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MP566-II Tube microphone preamplifier with HPF / Re: Possible ICs fried MP566-II

« on: June 07, 2026, 01:18:00 AM »

Sorry yes R53. I replaced it and it works! I just recorded bass tracks through it and it sounded great. Thanks for the help. 

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MP566-II Tube microphone preamplifier with HPF / Re: Possible ICs fried MP566-II

« on: May 21, 2026, 10:10:19 PM »

It looks like R3 is scorched. I measured it and it’s open loop. I Noticed the left lead looks burned. 

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MP566-II Tube microphone preamplifier with HPF / Re: Possible ICs fried MP566-II

« on: May 17, 2026, 08:48:14 PM »

I found 2 bridges which I fixed. 1 was between 2 joints that connect the main PCB to the tube support PCB. The other was on the HPF pot connection. I hooked up a signal generator at 1k 0.020v and used my oscilloscope to trace the signal after I fixed the bridges. I was getting no signal from TP3,4,5,6. TP2 had a slight signal. I replaced the U2 and U3 op amps and no signal. Here are the DC test values. So something is messed up somewhere. 
VO to V+ 16volts
VO to V- 0.817 volts
V- to B+ 13.8v
H+ to H- 18.96v
V0 to TP2,3 14.58v
VO to TP1 -0.003 v
VO to TP4 0.04v
VO to TP5 2.25v
VO to TP6 1.38v

😞

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MP566-II Tube microphone preamplifier with HPF / Possible ICs fried MP566-II

« on: May 07, 2026, 09:10:04 PM »

I recently built the MP566-II Tube pre and when I first powered it on I could not get any sound out of it. So I removed it and discovered I had a solder bridge on the back of the header pins to the tube PCB. I fixed the bridge and ran it again. It puts out sound but very quiet, not enough to register signal but I can hear it faintly. It also distorts heavily when I turn up the gain knob or output knob. I know shorting leads can fry the ICs. Does this sound like what I did? If so I will order new ones. Thank you.