Author Topic: Aion Lab L5 Preamp- issues with the limit circuit  (Read 254 times)

ElCapitan

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Aion Lab L5 Preamp- issues with the limit circuit
« on: February 11, 2020, 08:31:38 PM »
Howdy folks, Iíve built the Aion L5 preamp. Having a little trouble. One thing to note- I generally mount pots in the enclosure, then put the PCB on and solder.   I snapped photos before doing so.   Good news is, all of the knobs and switches do actually perform their functions. However, Iím having some issues with the unit sounding horribly splatty/spotty with the limiter engaged. Any amount of gain reduction results in a nasty electric buzz that sorta pulsates as the gain reduction goes away.   

I have some metal can CA3080s, and I initially put them both in backwards. Oops. The pedal didnít work, and the limit light stayed on all the time regardless of where the limit knob was set. Both got extremely hot to the touch. Iím pretty sure I killed them. I put a new one in the IC11 spot, this time oriented correctly, and the limit light issue resolved. I am still having an issue in that IC10 gets VERY hot. I had an NTE902, which is a rebranded CA3080, all shiny and new, and put it there. Now Iím sure itís roached as it got really hot and darkened.

The voltages on QX1 & QX2  are way off.   I've gone through and looked at the resistor color codes around those, just hoping I'd find something obvious.   All are correct.  Solder joints look good.  I've double checked all the electrolytic cap and diode orientations and they're correct.   
 
Whatís driving me nuts is I checked every single resistor and capacitor with a multimeter before install. It is still possible something was missed.   Hoping someone can point me in the right direction to look.   All of the knobs seem to work, but the sound is problematic. Iíve used NE5532 in place of the 4558s in all positions. Everything else is as specíd.   At this point I'm stumped.   The pedal is a bit noisy, but the preamp section sounds good.   I'd just like to get the limit circuit to work.   Any suggestions you might have would be appreciated.   Voltages below:

According to the test chart:

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


Actual measurements:

IC10 CA3080

1   -50mv (goes down)
2   -14mv
3   0
4   -15V
5:   -14.5v
6:   2.07V
7:   15.26V
8:   cycles down to -300mv

IC11:

1   23mv
2   0
3   0
4   -15V
5   -14.40
6   fluctuates
7   15.26
8   0

Qx1:
1   12V
2   12.5V
3   15.19V

QX2:
1   10.9V
2   11.4V
3   28mv

« Last Edit: February 11, 2020, 09:10:24 PM by ElCapitan »