Issue with General Tso and running it at 18V

[TucsonSean]

Hello Everyone,

I've got a question on the General Tso. What changes need to be made to run the Tso on 18V?

I know that the LED current limiting resistor (R100) and the current limiting resistors for the LDRs (R23 and R25) need to be increased to ensure they do not let the magic smoke out. Also, all of my caps used are at minimum 35V, so no issue there. Am I missing anything else?


Regards,
Sean

 

[jwin615]

Seems like messing with R23 and R25 would screw with your bias of those stages.
Also, will Q1/J113 need to be rebiased?
What are you looking to gain with 18V?

 

[TucsonSean]

I noticed a slight distortion sound when I was playing and I determined that it was from the level hitting the input to the pedal. I run active pickups and have looked at the output on an oscilloscope and saw peaks greater than 2V. I know that the input common mode range of the OPA1656 is power supply +V - 2.25V so running my pedal at 18V would extend this input range to greater than the 2V of peak signal that I currently get with a 9V supply.

I am also looking at changing the J113 to a J112 or even a 2N5458 as the input range is greater on those devices.

-Sean

 

[jwin615]

If you think it's the opamp clipping, maybe a R2R opamp will get you the headroom needed as it sounds like you're right on the edge

TLC2272 or the like

https://www.mouser.com/c/semiconductors/amplifier-ics/operational-amplifiers-op-amps/?m=Texas%20Instruments&mounting%20style=Through%20Hole&number%20of%20channels=2%20Channel&output%20type=Rail-to-Rail&package%20%2F%20case=PDIP-8

 

[TucsonSean]

Q1/J113 would not need re-biased as it is a follower. Any suitable JFET with a large enough VgsOff should work in that position.

As for the op amp, I could select another but I would have to order some other alternatives and at this point, I have enough op amps laying around as it is.

Anyone need any original Signetics NE5532s? I have over 110 with a date code before 2004. I'm about ready to get rid of alot of this stuff...

Anyway, back to the original question, anyone see anything else that needs to be changed to handle 18V supply?

Regards,
Sean