Can anyone indentify this stomp box?

[irishstu]

Hi all. First post (of many I hope).

I found this in a guitar shop here in Taipei. I'd be EXTREMELY surprised if a local made this, but stranger things have happened.

I've attached some photos below...

There are two main amplifying components on it, a little 8-pin chip and a transistor.

The chip is marked:
OP275
G 0338
03711

And the transistor is marked:
C550B
PH47

There are three controls on it, labelled volume, tone and gain. The gain pot is dual-gang.
There are two toggle switches. The one on the side is a 3-way, with capacitors in 2 of the positions. It works as a tone filter I guess. At the back is a two-way switch, which appears to work as a kind of turbo overdrive.

I guess this pedal sounds a bit like a tube screamer or something, but don't let that influence your guesses.

Any ideas? Or even any info on the transistor would help. I can't find much about it at all.







Many thanks.

[asfastasdark]

What are the pot values?

[irishstu]

What are the pot values?

Hey asfastasdark.

I'll get back to you on that. The pedal's at home and I'm at work at the moment.

[Paul Perry (Frostwave)]

There can't be many dual-gang pot gain devices in the world..
Dual pot filters, yes, but gain?
True, you can put gain pots in series, on the same shaft, to get a "super log" response, which might be useful for more precision when overdriving. But I have never actually SEEN one!
A very interesting first post, irishstu.

[irishstu]

Hi asfastasdark. I checked the pot values. They are as follows:

VOLUME - A100K
TONE - B100K
GAIN - A50K

Paul Perry (Frostwave) , thanks for the positive comments. My thinking on the dual gang gain was that maybe the overdriven part of the circuit needs its own gain control, separated from the gain of the main circuit (I hope that makes sense). However, I'll check to see if it's just wired up in series or something.

The pedal seems well made and I would be surprised if it is a one off. Unfortunately there don't appear to be any markings such as make or model name/number on the circuit board or elsewhere.

[caress]

reverse engineer the circuit... would probably help.   

[Br4d13y]

ive always wanted to find an unmarked, no-name box, just so i can have it in my rig, and when people ask me what it is, i can say "no mere mortal has laid eye upon the depths from whence i scavaged to claim this bounty!"

[grapefruit]

The chip is an OP275 dual op amp.
I'd be guessing the transistor is a BC550 since the 2SC550 is a UHF/microwave transistor.

Cheers,
Stew.

[aloupos]

I think the infamous "Klon" uses a 100K Linear dual ganged pot for gain to compensate for highs as the gain is increased.  Could be a clone? 

[fixr1984]

I think the infamous "Klon" uses a 100K Linear dual ganged pot for gain to compensate for highs as the gain is increased.  Could be a clone? 

Thats what I was thinking, but the Klon uses a charge pump to get 18v.
Unless the the maker planned on using an 18v wall wart.

[kurtlives]

I think the infamous "Klon" uses a 100K Linear dual ganged pot for gain to compensate for highs as the gain is increased.  Could be a clone? 

That's definitely not a Klon though.

[caress]

I think the infamous "Klon" uses a 100K Linear dual ganged pot for gain to compensate for highs as the gain is increased.  Could be a clone? 

That's definitely not a Klon though.

for sure.  the klon uses 2 opamps...

[aloupos]

It's not a Klon for sure.  I was only pointing out that the Klon uses a dual gang pot for gain. 

It could be locally made.  I found local FX makers in the strangest of places, including Marrakech and the northeast of Thailand (I posted gutshots here a while back). 

good luck finding out what it is.  An original, local design maybe? 

[kurtlives]

I think the infamous "Klon" uses a 100K Linear dual ganged pot for gain to compensate for highs as the gain is increased.  Could be a clone? 

That's definitely not a Klon though.

for sure.  the klon uses 2 opamps...

Yep...one for a buffer and one for normal clipping op-amp crap.

The Klon also dosent have any transistors and I have never seen a layout for a PCB so small.

[grapefruit]

Unless the brown blob in the bottom left corner of the PCB is a pair of diodes I can't see any diodes, so if it is an overdrive it's either using the transistor or op amp clipping. You'd really have to trace the circuit, at least partially.

I can't see any reason why it couldn't be built by a local, and be an original design.

Cheers,
Stew.

[irishstu]

Unless the brown blob in the bottom left corner of the PCB is a pair of diodes I can't see any diodes, so if it is an overdrive it's either using the transistor or op amp clipping. You'd really have to trace the circuit, at least partially.

I can't see any reason why it couldn't be built by a local, and be an original design.

Cheers,
Stew.

Hey Stew (and everyone else),
Thanks for the replies and info. I'll check if there's any diodes on there.
The reason I don't think it was a local is that that scene just doesn't really exist over here and also the parts almost definitely came from the states. I've spent a LOT of time trawling round just about every electronics shop in Taipei and it's impossible to get some of the parts that were used in this box. The pots, for example; here they all have split shafts. Since they are readily available here as split shafts, there would be no reason to get non-split-shaft ones from the States unless either you brought them over from there personally, or they were part of a kit bought online. I was kinda hoping someone would recognise the kit, but that doesn't look likely.
I know the local music scene pretty well here (believe me, it's small) and I've never heard of anyone offering homemade stomp boxes. The fact that this wasn't made on vero board also makes me think that this was not done by someone just experimenting with a one-off.

That said, I could be totally wrong! :p

I really am very appreciative of all the replies so far. I may get round to reverse engineering this at some stage, but the two kids keep getting in my way (HOW DARE THEY! ). Of course it would be much easier if I don't have to do that.

Still it would be kinda cool if it's an original local design. I would really love that. Just don't think it's likely.

[liddokun]

I've never heard of anyone offering homemade stomp boxes.

Perhaps you could start offering home made stomp boxes.  If might even be fun.  Here in Mississauga, I offer my friends my building services, and normally just charge for parts cost and a little more for my time.  It's a great way for me to practice my building skills.

[ayayay!]

The Blues Driver has a dual ganged gain pot and is a 3 knobber, but I don't even see any diodes and the board is too sparse to be a BD-2.

Where did this thing come from anyway?    Edit:  Ah, Taipei. 

[Dragonfly]

My initial thought was a modded VL Sparkle Drive type build, but that would have 2 op amps....   

[irishstu]

Hey guys. Thanks as always for the replies. They've been very helpful.
Here's a little more info now that I've had some time to look.

Unless the brown blob in the bottom left corner of the PCB is a pair of diodes I can't see any diodes, so if it is an overdrive it's either using the transistor or op amp clipping. You'd really have to trace the circuit, at least partially.

Firstly, here's a close-up pic of that brown blob (if you were referring to some other blob, then there's definitely no other ones that could be construed as diodes or anything. Just caps and resistors:



Secondly, I traced the path of the dual-gang gain control. One gang connects between pins 1 and 2 of the OP275 and the other gang goes between pins 6 and 7 of the OP275.

Here's the pinout of the OP275, in case anyone doesn't know:



Any thoughts?