Restoration/Upgrade Of Scribby31's Sansui AU-9500

Leestereo

Super Member
Scribby31 brought in a really nice Sansui AU-9500 for a complete restoration and upgrade; here is his original post: New Sansui AU-9500

The restoration/upgrade included the following:
1. Replace all power supply electrolytic capacitors with low ESR types (increasing capacity where appropriate and physically possible).
2. Replace of all of the signal path electrolytic capacitors with film types (whenever possible) or bi-polar electrolytic types.
3. Replace of signal path ceramic capacitors with C0G types.
4. Replace failure-prone 2SA726 transistors.
5. Replace output relay and variable potentiometers for bias and DC-offset adjustment.

A couple of pictures of the unit (with the top off) as received:



 
Power Supply & Protector Block Board (F-2030)

The F-2030 board contains the regulated power supplies for the preamplifier and the phono stages as well as the protection circuit.



Since modern electrolytic capacitors are physically smaller than their vintage counterparts, a desirable increase in the filtering capacity of the regulated supply can be implemented without any changes/modification to the PCB. Accordingly, C052 and C055 were increased from 100µF/75V to 330µF/100V; C054 was increased from 220µF/75V to 1000µF/80V; C058 was increased from 220µF/75V to 470µF/80V; C060 was increased from 220µF/50V to 1000µF/63V; and C062 was increased from 220µF/50V to 470µF/63V. The replacement for the shunt capacitor for the zener ZD501 was rated at 470µF/25V.

In the protection circuit, the replacement electrolytic capacitors were of the same capacity as the originals but rated for higher voltages. The bi-polar capacitors C901 and C902 were replaced with 47uF/25V capacitors; the remaining bi-polar capacitor was replaced with a 1µF/50V stacked film type. The capacitor C907, which provides local filtering for the protection circuit, was replaced with a 100µF/50V one. The capacitor for the relay delay, C906, was replaced with a 1000µF/25V one. The protection relay (RL901) was replaced with an OMRON MY2-02-DC24 which is a "drop-in" replacement for the original.



 
I'm really curious about this amp. How does it SOUND? i have fully restored amplifiers 999, 9900, 6500, 555a. I have read mixed reviews about this amplifier's sound and Im not sure whether to invest in one or not......cheers
 
The restored/upgraded AU-9500 sounds really nice; overall, its sound is very similar to the AU-717 restoration/upgrade which was completed a couple of months ago (details: Restored AU-717 Sound Impressions). The one area in which I did notice a sound difference, is in the phono stage: the AU-9500 can be described as being more "warm" sounding, whereas the AU-717 phono stage is more "neutral" sounding.
 
Main Amplifier Power Supply/Chassis Mounted Capacitors



The four large capacitors in the unregulated power supply for the main amplifier stage, C006-C009, are located on the right side of chassis (when facing the unit's front). The original capacitors were rated at 4,700µF/63V and the replacements were 10,000µF/63V low ESR types. Note that the capacitor clamps were also replaced to accommodate the smaller 35mm diameter of the replacements. Also, since the original capacitors utilized lug terminals, small ring terminals were soldered to the "snap-in" terminals to facilitate the installation of the wiring, the 12 ga. copper ground bus and the 8.2kohm bleed resistors. Also on the right side, closer to the faceplate, is the capacitor C014 which filters the raw DC for the +ve regulated supply on the F2030 board. The original capacitor was rated at 1000µF/80V and the replacement was a 2,200µF/100V low ESR type.









The local decoupling capacitors for the driver and output stages, C010-C013, are located on the underside of the chassis, near the driver stage "plug-in" slot. The original capacitors were 3.3µF/100V (the schematic lists 4.7µF/100V) and the replacements were 120µF/63V low ESR types.



 
Equalizer Block (F-2006)





The stock capacitors (C601, C602) in the input high-pass filter for the phono input were 1.0µF "low leakage" polarized capacitors and these were upgraded to stacked film types of the same capacity. The stock capacitors (C603, C604) for the RIAA network output were 10µF/10V polarized electrolytic types; these were replaced with 10µF/35V bi-polar types. The stock capacitors in the input low-pass filter (C605, C606) were ordinary 150pF ceramic capacitors; these were replaced with same value C0G capacitors. The capacitors C607 and C608, which determine the low end cut-off of the RIAA equalization, were 47µF/6.3V polarized capacitors; the replacements were 47µF/16V bi-polar types. The stock emitter-bypass capacitors (C613, C614) were rated at 47µF/6.3V; the replacements were 47µF/25V low ESR types. The capacitors (C615, C616) in the high-pass filter for the RIAA network were 4.7µf/50V "low leakage" polarized capacitors and these were replaced with 10µF/35V bi-polar types. The output high-pass filter capacitors (C617, C618) were polarized 3.3µF/50V "low leakage" types, these were replaced with same capacity stacked film types.

The failure-prone 2SA726 transistors (TR601, TR602) were replaced with hFE matched KSA992 transistors. Note that the pin-order for the original 2SA726 is "BCE" whereas that for the KSA992 is the current standard "ECB".

 
Tone Control Block (F-2019-1)

The F-2019-1 board contains the active preamplifier stage, which consists of three amplifier blocks; the actual tone controls and the filters are on separate boards. Each amplifier block has a high pass input filter as well as a high pass filter at its output.






Signal Path Capacitors:
Immediately following the volume control, the signal passes through the input high-pass filter capacitors (C701, C702) which were 0.47µF tantalum types; these were replaced with 0.47µF stacked film types. The stock capacitors (C709, C710) at the output of the first amplification block were 4.7µF low leakage electrolytic types; the replacements were 4.7µF WIMA stacked film types. Similarly, the original input capacitors (C717, C718) to the second amplification block were 2.2µF low leakage electrolytic types. These were also replaced with stacked film capacitors of the same capacity (2.2µF). The stock capacitors (C723, C724) at the output of the second amplification block were 4.7µF low leakage electrolytic types; the replacements were 4.7µF stacked film types. The original input capacitors (C725, C726) to the third amplification block were 0.22µF polyester film types and these were upgraded with 0.47µF polypropylene film types. The output capacitors (C731, C732) of this last amplifier block were originally 4.7µF low leakage electrolytic types; the replacements were 4.7µF stacked film types.

Non-signal Path Capacitors and other Components
The stock emitter by-pass capacitors (C703/04; C705/06 and C719/20) were replaced with 47µF/25V low ESR types. The local decoupling capacitors (C733, C734) were originally rated at 220µF/35V; the replacements were low ESR types rated at 680µF/50V. The C799 supply capacitor for the muting circuit was originally 220µF/25V and was replaced with a 470µF/35V low ESR type. The failure-prone 2SA726 transistors (TR703/04; TR709/10; and TR713/14) were replaced with KSA992 transistors, each pair was hFE matched.

 
Driver Block (F-2029)
The AU-9500 uses a F-2029 Driver Board for each channel.





Signal Path:
The stock capacitor in the input high-pass filter (C801) was a 2.2µF/50V low leakage electrolytic capacitor and this was upgraded with a 2.2µF/50V stacked film type. The stock capacitor in the low-pass filter (C803) was a garden-variety 33pF ceramic capacitor. This was replaced with a 10pF C0G capacitor (the lower value eliminates any high frequency phase shift within the audible range due to the filter F3). The input differential pair (TR801 and TR803), used the failure-prone 2SA726 transistors; these were replaced with hFE matched KSA992 transistors. The negative feedback resistors R827 and R880 (33kohm and 47kohm, respectively) were replaced with 33.2kohm and 47.5kohm 1% metal film types. The phase compensation capacitor C809 was an ordinary 9pF (the schematic lists it as 7pF) ceramic type capacitor and its replacement was a same value C0G type. The C807 capacitor, which sets the low end cut-off of the negative feedback loop, was originally a 220µF/6.3V polarized electrolytic capacitor. This was replaced with a 220µF/16V Nichicon ES bi-polar audio grade capacitor.

Non-signal Path Capacitors and other Components:
The local decoupling capacitors C815 and C817 were originally rated at 47µF/80V and these were replaced with 220µF/80V low ESR types. The variable resistors VR801 and VR803 (5.0kohm and 200 ohm, respectively) were replaced with same value Bourns single-turn cermet types. The thermal fuse which was glued onto TR807 was removed since it is largely unnecessary, and also the glue had started to corrode the fuse and its attachment clip.

 
Output Stage

The output stage of each channel consists of 2 complementary pairs of TO-3 transistors (TR823/827 & TR825/829), the 2SA706 bias transistor (TR831) and the F-2050 board. This particular AU-9500 was fitted with 2SA747 (PNP) and 2SC1116 (NPN) transistors and these were replaced with the originally specified transistors, 2SA679 and 2SC1079, respectively.







 
FANTASTIC!!! I bought my 9500 having already been recapped by the PO, will use your excellent info to go through it someday soon. . .
 
Sound Impressions of Restoration/Upgrade

Before starting the restoration/upgrade, the AU9500 was auditioned for a couple of days; it replaced a Hafler DH-110 preamp and harman/kardon hk770 power amp in one of my setups. Selected tracks from recordings (listed below) that I'm very familiar with were used to evaluate the AU-9500. Some notes were kept during these initial listening sessions (to avoid relying on just my sonic memory) for comparison with the restored/upgraded unit.

As received, the AU-9500 gave the impression of prodigious power, able to play loudly without any noticeable strain. The bass was particularly "full" sounding, with a lot of weight but it also had a somewhat "loose/underdamped" quality. The midrange had a non-fatiguing, smooth presentation, with vocals further back in the soundstage as compared to the Halfer and harman/kardon set. Similarly, the treble range could be characterized as smooth or soft, but it did not seem particularly extended (i.e., sounded rolled off). Overall, the unrestored AU-9500 was a powerful "warm" sounding amplifier, with a laidback presentation.

Following the restoration/upgrade, I was able to evaluate the Sansui for a couple of days before it was returned to its owner. The sonic difference from the stock condition was readily noticeable; the most obvious changes were in the sound of the upper midrange and treble range. Whereas before the treble range was somewhat "soft" and diffuse, it was now subjectively more extended and natural sounding (e.g., the different percussion timbres are easily discerned in Brubeck, "Take Five"). In the midrange, the sound of brass, violins/violas and acoustic guitars had more "bite", making them sound much more "real" following the restoration (e.g., in Ellington, "Cottontail", Pinnock/ECO, "Summer"; Clapton, "Hey Hey", respectively). Vocals were also rendered with improved clarity, some lyrics that were previously difficult to decipher were now more intelligible (e.g., Doors, "L.A. Woman). The change in the sound of the bass range (<240Hz) was more subtle than that observed in the mid and treble ranges: it too was now subjectively more extended and "tighter" sounding (the 2009 remaster of "Come Together" sounded particularly good). Another example of such was observed with "Aja", where there were gains in the clarity of the drums and bass. Overall, the sonic presentation of the restored/upgraded AU-9500 was more lively/dynamic than before.



A few more related comments:
In my experience, improving the preamp stage typically has a large impact on the sound of an integrated amplifier and that was the case here. Possibly due to the circuit topology requirements for larger signal path capacitors, the AU-9500 preamplifier stage reverted to the use of polarized electrolytic capacitors (as compared to the preamplifier stage of the earlier AU-999 which used primarily film capacitors). Fortunately, due to the miniaturization of film capacitors, during the restoration, all of the signal path electrolytic capacitors in the AU-9500 preamplifier stage were replaced with better film types and the single original polyester film capacitor was upgraded to a polypropylene type. Similarly, the main amplifier stage of the AU-9500 utilized polarized electrolytic capacitors in the input and feedback loop whereas the AU-999 had a film capacitor and a bi-polar capacitor, respectively, in these positions. The restoration of the AU-9500 main amplifier stage used a film capacitor and bi-polar capacitor in the same manner as in the main amplifier stage of the AU-999. Of course there were many other changes made during the restoration of the AU-9500, but the aforementioned are worth highlighting as they are probably responsible for the majority of the sonic improvements.

Recordings used in listening sessions:
Steely Dan/Aja; Miles Davis/Kind of Blue; Eric Clapton/Unplugged; Beatles/Abbey Road; Dave Brubeck/Time Out; ECO/Bach Brandenburg Ctos; ECO (Pinnock)/Vivaldi Four Seasons; Duke Ellington Orchestra/Digital Duke; Bohm, 1972 Beethoven Symphonies no. 6 & no. 9; Doors/L.A. Woman)
 
This is the second unit Leestereo has restored for me. The first was my Sony STR-6060F. With this Sansui AU-9500, my audio needs are set for a very long time to come.

The sound this unit produces is quite staggering. The Sony 6060F sounds amazing, but the Sansui sounds even better. No matter what I listen to (whether vinyl or CD) it sounds absolutely crystal clear.

You hear everything on the recording. Right down to the smallest sounds in the background. It makes old songs you've heard hundreds of time sound brand new! To say that I am very pleased with the results of this restoration would be an understatement.

I feel extremely fortunate to have located a very good example of one of Sansui's best creations......and even luckier to have it transformed into what you see here in this post by Leestereo!
 
Outstanding thread
I have an old 9500 and Leestero's description of the sound before restoration is how i would describe mine.
If only i was in the same country....
 
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