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Old 18th August 2011, 02:51 AM   #11
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Quote:
Originally Posted by gootee View Post
Probably not too much. So 26 AWG should be OK, eh? (Silver-plated might be OK but I'd stay away from gold unless you are very familiar with the associated problems of trying to mate or solder dissimilar metals.)

Actually, I was probably thinking more in terms of speaker cable lengths, where there are audible and measurable effects from the still-extremely-small inductances.

ON the other hand, considering that almost all amps are competent-enough to be indistinguishable when attempting the vast majority of audio reproduction tasks, the highest-quality amplifiers might therefore be differentiating themselves based on better performance at the extremes of "does it matter?", aka attention to minor details.

At some point, high-enough inductance would be "a bad thing". So why not minimize it, since you have the choice (and are not sure how much it will matter)?

Tom
I don't feel like arguing about this tonight. Sorry!
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Old 18th August 2011, 03:12 AM   #12
gootee is offline gootee  United States
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Originally Posted by VictoriaGuy View Post
I don't feel like arguing about this tonight. Sorry!
Roger that. Lately, I'm brain-dead after about 4 pm, anyway.
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Old 18th August 2011, 03:18 AM   #13
gootee is offline gootee  United States
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Originally Posted by DF96 View Post
I thought 'small' (i.e. thin?) wire has more inductance than thicker wire? But except for long lengths, completely irrelevant at audio frequencies.

Screened coax, or screened/unscreened twisted pair, should be fine. Decide which end you are going to ground: at the chassis socket or at the valve input. The latter is almost certainly better.
I'm curious about why grounding the shield at the tube-input end would be better than at the chassis end. I know why it would definitely be better if using unshielded twisted pair. But would it also be better for just the one-end-only ground of the shield of a shielded pair?
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Old 18th August 2011, 03:27 AM   #14
gootee is offline gootee  United States
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Originally Posted by Mark.Clappers View Post
Yes thin (or small ) wire has more pure resistance (for RG179 coax, 802Ohm / KM), but this doesn't matter for short lengths. Also inductance and capacitance are different per meter but again for audio frequencies it simply doesn't matter. It's a whole different story if used for RF or long cable runs, but that doesn't apply here. For audio signals usually the bandwidth is limited to 0 - 100KHz and pretty much all types of coax cable can handle this with ease. Same goes for a twisted pair though... I guess it all depends on your personal preference and availability of materials.
Yeah that all sounds about right (except 100 kHz should be 200+ kHz, in general). But we also don't want to give the impression that we are "only" working with audio frequencies and can completely disregard RF. RF is everywhere and all inputs (and internal stage inputs), all outputs, and all power inputs and outputs, should have RF filtering, unless we are SURE that they don't need it (which might very well be the case, here; but you have to think about it at least once, for every design of every type of circuit).
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Old 12th September 2011, 11:48 PM   #15
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Wow I forgot about this thread and I'm not sure why! I'm sorry and thank you to everyone.

Well inside the amp, the signal is actually going have to travel quite a bit. After coming in through RCA, it's being sent down the side of the case to 4-pole switch on the front panel which I'm using as a ghetto output selector. (It will switch the signal to go to either the headphone amp or the two power amp boards.).

After that, it has to go all the way to the back of the enclosure to the amp boards (or 3 inches if it's going to the headphone amp).

Also to note, as the signal goes to the output selector switch, it goes right past a huge toroid transformer and a small 6VCT split bobbin type transformer. Torroids don't generally make as much noise or interference, but they still DO and the standard split bobbin type makes a bit of stray junk.

So I guess I should use some shielding of a sort. Needless to say that I will probably not notice a thing...but to be safe. Any recommendations on some good online sellers. My poor excuse of a Radioshack is usually lacking in the wire department, so somewhere online might not be a terrible idea.

Also, I'm wiring two potentiometers to the front panel for volume control. I already wired them and used 3x 24AWG solid and kind of "twisted" them together. Any words of advice for wiring up those pots. The wire runs are about 1.5ft per pot. Kind of long, yes.
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Old 13th September 2011, 12:02 AM   #16
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Belden #8451. 100% foil sheilding. Used miles of it in high power transmitter / studio location. Now being superceded by Belden 110 ohm digital audio cable. But 8451 is hands down the DC-3 of the broadcast audio world.
Doc

www.belden.com/techdatas/metric/8451.pdf
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Old 13th September 2011, 12:19 AM   #17
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Thanks a lot. Doesn't seem to wildly expensive compared to the more expensive types...though I'm not sure exactly how much audio stuff I'll be doing after this to justify buying a lot of it, but I guess I'll find use for it eventually.
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Old 13th September 2011, 12:30 AM   #18
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Belden 8451 BY FOOT BLACK Paired - Audio, Control, and Instrument Cable, 22 AWG, By the Foot (Black) | Full Compass

By the foot.
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Old 13th September 2011, 12:36 AM   #19
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ooo thank you. Let's see about shipping now.
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Old 13th September 2011, 12:53 AM   #20
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Depending on where you live you might find a bunch of it fairly cheap. As I said with the move to digital everyone is shiffing (has shifted) to 110 ohm digital audio cable. The PBS station I worked for a few years ago yanked out a pile about 18 feet in diameter by 4 feet tall. It went of to University surplus. You might try such places or even give some local radio stations a call. Ask for the engineer and tell him you're looking for some surplus one pair beldfoil cable. Might get lucky.
Doc
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