Help Needed - Power Boost clone with low output

[fuzz guy]

I've just completed a build of a Fuzz Dog clone of the Colorsound Power Boost. It's passing a signal and all the knobs appear to do what they should, except the overall output is very low and sounds muffled. The build docs are here,

http://pedalparts.co.uk/docs/VintagePow-MkII.pdf

I used BC184L transistors and installed the charge pump too. I followed the build doc exactly, including the instruction to reverse the orientation of C10.

I took some voltage measurements thinking that maybe the problem was with the charge pump, but it doesn't seem that's the case as I'm getting 16+v in places.

Before I dive in with the audio probe, can anyone offer some advice to narrow down my troubleshooting search? Any likely culprits for low output?

I'm starting to learn some of this stuff I think, but this circuit has a bit more to it than the fuzzes and boosts I've built so far, so any advice is appreciated.

[GibsonGM]

Transistor(s) in backwards?  Cold solder joint not allowing V+ to get to collectors of transistors?   

I think it's time for audio probe   You can find out a lot very quickly with it.

R1/C4 node, R11/R12, R13/C11.     You may find something is 'up' with the last stage - a wrong R value maybe, something like that, so you're not recovering the level sucked up by the tone controls. 

[duck_arse]

The PCB has been designed to easily take either BC109 or BC169C without any fiddly leg twisting.
Only use one or the other sets of spots - Q1-3 or Q4-6.

I used BC184L transistors and installed the charge pump too. I followed the build doc exactly, including the instruction to reverse the orientation of C10.

exactly this. that doc really should state the differences between the BCxxxl transistor pinout and the BCxxx, BCxxxA, B or C pinout. but you checked the datasheet before building, so it must be something else, right?

[fuzz guy]

The PCB has been designed to easily take either BC109 or BC169C without any fiddly leg twisting.
Only use one or the other sets of spots - Q1-3 or Q4-6.

I used BC184L transistors and installed the charge pump too. I followed the build doc exactly, including the instruction to reverse the orientation of C10.

exactly this. that doc really should state the differences between the BCxxxl transistor pinout and the BCxxx, BCxxxA, B or C pinout. but you checked the datasheet before building, so it must be something else, right?

In the BOM the BC184L is also listed as using the Q4-6 pads, and yes I did check that the pinouts were the same.

[fuzz guy]

So it seems like the signal weakens after two components, R10 and C7. I have a strong signal on one side of those parts and it's weak afterwards. Both parts are the proper value and I've re-soldered both of them and it didn't fix the problem.



Does anyone have any suggestions?

[GibsonGM]

It will get lower there, because the tone stack 'eats' a lot of the signal (called "insertion loss").  The last transistor stage brings the level back up, it's called a 'recovery stage'.   BTW, hopefully you have good strong signal going INTO the tone stack at C5.  If so then what you want to do is see if Q3 is operating.   

Check at C11. If not increased volume there, something is messed up with the parts that run the transistor (wrong value resistor(s), transistor in backwards, a solder bridge short, burned out transistor from soldering heat, something like that).   If there IS good loud volume there, then the problem would seem to be your volume pot.    Odds are it's a simple mistake with a resistor or something around that last transistor (if the first stage is working).

[duck_arse]

The PCB has been designed to easily take either BC109 or BC169C without any fiddly leg twisting.
Only use one or the other sets of spots - Q1-3 or Q4-6.

I used BC184L transistors and installed the charge pump too. I followed the build doc exactly, including the instruction to reverse the orientation of C10.

exactly this. that doc really should state the differences between the BCxxxl transistor pinout and the BCxxx, BCxxxA, B or C pinout. but you checked the datasheet before building, so it must be something else, right?

In the BOM the BC184L is also listed as using the Q4-6 pads, and yes I did check that the pinouts were the same.

the pinouts aren't the same. the "l" suffix on BC series transistors indicates an end base connection, as opposed to the standard centre base connection. [I've seen only one datasheet where this does not hold.] so if your transistors are BC184l, they need leg twists to go on that board - as I understand it, from their docs, but not stated therein.

have you posted all your transitor pin voltages that we might see?

[fuzz guy]

the pinouts aren't the same. the "l" suffix on BC series transistors indicates an end base connection, as opposed to the standard centre base connection. [I've seen only one datasheet where this does not hold.] so if your transistors are BC184l, they need leg twists to go on that board - as I understand it, from their docs, but not stated therein.

have you posted all your transitor pin voltages that we might see?

From what I've found, the BC169C has the same pinout configuration with the end base connection.

I'll take voltage measurements from the transistors and post them.

Thanks so much to both of you for your knowledge and assistance.

[fuzz guy]

Check at C11. If not increased volume there, something is messed up with the parts that run the transistor (wrong value resistor(s), transistor in backwards, a solder bridge short, burned out transistor from soldering heat, something like that).   If there IS good loud volume there, then the problem would seem to be your volume pot.    Odds are it's a simple mistake with a resistor or something around that last transistor (if the first stage is working).

Ooops, yeah I had the wrong value at R12, 1.8k instead of 180k, and I missed it twice. Nice loud signal now, although it's too late here for a proper test, looking forward to that tomorrow! Here's some picks (in the obligatory orange enclosure)




Thanks so much Mike, I really appreciate you taking the time to help me out. Next time I'll check my values three times before asking questions. 

[GibsonGM]

It happens to everyone, Vance!  The most common reason a thing doesn't work is...us, ha ha.   But it's helpful to have other ppl tell you where to go looking!

Very nice-looking build!  You'll have to start on something else now! 

[fuzz guy]

Yeah, I've got a couple other kits sitting in the shed, next will be a Buzzaround fuzz and then a copy of the Skreddy Lunar Module.

Thanks again!