Boosting Circuit With Low Output

[Paul Marossy]

I recently built this "vibrato" circuit:

http://members.shaw.ca/roma/vib.gif

To me, it sounds kinda nice with (3) 3.3uF caps in the oscillator section vs. the 2.2uF caps specified.

Anyhow, I have one small problem with it: the effected signal output is considerably lower than the bypassed signal is. What can I do to remedy that? I was thinking of just putting a simple transistor amplifier arrangement at the output. What type of circuit should I use? Pros, cons?
Or is there an easier way to do it? I'm not quite sure about how to do things on these oscillator circuits....

[Ansil]

well there is the cheapo way and put a resistor in the switch to drop you bypass level down..  lol it is my baaastard solution for alot of things though.

[mattv]

That schem's bypass is weird...

Before inserting a boost-type circuit at the output (something like the LPB would be fine), try increasing the value of R10 (maybe with a trim pot). If I'm not mistaken, that should increase the opamps output and the effect's volume.

[petemoore]

how does it work...I don't understand transistor vibrato [isn't vibrato pitch change] nonethe less and all the more how doesthis ckt sound to your ears?//

[Paul Marossy]

mattv,

OK, I think I'll try changing R10 out with a trimpot first. That would be the simplest solution.

petemoore,

You can read the text at his site:

http://members.shaw.ca/roma

Go to "The Projects" --> "Guitar Effects" --> "Vibrato/Tremolo"
It's the circuit at the bottom of the page.

It doesn't really sound like a vibrato, just a fast tremolo. Sometimes there seems to be a hint of pitchshifting in there, but it is very subtle. I would really call it a tremolo circuit. Anyhow, it sounds OK, and it's pretty quiet. Changing the 2.2uF caps with bigger caps will slow it down, or vice versa.

[Paul Marossy]

OK, I tried changing R10, the 33K resistor in the opamp feedback loop. No matter what size resistor between 2M and none at all, the volume more or less stays the same. This is configured as a non-inverting opamp, so I don't know if that is why it behaves like that or not. Most of what I have built so far uses inverting opamps...

So, then I built the LPB circuit and put it at the output of the cicruit, but that still isn't as loud as the bypassed signal.

I'm a little perplexed. :?
The only thing I can think of is that maybe the FET is used (J201) has a really high impedence compared to the one he used (2N5484 or 2N5434).
Anyone up for theories on this one?

[ExpAnonColin]

To me, LM386s always remedy low output no matter what.  With a gain of 200 max, it'll boost you enough without too much distortion.  The site you're looking at has a circuit that's a bit complex, IMHO:

Normall I just put the input into 3, ground 2 and 4, put the input voltage to 6, and then take the output of it.  That's a gain of 20, if you want more, put a 10uf electrolytic in between pins 1 and 8 20 get 200 gain... then a value between 0 and 1k resistor in between pins 1 and 8 will lower the gain (try a 1k pot for gain control).  This can make you REALLLY loud, so just try it out.  Put a 1k pot in front of pin 3 for volume if you want, instead of the gain pot.

-Colin

[Jered]

Use the signal probe/tracer described in the FAQ. Follow the signal, you will hear the volume drop. That is where your problem is. This tool is so easy to use, works fast, requires no more than 4-5 parts to build yet invaluable.
 Once the probe is ready to go, it will take you 30 seconds to find your problem. If the signal is consistent through the entire circuit, then I would guess something is wired inncorrectly.
  Good luck,   Jered

[Nasse]

Paul, thank for posting the circuit and the link for site, there is nice info and circuits, better than it looks at quick glance.

I think Colin referred some other circuit than yours vib/trem problem :?: .

I just can not figure how it works, the text says the fet is affecting the biasing of the opamp. But looks somewhat like allpass or bandpass filter. I look if I find some old schem which may be somewhat similar. Or maybe it is not. The circuit that I have has propably signal connected to both + and - inputs of opamp so that it sums and result is silence, and another input is modulated by fet so it results tremolo.

If your circuit works and sounds nice can the level problem solved by putting another amplifier stage after the tremolo circuit :roll: