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Old 21st August 2016, 02:03 PM   #1
wanders is offline wanders  United States
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Default Chassis wire

I wired (signal) a tube diy preamp with Teflon jacket, silver plated, shielded twisted pair. Probably used 60' +/-. The stuff is bulky, inflexible, & hard to work. More important, it's not as quiet as I had hoped. Thinking about re-wiring with Mogami 2330 mini coax. Twenty five cents per foot at Markertek.

Any thoughts?

Last edited by wanders; 21st August 2016 at 02:06 PM.
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Old 21st August 2016, 03:42 PM   #2
JMFahey is offline JMFahey  Argentina
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Quote:
it's not as quiet as I had hoped. Thinking about re-wiring with Mogami 2330 mini coax.
All I can tell you and hope is encouraging is that "practice makes perfect".

Keep building stuff and progresively this kind of problems will minimize.

Not FULLY disappear of course, you will lways have * a little* background noise one kind or the other, but way less than today.

FWIW when I started with this (47 years ago) , I had the exact same problem, and tried the exact same solutions, including use of solid core wire so it stayed where I wanted it to, also used shielded wire for everything, including filaments, used tight and even twisting, bus bar grounding (then the state of the art technology ) , etc.

All of my friends complained that their SS amp projects oscillated like crazy, usually into self destruction.

Nowadays?: I use standard plain PVC wire, twist only some connections, hardly use any shielded/coax wire, ... and stuff does not hum/buzz/oscillate/catch radio , etc.

Not doing any special effort, just some wiring paths or grounding "do not look right" and simply are avoided.

No black magic involved, simply practice/experience.

Just keep building and youll see these problems minimize

Feel free to experiment with layout and grounding, youl find better ways to do it.

Often if you ground something "there" instead of "here", just an inch away , makes all the dfference.

Its not a *parts* problem if you know what I mean

A practical example: just yesterday, Saturday night, a Musician friend came worried because his Acoustic guitar amplifier hummed slightly.

Never noticed or worried about that because he always used it live, which implies a certain ambient noise level, but yesterdy, a *cold* day, (we are in Buenos Aires, Argentina, and Polar South wind has been blowing for a couple days) he stayed at home and in the silence of his bedroom he started recording a couple songs on his PC ... and background hum/buzz, although slight, now became *annoying*.

After some testing I noticed slightly flexing the preamp PCB, noise level changed a little.

Traced it to a brass mounting post to which the PCB was bolted to, which grounded it to chassis.

I replaced it with a plastic one so as to insulate it and put it out of the picture, soldered a short piece of wire to the PCB ground plane and started touching the chassis to different points until I found a spot, about 2 inches away, where hum/buzz fully disappeared.

Scratched the chassis until I got bright shiny metal and soldered the new grounding wire there, end of the problem.

This is an example of problems which can not be attributed to parts but to the way things are made.
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Old 21st August 2016, 04:29 PM   #3
rayma is offline rayma  United States
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just
Quote:
Originally Posted by wanders View Post
I wired (signal) a tube diy preamp with Teflon jacket, silver plated, shielded twisted pair.
Probably used 60' +/-. The stuff is bulky, inflexible, & hard to work. More important,
it's not as quiet as I had hoped.
Can you post photos of the chassis, and the schematic? That's a whole lot of wire for just one preamp.
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Old 21st August 2016, 07:15 PM   #4
DF96 is online now DF96  England
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I use copper, shielded, PVC insulation. Twisted pair is for balanced connections. In any case, getting the grounding right is the thing to concentrate on.
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Old 21st August 2016, 07:49 PM   #5
wanders is offline wanders  United States
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Quote:
Originally Posted by rayma View Post
That's a whole lot of wire for just one preamp.
The wiring is source input & output to/from front panel. Witb a dozen rca pairs at abour 18" of wire per jack, the footage adds up. (Not to mention waste, screw-ups etc.)

Think grounding advice is probably dead-on. Thd cumbersome teflon wire makes it difficult to work nside the chassis.
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Old 21st August 2016, 08:36 PM   #6
rayma is offline rayma  United States
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Quote:
Originally Posted by wanders View Post
The wiring is source input & output to/from front panel. Witb a dozen rca pairs at abour 18"
of wire per jack, the footage adds up.
I would keep all the input connections at the back panel on a pcb, and mount the selector switch
on it as well, with a shaft extender to the front panel.
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Old 21st August 2016, 10:33 PM   #7
nigelwright7557 is offline nigelwright7557  United Kingdom
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I have fallen foul of layout problems with valve amps.
1/ Keep wiring as short as possible.
2/ Keep valves and audio away from transformers and high VAC.
3/ If using a pcb use copper pours connected to ground.
4/ Beware of nasty charging impulses going into smoothing capacitors, if they get into the ground you will have huge hum. Keep the power supply separate and only connect to audio via output of smoothing capacitor not the other side where the rectifier is.

Its a good idea to use the classic metal chassis with transformers on one side and components on the other side.
The chassis acts as a shield.
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Old 23rd August 2016, 03:05 AM   #8
wanders is offline wanders  United States
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Goid to have this advice and exprience. Thanks all.
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Old 25th October 2017, 09:42 PM   #9
DualTriode is offline DualTriode  United States
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Quote:
Originally Posted by DF96 View Post
I use copper, shielded, PVC insulation. Twisted pair is for balanced connections. In any case, getting the grounding right is the thing to concentrate on.
DF96,

You know the history of things.

Why was silver plated teflon insulated wire specified for aerospace?

I recall reading a post of yours that said that silver plated teflon insulated wire does not benifit audio but has application for UF.

Yesterday I came across half a dozen partial 1000 foot rolls i purchased for $5 a spool.

DT
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Old 25th October 2017, 10:55 PM   #10
wanders is offline wanders  United States
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Fun to read this old thread again. FWIW, I did rewire using the mini coax. In the process I was meticulous in soldering and wire management. Finally got the grounding right too. Took a couple of months to get it right, but its dead quiet and has been flawless for over a year. Knock on wood.
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