Sansui AU719 cut traces driver boards!Original or Mod?!

mcgreg66

Member
Hello members,
I just discovered that there are cut pcb traces on both channels same !
First I thought I damaged them somehow with the screwdriver but then I saw it’s the same on both channels.
Anybody knows this modification?!Is it factory made or useful?!

Thanks
Gregor
 

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Sansui definitely made production modifications like that. What's the history of the amp? Is everything working normally?

- Pete
 
It should be totally quiet, no hiss or extraneous noise at all. But that's probably not related to these cut traces. These are fantastic amplifiers that will stand up to and probably exceed any modern amp. Look into correcting that hiss.

- Pete
 
If you are comparing the hiss with other modern amplifiers, then I assume that eliminates whether this is while using headphones or not, and the sensitivity of your speakers (same set in use?). But what input are you selecting on the AU-719, as obviously it will be noisier when Phono is selected, and what source (if any) is connected to the input that is selected?

With an input like AUX selected you should be able to turn the amplifier volume to max and be able to hear a not too loud hiss in the speakers, is it worse than this?
 
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No headphones!
Pretty sensitive speakers!
The amp is already recapped!
I don’t know if hiss is the right word .....it’s a audible noise floor like white noise!
Not loud but audible already 3m from the speakers!
And unattached to volume!
I’ve tried with preamp disconnected and it seems to be the same or even more!

Are there any critical noisey Transistors on the driver boards?!
 
Are there any critical noisey Transistors on the driver boards?!
No, but there are a couple in each channel of the Control Amp, type number 2SC1313 and/or 2SA726 which may be the culprits here.
 
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I adjusted bias and offset again!
Everything ok....
But DC on head amp circuit board was out of range and really hard to adjust!Jumping!
I can try and change 2SC1313 for KSC1815
 
Weird that the first pic depicts a cut across one source of the dual FET - maybe only one part of that FET (and only one source) is required to be used?

The second cut makes more sense to me - as its changes to the grounding path. You should see some of wacky mods to the grounding path that Sansui made with the X1 - black wires, trace cuts and extra components whacked-on everywhere.....
 
It‘s not possible to to adjust DC on equalizer board.....I adjust to 0+-50mV.....the next day it’s out of range again....0+-150mV.....
 
It‘s not possible to to adjust DC on equalizer board.....I adjust to 0+-50mV.....the next day it’s out of range again....0+-150mV.....
What parts if any, have you changed on the F-3095 Head Amp Board ? - Oh, and make sure Phono input is selected when you are doing the offset adjustment on that board.
 
What parts if any, have you changed on the F-3095 Head Amp Board ? - Oh, and make sure Phono input is selected when you are doing the offset adjustment on that board.
I changed all electrolytics and fuse resistors.....but F-3095 was hard to adjust before!
And I had change the Input selektor switch!
And I changed VR01 + 02 to new bourns trimpots!
 
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Can I adjust DC on F3095 without Drivers, because it’s so hard to get to VR02!
Technically I think you can, but I have to say I never needed to do that (i.e. remove the driver assemblies).

By carefully choosing the type of trimmer they are (both) quite easily accessible, even with the driver assemblies installed. By threading your trimming tool downwards past the EQ board components to get to the trimmer. I seem to remember having to carefully mount the chosen trimmer in such a way (at a slight angle), that the adjusting screw was accessible, but the main trick was getting the right trimmer(s) in the first place.

Trimmers that look like this:-
3296P_t.jpg
 
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Can this be caused by the suspect 2sc1313
Quite likely, as there are another 2 per channel in the EQ section but do make sure the phono input is selected when you are making this adjustment. I am saying this again as you did not confirm when I mentioned it before.
 
Quite likely, as there are another 2 per channel in the EQ section but do make sure the phono input is selected when you are making this adjustment. I am saying this again as you did not confirm when I mentioned it before.
Thanks for reminding but I tried also with Phono input selected!
 
I changed the 2SC1313 for KSC1815 on EQ board and it seems to be much quieter!
Maybe it will get even more silence if I change the 2SC1313 and 2SA726 on PSU board too
PS: DC is still ranging between +-50mV but much better!
 
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