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DIY Stompboxes => Building your own stompbox => Topic started by: duck0872 on October 05, 2012, 06:05:52 PM

Title: debugging tonepad small clone chorus
Post by: duck0872 on October 05, 2012, 06:05:52 PM
Hey folks,

I'm having trouble debugging the tonepad small clone chorus pedal that I've built.  http://www.tonepad.com/project.asp?id=8
I didn't substitute any parts, and all the IC's are socketed.  When the pedal is on I get a good dry signal coming through, but no chorus, so I'm assuming the problem lies on the wet side of things.  Also, when the depth pot is turned up I get a regular click and pop sound, almost like  drum machine.  At first look I didn't see any solder bridges.  I've swapped out all the IC and transistors and still no change.   Here's the voltages that I'm getting.

Input from the power supply- 9.37

at PCB-9.35

D1-  C= 7.52
       A= 7.90

D2-  C= 6.92
       A= .07

Q1 2N5087 -  E= 7.53
                    B= 8.62
                    C= 0.00

Q2 2n5088-   E= 8.02
                    B= 8.62
                    C= 8.82

Q3 2n5088-   E= 3.75
                    B= 3.96
                    C= 8.82

IC1 4558       1=4.41           8= 8.82
                    2= 4.41          7= 4.40
                    3= 3.51          6= 4.40
                    4= 0.00          5= 4.29

IC2 LM358    1= bouncing erratically      8= 8.82
                   2= 6.71          7= bouncing erratically
                   3= bouncing erratically  6= 3.50
                   4= 0.00           5= bouncing erratically

MN3007-     1= 8.03      8= 4.34
                  2= 3.98      7= 4.34
                  3= 7.64      6= 0.00
                  4= 0.00      5= 0.00

CD4047-      1= 7.89     14= 8.03
                  2= .07       13= 7.90
                  3= bouncing between 6.90-7     12= 0
                  4= 8.03     11= 3.98
                  5= 8.03     10= 0
                  6= 8.03     9= 0
                  7= 0         8= 0
Title: Re: debugging tonepad small clone chorus
Post by: PRR on October 06, 2012, 12:43:52 AM
> Q1 2N5087 -  B= 8.62

This voltage should be more like half of the supply voltage. Turning the 100K trim-pot should swing Q1 Base from 8V to 1V. Somewhere around 4V or 5V the BBD can pass signal. See if you can get into that zone.

When it passes signal (yay!), fine-trim the pot for cleanest sound.
Title: Re: debugging tonepad small clone chorus
Post by: Scruffie on October 06, 2012, 12:48:56 AM
Clock isn't working, should see half supplyish on pins 10 & 11 of the 4047 and on 2&6 of the 3007.
Title: Re: debugging tonepad small clone chorus
Post by: Keeb on October 06, 2012, 06:41:45 AM
This was my first pedal build and it refused to chorus (regardless of trim pot adjustment)... Until I'd placed the jumper between pin 12 on the CD4047 to ground (between the CD4047 and MN3007 on the layout).  :icon_redface:

So yeah, jumper in place?
Title: Re: debugging tonepad small clone chorus
Post by: duck0872 on October 06, 2012, 11:08:35 AM
trim pot adjustment doesn't make a difference, and yes the jumper is in place.  I did find a small solder bridge leading pin 6 from the 3007 to ground, but after fixing that it still isn't working
Title: Re: debugging tonepad small clone chorus
Post by: PRR on October 06, 2012, 12:16:29 PM
There are multiple problems.

Q1 and Q3 voltages don't make sense.

Are the electrolytic caps right-way-round?

Is the circuit-board pre-made or etched at home?

You said: 
1) At first look I didn't see any solder bridges. 
2) I did find a small solder bridge

It may be wise to look some more.
Title: Re: debugging tonepad small clone chorus
Post by: duck0872 on October 06, 2012, 02:42:15 PM
caps are all verified right way round, i etched the board myself and verified it before building, i have triple checked and no solder bridges
Title: Re: debugging tonepad small clone chorus
Post by: duck0872 on October 06, 2012, 04:08:14 PM
Most of the way there.  Found a bad ground, and now I have chorus signal, but still getting some clicks and pops with the depth pot all the way up, and the rate control doesn't seem to do much.  Also getting a pop now when the effect is turned on
Title: Re: debugging tonepad small clone chorus
Post by: pinkjimiphoton on October 06, 2012, 08:41:03 PM
sounds like a cold solder joint on an electro in the audio path..it charges and discharges as a pop, and changes as the temp does?
Title: Re: debugging tonepad small clone chorus
Post by: duck0872 on October 06, 2012, 09:22:53 PM
I took some updated voltage readings now that the chorus effect is audible, but still not working 100% correctly

input 9.37
pcb 9.35

d1- C 4.28   A 4.83
d2- varies on both a and c
q1- E 4.28 B 3.52 C 0
q2- E 8.46 B 8.98 C 9.08
q3- E varies B varies C 9.09

IC1- 1- 4.54     8 - 9.08
       2- 4.54    7 - 4.54
       3 - 3.61   6- 4.54
       4- 0        5- 4.42

IC2-   1- vary    8- 9.09
         2- 6.92    7- vary
         3- 6.68    6- 3.60
         4- 0        5- vary

3007- 1- 8.47    8- vary near 5
        2- vary    7- vary near 5
        3- 4.68    6- vary
        4- 0        5- 0

4047- 1-varies near 8.4    14- 8.46
        2- varies near .5     13- varies near 8.4
        3- vary                 12- 0
        4- 8.46                 11- vary
        5- 8.46                 10- vary
        6- 8.46                  9- 0
        7- 0                      8- 0
Title: Re: debugging tonepad small clone chorus
Post by: Keppy on October 06, 2012, 10:49:19 PM
Pins 3 & 6 of IC2 are too high. Three resistors make a voltage divider between 9v and ground to set the voltages on pins 3 & 6 of that IC. You should have about 4v on pin 3 and 2.2v on pin 6. Check the values of the 180k, 68k, and 82k resistors. This may be part of the reason for your oscillator troubles.
Title: Re: debugging tonepad small clone chorus
Post by: duck0872 on October 06, 2012, 11:32:37 PM
YOU'RE THE MAN KEPPY!!!!   At some point when I was building this thing (in between changing diapers and heating up bottles) I must not have been paying attention and transposed the 180K and 47K resistors.  Switched them out and now it works perfectly!!  Thank you everyone here who helped me chase the bugs out of this thing.  It's weird, I had a run of about 5 pedals there that worked perfectly first time out, and then this one decided to test my patience.  Time to rock!
Title: Re: debugging tonepad small clone chorus
Post by: bluebunny on October 07, 2012, 04:55:31 PM
YOU'RE THE MAN KEPPY!!!!   At some point when I was building this thing (in between changing diapers and heating up bottles) I must not have been paying attention and transposed the 180K and 47K resistors.  Switched them out and now it works perfectly!! 
That's good news!  This is a great chorus - my favourite.

Thank you everyone here who helped me chase the bugs out of this thing.
Yep, a great bunch of very knowledgeable and very helpful people here.  You can't help but grow to love 'em.   :icon_biggrin:

It's weird, I had a run of about 5 pedals there that worked perfectly first time out, and then this one decided to test my patience.  Time to rock!
Me too!  Built my first half-dozen without a hitch (somewhat miraculously).  Then a P45 that refused to play ball.  Turned out to be a broken pot (discovered thanks to RG's expert guiding hand - see #2 above!).
Title: Re: debugging tonepad small clone chorus
Post by: deadastronaut on October 08, 2012, 04:29:41 AM
ok i'm trying to debug mine now ::)....its weird, as i connect/disconnect the ground it does chorus for a second.....

here goes. hopefully i can get this going too.. :)...the only sub i made was swapping the 180k for a 220k..on ic 358 (which worked on another build)

not gettng any fluctuation in voltages though..no lfo etc...i get sound but no chorus...

if i manually turn the rate pot it chorus's...so i assume all connections are fine, it must be the clock/lfo


ic1 072:

1  4.40
2  4.40
3  4.29
4  0
5  4.38
6  4.40
7  4.40
8  8.85



ic2 358

1  1.71
2  1.62
3  3.55
4  0
5  1.70
6  1.95
7  1.63
8  8.85


4047

1  7.99
2  0.11
3  6.76
4  8.18
5  8.18
6  8.18
7  0
8  0
9  0
10  4.05
11  4.06
12  0
13  8.01
14  8.18

mn3007

1  8.18
2  4.06
3  4.48
4  0
5  0
6  4.04
7  5.08
8  5.08


edit:  i swapped out the 358, for a 5532 just to try a different opamp, it works but the lfo is just up down,and thump thump thump.. not smooth chorus....hmmmmm...i haven't another 358 at the mo to try...

but at least the voltages are going up n down now....still not proper chorus though.. ::)

Title: Re: debugging tonepad small clone chorus
Post by: Fender3D on October 08, 2012, 07:09:13 AM
5532 is a bad oscillator...
that bad it won't oscillate occasionally...
try a low current 062 or a 1458
Title: Re: debugging tonepad small clone chorus
Post by: deadastronaut on October 08, 2012, 07:53:16 AM
cheers, i haven't any of those at the mo...(i just tried the 5532 to see if it was alive...

what if i lower the 220k...which i put in place of the 180k?...to get more voltage to the 358 pin 3?...

i have some more 358's on order...
Title: Re: debugging tonepad small clone chorus
Post by: Keeb on October 08, 2012, 10:22:21 AM

what if i lower the 220k...which i put in place of the 180k?...to get more voltage to the 358 pin 3?...



Well, pin 3 of the lm358 is supplied by a voltage divider network of 9V->180K->pin 3->150K (68k+82k)->ground
With that setup pin 3 should see about 4.09V. With your setup it should see about 3.64V (you measured 3.55V).
Since pin 6 is supplied by that voltage through a divider made of 68k+82k it should see 2.24V. Your setup would give 1.99V (you measured 1.95V).

(I purchased the "TAB understanding electricity and electronics" book a couple of weeks ago and am trying to understand how everything actually works. Still, the datasheet for the lm358 makes my head spin so I don't know if this will fix it and I can't explain why it will or won't. I'm not Paul...!)

In other words, worth a shot I guess!

Good luck Rob!

Edit; realised Keppy had already done the math.
Title: Re: debugging tonepad small clone chorus
Post by: deadastronaut on October 08, 2012, 11:04:50 AM
hmmmm....its been on my debugging pile a while now...i just thought i'd best get it going as i need a chorus for recording some stuff....

1458's on order too........

i'll give it a whirl though... ;)
Title: Re: debugging tonepad small clone chorus
Post by: PRR on October 09, 2012, 02:02:35 AM
> the "TAB understanding electricity and electronics"

IMHO, 99% of what was published under the TAB imprint is a waste of time.

I have actually thrown-out TAB books to get them out of circulation.

Sloan's book *may* be an exception.

While the subject is indeed hard, you might do better with another book.

> the datasheet for the lm358 makes my head spin

Most of that stuff is NOT useful to you. It's an op-amp, it will do opamp things, if you stay below Max voltage and can stand a little leak on the inputs. I'm not sure why "5532 is a bad oscillator", unless it is being tried in very high-resistance circuits (5532 is good at many things but the inputs are quite leaky).
Title: Re: debugging tonepad small clone chorus
Post by: Keeb on October 09, 2012, 04:28:47 AM
> the "TAB understanding electricity and electronics"

IMHO, 99% of what was published under the TAB imprint is a waste of time.

I have actually thrown-out TAB books to get them out of circulation.

Sloan's book *may* be an exception.

While the subject is indeed hard, you might do better with another book.

> the datasheet for the lm358 makes my head spin

Most of that stuff is NOT useful to you. It's an op-amp, it will do opamp things, if you stay below Max voltage and can stand a little leak on the inputs. I'm not sure why "5532 is a bad oscillator", unless it is being tried in very high-resistance circuits (5532 is good at many things but the inputs are quite leaky).

Sorry for going off topic here...
I think I read somewhere on the forum that someone had recommended it so I gave it a shot. For $20 I thought I hadn't that much to lose.
Could you please recommend me a another book that you find more useful?

I'm planning on buying another book when I get through this one. I find reading a few books from different authors helps a lot in explaining things (sometimes when you read something explained differently; the words just make sense!) so I wasn't looking for a holy grail kind of book, just something to get me started.
Thanks for your input!
Title: Re: debugging tonepad small clone chorus
Post by: Fender3D on October 09, 2012, 04:32:34 AM
...I'm not sure why "5532 is a bad oscillator"...

I must admit it's not always 5532's fault...
most of oscillators out there just start "pushed" by op-amp internal noise...
and since 5532 has a very low noise, it won't start occasionally
Title: Re: debugging tonepad small clone chorus
Post by: deadastronaut on October 09, 2012, 04:37:48 AM
well the 5532 is the only bugger that gets some ''form'' of crappy  lfo going on this @#$%ing chorus...the 358 isn't ... :)
Title: Re: debugging tonepad small clone chorus
Post by: Lurco on October 09, 2012, 04:47:20 AM
On page 2 there are mentioned some "unique characteristics" : http://www.ti.com/lit/ds/symlink/lm158-n.pdf , the first one seems to be applicable here?
Title: Re: debugging tonepad small clone chorus
Post by: deadastronaut on October 09, 2012, 06:24:28 AM
ive swapped the 3007, and the 4047, the 2n3906, and the 2n5088's... stil no lfo/clock...hmmmm

heres my figures.  

D1

A: 6.31    C: 5.78

D2  A: 0.13   C: 6.88


Q1 : 2N3906

C  0.00
B  5.14
E  5.78

Q2 2N5088

C  8.83
B  6.09
E  5.53

Q3 2N5088

C  8.83
B  8.78
E  8.15

CD4047

1  7.93
2  0.13
3  6.87
4  8.15
5  8.15
6  8.15
7  0.00
8  0.00
9  0.00
10  4.00
11  4.02
12  0.00
13  7.96
14  8.15

MN3007

1  8.15
2  4.02
3  6.27
4  0.00
5  0.00
6  4.00
7  6.24
8  6.24

LM358

1  1.18
2  1.27
3  3.55
4  0.00
5  1.17
6  1.94
7  1.12
8  8.83


TL072

1  4.39
2  4.39
3  4.28
4  0.00
5  4.37
6  4.39
7  4.38
8  8.83

any suggestions?
Title: Re: debugging tonepad small clone chorus
Post by: Fender3D on October 09, 2012, 06:42:16 AM
Assuming you used Francisco's layout, did you put all jumpers?

Unless you you swapped any resistors value (or should they differ too much from their color code) that damn 358 should oscillate !!!!!!!!!

Title: Re: debugging tonepad small clone chorus
Post by: deadastronaut on October 09, 2012, 06:48:23 AM
yep its that layout, i built 1 before and it was fine with the same specs, including swapping the 180k for a 220k, 120k for 100k and all 12k's to 10k's...39k's to 33k's....weird!.


edit and jumpers ;)