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

jpfamps

Handsome_Chris said:

Do Carvin and Orange generally use the James tone stack as opposed to the Fender/Marshall tone stack?

The classic 70s Oranges generally use James tone controls (technically the controls aren't wired as a "stack" so probably shouldn't be referred to as a stack.

Not sure about Carvin.

Amongst other amps that use the James circuit are many Ampegs (eg B15, SVT), and a few Fenders (eg Blonde Twin).

I'm sure there will be Gibson's that use the James tone circuit as they have tried most circuits.

ICBM

jpfamps said:

The classic 70s Oranges generally use James tone controls (technically the controls aren't wired as a "stack" so probably shouldn't be referred to as a stack.

Most of the modern ones don't though, the Rocker/Rockerverb and AD series at least use 'Marshall-type' TMB stacks, and the Tiny Terrors have a crude Vox 'cut' type tone control.

ecc83

"FMV stands for "Fender Marshall Vox" and is used to describe the classic treble/mid/bass tone circuit (aka "tone stack") used in Fender and Marshall amps, although NOT Vox (so should really be called FM tonestack, or even just F as Marshall nicked it from Fender)."

No, I was just referring to the valve configuration not the tone stack.

Dave.

ICBM

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.

Clarky

Handsome_Chris said: As to why pre-amps sound so different, Cliff Chase (FAS/AF2 boss) said something like "A lot of amps are very similar; however, manufacturers put there own slant on tone stacks (ie component values) to give them their character". The advantage with digital modelling is that you can approximate the effect of adjusting stuff.  Our very own Mr @Clarky like to tinker with virtual amps to great affect. One of his beauties is a JCM800, with the master volume after the phase inverter, with I believe is a real world mod: It is a high gain monster. It does need a bit of judicious EQing on the low end or the bass goes a bit flubby.

that 'hot JCM800' is great ain't it.. it's kinda like a Plexi but with a little more bite..

Cliff [from FAS] was saying that it's quite a common real world mod..

I personally prefer that mod on the Boogie MkIIC.. it's like a 5150 mk3 Red channel but with a little less smoothness.. makes it kinda rough around the edges.. which I think is quite cool.. but like with the Dual Rec, if you want to run it hot, you'll need pre-EQ to keep the lows tight..

ChrisMusic

Hey @ecc83, I am still in the dark over this, please help my one existing tired little grey cell out on a Sunday morning.

I swear I won't sleep till I understand   :o3

FMV = ???

ChrisMusic

robinbowes said:

This is a damned good book too: http://www.ampbooks.com/home/books/bassman/

Another data point... I have an Ampmaker WF4 build. I can totally change the character of the amp (ie. Marshall vs. Fender) by changing just one capacitor...

Thanks for your book recommendation @robinbowes.

I am intrigued by your Ampmaker mod.

Could you add a little detail on where and what the cap change is and how it affects the circuit please ?

ChrisMusic

Handsome_Chris said:

I think that if you are trying to buy an amp to get what you want, and you don't know what you need to get what you want, then software modelling may be a starting point (I am now stepping into my fire suit).  It may give you a starting point as to what amps, cabs 'n' fx  you would like to look at.  It may also give you the opportunity to try stuff you hadn't thought of.

I like your thinking.

Interesting change of perspective there @Handsome_Chris.  I had been thinking that a better understanding of real world amps, and the topologies and components that drive them, would be a useful background when I finally get into playing around with modelling technology.

I like the way you have turned this around to look at understanding real world amps by using modelling.  I can see that has great potential, as long as the modelling is true to the analogy.  This could get expensive, but I have to admit, I do see an AxeFX in my future.

The ability to add virtual mods to amps is a powerful argument in favour of trying it out.  I guess that if the topologies and parameters are flexible enough you can build amps which have no real world analogue.  That sounds exciting, and maybe makes for exciting sounds too !

I think that resolving my understanding in either, or probably in both ways will be ultimately rewarding.  I still think that having a couple of quality real world amps is probably a good way to stay grounded throughout the process, and maybe beyond...

Hmmm now do I dare look at that bank balance   ^#(^

ChrisMusic

Thanks to everyone for your comments so far, whilst not that definitive, there are some useful, if slightly obtuse references, or maybe that's just me not "getting it" ?   A bit more background would be really useful for me, please, pretty please.

*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 really get ecc83's comments about commercial production and the drive to minimise costs, does that give CAA, Friedman, Lazy J, et al, the scope to improve tone just by adding marginal complexity and cost ?  Is it that simple ?

Is it really as simple as just gain stage and tone stacks, and if so what are those Magix that get sprinkled in some of the best sounding amps ?

And I suppose while I am here, what is it about a valve that creates a tone that still seems unmatchable, even by J or MOSFETs, which I assume are the closest analogue ?

robinbowes

ChrisMusic said:

I am intrigued by your Ampmaker mod.Could you add a little detail on where and what the cap change is and how it affects the circuit please ?

Look at this circuit:

(from this link http://www.ampbooks.com/home/classic-circuits/fender-champ-5e1-preamp)

The gain of each stage is determined by the value of Rk. However the first stage has an additional cap, Ck, which affects the gain in a frequency-dependent way. By changing the value of this cap, the pre-amp can sound Fendery (higher value, eg. 125uF) or Marshally (lower value, eg. 0.68uF).

R.

Handsome_Chris

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.

ChrisMusic

Thanks for the clarification @Handsome_Chris

ChrisMusic

robinbowes said:

ChrisMusic said:

I am intrigued by your Ampmaker mod.Could you add a little detail on where and what the cap change is and how it affects the circuit please ?

Look at this circuit:

(from this link http://www.ampbooks.com/home/classic-circuits/fender-champ-5e1-preamp)

The gain of each stage is determined by the value of Rk. However the first stage has an additional cap, Ck, which affects the gain in a frequency-dependent way. By changing the value of this cap, the pre-amp can sound Fendery (higher value, eg. 125uF) or Marshally (lower value, eg. 0.68uF).

R.

Excellent reply, I appreciate the detail, and especially the diagram, it all aids understanding, many thanks @robinbowes.

Handsome_Chris

@ChrisMusic, you're welcome. Do you understand how inductors and caps interact with frequencies?

ChrisMusic

@Handsome_Chris, back in a far distant galaxy, may eons ago !

A lot of water and a lot of bridges since then.

I am slowly getting my head back around all this stuff again.  So discussions like this really help regain some of what is clouded by the mists of time.

That's another way of saying "don't hold back on the simplistic explanations" but " "don't be frightened of added complexity either", ultimately, the full story is where I want to be.  Whatever it is, it will sink in, and can be researched, or maybe explained further in this thread I am sure.

That is an approach which I am sure will help others on here who are not to familiar with amps etc, but would really like a better grasp too.

robinbowes

I stumbled across this site while looking for details to reply to you previosuly:

http://robrobinette.com/AmpBuild.htm

http://robrobinette.com/5e3_Modifications.htm

http://robrobinette.com/How_Amps_Work.htm

R.

ChrisMusic

Thank you so much @robinbowes, I will work my way through them, cheers for the links  

ecc83

"And I suppose while I am here, what is it about a valve that creates a tone that still seems unmatchable, even by J or MOSFETs, which I assume are the closest analogue ?"

Some in the industry will say "nothing" i.e. it IS possible to create very good tones using solid state devices. Then, as greater computing power becomes even more available and affordable, modelling will blur the lines even further.

But, it is a fact that valves work in a different way to transistors. For one thing valves can draw "grid current" (or mostly not. Get Merlin's book ffs!) and there is no equivalent mechanism in transistors. Bipolars pull an input current all the time.

Triode anode current is sensitive to voltage (and hence they have intrinsic NFB) transistors are virtually immune to collector voltage variation.

There is really no sstate equivalent to the pentode tho' few pre amps use them.

Dave.

ChrisMusic

Brilliant, that makes sense @ecc83, great response, cheers.

And I would never have guessed the bit about Triode anode current's sensitivity to voltage either.  Suddenly this all makes a lot more sense.  My appetite for knowledge is truly whetted now.  

jpfamps

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.