1

EQ573 Equaliser / Glitching high shelf rotary switch

« on: March 01, 2024, 09:45:28 PM »

Hi!

I just finished my EQ573, and everything works like a charm EXCEPT for the high shelf rotary switch which is unstable.
When turning the knob, it boosts the signal very aggressively and when touching it, it keeps switching back and forth between normal signal and boosted signal - so quite glitchy.

I have checked the joints and everything seems fine. It is also sitting totally flat on the PCB.
Could this be a sign of a faulty rotary switch or something else?

Cheers

2

MP573 Microphone preamplifier / MP573 general power check and deviating DC voltages

« on: February 04, 2024, 04:00:27 PM »

Hello

I'm making the general power check on my MP573 build.
Without the output transformer connected the reading is 24.27 Volts and with the transformer connected, it says 24.20 Volts.

Is the last reading acceptable, even if it's just 0.07 Volts lower than the first?

With the output transformer connected, I checked the DC voltages, and some of the values are deviating from the intended ones:

A: 2.5V
B: 4.0V
C: 22.3V
D: 13.3V
E: 2.0V
F: 12.7V
G: 0.9V
H: 2.6 (deviating)
I: 0.03V
J: 2.0 (deviating)
K: 23.3V (deviating)
L: 1.5V (deviating)

OUTPUT TRANSFORMER RESISTANCE MEASUREMENTS:
Yellow - Orange: 7.8 ohms
Red - Brown: 6.8 ohms
Blue - Green: 20.8 ohms
Violet - Black: 20.8 ohms

INPUT TRANSFORMER RESISTANCE MEASUREMENTS:
2-4: 24.8 ohms
3-5: 24.7 ohms
7-9: 133 ohms 
8-10: 133 ohms

Do you have any idea where to look to fix this problem?

3

MP573 Microphone preamplifier / Resistor replacement

« on: January 28, 2024, 04:00:21 PM »

Hello

I'm building the MP573. Unfortunately, I soldered a 4K7 resistor to R6 and cut the legs. I've changed R6 to the right value, but now I can't use the 4K7 resistor as R62 because of the vertical orientation, and I need a new one.

Are these kind of resistors metal film, and should I be aware of anything else other than value, size, tolerance and power rating when buying a replacement? 

/Simon

4

MP573 Microphone preamplifier / Resistor values

« on: January 03, 2024, 10:10:29 AM »

Hello

I’m just about to build the MP573!!

I’m measuring all of the resistor values. Their outputs are as stated except for the following:

- R60 (330K) measures 0.321 (DMM 2M ohm setting)
- R55 & R59 (1M) measure 0.955 (DMM 2M ohm setting)
- R61 & R65 (2M2) measure 1.85 and 2.00 (DMM 20M ohm setting)

Are those transistors defect/weak, or is it normal for high values to fluctuate this much? Or could it be my 27€ multimeter that is inaccurate?

cheers
Simon