Boss MT-2 Metal Zone Schematic

[nickbungus]

I'll get it sorted.  Wont be until about this time tomorrow though.  Sorry

[vigilante397]

If you post the voltages of your ICs and transistors we could probably at least point you in the right direction for where to look When you've been around them enough you start to figure out what to expect on each pin regardless of what circuit it's in, moreso when it's accompanied by a schematic.

[swever]

How heedless of me not to post my voltages Here's what I get now:

Bat:9.16
+9: 8.94

U001 pin1: 5.74
U001 pin2: 5.74
U001 pin3: 5.71
U001 pin4: 0
U001 pin5: 4.28
U001 pin6: 4.33
U001 pin7: 4.33
U001 pin8: 8.94

U002 pin1: 4.33
U002 pin2: 4.33
U002 pin3: 3.93
U002 pin4: 0
U002 pin5: 4.28
U002 pin6: 4.34
U002 pin7: 4.33
U002 pin8: 8.94

U003 pin1: 4.24
U003 pin2: 4.27
U003 pin3: 4.22
U003 pin4: 0
U003 pin5: 4.22
U003 pin6: 4.28
U003 pin7: 4.27
U003 pin8: 8.84

U004 pin1: 5.75
U004 pin2: 4.26
U004 pin3: 4.26
U004 pin4: 0
U004 pin5: 2.75
U004 pin6: 2.74
U004 pin7: 1.96
U004 pin8: 8.82

Q010 E: 3.60
Q010 B: 4.17
Q010 C: 8.79

Q011 D: 8.79
Q011 S: 3.68
Q011 G: 3.82

Q008 E: 3.59
Q008 B: 4.16
Q008 C: 8.77

Q007 E: 0.07
Q007 B: 0.07
Q007 C: 8.77

Q001 E: 3.53
Q001 B: 4.09
Q001 C: 8.76

By the end of the measurement the battery (disconnected) voltage was  8.76 volts. I am not sure if it's just because of the cheap zinc-carbon battery I used or if something actually draws way too much current.

[nickbungus]

Hi.  I'll get you my voltages tomorrow when I get a moment.  I'm sure we can work it out.

[vigilante397]

U4 is an immediate red flag. I'll sit down with the schematic when I have more time and give a solid look through (nick will probably have his voltages by then ), but I would check your connections around U4. Also, did you socket your ICs? if so, pull U4 out and check the voltages in the socket. You should be seeing about 1/2 of your battery voltage on pins 5, 6, and 7.

[Kipper4]

That might be a bit of meter loading Nathan. I'm no expert. I just remember PPR mentioned it a few times.


Shouldn't Q7 voltages match those of Q8?
Looks to me like the BE junction is shorted.

[Les Turnbull]

  Behringer ultra metal UM300 is said to be a copy of the metal zone though with SMD components and on a youtube vid someone
picked out the matching mod components on boss and Beringer board .
C35 -> C18
C34 -> C16
C25 -> C19
C42 -> C12
D3 -> D4
D4 -> D3
C36 -> C27

[nickbungus]

I've put my voltages to the right of yours.

How heedless of me not to post my voltages Here's what I get now:

Bat:9.16
+9: 8.94     8.94

U001 pin1: 5.74                        4.43
U001 pin2: 5.74                        4.43
U001 pin3: 5.71                        4.41
U001 pin4: 0                             0
U001 pin5: 4.28                        4.33
U001 pin6: 4.33                        4.40
U001 pin7: 4.33                        4.40
U001 pin8: 8.94                        8.82

U002 pin1: 4.33                        4.40
U002 pin2: 4.33                        4.41
U002 pin3: 3.93                        3.96
U002 pin4: 0                             0
U002 pin5: 4.28                        4.36
U002 pin6: 4.34                        4.41
U002 pin7: 4.33                        4.41
U002 pin8: 8.94                        8.92

U003 pin1: 4.24                        4.37
U003 pin2: 4.27                        4.39
U003 pin3: 4.22                        4.33
U003 pin4: 0                             0
U003 pin5: 4.22                        4.33
U003 pin6: 4.28                        4.41
U003 pin7: 4.27                        4.39
U003 pin8: 8.84                        8.92

U004 pin1: 5.75                        4.41
U004 pin2: 4.26                        4.37
U004 pin3: 4.26                        4.39
U004 pin4: 0                             0
U004 pin5: 2.75                        4.31
U004 pin6: 2.74                        4.35
U004 pin7: 1.96                        4.36
U004 pin8: 8.82                        8.92

Q010 E: 3.60                            3.68
Q010 B: 4.17                            4.28
Q010 C: 8.79                            8.92

Q011 D: 8.79                            8.91
Q011 S: 3.68                            7.54
Q011 G: 3.82                            3.91

Q008 E: 3.59                            3.68
Q008 B: 4.16                            4.28
Q008 C: 8.77                            8.82

Q007 E: 0.07                            0.09
Q007 B: 0.07                            0.09
Q007 C: 8.77                            8.90

Q001 E: 3.53                            3.70
Q001 B: 4.09                            4.20
Q001 C: 8.76                            8.91

Because of the way it was squeezed in I was working on the back so I had to mirror the layout and find my way around so I might have made a mistake.   I also think I may have sprayed the circuit afterwards with some protective stuff but I cant confirm this  but if I stabbed hard enough I could get a reading.

[ElectricDruid]

Most of those look like they're in the right ballpark apart from Q11 and the second amp on U004. Swever's Q11 source is low, and the U004 amp is way low.

[highwater]

Something is pulling pin-5 on U004 low. The entire trace to R029 and C021 is surrounded by ground-pour, so it wouldn't be very difficult to get a solder-bridge there. It can't be on the *other* side of R029, though, because that would screw-up U003 too.

Pin-1 is high because that half is inverting the too-low signal going in. It's also connected (through R014) to pin-3 on U001, which explains the too-high voltages on pins 1-3 there.

I'm having trouble wrapping my head around how that could affect the tone pots, but it somehow seems reasonable that it would.

As for Q011, I dunno... the gate definitely shouldn't be higher than the source, but aside from that, JFETs are so variable that different voltages don't necessarily mean much. Double-check the pinout (it's not especially uncommon for different manufacturers to use different pinouts even for the same part-number), but since it's a source-follower input buffer for a distortion pedal, I myself would be inclined to let that particular sleeping dog lay where it is as-long as it passes signal.

[swever]

One thing I was pointed to on a local forum is that the polarity of C021 was reversed on the redrawn schematic and layout. I've been told that it could cause some leakage and be the reason weird voltages on U004. So I flipped it and got what looks like more correct voltages to me:

U004 pin1: 4.09
U004 pin2: 4.09
U004 pin3: 4.09
U004 pin4: 0
U004 pin5: 4.05
U004 pin6: 4.10
U004 pin7: 4.10
U004 pin8: 8.34

However, that has no effect on the LOW behavior - it's still the same.

[swever]

U4 is an immediate red flag. I'll sit down with the schematic when I have more time and give a solid look through (nick will probably have his voltages by then ), but I would check your connections around U4. Also, did you socket your ICs? if so, pull U4 out and check the voltages in the socket. You should be seeing about 1/2 of your battery voltage on pins 5, 6, and 7.

Yes I did socket. Not sure if it's still relevant after swapping the C021 polarity, but here's what i get on the socket with the IC removed:

pin1: on the first measurement starts with about 4.8 then drops rapidly to about 0.8 then start to rise slowly. After a few measurements settles at about 2.69
pin2: same as above
pin3: 4.10
pin4: 0
pin5: 4.06
pin6: seems to be the same as pins 1&2
pin7: seems to be the same as pins 1&2&6
pin8: 8.36

[swever]

I have a gut feeling that the problem is within the LOW gyrator. Maybe a dud or mislabeled cap. What would I do if I wanted to increase it's Q?

EDIT: dammit there's no caps in the gyrator other that 220nf, which I actually desoldered and tested. Anyway, how do I increase Q?

[swever]

Alright, guys. I am feeling very embarrassed right now. It was a cold solder on one of the C009 lugs. 

Thanks everyone for support and shame on me, lol. Again.

[nickbungus]

Hooray!!!

Well done.  I'm glad its not my crappy layout then!!

[swever]

The layout is top-notch! I started trying the various "mods" to find a configuration that I like the most.

[swever]

I've spent another weekend playing with the circuit. One thing I've discovered is that C017 is missing in the redrawn schematic as well as the layout. I thought I wanted to see what kind of effect it has so I made a small modification to my board (breaking two tracks and adding one jumper as well as the capacitor itself). I edited the component layout and pcb files to allow for adding this cap. I think it should be correct but take anything I say with a grain of salt.


Also fixed C021 polarity.

I actually liked the effect of adding this capacitor. It makes the whole thing sound even more "90's hifi" and again adds a mid-scooped character. The circuit is absolutely usable without it and has a tad more focus on mids and low mids. In fact, that may even work better at rehearsal/live levels with other musicians etc. For bedroom use I clearly prefer it with this cap.

I tried all the mods listed earlier (and tried different component values at each "mod point"). Ended up with this (I used a b100k dual pot for mid frequency which may have affected some of my choices):

C017: 47nF (473) (stock value)

C009: 100nF (104)
C024: 18nF (183)
C025: 330pF (331)
C034: 47nF (473)
C035: 5.6nF (562)
C036: 8.2nF (822)
C042: 1uF (105)


D003: 1N4739A
D004: d9d germanium

I think it sounds divine now Am going to etch a new board and make a new clean build (I completely ruined the current board with all these mods).

[nickbungus]

Brilliant.

Whoops, sorry for missing something. I can add it tomorrow and post an updated board if that helps.

[swever]

No worries, man. I am actually fine with my quick and dirty photoshop fix - so no need to fix it just for me.  I am sure other builders would enjoy an updated layout by you, though. Which they should because it is an amazing circuit and deserves much more attention among diy'ers than it gets.

[swever]

Etched, tinned and drilled a new pcb this weekend. This will hopefully make a "final" board to go into an enclosure.



Also spent a few hours more playing with my "prototype" board. I can't say enough how much I like this circuit. It's all sorts of 90's metal tones in a box at bedroom volume.

I noticed, however, that either with gain or guitar volume set low, or just very soft picking - basically anything that makes the input level go low, I get a nasty layer of fizz. It actually happens all the time, even with louder signals, but it get buried in the wall of METAL. But once I pick lightly or just let a note fade out naturally I get that bzzzbzz kind of "satellite" sound. It's also quite noticeable with those chugga-chugga palm muted notes and chords. I will try to record a sample later.

I've been wondering if it's an inherent feature of this circuit or not. I think I do remember my original one doing that, but I may be remembering what did not ever happen, lol. I also wonder if there is anything I can try to address this issue.

Nick (or anybody else who built this or has the original and see this message), could you please check if yours does the same?