Tech21 Character Series  [schematic]

All about modern commercial stompbox circuits from Electro Harmonix over MXR, Boss and Ibanez into the nineties.
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sssteeve
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Post by sssteeve »

Here is a folder on my Box.com page that has all of the drawings that I have collected from this thread. I will continue to add more files to this folder.

https://www.box.com/s/264rqj7469bk2wz3fqak

New twist on game plan for cabsim bypass on my "Version WTF" VT Bass: rather than focusing on the switch and its location I am going to try a "breadboarding" approach where I can patch in different caps and resistors until I get the sound I want (I am looking for cleaner sounds at lower gain levels.) I might skip the switch and just have it hardwired for a cabsim bypass... I am still trying to figure out the radically different layout on my pedal.

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12Bass
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Post by 12Bass »

Sorry I haven't replied to this thread sooner. Things have been busier than normal. Nice to see continued interest!

There are a variety of possible approaches to adding a speaker simulation bypass. Above I outlined only one of them, and I'm not sure exactly how Tech 21 went about it. The send signal could be taken from a few different places. Adding trimmers to match volume levels is a nice idea. Also, I used a DPDT switch in the most recent implementation - one side of the switch switches between the output of the sim circuit or pre-sim signal, while the other half is used to switch the low pass filter on when the sim is bypassed (sends pre-sim signal to ground via a small capacitor to offset the circuit's inherent treble boost). I encourage people to experiment to see what sounds best.

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Post by sssteeve »

Glad to see you checking in, 12Bass- I have been studying all of your posts here about adding the cabsim bypass switch to your VT Bass. I was going to suggest starting your own thread specifically about wiring up cabsim switches so the information isn't buried in 19 pages with 350+ posts.

Can you post the date code on your VT Bass? Mine is 1020 which I suspect puts it in 2010. Perhaps I have an intermediate design between Version 1 and Version 2 since it doesn't match up to any of the pictures here (the circuits also seem to be different for what I have checked so far.)

I think that the Joyo units might be more promising to mod- I would like to convert one of their $40 pedals into another VT Bass for experimenting. (I have all 4 Joyo Sansamp Character pedals and am not crazy about the California Sound so I might use that as a donor pedal...)

Thanks for all of your posts on the subject!

Steve Ahola
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artaommahe
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Post by artaommahe »

Can someone post result schematic with speakersim bybass? =) based on Liverpool shematic somethere in ththis read. it would be perfect ;)
thx for your work )

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Post by sssteeve »

artaommahe wrote:Can someone post result schematic with speakersim bybass? =) based on Liverpool schematic somethere in ththis read. it would be perfect ;)
thx for your work )
I am putting together a PDF file based on the various posts here regarding the cabinet simulation bypass, with all of the appropriate drawings. I should have it uploaded by the weekend.

Steve Ahola
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Post by sssteeve »

With my VT Bass cabsim bypass project getting more complicated I figured that I would do a simple mod to my Joyo AC Tone to make it more like the Liverpool by removing one resistor (R9, I think).
Great plan only the PCB in my AC Tone is completely different from the one in the AC Tone thread. :(
The date code on my board is 2011.04.19 (I'll post a picture when I find my camera.)
Does anyone have any information on the newer Joyo pedals?

Steve Ahola
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JOHNO
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Post by JOHNO »

Hi sssteve. If you search the forum for joyo british sound guts you will see the pics of the board that is in the unit i own. Seems joyo changed the layout. I have no more info than that.

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Fix_Metal
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Post by Fix_Metal »

Hello everybody. I just ripped a brand new VT Bass V2 and found out the missing values.
All electrolitic decoupling 2.2uF caps have been replaced by 1uF SMD ceramics too.
Plus
UPDATED TABLE AS 3 FEBRUARY 2013:

Code: Select all

        +------------------------------------------------------+-------------------------------------------+
        |                    T e c h   2 1                     |                  J O Y O                  |
        +---------+---------+------------+-----------+---------+----------+---------+------------+---------+
        | Blonde  | British | California | Liverpool | VTBass  | American | British | California | AC Tone |
--------+---------+---------+------------+-----------+---------+----------+---------+------------+---------+
R4      | *3.3k   |   10k   |            |   3.3k    |  3.3k   |   *10k   |         |            |   10k   |
E1      |  open   |   18n   |            |    22n    |  820pf  |   open   |         |            |   22n   |   Input &
Cin     |   22n   |   22n   |            |    22n    |  22n    |    22n ? |         |            |   22n   |  filtering
C2      |   47n   |   47n   |            |    47n    |  open   |    47n ? |         |            |   47n   |
--------+---------+---------+------------+-----------+---------+----------+---------+------------+---------+
C5      |   22n   |   10n   |            |    22n    |   10n   |    22n   |         |            |   22n   |
C6      |   22n   |   10n   |            |    22n    |   10n   |    15n   |         |            |   22n   |
R6      |    1k   |    1k   |            |     1k    |    1k   |     1k ? |         |            |    1k   |  Character
R7      |  100k   |  100k   |            |   open    |  100k   |   100k   |         |            |  100k   |   pre-EQ
R9      |    1k   |  3.3k   |            |   3.3k    |  3.3k   |   3.3k   |         |            |  3.3k   |
--------+---------+---------+------------+-----------+---------+----------+---------+------------+---------+
R14     |   47k   |   33k   |            |    47k    |   33k   |    33k   |         |            |   33k   |
C14     |  470p   |  470p   |            |   180p    |   470p  |     ?    |         |            |    ?    |  HP sim
C15     |  2.2n   |  2.2n   |            |   2.7n    |   2.2n  |   2.2n   |         |            |  4.7n ? |
--------+---------+---------+------------+-----------+---------+----------+---------+------------+---------+
C20     |   10n   |   22n   |            |    18n    |   10n   |    15n   |         |            |   18n   |   MID
C21     |   10n   |   22n   |            |    22n    |   10n   |    15n   |         |            |   22n   |    EQ
--------+---------+---------+------------+-----------+---------+----------+---------+------------+---------+
*Not used
Enjoy :mrgreen:

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Fix_Metal
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Post by Fix_Metal »

There's a CH34-7 (some schematic posted here showed CH34-4)part number. Don't really know if this info is worth something.
I was just wondering what layout should I use for making this pedal. I've sawn tarjeta 1 and 2 layouts. Plus, how you guys replaced that CH34 thing?

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Post by Fix_Metal »

And btw all pots are 100KB (linear), opamps are TLC2264.

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Post by artaommahe »

Tech21 VT Bass DI with Blend pot released - http://www.bassplayer.com/article/tech- ... ack/150583

We need this(blend pot realization)! :horsey:

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Post by DimebuGG »

artaommahe wrote:Tech21 VT Bass DI with Blend pot released - http://www.bassplayer.com/article/tech- ... ack/150583

We need this(blend pot realization)! :horsey:
Add a 2.2uF cap from the first opamp IC1a, connect the other end to the "CCW"(1) leg of the added pot as Blend(100K perhaps). Then connect the "CW"(3) leg to the out of IC1d. And finally, connect the Wiper(2) to the CCW(1) leg of Level pot. Problemo solved!(Skipper).
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Post by artaommahe »

DimebuGG, oh.. okay :|
i hoped there will be something more than a bass driver blend ;)

but what with clean and drived levels at blend pot? i mean that drive section has big gain and with 1v clean signal at blend pot i will have much more drived, so result signal will be more drived than sum with clean.
Also i use my vt bass clone as real preamp and connect it to Amplifier In(bypass native preamp) and with this blend system i will not be able to use it fully.

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Post by DimebuGG »

Correct. I was thinking actually by adding a FET or IC gain stage for the clean side but hey check this @ 4:36 - 4:42, .
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Post by artaommahe »

DimebuGG, hm.. it's mean that there is so simple blend?) realy quiet clean.. but how will blend work correct if we mix quiet clean and loud drived

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Post by Fix_Metal »

Is there anybody out there who still has the Simulink/Matlab/Spice simulation for these Character series?
I've managed to modify a Harley Benton (Joyo) British over VT Bass. I'm having some troubles actually because of a too low output level, but I'm working on that.
I found that the new layout by Joyo shows component names on silk screen, so I traced them out. There's a strange input FET switching stage, I will trace that out too on tomorrow.
Critical component values are here. Any would please plot them out? That 82pF value is wrong for sure, even it's the value I read. Maybe cooked-soldered-cap? :popcorn:

Code: Select all

        +------------------------------------------------------+-------------------------------------------+
        |                    T e c h   2 1                     |                  J O Y O                  |
        +---------+---------+------------+-----------+---------+----------+---------+------------+---------+
        | Blonde  | British | California | Liverpool | VTBass  | American | British | California | AC Tone |
--------+---------+---------+------------+-----------+---------+----------+---------+------------+---------+
R4      | *3.3k   |   10k   |            |   3.3k    |  3.3k   |   *10k   | 10k(R4) |            |   10k   |
E1      |  open   |   18n   |            |    22n    |  820pf  |   open   | 22n(C3) |            |   22n   |   Input &
Cin     |   22n   |   22n   |            |    22n    |  22n    |    22n ? | 22n(C1) |            |   22n   |  filtering
C2      |   47n   |   47n   |            |    47n    |  open   |    47n ? | 47n(C2) |            |   47n   |
--------+---------+---------+------------+-----------+---------+----------+---------+------------+---------+
C5      |   22n   |   10n   |            |    22n    |   10n   |    22n   | 3n (C8) |            |   22n   |
C6      |   22n   |   10n   |            |    22n    |   10n   |    15n   | 82p(C7) |            |   22n   |
R6      |    1k   |    1k   |            |     1k    |    1k   |     1k ? | 1k(R6)  |            |    1k   |  Character
R7      |  100k   |  100k   |            |   open    |  100k   |   100k   | 100k(R7)|            |  100k   |   pre-EQ
R9      |    1k   |  3.3k   |            |   3.3k    |  3.3k   |   3.3k   |3.3k(R10)|            |  3.3k   |
--------+---------+---------+------------+-----------+---------+----------+---------+------------+---------+
R14     |   47k   |   33k   |            |    47k    |   33k   |    33k   | 33k(R24)|            |   33k   |
C14     |  470p   |  470p   |            |   180p    |   470p  |     ?    |470p(C17)|            |    ?    |  HP sim
C15     |  2.2n   |  2.2n   |            |   2.7n    |   2.2n  |   2.2n   |2.2n(C18)|            |  4.7n ? |
--------+---------+---------+------------+-----------+---------+----------+---------+------------+---------+
C20     |   10n   |   22n   |            |    18n    |   10n   |    15n   |15n(C25) |            |   18n   |   MID
C21     |   10n   |   22n   |            |    22n    |   10n   |    15n   |22n(C24) |            |   22n   |    EQ
--------+---------+---------+------------+-----------+---------+----------+---------+------------+---------+
*Not used

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Post by Fix_Metal »

I'm sorry, I read E1 as 19nF actually and thought it to be 22nF + tolerance.
That'd be better 18nF as Tech 21 British.
Seems a 1:1 copy of the original, so I'm guessing C6=10nF (I must have read 82pF instead of 8.2nF man)
Updated table is here:

Code: Select all

        +------------------------------------------------------+-------------------------------------------+
        |                    T e c h   2 1                     |                  J O Y O                  |
        +---------+---------+------------+-----------+---------+----------+---------+------------+---------+
        | Blonde  | British | California | Liverpool | VTBass  | American | British | California | AC Tone |
--------+---------+---------+------------+-----------+---------+----------+---------+------------+---------+
R4      | *3.3k   |   10k   |            |   3.3k    |  3.3k   |   *10k   | 10k(R4) |            |   10k   |
E1      |  open   |   18n   |            |    22n    |  820pf  |   open   | 18n(C3) |            |   22n   |   Input &
Cin     |   22n   |   22n   |            |    22n    |  22n    |    22n ? | 22n(C1) |            |   22n   |  filtering
C2      |   47n   |   47n   |            |    47n    |  open   |    47n ? | 47n(C2) |            |   47n   |
--------+---------+---------+------------+-----------+---------+----------+---------+------------+---------+
C5      |   22n   |   10n   |            |    22n    |   10n   |    22n   | 3n (C8) |            |   22n   |
C6      |   22n   |   10n   |            |    22n    |   10n   |    15n   | 82p(C7) |            |   22n   |
R6      |    1k   |    1k   |            |     1k    |    1k   |     1k ? | 1k(R6)  |            |    1k   |  Character
R7      |  100k   |  100k   |            |   open    |  100k   |   100k   | 100k(R7)|            |  100k   |   pre-EQ
R9      |    1k   |  3.3k   |            |   3.3k    |  3.3k   |   3.3k   |3.3k(R10)|            |  3.3k   |
--------+---------+---------+------------+-----------+---------+----------+---------+------------+---------+
R14     |   47k   |   33k   |            |    47k    |   33k   |    33k   | 33k(R24)|            |   33k   |
C14     |  470p   |  470p   |            |   180p    |   470p  |     ?    |470p(C17)|            |    ?    |  HP sim
C15     |  2.2n   |  2.2n   |            |   2.7n    |   2.2n  |   2.2n   |2.2n(C18)|            |  4.7n ? |
--------+---------+---------+------------+-----------+---------+----------+---------+------------+---------+
C20     |   10n   |   22n   |            |    18n    |   10n   |    15n   |15n(C25) |            |   18n   |   MID
C21     |   10n   |   22n   |            |    22n    |   10n   |    15n   |22n(C24) |            |   22n   |    EQ
--------+---------+---------+------------+-----------+---------+----------+---------+------------+---------+
*Not used
I'm guessing the 820pF I read on that VT Bass may be a wrong read value too. Better to be 10nF (and maybe that's the critical part of my volume problem)

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Post by Fix_Metal »

Just some updates:
1)I'm confirming E1 to be 820pF. That's because C2 is missing and, therefore, that path doesn't affecte frequency response.
2)I'm having this very strange electrostatic pops here and there on the pedal. Sometimes it works without, sometimes works with'em, sometimes occours a HUGE volume drop (not even unity gain @ max level) and sometimes it doesn't work at all. Sounds to me like a bad solder somewhere but I already re-soldered 3 times all the joints where I put my hand in and the problem persist. I guess one of those 2264 cooked or something. Any tips?

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Post by Fix_Metal »

Fix_Metal wrote:Any tips?
After some debug, I found the problem. It's just about mis-biasing of almost every opamp on the board. That's because of very poor and tiny traces and a few messed up things I did.
I'm going through this and it seems to work.
Is there a schematic of the Speaker simulation switch anywhere? I just found "where-to-solder" pics in here...

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Post by Fix_Metal »

I ended up throwing in the bin that Joyo PCB. Actually it is possible to just modify that but you gotta be EXTREMELY careful during soldering process.
I ordered various samples from TI for SMD 226x ICs and changed up the parts a few times. In the end I was getting bad bias over opamps because of bad contacts which I couldn't resolve. I.e. I tried to isolate one feedback opamp for voltage measure because I couldn't figure out WHY it was not biased. Even if ALL the traces where isolated from other parts I was reading some real Volts. Plus, I had 2 pot chassis sweeped by voltage too, even if they were isolated on the board!!
I think the main problem is the real poor PCB job done on these, that gets worse and worse as soon as you heat it.
Just for having a complete reference about this pedal modification (Joyo over Tech21), here are the missing parts:
-R106 is missing in the British pedal (220K). It is located near U2 and it's R16.
-Bias voltages are all V/2 except for IC2a which is a bit higher (keep in mind that Vcc pass through R37//R38, and ground is elevated by R39//R40, so that what should be +9V will actually be kinda lower, ~7,5V)
-Switching part is shown in this schematic. It is not true bypass and the buffer alters frequencies, so I'd suggest just to get rid of that. There's no reference for diode/transistor as there's nothing written on them, but I'd suggest they are mosfet+zener protection diode (if it was JFET, a diode wouldn't be useful in that place)
-All pots are 100KB

I ended up making my own pcb for the V-Bass and it worked fine at first time. Oh, and I got rid of those Vcc/GND resistors. I think it's just pointless using rail-to-rail technology if you don't run them at full available voltage. The resulting voltage range is actually identical to what you'd expect from straight TL07x/TL06x.
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