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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Mbas974
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Post by Mbas974 »

I've noticed that the EQ section use different caps from type to type. ( C23 to C28 )

Why these are not mapped into the comparison matrix some posts above :hmmm:

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Mbas974
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Post by Mbas974 »

Question.... (stupid I think....)

R100, R103, R104 labeled NOT USED.... means that the Op-Amp are buffer or have the feedback loop has to be leaved open ?

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JiM
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Post by JiM »

Mbas974 wrote:I've noticed that the EQ section use different caps from type to type. ( C23 to C28 )
Why these are not mapped into the comparison matrix some posts above :hmmm:
That's because the first models to be traced (Blonde, British, Liverpool) do indeed have the same values there.
Feel free to expand the table.
Mbas974 wrote:R100, R103, R104 labeled NOT USED.... means that the Op-Amp are buffer or have the feedback loop has to be leaved open ?
Those resistors are open-circuit inside the gooped module. The feedback loops are not open though, look closer at the schematic. :wink:
I only give negative feedback.

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x-tn
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Post by x-tn »

bajaman wrote:...
Anyway - back to the CH34-4 module :wink:
This module uses the LINCMos TLC2262 dual op amp - internally entirely constructed with mosfets - it gain swing the signal full rail before it clips and Tech 21 have used this same device in all of their pedals from the original Sans Amp onward. It has a very soft clipping characteristic and can sound a bit "mushy' in the bass region in my opinion. However it's implementation in the character series pedal is a little different :wink: With reference to the schematics earlier in this thread you may notice two back to back 3.3v silicon zener diodes in the feedback loop of the second stage of the CH34-4 module.
It is THESE zener diodes that clip FIRST in this module according to my simulations NOT the op amp as in the original Sans Amp pedals. These zeners also roll off the high frequency response of this stage - the signal is -3dB down at 5khz and drops to over -22db at 100khz. Without the zeners, the response is flat to 100khz and beyond :shock:
I must emphasize that the signal is attenuated at high frequencies by these zeners EVEN when the signal is NOT being clipped by them :!:
The TLC2262 NEVER has the chance to influence the clipping behaviour in these pedals - all the clipping and high frequency rolloff is performed by the two back to back zener diodes - food for thought :secret:
Cheers
bajaman
bajaman wrote:I just bought a JOYO California sound pedal
...
I changed the dual op amp (TL062) - put a TLC2262 in it's place - i left the other two quad op amps (TL064).
...
bajaman
If "The TLC2262 NEVER has the chance to influence the clipping behaviour in these pedals" what would be the reason to change the TL062 with a TLC2262?

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bajaman
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Post by bajaman »

good point :wink:
be kind to all animals - especially human beings

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engineelite
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Post by engineelite »

How close are you guys to getting this finalized? I'm really anxious to build a tech21 blonde clone :mrgreen:

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Nocentelli
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Post by Nocentelli »

Hi all.

My bro-in-law has given me his Blonde to try and repair the intermittent footswitch. I knew it would be electronic switching from the schem, but I'm struggling to get it a part to check the actual board-mounted switch.

Do I actually have to de-solder the in and out jacks to get access to the board?
Steven_M wrote: 21 Jan 2011, 17:52
biffa wrote:Sorry,but u r not the only member here
I'm not? Well fuck this site then. I only want meaningful conversations with myself.

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jaylj14
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Post by jaylj14 »

What is the Q100(SOT-23) in the schematic?
Are they two 3.3V Zener?

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theV
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Post by theV »

Nocentelli wrote:Do I actually have to de-solder the in and out jacks to get access to the board?
No,
at least in my revision of VT Bass. Just unscrew the screws and all the nuts, and it comes apart.

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Stephanovitch
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Post by Stephanovitch »

I have mesured value of the California Joyo:

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 (R4) |   10k   |
E1      |  open   |   18n   |            |    22n    |  10nF   |   open   | 18n(C3) |  open (C3) |   22n   |   Input &
Cin     |   22n   |   22n   |            |    22n    |  22n    |    22n ? | 22n(C1) |   22n (C1) |   22n   |  filtering
C2      |   47n   |   47n   |            |    47n    |  open   |    47n ? | 47n(C2) |   47n (C2) |   47n   |
--------+---------+---------+------------+-----------+---------+----------+---------+------------+---------+
C5      |   22n   |   10n   |            |    22n    |   10n   |    22n   | 3n (C8) |   10n (C8) |   22n   |
C6      |   22n   |   10n   |            |    22n    |   10n   |    15n   | 82p(C7) |  open (C7) |   22n   |
R6      |    1k   |    1k   |            |     1k    |    1k   |     1k ? | 1k (R6) |    1k (R6) |    1k   |  Character
R7      |  100k   |  100k   |            |   open    |  100k   |   100k   | 100k(R7)|  100k (R7) |  100k   |   pre-EQ
R9      |    1k   |  3.3k   |            |   3.3k    |  3.3k   |   3.3k   |3.3k(R10)|  3.3k(R10) |  3.3k   |
--------+---------+---------+------------+-----------+---------+----------+---------+------------+---------+
R14     |   47k   |   33k   |            |    47k    |   33k   |    33k   | 33k(R24)|  33k (R24) |   33k   |
C14     |  470p   |  470p   |            |   180p    |   470p  |     ?    |470p(C17)| 560p (C17) |    ?    |  HP sim
C15     |  2.2n   |  2.2n   |            |   2.7n    |   2.2n  |   2.2n   |2.2n(C18)| 2.8n (C18) |  4.7n ? |
--------+---------+---------+------------+-----------+---------+----------+---------+------------+---------+
C20     |   10n   |   22n   |            |    18n    |   10n   |    15n   |15n(C25) |  22n (C25) |   18n   |   MID
C21     |   10n   |   22n   |            |    22n    |   10n   |    15n   |22n(C24) |  22n (C24) |   22n   |    EQ
--------+---------+---------+------------+-----------+---------+----------+---------+------------+---------+
*Not used


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moralo75
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Post by moralo75 »

Good afternoon, I am interested in buying an American or California Joyo to become VTBass ... you think that you may easily ??? Which would be better to buy ???
Thanks and sorry for my english ...

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rocket512
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Post by rocket512 »

Are there any values available for the Leeds ( Hiwatt)?

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Post by artaommahe »

About speakersim on-off switch.

It's strange to have 22k-10n chain after high pass filter C11-R13, because we have bass drop on speaker-sim off. It's important for VT Bass variation. So i think low pass filter 22k-10n can be moved before C11-R13 without any issues.

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Post by artaommahe »

I was wrong, the problem is in C13-R16 filter, that reduce bass response as bajaman noted above. But the solution is the same - move HP filter before C11-R13 ;)

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CloneME
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Post by CloneME »

Has anyone successfully modded one of these for less noise with the drive up?

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Post by artaommahe »

CloneME, it's opamp noise, so use them with low noise value(e.x.e TLC2272)

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azrael
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Post by azrael »

Stephanovitch wrote:I have mesured value of the California Joyo:

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 (R4) |   10k   |
E1      |  open   |   18n   |            |    22n    |  10nF   |   open   | 18n(C3) |  open (C3) |   22n   |   Input &
Cin     |   22n   |   22n   |            |    22n    |  22n    |    22n ? | 22n(C1) |   22n (C1) |   22n   |  filtering
C2      |   47n   |   47n   |            |    47n    |  open   |    47n ? | 47n(C2) |   47n (C2) |   47n   |
--------+---------+---------+------------+-----------+---------+----------+---------+------------+---------+
C5      |   22n   |   10n   |            |    22n    |   10n   |    22n   | 3n (C8) |   10n (C8) |   22n   |
C6      |   22n   |   10n   |            |    22n    |   10n   |    15n   | 82p(C7) |  open (C7) |   22n   |
R6      |    1k   |    1k   |            |     1k    |    1k   |     1k ? | 1k (R6) |    1k (R6) |    1k   |  Character
R7      |  100k   |  100k   |            |   open    |  100k   |   100k   | 100k(R7)|  100k (R7) |  100k   |   pre-EQ
R9      |    1k   |  3.3k   |            |   3.3k    |  3.3k   |   3.3k   |3.3k(R10)|  3.3k(R10) |  3.3k   |
--------+---------+---------+------------+-----------+---------+----------+---------+------------+---------+
R14     |   47k   |   33k   |            |    47k    |   33k   |    33k   | 33k(R24)|  33k (R24) |   33k   |
C14     |  470p   |  470p   |            |   180p    |   470p  |     ?    |470p(C17)| 560p (C17) |    ?    |  HP sim
C15     |  2.2n   |  2.2n   |            |   2.7n    |   2.2n  |   2.2n   |2.2n(C18)| 2.8n (C18) |  4.7n ? |
--------+---------+---------+------------+-----------+---------+----------+---------+------------+---------+
C20     |   10n   |   22n   |            |    18n    |   10n   |    15n   |15n(C25) |  22n (C25) |   18n   |   MID
C21     |   10n   |   22n   |            |    22n    |   10n   |    15n   |22n(C24) |  22n (C24) |   22n   |    EQ
--------+---------+---------+------------+-----------+---------+----------+---------+------------+---------+
*Not used

Which universal schematic does this refer to? Some of the links in the thread are to incomplete or dead images.

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av500
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Post by av500 »

mxrmxr wrote:
BTW, just got hold of a Sansamp PSA-1 rack preamp. Maybe that can be the next project after this one :wink:
Hi, don't know if you saw, I just posted PSA-1 traces and schematics: http://www.freestompboxes.org/viewtopic.php?f=7&t=25708

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gregchill
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Post by gregchill »

Has anyone got a schematic for the british

Cheers

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Post by JFace »

mxrmxr wrote:o.k here's the resistor values for the 'Goop Hybrid Module'.

This little baby still had a few surprises left.

R104 measured open circuit. My initial reaction was 'shit I've damaged it during the de-goop'. But no, closer inspection with a magnifying glass revealed that the laser trimming has cut completely through and across the resistive element, making it an open circuit. Phew, I can breath again. So, this resistor is not used.

R102 measured 218K laser trimmed. You can clearly see a couple of short laser cuts in the resistive element with a magnifying glass. So, this resistor will be 220K.

R106 measured 218K laser trimmed. You can clearly see a couple of short laser cuts in the resistive element with a magnifying glass. So, this resistor will be 220K.

R101 Measured 221K laser trimmed. You can clearly see a couple of short laser cuts in the resistive element with a magnifying glass. So, this resistor will be 220K.

R103 measured open circuit. Again, closer inspection with a magnifying glass revealed that the laser trimming has cut completely through and across the resistive element, making it an open circuit. So, this resistor is not used.

R105 measured 100K laser trimmed. You can clearly see a couple of short laser cuts in the resistive element with a magnifying glass. So, this resistor will be 100K.

R100 measured open circuit. Again, closer inspection with a magnifying glass revealed that the laser trimming has cut completely through and across the resistive element, making it an open circuit. So, this resistor is not used.
Ok, I realize this is an old post, but after breadboarding this schematic and hearing other's DIY build recordings, I have to ask, are we certain that the open circuit resistors are indeed resistors? With the amount of noise generated at the gain stage, and the obvious lack of capacitors compared to other tech 21 circuits, this leads me to believe these are in fact capacitors. Does anyone still happen to have this deconstructed and able to check the capacitance of: R100, R103, and R104?

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