Mini Mu envelope filter troubleshooting

[suryabeep]

Hi everyone,
I built an envelope filter according to this schematic (https://circuitsalad.com/2014/05/06/a-simple-ldr-envelope-filter-that-is-just-delightful-to-use/) but it does not work properly.

symptoms: large drop in volume, no treble whatsoever. sometimes when I hit the strings hard I can hear the bass frequencies increasing in volume.

Voltages:
Lm358
1- 5.98
2-5.98
3-5.98
4- 0
5- 0
6- 0
7- 1.56
8-9.39

2068D
1-6.00
2-6.00
3-5.80
4-0
5-6.00
6-6.07
7-5.97
8-9.39

2n3904
E-5.98
B-6.21
C-9.39

I am using green 5mm leds from tayda in homebrew LDRs. I noticed that the indicator LED also does not light up no matter which orientation I have it in. It is odd. Could someone please assist me? Thank you

[idy]

Did you use their pcb art, is yours surface mount like theirs?
Can you upload a photo?

[PRR]

> Lm358
> 5- 0
> 6- 0
> 7- 1.56

Short to ground near C5, R5, or both.

[suryabeep]

I'm using a board I made myself, a picture of the bare board is attached below.
Paul - There doesn't seem to be any short to ground, I checked continuity with a multimeter. The voltages on pins 5 and 6 fluctuate a tiny bit from -0.002V to 0.003V with no guitar plugged in.

[Kipper4]

As Paul says some how pins 5 and 6 look grounded.
If the layout maintains the pinout on the schematic? You'd expect 5 and 6 to be over your 5.98V.
The lm358 is acting as a diode charge pump rectifier and led driver.

Did the op amp come with a kit?

Do have a fiddle with the sensitivity pot too.

I'd think there should be no volume drop, in fact the opposite
Have you audio probed the bjt input buffer and 2068D filter.
Don't probe the lm358. It's not for audio.

Obviously there's insufficient voltage to light the leds and wobble the ldr resistance which should wah the signal going through the filter.

Superb filter btw.

[suryabeep]

I got the 358 from tayda. I swapped it out for another one just now, no change
The sensitivity pot seems to work - at one end of the turn I get unity gain from the 358 (at pin 1), at the other end I get a much louder signal.
The input BJT buffer also seems to work fine
At the intersection of R7 and pin 3 of the 358, I get normal signal. At the other end of R7, I get just a loud hum.
Probe results on the 2068:
1  - incredibly faint original signal and some hiss
2 - Loud hiss
3 - soft hiss
5 - even more incredibly faint original signal and some soft hiss
6 - loud hiss
7 - very faint original signal and some loudish hiss

Obviously there's insufficient voltage to light the leds and wobble the ldr resistance which should wah the signal going through the filter.

yeah, that's what I thought too. I don't know why the low voltage though 

[Slowpoke101]

Is there any chance that you could upload a screenshot of your schematic that you generated the board artwork from? I am beginning to suspect that you may have a layout error.

[suryabeep]

Here it is:
The pads marked R1A, R2B etc are where I solder in the ldr leads; similarly the pads marked L1A,L2A etc are for the LEDs. I tested that the LEDs are inserted the right way around just by connecting 9V--6k8--LED--gnd and checking which orientation results in lighting up.

[Prehistoricman]

It's a long shot but do you have any power decoupling for the opamp? I've had op-amps latch up before such that the inputs are pulled low (I was completely lost at the time) without decoupling.

[suryabeep]

It's a long shot but do you have any power decoupling for the opamp?

I think only the 2068D has a decoupling cap on its supply, but none for the LM358.
That said, I'm only 20% sure I remember what the word 'decoupling' means so it is quite possible that I have no clue what you're referring to 

[Kipper4]

Did you try going over the joints again with the iron as some of your solder looks a bit dodgy.

Especially that bank of 6 resistors to the left of the centre 2 caps. Some joints look like they didnt wet up.

How comes you boxed it before checking the circuit works?

[Prehistoricman]

It's a long shot but do you have any power decoupling for the opamp?

I think only the 2068D has a decoupling cap on its supply, but none for the LM358.
That said, I'm only 20% sure I remember what the word 'decoupling' means so it is quite possible that I have no clue what you're referring to 

You're right about the decoupling cap. Try putting one on the LM358 too.

[suryabeep]

Kipper - I always box them up before testing the circuit, I don't have a testing rig set up and I like that if a circuit works on the first go (rare, I know) I can use the finished pedal immediately.
I just finished resoldering all the joints on the board, no improvement. In fact, now I can't hear anything at all 

Prehistoricman - I'll include one in the next board I make, but the person who runs circuitsalad (he's on this forum somewhere, I just don't remember his username) built one just fine without a decoupling cap. I don't think that's the issue, but it is possible

[Kipper4]

Where are you losing signal now mate. Probe....

[suryabeep]

Whoops, I was dumb and left the volume too low.
After solder reflowing, no change in symptoms- still large volume drop and no envelope

[Kipper4]

Time for some continuity checks with the meter to make sure the componants around the led driver are connected as supposed to be.
Can you verify?

[suryabeep]

Just finished the continuity checks for almost the entire circuit (skipped the chunks that I know to be working). Everything seems alright. I am now even more confused as to what the problem is.

[Kipper4]

So if all componants are showing continuity to the envelope detector Ic1 A (Ray Rings schematic) and all componants to the led driver Ic1 B then it should work.
Did you check the attack pot?
I guess your still getting 6V on the detector and 0V on the led driver right.

If you hook up a signal does the voltage of the envelope change when striking a string?
Check with the meter between D3 and R4 (R Ring drawing)

We gotta sort out those led driver volts.

[suryabeep]

Yep, voltages on pins 5,6,7 of the LM358 fluctuate with hitting the strings.
Pin 5 and 6 fluctuate from about 2 mV to 180 mV
Pin 7 fluctuates from 1.5V to 1.88V

[Kipper4]

Did you check C4? orientation, working,leaking?
what voltage are you getting between C4 and D2? Assuming you still have 6V at pin1.