- This topic has 10 replies, 6 voices, and was last updated 5 years, 8 months ago by
.
-
Posts
-
Hi all, another pedal builder here!
I’m building a swah kit and I can hear sound in the output, in fact it sounds good, but there isn’t wah effect. It seems to me like a wah pedal that is always in the same position. It doesn’t responds to guitar volume output either.
BOM and wires have been reviewed. Transistor voltages seems to be higher than it should (all pots are closed):
Q1: 7.05 / 4.23 / 3.27
Q2: 4.98 / 5.50 / 4.98
Q3: 4.98 / 4.98 / 4.37
Any suggestions will be appreciated. Thanks in advance!
These are my suggestions based on several guesses without having anything to see.
First like a real wah pedal placement is everything. There will be a limited tonal change unless it is placed first in the chain and before any dirt especially.
Second it needs to be dialed in to your specific guitar. This autowah has features to allow you to get the most out of guitar or bass so that said if it is not dialed in for a guitar then it will be less than stellar. Once dialed in however it should be kept right where it is from there on out.
These are the two most common problems 1. Placement and 2. Settings
Barring a build error of course since the voltages are a bit odd (please recheck) and also note this circuit has been a go to for a long while now with no changes other than cosmetic. Make sure all IC pins are seated properly. Re-flow any suspect solder joints. Look for any potential shorting including the solder side of the board. Double check all off board connections and fix or reflow. If you cannot get it going we will need Clear Detailed Photos of both sides of the board! This is a larger circuit and there are just too many things that could go wrong so we have to be able to see it as close as if we were holding it.
Here is a good read.
Proper Q voltages for comparison (all pots full CCW)
Q1: (7.27 – 3.71 – 3.23 – DSG)
Q2: (5.05 – 3.75 – 2.90 – CBE)
Q3: (5.05 – 2.90 – 2.86 – CBE)
Hi Barry,
I left this pedal because I was working on other projects and now that I’m more unoccupied is time to come back.
I have reviewed everything twice, re-solder some joints, etc. Now I can hear the effect but just with all pedal pots open and when the guitar volume is very low (ie 1-2). I don’t know if this is very usefull. I’m playing with a les paul with classic humbuckers (no high gain), just one pedal and short cables. I can’t check it with other guitars for the moment. I have tested it both with battery and lab power supply. I have also read all post for swah in this forum… So if anyone have experience something like this or know how to hear the effect with more volume just let me know. Thank you very much.
Here are some pics and measurements:
Q1: 6.93, 4.17, 3.2
Q2: 4.98, 4.02, 3.58
Q3: 4.98, 3.94, 3.33
Regulator: 6.95, 0, 4.98
LM13700: 1.31, 0, 3.48, 3.48, 4.66, 0, 4.66, 3.46, 3.48, 4.69, 6.96, 3.47, 3.47, 0, 1.13
TL074: 3.46, 3.46, 3.46, 6.94, 3.47, 3.47, 3.47, 3.31, 3.49, 3.47, 0, 3.47, 3.46, 4.35
Vd4=0,71
Vr28=1.34
Vd3=0.29
The PCB is drawing around 13mA without the led.
Someone else will have to help with this as i cannot verify resistors etc..
I am having blurry vision issues and going to the ophthalmologist tomorrow.
Have you ensured the socketed trannies are seated securely? Sometimes, I have to use fine-tipped needle-nose pliers to “wrinkle” the leads of my trannies so they fit snuggly into the sockets.
Ii believe your supply voltage is quite low. Are you using a fresh battery or a power supply? Your voltages for IC1 seem low.
Your chips do not appear to have any markings. Is the LM13700 a good chip purchased from a reliable source? This chip is known to have some bad clones.
Thanks everybody!
Hopes everything going well, Barry.
Cybercow, I’ve pushed the ICs a little bit and seems to be well located on the sockets. No sound differences when pushing.
Wilkie1, i’m using a programmable power supply with 9.0v in the output. I’ve checked from off to 9.5 volts, interesting different sounds there but not an autowah. For me sounds like a wah or filter but in a fixed position. It seems like It is not changing according to input volume.
PCB and all components are from a musikding kit. I think IC1 is from national semico.
<hr />
Hi again,
Placing a buffer pedal between the guitar and the swah makes the effect works much better. It makes sense in the way that if the filter response depends on the input volume and impedance, a buffer will do the job. Still difficult to dial with, but now I can hear the wah sound and it’s funny!
However I think there is still something wrong there because without the buffer there is no wah at all.
Keep learning …
Hi,
Ive just built this same circuit and appear to be having the exact same issue as Alvaro. Im a pretty experienced builder, but have gone over this build with a fine tooth comb and im happy with component placement and connections. Its obviously possible that Ive missed something, but the behaviour being the same as OP its got me wondering.
It sounds exactly like the wah is stuck in a single position. Ive tried every combination of the dials, and have tried to copy demos on youtube with knob placement. ive got bias as a pot on the front and it sweeps up and down and makes the fixed position more or less pronounced but it doesnt sweep on its own or in response to picking attack.
Im wondering if its got to do with a transistor not operating at the right voltage, or possibly with capacitor choice. Ill attach some photos to a new thread.
Any help is much appreciated.
Did you try it with 2 good short cables (10ft or less) with only a guitar and no other pedals plugged in?
That way you can rule out several common issues right away. Remember we sold thousands of these worldwide over 10 years so there is no real good reason why one circuit would be different than the rest. The other thing I would do is a solid re-flow as part of a standard troubleshoot.
Other than that start a new thread with photos and voltages so we can have a look and we will be happy to try and help.
Thank you Barry, i did test it with short cables and no other pedals.
I wasnt trying to suggest there was anything wrong with the design, just that cap choice can have a large effect on audio circuits, and especially transistors being out of spec can be hugely frustrating to track down.
Ill tinker a bit more then make a proper post with pictures and voltages.
Thanks again.
- You must be logged in to reply to this topic.