PMA, I don't mind sharing, but I wish that I COULD get in a word or two on this thread. You haven't answered my question PMA, should we have used an aluminum foil plated cigar box, or its equivalent for our case? Are our huge and expensive cases, just a waste of time and money? Also, you are happy with putting ceramic caps in the power supply bypass? Please think, before reacting.
Dear John,
as far as I remember, the BT was a transconductance amplifier.
So maybe your answer could be guessed...but I'm curious.
In the case of voltage outputs, two schools of thought exists.
Those of maximising load currents through switches, connectors,wires, traces and solder joints and those which prefers a potentiometric approach.
This may be to a large extend a philosophical issue.
I'm curious about your general design philosophy on this.
Regards
as far as I remember, the BT was a transconductance amplifier.
So maybe your answer could be guessed...but I'm curious.
In the case of voltage outputs, two schools of thought exists.
Those of maximising load currents through switches, connectors,wires, traces and solder joints and those which prefers a potentiometric approach.
This may be to a large extend a philosophical issue.
I'm curious about your general design philosophy on this.
Regards
Hi Pavel,
Yes, I understood that. So far, I have had no reason to use feedthroughs in an audio design. Once I can worry about super low noise levels, I would choose carefully. For use in a preamplifier, I imagine that the higher impedances might demand a careful choice in dielectric.
I am somewhat confused about some of the descriptions for the feedthrough. What I'm used to is a wire with distributed capacitance, usually in the 10s of pF. Possibly up to 1 nF maybe (power supply feeds?). For higher impedance audio connections I would be thinking of an L-C section maybe. Something designed to kill 100 KHz (as a starting guess) and up. Since I have not used feedthrough caps for any audio signals, it's all guesswork on my part.
When values in the neighborhood of a few µF are being talked about, I start thinking of coupling capacitor that mounts through a bulkhead. Why? Isn't that an unnecessarily expensive component compared to a standard feedthrough and a standard coupling capacitor? Not only that, but the current trend is to eliminate all capacitors in the audio path, and a coupling cap would seem to buck the trend.
Hi John,
-Chris
Yes, I understood that. So far, I have had no reason to use feedthroughs in an audio design. Once I can worry about super low noise levels, I would choose carefully. For use in a preamplifier, I imagine that the higher impedances might demand a careful choice in dielectric.
I am somewhat confused about some of the descriptions for the feedthrough. What I'm used to is a wire with distributed capacitance, usually in the 10s of pF. Possibly up to 1 nF maybe (power supply feeds?). For higher impedance audio connections I would be thinking of an L-C section maybe. Something designed to kill 100 KHz (as a starting guess) and up. Since I have not used feedthrough caps for any audio signals, it's all guesswork on my part.
When values in the neighborhood of a few µF are being talked about, I start thinking of coupling capacitor that mounts through a bulkhead. Why? Isn't that an unnecessarily expensive component compared to a standard feedthrough and a standard coupling capacitor? Not only that, but the current trend is to eliminate all capacitors in the audio path, and a coupling cap would seem to buck the trend.
Hi John,
I don't think that's a problem for you! Just start banging away on your keyboard.
-Chris
Fellow audio loving adults, I do hope that we can go forward with some new ideas on this thread as it has continued, almost without break for 3 years or more, and we have discussed a few new ideas over this time. I do not wish it to be too difficult for those who are calculus challenged, yet not too easy, as if it were a high school class. There must be a happy medium, if it is to be productive. (Is this better?)
PMA there is nothing intrinsically wrong with feedthrough caps, and they have been around in laboratories since the very beginning of radio, I am quite sure. Jack Bybee, once showed me some 10 uF Sprague feedthrough caps taken from a defunct radio station more than a decade ago. The big problem with feedthrough caps is the material used to make the capacitance. It is usually ceramic, and I don't think this is good.
Now, do feedthrough caps do what they are supposed to do? Yes. Do we really need them in order to have a relatively quiet interior environment in a typical low RF environment, such as a home? I am not sure. Is the tradeoff between adding ceramic to the power supply buffering worth the relative purity of the power supply without the ceramic added, worth it? That is up to each one of us. I don't think that I would be comfortable living in such an RF environment, but when I was young, about 45 years ago, there was a radar pulse that would overwhelm virtually every audio system about every 15 seconds from a mountain above us. It might help in that case.
Now, do feedthrough caps do what they are supposed to do? Yes. Do we really need them in order to have a relatively quiet interior environment in a typical low RF environment, such as a home? I am not sure. Is the tradeoff between adding ceramic to the power supply buffering worth the relative purity of the power supply without the ceramic added, worth it? That is up to each one of us. I don't think that I would be comfortable living in such an RF environment, but when I was young, about 45 years ago, there was a radar pulse that would overwhelm virtually every audio system about every 15 seconds from a mountain above us. It might help in that case.
Homes aren't low-RF zones anymore, I fear. Just the contrary.
I gave up listening to foreign radio stations (on MW) for just this reason, it is all drowning in noise from the cell-phone relay stations, SMPS's etc. At least in cities.
I now use my hand-held receivers as noise detectors (hint to everyone... you'll be surprised how much dirt for example a PC spits out through its openings and from any cables. The receiver properly positioned and tuned can tell you a lot).
I take Pavels recommendations very seriously, he knows this stuff *and* can measure it... on occasion I also recommended feedthtrough caps for speaker outputs here, which I consider as a must, today.
- Klaus
I gave up listening to foreign radio stations (on MW) for just this reason, it is all drowning in noise from the cell-phone relay stations, SMPS's etc. At least in cities.
I now use my hand-held receivers as noise detectors (hint to everyone... you'll be surprised how much dirt for example a PC spits out through its openings and from any cables. The receiver properly positioned and tuned can tell you a lot).
I take Pavels recommendations very seriously, he knows this stuff *and* can measure it... on occasion I also recommended feedthtrough caps for speaker outputs here, which I consider as a must, today.
- Klaus
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