ID this Schematic (tremolo... maybe???)

[moosapotamus]

http://sapphia.s10.xrea.com/cgi-bin/img-box/img20030803185645.jpg

What y'all think? :?

~ Charlie

[Marcos - Munky]

Yeah, it's a tremolo. I have this schematic and the PCB layout here. I don't remember where I found them, but in the same site have schematics and layouts for a fuzz and a fuzz-octave I think.

[moosapotamus]

Have you, or anyone, built it? Judging from the optical circuitry, would expect it to sound pretty good?

~ Charlie

[Marcos - Munky]

I didn't built it, maybe someone built it.

[Arn C.]

Marcos,
Can you give me the schematic and layout for this tremolo and I will build it.
Arn C.

[Marcos - Munky]

Check your e-mail, Arn.

[Dan N]

In case anyone else wants the layout:

http://users.rio.com/senorris/junk/tre2.JPG

In one of my junk boxes I have a trem pcb from a small Columbia amp that is very similar. It used a darlington transistor.

[moosapotamus]

I had the impression that it was an optical trem circuit. But, the two LDRs are nowhere near the LED in that layout. I just assumed that those two resistors that are drawn like they are in parentheses were LDRs, and the LED in parentheses was the lamp. Am I just misinterpreting the scheme?

~ Charlie

[jrc4558]

I don't think these are LDRs. The cirquit seems to be using  th Q4 as the way of transmiting the 0v to the base of the Q1. Thus the depth control simply limits the degree to which the signal is shorted out before entering the base. I'll have to try it.

[Mark Hammer]

Constantin is right.  Q4 is used the same way the transistor is used in the Dr Q/Quack/Quacky.  It functions like a voltage controlled resistor to ground.  The 100k resistor just ahead of the depth pot, and the depth pot itself, form a voltage divider such that the amount of signal attenuation depends on the ratio of that 100k resistor to the effective resistance to ground of the depth pot and transistor.  As you turn  the depth control down, the transistor is placed in parallel with smaller and smaller portions of the pot's resistive element, with larger and larger portions of the pot being used as a fixed resistor.  So, assuming a linear pot turned down halfway, you have the attenuation set by the ratio of the 100k resistor divided by the 50k between the wiper and outside lug, plus whatever the combined parallel resistance is of the other 50k and the resistance to ground of the transistor.

I'm assuming that Q1 simly serves as a gain recovery stage to make up for the attenuation.  I'm not holding out hopes for the stock circuit to sound great from a noise perspective.  On the other hand, stick a gain stage ahead of the input to perk up the S/N ratio and replace the 100k resistor on the output with a 100k pot, and you may have something a little more worthy of building.

[Nasse]

I have an interesting small schematic snippet about a transistor tremolo from old book late sixties or so. It is not similar like under discussion. It has two transistor circuit attenuating signal which is connected in between transistors. This circuit claims to give a solution for a common problem, oscillator feedtrough to your amp and speakers.

I just drawed most part of it with Paint. I dont have a web site so I can´t post it. Anyone interested if I e-mail it for someone? Perhaps some one of you know how it can be shown in this forum? :oops:

[moosapotamus]

Sure! Send it my way. I'll be glad to post it here.

~ Charlie

[eaze]

Hello.

The schematic&PCB which Charley&Dan mentioned are just a Colorsound Tremolo(copy).
http://www.netshopboys.com/colorsound/pedals/lemain/250x250/38.jpg
which has appered in Japanese stompbox issue "Handmade Project ver.2"(out-of-print).
It is mainly concerned with articles of copy-ing old stompboxes .
(for example, Fuzzface, Maestro FZ-1A, Roland Sustain, Shin-ei OctaveBox, EH FrequencyAnalizer....)

===
eaze

[jrc4558]

Q4 is used the same way the transistor is used in the Dr Q/Quack/Quacky.  It functions like a voltage controlled resistor to ground. ]
Damn, Mark...    
If only I knew English as well as you do!!!
I resort to the meaningfull nodding.

[moosapotamus]

I have an interesting small schematic snippet about a transistor tremolo from old book late sixties or so. It is not similar like under discussion. It has two transistor circuit attenuating signal which is connected in between transistors. This circuit claims to give a solution for a common problem, oscillator feedtrough to your amp and speakers.

I just drawed most part of it with Paint. I dont have a web site so I can´t post it. Anyone interested if I e-mail it for someone? Perhaps some one of you know how it can be shown in this forum? :oops:

Here it is...

I found this one in a book that I have had for years. Sorry this pic is of
low quality and I have drawn only a part of the original circuit. I have
not build it and have no knowledge if this principle works. It is another
attenuator circuit but with two transistors and an arrangement where you
can trim oscillator feedtrough off, it claims. It could work, I have seen
somewhat similar things made with bipolar transistors, in compressor and
limiter applications. I draw only the attenuator part of the circuit, and
here are few notes about circuit:

- Transistors in attenuator were AC151´s, Ge pnps perhaps
- supply voltage is 4,5 V
- electrolytic cap "Out" goes straight to output jack

Not shown:

- there is input amplifier, looks quite "standard" 2 transistor job to
compensate level loss
- tremolo oscillator is two transistor sinewave thing, I believe


Nasse

Thanks, Nasse!
A couple questions...

So, the oscillator would look something like this?
http://www.commonsound.com/other/audiolfo.gif

What's the 22K trim do to the sound?

Is this a 9V circuit? Positive to ground, no?

Thanks, again!
~ Charlie

[Nasse]

Thank you very much, Charlie, for posting my pic. I was on a two-day holiday trip. We have 40 000 lakes here in Finland and a friend of mine invited me and my family at his summer cottage and for some fishing with his small outboard motor boat. Watching the sun go down at lake was magnificent.


Charlie asked a couple questions...

What's the 22K trim do to the sound?

When transistors are driven by tremolo oscillator they partly short-circuit the connection point of input and output capacitors to ground and v supply.  You can say that impedance drops but dc voltage stays all the time about half of power supply. 22k trim is used to adjust drive to transistors equal so that tremolo oscillator signal disappears at output.  


Is this a 9V circuit? Positive to ground, no?

The circuit in original article was made with Ge trannies, so it is positive ground like pnp fuzzface, and was designed for 4,5 volt battery. I think I should breadboard this thing and use npn silicone transistors and 9v supply and some tremolo oscillator with more common parts. I think the easiest is to put a opamp preamp in front of the circuit.

I propably saw somewhat similar attenuation circuit made with silicon transistors in a audio limiter. I think there was an opamp preamplifier and  resistor taken after transistors to negative input of opamp, so that limiter was in feedback loop to suppress distortion.

[RickL]

If anyone's still interested, I built one of these last night and it works. Nothing great about the sound, sort of half way between a square and sine wave trem, a tiny bit of thumping in time with the LFO. Beware that the effect cuts out at the extremes of the speed pot, both directions. Most of the usable depth is in the top half of the pot. Apparent volume is nicely balanced between effect and bypass.

[jrc4558]

Thanx for the info!
I am a tremolo junkie btw.