1

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

« on: May 31, 2024, 08:44:17 AM »

If I was you, I would try replace the suspected relay. At least thats what fixed my problem

2

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

« on: March 06, 2024, 11:24:56 AM »

Okay, I will try fix it. 

Anyway, I see this thread as solved. Once again: thanks for the help on this one - means a lot!!

3

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

« on: March 05, 2024, 05:46:13 PM »

I've checked, and they are all in the correct spots. But I guess the joints in these places could be better - could this influence the reactivity of the LED?

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

« on: March 03, 2024, 10:31:53 AM »

YES! I replaced RLY1, and the unit is now working as expected! Sounds amazing!!

Thank you so much for your help JPK - what a great service!!

If your having more time for this one:

The LED is turning red at the same time as the signal clips in my DAW. But shouldn't it do it -3 dB before clipping?

5

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

6

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

« on: February 21, 2024, 05:11:36 PM »

Okay, thank you. I will replace the relay when received and return with an update.

7

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

« on: February 21, 2024, 08:15:40 AM »

AZ850-24

Does this one match then?:

https://www.conradelektronik.dk/da/p/zettler-electronics-az850-24-printrelae-24-v-dc-1-a-2-x-omskifter-1-stk-507436.html?utm_source=google&utm_medium=surfaces&utm_campaign=shopping-feed&utm_content=free-google-shopping-clicks&utm_term=507436&gad_source=1&gclid=CjwKCAiAuNGuBhAkEiwAGId4aqwkE-ukmo-26AyVCPdMXlnMnhqiPyRikROEoGhgsfsoh5REAGXvOxoCpFkQAvD_BwE

I've noticed that on the relays from the MP573-kit it says "2A/30VDC", while it says "1 A at 30 VDC resistive" in the datasheet for the relay linked above.

Is this a problem? 

8

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

« on: February 20, 2024, 12:46:18 AM »

It could be one of the relays.

Actually, I don't know why I forgot to mention this, but as you can see in the attached picture, I accidentally touched the corner of RLY1 with the iron in the beginning of the build: https://drive.google.com/file/d/1Hkm66048bO6PcwcqzHrrULHdgh4NNYaw/view?usp=drive_link

Do you think this could cause the problem?

Is it the same in 300, 1200, line?

Yes. It's the same for 300, 1200 and line; they all drops to zero on the measurement points (incl. pin 2 & 5 on the primary). Except for line where the measurement on output transformer yellow wire keeps showing 0.020VAC after the sound has disappeared.

Is it the same from the DI input?

DI works fine - the sound doesn't disappear!

9

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

« on: February 19, 2024, 12:54:15 PM »

Yes. With an input signal of 0.1VAC, I get the following between pins 2 & 5:

Before sound disappears:
0.14VAC

After sound disappears:
0.00VAC

It also drops to zero.

10

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

« on: February 14, 2024, 07:18:20 PM »

Okay, I've now sent a sine signal with a generator plugin into the preamp. I only managed to send an input signal of 0.1VAC measured between pins 2&3 of the input XLR.

Measurements before the disappearance of sound:

• Input transformer pin 7: 0.59VAC
• TP1: 3.31VAC
• Output transformer yellow wire: 6.24VAC

Measurements after the disappearance of sound:

• Input transformer pin 7: 0.00VAC
• TP1: 0.00VAC
• Output transformer yellow wire: 0.00VAC

They all went to zero. The voltage starts to drop very slowly, and suddenly it drops quite fast.

11

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

« on: February 13, 2024, 07:10:18 PM »

Im quite new to this DIY world (but I'm keeping a steady learning curve!). How do I send a sine signal on input? Do I need a signal generator or function generator and an oscilloscope for this test? Maybe this is a newbie question, if so - sorry!

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

« on: February 12, 2024, 01:28:52 PM »

Yes:

A: 2v5
B: 4v1
C: 22v3
D: 13v3
E: 2v0
F: 12v7
G: 0v9
H: 4v1
I: 0v3
J: 3v5
K: 22v5
L: 3v0

13

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

« on: February 11, 2024, 12:25:00 PM »

U1, U2 and PTC1 doesn't get hot at all. Tried testing for some time now. 

I noticed that the time it takes for the input signal to disappear depends on how long I wait, until I turn it back on; the longer I wait, the longer time there is input signal. 3 minutes is the most after having it turned off the whole night.
- so its actually not around 45 seconds every time, but it fluctuates.

The signal disappears by first having small fade outs and then suddenly it disappears completely.

14

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

« on: February 08, 2024, 07:56:21 PM »

I've now made a visual inspection of Q4, Q5 and R41...R45, but I cannot see anything suspicious. I also did a continuity test with my DMM on the mentioned joints, but it seems like there is a continuous flow.

I've set the bias to 3.0V without any problems and connected a dynamic mic. Following things happen:

• After powering on there is a good clean signal, but after approx. 45 seconds, the signal disappears. Could this be a sign of a bad joint(s)? Seems like it happens when heat is generated. I've tried powering on the lunchbox, waited some time, then powering on again, and the signal is back for about 45 seconds, until it disappears again.
• LED is not turning red, when the signal is close to clipping, only green.

I tested the DI, and there doesn't seem to be any problem there. Signal is stable besides that setting to "LINE" (DI connected) does not output any sound (is it normal?)

Additional info:

• Gain switch is working
• "Trim" pot is working
• Impedance switch is working (beside the aforementioned LINE setting when connected to DI)
• Polarity switch is working in all three positions
• 48V is working with condenser mic (but the same problem with disappearing input signal happens)

15

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?

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MP573 Microphone preamplifier / Re: Resistor replacement

« on: January 29, 2024, 04:20:47 PM »

Thanks!

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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

18

MP573 Microphone preamplifier / Re: Resistor values

« on: January 03, 2024, 06:22:25 PM »

Thanks for the answer!
I found the problem; I was measuring while touching the legs with my fingers.

Looking forward to build this amazing kit!

19

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