Preamp signal wiring ideas ?

[gurevise]

Guys,
I'm looking for ideas on wiring for line stage preamp.
Should I buy a solid Teflon coated thin silver wire or plain copper will do?
Is thinner wire the better?
Should I use shielded wire for all internal signals wiring or unshielded will do?
Should I run all twisted pairs everywhere or separate signal and ground runs work just as well?
I'm looking for a fast, transparent and open sound.
I would appreciate all input on this subject.

Thanks
Sergey
Dayton, OH
USA

[ArtG]

Originally posted by gurevise
Guys,
I'm looking for ideas on wiring for line stage preamp.
Should I buy a solid Teflon coated thin silver wire or plain copper will do?

Silver is a better electrical conductor than copper, but not by much. I use mil teflon insulated silver plated wire because: 1/ I obtained a quantity of it, some time ago, at cheap prices. 2/ It's easier to solder (although more difficult to strip), than PVC wire. 3/ It may sound better (or it may not)! If you ask 100 people for their opinion of the sound quality of differant types of wire, you will get 103.14159 differant answers! If you spend the money to buy silver wire for your project, you will probably be convinced that it sounds "better".

Is thinner wire the better?

It depends upon the application. (See above) Most folks will use 18-24 awg for general tube circuit wiring. The larger is often used for lower voltage, higher current applications, such as filament runs.

Should I use shielded wire for all internal signals wiring or unshielded will do?

Again it depends on a number of factors. Short internal runs are typically run unshielded, as cable is far harder to work with and generally not necessary. I use cable for longer runs to input jacks, etc. and where a longer run will be near a potential source of interference, such as a transformer, or AC line voltages. I am careful, however, to use quality, low capacitance cable. It's a good idea to plan your layout so that signal leads are kept as short as practical, and away from AC supplies.

Should I run all twisted pairs everywhere or separate signal and ground runs work just as well?

I use twisted pairs only for AC supply, and AC filament wiring.

I'm looking for a fast, transparent and open sound.

As long as you do a reasonably good job of wiring the preamp, the results that you obtain will depend more on the circuit design, and parts quality than the wiring.

I would appreciate all input on this subject.

Thanks
Sergey
Dayton, OH
USA

[lndm]

My one of the 103.14159 possible responses () is that valve circuitry is generally high impedance and this is (the wire gauge thing) therefore for the most part, irrelevant. I do on the other hand think you should use heavy cable for your filaments/heaters.

You should twist pairs where the AC flowing in each will balance and would otherwise cause a problem. Examples are filament wiring and power supply wiring. For that matter, you should try to keep these physically apart from sensitive signal wiring and this is perhaps (IMO) the thing to keep in mind...keep your power supply and input stage separated.

[Miles Prower]

Originally posted by gurevise
Guys,
I'm looking for ideas on wiring for line stage preamp.
Should I buy a solid Teflon coated thin silver wire or plain copper will do?

Teflon coated silver wire is an excellent idea... for UHF circuits. At audio frequencies, it makes no difference. Good old PVC coated, copper hook-up wire is good enough, and costs way less.

Is thinner wire the better?

For audio, makes no difference.

Should I use shielded wire for all internal signals wiring or unshielded will do?

For sensitive sognal paths, what I use is RG-75 RF coax (because I have a bunch of it here). I use the center conductor for the signal, and ground the high impedance end of the shield braid at that one point. That way, the shield operates as a Faraday cage to shield against electric field interferance. Don't use that shield as a return otherwise it could set up a ground loop that induces PS hum into the circuit. A couple of places to use it might be a long run from an input to a first stage voltage amp, or the gNFB lead from the OPT back to the gNFB summing node.

Should I run all twisted pairs everywhere or separate signal and ground runs work just as well?

Can't hurt to twist all pairs. "Star" grounding goes a long way to keep PS noise out of sensitive inputs.

[frank754]

I have a bunch of coax, both video (75 ohm) and Ham xmitter linefeed (50 ohms).
Does the center conductor have any resistance or is it good for shielded wire coming
across the underside of the chassis for the purpose of line input, etc?
So far for the audio input on these amps, I've either been using antique shielded wire,
newer shielded wire from audio patch cables (which have RCA plugs on each end,
since I have some of these.

[ArtG]

Frank,

The cable that you mention has a characteristic impedance of 50 or 75 ohms which is differant from resistance. For general audio purposes, you can ignore both the impedance, and resistance of the cable, providing you aren't making extremely long runs between remote units. This is particularly true if you correctly ground only one end, as Miles Prower pointed out.
I personally prefer to use low capacitance cable made for audio use such as that manufactured by Mogami, since it's very flexible and easy to work with, as compared to RF cable, which usually employs braid shield (which I hate with a passion) and sometimes foil shield.
Then again if it's free...........I can't argue with that!

[CarlyBoy]

I've found Belden 89259 to be an excellent multipurpose cable. I originally bought it for DIY interconnect (capacitance is nice and low), but the jacket is good to 200 C so is fine as a shielded cable for tubes with caps.

[grhughes]

solid, silver coated copper, no larger than 24 awg for signal leads. short point to point wiring. It's sold on ebay. You can get it pre-cut. If you can find Belden 8450 or Alpha 2460C then use that for your heater leads. It's pre-twisted and sheilded. For your high voltage, B+ leads then use just Teflon coated, stranded hook up wire, 20 awg. For your ground bus try to find some BUSS BAR WIRE that is at least 12 awg, solder plated solid copper. This should be long enough to go from one end of your amp to the other and only grounded at one point to the chassis. All grounds come to this buss bar wire.