Colorsound Overdriver/Powerboost circuit "analysis"

[Rob Strand]

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.
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Edit:

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).

[Paul Marossy]

> 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.

[Mcentee2]

I've been playing about with this on the breadboard and have a few questions: First off, how does the EQ section work? At a glance, it looks Baxandall-esque, but there are no bass caps across the bass pot terminals, nor is there any connection to ground.

There is a cap across the bass pot terminals.

Hope this is too necro, but it's relevant!

I am thinking of building the Overdriver from the kit offered by Pedalparts, and have been doing  my due diligence by reading all the posts on DIYSB over the years.

The link to the kit PDF is  http://pedalparts.co.uk/docs/VintagePow-MkII.pdf , and contains the schematic whish seems fine apart from C10 which has the electrolytic +ve side facing away from Q3 collector, which seems against most of the advice in this thread, and maybe the cause of that "static-ey/crackly breakup" mentioned often for the OD/PB.

Can I just check with anyone what the up to date consensus is on this, and maybe also confirm what the current Castledine/Rothman reissues have re this cap orientation?

[Electric Warrior]

Vintage units have the plus side of that electrolytic connected with the collector and so does the Castledine made reissue.

[Mcentee2]

Vintage units have the plus side of that electrolytic connected with the collector and so does the Castledine made reissue.

Many thanks! Have I understood correctly about the effect in the Overdrive sound re this orientation?

Are there any other symptoms of one way Vs the other?