Fixed Resistor Clear Up

Thread Starter

AdrianKludge

Joined Jan 16, 2019
5
Hi, I'm wanting to replace the potentiometer R15 with a resistor so that the out signal is always maxed. After a little screwing around I'd rather go in knowing what I am doing. Looking up this subject online gave a variety of answers. Any help is appreciated. SLMS-Plus Page 1_schem.jpg
 

AnalogKid

Joined Aug 1, 2013
9,244
No resistor needed. Of course, you could just turn the output all the way up and then remove the knob. But if you want to remove the pot completely, replace it with a jumper wire from pin 2 to pin 3. That's it. In terms of this schematic, there is no need to have a fixed resistance from IC2-B pin 7 to GND. If you want the AR output to look the same to external circuits or equipment, leave the jumper in place and add a 100K resistor from pin 3 to pin 1.

These instructions assume that pot R15 is mounted to a pc board. I had to make that assumption because there is so little information in your question.

Photos?

ak
 

ericgibbs

Joined Jan 29, 2010
12,883
hi,
As there are a number of resistors connected to pin #1 of the R15 pot, I would replace the R15 , 100k pot with a fixed value 100k.
This should keep the DC levels the same to the other points along the pin #1 connections.
Use pin #1 as the output.
E
 

AnalogKid

Joined Aug 1, 2013
9,244
Given the high values of all of those resistors, their parallel combination is not nearly low enough to affect the output voltage of IC2-B and the DC levels of the circuit.

IMnsHO.

ak
 

AnalogKid

Joined Aug 1, 2013
9,244
Found the board layout. R15 is off board, and the only connection on the board for it is pin 1. (Note - the pot is wired backwards, or at least pinned backwards.) The wiper and GND wires to the pot are not indicated anywhere, although there is a group of 5 undedicated GND connections on the board.

http://musicfromouterspace.com/anal...TH_PLUS/pdf/slmspluspcwithlabels_assembly.pdf

SO - if the goal is to eliminate the pot completely, then cut and abandon the GND (pot pin 3) wire, remove the pot pin 1 and pin 2 wires from the pot and connect them together. Whatever the pot wiper connection is connected to now will be connected directly to the opamp output for maximum level all the time.

NOTE: The schematic copyright is dated *after* the pc board copyright. This can be an indication of an update, so the schematic might not be an exact match to the board as shown.

ak
 
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