Tech21 - Character Series.  [schematic]

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bucksears
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Post by bucksears »

I'm half tempted to get a Liverpool just to see what's inside, but if someone has already had a look, I'd be interested to hear it.
Supposedly, some guy on YouTube bypassed the speaker sim so he could use it with his amp - that's what I'm looking for.

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Post by Nocentelli »

I'd love to see inside the Blonde - My brother-in-law has one coming, so i'll try and convince him to let me open her up, and take pics (goop permitting). I half suspect it's all smd/chips.

As for cab emulation, I've no idea why they couldn't have wired it with two outputs, one straight out for amps and one with cab sim for the desk: Even Digitech managed this with their $30 Bad Monkey.
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Post by mxrmxr »

Just got the British pedal. The PCB looks the same as the pics posted by sonicvi of the Bass VT pedal (copied below). It must be just different value changes for each pedal.

Image

Image

I think the problem with these pedals will be the goop module that's in them. What's going on in there ? I'm tempted to have a go at de-gooping but it looks very fragile :hmmm: . It'll probably end in tears.

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Post by bucksears »

Thanks man.
That's what I was afraid of: surface mount parts. I'd love to know how that guy bypassed the speaker sim, though.

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Post by estragon »

mxrmxr wrote:Just got the British pedal. The PCB looks the same as the pics posted by sonicvi of the Bass VT pedal (copied below). It must be just different value changes for each pedal.

I think the problem with these pedals will be the goop module that's in them. What's going on in there ? I'm tempted to have a go at de-gooping but it looks very fragile :hmmm: . It'll probably end in tears.
Looking at the pictures and putting into perspective the cleverly embellished marketing info available at the manufacturer's site, I'm pretty confident these characters modules are nothing but a modified version of the sansamp GT-2. Let's go into more detail:

1) Three transistors visible, all with a diode in series with the middle pin. All of them part of the bypass/mute circuitry.

2) Two 14-pin IC's. Typically this would mean 8 opamps, just like in the sansamp GT-2.

3) No visible clipping diodes->opamp clipping only.

4) At this point I'd adventure to suggest a general topology:
- Input stage
- Preclipping equalization (aka Character control, just like the Amp setting in the GT-2)
- Gain control
- Gain stages
- Generic cabsim
- Speaker voicing (depending on the model, just like the mike positioning in the GT-2)
- Three band tone control (mid frequency set differently for the Blonde only)

5) Regarding the "personality module", its size as well as some basic economic considerations strongly suggest it contains just passive components like capacitors and resistors. Moreover, looking at the pictures you can see some connections go towards the input, while others go towards the output. This suggests some components define the preclipping equalization (character) while others define the post-equalization (speaker voicing). I bet you could just unsolder this element and do some measurements with a signal generator and oscilloscope in order to determine the internal topology and component values. Not as easy as measuring resistors and capacitors, I agree, but certainly doable.

6) It call my attention that the bottom layer shows some vias/pads labeled "C", "MB" and "BR". Perhaps unused options for a "bright" and "medium bright" switch? Maybe MB=mesa b00gie and BR=british? Maybe they are used on some of the other variations? All in all these pictures pertain to a bass amp version. ***It would be great to see pictures of the other incarnations of these pedals***

Time will tell, but for now these pedals are very close a "sansamp GT-3" to me.

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Post by DimebuGG »

Yeah, that's what I'm thinking too judging by the quads used..I was thinking the VT Bass is just a Bass Driver DI with mid control and some altered values..
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Post by mxrmxr »

Here's some naked pics of the Blonde Pedal. I used my camera phone so the pics are not brilliant. But it's better than nothing.

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Post by mxrmxr »

Some more....

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Post by mxrmxr »

and some more ........

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Post by mxrmxr »

and more........

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Post by mxrmxr »

and a couple more.......

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Post by DimebuGG »

That yellow-orange encapsulated SIP(opamp?) really intrigues me.. :scratch:

And before those 2264 chips were supposedly hidden/sanded, etc..
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Post by estragon »

Those pictures add more information. Let's see:

1) On both the VT Bass and the Blonde the yellow SIP is labeled CH34-4. Maybe it's just the case that these two pedals share the same personality module, while the others are different.

2) The Blonde has a 47nF yellow capacitor that's not installed on the VT Bass (you can see the empty pads).

3) The letters A, B, C, D & E are for zero-ohm resistors or jumpers. There is a hole under each location, so when the board is mounted with the components down one can easily tell which jumpers are installed. Clever. The VT Bass has only jumper "E", while the Blonde has only jumper "A". Points 2) and 3) mostly confirm the PCB is the same for all pedals in the series, just loaded and configured differently.

4) One of the pictures clearly shows that all pots are 100k linear, same as in the GT-2--a nice feature from the stock and parts cost point of view.

5) Not really relevant, but I'll mention it for completeness anyway: the look and shine of the solder joints suggest the boards is ROHS compliant (leadless solder).

As a side note, I've been looking at the demo videos on the pedals, and in particular, the Liverpool. The character control varies from 7 o'clock to noon from very bright and low gain to mid-gain and bassy (like a lot of bass cut to no bass cut). Then from noon to 5 o'clock varies from mid-gain and bassy, to high-gain and mid boosted (increasing the gain for the mids). Nevertheless the level control needs to be adjusted heavily to maintain the output level.

I haven't come up with a way to implement such function with a single control yet, so this is something that intrigues me. Looking at the videos for the other pedals, it seems this behavior is a common feature among the rest of the pedals.

Hope more pictures arise for the other pedals in the series. Each should reveal a bit more of information.

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Post by JiM »

2bis) In the VTBass, you can notice a small SMD cap missing next to the "missing" 47nF cap.

6) In the upper-right-hand corner, there are three grey 22nF caps in the Blonde that are white-ish 10nF (one of them sanded ?) in the VTBass.

The PCBs are indeed identical, they bear the same markings and references. The jumper-over-the-hole identification technique is useful for automated testing (e.g. a bed of nails), identifying the board by needle-like switches, or photodiodes.

The SIP module can be anything, standard or custom-made, but it reminds me of some passive filter networks found in TVs or old VCRs.

From an industrial point of view, it makes sense to standardize the custom parts along the series of products. The PCBs are identical, the pots are identical, i bet the SIP modules are identical too. The difference between the models then lies in the values of the (SMD or not) components fitted on the boards, including identification jumpers. Simply load a different program in the pick&place machine !

About the "character" control, it could be something remotely like the "contour" of a Marshall Valvestate. The latter goes from mid-cut to hi-cut, with quite flat and slight hi-boost in between.
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Post by estragon »

JiM wrote:The PCBs are indeed identical, they bear the same markings and references.
OK, this makes sense and eases things up.
JiM wrote:The jumper-over-the-hole identification technique is useful for automated testing (e.g. a bed of nails), identifying the board by needle-like switches, or photodiodes.
Cool!
JiM wrote:The SIP module can be anything, standard or custom-made, but it reminds me of some passive filter networks found in TVs or old VCRs.
From an industrial point of view, it makes sense to standardize the custom parts along the series of products. The PCBs are identical, the pots are identical, i bet the SIP modules are identical too. The difference between the models then lies in the values of the (SMD or not) components fitted on the boards, including identification jumpers. Simply load a different program in the pick&place machine !
Agreed.

About the SIP, being 8 pins it makes a lot of sense being a dual op-amp. After all, the character control is more complex than the GT-2, and also the transistor buffer present in the GT-2 is not present here, so its function may be covered by this SIP device as well.

Looking more carefully at the PCB you can figure out that pin 1 is GND, while pin 5 is VCC. This doesn't match the pinout of some representative devices such as NJM4559L or NE5532L. Nevertheless I still think it could be a disguised SIP dual opamp. It is clear that Tech21 changed their goop-based copy protection scheme to this odd device, otherwise it is pretty straight forward to lift the circuit. As the SIP is custom enclosed, nothing precludes them from having it with the pins numbered backwards, and indeed they are, since pin one is usually the leftmost when looking straight at the lettering, but in this case it is the rightmost. So, if this were a dual opamp, pin 8 becomes pin 1 and pin 5 becomes pin 4. Now this corresponds to the two typical power pins in SIP-8 packages, except that the polarity of the power pins is inverted with respect to the commercial standard. It is not impossible that they ordered a large batch of these IC's with a custom pinout and custom packaged.

Side note: I have seen that trick before in an IC used in Alfa Romeo cars for the tachometer circuit. This was a 3-legged TO-220 device (not a transistor) which was prone to failure. The original chip (stamped with Alfa Romeo logo and custom P/N) costed about 60 USD, but someone that used to work for A.R. suggested to get a certain common voltage regulator and cross pins 2 and 3 when installing. This indeed did the trick and costed about 1 USD. So apprently the "special" part used in the tachometer was a custom packaged and labeled voltage regulator. End of sidenote.

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Post by RnFR »

estragon wrote: Looking more carefully at the PCB you can figure out that pin 1 is GND, while pin 5 is VCC. This doesn't match the pinout of some representative devices such as NJM4559L or NE5532L. Nevertheless I still think it could be a disguised SIP dual opamp. It is clear that Tech21 changed their goop-based copy protection scheme to this odd device, otherwise it is pretty straight forward to lift the circuit. As the SIP is custom enclosed, nothing precludes them from having it with the pins numbered backwards, and indeed they are, since pin one is usually the leftmost when looking straight at the lettering, but in this case it is the rightmost. So, if this were a dual opamp, pin 8 becomes pin 1 and pin 5 becomes pin 4. Now this corresponds to the two typical power pins in SIP-8 packages, except that the polarity of the power pins is inverted with respect to the commercial standard. It is not impossible that they ordered a large batch of these IC's with a custom pinout and custom packaged.
nice catch! that does seem like it would be a cheap and easy way to add some confusion to the mix.
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Post by mxrmxr »

o.k.......... I was feeling very brave today so I decided to take the Sansamp de-goop challenge.

Here's what I've unearthed so far:
Goop module 1.jpg
Goop module 2.jpg
BTW has anyone started a schematic for this pedal yet ?

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Post by estragon »

WOW!

So, we have a TLC2262 and a transistor. Hopefully you would be able to read the transistor P/N to determine if it is a JFET or a bipolar device. Maybe the transistor is just the output buffer as in the GT-2.

Be very careful with those film resistors in there, so the value can be measured! When measuring them, try with both polarities of the meter. If you get the same reading both ways, you can be quite confident that the internal opamp circuitry is not affecting the reading. If you get different values, the component would need to be isolated for measurement.

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Post by mxrmxr »

Some more pics..

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Post by mxrmxr »

Some more pics...

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