Aion's Spectron : no sweeping in the modulation

[eh la bas ma]

Hello,

I am trying to finish a Spectron.

https://aionfx.com/app/files/docs/spectron_documentation.pdf

I can hear a filtering effect. All controls are doing something exept Decay and attack . But it isn't "wah-ing"... Filtering isn't going up and down. It sounds like a fixed wah.

Vactrols light up and stay fixed that way, they respond to Intensity, but no variation in the lights other than that. I have to keep turning this knob to hear a wah effect. SENS. led is either on or off according to the Sweep switch position, it isn't pulsating, same as vactrols.

I am using an LM358 on IC2.

As instructed, I jumpered pin 2 and 3 of the color pot, I made sure it was pin 3 by checking if it was connected to R15 (first picture).

Sweep lock washer is set on position 2, Range on position 4.

External trigger : I did cut the trace until my multimeter said there is no connection.





I wonder where to look to restore the sweeping. Any idea how I should proceed ?

It feels like very close to work ! Any help would be welcome.

[idy]

So you cut the pads for the external trigger mod, did you add a normally closed switching jack?

Have you confirmed that with nothing plugged in to that jack there is now continuity between those two pads? Until there is there will be no trigger...unless you have an external source hooked up.

[aion]

So you cut the pads for the external trigger mod, did you add a normally closed switching jack?

Have you confirmed that with nothing plugged in to that jack there is now continuity between those two pads? Until there is there will be no trigger...unless you have an external source hooked up.

It does look correctly wired based on the photo, but yeah, would be good to have confirmation that the white and blue wires have continuity where they meet the PCB.

I would try swapping out the LM358 for another one. I've had a couple of reports of similar issues and it usually is fixed by using another 358. They're not all made the same even within the same brand and they don't always bias up right in this application. I'm guessing there would have been some sorting done on the original Meatball units.

[eh la bas ma]

Thanks for your help !

Votage on LM358 :

1= 4.8 mV
2= 83.1 mV
3= 2.2 mV
4= 0.5 mV
5 facing 4 = 1.0 mV
6= 1.079 V
7= 1.079 V
8= 9.10 V

I am unboxing it to check the trigger pads...

edit : local store has LM358 ! I am running there...

edit 2 : I went through the christmas crowd and  bought 3 new chips (2 euros a piece, ...ouch!) new values with the first one :

1= 20.6 mV
2= 46.9mV
3= 1.4 mV
4= 0.5 mV
5= 1.0 mV
6= 1.528mV
7= 1.528mV
8 = 9.10 V

controls are set on instructions standard auto wah.

[idy]

Those voltages are about what you would expect: 9v on 8, 0 on 4, the other pins less than 1v.

So no triggering at all?

When you turn the sweep switch to "down", does the LED light up with no signal? It should.

You will want to confirm that signal is making it to that 358. Signal probe. It should sound lousy at pin 3 (and 2 and 1) because it is rectifying, but it should sound.

Then there is there is my hobby horse, biasing the 358. Pin 3. Putting a 100k pot from 9v to that pin should allow you to dial in a spot where the LED is barely lit with no signal, or lights with small signal. Mutron has 22k to ground on that pin, but it is bipolar, so a "proper" steal of the circuit would have done things differently. Meatball "gets away" with this error, maybe they had a certain shipment of opamps that worked... original opamp unknown because numbers sanded off...

[eh la bas ma]

I unboxed it and there is connection between the 2 trigger pads when the jack is empty, there isn't when I plugg a jack in there (ext. trigger).

Those voltages are about what you would expect: 9v on 8, 0 on 4, the other pins less than 1v.

So no triggering at all?

When you turn the sweep switch to "down", does the LED light up with no signal? It should.

I am not sure what is up and down. Sweep CCW sens. led and vactrols are off, position 2 they're always on. I unboxed it and messed with the controls so I ll answer you about the signal once it is back in place.

while it is unboxed, 2 pics (with and without flash) of the soldering side, in case someone can spot something obvious that i am missing :

[eh la bas ma]

You will want to confirm that signal is making it to that 358. Signal probe. It should sound lousy at pin 3 (and 2 and 1) because it is rectifying, but it should sound.

Then there is there is my hobby horse, biasing the 358. Pin 3. Putting a 100k pot from 9v to that pin should allow you to dial in a spot where the LED is barely lit with no signal, or lights with small signal. Mutron has 22k to ground on that pin, but it is bipolar, so a "proper" steal of the circuit would have done things differently. Meatball "gets away" with this error, maybe they had a certain shipment of opamps that worked... original opamp unknown because numbers sanded off...

And i thought i was so close...signal probing, IC biasing.... No way around that i guess...

I should mention that i am powering this build with a 9 V power supply, 500mA. Input signal comes from active hambucker pickups, through a few other circuits (compressor, etc. all powered off).

[eh la bas ma]

When you turn the sweep switch to "down", does the LED light up with no signal? It should.

Sweep fully CW vactrols light up and there is a signal (highs slightly boosted). Next position CCW, i hear a "iiiiiïwwouuuuh" like a wah effect, pitch is going down and the signal fades, If i turn the guitar volume fully up, i can hear the signal filtered (kind of bassy, high frequencies are filtered).

[idy]

There is a lot to unpack about this circuit. So many knobs and switches, several could cause no effect. Sensitivity up, Color up, Intensity up, Attack down, Decay higher than attack, bandwidth NOT  "off" ( not center.)

Your external trigger jack is apparently not the problem.

Your sweep rotary seems to work. In "up" mode the lights are normally off and your signal should trigger the detector and light them up. In "down" the lights are normally on and your picking should turn them down or off. Won't bore you explaining how this works...

And you can hear the difference, so the filter and buffer part of the circuit is working fine, the tl072s.


You could try the 100k pot/trimmer trick and see if it works. No probing, no thinking, just try... The object is to get that 358 up closer to the trigger point with no signal.

[eh la bas ma]

In "up" mode the lights are normally off and your signal should trigger the detector and light them up. In "down" the lights are normally on and your picking should turn them down or off. Won't bore you explaining how this works...

Thanks, but this wouldn't bore me at all, because this is precisely what is currently not happening on my Spectron. I would be very grateful if you could give more details about this process.

I tried the circuit without IC2 LM358, vactrols don't light up in any position. So LM358 does something at least. I have 4 of them now, I tried each one, but no success. I suspect there is some simple mistake i made by distraction somewhere, building too fast...

I wired the B100k middle lug to 9V (DC jack) and the outer lug to LM358 pin 3.

Now there is a beautiful wah effect when i turn the pot, so that's progress I guess, but it doesn't react to the picking. I have to turn the pot to have a modulation. Turning the pot makes the vactrols light up. The pot is very sensitive, the slightest move with my fingers gives some modulations.

Where should I go from there ?

Instructions page 3 : "The envelope detector is split off from the rest of the circuit and given its own input.
Then, a switching jack is used to restore the connection if no jack is inserted to the sidechain input."

Can you show me the part of the circuit where the detector is located ? I guess this isn't working at all in my build ?
I would like to know wich are the components involved so I can give them a closer look, and reflow them if needed.

[idy]

Not bore you because that difference, flipping the LED on and off, is not connected to the envelope detector...

It is a simple mechanical thing where a rotary changes the connection of those three LEDs (the visual and the "Vactrol" ones) between power and the opamp.

In one positions the cathode goes towards ground and the anode goes to the opamp that is supposed to put out DC, the second half of the 358. (The first half rectifies your signal, the second buffers it and drives LEDs.) So when voltage goes up (trigger!) the lights go on.

In the other position the anode goes towards 9v+, and the anode goes to the opamp! Because an opamp can "source or sink current." So when there's no  signal, the opamp output is low, and current goes to ground through there. When you play guitar, the voltage rises, and is not so far from 9 and the light goes out.

That works. What isn't happening is the first half of the opamp is not sending any volts when you play guitar, only when you "force" it with that pot. So maybe no guitar is getting to it...and the cut track to the "external trigger" was the first place I thought to look. The path is not complicated. Guitar to buffer (ic1a.) Buffer through c4, expression jack, sensitivity pot, r5, bandwidth switch and c5 or c6, into pin 2 of opamp ic2a.
Can you find that path on the schematic... and on the board?

one more thought; when you "force" the 358 with that pot to pin 3, and then set it so the LED is almost on, does your guitar trigger it then? Still no wah?

[eh la bas ma]

Thank you very much for your explanation.

There is a lot to unpack about this circuit. So many knobs and switches, several could cause no effect. Sensitivity up, Color up, Intensity up, Attack down, Decay higher than attack, bandwidth NOT  "off" ( not center.)

For all tests, I keep all settings on "standard auto-wah" as shown on the picture above (with the elephant, reply #3).

one more thought; when you "force" the 358 with that pot to pin 3, and then set it so the LED is almost on, does your guitar trigger it then? Still no wah?

No it doesn't, on both Sweep positions. No wah unless i move the extra pot to "force" it.

I am going to do the audio probe test you suggested earlier, and report.

[eh la bas ma]

 I recorded a guitar line in a looper. I connected the looper to the Spectron IN (nothing in the Spectron Out). I connected the audio probe's ground on the jack IN ground terminal. I connected the audio probe cable to an amp.

When i probe LM358 pin 3 all i hear is a loud pop with a quick flash in the vactrols. No signal not even lousy ( maybe there is something if I turn the amp volume up, but I am scared by the big loud pops).

On pin 1, I hear a continuous "shhhhhhh", like radio statics.

Nothing on pin 2.

I can hear the signal when i probe the tip of the cable coming from the looper, plugged in the IN input, i guess it means my audio probe is working.

I suppose next step, to find the culprit and solve this case, is to probe the audio path you described :

Guitar to buffer (ic1a.) Buffer through c4, expression jack, sensitivity pot, r5, bandwidth switch and c5 or c6, into pin 2 of opamp ic2a.

Edit : So, no signal on both tl72 pin 1 and 7 (supposed to be Out 1 and 2). No signal on C4 and both exp. jacks tip pads.

I will reflow IC1 and IC3 and try different tl72...

Edit 2 : There is something strange that I can't explain : I do have voltage readings on both tl72 :

IC3 :

pin 1 = 4.55 V
2 = 4.55 V
3 = 4.55V
4 = 0.2 mV
5 = 4.55 V
6 = 4.55 V
7 = 4.55 V
8 = 9.13 V

same on IC2 (sorry i mean IC1) exept on pin 3 :

pin 1 = 4.55 V
2 = 4.55 V
3 = 3.790 V
4 = 0.2 mV
5 = 4.55 V
6 = 4.55 V
7 = 4.55 V
8 = 9.13 V

I guess my problem is located in the first part of the circuit, RPD, C1, R1, R2, D2, D3. Should I have a signal if I probe them ?

[duck_arse]

In one positions the cathode goes towards ground and the anode goes to the opamp that is supposed to put out DC .....

In the other position the anode goes towards 9v+, and the anode kathode goes to the opamp! Because an opamp can "source or sink current." .....

your opamp voltages - if the output pin, pin 1, reads 4V55, then it has 4V55 at both of its input pins, pins 2 and 3. if pin 1 reads right, but the (usually) non-inverting pin reads low, it indicates meter loading of the biasing resistor. the output voltage is all that matters, if it's right, the inputs are right. carry on.


can I ask - if you set your meter on DC volts, and then short the red and black probes together, what does it read - exactly, please? whenever I see voltage readings on IC ground pins not showing as 0V, in your case 0.2 mV and 0.5 mV on the LM358's, I get worried.

[eh la bas ma]

can I ask - if you set your meter on DC volts, and then short the red and black probes together, what does it read - exactly, please? whenever I see voltage readings on IC ground pins not showing as 0V, in your case 0.2 mV and 0.5 mV on the LM358's, I get worried.

It reads 0.000 mV after one short second. First it oscillates briefly 0.001/0.002 mV.

on both tl72 pin 4 it reads precisely : 000.1 or 000.2 mV.
on lm358 pin 4, it oscillates a lot and finally reads 000.2 mV.

The meter (VC97A) oscillates alone when the ground clip is connected to the IN ground, and the red probe is free. I guess that's the auto-range feature.

[eh la bas ma]

I reflowed almost everything, now  i have a signal on both tl72, on C4, on Send and Return, but not on Sensivity and not on the Ext. Trigger pads...looks like it stops there.

Carrying on.

Edit : no continuity between C4 negative side and trigger pads...

Edit 2 : I replaced all wires on trigger pads, sucked out the solder on C4, I do have continuity now.

[idy]

You can be certain there is no problem with the tl072s. The pedal passes signal (so the buffer is working) and when you "force" it you hear a filter, so the other three opamps (the state variable filter) work also.

Sounds like you are narrowing it down...

[eh la bas ma]

I had continuity between C4 and a trigger pad for a brief moment, and then it is gone. I resoldered C4, still no connection. The positive side is connected to D3 though.

I will place a jumper between C4 negative side and the Switch trigger pad ( middle one) to make that connection.

Edit : I have a signal on LM358. It is kind of overdriven on pin 1, cleaner on pin 2 and very faint on pin 3, almost inaudible.

I guess i can put the audio probe away (I hope for a long time) and get back on the previous test.

[eh la bas ma]

Yeeeehaaaa ! wouhouuhouuuuuuu !

Vactrols are doing things on their own !

It is wah-ing quite well with the Sweep switch CW, it's not so effective on the other position, unless Bandwith is set downward. Is that to be expected ?

I wonder if I need the extra pot, if I set it on zero resistance, I guess it's as if it wasn't there...

[eh la bas ma]

Thank you so much for your help !

This effect sounds amazing, I am going to have so much fun...I can't stop smiling right now. I think I am going to dance...

For a second I thought all was lost, but i listened to Reverend Beat-Man & Izobel Garcia, followed Idy 's suggestions, and hope came back.

Never felt so much relief and joy just by looking at vactrols...

Many thanks  !