Houston, we have a problem! discharges/drop-out audio

[serpaven]

Hi to everybody,

my J99, later around 4 months of honorable service, it begins to do the whims.

on modulated signal it produces some discharges, a kind of distorsions on modulated vocal signal

it is very strange, just turned on the problem there is not but he introduces later around one minute of work.

I have tried with an external phantom PSU but it doesn't depend on the phantom.

mics is neumann TLM67, audiocard is MOTU HD192.

the defect there is not in the other modul (C84) I have tried to change mic and entry on another channel of the audio card but the problem it remains. on pure tone signal and continues the problem he doesn't introduce. the problem introduces him on varying signals as if the twin balance servo circuit didn't work well.

I have check the bias adj and I have gotten these values:

SC99 n# 1 (on pin 1 e 4 of U2) min gain 3,5 mV - max gain 2,7 mV

SC99 n# 2 (on pin 4 e 6 of the same op-amp) min gain 2,7 mV max gain 3,8 mV

make to know me what you think of it?

[serpaven]

You can listen in this file:
(don't listen on shared player but download the file)

http://www.4shared.com/audio/mzGynLag/J ... audio.html


other tests, the signal of the microphone has been undoubled (external phantom powered) and envoy both to the J99 and to the C84, same gain level (step 3 gain, fine gain turn on max).

wav @ 48KHz 24bit:
http://www.4shared.com/audio/ZVFPMYsC/t ... ooohh.html
http://www.4shared.com/audio/OfRw-eEc/t ... ooohh.html

mp3 @ 320 KBps 48 KHz 24 bit
http://www.4shared.com/audio/fBE4kJwL/t ... ooohh.html
http://www.4shared.com/audio/6UcKtCH3/t ... ooohh.html

here the defect of the J99 is very evident, I think that one of the two op-amps can be defective.

further test:

the clean signal recorded with C84 it has been sent (attenuated) to the J99 input, so that to get in exit an level of -3,3 dB. (some J99 setting gain on step3 fine gain turn max) also in this test the J99 returns the problem.

http://www.4shared.com/audio/s-_tzUkz/t ... ain_3.html
http://www.4shared.com/audio/PluvXblp/t ... ain_3.html

[tpryan]

SC99 n# 1 (on pin 1 e 4 of U2) min gain 3,5 mV - max gain 2,7 mV

SC99 n# 2 (on pin 4 e 6 of the same op-amp) min gain 2,7 mV max gain 3,8 mV

I don't know what this means. With no signal applied and gain at maximum, measure the DC voltages at pins 1, 2, 3, 5 and 6 of each SC99 and let us know what you find.

[serpaven]

U1/U8 n# 1 (on pin 1 e 4 of U2) min gain 3,5 mV - max gain 2,7 mV

U2/U9 n# 2 (on pin 4 e 6 of the same U2/U9) min gain 2,7 mV max gain 3,8 mV

I don't know what this means.

is your's Input Bias Current Adjustment instruction!

37. Install an op-amp at U1/U8 but not at U2/U9.
38. Short CONN1 pin 2 and pin 3.
39. Move the jumpers at J6 and J7 to the "ADJ" position, as indicated on the silk screen.
This connects the center pin of the header to ground and disconnects the servos while
you're making adjustments.
40. Connect a DMM between U2, pin 1, and U2, pin 4. Set it to measure DC voltages of 2V
or less.
41. Apply power to the J99.
42. Turn SW1 fully counter-clockwise (for minimum gain), and record the voltage at U2, pin 1.
43. Turn SW1 fully clockwise (for maximum gain) and measure the voltageagain. Adjust
R43 to try to make the voltage the same as the first measurement.
44. Repeat steps 42 and 43 until the voltage at each extreme of SW1 is as close as
possible. Note that the exact voltage doesn't matter. What you're trying to do is
minimize the difference between the voltages. You should be able to reduce the
difference to a few millivolts.
45. Turn off the power and remove the op-amp from U1/U8. Install the second op-amp at
U2/U9. Don’t use the same op-amp you just used at U2/U9, since the input bias currents may be different. Connect the DMM between U2, pin 4 and U2, pin 6. You can also monitor this signal (out-2) at R28 and L2 as shown on the schematic.
46. Repeat the process above, this time adjusting R47. Don’t worry if the voltage jumps around at the high gain settings, or if the voltage drifts a few millivolts.
47. When the voltages are as close as you can get them, turn off the power and move the jumpers at J6 and J7 to the normal position.

With no signal applied and gain at maximum, measure the DC voltages at pins 1, 2, 3, 5 and 6 of each SC99 and let us know what you find.

ok, I check it and I will make you know.

[serpaven]

you can feel better here the defect, it's very evident:

http://www.4shared.com/audio/PZhgGWU6/C ... from_.html
http://www.4shared.com/audio/BjTtSjIn/J ... 12011.html

(neumann TLM67, external phantom power, undoubled signal and envoy both to the C84 and to the J99 Gain step = 3 and fine-gain to max)


U3 measures:

1 = it oscillates among -50 and +50 mV
2 = -16.8 mV
3 = +8,5 mV
4 = -12V
5 = -12 mV
6 = +33,9 mV
7 = it oscillates among -700 and +700 mV
8 = +12V

--------------------------------------------
U2 measures:

1 = -0.5mV
2 = 0 mV
3 = +23.7V
4 = 0
5 = -23.7 V
6 = it oscillates among 0 ad +1 mV
7= +0.5 mV (not connected to SC99)


U1 measures:

1 = -0.1mV
2 = 0 mV
3 = +23.7 V
4 = 0 mV
5 = -23,7 V
6 = 0 mV
7 = +0.5 mV (not connected to SC99)

[serpaven]

this is the "null test" 2 track (neumann TLM67, external phantom power, undoubled signal and envoy both to the C84 and to the J99) J99 track inverted phase - master +12 dB level.

http://www.4shared.com/audio/ddkcJRuR/T ... phase.html

[tpryan]

Do you have an oscilloscope? If so, check for HF oscillation at the output of the main op-amps. It may be worth trying smaller compensation capacitors at C6 and C12, say 150pF. If that doesn't have an effect, we'll need to see it.

[serpaven]

Hi, no i don't have an oscilloscope,

with output connect the U3 pin 7 (some J7) now without audio signal is @ -56 mV but with audio signal it goes to 5,0 Volts (and not mV). also removing the signal remains @ 5 V turn OFF and turn ON without signal returns @ -56 mV

ON J6 no signal - 80 mV, with audio signal always -80 mVù


on J6 the tension grows increasing the steps gain,
on J7 it stays 5V also increasing the steps gain.

I have already ordered a new LT1013CP, I will try to change it.

[serpaven]

added the two capacitors by 150 pF on C6 and C12

be worse also!
any variation on the tensions J6 and J7 and besides the noise on the vocal modulation there is also a sweep of arrangement during the breaks (after the second and third ohhhhh)

http://www.4shared.com/audio/qAfGVCg-/J ... _C12_.html

[tpryan]

We'll need to see it. For return instructions send an e-mail to rma@seventhcircleaudio.com

[serpaven]

Hi,

I have replaced U3 (LT1013CP)
I have exchanged U1 with U2
to the moment the most annoying defect (breckout audio) with the finegain to min (gain step 4) there is not.

if I bring the finegain to the max there is often the small modulation arrangement noise after the vocal modulated tone.

I will purchase a new SC99, I will try it on the my J99 and if one of my SC99 will result defective I will re-send it. if instead it will work I will hold aside it.

thanks for your availability.

[serpaven]

also with the finegain to min the small breckout audio are always there.



listening the old recordings I have however noticed that the defect there is alone when the J99 modul is connected to the motu HD192,
while the defect not being is not connecting the J99 to the motu 896HD or at the motu traveler or at the Lucid AD9624 converter.

A12 and C84 modul they work fine with motu HD192

the micro modulations of arrangement stay in always the breaks.


what it can produce this incompatibility among the J99 modul and the motu HD192?