ilovefuzz.com

First time poster, occasional reader, fuzz enthusiast...

I'm attempting to build a Soda Meiser based on Devi's schematic and I was hoping I could get some help from those on here who are more knowledgeable than I am, because I'm just about ready to pull my hair out. I've built pedals before with reasonable success, but I'm very much a "follow a schematic" kind of person - i.e. my knowledge about what's actually going on inside the circuit is fairly limited.

Anyhow, I've attempted to build this thing twice now, first using a layout that I found and then, when that failed, laying it out for perfboard myself, and both times I get the exact same result - a completely unmodified signal that is unaffected by the presence (or lack thereof) of electricity. Furthermore, just to see if I could, I snipped the lead between the 3.3m resistor and the 4th cap -- and the signal is unaffected. Again, this has happened with both a third party layout and the attached layout, which I put together myself and specifically designed so that the signal path would be easy to follow. There are no accidentally joined soldering joints either...

Perhaps this phenomenon I'm describing is easily attributable to some obvious error that I've made, but if anyone can help me determine what that is, I would really appreciate it! Thanks!

Try flipping your transistors around.

nbabmf wrote:Try flipping your transistors around.

exactly. your MPSA18 are incorrectly oriented - keep the middle leg the same, just turn them so they're facing the opposite direction - the 2N3906 can be either way, according to the schematic... the way you have it now will be the VFM.

hmmm, there are a couple of things about that particular build design that i don't like (the board for one is HUGE).... go here instead:

http://www.freestompboxes.org/viewtopic.php?f=7&t=4101&hilit=SODA+MEISER#p44852

very informative breakdown of the pedal and a verified RNFR layout that's easier and better.... these circuits aren't too complicated but are greatly affected by the position of the transistors... they are so versatile in fact that unless you have the trannies exact you will get some sort of decent tone coming out of it (just not a true SM tone)... actually for a perf design it's not bad, but socket those trannies and check the CBE direction on the datasheets for the mpsa18's and the (did you say 2n3906??? i thought the SM was a 2n3907a???

2n2907a according to the source in devi's forum - pnp just like the 2n3906. should be fine...

smallsnd/bigsnd wrote:2n2907a according to the source in devi's forum - pnp just like the 2n3906. should be fine...

D'OH! this is why my lazy ass isn't an accountant for a major corporation.... yes, 2n 2!!! 907a.... my bad...

I have a bunch of metal can 2N2907's. I should build one of these and find out what all the fuss is about.

nbabmf wrote:I have a bunch of metal can 2N2907's. I should build one of these and find out what all the fuss is about.

if you can you should, you would like the fuss... and keep in mind that flipping the 2n907a's direction takes you from Soda Meiser goodness to Vintage Fuzz Master goodness... it's a sweet fuzz circuit too... but it won't have the DEFX mojo like the real thing.....

First of all thank you to everyone for responding to my post! I took the collective advice and flipped the (unfortunately unsocketed) transistors and now I get... no signal at all. I'm thinking that somewhere along the line in my overzealous desoldering and resoldering I burnt out one of the transistors, although I did make a point of using heatsinks and a 20 watt soldering iron.

At any rate, I had started out by using the veroboard layout but to no avail - which is why I made what I thought was an idiot proof perf design, but apparently I am still an idiot (for my own dignity, I will note that I had flipped the 2N3906 on the actual build). I live in Japan though, where stripboard is unavailable for whatever reason, which is part of the reason that I decided to switch to my more easy-to-follow perfboard design. I am, however, slightly confused - everyone seems to agree that I have my transistors oriented the wrong way, so I'm inclined to agree with you all, but aren't MPSA18s CBE and, unless I'm misreading the schematic (which is definitely possible, if not very likely), shouldn't the emitted be pointed to the ground?

At any rate, this failed iteration has led to a serendipitous discovery of a parts supplier here that sells both 2N2907A's and MPSA18's for cheap - I had brought the MPSA's home with me last time I was in the states, because in general they're unavailable here.

Not sure if I burned out a transistor or if the solution is more obvious, but I've spent a bunch of time on this thing and I'm just about ready to pull my hair out, so I figured that getting a fresh start (with socketed transistors) wouldn't be a bad thing. I'll post the results of my next attempt sometime next week - hopefully they'll be good ones!

dmk2113 wrote:I am, however, slightly confused - everyone seems to agree that I have my transistors oriented the wrong way, so I'm inclined to agree with you all, but aren't MPSA18s CBE and, unless I'm misreading the schematic (which is definitely possible, if not very likely), shouldn't the emitted be pointed to the ground?

At any rate, this failed iteration has led to a serendipitous discovery of a parts supplier here that sells both 2N2907A's and MPSA18's for cheap

no. you're right about the MPSA18 orientation... brain fail on my part. datasheet for MPSA18 shows CBE and you have them right according to your layout. uggh... sorry about that.
although it is good news that you found a parts supplier because of it!

your layout looks ok. what kind of switching were you using? next time you can use an audio probe and you should be able to hear a change in your signal right after the input pot. then check at the collector of the 1st transistor, 2nd, then 3rd... you should hear more fuzz/boosted signal at each junction.

I had started with DPDT true bypass switching and then, when trying to figure out why my signal still sounded bypassed, wired it straight through with no bypass, and I continued to get what sounded like a bypassed signal - turning the pots produced some mild crackling but no discernible effects in the tone.

I'm glad that I had the transistors placed correctly, if only because I feel slightly vindicated. I was using 50V caps, although I believe the original calls for 250, but I can't imagine that that would make a difference. I still, however, can't for the life of me figure out what in the world was going on.

Smart call with the audio probe, I've always been meaning to make one of those... I've been bitten by the pedal bug lately, and I've never had any problems like this up until now, although I've only built two other pedals with perfboard.

One thing to clarify, and this is a really elementary question, but since all of the other pedals I've built have the input and output on the board itself, in this case, I am doing the correct thing by wiring the wipers of the two pots directly to the switch for signal send and return, yes?

*Ed: Also, in looking backwards and trying to think of things that I could have possibly screwed up, if, for whatever reason (and I don't think I did, but just in case I did) I accidentally swapped the wiring for lugs 1 & 3 on one or both of the pots, what would be the net effect?