1

MP599 Microphone preamplifier / Re: MP599 not working SK99 ok

« on: August 05, 2021, 12:47:26 PM »

Hi again,

Vrms at IN was a writing mistake. It was 2,56V

BUT: I think, i´ve found the error! Also on on R24 was a sinus, and also on R25. So i thought, thats really the last point of the circuit, so it has to work. Then i´ve tried the preamp without the XT500 and it works! So it really was the XT500 not the preamp! Sorry, that didn´t come in my mind, because i´ve used the XT500 quite often for former preamps. Nevertheless: Thanks a lot for your help! I´ve learned a lot about checken errors in a circuit.

All the best
Werner

2

MP599 Microphone preamplifier / Re: MP599 not working SK99 ok

« on: August 02, 2021, 08:34:14 PM »

Hi again,

I´ve controlled and resoldered the pins of all relays and controlled the TPs again with a oszilloscope now, not with my cheap multimeter. Here are the actual values:

Signal: Sinus 1Khz -7dB
slightly under clipping, when i switch the gainswitch on high and the gain-poti P1 nearly to about 75% full

IN:
VPP: 7,35V
Vrms: 2,56mV

V+: 15.4V
V-:15.2V

TP1:
VPP: 96mV varies with the inputsignal
Vrms: 29mV varies with the inputsignal

JMP2:
VPP: 13.2V varies with the inputsignal
Vrms: 4.32mV varies with the inputsignal

R1: same values as IN high, varies with the inputsignal
R2: same values as IN high, varies with the inputsignal

TP2: 
VPP: 12,9V gainswitch on high, varies with the inputsignal
Vrms: 4,19V gainswitch on high, varies with the inputsignal
VPP: 2,05V gainswitch on mid, varies with the inputsignal
Vrms: 700mV gainswitch on mid, varies with the inputsignal
Nothing to sse on oszi at gainswich on low 

TP3: 
No VPP
No sinus
Vrms 458mV falling,gainswitch on high
Vrms 540mV falling,gainswitch on mid
Vrms 550mV falling,gainswitch on low


TP4: 
light sinus
VPP: 37mV, varies with the inputsignal
Vrms: 10mV, varies with the inputsignal

Out:
VPP: 450mV distorted
Vrms: 103mV distorted
DAW-Input about -33,5dB

Thanks for help,

best,
Werner

3

MP599 Microphone preamplifier / Re: MP599 not working SK99 ok

« on: July 26, 2021, 12:12:30 PM »

gain switch on high, strong sinus (more than last time) at 1kHz:

during the test something get connected or cleaned through: now i get the inputsignal of a mic or the sine into the preamp when i connect jmp2. the clipping-led is working right, i think. but it comes out very low volume and distorted.

0V to R1: 6.3mV not depending on the inputsignal
0V to R2: 1,8mV not depending on the inputsignal
R1 to R2: 4,4mV not depending on the inputsignal

0V to TP1: 1.8mV not depending on the inputsignal

0V to JMP2: 0mV or not steady (first about 3mV and than going down until around 0mV) (thats new, i can´t measure a input depending voltage here)

0V to TP2 and 4: 0mV

0V to TP3: there´s now a voltage depending on the gainswitch, but it rises (high gain) or get down (low gain) getting slowlier, between about 160mV and 550mV.

the solderjoints on the relays are looking good, but i will do them again in the next days for safety.

best,
werner

4

MP599 Microphone preamplifier / Re: MP599 not working SK99 ok

« on: July 23, 2021, 06:49:44 PM »

Hi,
Thanks for fast response.

I hear the relay clicking.
0,8mV on TP1 when i send a strong signal into the xlr-input
6mV on JMP2 Gain maximum
3,4mV on JMP2 Gain minimum

best,
Werner

5

MP599 Microphone preamplifier / MP599 not working SK99 ok

« on: July 22, 2021, 10:50:08 AM »

Hi,
I hope, thats the right adress for problems with my MP599 build.

I´ve no input and output on my MP599. Do you have an idea, what could be the problem after the following infos?

SK99: is working fine. I´ve tested it on my working MP512

voltage on testpoints without SK99 (only jmp 1 is integrated): 0 to V+: 15,5 or 15,6/ 0 to V-: -15,5
voltage on testpoints with SK99 (only jmp 1 is integrated): 0 to V+: 15,6/ 0 to V-: -15,0
voltage on testpoints with SK99 (jmp 2 is also integrated): 0 to V+: 15,6/ 0 to V-: -15,0/ 0 to TP2: 1,3mV/ 0 to TP1/3/4: 0,6mV

before i´ve checked all the parts again, if they are on the right position, especially the resistors
diodes look in the right directions (only the led i can´t control for sure, but it should be right)
C4 isn´t mounted as nice as the others but the connections should be ok
all solderpoints look good

any idea?

all the best
Werner