1

MP573 Microphone preamplifier / Re: MP573 problems with new build

« on: August 06, 2024, 03:44:52 PM »

Success!
I checked and everything is working.
Thanks JP 

On to the next Modules ;-)  

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MP573 Microphone preamplifier / Re: MP573 problems with new build

« on: August 05, 2024, 06:42:07 PM »

Thank you JP, i think i got it. 
I changed Q4 and Q5 with new ones and the voltage gets stable to 24.1V after a second after pluging in the transformer. 
Also the voltages are like in the troubleshooting guide. So i guess it is working now.
I will do a soundcheck tomorow and report back. 

Thank you very much!!

Cheers
Max

3

MP573 Microphone preamplifier / Re: MP573 problems with new build

« on: August 05, 2024, 11:56:33 AM »

Check the DC voltage on TP2, relative to 0 V with the output transformer disconnected.
Check the output transformer DC resistances as shown here. Measure with the transformer unplugged then plugged.

With Transformer unplugged TP2 to 0V is -9V
The resistances of the transformer are ok. measured while plugged in through the PCB.

But still the voltage drops if i plug in the transformer. Unplugged the input voltage is as expected. really weird
Cheers Max

4

MP573 Microphone preamplifier / Re: MP573 problems with new build

« on: August 02, 2024, 11:23:04 AM »

Hi JP, 
thx for your help.

V+ to V0 is 15V
TP2 to V0 is 1.5V

i checked thoroughly for shortcircuits and could not see any suspects. 

i remember that i washed the PCB with isopropyl alcohol before testing. although i blew it dry with compressed air, is it possible that the IPA caused a short and klilled a component? 

Thanx again for your help and the making of these beautiful kits!

Cheers Max

5

MP573 Microphone preamplifier / MP573 problems with new build

« on: August 01, 2024, 01:40:36 PM »

Hi There,
i have built the 73 Preamp and have some Problems: 
At general power check after plugging in the Transformer, the Voltage drops to from 24.3V to below 15V and U1 gets hot! (i unplugged the transformer immediatly)

I traced the DC Voltages: 
A-F is fine
G=0v4
H=0v4
I=0v4
J=0v0

Any help ist greatly appreciated

Cheers Max