The Q-Tron, The Adaptor, And Dying Battery Simulation.

[Higgie]

Hi, I'm pretty new here. Been Reading alot, but not posting. Anyway, on to the point....

Anyone here who has a Q-Tron will know that it only operates by a Power Supply, and that it is 24V DC. Now, what I want to do is Modify the power supply for "Dying Battery Simulation" in an attempt for that "Sir Psycho Sexy" Sound. Now, Firstly I would like to know how I would do this. I e-mailed the guy from SmallBear Elec and he said:

Generally speaking, dying battery simulation is simply putting a potentiometer in series with the power supply output to simulate a high internal battery resistance.

But he said he's never experimented with a 24V adaptor and was unsure of the proper value of resistance. I was hoping somebody here would know the answer and possibly be able to help me do this project. I have some experience in Soldering and Electronics, so it shouldn't be THAT hard.

Thanks guys,
James

[Mark Hammer]

Um, I'm not so sure anything that operates from a 24vdc supply is really a good candidate for "dying battery" simulation.  Seems to me that the pedal is engineered for maximum cleanliness.  Moreover, dying battery effects are usually the sort of thing when you start out with 9vdc, and dropping to maybe 7.5 makes a big difference in the performance of specfic transistors.  There is a humungous gap between what the power supply provides and what would likely detract from the circuit's performance enough to produce a drastic (but predictable) change in performance and tone.

[Higgie]

Thanks for the reply. But would it be possible? Because if it is, then I wanna do it

[sir_modulus]

it is possible....but I don't know how to do it...so bump!

[Higgie]

Thanks for the bump mate

[Travis]

The LM317 can put out regulated voltages of up to 37V, as I recall.  Use pots or trimmers, and you can make a variable psu.  Check GEO for the rest.

[Johnny G]

the way that the whole dying battery thing works is pretty simple

as batteries get older they get a higher internal resistance from all the dead electrolye etc inside them.

now this internal resistance acts exactlly like a resistor in series with the battery. as the effect is going its drawing a certain amount of current.

ohms law states that a given current through a given resistance = a given voltage drop across said resistance.

so lets say you have your fuzzbox and you put a 5k pot in series with a shiny new battery. for arguments sake the fuzz draws 3 ma, the battery is dead on 9 volts output and the pot is set to 1k resistance in series

the 3ma for the fuzz has to go through 1k resistance IR = 0.003 * 1000 = 3 Volts

so the fuzz will only see 6 volts. obviouslly these numbers are open to much changing


so for you to work out what value you need the easiest thing to do would be to work out average current draw and the voltage range you want to be able to change over. then just plug the values into ohms law

[Higgie]

Thanks alot mate, that should be very helpful

[Higgie]

So theoretically could I mod the Power Supply to have a switch to turn on/off Dying Battery Sim. and a Pot to adjust how strong I want the Dying Battery Sim. to be?

[Paul Perry (Frostwave)]

So theoretically could I mod the Power Supply to have a switch to turn on/off Dying Battery Sim. and a Pot to adjust how strong I want the Dying Battery Sim. to be?

Yes. I would start with a 1K or maybe 10K pot, B (linear) taper if you can get it. (yes, it's going to be a low value). I'll be interested to know what happens!

[Higgie]

Cool. Thanks. Now, just gotta take this Power Supply apart and find out where to make the modifications. :twisted:

(It would be a good idea to buy another power supply, just incase I @#$% it up, right? :p)

[Johnny G]

Cool. Thanks. Now, just gotta take this Power Supply apart and find out where to make the modifications. :twisted:

(It would be a good idea to buy another power supply, just incase I @#$% it up, right? :p)

it would probablly be most wise indeed. we never intend to make mistakes, it just happens that way

[puretube]

be aware, that it`s not "another fuzz box", which will gladly react the way you suppose to the crapping out battery,
but rather a state-variable filter, which might simply not function the way it`s supposed to, or not function at all, or won`t "move" the frequency properly anymore, when facing an intended "power-failure"...

you can check out how it will sound/react, when you unplug the wallwart while playing...

[Higgie]

Well it only runs on the Power Supply, so taking it out while playing just turns it off, since thats removing ALL power from it. Only taking a bit off will be different than removing the power source altogether.

[Paul Perry (Frostwave)]

Higgie, what he means is, if the power supply has a large enough cap inside, when you turn off the power, there is a second or so where the voltage sags down & you might get some idea from that.

[puretube]

right - that`s what I intended, tnx Paul.

upon 2nd thought however, when the large cap(-s) is (are) situated in front of some voltage-regulator(-s), the voltage after it (them) will simply shear off;
so this experiment might not work here... (?)

[Higgie]

Yeah I think that maybe the case. I've just had a post from another forum I'm on and was told this:

Dying battery emulation? You could get a cast metal box from Maplin, a DPDT footswitch, some stripboard and a coupla 1k 1W resistors and knock up something to achieve the same thing for about a tenner!

1W resistor? Is that 1 Watt? and also if I was going to make a Dying Battery Stomp Box I suppose, how would that work in regard to powering the Pedal?

[Mark Hammer]

Once again an "umm".  Are we sure that the intended effect IS accomplished with a starved power supply, or are you just going on the basis of something like a rumour circulating on H-C?

It can be the case that some sort of envelope-controled filter IS influenced in the desired manner, but that may well be the filter section only, or it may be some specific constellation of circumstances.  Keep in mind that underpowering the envelope follower is not going to result in much of an envelope signal to drive/sweep the filter.  Perhaps what is needed is a means of separately underpowering the filter per se, while at the same time adequately powering the input and output stages and the envelope follower.

[loki]

I know what' you're looking for Higgie.... the problem is that the sound achieved in RHCP's "Sir Psycho Sexy" was obtained with a vintage Mutron III with dying batteries. It's true the Q-Tron is a quite similar, if not a successor of the Mutron III, but i believe (correct me if i'm wrong) that their schematics are not exactly the same.
Plus the Mutron III was powered by 18v (two 9v batteries) while the Q-Tron requires a 24v power supply.
I mean, you can try if it works... but know that even Flea himself got that sound just once out of luck, 'cause the batteries were low, once he replaced them he never got it again and stayed with the track he had previously recorded. It was basically just a one off thing. And for the same part live he uses a Q-Tron, without low-powering it.

[Higgie]

Yeah I suppose so. Thanks alot for all the help and info guys. Anyone know the settings he uses live?  :twisted: