ColorSound Overdriver OD - What Transistors ??

[HOTTUBES]

I've been asked to build a old school ColorSound Overdriver OD , i was wondering what Transistors would be the best and most accurate ?

Thanks for any help !!

[deadastronaut]

many use BC109'S...

[Dingus]

I've seen/heard of three different transistor sets in original Power Boost/Overdriver models:

Q1-Q3: BC109Cs  ("BC109" is what is specified on the factory schematic from June 14, 1971) http://i410.photobucket.com/albums/pp189/grievousangelphotos/colorsound_od.jpg

and

Q1-Q2: BC169C
Q3: BC184C

and

Q1-Q3: BC184L (this is what is used in the Macaris RI, but also is what Stuart Castledine says was in his original '72 Power Boost version)

I've personally only ever tried the BC109Cs as that's what I built forever ago.  The only noted differences I could find were from Pedalparts.co.uk about their kit, which addresses the difference between the Power Boost and Overdriver and how these trannies sound in relation to that:

"This kit offers the choice of making the Power Boost (which ideally needs an 18V supply - 2 x PP3 battery will do it if you don't have 18V DC) or the Overdriver, which runs at 9V. They both sound great, but the Power Boost has a lot more headroom to play with, sounding much fuller and punchier. Both will run happily with either BC169C or BC109 transistors. It's a matter of personal choice. The BC169C are a lot clearer with the 18V, the BC109 getting a little squishy when fully cranked. In the Overdriver the BC109 are the better choice. Please note: the BC169C require a little leg twist to go into the boards, as they have a non-standard BCE configuration. The BC109 drop right in there."

[frogman]

Fwiw, I built one of these as my second build a few months ago, I breadboarded and switched out a bunch of nos bc109's (regular bc109's, bc109b's, two different kind of bc109c's) and a set of 2n2222a's. Out of the bunch I remember the most about the telefunken bc109c's. They had the most gain and a good cranked fuzzy overdrive sound and rolled off to a nice warm od - slight od noticeably better than the other transistors did. I didnt care much for its low gain settings so if your guy is looking for slight breakup for a clean sound, the straight up bc109's or 2n2222a's might work better. The 2n2222a's were less compressed and had more high/mid frequencies going on, at least compared to any of the 109's. A lot of this is all just my opinion though. Good luck.

[Electric Warrior]

I've seen/heard of three different transistor sets in original Power Boost/Overdriver models:

Q1-Q3: BC109Cs  ("BC109" is what is specified on the factory schematic from June 14, 1971) http://i410.photobucket.com/albums/pp189/grievousangelphotos/colorsound_od.jpg

and

Q1-Q2: BC169C
Q3: BC184C

and

Q1-Q3: BC184L (this is what is used in the Macaris RI, but also is what Stuart Castledine says was in his original '72 Power Boost version)

I've personally only ever tried the BC109Cs as that's what I built forever ago.  The only noted differences I could find were from Pedalparts.co.uk about their kit, which addresses the difference between the Power Boost and Overdriver and how these trannies sound in relation to that:

"This kit offers the choice of making the Power Boost (which ideally needs an 18V supply - 2 x PP3 battery will do it if you don't have 18V DC) or the Overdriver, which runs at 9V. They both sound great, but the Power Boost has a lot more headroom to play with, sounding much fuller and punchier. Both will run happily with either BC169C or BC109 transistors. It's a matter of personal choice. The BC169C are a lot clearer with the 18V, the BC109 getting a little squishy when fully cranked. In the Overdriver the BC109 are the better choice. Please note: the BC169C require a little leg twist to go into the boards, as they have a non-standard BCE configuration. The BC109 drop right in there."

I don't think I've ever seen an Overdriver with BC109s, but I'd have have a closer look at my database to say for sure.
That factory schematic is quite funny. It predates the Overdriver by 12 months. They were making the 18V Power Boost at least until July of 1972. The earliest 9V Overdrivers have mid-72 pot codes as well.
By the time they made that pedal they had moved the 12k resistor form Q1's emitter to the joint of the 22µF cap and the volume pot, so I don't think there's a pedal that's exactly like the schematic. The Power Boosts had it wired up like that, but it was running on 18V and the resistor values were different

It seems the Power Boost started out with BC108.
Mine (D-0 pot codes) has BC184Ls, like Stu Castledine's.



Around the same time they were using BC169Cs as well.

Some of the first Overdrivers had BC184Ls. Around 1974 they often had BC169Bs. I've also seen some with BC184Cs.

Just try a couple of types and see what gain range you like best and what type sounds best to you - if the part number or make makes a difference at all.

[Davelectro]

By the time they made that pedal they had moved the 12k resistor form Q1's emitter to the joint of the 22µF cap and the volume pot, so I don't think there's a pedal that's exactly like the schematic.

That's interesting. I built a couple of CSOD (master / non master volume) and both of them have the 12K resistor connected to Q1's emitter. I wonder if that's the cause for the not-so-good light overdrive settings. I mean clean range is great and the fuzz is magnificent, but there's this annoying static-like noise on notes decay when overdrive shows up (pretty sure it's not a biasing issue 'cause I spent a LOT of time trying different collector voltages).

[Electric Warrior]

Yeah, it sounds kinda funny when cranked up, but once you hit the sweet spot of an amp with that it sounds fab.

Not sure if the wiring of that 12k will make it sound or behave any different..

[slacker]

It shouldn't make any difference how you wire the 12k, the cap before the volume pot will pass all audio frequencies so for the signal either side looks essentially the same. The only difference is that there's some DC voltage at the emitter but there's nowhere for DC current to flow through the 12k, because all paths have DC blocking caps, so it plays no part in the circuit DC wise.

[Davelectro]

So I guess that's the nature of the beast. After all it's an overdriveR, not an overdrive by itself.

[Electric Warrior]

Yup. When it was called the Power Boost it was more aptly named. But then again you use it push an amp into overdrive..

[JRM]

I've done mine with BC109 and I'm quite happy. It gives a nice clear and high boost (this boy is really loud) that can change to a strong OD with a change in the gain knob.

[PRR]

> what Transistors would be the best and most accurate ?

Hardly matters. Transistors are locked-in with negative feedback. They do what the resistors tell them to do. Any high-gain SI NPN is as good as any other here. 2N5088 is a fine choice, and may be sold as BC109 on alternate days. Modern 2N2222 will be fine also. BC169C seems to be an old part, which may be why Sola used it (it was cheap when it was going out of style).

[Bret608]

I have a question on the original factory schematic as well. It has the 25uf electro that connects the 4.7k resistor and the 220n cap near the Q3 collector oriented opposite to what I've seen on most schematics with roots in the DIY community. It has the negative side toward the 4.7k resistor and the positive side toward the 220n cap.  I've seen it suggested somewhere that how this cap is oriented is actually what causes the fizzy decay that some report.

Is there anything to this? How is that cap actually oriented in original units?

[slacker]

Logically the 25uF cap should go with positive end towards which ever part of the circuit has the highest DC Voltage. The collector of TR3 is at about 5 Volts, the tone controls are at a much lower level, about 1 Volt from memory. So the cap should go with the positive end towards the collector, which is how it's shown in the factory schematic. You can see that the white ends of the caps are the positive side if you look at the ones that go to ground.

I don't know if putting it the other way round does anything noticeable. 

[Electric Warrior]

How is that cap actually oriented in original units?

Positive end towards the collector. 

[Bret608]

Thanks for confirming!    That's what I suspected.

I don't know what difference it actually makes in sound, but I think it's worth noting that Fuzz Central's schematic and quite a few DIY layouts after that have the negative side toward the collector. I may socket that cap on my build just to see what it does when you flip it one way or the other.

[bordonbert]

Here's the original schematic in clear readable form.  You can see the trannies are BC109s.  In truth, in this application and most others we are interested in here, the transistors you use will have no real bearing on the sound as long as they are high enough gain.  It's another myth!

https://dl.dropboxusercontent.com/u/21235584/colorsound_od.jpg

EDIT:  And all of the electrolytic capacitors are shown the right way around.  Putting them the wrong way round will DEFINITELY have bad consequences.  They do not like reverse voltages.  Don't do it!

[joens]

I have an original Unit and the 3 trannys are BC184LB