about Tremolo and Vibrato schem's

[nordine]

hi there,

i'm new, so... nice to meet everyone!
this seems a great place to learn, trade experiences, and all that stuff

well, i've been struggling a lot last days w/ a tremolo circuit i want to build, but got no success, the thing is completely dead, and (to make matters worse) its becoming normal for me that a circuit you've spent hours with WON'T work, that's a fact of life  :cry:

here is the thing:




i'm feeding it w/12V ( thats the max i can afford).... would that be the cause of non working?

also, do anyone has a simple "real" vibrato circuit??
(real = pitch modulation, not good ol' tremolo)

thanks

[gez]

A common problem with the type of LFO used here is that if the gain of the transistor is too low no oscillation occurs.  Use a higher gain trannie and see what happens.

Is this on a breadboard or have you built it on perf (or something similar)?  When you say it doesn't work, what are the symptoms?

PS  Supply voltage will affect bias (and gain) so this may be contributing to your problem.

[travissk]

I think the 12V vs 15V -might- be a problem. Have you made an audio probe, or do you have an oscilloscope so you can see what the signal is doing at any point? Also, do you have a multimeter? You can see what that left transistor is doing.

If you have no tools, try adjusting that 33k resistor from the supply... maybe put in 20K instead?

I sort of understand what that circuit is doing but don't have any more insight on what the problem would be without information on what's going on. Have you checked your wiring?

[nordine]

thanks for que quick replies!

i'm using two 2n3904... are they low gain tr's, or are they ok? what would you suggest me to use instead?

sorry for have not been more explicit describing the symptoms

i did an audio probe, and w/ dead i mean it does not do a slight noise
( the audio probe consist on a personal stereo and a pair of headphones). i get no -apparent- signal from it

i'm setting the components in a protoboard ( so errors wont be irreversible)

i've checked wiring and everything.. i think i've built it 10 times or so

thanks guys

[nordine]

now that i think about it... is a personal stereo and a pair of headphones a proper audio probe?? ( is the input too low, or something like that?)

[travissk]

Do you have a multimeter? If so, could you check what the voltage is at the base of the both of the transistors?

Also, do you have your transistor pinouts correctly identified to match the schematic? The emitter is the pin with the arrow; it looks like the one on the right is flipped. In that case, the collector is connected to ground.

[Marcus Dahl]

I would say 2n3904's would work, but I'm confused. Your in and out is in the same area. Wouldn't you need to come in where the .68mf or the 1mf is?

I'm new to tremelo and modulation circuits. Please forgive my ignorance. It looks to me that all you will get is dry signal and no tremolo.

[travissk]

The stereo probably works since it has an amplifier in it; you can try plugging into a guitar effect that does work and make sure though.

[gez]

i'm using two 2n3904... are they low gain tr's, or are they ok? what would you suggest me to use instead?

Could you do a search for the data sheet and post the link?  Have a look at similar tremolos to get an idea of subs.  Have you checked out the Coloursound trem that Stephen Giles posted at the weekend?  It's a very similar schematic.

[gez]

but I'm confused. Your in and out is in the same area. Wouldn't you need to come in where the .68mf or the 1mf is?

It's pretty standard Marcus.  I can't see the schematic as I type this but the transistor and stop resistor act as the lower resistor in a simple divider, the junction of which is fed to the amp.  You usually see a gain recovery stage, but it's absent here (that's why I suggested taking a look at the Coloursound).

[nordine]

here is the datasheet:

http://www.datasheetcatalog.com/datasheet/2N/2N3904.shtml

well. since i'm a bit ( JUST A BIT :roll: ) tired of this schem.. i'll get the parts of that colorsound one ( at least to see something new)

that circuit says i can use 2n5088.... is it possible to recycle the 3905's i have??

[Ge_Whiz]

The unbiased transistor with AC going in the emitter acts as a variable resistor? Er... can this actually work? I'm amazed.

In answer to the other question, there are several 'true' vibrato circuits around, but they are much more complicated - similar circuitry to phasers.

[R.G.]

The next step *requires* you to have - or borrow - a voltmeter. It's impossible to determine except by luck what is happening in your circuit.

Get a meter, and measure all the DC voltages on both transistors. That will give us something to go on.

In answer to some of the other questions:

do anyone has a simple "real" vibrato circuit??

Yes. Read "The Technology of Phasers and Flangers" and "The Techology of the Univibe" at GEO (http://www.geofex.com). In fact, read the other stuff at GEO, including the Guitar Effects Debugging page. It would be helpful right now.

i'm setting the components in a protoboard ( so errors wont be irreversible)
i've checked wiring and everything.. i think i've built it 10 times or so

One of the most common things we hear here is that "I'm sure it's all correct, I've checked (or built) it  several times already." If you have really used the right parts and connected it up correctly, it will work. Mother Nature is trying to tell you that you've overlooked something. One thing that comes to mind is the protoboard itself. These things get unreliable after a number of parts insertions into the holes, and the contacts get where they don't. It is possible that one of the connections you've checked several times isn't really connected. The answer - get a voltmeter and see what the transistors, resistors, etc. think the voltages are not what the layout says they are.

i'm using two 2n3904... are they low gain tr's, or are they ok? what would you suggest me to use instead?

2N3904s should work as well as other things here.

I'm new to tremelo and modulation circuits. Please forgive my ignorance. It looks to me that all you will get is dry signal and no tremolo.

Good observation. The ratio of input resistor to shunting resistor of 100K to 39K means that even if the transistor was a short circuit, the sound would be decreased by 39K/139K = about 1/4th, which is a just noticeable  tremolo. This thing won't make huge tremolo swings, even it works perfectly. It's probably adapted from some other application, like maybe organ.

The unbiased transistor with AC going in the emitter acts as a variable resistor? Er... can this actually work? I'm amazed.

Yes. The unbiased transistor is being used as a variable resistor in the region where there is not enough collector voltage into the collector saturation region. This is one old way to use bipolars as variable resistors. They have big problems being used this way, but it does work. And it does work better if you flip emitter for collector and run them in inverted mode.

Again, you need a voltmeter (at least) to tell what's going wrong.

[Marcus Dahl]

I'm new to tremelo and modulation circuits. Please forgive my ignorance. It looks to me that all you will get is dry signal and no tremolo.

Good observation. The ratio of input resistor to shunting resistor of 100K to 39K means that even if the transistor was a short circuit, the sound would be decreased by 39K/139K = about 1/4th, which is a just noticeable  tremolo. This thing won't make huge tremolo swings, even it works perfectly. It's probably adapted from some other application, like maybe organ.

This is one old way to use bipolars as variable resistors. They have big problems being used this way, but it does work. And it does work better if you flip emitter for collector and run them in inverted mode.

Again, you need a voltmeter (at least) to tell what's going wrong.

Thanks for the complement, and setting me straight. Flipping the emiter and collector was what I was thinking may be wrong also. The 100k - 39k makes a little more since to me now. I'm more of a trial and error guy listening to what the circuit is doing in the signal chain. So this information helps me a lot. Believe me when I say I don't no it all. Thanks again for setting me straight.

[nordine]

hi again

first of all, i want to thank all people for the valuable info, you're very nice


well, i -instead of doing the colorsound tremolo, because of lack of parts- tried to build a modified version of the original file i uploaded. the guy that did it changed it in a way that it can run on 9V, and use PNP tr's. here is it:




used the 3904's and switched all polarities


....nothing came out of the speakers


then i changed the first 100k resistor for a 220ohm resistor (!)... just for the sake of seeing what would happen.. and there was the signal i was feeding to the input, plus a pulse... must be 4hz ( its a distorted pulse that goes thmp thmp thmp... you get the idea)

the very question i have is: why is the input filtered by a 100k resistor, and then nothing appears to give its gain back?? (i saw a 100k resistor in other audio fx. it was variable, and the creator said it was used as a preset volume stage; could it be that here it is as well a gain limiter?)  ...the guy who did this second circuit said it worked for him... he said the effect mellowed the signal so he had to eq it, but nothing more, neither talked about a massive loss of gain  

as far as i know, the left "tr" is the one that is doing the pulsation, because when i take off the right one, nothing happens

then again... if i input a signal of X intensity, what i'm gonna get in the output?? X/2?? X/4?? or just X??

[Marcus Dahl]

hi again

first of all, i want to thank all people for the valuable info, you're very nice


well, i -instead of doing the colorsound tremolo, because of lack of parts- tried to build a modified version of the original file i uploaded. the guy that did it changed it in a way that it can run on 9V, and use PNP tr's. here is it:




used the 3904's and switched all polarities





....nothing came out of the speakers


then i changed the first 100k resistor for a 220ohm resistor (!)... just for the sake of seeing what would happen.. and there was the signal i was feeding to the input, plus a pulse... must be 4hz ( its a distorted pulse that goes thmp thmp thmp... you get the idea)

the very question i have is: why is the input filtered by a 100k resistor, and then nothing appears to give its gain back?? (i saw a 100k resistor in other audio fx. it was variable, and the creator said it was used as a preset volume stage; could it be that here it is as well a gain limiter?)  ...the guy who did this second circuit said it worked for him... he said the effect mellowed the signal so he had to eq it, but nothing more, neither talked about a massive loss of gain  

as far as i know, the left "tr" is the one that is doing the pulsation, because when i take off the right one, nothing happens

then again... if i input a signal of X intensity, what i'm gonna get in the output?? X/2?? X/4?? or just X??

Again I'm very ignorant on this subject.

My thoughts are one of your transistors is not right. If you look at both schematics. Your emiter, collector, and base are in different positions. Also the othe schematic has 2 different trannies.  Easiest solution: find a data sheet online of some transistors that match up to either schematic or find a schematic that matches the trannies you already have.

[gez]

If you're getting a pulse then the LFO is working.  I can't see the schematic again, but (if you've wired the modulating trannie up right) the distortion is probably a result of too much signal voltage across the trannie - you made the 100k miles too small.  

The schematic you've just posted has no rate control, so you're stuck with one speed.  It has no depth control (also a possible cause of the thump - too much modulating voltage on the base of the trannie). It has odd cap values too (don't know why that is), though it's obviously working.

Better to spend your time on something that has been proven to work - EA trem, or try the Coloursound that Stephen so kindly posted over the weekend; as far as I know that hasn't been verified yet, but it looked fine and is very similar to what you originally posted (though a better design in my opinion).

[Tim Escobedo]

I copied the phase shift oscillator design from the runoffgroove Phozer. It's novelty is that it has a LED in series with the collector resistor. Interestingly, I found the LED was more than just a blinky light. It also seemed to reduce the "thump". I don't know why.

[gez]

I copied the phase shift oscillator design from the runoffgroove Phozer. It's novelty is that it has a LED in series with the collector resistor. Interestingly, I found the LED was more than just a blinky light. It also seemed to reduce the "thump". I don't know why.

Interesting, did you scope it Tim?  I should think that the amplitude of the sine output would reduce slightly with the LED in there, which could account for less thump.  Perhaps had you just divided down the output a little more you'd have got the same result?

[petemoore]

Kind of a cool idea...as soon as I saw the input going throught the 100k to the output, and the rest of the circuit as some kind V/R, LFO type affair, I became less interested. Justt seems like a 'limited returns' affair.