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How does one improve on the Sansui Alpha 607s? 

 

You tweak the circuit to reflect the refinements found in the later 907s!! :) 

 

This approach has been adopted by a few European alpha fans doe a while now, and in subjective listening comparisons they believe the heavily tweaked 607s can approach the sound of the later 907s and the B-2105 power amp. 

 

Below is a big stash of Elna Silmic IIs, resistor upgrades (Riken, Amtrans, Takman and PRP), Polystyrene and polypropylene shunt capacitors, and some Nichicon Muse bipolars. 

 

I'll soon be indulging on some work on my own amps for the first time in many years. I can't wait to hear the results!!

 

 

IMG_1213.JPG

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  • 2 weeks later...
We are finally underway on the AU-X711!
 
I decided to recap the regulated PSU and one channel first, so that I could hook up my meters to the hot and cold amps at the same time when setting bias and DC offset.
 

I mentioned earlier that czubsi helped me enormously with his formula for enhancing the 711/911 (thanks again Paul - greatly appreciated!!)  Unfortunately my work isn't exactly like czubsi's, mainly as I can't find the rare Elna Silmic Alpha Super Gold caps, the Black Gates, the polypropylene U-Con caps, and the vast range of Riken RMG and Amtrans AMRG resistors really starts to add up in cost. This is why I went for the lesser Amtrans AMRT in many locations, along with Takman REY. I note that Amtrans use these exact resistors on their high end stepped-attenuators, so they can't be too bad ;)

I ended up using Panasonic polypropylene caps in place of the U-Cons too. Again, sourcing these for realistic prices is just too difficult.

 
In short, the upgrade makes use of empty spaces on the PCBs for things like extra capacitors, bypass caps etc which are found on the higher-end models but not on the 607s. There's nothing particularly revolutionary about the tweaks  - they follow Sansui's own recipes.
 
All of the Nippon Chemicon caps have been replaced with Elna Silmic IIs, (apart from two in the power supply due to size issues). I've never done this before, as I always use long life, high temp, low ESR caps in the PSU. However, sticking true to Sansui's formula, I figured I'd give it a shot. Polypropylene and polystyrene caps are fitted where possible. The Silmics are much larger than the originals!
 
power%20supply_zpssmojwj0p.jpg
 
power%20supply2_zps39z2xthp.jpg
 
Due to a lack of space between the amp board assy and the chassis on one channel, two of the 470uf 50V Silmics are tilted over. In czubsi's mods, these are remotely mounted near the filter capacitors via flying leads. However, I prefer to have them installed on the PCB to reduce inductance due to the long wiring. This means that I've used the spare bypass capacitor location to accommodate a pair of 100uf 50V caps. As a result, I've fitted the polypropylene bypass caps on the underside of the PCB as there is ample room, along with all of the 4700pf Siemens polystyrene bypass caps.
 
one%20driver%20board_zpsqfdlcdxr.jpg
 
one%20driver%20board2_zpspgrb7ceo.jpg
 
Simple tweaks such as removing wire jumpers and fitting caps in a back-to-back pseudo-bipolar configuration in certain locations (as per the upper end models) is easily done, with polystyrene bypass caps installed.
 
silmic%20bypassed_zpst5ebx0bv.jpg
 

one%20driver%20board3_zpsq5zzeiuc.jpg
 

 
 
A paralleled polystyrene and polypropylene bypass caps is also fitted across the wiring from the filter caps to the amp PCBs.
 
I was only able to replace the DC offset trimpots at this stage, as the bias trimpots have a reversed pin configuration vs the DC offset trimpots, thus the usual Bourns-style trimpots would not fit. Thankfully I was able to set bias easily with the originals. The Bourns-style multi-turns certainly come in handy with the DC offset on the Alpha X-balanced Sansuis, that's for sure!!
 
The PCBs have quite a lot of flux residue on the top side. I'm progressively cleaning it off as I go, but at the end of the day, it's only cosmetic. The zener diodes were placed very close to the PCB and caused localised heating and darkening of the flux. I've since replaced them with new units mounted higher off the PCB. You can see the discolouration under the original zener here:
 
zener1_zpsiwbf8yww.jpg
 
Next step is the other channel (currently partly stripped), the protection circuit, and the EQ/phono boards.
 
one%20board%20completed%20and%20psu_zpsl
 
 
I'm very much looking to forward to the first listening test, and further pics will come!
Edited by pete_mac
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1 hour ago, blakey72 said:

On it's way ;)

AU7700-1.JPG.3736f914eda4433827ff28d4e2c73d66.JPGAU7700-2.JPG.ca7dc39b9711b2bba5f778c6c2e8164d.JPGAU7700-3.JPG.af3519a8ea524b362c1def2e7d0c5f84.JPG

 

On 12/03/2017 at 9:27 AM, Ugly said:

She is a beauty@blakey72

Definitely my favourite series of Sansui from a looks perspective

This is the series I find has nice lines, also love the positive action when throwing the levers 

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2 hours ago, gator2310 said:

Cool - I have a gorgeous 5900 (fully restored) bought from a member here - love it to bits. If you get another case of upgrade- itis let me know!;)

Did you buy the 5900 off Cafad by any chance?

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Nope - it was off another member in Brisvegas. Possibly rejuvenated by someone (also a member) up that way I think. I have 3 smaller Suis a 317 and 217mk ii which are also both in good order but the 5900 is exceptional - and looks cooler too of course.

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Both amp boards are now finished!
 
two%20711%20amp%20boards_zpsr8ktrk4p.jpg
 
You can see the polystyrene and polypropylene caps on the rear of the amp board PCB here:
 
bypass1_zps46jl41cc.jpg
 
More Amtrans and Riken resistors:
 
amtrans%20amrt_zpsbqwhz8ug.jpg
 
amtrans%20and%20riken_zpsgm10fk85.jpg
 
I'll definitely look into alternative Bourns trimpots with the correct leg configuration for the bias pots, or will modify some to suit.
 
The phono board has been fully reworked, with Silmics and a lone WIMA cap, and the three key signal path resistors per channel replaced with Takman REY. Those 1000uf 10V caps are too wide and rub shoulders with each other.
 
711%20phono_zpsw2ziftxz.jpg
 
phono%20takman%20input_zpsvjxgjzdb.jpg
 
phono%20takman%20output_zpsmoq0mn5b.jpg
 
I took no photos of the EQ and protection circuits, but they are also fully Silmic'd/recapped/tweaked/bypassed/unicorn-dusted as appropriate.
 
Taking a leaf of out Sansui's book re: dealing with resonances, I've applied foil-backed butyl deadener on the larger panels throughout the amp.  This is a tiny snapshot of what I did. The amp is now noticeably heavier and the chassis sounds less 'clang' and more 'thud' when tapped.
 
711%20deadening2_zpsoyquamuo.jpg
 
711%20deadening_zpsltodmi7h.jpg
 
 
She's all ready to clock up some mileage before serious listening. However, even straight off the bench after some DC offset and bias adjustments, she sounds fantastic! Noticeably better than in original stock form. The big question is... should the 607MRX be worried?? Let's wait and see!
 
711%20listening2_zpson7lirx1.jpg
 
711%20finished_zpsotm3kqtr.jpg
 
711%20listening_zps7ghrarks.jpg
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I don't have any new Sansui amps (which is a pity) but I did happen to see an auction for some circuit diagrams on Yahoo Japan.  So I bought them (of course!).

liubaohua78-img600x600-1489371654ne2q0b7763.jpg.c806ff28416a9f2ab6d76cd0b042418b.jpg

 

I'm hoping I now have the bias settings for the Alpha 907 NRA.  Once they arrive I'll scan them and see if I can find a Japanese translator that can tell me exactly what it is that I've got.  The translation of the auction description was "adjustment method" so here's hoping that means bias settings!

 

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28 minutes ago, Cafad said:

I don't have any new Sansui amps (which is a pity) but I did happen to see an auction for some circuit diagrams on Yahoo Japan.  So I bought them (of course!).

liubaohua78-img600x600-1489371654ne2q0b7763.jpg.c806ff28416a9f2ab6d76cd0b042418b.jpg

 

I'm hoping I now have the bias settings for the Alpha 907 NRA.  Once they arrive I'll scan them and see if I can find a Japanese translator that can tell me exactly what it is that I've got.  The translation of the auction description was "adjustment method" so here's hoping that means bias settings!

 

 

Well done!!

 

I'd be VERY interested in a scanned copy of the above. I'm compiling data on the 907s to assist in tweaking of the lesser models, plus it's a big plus to have this info on-hand to enable servicing of these beasts.

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28 minutes ago, pete_mac said:

 

Well done!!

 

I'd be VERY interested in a scanned copy of the above. I'm compiling data on the 907s to assist in tweaking of the lesser models, plus it's a big plus to have this info on-hand to enable servicing of these beasts.

I'm sure we can arrange that Pete.  I may be a hoarder of amps but I don't believe in hoarding information that could be beneficial to the community as a whole.

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