LOW LEVEL SIGNAL ON MY J99!!!!!!!!!!!

[agno]

Okay, my Rosetta 800 is calibrated at +4dB, and when my A12 is at notch#1 I'm peaking at -4.38dB, where as on my MP2NV it's at -23.4dB. There's definitely something wrong.... I'm clipping on my Rosetta at notch #3... with the output all the way down. Even with a -25dB inline pad my J99 is still hotter than my MP2NV with no pad.

Let me know what i need to do..... thanx......-Agno

[tele_player]

I'm stumped - maybe Tim will think of something.

[tpryan]

The gain of the J99 is determined by the ratio of resistors, not by the power supply voltages or the jumpers on the input transformer. First, verify that R10 and R16 are what they should be. You can get a reasonable measure of them in-circuit with the power off and the op-amps removed. Let us know what you find.

[tele_player]

Tim - the input transformer jumpers don't alter the overall gain through the J99?

From 'About the J99':

High Gain The J99 can provide 70dB of gain, not including the voltage step-up provided by the input transformer. Jumpered for a 1:5 ratio, the maximum gain available is almost 84dB.

[tpryan]

Switching from 1:2.5 to 1:5 will add not quite 6 dB. Using a 10K feedback resistor instead of a 1K would add 20 dB. I'm just trying to focus attention on the likely suspects.

[agno]

The gain of the J99 is determined by the ratio of resistors, not by the power supply voltages or the jumpers on the input transformer. First, verify that R10 and R16 are what they should be. You can get a reasonable measure of them in-circuit with the power off and the op-amps removed. Let us know what you find.

TIm,

R10=2k0
R16=320 (under 1000 ohms)

now I know that ain't right....... what do you think....?


THanx again......

[tele_player]

What are the color bands on R16, and what's the resistance measured across R17 (pins 1 to 3)?

[tpryan]

Make sure R17 is fully CW and the gain switch is fully CCW. The highest reading you'll get in-circuit is about 530 ohms.

[agno]

What are the color bands on R16, and what's the resistance measured across R17 (pins 1 to 3)?

Brown-black-black-brown..... I'll check on the R17 pins 1-3 - I have a buddy of mine checking it out... I'll post my results......

[tele_player]

Well, R16 is supposed to be 1.0K, brown-black-red.

[agno]

Well, R16 is supposed to be 1.0K, brown-black-red.

That's not what it says on the BOM.... that's weird

[tele_player]

I see - looks like the color code has been expanded since I went to school. Doh! So Br-Blk-Blk-Br would be 1-0-0 with one zero following, or 1000. I see.

Note what Tim wrote above about how to set the gain selector when measuring that resistor in-circuit. Full counter-clockwise.

[agno]

I see - looks like the color code has been expanded since I went to school. Doh! So Br-Blk-Blk-Br would be 1-0-0 with one zero following, or 1000. I see.

Note what Tim wrote above about how to set the gain selector when measuring that resistor in-circuit. Full counter-clockwise.

Cool.... I thought I was going crazy..... I'll update you once I get the results from my buddy.

-Agno