zaxour
180K resistors required for headphone audio restoration - VA6
For VA6 console, I found it necessary to utilize 180K resistors in series with the outputs of the TL972 to achieve proper audio levels from headphone connector. Directly connecting the L/R outputs from the TL972 to C42/C44 anode connections (+), results in severely distorted headphone audio on a VA6 with original 3BPV2 board.
To be clear: TL972 pin 1 (R audio channel) --> 180K --> C44 (+), TL972 pin 7 (L audio channel) --> 180K --> C42 (+).
All instructions in your guide were followed. The following components are removed on my VA6:
C40, C41, C42, C43, C44, C62, C62 (top side of PCB), C45, C46, C47, C48, R34, R37 (bottom side of PCB)
I am happy with the results of the 180K resistors. However, it's possible 150K may offer slightly higher amplitude from headphone output, but my unscientific ears may have observed some remaining compression artifacts. I also experimented with 100K and 10K. 100K had noticeable compression artifacts on higher frequencies (such as Sonic picking up rings); 10K was severely distorted/compressed and is unusable.
I haven't experienced that myself, but looking at the schematics, the gain for the signals on the 3BP for a model 1 should be:
FM - 30 (300k / 10k) PSG/CD/EXP - 1.43 (300k/210k)
Since the gain resistors for headphone audio are 10K (R40, 41 va3), that should knock the amplitude back down quite a bit, since everything will be going through a 47K resistor (R38, R39 for VA3), which would set the overall gain to ~0.18. Multiplying that by the original gain values puts the overall gain back in the same territory as the original circuit (10k/2.2k for FM, 10k/47k, 10k/51K for the others). That you would need threefold the resistance to remove distortions might point to another problem. Would you mind sending photos of your install to "zaxour" via gmail? It's possible that the ref-des got updated between revisions and the wrong resistors may have been removed, which means I need to update my instructions. Thanks!
On Tue, Dec 19, 2023 at 8:39 AM p25dotca @.***> wrote:
For VA6 console, I found it necessary to utilize 180K resistors in series with the outputs of the TL972 to achieve proper audio levels from headphone connector. Directly connecting the L/R outputs from the TL972 to C42/C44 anode connections (+), results in severely distorted headphone audio on a VA6 with original 3BPV2 board.
To be clear: TL972 pin 1 (R audio channel) --> 180K --> C44 (+), TL972 pin 7 (L audio channel) --> 180K --> C42 (+).
All instructions in your guide were followed. The following components are removed on my VA6:
C40, C41, C42, C43, C44, C62, C62 (top side of PCB), C45, C46, C47, C48, R34, R37 (bottom side of PCB)
I am happy with the results of the 180K resistors. However, it's possible 150K may offer slightly higher amplitude from headphone output, but my unscientific ears may have observed some remaining compression artifacts. I also experimented with 100K and 10K. 100K had noticeable compression artifacts on highly frequencies (such as Sonic picking up rings); 10K was severely distorted/compressed and is unusable.
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