Trouhbleshooting an Aion L5 Lab Series Preamp

[rmjlmartin]

Hi everyone, and thanks in advance for your help.

I'm troubleshooting an Aion L5 Preamp for a friend, and I'm relatively new at pedal building and troubleshooting, so I'm bumping up against the limits of my skills.

First off, here's a link to Aion's page, which has a link to the build document- https://aionelectronics.com/project/l5-preamp/

I'm trying to upload a picture, but my internet is slow and I don't seem to be able to at the moment. But I'll try to get one up later, if I can.

My friend built this and was unable to get it to work, so he sent it to me. So I got it completely assembled. I found and repaired a power supply problem on it, and he originally had it wired so the yellow wire was connected between the footswitch boards, which was supposed to make so the channel indicator leds turn off when the pedal is in bypass, but the power led stayed on all the time, so I wired it to the ground pad so the channel leds will stay on all the time. I also added the ground wire for the output jack on the right so I could test it out of the enclosure.

Using an audio probe, I get the signal all the way through the circuit to the input (pin 2) of IC10. On the output (pin 6), I get no sound with the probe, unless I hit the strings pretty hard, and then I get a very fuzzy, splatty sound like the power supply is too low.

I found another post on here (https://www.diystompboxes.com/smfforum/index.php?topic=121736.0) where Kevin from Aion posted a link to his voltage test chart, which is here- https://docs.google.com/spreadsheets/d/1GbYmJUXo2WXESJkMD1xxxkrgvPOt8DurWDE5TvscMMk/edit?usp=sharing

I've tested the voltages , and everything seems to be correct, except the 2 CA3080 chips (IC10 and IC11) and the 2 2N5088 transistors associated with IC10 (QX1 and QX2). According to the test chart, the voltages should be-

IC10- (CA3080E)
1- 0
2- 0
3- 0
4- -15.2
5- -14.5
6- 0.9
7- 14.73
8- 0

IC11- (CA3080E)
1- 0
2- 0
3- 0
4- -15.2
5- -14.62
6- 0.23
7- 14.73
8- 0

QX1- (2N5088)
1- 0.4
2- 0.9
3- 14.66

QX2- (2N5088)
1- -0.22
2- 0.4
3- 13.21

The voltages that I have, measured with the negative lead on my multimeter on the center test point at the top right next to the power supply section, are-

IC10-
1- -14.69
2- 0
3- 0
4- -14.91
5- -14.65
6- 13.11
7- 15.1
8- 14.41

IC11-
1- -14.85
2- 0
3- 0
4- -14.92
5- -14.85
6- -2.06
7- 15.11
8- -0.73

QX1-
1- 12.63
2- 13.16
3- 15.02

QX2-
1- 11.98
2- 12.64
3- 12.26

I have more 2N5088 transistors on hand, and I've tried swapping them out (no change), and I've tried swapping IC10 and IC11 (also no change).

But since I know the CA3080 isn't just a standard op amp, and doesn't test the same, I'm a little at a loss of where to go from here. Do I likely just have 2 bad CA3080 chips? Or is there something else I should be looking at?

Again, thanks for taking the time to read this and especially for offering good advice!

[Slowpoke101]

Welcome to the forum. Hopefully you will enjoy the fun.

Now this little preamp that you are playing with is quite complicated but should be repairable.
The first and most glaring problem is your voltages on IC10 and 11. A genuine CA3080 has no electrical connections in the chip itself connecting to pins 1 and 8. There should be not be any voltage on either pin. They should be at 0V.

Unfortunately you do have voltages on these pins which means that you do not have genuine CA3080s installed. I think that Smallbear have re-issue CA3080s in stock and they do work.

http://smallbear-electronics.mybigcommerce.com/ic-ca3080ae/

[rmjlmartin]

Thanks!

Yes, I wondered about that, since the datasheet shows them as dead pins, and the schematic shows no connections to them.

I was going to mention, too, that the odd voltages are only present with the chips installed. And I've checked for solder bridges, but I can't find any with my multimeter.

So maybe we need to try a pair of different chips. These are Intersil brand, but I'm not sure where my friend sourced them.

[mozz]

Just finished one of these 2 days ago. The bypass wiring is not very clear and doesn't work the way it says it will. But, mine worked just the lights weren't right. As for those voltages, i can measure mine and see what's there. My ca3080 were taken from old 80's equipment so i know they are genuine.

[rmjlmartin]

Thanks! I'm sorry to be a little slow replying here.

I have this posted on another forum as well, and the consensus (there, as well as here) seems to be that we have defective or fake CA3080 chips. My friend that built it has more (hopefully from a different supplier) and will be sending them to me to try. But he's out of state and very busy at work right now, so it may be a month or more until I get them.

I'll update this when I get the chips and try them.

[rmjlmartin]

Hi again. I'm finally back and updating this after getting the replacement chips from the friend who built the pedal.

I'm happy to report that the chips solved the problem. With the different chips, it seems to work as it should.

Thanks again to all of you who took the time to read this thread, especially the ones who offered to help a relative noob!