Covington Fireplace Ultra Treble Booster Trace

[nickbungus]

Hi All

As mentioned on another post, I recently repaired a Covington Fireplace Ultra Treble Booster for a friend.  While I had the pedal I took some gutshots with a view to do a trace.  Never done it before so I thought it would be good fun!

I do have a couple of questions but here are some images of where I am currently.






This is what I'm seeing but the signal path doesn't seem right and neither does the powering of the transistor.

.

Lastly, I have a couple of mystery cap values:


I'm guessing the 2A102G is a 1n but the .01K 50/100 one has me baffled.

The circuit does seem very similar to the Greg Fryer Treble Booster.

[Joe]

I'm pretty sure that's .01uF:

http://www.diystompboxes.com/smfforum/index.php?topic=76079.0

[lethargytartare]

102 should be .001uf.

The .01 is just a .01uf.

[nickbungus]

Brilliant.  Cheers guys.  Caps sorted.  A 1n and a 10n (0.001uf and a 0.01uf).

Does the trace look right?

Like there's a 100ohm resistor between the 9Vdc and the signal out?  Also, I'd expect the transistor to be a bit more directly linked to the power?

Without knowing enough, I just feel there's a mistake somewhere on my trace.

[duck_arse]

bungus - I don't think the "out" should connect to the 9V via a 100R, it don't sit right, somewhere. can you draw the circuit out for us? liberal use of the ohm-meter is allowed.

can we see the pot wiring/off boards as well?

[nickbungus]

Cheers Ducky.

It doesn't look right to me either and I'm an idiot.  I did intend to draw it out properly and then create a PCB layout but the fact that my trace doesn't look right is making me hesitant.

I'm pretty sure I am missing something (or I've added something) in the copper trace.

[duck_arse]

you draw it, we'll poke at it (also, like idiots). then worry about the pcb.

[nickbungus]

Okey dokey ducky.  I'm actually starting to suspect I've got the pads labelled wrong.   I'll go over all the images I took.

[Cozybuilder]

I did a trace on this, and have the following:

[nickbungus]

Thanks Russ

That's excellent

[nickbungus]

C6 and C7 are definitely the same value.  Unfortunately, the values had been worn off but I was going with 47ufs

[Cozybuilder]

47uF for C6 gives a low pass filter knee of 33.9 Hz, while a 100uF would give 15.9 Hz- I think either is fine. Probably anything from 1uF on up would make you happy at C7.

Thank you for posting the photos, these were nicely done. On the way home now (India trip), I plan to bread this one too

[Kipper4]

What jellybean are you using please?

[duck_arse]

the transistor is a BC-scribble-C, isn't it? what's going on with the 1M's and shadows? more wierdness.

[slacker]

Unsurprisingly given its name it's basically a Brian May Treble Booster http://www.diystompboxes.com/smfforum/index.php?topic=27422.0

[Kipper4]

I've built at least 4 times great circuit the BM treble booster and to my ears bc182 sounds best
Thanks

[Gus]

If  Cozybuilder schematic is correct

I will be nice

Is the 6.8k a bias control? is it external?
A better place to adjust bias is the 2.2k because it is cap bypassed gain is going to be about the same with different values because the emitter resistor is bypassed by a big enough cap value. You can adjust the C value to R selected

OR the 100k from 1k(base) to +9VDC because this should  change the input resistance only a little with different transistors of about the same hfe/beta range you could try a 68K or 82K with a 50k trim in series

The 1meg input is not needed there is a 120k

C4?

[nickbungus]

The 6k8 is a pot and its labelled Gain

[Gus]

How is the gain potentiometer wired?
Is it a variable resistor like Cozybuilder trace?
Or does it have the wiper going to Switch?

[nickbungus]

Whoops, I forgot to take an image but I can tell you its a 10k Linear pot with a 22k resistor between Pins 1 and 3 to give 6k8.



The left pad was connected to Pot pins 1 and 2 and the right pad was connected to pin 3.