1

MP573 Microphone preamplifier / Re: MP573 trim pot Faulty?

« on: June 24, 2021, 12:17:51 AM »

Ok, the second measurement was with the jumper still on CN1. Is that why?
Would an incorrect Pot value would cause the issue I have?

2

MP573 Microphone preamplifier / Re: MP573 trim pot Faulty?

« on: June 22, 2021, 10:37:05 AM »

between the outer pins of the faceplate side potentiometer 
0 ohm at +10 
smoothly to 600 at 0
990 at-10
between the middle pin and 'centre' pin (farthest from led) 0 ohm at all positions

closest to led pin and middle pin on other pot 0 ohm to 600 to 989

3

MP573 Microphone preamplifier / Re: MP573 trim pot Faulty?

« on: June 15, 2021, 09:38:54 AM »

I'll check the Caps tomorrow

4

MP573 Microphone preamplifier / Re: MP573 trim pot Faulty?

« on: June 15, 2021, 09:36:08 AM »

The trim pot distorts at all points except the extremes with the signal degrading completely at the 'O' point. 
It's the same a t all gain switch positions
There is no gain increase between -10 and +10 on the trim knob.
The gain switch works in all positions

5

MP573 Microphone preamplifier / Re: MP573 trim pot Faulty?

« on: June 14, 2021, 10:23:49 AM »

With the gain at 10, the trim at 0 and 1200ohm

a-2.3
b-3.8
c-22.1
d-12.5
e-1.8
f-11.9
g-0.89
h-4.33
i-0.32
j-3.79
k-22.1
l-3.29

6

MP573 Microphone preamplifier / Re: MP573 trim pot Faulty?

« on: June 04, 2021, 01:30:43 AM »

All the solder joints are sweet. No dry joints or bridges.
'0' position resistance measurements

Transformer side closest to LED - 2.74k 
Transformer side farthest fro led - 2.46k

Faceplate side closest to led - 565
Faceplate side farthest from led 001

7

MP573 Microphone preamplifier / MP573 trim pot Faulty?

« on: June 01, 2021, 06:25:19 AM »

Hello,

I've just finished building and testing my mp573. Everything works fine except the trim pot.
At the extremes (-10/10+) the signal passes for all inputs at all switch positions, 
but when the trim pot is set at '0' the signal is clipped and extremely distorted.
The gain difference at -10 vs 10+ is not any different either. Same metering on my interface at -10 as 10+.
I'm assuming this is a faulty pot.