Metal Simplex NIGHTMARE!!!

[stand]

Hi everyone!

Today I've finished my first DIY pedal. I decided to go for something simple, and it's Howie Metal Simplex, pedal that sounds quite decent on sound clips and is not too complicated to make. So, I made it on protoboard in layout that is very similar to schematic itself (with few parts you don't have to worry about space...). I also installed 4 halves of IC sockets to be able to play with different transistors and diodes.

I checked all connections and lines and everything seemed to be OK. I connected 9V battery clip, then I turned ,,on" my mixer and power slave (no classic guitar amp, sorry...)  and – shock! Instead of normal GRRRRRRRrrrrrrrrr sound I've got just mild GRROAaarrooooaaaoooaaa... Sounds is dull (almost no highs at all) and distortion is rumbling and very short (approx. 2-3 seconds, then it fades into ,,clean" sound which ends very soon). Somewhere behind this stupid sound I've heard sweet buzzing RRRZZZzzzz  that I want, but it's much quieter than it should be. I just imagine how good it could be to have it instead of this weird short distortion that I've got.

I also tried LED, Si and Ge diode (and diodes in opposite directions) to make things better, but with or without diodes sound was almost the same (see above). BC550Cs gave me more distortion than original 2N3904s, where hFEs were about 480 (for BC550C) and 270 (2N3904). I thought that BC550Cs should have gain 800+

I also measured voltages on collectors and bases (both emitters are on ,,ground") and here are results: 
T1 Base = 0.62v, Collector=0,88v
T2 Base = 8.33v, Collector=8.94v

I am suspicious why these values are so close (0.26-0,61v). I am a beginner and I don't know so much about transistors, but I think it could be too small ,,space" for gain if these voltages are so close...

I checked out all contacts few times, no wrong contacts, false contacts, it's so easy and simple schematic, isn't it? I checked out few transistors and diodes, I also checked out my guitar, it works fine ,,clean", pickups are strong enough... Now I have neither clues nor any ideas what to do...

So, I beg all you good DIY-ers who remember similar problem or ever made this pedal or anyone who could give me some advice about it. I'll repeat:  I checked out all resistors, capacitors and IC sockets, everything is OK (including two 9V batteries that I used simultaneously, and both of them are OK / brand new).

Finally I must say that I had similar result (mild & short distortion) with some old booster if battery was too weak...

I can't wait to get a ,,feedback" from you... I'd be very disappointed if I fail on such a simple project... Any ideas?

Dejan

[Joep]

There must be something wrong in the wiring. The voltages definately look wrong!

BC5xx and 2N3904 have different pinouts!

Joep

[stand]

I checked all wires and parts again, and couldn't find any problems...

Joep, please look at this picture - http://i46.photobucket.com/albums/f138/stand21/metalsimplex2.gif
I drew paralel shematics and protoboard layout (which are almost the same) so you can probably see why I've got these strange voltages on Bs and Cs of transistors. Those voltages are on this picture, too. Can you see if pots are wired properly (they work, but maybe I did something wrong. Or, what could else could produce such violtages (I checked 6 BC550Cs, I don't think it's about tranzistors and all 4 resistors are OK).

I really don't what to do... When I pull out T2 I've got almost the same sound, but it's quieter and with sligtly less distortion... Diode almost doesn't make some difference at all...

I don't know what to do...

Thanks for your answer, I hope that I didn't bore you too much.
Dejan

[Paul Marossy]

Check your transistor pinouts and double check your wiring.

[Ge_Whiz]

I also measured voltages on collectors and bases (both emitters are on ,,ground") and here are results: 
T1 Base = 0.62v, Collector=0,88v
T2 Base = 8.33v, Collector=8.94v

I am suspicious why these values are so close (0.26-0,61v). I am a beginner and I don't know so much about transistors, but I think it could be too small ,,space" for gain if these voltages are so close...

Hang on a minute, please check the way that you have reported those values, especially as you say they are "so close". Surely, you mean the first line are both base voltages, and the the second line are both collector voltages.

[stand]

Yes, I am sure about it. T1 Base=0.62v, T1 Coll=0.88v, T2 base=8.33v, T2 coll=8.94v. Battery gives about 9.7 volts.

I checked out all traces again, no problems here. Paul said that my transistors could be saturated because their hFE is higher than 2N30904 hFE on original M.Simplex diagram. I don't know how someone used there 2N5089 with hFE=800...

I've got advice to use 2 trimmer pots instead of those 10k resistors and to adjust resistance to the best level. Do you think this way I could get the best sound (better & longer lasting distortion).

Thanks for your advices and help, good people!

Dejan

[stand]

To all members of DIY-pedal tribe, and especially to those who gave me some advices here or there. They're so helpful!

So, after few days of investigation (almost more days than parts on Metal Simple diagram) I finaly found the cause for strange sound and wrong voltages at Q2... All contacts and traces seemed to be OK. Just before I decided to de-solder whole pedal and to do it all again I have noticed that there is no connection between Q2 base and the closest capacitor... Also, there was not contact between Q2 collector and the closest resistor...  I used transistor sockets and there was "cold joint" at pins of Q2 socket. Actually on the other side everything was fine but beneath small tin cones at socket pins there was key of this mistery. So, after I soldered it again and checked contacts (this time it was OK) I measured voltages and those were almost the same as computer simulation proposed.

Sound of this pedal is really interesting, compressed, sustain is long and all in all it was worth investigating to find which Q1&Q2 (2N3904 and BC550C) combination sounds the best. Original (both 2N3904) sounds good, stable (think about good old AC/DC), BC550C on both Q1 and Q2 positions is very compressed and even sounds like it's gated, but not very good if you want people to know what notes you're playing ;-). We kept BC550C as Q1 and 2N3904 as Q2, it gave me wide and vibrant distorion with lots of sustain. Opposite version lacks in both high and low frequencies, sound is somehow "boxy", dull, but someone cold prefer it. Finally, I tried both red and green LEDs and I think that the green one gave me more highs which is OK since it's possible to adjust them with tone control.

So, it was my first DIY pedal, I hope it won't be the last one....

Big THANKS goes to:

Marin Lovric
Dwight Seiden
Joep
Paul Marossy
Ge_Whiz
Scott (burnt_fingers)
Pete Moore
Mark Hammer
Eric Hansen
pi22seven

I'd go for "Obsidian M" soon, so I hope that some of you'd be willing to give me a hand here or there.

See you...

Dejan

[Paul Marossy]

Congratulations!