Switchable FMV/Bandaxall ToneStack - HOW?

[Chuck H]

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

You can't make an amp that is equally suitable for P.A.. bass and keyboard applications and expect it to sound like a guitar amp no matter what tone stack you use. Maybe you can get a clean tone that's close, but that'll be it and far from perfect. And you can't make an amp that's "right" for processing a guitar signal that also sounds good for sound reinforcement or bass/keyboards. Perhaps at very low output, and again, far from perfect. They're just very different applications. A guitar amp is a signal processor. A P.A. is a signal reproducer. A bass/keyboard amp is like a P.A. Sometimes with added frequency tweaks and/or compression. If someone could make an amp equally suitable for all instruments they would be doing it. And there are greater minds than yours or mine that would have done it by now if it were possible. About the best you could hope for in attempting to conglomerate duties like this wouldn't be an amp that is equally bad for everything rather than equally good. They also don't make:

A commuter car that's good for hauling hay.
Cuisine that is both a sweet dessert and a healthy entre.
A gun that is both useful and safe.
Decaffeinated coffee you can stand to drink.

Ok, I just threw in that last one, but you get the point. To this end I think the suggestion of different preamps, at least, is unavoidable for your end goal. You just can't turn a bass amp into a guitar amp by changing the tone stack and vice versa. Not without it ending up a poor compromise for either anyway.

Sorry to be all "Captain Buzz Kill pissing in your Cheerios" but my goal is actually to help. I can't say what amp is right for you. Everyone has their own preferences. I can say that most guitar players wouldn't be happy playing through a SVT just because it has a FMV tone stack and most bass players wouldn't be very happy playing through a tweed Deluxe just because it has a James tone stack. Forget trying to sing through either

[MarkusBass]

Felipe,

You haven't specified whether you are going to have two different sets of potentiometers in your amp. I assume that yes, since James and FMV tone stacks use different pots. So I assume that you have space for two sets of pots in the front panel of the amp.
I this is the case, please note that a typical tone stack has input, output and ground connections. If you leave the ground connection permanent (there is no need to switch it), you are left with input and output which should be switched in and out of the preamp. This can be achieved with single DPDT relay or switch. If you decide to build a separate preamp for the second tone stack, you need only one SPDT switch, or relay. I suggest to contact Juan regarding this because it's very basic wiring and he will do it in few minutes.

Mark

[Chuck H]

Felipe,

You haven't specified whether you are going to have two different sets of potentiometers in your amp. I assume that yes, since James and FMV tone stacks use different pots. So I assume that you have space for two sets of pots in the front panel of the amp.
I this is the case, please note that a typical tone stack has input, output and ground connections. If you leave the ground connection permanent (there is no need to switch it), you are left with input and output which should be switched in and out of the preamp. This can be achieved with single DPDT relay or switch. If you decide to build a separate preamp for the second tone stack, you need only one SPDT switch, or relay. I suggest to contact Juan regarding this because it's very basic wiring and he will do it in few minutes.

Mark

Thank you Mark, for addressing the OP. I had intended to do that, but simply got side tracked before I finished my peripheral observations. Just to add then...

It might be necessary to include some resistors across the switch to avoid popping. If that's important. Another thing I'll note is that on the James diagram used on Duncan TSC there is no gross DC blocking cap. So there is a DC path to ground and through the circuit if it were to be implanted that way. Including a gross DC blocking cap would be necessary in order to do the switching as suggested. It will also cause a LF roll off at some frequency specific to that cap value @ impedance. This can skew the "flat" response of the James stack. Perhaps somewhat equalizing it to the FMV stack. A bad side effect if the flat response difference is the goal.

[MarkusBass]

It might be necessary to include some resistors across the switch to avoid popping. If that's important.

Of course. I wouldn't implement it without, let's say, 10 MOhm resistors across the switch/relay. This is something that I'm sure Juan knows.

Another thing I'll note is that on the James diagram used on Duncan TSC there is no gross DC blocking cap. So there is a DC path to ground and through the circuit if it were to be implanted that way.

Duncan TSC does not show the cap but every practical circuit has it. Otherwise, you can only imagine scratching in the amp when turning the Bass pot. Usually, it is 100nF capacitor and it does not change the frequency response of the tone stack. Please check Selmer Stadium amp schematic as an example:



The same applies to Ampeg B12 (22nF capacitor), Ampeg B15 (100nF capacitor), and most probably every amp with James tone stack.

Mark