Switchable FMV/Bandaxall ToneStack - HOW?

[el_fela]

Hi there! I want to build a switchable tonestack between a FMV and a *James* tonestack for a sunn s100 clone. I thought of using 3 dpdt relays to switch the wires from the tonestacks and to the pots, and a single spst to switch the input from the preamp to the tonestack.

As I know very little about relays, can anyone help me with component selection? The ideal would be something small than can be powered using the filament power (6v?). I really don't know what's available where I live.

I don't know if this has been done before, but I couldn't find anything yet. Any information is welcome.

Peace.

Felipe

[J M Fahey]

I really don't know what's available where I live.

We neither, because, to begin with, you don't state *where* you live
As of switching between FMV and Baxandall tone stacks, in general it isn't possible because one is passive, the other active, *very* different beasts.

Unless you are calling "Baxandall" what actually is a "James" .
Please post schematics of what you are trying to use.

[el_fela]

Hehe I'm from La Plata, Buenos Aires, Argentina. It is actually the James tonestack, I'm correcting that on my previous post. It seems i got caught in tne bandaxall / James confusion-

[Justin Thomas]

El Fela,

I think you should support your friendly neighborhood tech/amp manufacturer. He's one of the best... I'm jealous!
See post #2...

Justin

[el_fela]

Wow, I had no idea. What a coincidence !

[Chuck H]

FWIW I would suggest that you breadboard each and try the amp both ways. Then pick whichever you like because the difference it makes in the overall amp tone will be subtle. The amp will still be using the same tubes at the same voltages, the same preamp topography, the same iron, same speakers, same cabinet, same guitar plugged in, etc. The real world difference between the two types of tone stacks will definitely NOT be like having two different amps in the same box. I'd even venture to say that aside from a small difference in gain and target frequencies that there is no difference because you can alter the circuit of either tone stacks component values to emulate those characteristics of the other type. I'm speaking from my own similar experience WRT how the same tubes, voltages, transformers and speaker just make an amp sound a certain way that cannot be altered significantly. I just think it would be a lot of added circuitry and trouble for not much bang.

[el_fela]

FWIW I would suggest that you breadboard each and try the amp both ways. Then pick whichever you like because the difference it makes in the overall amp tone will be subtle. The amp will still be using the same tubes at the same voltages, the same preamp topography, the same iron, same speakers, same cabinet, same guitar plugged in, etc. The real world difference between the two types of tone stacks will definitely NOT be like having two different amps in the same box. I'd even venture to say that aside from a small difference in gain and target frequencies that there is no difference because you can alter the circuit of either tone stacks component values to emulate those characteristics of the other type. I'm speaking from my own similar experience WRT how the same tubes, voltages, transformers and speaker just make an amp sound a certain way that cannot be altered significantly. I just think it would be a lot of added circuitry and trouble for not much bang.

Thanks Chuck, I get it, but I differ... 2 tonestacks means 2 diferrent eq settings, and 2 different ways of control.

James and FMV are VERY limited, but also very simple. I prefer to have 2 tonestacks instead of a graphic 5 band. Besides, it would allow the amp to be used by different people for different instruments, for example a guitarist using a guitar is probably going to feel more confortable with the more familiar FMV tone control, while a bass player might find it unsuitable for bass guitar. Also, this amp I built, using FMV TS, sounds great with a fender deluxe kind of speaker. With the FMV tonestack you are certainly able to get some classic tones from the amp I built, and the James TS is more useful, at least to me, for bass. With the James tonestack you are able to get a flat response which is good for keys and voice.

So the goal would be to make an amp thats suitable for different instruments, or at least bass, guitar, keyboards and voice, using different speaker systems or cabs.

Is it too much work? I don't know yet, but I wouldn't mind building a dual tonestack pcb style board with relays on it. Sounds interesting at least, doesn't it?

Cheers,

Felipe

[Tom Phillips]

An idea for you...
Consider adding another preamp section to your amp. Then you can have a preamp with each tone stack and each preamp can be optimized / customized as desired. Do you have room to do that? It doesn't appear that you need to switch on the fly. If that's true then you can just switch by plugging in to a different jack or even run both preamps in parallel for additional setting versatility.

[J M Fahey]

What Tom Philips said, you can even add an extra channel (how's that for versatility?), even a completely different one: a Fendery/Marshaly one and an Ampeg type, each with the proper tone stack.

That said, *if* the amp drives the tone stack from a cathode follower (didn't check), it can drive *both* stacks at the same time, you then just pick one or the other with a simple SPDT switch or relay.

[el_fela]

What Tom Philips said, you can even add an extra channel (how's that for versatility?), even a completely different one: a Fendery/Marshaly one and an Ampeg type, each with the proper tone stack.

That said, *if* the amp drives the tone stack from a cathode follower (didn't check), it can drive *both* stacks at the same time, you then just pick one or the other with a simple SPDT switch or relay.

Yes I can see that what I want is actually what Tom says... and that everyone think that what I want to do isn't such a great idea, but at least is pretty original. Please help me start on the relay stuff! I'll check simple channel switch info .

Felipe

[el_fela]

An idea for you...
Consider adding another preamp section to your amp. Then you can have a preamp with each tone stack and each preamp can be optimized / customized as desired. Do you have room to do that? It doesn't appear that you need to switch on the fly. If that's true then you can just switch by plugging in to a different jack or even run both preamps in parallel for additional setting versatility.

Hi Tom, that would be awesome, but I should have thought that beforehand. I cant add new stuff nor drill more holes

[J M Fahey]

At least do you have enough front panel holes for all pots?
AFAIK you need 3 fror FMV (Treble/Middle/Bass) and 2 for James (Treble/Bass) .

If you *think* to use the same pots for both, but switching caps and resistors, forget it.

[dchang0]

It is worth asking, since it could save you time and money: have you tried playing around with the Duncan Tone Stack calculator to see what the different stacks would look like on a graph?

You might be able to rule out a tone stack based on the visible changes in the curves as the knobs are virtually turned.

And you might also find out that there isn't enough of a difference in the curves between your choices to warrant building both and switching between them.

TSC

[J M Fahey]

I have used both ... or to be more precise all 6 (Black/Silverface - Marshall/Tweed - James (Ampeg) - VOX - Baxandall - Big Muff) since forever, often trying *all* or most on a new design, and the nutshell is:

1) if you want that, all can be designed so "on 10" you achieve the same curves
In fact you can even design a *fixed* 2 cap, 2 or 3 resistors net which achieves the exact same curve, only that it's "fixed" of course.
I often do that for 2 purposes: sometimes I need that specific curve somewhere (before/after distortion, or to correct unliked reverb tank or speaker curves os simply as "seasoning")

2) the main difference lies on how they *respond* to your touch, and on interactivity:

a) F/M/T are very interactive, and boosting highs definitely cuts Bass in any real situation (not very visible in TSC because it basically analizes tone stacks on their own, isolated) .
Good in Guitar amps played loud because boosting highs cuts mud and fartiness, makes overdrive much cleaner.
They are also basically boost only ... not too bad in a Guitar situation.

b) Vox type is unique: Bass control from 0-5 rises bass ; from 5-10 also cuts mids *heavily* ...no way you can avoid that.
Also basically boost only .

c) James/Baxandall : Treble and Bass are beautifully independent, predictable, smooth, symmetrical, and also provide *strong* boost and cut.

All this heritage from their Hi Fi roots, and in general a problem with lazy designers, because you just can't throw any design you found into your amp and expect it will work, the probability of boosting way too much Bass and cutting too much Treble is there, to mess with your sound.

Of course, with some care, you can exactly duplicate any of the above.

3) Big Muff looks like a joke, but with carefully chosen values it can be very useful and musical.
Example: the single tone control knob found on Dr Z amps, not exactly it but very close.
VERY clever designer, many complain "how can this guy call "boutique" amps as basic as can be, some with not much more complexity than a .... Champ ? " ... yet they sound and perform killer

A similar simple one: Marshall 20W (inherited from the Watkins Dominator)

4) almost forgot: other tone control which "shouldn't work" ... given that Bass and Treble are "cut only"
the one found in Matchless amps ... yet it's killer and VERY musical .

Again: no black magic but endless tweaking into perfection.

[Chuck H]

Hi Tom, that would be awesome, but I should have thought that beforehand. I cant add new stuff nor drill more holes

Is this to say that you can't add another volume knob? You could make the FMV stack the treble and bass only version with a fixed mid resistance. Still versatile and that would free up a knob space.

Or is it that you only have holes for one channel and one stack and are planning to use the same pot values for both? In which case you could use dual ganged pots for the tone stack and volume controls with one gang for either "channel". If you weren't going to have individual tone stacks anyway you don't lose any versatility by doing this. Not a channel switcher per se, but still two different amps on a switch.

I appreciate your position, but if all you change is the tone stack the amp will sound basically the same, but with different frequency tuning at only one gain stage. And you could do that by just adding a couple of boost/cut switches. And you can get pretty damned flat with the FMV tone stack too. It just requires weird settings that might bug you to look at. Aesthetics mean less to me perhaps, but I don't mind extreme settings. Some people get bent if they can't get their tone withing certain preconceived knob settings. The circuits, however, don't care.