Aion Helios RAT No Sound

[Fazzer]

Hi,

I'm new to this website but it looks extremely good.

Anyway I've built an aion helios RAT pedal but I'm getting no sound out

the schematic  is this one with no modifications (all the controls are included ,sweep filter, diode switch ect)
https://aionelectronics.com/project/helios-proco-rat-distortion-pcb/

I'm using an v9 battery 8.84v out of the battery and also 8.84v into the board

socketed LM308N from smallbear
1) 8.04v
2) 4.4v
3) 2.16v
4) 0
5) 0
6) 4.4v
7) 8.8v
8.) 4.47v

these look ok I think.
I've got audio going into pin 3 but no audio coming out of pin 6 or any of the other pins

2n5457
1) 8.8v
2) 1.47v
3) 0

all clipping diodes have 0v on both sides D5 1n4002 has 8.8v on the positive side
C7 has 4.4v on the positive side.

any ideas?

my worry is the opamp is a faulty one.
I have a TL072CP hanging around could I just put this in to check if this is the case?

Many thanks

[Kipper4]

The op amp is a single so you can't replace it with a dual tl072. Differant pinout.
Pin 3 should be around the same voltage as 2. Check everything in the feedback loop
C4, 100 k dist and the filters too so c3 r3 r4 c5 c6. Sweep pot.
Is the chip orientation right?

Pins 2, 3, 6 should all be around 4.5v

[aion]

Pin 3 on the op amp looks low. It should be right around 4V. Fortunately there isn't much that comes before pin 3, so I would check C1, C2, R1, R2 and RPD to make sure they are the correct values (especially R1) and reflow the solder on those as well just to be sure. Also triple-check the wiring.

Since the voltages look fine except for the non-inverting input, I think the 308 is fine. It uses a different pinout than a TL072 so unfortunately you can't swap it out easily (except for another similar single like the OP07) but that wouldn't be the first place I would check.

Feel free to post pics as well - sometimes that can be a huge help in debugging.

[Fazzer]

Yep pin 3 does look low.

Cheers everyone I'm going to check the suggestions and get back to you with hopefully a solved board

[duck_arse]

lift one end of R5, audio probe pin 6 again. anything? inject signal into the 100k filter pot, and monitor at the R8. is that string to the fet good?

pin3 is fine, it's being loaded by your dmm. you could poke in an LM741/TL071 just for test.

[PRR]

> Pin 3 on the op amp looks low. It should be right around 4V.

Pin 3 is biased through a 1Meg resistor.

If his meter is 1Meg, it would read like he says.

The fact that pins 6 and 2 both read 4.4V is fairly good assurance that pin 3 is correct when he is not poking it.

Good DC and no sound usually mean wiring-error into or out of the chip.

[Kipper4]

I should have known better about the low pin3. I'll get the hang of it one day.
No audio on pin6 though. Hmmmm

[Fazzer]

> Pin 3 on the op amp looks low. It should be right around 4V.

Pin 3 is biased through a 1Meg resistor.

If his meter is 1Meg, it would read like he says.

The fact that pins 6 and 2 both read 4.4V is fairly good assurance that pin 3 is correct when he is not poking it.

Good DC and no sound usually mean wiring-error into or out of the chip.

very interesting learned something new.

I've ran out of time over the weekend I'll try again on Sunday

[Fazzer]

lift one end of R5, audio probe pin 6 again. anything? inject signal into the 100k filter pot, and monitor at the R8. is that string to the fet good?

pin3 is fine, it's being loaded by your dmm. you could poke in an LM741/TL071 just for test.

this looks like a sensible approach. I'll give it a whirl

[Fazzer]

Update:

pedal is working and sounds awesome I have a pair of socketed D9Es in the diode clipping section so I might try a few different types to see which work best.
The pedal has zero background hum as well really thrilled with it.

I just resoldered a few of the resistors and hey presto it worked.
I'll post the voltages and ohms of all the components using my cheap multimeter when I get time over the weekend.

Cheers everyone

[aion]

Fantastic, glad you got it working! Enjoy!