Crazy Tube Circuits - Starlight [trace in progress]

tuck · Post by **tuck** » 05 Jan 2013, 19:26

Hi you lovers of the goopy dessection,

my first contribution. This is a work in progress by a dissection rookie

I managed to remove the goop without damaging the parts (ok one cap is scratched....) but I'm not able to create a suitable schematic. Still trying

The parts on the schematic are arranged like they are on the pcb. I'm going to tinker around a bit to get an arrangement for a suitable schematic.
Feel free to add suggestions, there might be a lot of errors e.g. the order of the trimmer pins or the transistors.
Some things to mention in my crappy pictures: R13 is not available, C6 is C16. Some values are just writen like they are printed on the parts.
The transistors are all without a name on it. they were sanded I think and painted with silver varnish wich I removed with petroleum benzine (if that's the right word fo that stuff).
Is µ22k = 220nF?

jymaze · Post by **jymaze** » 05 Jan 2013, 22:52

The pins of the fets is as follows for Q1 from left to right: Drain - Source - Gate.

It should help you get the schematic right.

It looks like cascaded jfet gain stages (quite trendy these days) with the trimmer on the source and bypassed with a large cap.

Another thing is that Q2 is used as a clipping diode to group for example (to give some asymmetrical clipping).

It should help you understand the rest of the circuit better.If you can't figure it out, I'll look at it more.

Nice job and thanks for the contribution!

jymaze · Post by **jymaze** » 06 Jan 2013, 03:18

OK, I could not help, and it was an easy trace overall. I did not take the time to redraw on computer though.

It does not follow your trace around the tone section (which was a little trickier), but I think it is correct (it makes the most sense).

So it is using jfets as gain units (2N5457 or J201 or anything with similar pin-out) and 2 mosfets as clipping diodes to ground.

The tone control is basically controlling the mid-scoop in an otherwise fixed TMB tone-stack. So it is more a "character" pot than the usual "treble" pot that is used for tone control.

Then after the tone-stack comes a volume-recovery gain stage, and it ends with a double low-pass filter.

I am sure it sounds good.

Thanks again for the pictures!

tuck · Post by **tuck** » 06 Jan 2013, 14:59

Wow thank you!

It really does sound good!

atreidesheir · Post by **atreidesheir** » 06 Jan 2013, 20:30

congrats on a clean degoop. I have been scared to death to do that yet.
But I also have never bought a gooped pedal.

tuck · Post by **tuck** » 06 Jan 2013, 20:40

I got it for a very fair price and thought to my self "now or never". My heart stopped because of the cracking noise when the tranies popped out of that stuff.
It was quiet easy but after that my fingers hurt for two days because I had to put a lot of force into the carefull goop pulling process

jymaze · Post by **jymaze** » 07 Jan 2013, 13:51

I put a cap in the tone-stack where obviously it should be a resistor. I also did not include the law of pots. So here is the corrected version:

A simulation of the tone-stack show that it is a bass-boost (around 6 dB) with shallow mid-scoop (3dB at mid-pot). And the tone pot controls the amount of treble and the mid-scoop.

A pretty nice circuit. Not original but nice.

Ice-9 · Post by **Ice-9** » 07 Jan 2013, 17:46

Looks like an interesting circuit and the tone section could be revised to add all three bass mid and treble controls.

jymaze · Post by **jymaze** » 07 Jan 2013, 18:02

I actually think they made a good choice to limit the tone-stack to one knob since I find 3 knobs on the pedal AND 3 knobs on the amp a little overwhelming and difficult to tweak sometimes. With only one knob they make a statement by giving a strong sonic personality to the pedal at least.

Actually, I think that a BMP tone-stack with variable scoop is one of the best choice you can make on a pedal to balance versatility and tweakability.

tuck · Post by **tuck** » 07 Jan 2013, 21:54

Dammit you're so fast... I create a schematic on my own just as a matter of principle

At first I thought I want more treble but the more I play it the more I like it the way it is.

soulsonic · Post by **soulsonic** » 07 Jan 2013, 22:01

Good job removing the goop! I've never been able to get it to come off so cleanly. It usually tears all the insulation off the electrolytic caps, at least.

jymaze · Post by **jymaze** » 07 Jan 2013, 22:38

Tuck,

If you want to try more treble ( like high treble, think "sparkle" or "brightness"), you can desolder C10, and even C12 too for even more treble.

The only difficulty is not to destroy the caps while desoldering them since these can be fragile if the proper technique is not used (need a good pump and desoldering wick, and not to overheat them).

tuck · Post by **tuck** » 27 Feb 2013, 11:48

There are two or three connections missing or plain wrong in my schematic. I had no time to correct them yet....

jymaze · Post by **jymaze** » 27 Feb 2013, 13:08

I know, I retraced from the board pictures and I noticed a few mistakes on your schematic. I am 99% sure about mine, don't worry!

tuck · Post by **tuck** » 27 Feb 2013, 18:40

that's the part were I made an error. R9 is not connected to c8 and c23.
Unfotunately i don't know where the other errors are I thougt I saved the file at the end of the retracing....

jymaze · Post by **jymaze** » 28 Feb 2013, 20:13

It was in the tone-stack area.

My schematic is correct. I noticed it was wrong on your schematic and I corrected it when I drew mine.

hozy31 · Post by **hozy31** » 14 May 2016, 16:55

Just verified a vero of this over at Guitar FX Layouts if your interested. Great pedal.

Crazy Tube Circuits - Starlight [trace in progress] [traced]