help me with 2 channel tremolo *little update*

[birt]

i finally built it.

i used an astable multivibrator circuit that drives two leds that light up one at a time wich i use as speed indicators. in series with those leds are 2 TIL111 optocouplers ( http://www.datasheetarchive.com/search.php?search=TIL111&sType=part ). the transistor part of those optocouplers are used in 2 amz muffer circuits wich are the audio channels. they both have a distortion switch (the diodes in or out of the circuit) and a volume control. both channels also have a true bypass stompswitch.

the channels have seperate inputs and a switch to connect them, same deal with the outputs. Both inputs also have one in parallel as a splitter so i can send my guitar in the first input, out of the splitter in to an effect, out of the effect into the second input so i can tremolo between wet and dry (well it goes trough the muffer) signal and send that to one or two amps. the second channel also has a switch to put another cap parallel with the one in the multivibrator so the capacitance increases and that channel will go slower than the first.

now the problems:
it pops. loud.
the muffer circuits sound a bit dull and have no sustain (maybe a bias problem? or are those transistors really low gain?)

and if i have those problems solved i want to add a modulation switch with a led/ldr like in the uglyface on both channels so i can have some kind of weird wave texture instead of square waves.

the circuits:

-astable multivibrator


-AMZ Muffer


i've been thinking about switching the inputs instead of the transistors. or maybe keep the transistors "on" (with minimum gain when the led is out) all the time so they don't pop?
i'm not sure...

[birt]

i just found this: http://xoomer.virgilio.it/luixssj3/index/elettronica/effetti/Schemi%20elettrici/Valvenstein%202.gif

it uses a BF245 fet to switch signals. does this mean i can throw out the optocouplers, use the current from the leds to feed 2 of those little fet circuits (only 1M, 220pf and a diode?) and switch the inputs of the muffer circuits like that? so i can just use normal transistors for the muffers instead of the phototransistors in the optocouplers.

i really want to get this thing to work because i have all those sounds in my had to mak with it when it's finished. (tremolo between guitar and siren for example, or between bassy guitar tone and trebly guitar tone.)

[gez]

Seeing as nobody has answered, here goes.  Not really sure how/why you're doing things Birt.  Are the optos for a clean tremolo effect or are they there to modulate distortion?  It would help if you explain how you're using them.  What resistor(s) are they subbing in for?  Basically, what are you trying to do (it's not very clear from your post)?

The popping is probably a layout issue.  You need separate ground paths for LFO and audio and join them at the -ve terminal of your PSU/battery connection.  Also, leads can couple through LFO spikes so need to keep them well away from audio circuitry/wires, or use shielded wire.

[birt]

Seeing as nobody has answered, here goes.  Not really sure how/why you're doing things Birt.  Are the optos for a clean tremolo effect or are they there to modulate distortion?  It would help if you explain how you're using them.  What resistor(s) are they subbing in for?  Basically, what are you trying to do (it's not very clear from your post)?

The popping is probably a layout issue.  You need separate ground paths for LFO and audio and join them at the -ve terminal of your PSU/battery connection.  Also, leads can couple through LFO spikes so need to keep them well away from audio circuitry/wires, or use shielded wire.

the optos don't have ldr's in them but phototransistors. these are used in 2 muffer circuits. if a led is on, the transistor works, if the led is off, there is no sound.
since the leds blink one at a time the first muffer works when the second is off and vice versa.

this pops really loud and doesn't sound very good (the nature of the beast i guess, those optocouplers aren't made for audio purposes) so i was thinking of another way to make the 2 channels go on and of one at a time. i would start by using normal transistors for both muffers/channels and try to switch the inputs on and off instead of the transistors.

what i am trying to do is to find a way to make the inputs switch on and off at the rate of the astable multivibrator.
the first thing i found was that simple FET switching circuit wich i think/hope i can use to turn the inputs on and off.
if this works there's just the problem on how to feed those FETs.

can i do this by just using the current from the multivibrator? i mean that i put the FET circuits in series with the leds that indicate the speed of the multivibrator. so the - from the first led goes to the + of the FET circuit. The - from the FET circuit goes to the 1K resistor that's connected to the collector. and then the smae with the second led and FET circuit.
i can imaging this would give some problems since the FET circuit has completely different characteristics (current flow, resistance etc.) than the leds wich the astable multivibrator circuit is intended for.

if it doesn't work i suppose i have to use those optocouplers again to feed the FET circuits in some kind of way.

i hope this is a little more clear to you. It's kinda hard for me to describe all this since my elektronics knowledge isn't that great and english isn't my native language.

[gez]

Whoops, of course you meant phototransistors, my appologies.

I'm still a bit confused.  You're trying to build a stereo tremolo that does on/off chop, only with distortion...and you can vary the amount of distortion for each channel...yes?

There could be a number of reasons for the popping/clicking.  As well as layout  possibilities (and you'd have to be careful to keep connections to the LED in the chip well away from the transistor's connections) it might just be the way you're doing the switching.  Are the transistors AC coupled?  It would help if you could draw up a schematic showing how you're doing the switching...doesn't have to be the whole circuit.

Re the sound being muddy, the muffer has low input impedance so you're probably loading your pickups.  An input buffer would help.  Also, you're probably going to need more than one stage if you want sustain.  Might be an idea to post voltages anyway.

[gez]

Ah, I think I've got it...you're actually using the transistors in the optos as the trannies for the muffers?!

No wonder it clicks!! 

I thought you were using them at the outputs of these circuits to ground the signals...or something like that.

[R.G.]

the optos don't have ldr's in them but phototransistors. these are used in 2 muffer circuits. if a led is on, the transistor works, if the led is off, there is no sound.
since the leds blink one at a time the first muffer works when the second is off and vice versa.
this pops really loud and doesn't sound very good (the nature of the beast i guess, those optocouplers aren't made for audio purposes)

It's likely that the popping is because it's turning the DC conditions on and off in the muffer circuit. Any time you suddenly change the DC level in an effect output, it makes a pop.

I think you could get a full mute on/off of a signal level with phototransistor output optos if you were careful to do this by shunting the signal to ground at a point where there was no DC level with the signal.

the first thing i found was that simple FET switching circuit wich i think/hope i can use to turn the inputs on and off.
if this works there's just the problem on how to feed those FETs.

JFETs do work nicely for signal on/off circuits - that's what switches all Ibanez and Boss effect bypasses. There is an example of how to do this at GEO. See the "Stutter Pedal" article.

Here's how to set up an N-channel JFET on/off switch.
1. Get your JFETs and read the datasheet. You need to find the Vgsoff - this is the reverse-bias gate voltage that turns the JFET entirely off. You will have to bias the JFET source and drain up to at least this voltage, preferably more. If you use a low Vgsoff JFET like the 2N5292, 2N5485, or 2SK30AY, you can use a bias voltage of 1/2 the battery voltage.
2. set up the JFETs; place capacitors in series with the JFET drain and source. Place resistors of 100K to 1M from the source and drain to the bias voltage. Place a diode in series with the JFET gate with anode to the gate, cathode away from the gate. This lets you pull down on the gate, but lets it float up on its own. From the cathode of the diode, place a capacitor to ground of about 0.01uF. From the cathode of the diode, take a 1M series resistor to your on/off switching signal. This can be the collectors of your transistor flipflop. The switching signal needs to rise above the bias voltage and drop to nearly ground.
3. hook up the signal to the JFET. Signal goes into the drain-side capacitor, comes out the source-side capacitor. The capacitors need to be chosen for the load that follows the souce-side capacitor. The capacitors need to pass the lowest frequency you want to this load. If it's 10K, they'll need to be C = 1/(2*pi*F*10K) = 0.388uF at least, so use 0.47uF. If the load resistance there is bigger, you can use smaller capacitors; for 100K, 0.047uF; for 1M, 0.0047uF.
4. Finally, you'll have to set up the rest of your circuits. Generally I'd use a buffer in front of the JFET and after it. In fact, the circuit becomes what I did use in the Stutter Pedal.

[birt]

i don't understand this
can you possibly make a little sketch or something? i have those 2sk30's tough, that's a start.

as far as i understand i've got the mutivbrator as a building block, 2 muffer circuits and 2 FET circuits.
the FET circuits are in front of the muffers, the guitar signal is switched on and off by them right?

no i still don't understand the FET circuits you just explained (probably due to the langauge and my not so great electronics knowledge, i thought thos switching circuits were simple )
and i i also still don't get how i should switch the FETs with the multivibrator.

i hope i can get this project to work tough because i think it can be a really nice effect.
thanks for the input so far you guys.

[birt]

i've made a sketch of how i think it would work:

[R.G.]

I think what you have there will work, with a couple of changes. I would change the 1M pot to a 1M fixed resistor and put the 1M pot in the source lead of the JFET.

The way you have it now, The sound will always be switched fully off, but the loudness when it's on will be varied by the 1M pot. If you make the changes I mention, the loudness when on will be fixed, but the "off" sound will be varied down to full off by the pot.

As a result of the quirks of the following Big Muff fractional circuit, you may also have to lower the impedance this works at. That would involve lowering Rseries to about 10K and the 1M pot to maybe 100K.

Experiment and see.

[birt]

thanks for your advice!


i thought there would be a problem in the multivibrator. the on/off pulses in that circuit are in series with the leds and i didn't know if i could just 'tap' in there for the FET circuit wich lets the current go to ground instead of keeping it in that multivabrator circuit.

but i'm gonna make a perfboard lay-out and try this as it is now (with your mods)