PCB construction technique question

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FotisGR

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Jun 11, 2005
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I have some questions about pcb technique for mic pre applications and special for tube mic pres.
a. Is there an audible reason or somithing else for point to point vs pcb construction?
b. What about double sided pcb ? I mean that the connections will be on bottom side and the up will be the ground. (Moslty used at RF designs). Is this helpfull for avoid ground loops on tube mic pres? I build 2ch 1176 and 2ch green with this technique with no problems but with tubes i am little scared...
I am going to design a pcb for Slowblow (ssssss, don't tell it to him...) but i am not sure about resaults...
All opinions welcome
Fotis

Avoiding confussion , pcbs will not been for sale only for share....
 
I have seen some PCB guitar amp boards were the pcb mount socket pin solder joint went bad. This could have been from vibration an/or heat. The Cu might have been to thin as well

I have not made a PCB for a tube unit but I would use the thicker Cu and make the traces to the fil and any place that might have some heat as big as I could, to act as a heatsink
 
If you don't have much experience with PCB design it's generally safer to stick with PTP, it's easier to rearrange grounding/high voltage and signal wires to minimise hum etc. Once on PCB you're stuck with what you got.
 
You are confined to planes with PCB's so you lose a degree of freedom. It's tougher to control a.c. heater fields compared to tightly twisted wires, for example.

However, with PCB's the results are more consistent than any but the most precision hand-wiring.

Having one layer of a two-sided board devoted to a ground plane can help confine high frequency signals and act as a partial shield against external electric fields.

Another, subtler effect can be due to the lower quality dielectric properties of typical PCB material. This will typically be significant only at high impedances in audio, and very high frequencies in RF work. Improperly cured glass epoxy bedeviled Tektron*x years ago when they tried to integrate small capacitors on the PCB as part of the copper: they dubbed the signal distortions "hook".

There are some very low loss board materials available now, although they are pricey, and many board houses don't know much about using them. Madrig*l touts the use of some esoteric board material in their audiophoolery preamps.

Air, by comparison, is a nearly perfect dielectric until potentials get really high and you start getting field emission, or worse, arcing---not usually a problem for our work. But a circuit in air has to be supported mechanically somewhere, and then there's the microphonics from vibration of conductors with a voltage on them.
 
If you know what you are doing it's better with pcb's and you can get more predictable results. It's also an advantage to keep things compact in order to reduce stray inductances' and also all sorts of loops, less pickup of electrical and magnetic fields. I'm not a fan of P2P but this may have something to do with that I'm designing pcb's for a living :grin:

Still, if the amp consists of few parts it may work pretty good with P2P.
 
I can't speak for tube stuff but my SS designs behaved much better (esp. regarding stability) on double-sided PCBs than with P2P. And I don't consider myself an expert on board design.

Samuel
 
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