What the heck is that???

[digi2t]

I've always had a keen interest in the obscure stuff, I think everybody in these parts already knows that. Especially the Japanese effects world. I was bidding on an Anderson Crazy Muff (a.k.a. Rozz Dead Heat) pedal lately, but unfortunately, it went for crazy money. Too rich for my blood, but...

I did manage to make off with this little gem on the cheap. From the Rozz/Anderson family, I present the Tone Banker;





So, the $64 question. What the heck is that encapsulated module inside?







What does it do? It's a parametric EQ. You have volume, Frequency, and a Notch adjustment. Does some really cool %^&*ed wah tones, and the range on a whole is really interesting. I'm actually kinda glad I missed out on the Heat, otherwise, I may have never found this little jewel.

But what in the heck is that module??? Inductors perhaps? I can't find anything on the net on it, but I have found a site for Taiyo, Taiyo Yuden to be exact, and they do make inductors. Maybe I should drop them a line.

[Beach]

It is a hybrid circuit. i.e. part of the circuit is 'integrated' with discrete components on sort of a chip. Since this is an equalizer the bulky parts in the green could very well be inductors. Inductors are very hard to put in a real integrated circuit. It takes a lot of space and the specs are very bad. Same for capacitors. Transistors, however, are very cheap in an IC and can be used abundantly

It is probably a 'special', maybe even only for this application in which case it will be very hard to get info on the circuit.

You could indeed try and email the manufacturer. Sometimes they will just give you the circuit schematic...

[Gus]

I would guess it is a passive circuit with the EQ network inside because there are two TA7504 opamps.
If they used IC opamps I would guess the hybrid is not a opamp.

You might be able to reverse/guess some of it from looking at what part of the circuit each of the pins go to and measuring between pins. This might require removing it from the board and maybe damaging it HOWEVER, the ICs are socketed and maybe if you remove them you can use the socket connections to take measurements with a low cost LCR meter.

The parts do show a shape maybe there are caps and resistors under the coating. I once trioed to remove the coating from an old 70's custom hybrid to repair a circuit I did not have any success the ceramic like coating was hard to remove even with heat

[Rob Strand]

An alternative to Gus's account is the hybrid  is a state variable filter.     The reason I suggest that is there's a good chance that circuit uses a state-variable filter.  The TA7504's are only single opamps so there doesn't seem to be enough opamps.  So I'm suggesting the TA7504 opamps for some sort of input and output and the guts of the EQ is in the hybrid.

You will need to do some tracing to get the structure of the circuit.

DC voltages on the hybrid chip might be helpful as well.

A good deal of the hybrids I've seen end-up being some sort of opamp/preamp but it doesn't seem to fit here.  For example it could be used as a front-end preamp.   That would mean a circuit different to a state-variable filter.   There seems to be too many pins on the hybrid for a simple preamp.

[ElectricDruid]

I quite like Rob's SVF suggestion. There are a lot of pins on that little module.

It reminds me a lot of the black-glooped modules from some of the Roland Synths (Juno106 VCF/VCA module is done like this, for example). It's not one of those though!

[mozz]

Couplate. Some US sold ones back in the day there are schematics for. Sprague used to make them.

[digi2t]

You will need to do some tracing to get the structure of the circuit.

DC voltages on the hybrid chip might be helpful as well.

Tru dat. That's numero uno on the to do list for this. Placing the surrounding characters, and their voltages, may help greatly, for sure. I won't be able to get to it until the weekend though. I'm just finishing up a Guyatone PS-025 trace, and I'm on the road for work all this week, so nogo on tracing till I get back.

Couplate.

I checked with Mrs. Digi, and she says she's game.

No, wait...

Whaaaaat???

[deadastronaut]

deffo a filter...

[digi2t]

So, I did a quick trace, and this is what the landscape looks like....



Supply voltage is 18.82v, which steps down to 16.89v after the LED. All the rest of the voltages indicated are with all the pots at maximum, with no input.

[Rob Strand]

So, I did a quick trace, and this is what the landscape looks like....

After a late night my brain isn't up to unraveling that today.  Too many options resulting in brain overload.

Maybe I can ask a question instead  .
How do the controls actually work?
Is Volume like boost/cut, or boost only, or just like a normal distortion pedal volume which goes to zero?
Is the "Peak" control like a Q control or is that the boost/cut etc. control.

Identifying the control that does the boost/cut (or however it does it) will help pin down the connections.

At the moment the connections to both the opamp - pins aren't quite right but it's hard to massage the connections without knowing how the controls work.    The first opamp is buffering the input and last opamp is providing the output drive but how either or both of the opamps are involved in the boost/cut function isn't obvious yet.

It has a kind of state-variable flavour about it but it's not 100% certain at this point.

[imJonWain]

It might even just be resistors and caps ( I think I can see what looks like two resistors?).  It doesn't look house made so it's probably an OTS Taiyo Yuden couplate (like mozz said) and I would guess they weren't buying anything special or expensive for a guitar pedal at the time. 

I have a a guitar amp with a baxandall tone stack and all the components are on a sealed couplate mounted directly on the pots.

[digi2t]

It doesn't look house made so it's probably an OTS Taiyo Yuden couplate (like mozz said) and I would guess they weren't buying anything special or expensive for a guitar pedal at the time. 

I thought about that, so I dropped Taiyo Yuden a line. This is the response I got back;

Hello,

Thank you for the inquiry.
We cannot confirm that "TOC-7" is a Taiyo Yuden part number or our product.




Regards,
Kenneth Moore
kmoore@t-yuden.com
Inside Sales
Taiyo Yuden (U.S.A) Inc.
Direct Line (858) 350-6820

I've written back to them, giving them more context. Hopefully, they'll do a little more digging.

[imJonWain]

Yeah, hopefully you get someone who's willing to dig a little.  Those records are probably all gone, my work barely has records of our stuff from the 1990s.

Could be fun to measure R and C with a DMM between the various pins and see if we can sort it.


Here's Sprague's old catalog of what they sold for PECs, could be used as a ref but I don't see any with that many pins...
http://bama.edebris.com/download/sprague/pc/Sprague%20PrintedCircuits.pdf

[digi2t]

You know.... the fact that this module has V+ going to pin 1 makes me believe that there might be a transistor or two hiding in there. Perhaps not totally passive?

Just spitballin'

[Rob Strand]

You know.... the fact that this module has V+ going to pin 1 makes me believe that there might be a transistor or two hiding in there. Perhaps not totally passive?

Just spitballin'

Highly likely to be a 3 transistor (or 2 JFET + BJT) discrete opamp, similar to what Boss use, for example the BD-2
It will have at least two of those discrete opamps.

Something along the lines of this,


There's so many minor variations on the basic theme.   Some simple variations are (some use more transistors),
- different output configurations
- swap the use of pnp and npn in each position.
- use current sources instead of resistors.

[ElectricDruid]

The "Notch" control on this reminds me of the parametric EQ circuit that you'd commonly see (for example, at the bottom of this schematic: https://sound-au.com/articles/st-var-f4.gif)

The module itself has enough pins to be a state variable filter. Comparing with the basic schematic for such a thing:



We have one input and three outputs: HP, BP, LP. We have two connections for the resonance resistor, and four connections for the two frequency-setting integrator resistors (and note that the Tone Banker uses a dual-gang pot for frequency adjustment, as you would for a 12dB filter of some type). That's ten wires.

Oh! We need power. How about +V, -V and Ground? That makes thirteen. Now guess how many there are on that module?


(Clearly this is by no means conclusive, but I do think it supports Rob's initial idea.)

[bluebunny]

You know.... the fact that this module has V+ going to pin 1 makes me believe that there might be a transistor or two hiding in there. Perhaps not totally passive?

Just spitballin'

Agree.  A couple of those green bumps did kinda hint of a TO-92 outline or similar.

[Kevin Mitchell]

Is there enough value in the pedal to not cut that thing open? The suspense is killing me...

[Rob Strand]

Is there enough value in the pedal to not cut that thing open? The suspense is killing me...

I don't think it's necessary to go that far.   It's looking more and more like three opamps wired as a state-variable filter.

If digi2t could recheck some of the tracing around the opamps it would be clearer how state-variable circuit, like
the one ElectricDruid posted, could slot in.    There's a lot of variations on state-variable EQ's and that's why
it would be best to pin down the surrounding circuit as tightly as possible.     I'm not sure what the trimmers are about
but there are some state-variable EQs that needs trimmer to set the notch depth and also the maximum boost
since the circuit is sensitive to part values.   IIRC it's the circuits which have a notch in the cut position and
single pot Q controls which end-up like that.   

If it's going to be cloned it's probably best to use opamps instead of emulating the discrete parts.  No doubt the opamp circuit will need to emulate some of the resistor values in the hybrid device.   For example there's no resistors in series with the Frequency pots to set the upper frequency limit so you would expect the resistor to be in the hybrid chip.  Some of the resistors could be derived from external measurements with a multimeter.     Others could be derived from AC measurements outside of the hybrid chip.   Measuring current draw is another trick of working out what is inside.

When I look at the digit2s voltages I can see a few points which are 0.7V below others.  So that could be a fluke from bias current voltage drops across internal resistors in the hybrid, or, it could be a Vbe drop of a transistor buffer.   A DMM diode test might resolve that.

Some years ago RG, moosapotamus and myself reverse engineered the Roland Fat Cat AG-5.   I managed to work out the modules were discrete opamps and then RG did a version which used opamps.    IIRC I made one small error which I picked up some years later.   When RG did the opamp version he made a tweak to compensate for the (unknown) error.   The fix got itworking fine but the result was its not *exactly* like the original.  The error is easy to rectify and doesn't need the fix.   The stuff RG and I did was done using only the pcb pics, so no circuit to play with.   The moral of the story is  there's always a risk of making an error unless you can compare the original and clone.

Another angle is to measure the frequency response from outside the box.   That would let you get the frequency range, Q's, boost-cut behaviour.   You then speculate a clone and check that it has the same behaviour.

[digi2t]

Is there enough value in the pedal to not cut that thing open? The suspense is killing me...

I reeeeeeaaaaaally prefer not to do that. I haven't seen to many of these around, and would prefer to leave it as "unmolested" as possible. Besides... I really hate having to destroy something working, just to satisfy a curiosity.

On the other hand, I may just ring up my dentist again for another X-ray session. She was really cool about doing so for my Breg Sweep wah, so maybe she'll be game once again.

As for the trimmers, the 50K trimmer seems to set the maximum resonance of the particular frequency being boosted. If you crank it, with the notch pot at max, the circuit will self-oscillate across the board frequency-wise. As you dial back the trimmer, the self-oscillation slowly narrows down to a particular spot on the frequency spectrum, and then you nudge it back a bit more to clean up the oscillation completely. I found it was set quite low when I got it. It really resonates well now with the notch pot maxed out now.

The 100K trimmer just seems to set the final output volume, but I didn't have the time to fiddle with it more in different modes. I'll play with it some more tonight.

In the meantime, if there are more tests that you would like me to run, just give me a test script and I can run through it.