HF-Noise on my J99

[manfi]

Hi,

my two J99 with AD797 OPAmps make a lot of noise. bouth make the same noise. It is a high frequency noise when i move the potis. like filtered pingnoise that change the fequency and amplitude by moving the trim potis on the front. And the noisefloor was much higher as by the A12 or the N72. I can't find a wrong. i think i understand something wrong on the instruction or on the stickie with the version 3.1 instructins because i have the same problems on bouth J99.

Do you have an idee were i can search?

[tpryan]

Did you install the correct parts at C21, C22, R27 and R39?

[manfi]

hi,

the parts at c21,c22,r27 and r39 are ok.

if i change the jumper j3 and j4 to power ground (bin1-2), then the Noise are gone. but then i have ground loop hum.

[tpryan]

Do you have the input transformer jumpered correctly? See this thread: http://seventhcirclestudios.com/SCA/php ... .php?t=874

[manfi]

hi tim,

the jumpers are installed correct. i send to your e-mail adress an mp3. listen to it. you can hear on the mp3 my problems. the other preamps (a12 and n72) works fine.

best regards.

manfred

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[tpryan]

Are you sure that the trim pots are 1K parts and not 10K? You can verify by measuring the resistance across the two outer pins with the pot turned fully clockwise. Also, verify that the resistors at R10 and R16 are 2K and 1K respectively. Please verify by measurement and not by visual inspection. Let us know what you find.

[manfi]

on the poti, the indications are correct. i set my multimeter to 2k and when i measure the poti on the back of the board across the two outer pins, then the multimeter shows 0.556 with set the poti fully clockwise. R10 is ok (2.05 set the multimeter to 20k) and R16 shows me 0.55 set the multimeter to 2k. All measuremets are made on the back of the board with mountet parts.

The color code on each part is correct.

best regards

manfi

[manfi]

Hi Tim,

I'm back with my noise problem on my two J99. I can't find the problem. i have 3 pictures of my board and i send you via e-mail a new audiofile with the noise and the pictures. is it possible that all opamps are bad?

i can't finde the right bill of materials of my version. so its hard to check all resistors and so. but i have found an other pictrure on this forum an i have check this picture with my board. all was fine.

any idee where i can search next?

Please check the mail. i have send it to support@seventhcircleaudio.com

Best Regards


Manfi
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