Tech21 Character Series

estragon · Post by **estragon** » 05 Aug 2009, 20:26

DimebuGG wrote:I kinda revised the schem and corrected some minor mistakes in the feedback loop at the input stage. The EMPTY pads on it appears to be a capacitor on VT Bass.

Excellent. May I suggest for clarity sake that pins 1 and 3 of the character pot be interchanged. In this way this stage can be drawn identical to the MID control stage.

estragon · Post by **estragon** » 05 Aug 2009, 20:29

mxrmxr wrote:Great work DimebuGG & estragon
Here's a pic of the PCB with the through hole caps removed, and some pics showing the values of the Electrolytic caps.
I also removed the 4013 ic as well. What the hell Gone this far.
Hopefully this will get us close to the final Schem.
In the mean time, I've got a pedal to rebuild

Man, I salute you for your dedication in this quest. Just hope you'll be able to measure the SMD caps in the main board and the resistors in the hybrid device. There are three resistors in this device which are not possible to measure independently of the others (R103-R105-R106). Let me know if you need help on how to do this without having to furher intervene the board--it is possible.

Post by **mxrmxr** » 05 Aug 2009, 21:20

estragon wrote:
mxrmxr wrote:Great work DimebuGG & estragon
Here's a pic of the PCB with the through hole caps removed, and some pics showing the values of the Electrolytic caps.
I also removed the 4013 ic as well. What the hell Gone this far.
Hopefully this will get us close to the final Schem.
In the mean time, I've got a pedal to rebuild
Man, I salute you for your dedication in this quest. Just hope you'll be able to measure the SMD caps in the main board and the resistors in the hybrid device. There are three resistors in this device which are not possible to measure independently of the others (R103-R105-R106). Let me know if you need help on how to do this without having to furher intervene the board--it is possible.

Yeah I will be measuring the remaining caps and the hybrid resistors. I'll post as soon as

DimebuGG · Post by **DimebuGG** » 06 Aug 2009, 16:33

This should be the final corrected schematic including the CMOS switching. This is assuming the hybrid device's Q100 is correct. I actually wrote a "semi-final" revision since SMD cap values, zeners, and the resistor values in the hybrid module is still unknown for the mean time.

mxrmxr, what's the ID of those two parallel resistors along the positive terminal of the DC jack?. They're blurred in the photo so I can't confirm their values. It looks like 68 or 56 ohms to me. Anyway, I put 68 ohms in the schematic.

PS:
Please disregard the two previous schematics as they have errors.

Post by **mxrmxr** » 06 Aug 2009, 18:39

DimebuGG wrote:This should be the final corrected schematic including the CMOS switching. This is assuming the hybrid device's Q100 is correct. I actually wrote a "semi-final" revision since SMD cap values, zeners, and the resistor values in the hybrid module is still unknown for the mean time.

mxrmxr, what's the ID of those two parallel resistors along the positive terminal of the DC jack?. They're blurred in the photo so I can't confirm their values. It looks like 68 or 56 ohms to me. Anyway, I put 68 ohms in the schematic.

PS:
Please disregard the two previous schematics as they have errors.

Great work DimebuGG

Yeah no problem I'll confirm all the comps. Actually, we need a comp ident layout diagram for the Tech21 PCB so the PCB matches the schematic. What do you think ?

JiM · Post by **JiM** » 06 Aug 2009, 18:57

Kudos DimebuGG !

mxrmxr, could you please also try and confirm the SOT-23 zener hypothesis ? Hopefully checking the diode thresholds with a multimeter should do.

Next step : find out the differences in the other models of the series. We already have gutshots of the VTBass, let's hunt gutshots of the others !

Post by **mxrmxr** » 06 Aug 2009, 19:26

JiM wrote:Kudos DimebuGG !

mxrmxr, could you please also try and confirm the SOT-23 zener hypothesis ? Hopefully checking the diode thresholds with a multimeter should do.

Next step : find out the differences in the other models of the series. We already have gutshots of the VTBass, let's hunt gutshots of the others !

Sadly the SOT-23 broke in half when removing

My only casualty in this venture. It's got to be a zener pair as denoted by the V3 marking.

bajaman · Post by **bajaman** » 06 Aug 2009, 20:09

Yes - 2 x 3.3v zeners should work fine

great work guys

i ran the preliminary circuit with a few guesses in microcap 9 simulator - onmce final values are confirmed I will publish response curves for everyone's enjoyment.
cheers
bajaman

DimebuGG · Post by **DimebuGG** » 07 Aug 2009, 06:53

Added component numbering in the schematic for reference.

Post by **mxrmxr** » 07 Aug 2009, 07:34

DimebuGG wrote:Added component numbering in the schematic for reference.

You beat me to it DimebuGG.......I was going to make a start on that pic and add the comp idents. Your too quick man

You've saved me a job anyway

Great work. The schematics looking cool as well

I'll get to work over the weekend and get all the component values.

BTW......Could you add idents for the pots as well. VR1, VR2 etc, etc. Thanks

bajaman · Post by **bajaman** » 07 Aug 2009, 21:30

I just bought the British.
When it arrives I will crack it open and reverse engineer it for everyone's information.
Should be a breeze to do after all the hard work put in by you guys on the Blonde

Anyone willing to do the same for the California, Liverpool or VT Bass models?
cheers
bajaman

Post by **mxrmxr** » 08 Aug 2009, 15:11

o.k here's the SMD component values for the main PCB:

c101=22nf
c30=47nf
c103=47nf
c102=47nf
c23=100nf
c24=10nf
c28=22nf
c27=120pf
c20=10nf
c21=10nf
c19=120pf
c18=120pf
c26=4.7nf
c25=1nf
c15=2.2nf
c13=47nf
c16=1nf
c14=470pf
c12=10nf
c11=47nf
c104=47nf
c1=1nf
c4=120pf

R209=103
R210=103
R37=680
R38=680
R39=471
R40=471
R207=103
R208=103
R35=103
R36=103
R206=104
R205=223
R204=103
R200=222
R202=1M
R211=1M
R201=1M
R32=102
R1=103
R2=1M
R203=1M
R34=102
R33=104
R25=332
R27=332
R26=1M
R29=104
R31=332
R19=103
R28=332
R30=1M
R24=332
R21=104
R23=104
R20=104
R22=332
R18=333
R17=333
R16=103
R15=333
R14=473
R13=104
R12=332
R11=332
R9=102
R6=102
R7=104
R8=104
R5=223
R4=332
R3=223
R10=103

Q1, Q2 and Q3 have a marking that looks like 'GG' Nothing else is visable.

ZD1=C10V
ZD2=C4V7

The remaining diodes appear to be just standard 1N4148 diodes or equivalent.

Values on the goop module to follow

estragon · Post by **estragon** » 08 Aug 2009, 16:02

mxrmxr wrote:o.k here's the SMD component values for the main PCB:

Yeeehaaa!

mxrmxr wrote:Q1, Q2 and Q3 have a marking that looks like 'GG' Nothing else is visable.

If it were "6G" you get an N-channel JFET type 2N4393, which would make sense, as seen here: http://www.marsport.org.uk/smd/smd6.htm
"66" or "GG" don't come up with something reasonable.

mxrmxr wrote:ZD1=C10V
ZD2=C4V7

10V and 4.7V zeners

Post by **mxrmxr** » 08 Aug 2009, 16:44

estragon wrote:
mxrmxr wrote:o.k here's the SMD component values for the main PCB:
Yeeehaaa!

mxrmxr wrote:Q1, Q2 and Q3 have a marking that looks like 'GG' Nothing else is visable.
If it were "6G" you get an N-channel JFET type 2N4393, which would make sense, as seen here: http://www.marsport.org.uk/smd/smd6.htm
"66" or "GG" don't come up with something reasonable.

mxrmxr wrote:ZD1=C10V
ZD2=C4V7
10V and 4.7V zeners

Yeah '6G' they will be then. The marking on them is not brilliant. I thought it was either 'GG' or '6G'. Now that you've looked into it, that just confirms it

Yes the two zeners are 10V and 4.7V respectively.

bajaman · Post by **bajaman** » 08 Aug 2009, 20:10

Almost any N channel Jfet will work - they are merely solid state switches and have negligible effect on the sound of the pedal.
Excellent work guys

I am looking forward to the module values to complete my circuit simulation graphs.
Has anyone got the VT Bass yet? I saw some pictures earlier in the thread. It would be cool to get the different component values, now that we have a numbering scheme.

cheers
bajaman

sonicvi · Post by **sonicvi** » 09 Aug 2009, 06:37

I have the Bass VT, but sorry, there's no way I'm taking that thing apart again to read component values. I'm lucky I was able to get that thing apart and back together without destroying it.

bajaman · Post by **bajaman** » 09 Aug 2009, 12:14

bajaman

Post by **modman** » 09 Aug 2009, 17:08

sonicvi wrote:I have the Bass VT, but sorry, there's no way I'm taking that thing apart again to read component values. I'm lucky I was able to get that thing apart and back together without destroying it.

What kind of attitude is this? Why did you take it apart at all without noting down the details?
Seriously, here will find all the support to put it back together again.

First time I dissembled stuff, I took a lot of digital pictures to remind me where everything went. It's a way to learn. BTW these boxes are constructed to that they can be taken apart and worked on...

now I had to take this one off-topic too,

Any other more daring volunteers?

Dirk_Hendrik · Post by **Dirk_Hendrik** » 09 Aug 2009, 17:47

Although in essence I agree with you modman, I do understand the reluctance. Tech21's are bitches to disassemble in general and doing it too often can lead to a lot of trouble getting em to function again. When not too experienced they can be a tough job.

Other than that,
One of the best threads in a long time. My deepest respect for all involved.

bajaman · Post by **bajaman** » 09 Aug 2009, 21:11

Please mxrmxr - the CH34-4 resistor values

bajaman

Tech21 Character Series [schematic]