Tech21 - Character Series.  [schematic]

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VT Bass Version WTF cabsim bypass

Postby sssteeve » 01 Jan 2013, 08:36

I came up with a game plan to add a cabsim bypass to my "Version WTF" VT Bass. I can tap the bypass signal from either Pin 6 of the module or a pair of copper pads which have a resistance of 22k to P6. There are 3 pair of double pads near the module- the pair closest to the module has a 22k resistance to P6, the other two pairs are all connected together with no resistance to P6. (I might check for capacitance tomorrow- those 4 pads could be connected to P6 through a 22k resistor and a coupling capacitor.)

There is no jumper going to the hot terminal of the Volume control as in the Version One drawing. However there is a small copper ring connected to the hot terminal by a short trace which could be cut. So that copper ring would be cabsim signal, with the common terminal of the switch connected to the pot terminal pad.

To connect P6 to the volume control I will run it through a .047uF cap and then from that point I will have two 100k trim pots, one going directly to ground and the other one going to a 0.047uF cap connected to ground. With the trimmers I can match the volume levels and have some adjustment over the tone of the bypassed signal. To get this to work transparently I will need to use a DPDT switch so that circuitry is not connected to P6 when the cabsim is not bypassed. So I just need to figure out a good place to locate the DPDT switch.

Steve Ahola

P.S. I was able to remove PCB from box without having to remove any jacks- although I did loosen the solder on the output jack. So I was able to test the pedal after removing the board to make sure that it was still working. Perhaps someone can post the date code on their VT Bass to help determine if this board came before or after the Version 1 drawings and pix posted here.
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Re: Tech21 - Character Series.

Postby sssteeve » 02 Jan 2013, 03:42

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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Re: Tech21 - Character Series.

Postby 12Bass » 02 Jan 2013, 07:30

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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Re: Tech21 - Character Series.

Postby sssteeve » 02 Jan 2013, 10:27

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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Re: Tech21 - Character Series.

Postby artaommahe » 02 Jan 2013, 15:52

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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Re: Tech21 - Character Series.

Postby sssteeve » 03 Jan 2013, 10:41

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.

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Re: Tech21 - Character Series.

Postby sssteeve » 05 Jan 2013, 09:25

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?

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Re: Tech21 - Character Series.

Postby JOHNO » 05 Jan 2013, 09:31

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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Re: Tech21 - Character Series.

Postby Fix_Metal » 03 Feb 2013, 15:06

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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Re: Tech21 - Character Series.

Postby Fix_Metal » 03 Feb 2013, 15:13

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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Re: Tech21 - Character Series.

Postby Fix_Metal » 03 Feb 2013, 15:14

And btw all pots are 100KB (linear), opamps are TLC2264.
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Re: Tech21 - Character Series.

Postby artaommahe » 21 Feb 2013, 17:56

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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Re: Tech21 - Character Series.

Postby DimebuGG » 21 Feb 2013, 20:28

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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Re: Tech21 - Character Series.

Postby artaommahe » 21 Feb 2013, 21:27

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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Re: Tech21 - Character Series.

Postby DimebuGG » 21 Feb 2013, 21:53

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, http://www.youtube.com/watch?v=MSmUe5mDI5I.
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Re: Tech21 - Character Series.

Postby artaommahe » 21 Feb 2013, 22:24

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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Re: Tech21 - Character Series.

Postby Fix_Metal » 26 Feb 2013, 01:52

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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Re: Tech21 - Character Series.

Postby Fix_Metal » 26 Feb 2013, 01:58

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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Re: Tech21 - Character Series.

Postby Fix_Metal » 28 Feb 2013, 10:46

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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Re: Tech21 - Character Series.

Postby Fix_Metal » 07 Mar 2013, 12:07

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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