Debugging Decimator G-String kit

[abakuzam]

Hello folks, hope  you all having nice time here. So, i'm built this kit : http://www.efekty-diy.pl/pdf/Decimator%20G-String%20ENG.pdf and when i plug only my guitar to amp input ( Guitar IN - Gate OUT ) in bypass, i get guitar signal from amp, i used switching jacks ( i checked them , they do their job properly, no loose contacts ) , but when i activate the pedal, i don't get any sound ( i played around 1M trimmer, no differance ) .

Substutions: i used metal canned 2N2222A (hFE = 174 ) instead of MPS2222A, 1N5817 instead of 1n4007 ( power section ) and 2*100k resistors in series intstead of 200k . Also i obtained my THAT2181C from banzaimusic, i assume it's legit.

That's what i did so far:

- Checked pcb tracks , solder bridges, cold solder joints ( resoldered all the joints again, not to have a question about it ), all OK.
- Checked cap orientations, component values, shorts between components ( if they touch their leads to each other ), all OK.
- Haven't tried the pedal with other pedals in the chain ( first 4 wire configuration in the documents )
- Searched in the forum, didn't find similar problems. So i had to open a new topic.


Measurements with Duracell 9v battery @ 8.66v and when connected to the circut while led on ( CLR = 12k ) @8.33v. Threshold potantiometer is all the day down. Drawing about 40mA when led is on ( CLR = 12k )

U1 ( LF353P )       

1: 7.8
2: 8.05
3: 8.05
4: 0
5: 4.63
6: 4.67
7: 6.78
8: 8.04

U2 ( LF347N )

1: 1.27
2: 1.27
3: 1.18
4: 8
5: 1.97
6: 1.98
7: 3.17
8: 2.55
9: 2.55
10: 2.51
11: 0
12: 3.8
13: 8
14: 8

U3 ( THAT2181C )

1: 7.09
2: 6.28
3: 7.97
4: 6.27
5: 5.1
6: 7.96
7: 7.96
8: 7.96

U4 ( LF347CN )

1: 6.67
2: 6.67
3: 4
4: 7.95
5: 7.95
6: 5.93
7: 6.66
8: 6.66
9: 6.63
10: 7.94
11: 0
12: 6.29
13: 6.33
14: 1.6

U5 ( LF353P )

1: 7.35
2: 7.35
3: 0
4: 0
5: 3.94
6: 7.05
7: 7.05
8: 7.92

Q1 ( 2N5551 )

C: 2.52 then pot is all the way down, 6.77 when it's max
B: 1.57
E: 1.13

Q2 ( 2N222A )

E: 0
B: 0.6
C: 5.05

[Slowpoke101]

Q2 (2N2222A) does not appear to be working.
Check that it is installed correctly. If it is then see if you can test it or just swap it with another.
Almost any common NPN transistor can be used for Q2.

[abakuzam]

Q2 (2N2222A) does not appear to be working.
Check that it is installed correctly. If it is then see if you can test it or just swap it with another.
Almost any common NPN transistor can be used for Q2.

Hello, i tried different 2N2222A's and 2N5551's but same result, i tried 2n3904 , here is the voltages, E:0 B : 0.61 C : 5.25, which make sense because Emitter of Q2 connected to ground, Base volatge mae sense too. Maybe you said it's not appear to be working because Emitter of q2 is 0v? My cables are okay too. i guess i will pull apart everything and start the debug methodologically

[diffeq]

Q2 (2N2222A) does not appear to be working.
Check that it is installed correctly. If it is then see if you can test it or just swap it with another.
Almost any common NPN transistor can be used for Q2.

Hello, i tried different 2N2222A's and 2N5551's but same result, i tried 2n3904 , here is the voltages, E:0 B : 0.61 C : 5.25, which make sense because Emitter of Q2 connected to ground, Base volatge mae sense too. Maybe you said it's not appear to be working because Emitter of q2 is 0v? My cables are okay too. i guess i will pull apart everything and start the debug methodologically

Don't strip it down just yet. Shouldn't Q2's base voltage be higher, set three diode drops above ground by that string of diodes?

[abakuzam]

Q2 (2N2222A) does not appear to be working.
Check that it is installed correctly. If it is then see if you can test it or just swap it with another.
Almost any common NPN transistor can be used for Q2.

Hello, i tried different 2N2222A's and 2N5551's but same result, i tried 2n3904 , here is the voltages, E:0 B : 0.61 C : 5.25, which make sense because Emitter of Q2 connected to ground, Base volatge mae sense too. Maybe you said it's not appear to be working because Emitter of q2 is 0v? My cables are okay too. i guess i will pull apart everything and start the debug methodologically

Don't strip it down just yet. Shouldn't Q2's base voltage be higher, set three diode drops above ground by that string of diodes?

Mr.PRR wrote this on previous debug threads:

https://www.diystompboxes.com/smfforum/index.php?topic=112176.msg1034271#msg1034271 , i think my Q2 ( 2N2222A ) voltages are correct.

[bluebunny]

Your VCA has pretty much the same(-ish) voltage on each pin - nothing is 0V.  And there's not much evidence of any voltages at half-supply on the opamps.  I'd go looking for shorts.  Got pictures of your board, top and bottom?

[abakuzam]

Your VCA has pretty much the same(-ish) voltage on each pin - nothing is 0V.  And there's not much evidence of any voltages at half-supply on the opamps.  I'd go looking for shorts.  Got pictures of your board, top and bottom?

i plugged of the circuit from the box, used wall adapter, nothing connected except the potantiometer here is my results, and i was trying to get VAA ( i assume its around 4,5volts, even without chips, i get around 9v, i checked bridges again but couldn't find any , not yet i guess)

         


Wall adapter @9,28v after protection diode @9v , pot @minimum                                 

   U1 (LF353P)
1   8,37
2   8,09
3   9
4   0
5   9
6   8,17
7   5,52
8   9

   U2(LF347N)
1   2,03
2   2,03
3   1,96
4   9
5   2,58
6   2,6
7   3,55
8   2,88
9   2,88
10   2,84
11   0
12   4,3
13   9
14   9

   U3(THAT2181C)
1   8,72
2   8,71
3   9
4   8,71
5   6,12
6   9
7   9
8   8,09

   U4(LF347N)
1   7,69
2   7,69
3   5,13
4   9
5   9
6   6,9
7   7,69
8   7,69
9   7,65
10   9
11   0
12   7,3
13   7,35
14   2,45

   U5(LF353P)
1   8,69
2   8,69
3   0
4   0
5   5,43
6   8,21
7   8,21
8   9

   Q1(2N2222A)
E   2,27
B   2,44
C   2,89

   Q2(2N5551)
E   0
B   0,64
C   6,12

[Slowpoke101]

The VAA voltage should be around 4.5V, but 9V without the ICs installed does point to a short circuit somewhere. Below is a picture that shows some solder connection areas that you may need to redo.



Remove all ICs other than U2D (LF347) which supplies the VAA voltage (pin 14) and resolder the indicated connections. Apply power and see if U2 pin 14 is now at 4.5V (or close to it). If it is then reinstall the other chips and test again.

If VAA is still at 9V then there is definitely a short circuit that is not obvious. The PCB has a certain "home-made" quality to it. The board is quite good but I can see a few areas that are concerning - mainly closely spaced track runs that get too close. Not to worry.

[abakuzam]

The VAA voltage should be around 4.5V, but 9V without the ICs installed does point to a short circuit somewhere. Below is a picture that shows some solder connection areas that you may need to redo.



Remove all ICs other than U2D (LF347) which supplies the VAA voltage (pin 14) and resolder the indicated connections. Apply power and see if U2 pin 14 is now at 4.5V (or close to it). If it is then reinstall the other chips and test again.

If VAA is still at 9V then there is definitely a short circuit that is not obvious. The PCB has a certain "home-made" quality to it. The board is quite good but I can see a few areas that are concerning - mainly closely spaced track runs that get too close. Not to worry.

i mixed q1 and q2 names on previous post and here is new voltages with correct semiconductor names. i used battery on this measurements @8,44 after protection diode drop 8,25volts. i didn't use the adapter because its general purpose smps one, voltages were not that stable to measure, they were boucing 0.3v +-, potantiometer is all the way down.

i de soldered everthing, didn't work, i messed up big i guess, then i etched a new board, populated components , measured it all before i put in, now, i get a fuzzy , reaaaally gated sound , my guitar doesn't even ring, i need to push a really hard note to hear it, like a fuzz gate on specific pot location, around 2 o clock, i played with trimmer , didn't help with the issue, and i tried 2n3904 in place of the 2n2222a, and changed the 2n5551 again, no differance, i checked every solder joint, and did continiuty check, i checked the pcb under a bright light now, to make it easier to see traces etc. also lesson learnt, i should be more careful and follow basic steps more clearly to not take people's valuable time in here.





   U1 (LF353P)
1   7,53
2   3,25
3   4,13
4   0
5   2,7
6   2,7
7   4,12
8   8,25

   U2(LF347N)
1   1,32
2   1,32
3   1,32
4   8,25
5   2,41
6   2,41
7   4,25
8   1,32
9   1,32
10  1,29
11   0
12   3,91
13   4,1
14   4,1

   U3(THAT2181C)
1   3,26
2   3,94
3   4,1
4   3,94
5   1,14
6   4,1
7   8,2
8   3,21

   U4(LF347N)
1   4,1
2   4,1
3   2,05
4   8,2
5   4,1
6   4,1
7   4
8   4,2
9   4,1
10   4,1
11   0
12   3,8
13   3,83
14   3,08

   U5(LF353P)
1   7,6
2   7,6
3   0
4   0
5   2,05
6   4,1
7   4,1
8   8,2

   Q1(2N5551)
E   1,2
B   1,9
C   1,3

   Q2(2N222A)
E   0
B   0,72
C   1,13

[Slowpoke101]

That was fast with making another board. A board that size would've taken me at least 5 hours to get from a blank board to a populated board. Well done.
Q2's Collector voltage is now looking better and so is VAA at pin 14 of U2. There is a voltage reading that is pointing to a problem - pins 2 and 4 of the THAT2181C are meant to be connected - they are not. This may be the problem.
I do suggest that you also get ready to do some audio probing of the if reconnecting the THAT2181C pins 2 and 4 doesn't get things working correctly.

I've wanted to make one of these units for a while now. Where did you get the artwork for the board from?

[abakuzam]

That was fast with making another board. A board that size would've taken me at least 5 hours to get from a blank board to a populated board. Well done.
Q2's Collector voltage is now looking better and so is VAA at pin 14 of U2. There is a voltage reading that is pointing to a problem - pins 2 and 4 of the THAT2181C are meant to be connected - they are not. This may be the problem.
I do suggest that you also get ready to do some audio probing of the if reconnecting the THAT2181C pins 2 and 4 doesn't get things working correctly.

I've wanted to make one of these units for a while now. Where did you get the artwork for the board from?

oops, my bad, pin 2 and 4 of the 2181C is the same 3,94 volts, making those pcb's all day gave me "keyboard blindness".  i will audioprobe it tomorrow, maybe , i messed up the switching wiring, or bad parts, i should try tl072 and tl074 , and thank you, it took me 15 mins to etch the board and drill , another 2 hours to populate Here is the artwork.

[Slowpoke101]

Thank you for the artwork - another project for the pile of "Stuff To Build". I will order the THAT chip today.

OK on the keyboard blindness. Errors always creep in. Speaking of which, have a look at the following pictures. The first one shows the area of interest one the board. The second picture shows possible issues that may need checking.

[abakuzam]

Thank you for the artwork - another project for the pile of "Stuff To Build". I will order the THAT chip today.

OK on the keyboard blindness. Errors always creep in. Speaking of which, have a look at the following pictures. The first one shows the area of interest one the board. The second picture shows possible issues that may need checking.

Hello again, i checked all the close traces with DMM including the traces on your post, no short and bridges, it was just a bent component lead, i guess i'm audioprobing tomorrow, when i get it to work, i will share my voltages for archive. Thank you , again.

[abakuzam]

Hello again,

I audioprobed the circuit, that2181C gets the signal ( i ran music trough my phone ) so jack switching thing does it's job, i have signal in "gate in" pad in the circuit, then it hits the c15. but after r26 i get a huge volume drop ( i changed the resistor, and checked the soldering ) , and pin 1 of the that2181C gets the signal but, it only works very specific place of the trimpot, , i only get sound trough that2181c when i adjust to trimpot so pin1 of the U1 goes around 7,2 volts at 8 volts VCC, when i short the pin1 and pin2 of the u1 i get unity volume, i checked the r3 and c3 as well as r2. So im pretty confused about all, i hope i can solve the problem, i will change the trimpot with a decent 1m potantiometer, and see if its the bad trimpot.

Also i have signal on u4's 7 ,8 and 14 but on the 14th pin, it gets really low volume.

i really appreciate some advices. Thank you.

[abakuzam]

Hello again!

Sorry for spams, so i got it to working, on the 3rd board, maybe it's my etching or traces, i will check them out . ( that means i would have 3 g strings  ) Probably because of my dead-bug style wiring in a very RF noisy environment, circuit adds a bit noise, even on clean channel i can hear, but i have poor grounding in my home. it'll probably go back to normal when i box it. Haven't tried the fx loop style connection, just guitar and amp. it probably works like that too.

Here is my verified voltages for other people, it may helpful. Battery voltage is @8,17v after protection diode while led on, threshold is all the way down, i used 2n2222A , no other substitutions. i learnt quite a few stuff in the process, i should be more careful next time.

U1 (LF353P)
4,07
4,07
4,07
0
2,65
2,67
4,07
8,15

U2 (LF347N)
1,29
1,29
1,29
8,14
2,38
2,40
4,25
1,29
1,29
1,29
0
3,97
4,04
4,04

U3(THAT2181C)
4,04
4,04
4,04
4,04
1,19
4,04
8,12
4,04

U4(LF347N)
4,04
4,04
2,02
8,11
4,04
4,04
3,94
4,15
4,04
4,04
0
3,75
3,75
3,21

U5(LF353P)
7,51
7,51
0
0
2,00
4,03
4,03
8,10

Q1 ( 2N5551)
E: 1,28
B: 1,19
C: 1,28

Q2(2N2222A)
E: 0
B: 0,64
C: 1,18

Have a good one!

[pinkjimiphoton]

ummmmm.....
these things hook up weird, it can't pass signal from guitar in to gate out. it doesn't work that way.

you plug your guitar in to the input. take the guitar out to your effects chain input.

gate in is from the OUTPUT of your effects. gate out is to your amp or time domain fx or whatever.

i had an issue with it driving me batshit @#$%ing crazy when i built the same project. it turned out i was hooking it up wrong. once i figured out my mistake, it worked perfectly. no noise, no hums, no bullshit!

so... guitar to guitar in. keep the threshold control fully counterclockwise when testing!!...gate in to fx, gate out to amp. strat noise reduction is usually before 10:00 on the pot. too much gate, no signal will get thru at all.

this is the best gate of all the ones i tried, once i hooked it up right.

[pruttelherrie]

Also, please note that the 2181 is current-driven, so checking waveforms at pin 1 makes no sense. You could however probe across the input-resistor.