Wednesday, 22 February 2012

Tag board vs PCB construction.

Whilst I have a deep loathing for voodoo electronics one conclusion I have arrived at is that tag-board construction will produce a different tone from the same design based on a PCB, and I believe that tag-board can prove best. So how did I arrive at this conclusion? 
I built a tag-board (not a turret board) based amp a while back with a fault. It was missing a wire that connected the preamp signal to the power output stage. So the amp was dead, right? Well no, it carried a very trebley signal at a low level to the speaker just because the components on the tag-board are forced to be so close together. This isn’t voodoo its called crosstalk and is well understood. I found the fault and the amp sprang to life. So it has a feed-forward path and a bit of treble gets added from somewhere to somewhere else, well so what.   
Well try an experiment, find a HiFi loudspeaker that has a Bi-wire option and play something familiar. Now disconnect the tweeter and have a listen, half the sound disappears and what is left is muddy and pretty torrid.  Lastly disconnect the woofer and connect just the tweeter.  It’s all treble as expected but the volume level compared with the woofer is fractional. Conclusion:- A small amount of treble carries the weight of the sound. Now back to the tag board where co-located components will cross-talk and bleed treble forward in the amp. I loaned the amp to a friend to check it out at volume, he concluded that it had an “air” …. and I think I know where it comes from.

1 comment:

  1. I think you are correct here, in that a bit of crosstalk (in places) will give an amp some "air".

    This is mentioned in The Guitar Amp Handbook, in the section on simple Fender amps, and is mentioned as important by the fellow who makes clones of Champs at Victoria, IIRC.

    Also Alexander "Howard" Dumble reportedly (by Ken Fischer) liked the sound of rosewood circuit boards, and as wood is quite hygroscopic I imagine such amps not only had "air", but this quality almost certainly changed with the atmospheric humidity - which may be okay when you live in a stable environment or a desert, but a variable environment would probably influence the amp's tone, and in a terribly humid environment, that "air" might get to be a problem!

    [...Which reminds me of why Goa (trance) was made with tape players and MIDI equipment - because records were too sticky to play in the heat of tropical coastal India! Xp ]

    Lastly, point-to-point amps are often said to be superior to other construction methods re guitar amplification; I have heard it said that p-t-p amps have more "air". Of course, p-t-p amps also have a high incidence of problems with crosstalk (and apparently, when laid out sensibly, some advantages).