Effects with 5,5V (or 5V) Supply voltage

[WhenBoredomPeaks]

I made a circuit which uses microcontrollers and other ICs and it can interact only with 5v-5,5V signals. If it will get a stronger input signal it will die.

Now i think if i don't use a booster, and i keep my effected signal as loud as my clean signal then my effected signal won't be stronger than my clean signal. And since pickups outputs around 1V then my effected signal will be around 1V too if i keep it at the same volume as my clean.

However internally before the volume pot attenuates the signal, in some effects like overdrives and fuzzes, the signal can be stronger than 5V right?

So what if for maximum "security" i would make an effect which operates on 5,5V. Actually i wanna make an EQ. Now if i can get an Opamp which can work on 5,5V, then making an eq with 5,5V supply is possible right?

I can loose headroom only this way i think. So if i get a stronger than 5,5V input signal then it will distort and or die.
I have an EQ pedal but i have never boosted anything by more than 5dB with it so and lot of the times i use it for cutting frequencies so a weaker 5,5V EQ could be work for me, right?

(to make the whole thing more understandable, i wanna substitute the EQ pots with digital pots to be able to save EQ presets. i got the digital pot part working but i have never hooked up it to real guitar circuits, because i fear that their 9V supply will destroy my pot, i am just fading leds and stuff with it.)

[gtudoran]

Well... why don't you use 9 or 12v supply and regulate with LM7805 the 5v supply for the uC? Just a thought. And what are the operations that you do with the signal and uC? do you do any ADC? or you controll some devices with the uC?

Best regards,
Gabriel Tudoran
Analog Sound

[WhenBoredomPeaks]

Well... why don't you use 9 or 12v supply and regulate with LM7805 the 5v supply for the uC? Just a thought. And what are the operations that you do with the signal and uC? do you do any ADC? or you controll some devices with the uC?

Best regards,
Gabriel Tudoran
Analog Sound

The power supply is not a problem, i have some 5V regulators, actually i use an arduino as a uC which have an on-board regulator so you can give it a 9V supply, it will regulate it to 5V internally. But the uC will just control the digital potmeter. The problem is with the digital potmeter. The datasheet said that the strongest signal which can hit the potentiometers wiper and two other legs' is the same as the digi pots supply which is 5V. This means if i have for example a SHO (Super HardOn booster) which capable of a 8-9V output and that strong guitar signal hits my digi pot, then the pot will die.

I wanna use the uC to control a digi pot. This digi pot have the same 3 legs as a normal pot. So instead of wiring real potmeters into the circuit, i would connect the digi pots legs there. (this digi pot actually have 6 pots inside) Then i can store different resistance values in the uC (those values will be sent to the digipot) and scroll through them like a preset EQ and other smart things. The circuit would be an EQ circuit.

[Gurner]

I've hit similar problems - ie digital pots normally being confined to about 5.5V supply max, but I'd have liked to pipe a signal through that's rail to rail on the 9V analogue side.

My solution is just to push a less hot signal through the circuit - not ideal, but you got s to work within the limitations of the components on offer.

(btw I use LDOs to regulate the 9V down to 5V - way more battery friendly, but the cost is noise/output impedance of the regultator.)

[Taylor]

Technically you could use a compander setup: compress before the mcu, expand after. In real life I think you should just run your opamps and whatever else on 5v and not hit the effect with anything bigger than 5v peak to peak.

I can't think of any reason to run a SHO before something with only 5v headroom, anyway, unless you are trying to clip the 5v circuit. Maybe digital pots clip interestingly? That might be the next clipping fad. Replace tubes with digital pots... 

[darron]

so you are worried about a signal too hot hitting your chip and damaging it?


i suppose the best thing to do which is really easy is to make sure the signal gets hard clipped JUST below the 5V line. this would be very easy with a couple of 4.7V 1N4732 zener diodes going to ground back to back at the input (then maybe follow it with a 100ohm-1k in series with the signal just to be safe. if you already have a series resistor there for RF filtering or something then put them before that.

i think this is what zvex actually did to protect the SHO which kept dying from static electricity when plugging in a cable....

other than that your idea would be valid, if you had the signal go through an opamp buffer or boost just before your effect and fead it only 5V then it should have a limited headroom and clip before that. but this may be over processing the signal?

[WhenBoredomPeaks]

@Taylor: that was just a worst case scenario (a booster before this)

@darron

so you are worried about a signal too hot hitting your chip and damaging it?

yes

i suppose the best thing to do which is really easy is to make sure the signal gets hard clipped JUST below the 5V line. this would be very easy with a couple of 4.7V 1N4732 zener diodes going to ground back to back at the input (then maybe follow it with a 100ohm-1k in series with the signal just to be safe. if you already have a series resistor there for RF filtering or something then put them before that.

i think this is what zvex actually did to protect the SHO which kept dying from static electricity when plugging in a cable....

other than that your idea would be valid, if you had the signal go through an opamp buffer or boost just before your effect and fead it only 5V then it should have a limited headroom and clip before that. but this may be over processing the signal?

the diode thing i a good idea

on the other hand: i looked at the TL072 datasheet and it said that from a 9V supply, the maximum output voltage it can produce is around 6,5V So using a 8V supply (regulators or diodes or something) i would be in the ballpark.


edit: found some digipots which maximum supply rating is 15V+ but they are in TSSOP package which is probably something miniscule, unusable SMD size. Is there any DIP adapter for them?

[Hides-His-Eyes]

Surely back to back zeners would just clip at v_forward?

[darron]

i was thinking along something like this:
http://analogguru.an.ohost.de/193/schematics/Zvex_SHO.gif


but didn't realise they were only 1n4148s..... wouldn't that have significantly changed his circuit installing those???

[cloudscapes]

I use vactrols/optoisolators when I want to control an analog circuit with a microcontroller. completely isolated.

[WhenBoredomPeaks]

I use vactrols/optoisolators when I want to control an analog circuit with a microcontroller. completely isolated.

how hard is to get them work like you want them? can you "tailor" them with resistors and stuff in the circuit and modify the uC code (like setting up low and high limits etc.) until they behave like a linear pot? Have you ever dropped them in place of like a 100kOhm linear pot or you have to design the circuit around them?

also if i use like 8 of them in an EQ i would like them to work more or less similar to the other one.

[Hides-His-Eyes]

I suppose if you used the dual ones, you could set one up as 'feedback' to the uC, but those things are slow enough as it is (~100ms) without having to deal with feedback too (even accounting for hysteresis)

That said most posts are +-20%; I think they can cope with an LDR pair being slightly out.

[cloudscapes]

Yeah I just don't sweat it if the optoisolator/micro combo isn't exactly the same as a linear pot (it usually isn't). If I absolutelly have to, I can compensate for it in code and give it any sort of curve I want. You could hook up the photoresistor to one of the micro's ADCs and have it automatically find the best PWM/DAC/vactrol outputs for a linear slope.

[PRR]

You don't need 256 steps for audio EQ. There ARE other "pots" with greater voltage compliance. CD4051(?) is a 1-of-8 analog switch which can take a 0V/5V digital (but parallel) input and switch analog signals to +7V and -7V. LMC835 is the pot-engine for a slick high-end EQ (however they are not in-stock at the usual places).

But you have 5V pots and they work. Fine. Put a 5V Zener to ground on each wild-input pin of the pot. Set up your "V/2" reference voltage at 2.5V. This will work in 9V systems, with early clipping.

Better to work your opamps from 5V. The TL072, like most old-time popular opamps, has an internal 7V reference and punks-out for lower supply voltages. The LM324 will work fine down at 5V supply. You can actually run it on 6V, because the output won't pull within 1V of the rail. Its (unspecified) noise is suitable for guitar work. Its major audio fault, class B output, can in wall-power applications be corrected by tying a 2K resistor output to ground. Again, use a 2.5V reference.