What if the problem is actually the output getting into the phono input and creating unwanted feedback? That would explain why it depends on the volume pot setting. This sort of thing can happen with either bad ground connections (bad solder joints or cracked PCB - does the unit show signs of mechanical damage?) or tired electrolytic capacitors in the phonopre power supply.
BTW, saying the phonopre has 150 mV of output while a CD player has 2 Vrms is comparing apples to oranges. 2 Vrms is full-scale and was chosen for a good amount of headroom above nominal 300 mV consumer line level. Even with loudness war related level creep since then, I would expect 600 mV to 1 V average at most, so probably closer to 12-16 dB of difference if the cartridge has somewhat normal output level. On a typical volume pot, this might be the difference between 10 and 12 o'clock.
BTW, saying the phonopre has 150 mV of output while a CD player has 2 Vrms is comparing apples to oranges. 2 Vrms is full-scale and was chosen for a good amount of headroom above nominal 300 mV consumer line level. Even with loudness war related level creep since then, I would expect 600 mV to 1 V average at most, so probably closer to 12-16 dB of difference if the cartridge has somewhat normal output level. On a typical volume pot, this might be the difference between 10 and 12 o'clock.
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I do checked all the capacitor & all seems fine. No visible damage to the solder & board. I have make some cap replacement.
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Hi Duncan,
I have installed the both BJT BC550C & BC560C. Indeed they help. The increasing of gain is subtile but the overall performance is noticeable improved. My Sansui sound much more dynamic & controllable when I increase the volume above 12 o'clock . Thanks for the advices.
I have installed the both BJT BC550C & BC560C. Indeed they help. The increasing of gain is subtile but the overall performance is noticeable improved. My Sansui sound much more dynamic & controllable when I increase the volume above 12 o'clock . Thanks for the advices.
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I am glad you are happy .
Those BJT,s were specifically made for audio and I used them for years as did JLH , yes there are exotic audio BJT,s and some people put them down as "old fashioned " but they work well have low noise and the "C" version has high gain and have been used by many professional engineers so I would still use them even now if needed.
Those BJT,s were specifically made for audio and I used them for years as did JLH , yes there are exotic audio BJT,s and some people put them down as "old fashioned " but they work well have low noise and the "C" version has high gain and have been used by many professional engineers so I would still use them even now if needed.