Boss Metal Zone - Power Issue

[nickbungus]

Hi All

I used to own a Boss MT-2 Metal Zone, and although a lot of people hate them, I loved mine.  But I decided to sell it when I got into making my own along with lots of other pedals.  This was to keep the wife off my back regarding all the bits and bobs I was buying!  The plan was to build one and so I have.

Anyway, its not working at all at the moment.  The problem is to do with the DC.  When I connect it up to my test chassis, if I measure the DC where it connects to the board it drops from over 9v to about 2.6v.  It looks like on the board, there is a millennium bypass circuit that's not on the schem.  After the bypass circuit the voltage is down to about 1.6v.  I tried connecting the power directly to the power rail  but the voltage drop is still there.

I'm guessing the issue is down to a solder bridge somewhere but I can't find any.  Because my understanding is so limited, I don't really know what would cause this issue.  I'd expect the voltage to be around the 9v mark all along the power rail.

Here's the schematic



and heres the layout



The layout is not the clearest.  The power connects to the top right section on the board and is labelled 'Control'.  The labels are in Spanish. (Entrada -> Signal In, Salida -> Signal Out).

Any advice as to what I should be looking for would be most welcome.  The Opamps are getting the same voltage as the power line as I would expect.  I can post the voltages of all trannies and opamp pins if it will help?

Thanks

[antonis]

Maybe I'm blind but after a quick tracing I can't find any PCB connection pad to +9V..

If the Control pad is for power supply connection then I presume that 1N4148 series protection diode (despite of schematic's parallel 1N4007) is quite inadecuate for this purpose..

[nickbungus]

Maybe I'm blind but after a quick tracing I can't find any PCB connection pad to +9V..

If the Control pad is for power supply connection then I presume that 1N4148 series protection diode (despite of schematic's parallel 1N4007) is quite inadecuate for this purpose..

It had me scratching my head for a while, but that's the conclusion I came to too.

[duck_arse]

following the opamps supply, from pin 8, suggests to me that the 1N4007 is forward biased, as shown on the layout. that will put a crimp on your day.

also, I think "control" actually is control, the millenium bypass control line.

and no, I no see no supply pad/hole, neither.

[Cozybuilder]

I'm with Duck, turn that 1N4007 around, and drill a small hole in the power rail to connect 9V, I'd suggest that triangular shaped area near "Salida".

[nickbungus]

Duckster, always good to hear from you!

following the opamps supply, from pin 8, suggests to me that the 1N4007 is forward biased, as shown on the layout. that will put a crimp on your day.

also, I think "control" actually is control, the millennium bypass control line.

and no, I no see no supply pad/hole, neither.

Oh yes, I take it that's for polarity protection?  That is the wrong way.  Would that explain it at all?

I think tonight, I'll take out 1n4148 in the millennium section and just drill a hole on the power rail somewhere are connect it to the supply.

[nickbungus]

Thanks Cozy

I was replying at the same time as you.  I wasn't doing that thing that all good bosses do (mine especially) and just repeat a very good idea that's just been said

[Cozybuilder]

I haven't chased the whole circuit, but that should take care of the power problem.

Read this to understand the Millennium section:

http://www.geofex.com/article_folders/millenium/millen.htm

[nickbungus]

Thanks again Russ

I'm expecting this one to take a while.   I'm sure there are more errors in the layout and I'm sure I probably made a few on the way too but its all good fun (and an education).

[duck_arse]

cozy! I'm surprised you didn't notice - the "mill" is led to ground, not supply to led. what would RG say?

and bungus [such kind words!] - leave that 1N4148 where it is, it's already protected you once.

[Cozybuilder]

Yeah, I noticed, but how many times should I point it out? I was hoping the reference would pique other's curiosity.

[ElectricDruid]

Maybe I'm more autistic than some of the other people here, but I think that layout was bound to lead to problems.

What's wrong with having all the op-amps in a neat row down the middle of the board, with all the resistors lined up above and below them? Signal should (as far as possible, and giving due consideration to other things) come in at one end, travel along the chain and come out at the other. Sometimes with things like delay layouts (I recently did a flanger) it makes more sense to go in, then along the top and back along the bottom, before finishing up at the output mixer next to the input buffer where you started.

If the problem is as simple as "diode wrong way around" then you can ignore me, but in my head, the Metalzone is a complicated enough pedal as it is, without making it more confusing by laying it out all over the place. Personally, I'd struggle to debug a layout like that. YMMV.

Tom

[nickbungus]

Its not the prettiest layout.  If there is another out there I'd prefer that.  This is just one I found by using the gift of Google.

I'm still not working but the power issue is resolved with the reversal of the diode and adding a 9v dc hole.

I'm following the audio signal and I'm only getting as far as pin 3 on IC1!  I take it I should be getting something audio on my probe at pin1?

I'll post some voltages soon.

[nickbungus]

This is doing my head in, I'm trying to figure it out myself hence why I haven't posted voltages.

I am right in thinking that if I can follow the signal with the probe to IC1 pin 3, I should be getting a signal (with more gain) from pin 1?

I can also hear audio at Pin 2.  Is that also right.  I have watched a few Youtube videos on Opamps and trying to learn.

[antonis]

I am right in thinking that if I can follow the signal with the probe to IC1 pin 3, I should be getting a signal (with more gain) from pin 1?

Yeappp...

Your signal enters through the Emmiter (Source  ) follower to pin3 (IC1) and comes out of pin1 with a gain of 4.68 - 22.7 (rough math.. depending on frequency..)
At pin 2 you should get signal of the same level with this at pin3 but with reversed polarity..

Same case for pins 5 & 6 (IC1) and at pin7 signal with gain depending on Distortion pot..

At pin 3 (IC2) signal of 650mV (more or less) and so on...

[anotherjim]

Crazy thing to work with. The layout doesn't quite match the scheme. IC4 halves A & B pinouts are swapped (B is pins 5,6,7). IC3 & 4 some inputs are referenced to ground instead of 1/2 supply on scheme and layout e.g. IC3A pin 3 via 100k to ground - that don't look right.

[nickbungus]

News just in.  I have it working.   

There was two errors:
1.  I'm an idiot
2.  I am such as idiot.

Error 1: I subbed the 2SK30A for a 2n5457.  I checked the pinouts at the time (just not very well).
Error 2: Now I always do my building late at night, that tends to lead to a lot of really silly mistakes made.  I must of opened the wrong packet and put all LM308n's in, instead of the recommended TL072s.  With my limited knowledge, I would still expect it to work but I take it I could have fried the original op-amps when I had the diode issue?

There's not a lot of love on here for this layout and we've already found a few errors.  Perhaps the best thing for me to do is to draw up the schematic in my favourite software package and then do my own layout.

Thanks everyone for the help.  It is so appreciated. 

[J0K3RX]

Looks like the "control" section in the corner are additional parts that are not on the schematic. Looks to me like they put a millenium bypass in the layout in line with the power...

[garcho]

just in case this helps

[PRR]

> LM308n's in, instead of ....TL072s.  With my limited knowledge, I would still expect it to work

No. '308 is a single opamp. '072 is a dual opamp. For historical reasons, the pinouts are NOT even close.

> I could have fried the original op-amps

You sure could have fried the '308 when you powered-up as '072 pinout. Pin 8 is V+ on '072, but COMP on '308. COMP is usually a VERY low-power point inside the opamp.

Squinting the '308 gut-plan, +9V on pin 1 forces Q8 Q10 into reverse-bias base-emitter. On normal transistors this leads to breakdown. This breakdown may not be fatal; and these are not normal transistor but "lateral PNP" with high breakdown. So I dunno. However these set-up Q5 Q6 which cascode Q1 Q2, the "magic" hyper-Beta input transistors which have absurdly low and easily-fatal breakdown voltage.

I would assume the '308 is dead until proven otherwise.

It is possible it is "degraded" in ways that won't hurt your use in a fuzz-box. If the specified low-low-low input current got 100X worse, it would suck as an S/H or a pH meter, yet amplify/mangle guitar just fine. If you are lucky.