Sansui 771 hiss

[quadmatrix82]

I was thinking also R31/32 (100K) could be contributing to noise. The last thing is. the volume pot itself, not sure how, but I've seen noisy volume pots.

I’ll try these too cheers!

 

[quadmatrix82]

I was thinking also R31/32 (100K) could be contributing to noise. The last thing is. the volume pot itself, not sure how, but I've seen noisy volume pots.

These were 470k not 100k I changed them anyway and the 100k resistors in r17-8 I’d say it’s the same still unfortunately

 

[quadmatrix82]

If you have a couple of zeners to get 35 volts plus or minus a volt or two it is worth a shot. The EQ board only comes into play for the phono input, which I would expect a little noise out of. I don't think you need to re-flow the FET's.

Replaced the zener no change unfortunately I did notice the fets have black legs left them as is might have to just leave it as is sounds good still but certainly not a quiet one

 

[bluscombe]

Hi sansui experts, I recently purchased a mint 771 receiver that wasn’t working, after a recap and replacing all the 2sa726/2sc1313 transistors and zener diodes it’s working very sell however I do notice quiet loud hiss on without music playing I am wondering if the transistor substitute chosen are causing this issue?

I used ksc1815 in place of 2sc1313 on the tone board note gain was approx 211 instead 560 of originals - should I replace these with ksc1845 instead given the higher hfe available?

I used ksc1845 on the equaliser board in place of 2sc1313 approx 430 gain vs 560

Any thoughts or recommendations here would be appreciated Thankyou

I have done a complete restore on my 771 and used KSC1845s and have the hiss

 

[bluscombe]

I have done a complete restore on my 771 and used KSC1845s and have the hiss. Madening!

 

[The Fuxtor]

I think Leestereo did a whole 771 upgrade thread where he addressed the hiss issue on these?

 

[mrk229]

I think Leestereo did a whole 771 upgrade thread where he addressed the hiss issue on these?

Yes have a look here. The gain of the power amplifier in the 771 is very high, @Leestereo performs a mod to reduce the gain of the power amp section to reduce the hiss.

Post in thread 'Leestereo Mods, Tweaks and Tips for the Sansui 771'

Jul 30, 2025

Part 2: Constant Background Hiss & Hum

With the volume control at minimum, a constant low-level hum and hiss noise in both channels was heard over speakers or headphones; noise is much more intrusive when using headphones. During loud playback levels, the noise is apparent during the "silence" between music tracks, and is independent of input source. Unlike the the "popping" noise/fluctuating DC offset issue, this noise issue was affected by the preamp controls, e.g., the -20dB muting switch makes the noise virtually inaudible with the volume at minimum. This behavior suggests...

• Leestereo

• 
• 

 

[bluscombe]

I think Leestereo did a whole 771 upgrade thread where he addressed the hiss issue on these?

Thank you! It’s like striking gold!

 

[bluscombe]

Yes have a look here. The gain of the power amplifier in the 771 is very high, @Leestereo performs a mod to reduce the gain of the power amp section to reduce the hiss.

Post in thread 'Leestereo Mods, Tweaks and Tips for the Sansui 771'

Jul 30, 2025

Part 2: Constant Background Hiss & Hum

With the volume control at minimum, a constant low-level hum and hiss noise in both channels was heard over speakers or headphones; noise is much more intrusive when using headphones. During loud playback levels, the noise is apparent during the "silence" between music tracks, and is independent of input source. Unlike the the "popping" noise/fluctuating DC offset issue, this noise issue was affected by the preamp controls, e.g., the -20dB muting switch makes the noise virtually inaudible with the volume at minimum. This behavior suggests...

• Leestereo

• 
• 

Thank you so much!

 

[raycarr00]

Just did all the leestereo mods and it's dead quiet. Unfortunately, I didn't get to hear a before the mods hiss everyone complains about. Many of the resistors on the tone board were way off and the caps throw off the readings when checking. So, lift legs to test. Replacing them improved the sound considerably. Watch out for the itty bitty wires that easily break on the tone board. Take pics.