Sansui AU999 Pre-amp mod.

lissenup said:
Has anyone come up with a definitive answer if this can be done to a AU-888?
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I believe the AU888 has the same pre-amp board....
Might just pay to have a look at the schematic to be sure, I reckon they probably even have the same "F" designation....

Yeah just checked the AU888 has a F-1209A and the AU999 has a F-1209, so there might be some small difference, just get the schematics and check it, I would say its quite likely you can work my mod on a AU888....
 
kevzep said:
Seriously? its 4 resistors on a circuit board, the rocket science was working out the values not posting pictures of where they go....
You do not need pictures to find these resistors, the AU999 is one of the simplest amplifiers to work on....
I almost posted pictures, but seriously, it looks like 4 resistors on a circuit board, its just a waste of AK's server space to be honest, it does not show anything revolutionary, as I said, its in the resistor values...

I am considering posting part 2 which is the gain and slope mod to the Bass EQ in the AU999.....That will need pictures, because the resistors which need changing are not on a board, they are not easy to find without directions and pictures.....
We will see how this thread goes first.....
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Hi Kev This is great stuff !! Thanks so much....i just acquired a mint condition au-999 from an owner who kept it for a good 40 years plus.Did a quick sound check and all seems good, but i do agree the bass seems lacking . One thing which puzzled me was thr transistors used on mine is the NEC 2SA640 instead of XA495 as in manual.Was there some improvements done later on to overcome the headroom issue?Thanks and in advance
 
Just to confirm the 888 uses a different board and upon checking the schematic it's a different design this mod made no difference when I tried it but does wonders on a 999 hope that helps
 
transduceren said:
Hi Kev This is great stuff !! Thanks so much....i just acquired a mint condition au-999 from an owner who kept it for a good 40 years plus.Did a quick sound check and all seems good, but i do agree the bass seems lacking . One thing which puzzled me was thr transistors used on mine is the NEC 2SA640 instead of XA495 as in manual.Was there some improvements done later on to overcome the headroom issue?Thanks and in advance
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I believe the AU999 has the same design in terms of power amp, pre-amp design, but at some point they changed the transistor designation to a newer more reliable substitute.
Yes I have an AU999 on my bench I would like to get to and do all these mods to.....really transforms them substantially...
 
quadmatrix82 said:
Just to confirm the 888 uses a different board and upon checking the schematic it's a different design this mod made no difference when I tried it but does wonders on a 999 hope that helps
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Yeah, different, I would hedge a bet that the AU999 came before the AU888, and they resolved that issue with the "A" variant of that F-1209 board.
 
Kevzep , you disliked 9500 for your 999 and now this !!!!!! im in dismay ....

Im wondering how the mods would further beautify the already "too good" amps .....

those film resistors mod you did on the 999 and other steps , id think they would also improve my 9500 ....
 
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well ofcourse what i meant was that there are mods for the 999 and then there should be mods specific for the 9500 :D....
 
kevzep said:
Yeah, different, I would hedge a bet that the AU999 came before the AU888, and they resolved that issue with the "A" variant of that F-1209 board.
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According to the serial numbers on file, they were built at more or less the same time but the 999 a few months earlier. The earliest 888 on file was built in October 1970 and the newest one in February 1972. There are only 15 AU-888s on file. There are 73 AU-999s on file. The serial numbers point to a production run from March 1970 to September 1972.

Today's database fact. I now return you to your regular programming. Carry on.

- Pete
 
Interesting thing about the 888 - I had one briefly and when I fired it up (totally unmodified), it sounded close-to-on-par with my fully modded 999. So I guess Sansui did some learning somewhere along the line between producing the 999 and then the later 888.
 
I did read the thread and saw that.
I was asking about gain, not maximum unclipped output.

If I input a 1 VRMS AC signal, how many AC volts RMS will be measured on the pre amp output?
Thanks.
 
quadklipsh said:
well ofcourse what i meant was that there are mods for the 999 and then there should be mods specific for the 9500 :D....
Click to expand...

There is no deficiency in the design with the AU9500 like there is with the AU999, so no modification is necessary, and there would be no advantage to do so....

quadklipsh said:
Kevzep , you disliked 9500 for your 999 and now this !!!!!! im in dismay ....

Im wondering how the mods would further beautify the already "too good" amps .....

those film resistors mod you did on the 999 and other steps , id think they would also improve my 9500 ....
Click to expand...

It's not the type of resistors I used which makes the improvement, its the changes in values of the components. You could for intents and purposes, use any type of resistors really, and the result would be the same...
Although the "flat earth" people would probably disagree....
 
santa said:
I did read the thread and saw that.
I was asking about gain, not maximum unclipped output.

If I input a 1 VRMS AC signal, how many AC volts RMS will be measured on the pre amp output?
Thanks.
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Why do you need to know that? Are you using the AU999 pre-amp to drive another poweramp?
 
santa said:
Can anyone tell me what the voltage gain of the pre section is after the mod?
Thanks
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I was just reading through this thread looking for info and see you've already been here!

kevzep said:
Why do you need to know that? Are you using the AU999 pre-amp to drive another poweramp?
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I'm currently using an AU-999 with this mod as a preamp to drive an Ampzilla with modified JFET input stage. What Santa and I are trying to discern is whether a tube pre that he's selling would be compatible with the modded Ampzilla. Input impedance and gain information on an Ampzilla with the JFET input modification is difficult to come by, so info on the AU-999 would be helpful as a reference point.
 
MATT0404 said:
I was just reading through this thread looking for info and see you've already been here!


I'm currently using an AU-999 with this mod as a preamp to drive an Ampzilla with modified JFET input stage. What Santa and I are trying to discern is whether a tube pre that he's selling would be compatible with the modded Ampzilla. Input impedance and gain information on an Ampzilla with the JFET input modification is difficult to come by, so info on the AU-999 would be helpful as a reference point.
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Yeah sorry I never measured that parameter when I did the mod. I doubt it would in any way change the output impedance though.
Possible that it has changed the voltage gain, I should have measured it when I completed the mod.
I am about to do another AU999 so when I do I will measure it...
 
kevzep said:
The preamp will now do 7.2VRMS (+19.3dBu) before it clips......

Now the amplifier can now produce 72watts easily before it clips.........before it would barely make its rated output...
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Kev, many thanks for sharing this mod. Is there any chance that the 7.2V is p-to-p not Vrms? I get 7.2Vpp (2.5 Vrms amplitude) on my unit. I have also just seen the same pre and post mod voltages that i got on Noah Schumacher's site. http://marantzhallo-fi.blogspot.com/2017/10/eds-sansui-au-999-with-pre-amp.html

Also was the 72 W measured into 8 ohms both channels? After mod I thought i had exactly 72 W (24Vrms previsely swinging at speaker terminals)...until i realized i forgot to hook up speaker loads... Then i had to settle for 46 W at rated distortion once i hook up 8 Ohm loads.

Forgive me for asking these types of questions as you are much more pro than me and you are unlikely to have goofed...but i am trying to get my head around my new acquired AU-999 and the coincidences with the numbers seem worth asking.
 
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