Colorsound Tremolo Troubleshooting (No Effect)

daveed235 · Post by **daveed235** » 09 Mar 2018, 21:40

Hey all,

I tried to build the Colorsound Tremolo today, but I could not get an effect out of it, it only sounds like the dry signal, but more noisy. Also, the LED does not flash or turn on at all. I haven't built a tremolo (or used perfboard) before, so I'm not sure where to begin debugging. Anything helps!

Attached is the layout I used, which is from this link (which says the schem is verified).
http://effectslayouts.blogspot.com/2017 ... emolo.html

Thank you so much,

Dave

roseblood11 · Post by **roseblood11** » 11 Mar 2018, 09:42

I've built a paper plane. It doesn't fly. What should I do?

Got it?

snk · Post by **snk** » 24 Mar 2019, 00:08

Hello

I built the Colorsound tremolo today, using the tagboard layout : it works fine, but I found that the max and minimum speeds could be... faster and slower.
I changed one 3.3 cap to make the max speed faster, and increased the RATE pot from 250K to 1M to reach slower minimum speed.
I also added a speed indicator led (blue led with a 20K resistor).
Now i am experiencing a strange behaviour : With the 1M speed pot, everything is fine passed the second half, but since i turn the knob below 12 o clock, the tremolo sound starts vanishing.

I guess it is some kind of warning telling me this unit hasn't been designed for a 1M pot, but i am wondering two things :
1- What is the technical reason of the "tremolo vanishing" ?
2- What can i do to get slower minimum speed than with a 250K or 500K knob ? Can i have the nice slow speed i get with the 1M pot, without having the tremolo "vanishing" ?

(note : i have a "speed indicator led" : when the tremolo vanishes, i can see the led getting weak and then stopping to work too.

Manfred · Post by **Manfred** » 24 Mar 2019, 03:12

1- What is the technical reason of the "tremolo vanishing" ?

The oscillator is a gain stage with frequency-dependent feedback using a phase shifting filter network.
The stage oscillates if the filter delivers a sufficient phase shift value.
For a potentiometer resistance greater 500kOhms the phase shift is not longer sufficient, the oscillating stopps.

2- What can i do to get slower minimum speed than with a 250K or 500K knob ? Can i have the nice slow speed i get with the 1M pot, without having the tremolo "vanishing" ?

Replace the three 0.47uF Capacitors by higher values.

: ColorsoundTremoloSchematic.bmp (35.56 KiB) Viewed 1400 times

snk · Post by **snk** » 24 Mar 2019, 09:37

Hello, Manfred.
Put like that, it's perfectly clear.
Once again, thank you so much for your explanation and your kindness !

snk · Post by **snk** » 24 Mar 2019, 09:49

PS : Can the capacitors be of any kind (Mylar, Box, ceramic, tantalum, etc) ?
For such values, my green Mylar and box type are quite big (and ceramic are also cheaper)...

Manfred · Post by **Manfred** » 24 Mar 2019, 10:49

snk wrote:PS : Can the capacitors be of any kind (Mylar, Box, ceramic, tantalum, etc) ?
For such values, my green Mylar and box type are quite big (and ceramic are also cheaper)...

Take foil capacitors with narrow tolerance.
As far as I can see, the raster size of the caps is 7.5 Millimeters, there are small capacitors up to to 1 Microfarad availabe.
The lowest osciallation frequency is about 1.8 Hz at a capacitance of 0.47 Microfarad capcitors and about 0.8 Hz at 1 Microfarad.

snk · Post by **snk** » 24 Mar 2019, 11:53

Like that (5% tolerance)?
https://www.wima.de/en/our-product-rang ... apacitors/

bool · Post by **bool** » 24 Mar 2019, 12:25

I think you would also have to increase the 0.22uf coupling cap to Q4 a little. Perhaps use a 0.47 here.

snk · Post by **snk** » 24 Mar 2019, 13:02

Ok, thank you for the tip.
What would it do ? Would it lower the minimum speed also, or is it somehting needed when you change the other capacitors value ?

snk · Post by **snk** » 24 Mar 2019, 17:17

Hi,
I only have 2 box type film capacitors in stock

But i have several ceramic and tantalum 1µF caps... Would it do the trick ?
Should i wait, and order foil caps, or may i try with the ceramics (or the tantalum) ?

[edit] Ok,i found out it :

ceramic caps tend to be less precise, and have capacitances that vary with voltage. In short: it'll probably work, but there might be weird side effects. Better to stick with film caps.

I have one question also : Out of curiosity, what would it do if i don't take the same values for all of them ? What would be the incidence on the sound ?

Manfred · Post by **Manfred** » 24 Mar 2019, 18:04

I have one question also : Out of curiosity, what would it do if i don't take the same values for all of them ? What would be the incidence on the sound ?

A Tantal capacitor got a leakage current of few Microamps which could flows into the base of Q2 and causes a shift of the bias point.
You can take ceramic capacitors too, but a selection of the capacitance value by measuring is needed.
You can also take capacitors with 820nF, in that case the minimum oscillation frequence is about 1 Hz.

I think you would also have to increase the 0.22uf coupling cap to Q4 a little. Perhaps use a 0.47 here.

Hi Bool, thanks for the hint, you are right.

snk · Post by **snk** » 24 Mar 2019, 19:31

Thank you both.
What would be the incidence on the sound if i don't take the same values for all of these 3 caps (I am wondering what they are doing in the circuit, in order to understand it better) ?

snk · Post by **snk** » 24 Mar 2019, 21:26

Hello,
I replaced the 220nF cap with a 470nF, and the 3x470nF with 1µF (with my 2 Wima and one socketed ceramic i had left... I may replace it later with a new Wima), and changed the Speed pot for a 250K as advised, and now i can get a nice and slow tremolo

I also want to add that with these changes, there is no "vanishing modulation" anymore, the tremolo is the same at both slow and high speeds.
So, i now have a nice vintage tremolo with a decent range of modulation (the slow speed is not "ultra slow", and the fast one is not "thunder speed", but i like to have a useful, musical range of RATE).
Thank you all for your great help, and all the technical informations !

(Still, having my pedal working the way intended did not kill my curiosity : i would be curious to know what to expect sound-wise if do not use the same cap values for the 3 x 470nF caps ?)