SOLVED Inadvertent Octave Up in Promethium

[bcm2216]

I've built a Promethium in the past and it worked like a gem first try but I built another for a buddy and now I've got this bizarre octave up that sounds like the sort of full wave rectification you would get from a Green Ringer or a TB Octavia (I understand that they achieve their octaves in slightly different ways). Any suggestions where to start troubleshooting?

 

[Robert]

I'd start by measuring your VREF voltage throughout the circuit. (R2, R17, R24, R21, R22, R23, R31)


If that doesn't help, post pictures.

 

[bcm2216]

Vref of 4.288v
R2 3.917v
R17 3.704v
R21 4.251v
R22 4.251v
R23 .051v
R24 4.262v
R31 3.92v


R23 being the obvious odd man out, it's on the lower frequency voice of the two active eqs on the "high" control

 

[bcm2216]

Each of the vref bias resistors read 4.288v on the voltage divider side of the power supply, readings are taken after each point's respective biasing resistor****

 

[neiltheseal]

When you find out what it is please let me know. That sounds cool.

 

[Robert]

That's definitely something to investigate. Look for solder bridges or bad solder joints in that area, R23, C15, IC3 pins 5,6,7.

If you socketed the opamps pull IC3 out and measure the voltage on pin 5 of the socket with no IC installed.

 

[bcm2216]

I literally just finished replacing the IC with a socket so I should have a number for you in just a moment!

 

[bcm2216]

Alright yeah it was definitely IC3 being bunk, new chip works great. I haven't ordered op-amps in about 2 years (I've been surviving off of a personal hoard) so I guess one of them was gonna fail if I kept them jumbled around in a box of parts long enough. Performing as intended now. Anyone have any luck with changing taper on the eq gain pots?