Author Topic: Colorsound Overdriver/Powerboost circuit "analysis"  (Read 7536 times)

Rob Strand

Re: Colorsound Overdriver/Powerboost circuit "analysis"
« Reply #20 on: March 07, 2018, 11:08:02 PM »
in colector Tr2, 6.4u? or my eyes plays trick on me?
bzzzzzzt    Good question!
You've got me questioning my own sanity.

I could have sworn I've seen that value somewhere so I didn't question it.
Now I look at some PCB shots; presumed '76 model. In one I see:
- 2 x  small electro 0.47uF 63V          ;  the '0' looks funny so from distance it looks like 6.4 but it's not!
- 3 x 22uF 25V (not 25uF)
- 1x Part I can't see it's different to the other.  Smaller than the 22uF.
   As far as I can guess it's the cap that goes to the gain pot.
   It looks like 10uF and lower voltage.
   (In another pic it looks like the 22uF's in size/shape but I can't read the values.)

I'm now confused about what is correct.   There could be variations.

OK I've got no idea.   Thought this was sorted long ago!.

From various pics:
- PSU + emitter caps:   22uF to 33uF
- Gain pot cap:   10uF to 33uF
- 2x Electros around tone control:   2x0.47u or 2x4.7u or 2x10u

One of these variations is covered in the schematic given early in the thread (the three schems).
« Last Edit: March 07, 2018, 11:43:57 PM by Rob Strand »
The mind often distorts without gain.

Paul Marossy

Re: Colorsound Overdriver/Powerboost circuit "analysis"
« Reply #21 on: March 08, 2018, 09:51:04 AM »
> 1 - Bypass cap on Q1 is 25uF, not 10uF
> 2 - The coupling cap on the collector of Q1 is 6.4uF, not 4.7uF
> 4 - The cap from collector to base on Q1 is 200pF, not 500pF
> 5 - The coupling cap on the collector of Q3 ...should be 25uF, not 4.7uF

These are less critical. If this were a studio mike preamp Q1 Ce would be large to allow full bass at maximum gain. I'm less sure that guitar needs 55Hz response at high gain. #2 (you mean Q2?) should be much more than 2uFd (to pump R7) but 5 or 7u is whatever falls to hand. I could argue that C10=C5, or C10>>C5, and don't think it matters much. C4 limits gain to 1.1MHz or 2.8MHz, and even my dog does not care.

Sorry, I meant to say Q2 in comment no. 2.

I finished it last night using the values on the factory schematic, and I like this little circuit. As you point out, I guess some of those values aren't that critical. I managed to get it to work with 2N5089s, and with the batch of them that I have in my parts drawer I was able to get pretty close to 5V on the collector of Q2 & Q3 with the 1.8K resistors.

From reading the other comments, I guess these units probably had variations in the exact values of the parts used in them. As did many other circuits back in the day.