AU-D907 LIMITED vs 919

[ghamilton]

My replacement TO-3 output transistors that's in my 919 are by ST
and they are 2ST2121/2ST5949.
Maybe they will do another run one day.

 

[Sui-Yogi]

For the driverboard this is the difference in transistors used, you go from drivers fT 30 MHz to 100 MHz and outputs from (supposed) 25 MHz to 50-70 MHz.
On the driverboard the compensation capacitors C23-26,53-56 ( polystyrene) are smaller, from 3pF (AU-919/D907) to 1pF in the D907 Limited. Further there are bypass film capacitors C57-60 for the decoupling capacitors C01-04. Although they are in the schematic of the AU-919 they are not always there ( they are in my AU-D907) in all the AU-D907 Limited I have they are.
There are more small differences, I will post them when I get to restoring one.

Hi GrisPato,
Which transistors are in the “limited” for drivers, instead of the NEC’s ?
Cheers

 

[GrisPato]

Toshiba 2SA968/2SC2238, same drivers and outputs as the AU-X11

 

[GrisPato]

This is getting exciting.

It rubs the eternal itch of upgrading in a right way.

If the changes are subtle and are limited to only components ( transistors, capacitors ) One can try this upgrades on a AU919 which will be going for a recap anyway.

So that will be the contribution of AK to take an already superb sounding amp to the next level.

Few mods and you can have a gem of an amp of your own baking (pun intended ) .

Just don't forget to copperplate the chassis and make a bronze baseplate for the powersupply .
This was the reason Sansui made the Limited edition in the first place. They tried aluminium but found that it sounded like, aluminium, and apparently they did not like it that much.
They liked the copper sound, as is evident in that they continued using it in the AU-D907F (AU-D11),AU-X11, D707/907G Extra, D707/907X. Then they stopped using it in the integrated amplifiers (D907X Decade, alpha 907/907i/907L Extra) but used it in the C2301/B2301/2/2201and in the cdplayers of the first alpha series.
With the later alpha series starting with the AU alpha 907DR they used it in the 907 model.
That's why I like the AU-D907 Limited, because it's the amplifier where this started!

 

[ghamilton]

My 919 is running a little warmer than it use to before those new drivers were put in. Wonder why?

 

[Hyperion]

My 919 is running a little warmer than it use to before those new drivers were put in. Wonder why?

Part of the process of changing them should have included resetting Bias and DC offset - both of which will be affected if you change driver transistors. Did you do this?

For the record AU-919's do run 'comfortably' warm, not really hot like an 'AU-α907 Limited', or cool as a cucumber like an 'AU-D11 II'

 

[ghamilton]

Of course I reset it per the SM.

 

[Hyperion]

Of course I reset it per the SM.

OK, well it is common for bias to drift low over time, so you probably corrected that, hence the warmer running. However, resetting the bias without changing the driver transistors might have given the same listening improvement.

 

[ghamilton]

OK, well it is common for bias to drift low over time, so you probably corrected that, hence the warmer running. However, resetting the bias without changing the driver transistors might have given the same listening improvement.

Possible, but I dought that was the reason because I had already checked it a few months ago. I keep a check on it. Perhaps I will recheck it again soon.