Author Topic: Yet Another Snow White Autowah Help Post  (Read 897 times)

acraigwilliams

Yet Another Snow White Autowah Help Post
« on: August 14, 2018, 03:58:10 PM »
Hi everyone. This is my first post here although I've been lurking around for probably a couple years. Would love to get some advice on troubleshooting this pedal--I'm not gonna let this one beat me! I've been through tons of past posts re: the SWAW, but I am still having trouble figuring it out.

Background
I'm trying to put two effects into a single pedal--the SWAW and a Colorsound 1-knob fuzz. I tested both before adding them to the enclosure; both worked as they should. In the enclosure, they both worked as they should. Sounded great actually. I then proceeded to put the backplate on and fry something in the SWAW, because after that I started getting a loud whooshing. I took it back out and fought that one for a while, then decided it would be better to just rebuild it. So that's where I am now.

Now
I've now built my second SWAW, and this one is very, very quiet. I can hear it if I turn my amp up to 10, and then the envelope filter isn't being applied. It just sounds like a straight guitar signal.

I've checked with an audio probe. The first place I lose signal is on a 10k resistor (circled here: https://imgur.com/a/N1Oso7r). Also, D2 sounds really fuzzy through the probe. I replaced both of those but no change.

I have voltages below--looks like I'm having a serious power issue but I'm hoping somebody here can point me in the right direction on where it might be originating from.

Info
1.What does it do, not do, and sound like? Extremely quiet. With amp at 10, I can hear guitar signal but no effect applied.
2.Name of the circuit = Mad Professor Auto Wah (modded version)
3.Source of the circuit (URL of schematic or project) = http://tagboardeffects.blogspot.com/2013/04/mad-professor-snow-white-autowah.html
4.Any modifications to the circuit? No
5.Any parts substitutions? Used 8.2k resistors instead of 7.9k
6.Positive ground to negative ground conversion? No


Voltage at the circuit board end of the red battery lead =9.23
Voltage at the circuit board end of the black battery lead =0

Q1
D = 8.3
S = .25
G = .01

Q2
C= 5.07
B= .23
E= .55

Q3
C= 5.07
B= .51
E= 1.07

VR
I= 8.3
G= 0
O= 5.07

IC1
P1= 1.07
P2= .02
P3= .01
P4= .01
P5= 0
P6= .01
P7= 0
P8= .01
P9= .01
P10= 0
P11= 8.33
P12= 0
P13=.01
P14=.01
P15= .02
P16= 1.07

IC2
P1= .23
P2= 1.33
P3= .01
P4= .56
P5= .01
P6= .02
P7= .03
P8= .01
P9= .01
P10= 4.16
P11= .01
P12= .02
P13= 1.32
P14= 1.05

D1
A (anode, the non-band end) =5.07
K (cathode, the banded end) =8.32

D2
A =9.19
K =8.54

D3
A =1.33
K =1.07

D4
A =.25
K =.24

D5
A =1.07
K =1.34



EBK

Re: Yet Another Snow White Autowah Help Post
« Reply #1 on: August 14, 2018, 04:25:01 PM »
Welcome to the non-lurking world!

Could you post some pics of your build?
I definitely don't like those transistor voltages.  Something is not right there.... Emitter voltages should be higher, for one thing (around 2.9V, from what I've been able to find), and the base voltages should be slightly higher than the emitter voltages.  Haven't looked at the rest of the values in detail yet.
  • SUPPORTER
"I want to go back to being weird. I like being weird. Weird's all I've got. That, and my sweet style." --Maurice Moss

acraigwilliams

Re: Yet Another Snow White Autowah Help Post
« Reply #2 on: August 14, 2018, 06:27:20 PM »
Quote
Could you post some pics of your build?

Yes! Here are some pics. https://imgur.com/a/mXb5ouS Let me know if any others would help.

Slowpoke101

Re: Yet Another Snow White Autowah Help Post
« Reply #3 on: August 14, 2018, 06:51:35 PM »
You don't seem to have +9V going to the LM324 IC. Pin 4 of IC2.
Have you soldered the link under that IC correctly?

acraigwilliams

Re: Yet Another Snow White Autowah Help Post
« Reply #4 on: August 15, 2018, 02:18:49 AM »
You don't seem to have +9V going to the LM324 IC. Pin 4 of IC2.
Have you soldered the link under that IC correctly?


Progress! You were right, I had missed soldering the link under IC2. Fixed that up and the filter is working. Now my new issue is a loud whooshing noise (like I had the first try building this). Wife asked why it sounds like being on an airplane.

Here are my new voltages:

Voltage at the circuit board end of the red battery lead =9.2
Voltage at the circuit board end of the black battery lead =0.0

Q1
D =8.15
S = 4.15
G = 3.67

Q2
C=5.07
B=0.78
E= 0.83

Q3
C=5.07
B= 0.87
E=1.2

VR
I=8.15
G= 0.01
O=5.07

IC1
P1=1.2
P2= 0.74
P3= 4.08
P4= 4.06
P5=5.24
P6= 0.01
P7=  5.24
P8= 4.06
P9= 4.07
P10=  7.34
P11=  8.14
P12= 7.33
P13= 4.07
P14= 4.07
P15= 0.8
P16=1.2

IC2
P1= 1.82
P2=  4.07
P3= 4.08
P4= 8.15
P5= 4.08
P6= 4.08
P7= 4.08
P8= 4.08
P9= 4.08
P10=4.07
P11= 0.01
P12= 4.06
P13=  4.08
P14=  3.98

D1
A (anode, the non-band end) = 5.07
K (cathode, the banded end) = 8.13

D2
A = 9.17
K = 8.5

D3
A = 4.07
K = 3.96

D4
A =1.2
K =0.83

D5
A = 3.94
K =4.04

Slowpoke101

Re: Yet Another Snow White Autowah Help Post
« Reply #5 on: August 15, 2018, 04:00:00 AM »
The voltage on pin 1 of IC2 is low. I would expect about 4 Volts there with no input signal.

The volts from pin 1 goes through a 330R resistor and then to D4. There appears to be a fairly high current draw in this area judging from the various voltage drops.

Check for any shorts (slivers of copper or cuts that have a tiny amount of copper left) and incorrect value components. The main areas of interest are pin 1 of IC2, 330R resistor, D4 and the immediate area around Q2. But do check over the entire board thoroughly. Make sure that the wiring to the Decay pot (and the others) is OK and that there are no frayed wires.

I noticed on the tagboard site that several other people have got the same problem as you do and their measured voltages are extremely close to what yours are. Unfortunately no solutions were posted. Other people have successfully constructed this effect so it is unlikely that there is an error with the layout.

I am curious as to if you are using BC550 transistors and what type of JFET did you use?

acraigwilliams

Re: Yet Another Snow White Autowah Help Post
« Reply #6 on: August 15, 2018, 02:57:38 PM »
Nice. I'll investigate when I get home from work.

I noticed on the tagboard site that several other people have got the same problem as you do and their measured voltages are extremely close to what yours are. Unfortunately no solutions were posted. Other people have successfully constructed this effect so it is unlikely that there is an error with the layout.

I am curious as to if you are using BC550 transistors and what type of JFET did you use?


 I'm using the BC550's and a 2N5457 JFET. Like you said about others successfully building it, I've built it once successfully only to short something out when I put the backplate of the enclosure on. So I know it can work!

acraigwilliams

Re: Yet Another Snow White Autowah Help Post
« Reply #7 on: August 16, 2018, 12:33:35 PM »
Quick update. Checked the 330R resistor and the area around pin 1. Cleaned around with an Exacto knife to try to catch any shorts. I also flipped D4 around, because someone on tagboard mentioned it:

Quote
Please note for those who find the effect "subtle" that you got the orientation of D4 correct! a 1N34A sometimes has the band on the positive side instead of the negative. double check the polarity of the diodes!   

That didn't work, so I have D4 back oriented the way it was originally. I'm going to work my way through it with an audio probe again tonight because the first time I did was back when I wasn't getting any signal through. I'm also planning to check on the Decay and Bias pots. Bias, in particular, seems to have a strong effect on the whooshing sound.

acraigwilliams

Re: Yet Another Snow White Autowah Help Post
« Reply #8 on: August 17, 2018, 01:51:38 PM »
SOLVED! :) Went through with an audio probe last night. Turns out IC1 was bad. Replaced it and everything's sounding great. Now to box it up.

Slowpoke101

Re: Yet Another Snow White Autowah Help Post
« Reply #9 on: August 17, 2018, 04:31:45 PM »
Fixed! That is good news  ;D
The good old audio probe is a very handy tool to have  8).

LM13600 / LM13700 chips are easy to damage and you do need to be careful with them.
Perhaps you may now wish to fault-find the first Snow White that you built and see what got damaged with that build.

Now just to clarify IC2 pin 1's expected behaviour - With no signal input to the effect, the voltage on pin 1 should be below 0.8 Volts. With signal applied (pluck a string on the guitar), the voltage should go up to over 7 Volts and start to fall as the input signal decays. Since that part of the circuit is set up as a type of envelop follower this is to be expected. Once I found a circuit that was close enough, it became obvious that I was wrong with what I posted previously  :icon_redface:  Opps.....Sorry...

Enjoy your new effect and good luck with your next build.