SO ~ the PRE-AMP in an amp, why do they sound so different ??? .

jpfamps

ICBM said:

The funny thing is that the Vox Top Boost tone stack *is* a Fender/Marshall type - with a fixed mid control - but has a mistake in it... the bass pot is grounded when it should be floating, so as the bass approaches full-up it becomes a mid cut as well. It seems likely that this is because it was copied from a Gibson schematic which has this mistake in it. Chinese whispers!

This mistake makes it very effective around 2-3 o'clock on the bass knob, depending on where 'zero' is set, and since it's also quite interactive with the treble control as well, you get a huge amount of variation from just the two knobs.

Top boost circuit is an EXACT copy of the Gibson GA-77 and GA-70 tone circuits.

Handsome_Chris

jpfamps said:

Handsome_Chris said:

ChrisMusic said:

*Not* limited to the following:

Whilst here, what tone stacks and circuits get used in guitar (and bass) amps then, I see the Fender & TMB version mentioned, and the James circuit (whatever that is).  Do I take it that Baxandall circuit is limited to use in HiFi type situations then ?

I believe that the Baxandall and James are one in the same.

Baxandall and James are NOT one and the same.

The James circuit is often incorrectly referred to as the Baxandall; the the circuit invented by Peter Baxandall superficially looks similar but employs negative feedback so works in a different fashion to the passive James controls.

Sorry.

Handsome_Chris

@JPFAmps, I see what I've done wrong.  @ChrisMusic this should clear things up over the Baxandall and James issue.

http://static.cinemagia.ro/img/db/actor/01/05/35/helen-baxendale-633863l.jpg

http://www.forty5.co.uk/wp-content/uploads/2014/05/featured-james-band-163457283.jpg

ChrisMusic

Lol, ya mad bugger   

ChrisMusic

So, just to re-cap.

( see what I did there, a little vintage amp related pun, ok,ok, don't milk it or you will die-electric )

That's a complete phase inversion on the Baxandall.

I must say, Peter does look somewhat better after the sex change though.

And it seems with too many components added, the James stack now has multiple personality disorder.

Or is that just adding characters ?

There seems a little less "hair" with this version too.

ChrisMusic

What this discussion needs is the ability of one man to simplify the complexities of guitar amp designs over the last fifty or so years, someone who we know can reduce and explain those things concisely in an understandable way to us mere mortals.

With a talent to bring out the salient design features, and relate that to the sounds we guitarists are chasing.

Maybe someone who has lots of amps passing through his hands and needs to review the schematics to keep breathing life into them.  And who has the hunger to understand how everything interacts.

I am sure there is someone here with the unique talent to move this discussion forward, further into the light of knowledge.

Now who could I possibly be thinking of ?

Handsome_Chris

Bruce Keir?

ChrisMusic

Good guess, we could get the ISF knob explained I suppose, but I was thinking of a more local "star" actually.  

ecc83

Handsome_Chris said:

Bruce Keir?

No.  I think it is safe to say that Bruce's comment about 95% of the discussion in this thread would be ..."Load of |%^&*g Bollocks!"

(not my bits naturally!)

It is said (anon?) that " Any activity or process with more than seven variables ceases to be science and becomes Art".  Then a year or so ago I read  some top "studio gear" modellers saying that the overdriven guitar COULD probably be modelled perfectly but it would take far too much processing power to be practical.

So, in 10 years time when you can have an i7 for 5quid and a laptop will be capable of running the economy, modelling amps will be just as good as the hot jobs. Of course the V snobs will never have it! ...There are peeps that have never moved on from 78s and thorn styli.

Dave.