EM3207 (v1.1) - MN3207 based EHX Electric Mistress (9V) clone

[Oneoff1]

hi all!
i finished the EM3207 but unfortunately it's not working. what actually happens is that R36 (47ohm) is on fire even when i use 9v battery.
i checked all my connections chips and caps positions and if the board has any shorts ... nothing to be found.
any ideas?

[DLC86]

Check the zener diode orientation

[Oneoff1]

hi, thank's but the zener was the first thing i checked...
it's got to do something within the PSU area but i cant find any flaw here

[Dave W]

V's please.

[Oneoff1]

V's please.

can you please explain what do you mean?

[armdnrdy]

He means voltages.

Voltage readings from the pins of the op amps and transistors. Pins to ground if you don't know that! 

[Thomeeque]

 Guys, when some part is burning it's not exactly good time for taking measurements on all IC's and Q's pins

Only voltages I'd maybe advice to quickly measure would be voltages on both pins of R36 (against GND), this can tell us more about character of shortage causing R36 to burn.

D3 (zener diode) cannot cause the problem, R35 would be burning, not R36. Shortage is somewhere after R36, which is VDD supply rail.

First pull out IC3 (LM324) and check if it changes situation - if yes, use new one. If not left IC3 out until issue is fixed and check rest of the VDD path (bridges on PCB, C20, RT2, jumpers.. follow schematic), there must be something.

Good luck, T.

PS: If you want other set of eyes to help, make sharp photos of the PCB (both sides) and let us look.

[Oneoff1]

Thomeeque, thanks a lot for the reply!
i will check everything again thoroughly and i'll post some pictures if nothing is found.

[Oneoff1]

OK guys! i got it !  -it was a nasty little bridge on the PCB,  a flaw in my etching , i got it and i cant believe i did because it was so tiny...

BUT unfortunately i cant get the flanger to work properly.
i can hear the output as is , no influence on the sound. it distorts when i put up the input gain but it's probably normal...

i don't think that there is a clock in my circuit whatever i do with RT2. and the SW_mode isn't effecting anything .
i started with the bias setting and set that exactly as Thomeeque explained before. V bias (at pin 3 of the bbd chip) = 0.42 +0.54*Vcc
which is 0.42+0.54*9.08 = 5.32V
i tried to replace the BBD chip twice but without any difference.
i guess i have no effect because the clock is not present?

one thing to say is that i didn't connect anything yet to pads 10 and 11 (CC) should I?

[Thomeeque]

OK guys! i got it !  -it was a nasty little bridge on the PCB,  a flaw in my etching , i got it and i cant believe i did because it was so tiny...

Great, congrats

BUT unfortunately i cant get the flanger to work properly.
i can hear the output as is , no influence on the sound. it distorts when i put up the input gain but it's probably normal...

At this point (no fire ) following DEBUGGING - What to do when it doesn't work instructions is most effective way how to let us help you..

i don't think that there is a clock in my circuit whatever i do with RT2. and the SW_mode isn't effecting anything .

To check clock+BBD build audio-probe and check BBD output.
To check clock measure DC voltage at BBD's clock inputs CP1 and CP2, normal DMM in DC mode should see there cca half of VCC.

i started with the bias setting and set that exactly as Thomeeque explained before. V bias (at pin 3 of the bbd chip) = 0.42 +0.54*Vcc
which is 0.42+0.54*9.08 = 5.32V

Well done

one thing to say is that i didn't connect anything yet to pads 10 and 11 (CC) should I?

No, it is for delay range mod, leave mods until basic circuit works.

T.

[Oneoff1]

thank's a lot !
i'll try to debug and measure according to the instructions... very useful!

[Oneoff1]

ok I got the flanger working ! 
there was something wrong with the 324 so i tried another chip ... and after setting RT2 and fiddling  with C17 a bit with another cap in parallel i got a beautiful 'airplane' kind of effect !
now , the only problem is that the rate knob is not effecting the rate . i got a steady slow rate . mmm. 
after checking the schematics again i noticed that the middle pad of the rate pot is not connected to anything???
is it just me or there is something strange with it?

[Thomeeque]

ok I got the flanger working ! 
there was something wrong with the 324 so i tried another chip ... and after setting RT2 and fiddling  with C17 a bit with another cap in parallel i got a beautiful 'airplane' kind of effect !

Great! So what capacity you have at C17 now?

now , the only problem is that the rate knob is not effecting the rate . i got a steady slow rate . mmm. 
after checking the schematics again i noticed that the middle pad of the rate pot is not connected to anything???
is it just me or there is something strange with it?

You have somehow missed build note 7..

T.

[Oneoff1]

You have somehow missed build note 7..

that's right! i thought that if i'm using the REV LOG potentiometer i should leave this pad as is...
now all is good   i have a great flanging effect.
i still don't know how exactly to set up RT3 to the "right" set up , something there is not linear and kind of confusing as the trimmer starts to effect the clock in a certain area and then it get to have a 'intermittent' effect on the range pot. i'm not sure how to describe it
what should be the right setup with RT3? what should be the resistance there?

Great! So what capacity you have at C17 now?

Ok, so because i'm using this effect as a part in my DIY modular synthesizer i want to give it some more options.
so i decided to have a 6 position switch with different capacitors this can be useful for making a subtle flange
with strings or a total chaos with a drum machine for instance. i found out that when i'm touching the leads of C17  i'm
changing the range in different ways so maybe i'll add a touch pad to that section...
i'm also going to try to add some vactrols to the circuit in order to have CV control over the pots.
i guess that the experiments can be endless with that circuit...

the caps i'm using for C17:
1nf (the more 'standard' effect)
1.1nf
2.2nf
3nf
10 nf
27nf (meteor crush effect
and i'm still trying more values...


BTW i found out that when using the NJM4558D i got a nicer sound . i also found differences between different 3207 ic's.

Thank's a lot for this great project!!

[Thomeeque]

i still don't know how exactly to set up RT3 to the "right" set up..

RT3 is there for fine-tuning sweep range, there is some factory alignment procedure, see this post again, but you can simply dial range you like and be happy with it - it is yet more complicated in your case, bacause original factory alignment procedure expects one specific C17 value (47pF probably) and you have many.

Ok, so because i'm using this effect as a part in my DIY modular synthesizer i want to give it some more options.
...
Thank's a lot for this great project!!

1nF to 27nF? It's pretty far from original 47pF It would be nice if you would create some demo of the way you use it, as it seems unique and interesting in more aspects.

Btw. consider this simple "odd/even" mod, there are links to demo where you can hear it, I think you may like it

BTW i found out that when using the NJM4558D i got a nicer sound . i also found differences between different 3207 ic's.

Yep, could be.

T.

[Oneoff1]

there is some factory alignment procedure

i went back to that post but i cant find it... should i look in the IC spec sheet?

1nF to 27nF? It's pretty far from original 47pF

yes, i cant get any effect with 22pf installed alone,but when i add 47pf in parallel i get it. i have nicer results with 1000pf...
strange ha? i probably made a mistake somewhere or set the clock trimmer way off but whatever i tried with PR3 the results with C17 (22pf) alone are the same- no flanging effect.

Also when experimenting with small values (in the 22pf -100pf area) caps in parallel to C17
i get some noise / clipping sound (depends on the position of PR3) when the effect sweeps to it's 'peak' . that can't be avoided
no matter what i do withe the trimmers. this, for example isn't happening with 1000pf cap installed...

i'm lucky that i like noise sometimes

It would be nice if you would create some demo of the way you use it, as it seems unique and interesting in more aspects.

sure , i will post a demo when ill finish (and solder everything together). right now it's a mess...

also , thank's for the odd/even mod info,
i appreciate your replies and help!

[Thomeeque]

there is some factory alignment procedure

i went back to that post but i cant find it... should i look in the IC spec sheet?

Post contains link to the web page dedicated to all possible EM's alignment procedures..

yes, i cant get any effect with 22pf installed alone,but when i add 47pf in parallel i get it. i have nicer results with 1000pf...

Frequency range of EM's clock is limited (going beyond this limit freezes clock which leads to audible pops when limit is crossed), that is correct behavior.

On the other hand if you were not able to adjust RT3 even with C17=22pF to the position, where full sweep range worked, you still have something fishy there.

Btw. I do not recommend 22pF as C17 anymore (since I know that clock frequency is not doubled this way properly and natural sweep gets cripled), use 47pF there.

T.

[carfranca]

Wow! Excellent pedal! Congratulations Tomas. I had similar problems to the user ricbox and decided checking all tracks. Before, I reviewed all components. Disassembled and remade the circuit carefully. The problem persisted. Then, using a magnifying glass I reviewed all the tracks and bingo! There was a short track by a thin layer of copper. Problem solved! My EM3207 is 'flanging'... 

[Thomeeque]

 Thanks and congratulations to successful debugging, I'm glad you like the result

[DrAlx]

I have done a stripboard layout for the EM3207 and built it.  It worked first time  
I am pleased with the result and the layout is only slightly larger in area than Thomeeque's PCB.

To make the layout compact, I swapped the order of some series components in a couple of places
(e.g. I swapped the order of RT3 and R33).

Here are links to the design (the strips run vertically)

1) Component-side view.  Using the same labels as Thomeeque's v1.1 PDF.
http://www.imageshack.com/i/j8cs0wj

2) Component-side view.  Showing the values.
http://www.imageshack.com/i/nqhb58j

3) Component-side view, with "x-ray" through to the strips below.
http://www.imageshack.com/i/1fcvt5j

4) Strip-side view (mirror image of other views) showing where to make breaks (dark horizontal lines) in strips, and where to join
adjacent strips with blobs of solder (the ellipses).
Tip: Make all the breaks in the strips BEFORE soldering all components,
      and join adjacent strips with solder AFTER soldering all components.
http://www.imageshack.com/i/0hzxt0j

Note that the colors of the strips in 4) don't always match the colors in 3).  
That's not an error, it's just the coloring algorithm I used in the program that produced the pictures.

I will link to photos of my build later.