does this circuit board seems familiar to anybody?

[Marcos - Munky]

I was cleaning a wardrobe where I keep my pedals and parts, and found this pedal I got some time ago. It's a "Heavy Metal" from a brazilian brand called Chorus (yeah), which made pedals back in the 80's. It sounds like, well, it was a bad idea to use it from the beginning lol. Lots of stuff made here back then were clones of other stuff like Boss pedals, so this one it's probably a clone of something. Does anybody recognizes this board? While the pics aren't from my unit, mine have the same board including the two caps soldered on the traces side.

http://www.effectsdatabase.com/model/chorus/a/hya3#pictures

[garcho]

It looks like Boss switching on the bottom right.
Dear lord the underside of the PCB is, how shall we say... horrific?
8 op amps?
Ge clipping diodes, 3 controls... maybe just a Tube Screamer variant? Not sure about the 2 quad opamps.

[Ice-9]

Dear lord the underside of the PCB is, how shall we say... horrific?

A lot of old pcb's as well as old 's had that crinkly look about them, it sort of looks like lacquer coating which has reacted when sprarng on. You see this on old Sony, Teac etc. tape decks and if you have ever looked at an old video recorder PCB you may have seen a similar crinkly look.

[Marcos - Munky]

It sounds too bad to be a ts variant . And have much more gain. Mostly like a fuzz than a overdrive.

On the underside look, I believe it's a combination of a not so good camera, old lacquer coating and the flash of the camera being reflected by the lacquer coating. Mine surely lokks way better. I'll have to open mine to replace a broken pot and I'll take the chance to check if the ICs are sanded. But they're probably just plain quad opamps.

[Rob Strand]

The 2xGE diodes and the silicon's near by made me think of the Boss HM-2 but it (ie. the Chorus brand) only has a single tone control.

Then I started to think of some of the old Ibanez over drives with the Ge diode (OD-850, OD-855 bit watch out for many versions) but IIRC those didn't have the other diodes.

One thing not clear is if both IC's are quad opamps, or, one is a quad opamp and the other a CMOS gate for the footswitch, or it's some other IC which isn't a quad opamp but is just one of those older single or dual opamps in a larger package.

The parts in the bottom right look like they could be a BJT flip-flip but then I can only see 100ks, no 56k's.    Maybe it uses the BJT as gyrators!

Too many roads to take to identify what each part is doing without tracing the circuit.   There's a pic of the traces which could be traced. 

[Radical CJ]

The 3xGE diodes and the silicon's near by made me think of the Boss HM-2 but it only has a single tone control.

I also immediately pulled out a HM2 schematic. There are three JFETs and/or transistors that could be the input stage, and what might be inline GE diodes, although the visible cap values appear to be different, and no bass pot?

[Rob Strand]

I also immediately pulled out a HM2 schematic. There are three JFETs and/or transistors that could be the input stage, and what might be inline GE diodes, although the visible cap values appear to be different, and no bass pot?

It's possible they put the EQ on the same tone knob.  The Ibanez Power Lead (PL-5) did this.   It's loosely based on the HM-2.



There's a few others like the DOD FX59,


DOD FX56 was the other DOD one,
http://www.freeinfosociety.com/media.php?id=1911

The power pins seem to imply that both devices are quad opamps.   If someone else want to confirm please do.

[Prev post should be 2xGE not 3xGE; typo]

[Radical CJ]

I also immediately pulled out a HM2 schematic. There are three JFETs and/or transistors that could be the input stage, and what might be inline GE diodes, although the visible cap values appear to be different, and no bass pot?

It's possible they put the EQ on the same tone knob.  The Ibanez Power Lead (PL-5) did this.   It's loosely based on the HM-2.

I'm kind of fascinated by the idea of having 3 gyrators and so many components for a 1 knob tone control! Is it a good tone control? My knowledge is crude, but it sort of looks like the first gyrator scoops mids (790hz) and the third boosts bass. But the second one (on the pot) also seems to relate to lower frequencies/bass? 

[Rob Strand]

'm kind of fascinated by the idea of having 3 gyrators and so many components for a 1 knob tone control! Is it a good tone control? My knowledge is crude, but it sort of looks like the first gyrator scoops mids (790hz) and the third boosts bass. But the second one (on the pot) also seems to relate to lower frequencies/bass? 

There's no reason why it shouldn't work.  If you think of a graphic equalizer you have a whole heap of gyrators.

Yes, the PL5 had a mid scoop.  It sounded OK to me.     The circuit has a fixed bass boost and a variable bass boost.   I didn't like the sound of the tone (ie. bass) control.   It needed work but I end-up selling the pedal instead of modding it - I had too many at that time and off-loaded a heap. 


[Forgot to mention, I'm pretty sure the gyrator caps on one or both of the DOD FX56 and FX59 are incorrect.  (DOD schematics often have errors.)

You can see 10n and 15n caps on this 1986 FX56 pcb pic,
http://img-cdn.jg.jugem.jp/698/2938743/20141115_897950.jpg
From old thread,
https://www.diystompboxes.com/smfforum/index.php?topic=123145.0
]

[Marcos - Munky]

My first bet was it's a direct clone of the Boss HM-2 because of their names, but then I checked the pots count.

Didn't opened mine yet, but then I'll check the ics for all info I can get. I'll also check other important things like transistor values, and can give it a try on tracing a few parts of the circuit.

[Rob Strand]

My first bet was it's a direct clone of the Boss HM-2 because of their names, but then I checked the pots count.

Didn't opened mine yet, but then I'll check the ics for all info I can get. I'll also check other important things like transistor values, and can give it a try on tracing a few parts of the circuit.

The two DOD pedals would be on the top of my list for a match because they have three knobs and follow the HM-2 design.


FWIW, I had a quick look at the part values and I'm not so certain it matches any of the commercial pedals.  While it might follow the general structure the value seem different.  It's probably going to take some effort working out the correct part values.

[iainpunk]

i bet its an HM-2 with a simplified tone control. demo's on the you tube seem to sound just as fuzz-like as an HM-2. which i would take to mean that its a DOD clone, or its a HM-2 based circuit that they themselves changed up.

the brand does have a 4-knob HM2 clone, HY-20, which is quite popular in the local death-metal scene because they were imported by a local music store in the late 00's to early 10's of this century, in response to the local death-metal boom.

cheers, Iain

[Marcos - Munky]

I'll use the DOD/PL-5 ones as a reference, so I can check if this one is a DOD/HM-2. I already printed them, so I can write down the part values if it indeed matches any of those schematics. If we assume one of the ICs is for bypass and the other is a quad opamp and add the fact this one have 3 pots in the exact order as DOD's, it kinda makes sense they're similar circuits even having different board layouts. I'll also compare the sound with a PL-5/DOD/HM-2 soundclips.

Interesting to know this brand were exported to Netherland. It was a pretty cheap and not so good sounding brand when they was still in production. I saw the HY-20 on the internet, but didn't saw one in person. I remember playing one or two units from this brand, but it was more than 15 years since last time I saw any of them being used.

[bushidov]

I was thinking Boss HM-2 as well. I made a clone of a DOD Thrash Master, which is pretty much an HM-2 with a single tone knob. Sounds... uh... thrashy? I even made a pink enclosure for that one to match its original.

[Rob Strand]

Interesting to know this brand were exported to Netherland. It was a pretty cheap and not so good sounding brand when they was still in production. I saw the HY-20 on the internet, but didn't saw one in person. I remember playing one or two units from this brand, but it was more than 15 years since last time I saw any of them being used.

The HM-2 is supposed to be popular in that area of the world.

I've owned a HM-2 and a PL-5,  the sound is completely different due to the voicing of the EQ.   The PL-5 was an OK "rocker" pedal but the bass region needed work.   The HM-2 is far far away from my type of sound.   I only used the HM-2 for AB comparisons and probably less than about 10 times.  The treble control was more like mids than treble.

IIRC, there's also a Digitech pedal based on the HM-2.  I might have seen it on Electric Druid's site.

[ElectricDruid]

IIRC, there's also a Digitech pedal based.  I might have seen it on Electric Druid's site.

You're probably thinking of this:

https://electricdruid.net/digitech-pds-1550-distortion-pedal-analysis/

The actual HM2alike part is very much the same thing. They *didn't* simplify the tone controls, and in fact *added* elements like the slap-back echo/thickening on the end. So I'd doubt if the DOD PDS1550 is the model for this this we're looking at. Much more likely they're both different ideas using the HM-2 as a stepping off point.

Tom

[Rob Strand]

You're probably thinking of this:

https://electricdruid.net/digitech-pds-1550-distortion-pedal-analysis/

Yes, that's the one I was thinking of.   So the digitech tone control looks a bit closer to the DOD version.

[Marcos - Munky]

So I took a time to "trace" part of the circuit. Not to trace it itself, but to compare some parts of it with the DOD FX59 schematic, because I suck on tracing circuits . And it indeed is very similar with the FX59, but with a few differences. The gain pot is wired as a variable resistor on a opamp feedback loop like on PL5, tone pot have a different value and different frequency range (the HY-A3 have a big mid boost) and a lot of parts with different values. Thanks for all your help to identify this circuit!