TC Electronic - Spark Booster

miklax · Post by **miklax** » 05 Mar 2014, 22:48

Hi there friends,

I've received a faulty Spark booster for repairs, and after trying everything I could imagine, and with no success, along with my client, we've decided I should take apart, trace it and build a new one.

I've traced it, and already build it, but the resulting boost is not very noticeable. Not near the original.
I'll attach the schematic and Hi-Res pics from the board, can anyone take a look? Maybe I've skipped any connection.

https://www.dropbox.com/sh/avx50cks3pryvjd/pTJFjXekaA

Cheers

miklax · Post by **miklax** » 06 Mar 2014, 00:45

Hi there!

I've found a little bug on my schematic!!

I'll update the corrected one! It was on the R67 connection.
I think its 100% now... will see tomorow.
By the way, there are many components i've ignored, as they are not present in this pedal, or are used for TC's bypass scheme..

Cheers!

commathe · Post by **commathe** » 06 Mar 2014, 03:40

Awesome! I had been looking for this.

andershenrik · Post by **andershenrik** » 06 Mar 2014, 12:36

Hi miklax

Thanks for your good work, but i think something is wrong with the drawn conections to IC2b . The amplification is feedbackresistor/r5 . and the feedbackresistor is 0R !
so nothing will pass.
kind regards anders

andershenrik · Post by **andershenrik** » 06 Mar 2014, 13:03

Hi again.

It might be right after all . Ic 2b is making midpoint voltage.
sorry for the noise.
kind regards anders

miklax · Post by **miklax** » 06 Mar 2014, 17:47

Wellll... I've re-verified the schematic, and my first version is correct, at least regarding the connection I thought it was wrong..
I'm missing something for shure!!!

lukatosh · Post by **lukatosh** » 06 Mar 2014, 23:28

Hello miklax!

Is there a way that you could post some Guts to help in the trace?

Thanks!

miklax · Post by **miklax** » 07 Mar 2014, 01:39

lukatosh wrote:Hello miklax!

Is there a way that you could post some Guts to help in the trace?

Thanks!

I've uploaded some pic's I've taken prior and after the initial IC-Swap. (I wanted to fit some OPA2134's in there). Don't know if they will be any good for this..
Dropbox Folder

Also, I've realized that two of the cap's had incorrect value.
Updated schematic in here

I'm really getting a hard time with this one... Any new ideas?
Cheers!

alexradium · Post by **alexradium** » 07 Mar 2014, 14:25

do you want ideas to make it work or to guess if the schematic makes sense?
IMO there is something missing,but i cannot confirm it without having it under my eyes.
Anyway it looks a lot like a RC Booster,with a filter in front.
Not too bad priced though...
How is the opto chip used?
is it like in the Voodoolab series ?

coldcraft · Post by **coldcraft** » 07 Mar 2014, 14:47

please allow me to analyze. The input is a bootstrapped Opamp buffer. Then it goes to IC3A&B, which is a lot like a Bluesbreaker or King of Tone. From there it goes to a non-inverting amplifier (IC6A) and onto IC6B which is an active Baxandall, not unlike the Xotic Pedals.

IC2B is just supplying a Buffered 4.5V signal.

coldcraft · Post by **coldcraft** » 07 Mar 2014, 15:28

Here's my redrawn schem of just the audio portion. The 4.5V buffer has been dropped and is basically what I have called VR. The clipping diodes come between VA and VB

miklax · Post by **miklax** » 07 Mar 2014, 17:52

Hey Coldcraft!

Thanks for your schem!!

Great work!

A few questions.. For the VR, we can simply use a regular voltage divider?
On my schematic, I've got 220 nF for C41... you used 1uF (C12).. any particular reason for that exchange?
Also, you use 1K on R17, when the original one was 47K, any reason in particular also?

Cheers!

coldcraft · Post by **coldcraft** » 07 Mar 2014, 19:00

i just forgot to change the value of those after i copied them.

coldcraft · Post by **coldcraft** » 08 Mar 2014, 01:28

miklax wrote:Hey Coldcraft!

Thanks for your schem!! Great work!

A few questions.. For the VR, we can simply use a regular voltage divider?
On my schematic, I've got 220 nF for C41... you used 1uF (C12).. any particular reason for that exchange?
Also, you use 1K on R17, when the original one was 47K, any reason in particular also?

Cheers!

you could just use a divider, but you'd have an extra opamp anyway, if using duals and/or a quad so I think its best to use the 4.5V buffer.

miklax · Post by **miklax** » 08 Mar 2014, 01:55

So, I've rearranged my schematic, according to your version, and here it goes!!

Full schematic (minus truebypass switching, that uses an optocoupler similar to the voodoo lab circuitry).
I'll test it tomorrow, to see if it's finally 100% working!
I've changed the two cap's for the correct value and everything seems to work ok.

I'll keep you posted!!

Cheers!

alexradium · Post by **alexradium** » 08 Mar 2014, 10:45

thanks for the schematic
It should be interesting to point out the choice of capacitors,there are through hole and smd,i heard smd elcos have a bad reputation soundwise as coupling caps.
Anyone can confirm this?

coldcraft · Post by **coldcraft** » 08 Mar 2014, 14:45

r6 and r47 puzzle me. I've not seen resistors to actual ground like that with opamps used at a 4.5V virtual ground.

marshmellow · Post by **marshmellow** » 09 Mar 2014, 21:53

coldcraft wrote:r6 and r47 puzzle me. I've not seen resistors to actual ground like that with opamps used at a 4.5V virtual ground.

They are supposed to bias the opamp into class A operation. Of course a resistor makes for a rather primitive current source, the current draw will be dependent on the audio level at the output.

miklax · Post by **miklax** » 11 Mar 2014, 00:32

A little update:
The schematic is now verified! Works great!!

Cheers!

miklax · Post by **miklax** » 11 Mar 2014, 02:14

By the way..

What do you think about the active filter section?

Any Idea on how to calculate the corner frequency for each of the switch positions?

https://www.dropbox.com/s/l1p41wjfl27o8zq/Untitled.jpg

Cheers!

TC Electronic - Spark Booster [traced]