Newbe here.... This is my second build
I have a partially working unit. It does 'yeow' (or down) but does not 'wha' (or up) and the peak pot has no effect. I assume that if the effect partially works, the Hi/Lo & LP/BP/HP switches work and the gain & volume pots work that the wiring is OK. The Peak pot itself appears to work based on measuring it in the circuit.
I have done the following:
Checked are rechecked components and values - OK
Reflowed the solder
Following are voltages measured with the effect bypassed and input V=11.7:
1 2 3 4 5 6 7 8
IC 1 3.3 3.3 1.5 0.7 5.2 6.2 2 11.2
IC 2 2.1 1.7 1.6 0.7 4.5 4.2 8.6 11.2
IC 3 10.2 0 0 0.7 0 4.8 10.4 11.2
IC 4 1.4 6.1 0 -4.8 -10.6 2.5 3.7 11.2
Inputs Outputs
VACT 1 8.6 6.8 0 2
VACT 2 8.6 6.8 4.9 10.2
I am concerned about the output of VACT 1 being so low. Could it be bad or could it be a problem in the circuit after it?
Any other suggestions/ideas welcome.
Thanks.....
Based on the 11V you're putting into this circuit and the -10.6V you're reading on IC4:pin5, I don't understand why you're getting ~0V on pin 4 of IC1, IC2 and IC3. Those should all be at or around -10.6V. There might be an issue with VACT1, but I'd concentrate on that missing negative voltage on your op amp ICs first. Good luck!
I just happen to have my Naughty Fish sitting open right now as I've just screwed up putting a decal on it, but that does make it easy for me to take some voltages. Mine's the 2014 version. I don't think that'll make a difference.
Pots are both at 12:00. Toggles are set to LP, Down, Hi
The input voltage is at 9.25V
IC1:
1 0V
2 0V
3 0V
4 -8.23V
5 0V
6 0V
7 0V
8 8.66V
IC2:
1 ~80mV drifting
2 22mV
3 22mV
4 -8.25V
5 3.44V
6 2.57V
7 6.48V
8 8.66V
IC3:
1 0V
2 0V
3 0V
4 -8.25V
5 0V
6 0V
7 0V
8 8.66V
IC4:
1 1.37V
2 4.62V
3 0V
4 -3.88V
5 -8.24V
6 2.55V
7 1.41V
8 8.66V
Vactrol 1:
1 6.48V
2 4.93V
Resistor side both pins at 0V
Vactrol 2:
1 6.48V
2 4.93V
Resistor side both pins at 0V
If a voltage read less than 1mV, I put it at zero.
Mycyk, take a look at Rob's IC1 and IC3 voltages as well as pin4 on IC2. Those are the places where it is the most glaringly obvious that something is horribly wrong with your negative power rail. What's strange is that you have correct negative voltage on IC4:pin5, but not on any of your op amp ICs. From the schematic that looks totally impossible -- there are direct connections from IC4:pin5 to the negative voltage supplies on IC1-3.
I think there are three possibilities (in order of probability):
1. Cold solder joint on IC4:pin5
2. Broken trace (especially the pad at C14)
3. Cold joints on IC1-3:pin4
Can you confirm whether or not you have approximately -10.6V on the negative lead of C14? Decent photos of both sides of your board would help tremendously, too.
Thanks for your replies. I feel like a dope - obviously supply voltages should be the same for all the IC's. Let me try again - I have remeasured them and they are similar to RobA's:
IC 1
1 0
2 0
3 0
4 -10.5
5 0
6 0
7 0
8 11.0
IC 2
1 3.5
2 0
3 0
4 -10.5
5 4.4
6 4.4
7 4.5
8 11.0
IC 3
1 0
2 0
3 0
4 -10.5
5 0
6 0
7 0
8 11.0
IC 4
1 1.4
2 6.0
3 0
4 -4.8
5 -10.6
6 2.5
7 1.4
8 11.0
Inputs Outputs
VACT 1 4.4 2.7 0 0
VACT 2 4.6 2.8 0 0
I had to substitute C1 and C9 with tantalum, and C4 is a large cross-over cap so I had to lay it down to fit it in the box. I replaced C13 because I thought it was bad but I still have the same issues. Pictures attached.
The pedal works as expected with the Range switch 'Down' but not with it 'Up'. The voltage to the Vactrols appears to be too high because the LED is lit even with the gain control at minimum, but I can't read the schematic well enough to figure out why........
I made an audio probe and listened to many different points tonight but nothing really makes sense to me. Anything on IC 2 sounds very distorted, but inputs and outputs from the board are fine.
Thanks again!
Confirming that I do have -10.4 V at -ve pin on C14.
Thanks for correcting those voltages and posting the photos. All of the resistors down in the "Range" potion of the circuit look fine.
I'm having trouble reading your R6, though. Is that a five- or four-band color code? If it's four-band, I would expect orange - white - yellow - gold. If it's five-band I would expect orange - white - black - orange - (brown?). To me it looks like orange - white - brown - gold (390R). Apologies if I'm just misreading that.
Yes you're absolutely right. Even though I checked it twice (I saw what I wanted to see!) R6 is 390R not 390K. Will swap them and let you know what happens.
Thanks!
Cool. I hope that's it. That was certainly what was making the Peak control unresponsive. The 390K resistor is in parallel with the 250K pot to bring the maximum value down to about 150K, which is what's in the original Mutron III. A 390R in the same position brings the maximum setting to, well, about 389R. :(
I'm not sure why that would affect the Range functionality, though. I wonder if we'll find something else after you've fixed that. Fingers crossed, though!
Thanks mgwhit!
Changing the resistor did fix the sweep and peak controls. They both work really well now.
Still have the issue with only the 'Down' switch working. The 'Up' is a little better but still has too much voltage so it's basically almost full open even with the Gain pot at minimum.
I tried a regulated power supply at 9 volts and it is about the same, but the 'Down' does not work as well. The range of sweep and the sensitivity are limited. The indicator LED does not come on at all in the 'Down' position but is still on all the time in the 'Up' position.
Input is now V=8.96:
(omitted all zeros to make the list shorter)
IC 1
4 -7.8
8 8.4
IC 2
1 1.7
4 -7.8
5 2.9
6 2.8
7 4.4
8 8.4
IC 3
4 -7.8
8 8.4
IC 4
1 1.4
2 4.6
4 -3.6
5 -7.8
6 2.5
7 1.4
8 8.4
With the range switch in the up position only IC 2 changes to these:
IC 2
1 4
4 -7.8
5 3.3
6 3.4
7 2.5
8 8.4
I'm looking into the supply for IC 2 and checking my values and soldering again.
Looking forward to any other suggestions the group might have.
Thanks again!
Cool. Glad you're making progress! Can you post the voltages at the anode and cathode of your LEDs (LED1, VACT_1A, VACT_2A) with the Range switch in the Up and Down positions?
Here are 2 sets of measured voltages with no input to the pedal. The first is with the 11V supply:
Range switch Down
Vactrol 1
Anode 5.1
Cathode 3.3
Vactrol 2
Anode 5.1
Cathode 3.4
LED
Anode 1.71
Cathode 0
With Range switch Up
Vactrol 1
Anode 4.1
Cathode 2.3
Vactrol 2
Anode 4.1
Cathode 2.3
LED
Anode 1.65
Cathode 0
Using my regulated 9 V supply:
Range switch Down
Vactrol 1
Anode 2.8
Cathode 1.0
Vactrol 2
Anode 2.8
Cathode 1.0
LED
Anode 1.38
Cathode 0
With Range switch Up
Vactrol 1
Anode 4.2
Cathode 2.4
Vactrol 2
Anode 4.2
Cathode 2.4
LED
Anode 1.67
Cathode 0
All of these change a lot with music from my MP3 player into the pedal. Vactrol anode voltages swing between -5 to +5 with the Range switch Down but are pegged at 6.4 with the Range switch Up.
Thanks for any further assistance or ideas.
Thanks! I've gotta admit that I'm in over my head here. I'm going to throw out some ideas and maybe someone with more experience with this circuit can chip in. I 'd like you to try two more things:
1. In both Up and Down positions of the Range switch, check to see if the voltage on the cathode of D2 wiggles when you play music through the effect. It should move up and down in both switch positions. If it does in the down position and doesn't in the up position then we know the problem is in the rectifier (IC2_A). If it moves in both positions, we can assume that the problem is in the inverting amplifier of IC2_B.
2. With the power off, do a thorough continuity test of all of the lugs on your Range switch. Test to confirm that the correct lugs are connected in each switch position and that the incorrect lugs are not connected. (If you don't know how to do this, let us know.) Confirm that none of the lugs has any continuity to ground in either switch position.
Thanks for keeping up with this thread. Every time you post more information here, you get closer to finding the problem...even if it feels like it's taking forever. Good luck!
Okay, # 2 first: I measured the range switch in situ with my ohmmeter and it appears to be working properly. There is no direct connection to ground and the pins show the correct connections when switched.
Cathode of D2 shows voltage sweeps in both switch positions. I also swapped the IC TL072s and D2 shows the same for all 3 different IC TL072s in all 3 IC sockets. Also pin 7 of all 3 ICs show voltage swings at all times whereas pins 5 & 6 only show voltage swings with the Range switch in the Up position. Based on this data it appears to me that all 3 IC TL072s are working, at least all 3 are the same.
With the Range switch in the Up position I am now able to hear some 'wahing' with full range signal but it is very slight and only in the upper treble range (above about 2K Hz, which is why I couldn't hear it previously when testing with my bass). With the Range switch in the Down position the effect is very noticeable and can be adjusted from low through higher frequencies with the mode and Hi/Lo switch, which I consider normal. If this was the effect I wanted I would stop here and box it up but the Up effect (basically an autowah for my bass) is what I'm really looking for.
Any ideas on how I can get the effect down to lower frequencies with the Range switch in the Up position? Based on observation of the LED the voltage appears too high because it never goes off. Is there a mod to the circuit which would affect this?
Thanks again for all your help. I have been working on this build on and off since November so any progress is good at this point.......
I've gotta admit, I'm stumped, but this would be as good a time as any to triple check the values of all of your capacitors. C4 controls the frequencies that drive the envelope, so that's a great place to start. Not sure why it would only affect the Up position, though, especially since your R12 and R13 values look good.
Well, Mycyk, if no one else chimes in here anytime soon, don't despair. I ordered the components to build mine today. Between this thread and the fact that my band is rehearsing "Sugar Magnolia" I decided it was time to get on it. In a week I should either have a nice reference model to compare yours to or my own Tech Help thread going. ;)
I'll try to pull mine back out and take some measurements with different settings tomorrow. Although, I can't guarantee the accuracy -- I've got a nasty head cold right now and it's leaving me kinda goofy.
A couple of notes about my build that might be relevant; It seems to be pretty sensitive to the Gain pot setting, Mine is really distorted in some setting when I first turn it on.
One the first point, in some toggle settings it just doesn't respond much at all until the gain setting is just right. When the Gain is dialed to the right point, it pops into being very touch sensitive and a ton of fun to play with.
The weird thing about the second point is that it goes away after about a minute or so and become completely clean and it doesn't seem to do it with my Marshall amp. The Marshall thing could be because of the difference in the tone settings and responses of that particular amp, or maybe it's the input impedance or ... I don't know. At this point, I don't have a grasp on why it's noisy at startup or why the distortion stops after a bit of warm up. I really need to do some more testing on why this happens. But, it doesn't bother me in practice because it goes away pretty quickly and the thing sounds great.
Edit: Don't know why I didn't think of this before, but it just hit me that the most obvious guess for the initial distortion is the high dark resistance of the Vactrols at startup. I'll investigate that.
Thanks, Rob!
I would be happy to take some voltages if they are still needed. What settings do you want?
In the mean time, I have recorded a (crappy) demo of mine on bass. It's pretty bad in terms of sound quality, playing (I play guitar), and as a bass effect generally. But maybe the video will help.
Mike, if you wanted to post voltages with the Up - Down switch in the "Up" position, that would be great. That's the setting we're trying to debug. RobA was kind enough to post his voltages, but his switch was in Down mode and that totally changes the readings on IC2_B.
Sorry about not getting the voltages in yesterday. The cold got the better of me. Warning: these voltages should be thought of as tentative, I've been drinking tea with a bit of whisky, taking decongestants and antihistamines, and haven't slept in more than 1 and 1/2 hour stretches for two days. So my thought processes may be slightly altered :D.
With that warning in place,
Knobs at noon, LP, Up, Hi
Vin = 9.23V
IC1:
1 0V
2 0V
3 0V
4 -8.21V
5 0V
6 0V
7 0V
8 8.65V
IC2:
1 ~330mV drifting
2 22mV
3 22mV
4 -8.15V
5 ~40mV drifting slightly
6 41.1mV
7 -450mV
8 8.64V
IC3:
1 0V
2 0V
3 0V
4 -8.20V
5 0V
6 0V
7 0V
8 8.64
IC4:
1 1.37V
2 4.55V
3 0V
4 -3.83V
5 -8.19V
6 2.55V
7 1.41V
8 8.59V
Vactrol 1:
1 -620mV drifting
2 36mV
Resistor side both pins at 0V
Vactrol 2:
1 -520mV drifting
2 36mV
Resistor side both pins at 0V
Leaving everything else the same but moving Gain to 9:00
I only put in a voltage if it changed significantly from the noon voltages.
IC2:
1 ~300mV drifting
2 22mV
3 22mV
4 -8.15V
5 ~20mV drifting slightly
6 ~25mV drifting slightly
7 ~ -1.18V drifting slightly
8 8.64V
Vactrol 1:
1 -1.16V drifting
2 22mV
Resistor side both pins at 0V
Vactrol 2:
1 -1.19V drifting
2 22mV
Resistor side both pins at 0V
I took voltages with every switch combination.
XLS isn't an allowed filetype, so here you go: Naughty Fish Voltages (http://www.justonemorebuild.com/wp-content/uploads/2015/02/Naughty-Fish-Voltages.xls) [XLS]
Mike
Thanks for all the input guys. I'm still not getting anywhere new with mine. I replaced the 2 tants (C1 and C9) with bipolar electrolytics, and I don't think it sounds as good, but maybe that's just frustration clouding my hearing. :(
Rob I hope your feeling better.
Mike your's sounds great and looks good too!
Let us know how your build goes Matt.
Thanks again all.
Thanks everyone for uploading voltages! I've made a table of what I think are the relevant test points with as similar settings as I could get (RobA LP/Up/Hi Gain=9:00, RobA LP/Up/Hi Gain=12:00, Mike LP/Up/High Gain=12:00, Mycyk Range=Up w/ 9V supply):
| Test Point | RobA (Gain 9:00) | RobA (Gain 12:00) | Mike (Gain 12:00) | Mycyk (Gain ?) |
| IC2_B 4 | -8.15 | -8.15 | -7.58 | -7.8 |
| IC2_B 5 | 0.020~ | 0.040~ | 0.16 | 3.3 |
| IC2_B 6 | 0.025 | 0.041 | 0.17 | 3.4 |
| IC2_B 7 | -1.18 | -0.450 | 1.85 | 2.5 |
| IC2_B 8 | 8.64 | 8.64 | 8 | 8.4 |
| VACT_1A (a) | -1.16~ | -0.620~ | 1.85 | 4.2 |
| VACT_1A (c) | 0.022 | 0.036 | 0.17 | 2.4 |
| VACT_2A (a) | -1.19V~ | -0.520~ | 1.85 | 4.2 |
| VACT_2A (c) | 0.022 | 0.036 | 0.17 | 2.4 |
I expected to see lower voltages on the anodes of the vactrols than on the cathodes: RobA has that, but Mike and Mycyk don't. I expected to see the same voltage on IC2_B pin 7 as on the vactrol anodes, which Mike has exactly, RobA has approximately and Mycyk doesn't have at all (but could possibly be backwards).
Mycyk, this should give you some things to think about. The first question I'd have for you is, Are you labeling the anodes and cathodes of your vactrols correctly? The second question is, How are you getting over 3V on IC2_B pins 5 and 6 with the Range switch in the Up position? That's probably where your problem is. If you can remeasure with your knobs at 12:00 and your switches at LP/Up/High that might help, too.
Cold's still here -- but no antihistamines yet today so maybe I can reason a bit better now. The square pad of the Vactrol should be the more positive pad. So my readings confused me. And then I thought to put it on the scope. My DMM sucks at averaging AC voltages and has a pretty slow response time. So, what I got when I put it on the DC coupled setting on the oscilloscope with no guitar signal coming in is an AC signal of about 400kHz that just barely pokes positive but with the majority of the sinusoidal-ish waveform on the negative side. That isn't really going to do too much with the filter as the LED is never really going to turn on. So, I plugged in the guitar and hit a string. The oscillations stop instantly and the now flat voltage pops up to about 9V (gain setting at 12:00) and proceeds to track the fading input signal down to 0V at which point the oscillations come back in.
The gain setting sets how high the voltage will go up and to a degree how fast it fades.
I think getting the readings for IC2 in the Up setting would be more useful with an input signal. It should start high and track down as the signal level decreases.
Thanks Matt for pulling all this together.
Okay, here's measurements with switches in LP/Up/Hi and pots at about 12 noon:
IC2_B 4 -7.76
IC2_B 5 2.65
IC2_B 6 2.65
IC2_B 7 4.48
IC2_B 8 8.36
VACT_1A (a) 4.48
VACT_1A (c) 2.71
VACT_2A (a) 4.49
VACT_2A (c) 2.70
When I pluck a bass string the voltage at IC2_B 7 and both VACT anodes (square pads marked + on the schematic) goes up to about 6.3 then decays. So the main differences are that I have significant voltages at my IC2 B 5, 6 which the other builds don't and mine is not producing the same voltage change with an input signal.
This still makes me think that there's a problem with the circuit supplying (or controlling) IC2. Will look at this more today or tomorrow.
Thanks again guys.
I think your analysis is right. Check the connections around R17, R16, and C10. Maybe there is a problem with the switch. Check for continuity across the switch between the outside pins. Check the resistance across them too. Check the value of R20 because it works differently in the Up mode from the Down mode.
I'm also wondering what would happen if there were either low or high frequency inaudible noise hitting the envelope generator. If there were noise getting in there, it might cause the envelope to be offset and not get the full sweep. I guess that C10 should be filtering out most of the high frequency content. Maybe it's not working right?
Next steps:
I replaced C10 with one I tested to ensure it was working = no change
I removed the Range switch and tested it = it's fine.
I replaced the Range switch with jumpers and got the same behavior I've had all along in both positions.
I then opened the jumpers and inserted a 1M pot between R5 and Pin 5 of IC2B (Pins 2 & 3 of Range A switch on the schematic). By adjusting this pot I can get the unit to give a mediocre Up (autowah) sound. However it does not seem as sensitive as the typical Down position sounds.
I also have significant high hash noise when the Mode switch is in the HP position. This may be the issue you mentioned Rob, but using an audio probe I couldn't figure out where it was coming from. Basically the input pad is good, C2, C3, IC1_A1, R2, R3, all are noisy. Do you think it could be the Gain pot? It sounds fine when I touch each leg so I don't don't understand what's going on with this. I also don't understand why I can't hear audio when touching either leg of C1 but get audio after it...... Am I not using the audio probe correctly? Can one of you that have a working unit try this and let me know what you find?
Any help is appreciated...... Thanks again!
IC1_A is in an inverting op amp amplifier configuration. What this means for what you are seeing at C1 is that the op amp tries to move the output voltage so that the feedback through R3 and C2 will keep the voltage at pin 2 of the op amp zero. How much it needs to amplify the signal will also depend on the attenuation of the input signal by the Gain pot and R1 (and a bit by C1 in really low frequencies). So, the audio at pin 2 will be tiny. The inverting input of an inverting op amp amplifier is considered a "virtual" ground point. So, what you are seeing there makes sense.
The Gain pot will add a lot of resistor thermal noise to the circuit when it is set to a low gain value (high resistor value). If the pot is noisy in addition to this, it could be adding a bunch of noise. One thing you could try is clipping a 33pF cap or so across C2. That'll reduce the gain through that amplifier for higher frequencies.
My switches finally arrived today. I'm taking the day off tomorrow (very important soccer match to watch!), so hopefully I can get mine populated pretty quickly and start looking at this again.
Latest attempt:
I replaced R12 thru R21 and C1, C9, C4 & C12. No change.... :o
That covers just about all the components on the driver side of the Vactrols.
I don't believe it is in the power supply or the sensor side of the circuit because it works in the down position.
At this point I'm thinking it's the board itself although I can't see anything obvious with it......
Any other ideas???
Thanks!
Just so you know, I've populated my board and soldered in the switches, but Smallbear sent me a C50K pot instead of the C500K I intended to use for the Gain pot. :P
I just built two of these today, and am having the same issue with the "range" switch on both of mine. I am hoping someone solves this one soon!
...well, I spoke too soon. I was able to solve my issue with the range switch only working in one position. As it turns out, I had wrongly assumed that the white dot on my vactrols indicated the cathode of the LED. The dot in fact indicated the anode (+) side. I verified this by lighting the led with a battery/CLR while measuring the resistance of the vactrol.
I feel like a dummy for having put the vactrols in wrong polarity on both builds. I desoldered them and put them in the right way, and now everything works great. Hopefully this helps prevent someone else from making the same mistake.
Hey Jeremy,
Just out of curiosity which way did it work? Up (wah) or down (yeow)? This may be a solution to my problem.....
Thanks