Tech21 Character Series [schematic]

[DimebuGG]

I'm dying for a VT Bass's component values too..

[sonicvi]

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.

The attitude of caring whether of not the pedals that I spend my money on continue to work or not. It has nothing to do with inexperience or not knowing where things go. These are a total pain in the ass to get apart and back together. They are not really desinged to be disassembled without having to desolder the jacks and the solder pads and traces are just not robust enough to withstand very much abuse. I took those pics months ago just to show what was inside since there weren't any pics out there yet and no effort to trace the circuit had begun. Sorry to disappoint, I'd like to help, but I'm not gonna do it. Surely I'm not the only person here who has one.

[mxrmxr]

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.

[bajaman]

Thank you mxrmxr
I wonder if the unused resistors are used in a different module - it will be interesting to see whether the British pedal ( I have one in transit to me) uses the CH34-4 module
I have already cloned the double sided SMD mainboard. Next I will adapt it for through hole construction - do not hold ypur breath though as this could take several night's work.
cheers and thanks again for all your unselfish work - hope you get your pedal back together and working again
bajaman

[mxrmxr]

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

Hi bajaman,

Any chance you could share your microcap 9 files for this pedal ? I've just acquired a copy of microcap 9 and this would be a cool way to get familiar with the program

[mxrmxr]

Thank you mxrmxr
I wonder if the unused resistors are used in a different module - it will be interesting to see whether the British pedal ( I have one in transit to me) uses the CH34-4 module

Yeah I was thinking that as well. We shall see.

I have already cloned the double sided SMD mainboard. Next I will adapt it for through hole construction - do not hold ypur breath though as this could take several night's work.

What PCB software are you using ?

cheers and thanks again for all your unselfish work - hope you get your pedal back together and working again

Cheers no problem

bajaman

[bajaman]

What PCB software are you using ?

I have drawn it in CorelDraw at this stage, but I will publish a final design with through holes eventually in Sprint Layout 5.
I also have Protel 99SE, but it is a mother of a drawing program to use - Sprint is a lot easier AND it allows the importation of jpg images etc (very easy to clone) and the exportation of jpg pictures as well as gerber files etc.
himister ( a member here) put me on to Sprint Layout 5 - I am sure you can "acquire" a copy just like microcap 9
cheers
bajaman

[himister]

I have drawn it in CorelDraw at this stage, but I will publish a final design with through holes eventually in Sprint Layout 5.
I also have Protel 99SE, but it is a mother of a drawing program to use - Sprint is a lot easier AND it allows the importation of jpg images etc (very easy to clone) and the exportation of jpg pictures as well as gerber files etc.
himister ( a member here) put me on to Sprint Layout 5 - I am sure you can "acquire" a copy just like microcap 9
cheers
bajaman

Well done Steve.

Maybe we should start a new thread in Software Room about SL5 and upload some macros for the start.
Sprint Layoutgelism.

So when we can expect a pcb layout for this one?

Cheers

[mxrmxr]

This threads gone quiet all of a sudden....

DimebuGG.........not sticking around to finish the schematic ?

estragon ?

They've suddenly gone quiet

[estragon]

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.

Well, this explains some things. It was intriguing to have a resistor loading the output of the opamp to VCC, unless something special happened to the IC in this condition (R103). Also, the simulation indicated that R104 was unnecessary, so it looked to me like someone decided it was not good to leave a pin of a component unconnected and added it anyway. Finally, R100 is not really necessary as it is replaced by the GAIN pot resistance.

I wonder what we would have done if instead of opening and measuring the device we had to work with just an X-ray showing several resistors, a shape like a transistor and an opamp. It was clear that degooping was the way to go.

Another thing that bothers me is why only 4 capacitors are of the boxed type intead of smd. From the description there should be other capacitors that change from model to model, and they are also in the audio path. It is not a matter of value either.

By the way, the first opamp is biased around 5V instead of 4.5V (for some assymmetry), while the second opamp is biased around 4.5V and has the zeners probably to provide softer/better/nicer clipping. This seems to be a refinement over the previous previous sans amps (classic and GT-2).

[estragon]

This threads gone quiet all of a sudden....

DimebuGG.........not sticking around to finish the schematic ?

estragon ?

They've suddenly gone quiet

I'm still around! Hope the Liverpool surfaces some time. It was what caught my interest in this in the first place. After all, the other pedals were already covered by the GT-2 (except the VT). Looking back it is a bit funny how I was led to believe that the character control was something super-special, based on the hyped marketing info and sound samples. Nevertheless I'm pleased to see there was at least some evolution in the clipping department.

[bajaman]

By the way, the first opamp is biased around 5V instead of 4.5V (for some assymmetry), while the second opamp is biased around 4.5V

actually the first opamp (in the goop module ) is biased at approximately 6.2v dc.
Interestingly the second gain stage is biased at 4.5v dc, but the output terminal is biased to 6.2v dc through the 220k load resistor. I wonder what effect this has on the back to back 3.3v zener operation, because there will exist a dc voltage differential of 1.7v dc across them - (the inverting input will be biased at 4.5v dc)
bajaman

[estragon]

By the way, the first opamp is biased around 5V instead of 4.5V (for some assymmetry), while the second opamp is biased around 4.5V

actually the first opamp (in the goop module ) is biased at approximately 6.2v dc.
Interestingly the second gain stage is biased at 4.5v dc, but the output terminal is biased to 6.2v dc through the 220k load resistor. I wonder what effect this has on the back to back 3.3v zener operation, because there will exist a dc voltage differential of 1.7v dc across them - (the inverting input will be biased at 4.5v dc)
bajaman

If you just consider that resistors R105 (100k) and R101 (220k) form the voltage divider, yes you endup with 6.2V since 9V*220k/(220k+100k) = 6.1875V or aprox. 6.2V.

But in the above you are omitting the fact that R106 (220k) is also connected to that node, and its other end (assuming audio signal is 0V for now), is tied to a DC voltage as well since the output of the second opamp is biased at 4.5V from the outside. This is valid even when there is an audio signal present, since there is a huge 47uF filter capacitor tied to that node that filters out any audio component (to be verified later).

So in fact we need to calculate the voltage of a node fed from three sources: 9V, 0V and 4.5V, which correspond to the following resistor values: 100k, 220k and 220k, respectively. One way to go is to calculate the node voltage by superposition, which assumes in order that one and only one voltage is active at a time, and the others are zero. Then the three partial results are added up to obtain the final value. This would be:

A) 9V*(R101//R106) / (R101//R106 + R105) = 9V*110k/(110K+100k) = 4.71V
B) 0V*(R105//R106) / (R105//R106 + R101) = 0V*68.75k/(68.75k+100k) = 0.00V
C) 4.5V*(R101//R105) / (R101//R105 + R106) = 4.5V*68.75k/(68.75k+220k) = 1.07V

Then, A+B+C = 5.77V or aprox. 5.8V. (the value of 5V in my previous post was wrong, 5.8V is the correct one).

Going back to what happens when there is audio present, we see that the node impedance is R101//R105//R106 = 52.38k
If we calculate the cutoff frequency with the 47uF capacitor we obtain 0.064 Hz, menaing audio signals won't affect this node.

P.D. I don't think the 220k from the output of the second opamp to this node with different voltage would make a difference. If the resistor were close to 1k you'll probably notice some effect in the way the opamp clips or reaches its limiting levels, but this new design clips before thanks to the zeners. In my simulation a get a clipping level around +/- 3.2V using 3.3V zeners. In theory this is possible, as the actual current through the zeners is very low in comparison to the zener's rated current of tens of milliamps.

[mxrmxr]

Another thing that bothers me is why only 4 capacitors are of the boxed type intead of smd. From the description there should be other capacitors that change from model to model, and they are also in the audio path. It is not a matter of value either.

I bet thats all they change depending on the character pedal, and possibly a different goop module as well. The rest of the board is just a generic board that can be used on all the pedals. That's my guess anyway.

Also why goop that circuit. There's nothing ground breaking going on there. I wonder how much those zeners effect the tone. I must try with and without, see what difference it makes.

[bajaman]

I now have the Liverpool coming across the sea to me, as well as the imminent arrival of the British, so we shall all see the differences very soon.
cheers
bajaman

[estragon]

Another thing that bothers me is why only 4 capacitors are of the boxed type intead of smd. From the description there should be other capacitors that change from model to model, and they are also in the audio path. It is not a matter of value either.

I bet thats all they change depending on the character pedal, and possibly a different goop module as well. The rest of the board is just a generic board that can be used on all the pedals. That's my guess anyway.

Also why goop that circuit. There's nothing ground breaking going on there. I wonder how much those zeners effect the tone. I must try with and without, see what difference it makes.

The marketing info states that for each pedal the MID control frequency is set according to the pedal type, the CHARACTER is set to that particular amp, and the CABSIM is voiced for a particular type of speaker associated with the amp.

So far the boxed caps pertain to the CHARACTER control only, so other caps/resistors around the MID and CABSIM sections should be different, which means some SMD components should change as well.

http://www.tech21nyc.com/products/sansa ... eries.html#

At least the MID control is specified as +/- 12 dB gain and 500 Hz for all pedals but the Blonde, which is said to be centered at 1 kHz. We'll see how this stands when other models surface.

[estragon]

I now have the Liverpool coming across the sea to me, as well as the imminent arrival of the British, so we shall all see the differences very soon.
cheers
bajaman

This is very good news!

[mxrmxr]

I now have the Liverpool coming across the sea to me, as well as the imminent arrival of the British, so we shall all see the differences very soon.
cheers
bajaman

Yeah great news bajaman I can't wait Should be interesting

[mxrmxr]

Another thing that bothers me is why only 4 capacitors are of the boxed type intead of smd. From the description there should be other capacitors that change from model to model, and they are also in the audio path. It is not a matter of value either.

I bet thats all they change depending on the character pedal, and possibly a different goop module as well. The rest of the board is just a generic board that can be used on all the pedals. That's my guess anyway.

Also why goop that circuit. There's nothing ground breaking going on there. I wonder how much those zeners effect the tone. I must try with and without, see what difference it makes.

The marketing info states that for each pedal the MID control frequency is set according to the pedal type, the CHARACTER is set to that particular amp, and the CABSIM is voiced for a particular type of speaker associated with the amp.

So far the boxed caps pertain to the CHARACTER control only, so other caps/resistors around the MID and CABSIM sections should be different, which means some SMD components should change as well.

http://www.tech21nyc.com/products/sansa ... eries.html#

At least the MID control is specified as +/- 12 dB gain and 500 Hz for all pedals but the Blonde, which is said to be centered at 1 kHz. We'll see how this stands when other models surface.

Yeah good point about the cabsim section. I guess we wont know for sure until we see the others

[bajaman]

Woo Hoo
My British pedal just arrived from Dale Rowley (ebay seller - proaudioland on Ebay) in California USA.
My first impressions on opening the package ( while eating my breakfast) were, that the TECH 21 guys have done a really nice job at packaging this product. You get a sticky label (to help advertise their product), a pressed black tin embossed with TECH 21 in gold writing on it - no cheap brown cardboard box!!!
Upon opening the tin, I was greeted by the pedal, sticky label and instruction manual - the bottom of the tin box even has a small piece of foam plastic to cushion the contents - nice touch TECH 21.
I hastily removed the pedal from it's plastic bag and what is this - a small black plastic quick release battery cover on the bottom of the case - no need to own a screwdriver to change the battery
The graphics are amazing and even the stomp switch and input and output sockets are dull brass coloured to mimic the Marshall gold.
Must get dressed now and get on with the repairs
More later
cheers
bajaman