VP312DI signal drops / distorts

[JLegnon]

My VP312DI is acting strange . During an hour long drum session , half way through I could see the WAV file for the kick mic had a small 20 second section where the signal dropped , got lower , then goes back to normal for the rest of the session . I've attached an audio sample of this track where the dropped distorted signal suddenly goes back to normal so you can hear it .

I though it was a freak thing because it worked fine after that for the rest of the session and I've been using it for about a week with no problems . But yesterday I was going to track Bass guitar through the DI and it starts doing it again , so I had to use a different mic pre . Weird thing is , after I tracked the bass with a different mic pre I go back to the VP312DI and it works fine with no problems .

Maybe from the audio clip someone can have an idea . I did not edit the audio clip , it seems to fix itself right on beat . Youtube compression seems to be making the audio sound a little strange but I think you can get an idea .

http://www.youtube.com/watch?v=PdRrqilu8cY&feature=channel&list=UL

 

[pucho812]

I would suspect a faulty solder joint. Most of the time Random faults can be attributed to bad joint. It won't hurt you to re solder your joints. If you do close inspection with a magnifying glass you will fine one or several that are either cracked or not well flowed. Now signal dropping and distorting would be a result of loosing the required voltage to your opamp.  So what you want to look for is faulty joints in the power rails

 

[JLegnon]

Thanks for the help . I'll check it out .

 

[JLegnon]

I would suspect a faulty solder joint. Most of the time Random faults can be attributed to bad joint. It won't hurt you to re solder your joints. If you do close inspection with a magnifying glass you will fine one or several that are either cracked or not well flowed. Now signal dropping and distorting would be a result of loosing the required voltage to your opamp.  So what you want to look for is faulty joints in the power rails

Where exactly are the power rails on a VP312DI mic pre ?

 

[desol]

Try to find the pinout for the edge connector that the card plugs into...then just follow the traces on the back of the card that correspond to the +/- power rails. You can usually see a suspect solder joint if you look close enough...but not always. There shouldn't be that many solder joints to inspect/redo. Probably good to redo the ones for the opamp itself.. also the opamp itself could be having issues. I've had a few old ones go bad...but they usually begin exhibiting signs first like strange whistling, etc.

 

[JLegnon]

Try to find the pinout for the edge connector that the card plugs into...then just follow the traces on the back of the card that correspond to the +/- power rails. You can usually see a suspect solder joint if you look close enough...but not always. There shouldn't be that many solder joints to inspect/redo. Probably good to redo the ones for the opamp itself.. also the opamp itself could be having issues. I've had a few old ones go bad...but they usually begin exhibiting signs first like strange whistling, etc.

Ok , so I need to get the 500 series edge pinout to find the +/- power rails .

I have tried swapping out the opamp with a known working one and it did not fix the problem . I am using Red Dots DOA's .

I did reflow solder to the opamp socket pins and it didn't fix the problem .

 

[JLegnon]

Pin Description
1. CHASSIS
2. Plus 4 Output “+”
3. option
4. Plus 4 Output “-”
5. Audio Ground
6. 525 Stereo Link
7. option
8. Plus 4 “-” Input
9. option
10. Plus 4 “+” Input
11. Gain Adj 550b, 560b
12. +16 volts DC
13. Power Ground
14. -16 volts DC
15. Phantom +48 VDC

So 14 and 12 are +/- 16 volts DC .

What about 10 and 8 ? They are Plus 4 +/- input . Should I check these out too ?

 

[mulletchuck]

don't forget the 24V rails, which power the DI Hi-Z Plugin boards. 

 

[pucho812]

pins 10 and 8 are audio connections. 10 being the hot side of your balanced connection(pin 2 on an xlr), 8 being the cold side of your audio connection(pin 3 on an xlr). I doubt your drop in volume is due to them but hey doesn't hurt to check them.

don't forget the 24V rails, which power the DI Hi-Z Plugin boards.

there are 2 version one using the +/-24VDC in the 51X format and another version that is regular api style. I believe he is working with the regular api version.

 

[mulletchuck]

if he's using the FET/IC Hi-Z Plugin board, then he's using the 24V version.  only the Pikatron Hi-Z plugin doesn't require 24V

 

[JLegnon]

Yeah I'm using the standard api lunch box .

 

[JLegnon]

I think I fixed it !! Its been working perfectly .

I followed the power rails at first , but then I said screw it theres not that many places to reflow solder , so I pretty much hit them all but the DI section .

Thanks for the help guys  8)

 

[pucho812]

I think I fixed it !! Its been working perfectly .

I followed the power rails at first , but then I said screw it theres not that many places to reflow solder , so I pretty much hit them all but the DI section .

Thanks for the help guys  8)

sometimes that the fastest.

 

[[silent:arts]]

if he's using the FET/IC Hi-Z Plugin board, then he's using the 24V version.  only the Pikatron Hi-Z plugin doesn't require 24V

wrong. all Hi-Z plugins are fine with 16V. running them on 24V gives just a little more headroom.

 

[mulletchuck]

if he's using the FET/IC Hi-Z Plugin board, then he's using the 24V version.  only the Pikatron Hi-Z plugin doesn't require 24V

wrong. all Hi-Z plugins are fine with 16V. running them on 24V gives just a little more headroom.

!!!!  that clearly ain't in the documentation(schematic)

 

[[silent:arts]]

sorry, must have missed this little point 

 

[mulletchuck]

Volker, could you explain why there is such a large signal drop when using the FET DI board combined with Pre/Post2622 modes.  the Pikatron and IC1 DI board have very different amounts of signal drop depending on the pre/post2622 setting.  I don't know much about the HI-Z circuit, I just know that depending on which DI board I have plugged in (I have a stereo pair of these VP312DIs, btw) I sometimes need 0db Preamp Gain, gain knobs at 12 o'clock, or gain knobs btwn 3-5 o'clock. 

 

[JLegnon]

Volker, could you explain why there is such a large signal drop when using the FET DI board combined with Pre/Post2622 modes.  the Pikatron and IC1 DI board have very different amounts of signal drop depending on the pre/post2622 setting.  I don't know much about the HI-Z circuit, I just know that depending on which DI board I have plugged in (I have a stereo pair of these VP312DIs, btw) I sometimes need 0db Preamp Gain, gain knobs at 12 o'clock, or gain knobs btwn 3-5 o'clock.

I had the FET DI board also and theres a huge signal drop ! Made it more difficult to compare with and without it .

 

[[silent:arts]]

We have different signal drops since we have different circuits?
With different "gain"?