/showthread.php?s=&threadid=27298&highlight=
Till now nobody have been able to come up with more than theories about the existance of such a problem.
Magura
http://www.diyaudio.com/forums/showthread.php?s=&threadid=27298&highlight=
Till now nobody have been able to come up with more than theories about the existance of such a problem.
Magura
fdegrove said:
marz.tv said:
copperweld was part of LTV that survived the bankruptcy of LTV. It makes mostly tubing, but started its life as a manufacturer of copper clad steel and aluminum wires. such wires offer the electric conductivity of copper (copper outside), with the strength and low-cost of steel, or light weight of aluminum.
Since copperweld isn't an alloy, you cannot exactly call it a "chemistry" as you would to steel.
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