Sansui AU-7700
S.N. 814110411
Complete Recap with audiophile grade modifications
$1974
Sold
FMI HiFiHealthCare@Gmail.com
The AU-7700 is regarded by many to be one of Sansui’s most refined sounding amplifiers, built at a period in Sansui’s history where the president of the company spared no expense on design. Being an audiophile himself, Kozo Kikuchi’s philosophy was “Let our products speak for themselves”. In 1972, the AU-7700 sold for $399 which in today’s dollars is over $2500 reflecting the build quality and components chosen to produce an outstanding amplifier of this caliber.
The selection of components used in the rebuild reflect the same philosophy and most likely would have been chosen by Mr. Kikuchi if they were available during the original production. All electrolytics and select ‘audio critical’ capacitors have been replaced and upgraded. Elna “SILMIC” Silk Fiber Capacitors, Nichicon “MUSE”; UKA Series and WIMA Series Polyester Film Capacitors were used in the rebuild for their superior performance characteristics. Original Sanken Output Transistors, for that genuine ‘Sansui Signature’.
This unit has recently been recapped with regard to ultimate fidelity using some of the best components in the industry. All caps, where reasonable, were upgraded to poly Stacked Film components. Particular attention was given to the phono section.
The main power supply capacity for this amplifier was significantly increased, by 50%, From 10000uF/Ch to 15000uF/ch. making the supply rails rock solid as is evident in the power tests performed (See Attached Oscillograms and performance evaluations). For optimal performance at higher frequencies and to provide an overall better ESR Poly Stacked film Capacitance was added in parallel to the main filter caps.
The Input Board RCA’s were all reflowed to eliminate known problems with this design over the years. All RCA contacts were cleaned and tested to < 1ohm .
One of the leading causes of catastrophic failure on this vintage amplifier is thermal runaway.
After time the original Thermal Grease dries out and no longer is able to conduct heat from the power transistor to the heatsink leading to avalanche effect and destruction of these precious original devices that are the final stage making the ‘signature’ of the Amplifier. In 1970’s this method of heat transfer was the defacto standard mostly due to a lack of better alternative. As part of a rebuild consideration we choose modern solutions to this and upgrade the Mica and Grease to high tech thermal conduction pads that have 10 fold the life expectancy of the 1970’s thermal grease.
In order to provide the best connection from this retro piece we needed to update the speaker terminals from pinch wire style to Audiophile Grade Gold Plated Universal Binding Posts
Polyester stacked film capacitors were used in the phono section. The transistors originally employed for this phono stage became historically problematic and had to be upgraded with a complete compliment of modern equivalents with much better performance and lower noise floor.
One of the best effort / reward areas is in the pre-amp. This area is so critical to the overall performance of the integrated amplifier as it is the most susceptible to the amplification of minute failures. It is unknowingly one of underlying aspects as to why “It just doesn’t sound as good as it use to” feedback from customers. The audio path of this piece was populated with the top of the line audio performance capacitors from Nichicon including UKA, Muse and FG series audio grade electrolytics. For the main input of the preamp we chose WIMA Stacked Film for the best performance overall. All known problematic transistors were upgraded to modern equivalents with lower noise floor and higher reliability
The Pre-amp will only perform well if it has a rock solid DC Supply. The DC Supply was completely rebuilt and the old Elna caps were upgraded to Nichicon Fine Gold series capacitors. We also increased the voltage from 50vdc to 63vdc to provide extra headroom for safe and reliable operation in this stage
The Main Amplifier driver board was removed and all problematic transistors were replaced with modern equivalents for upgraded performance and reliability. Nichicon Fine Gold and MUSE series caps were used for upgrades
The final link to the speaker is the output relay. As a standard measure for restorations, we always remove this device and tear it down to inspect / recondition contacts using a proprietary restoration method that is non destructive to the contact surface as ‘burnishing’ can be. This process takes over 12 hours and the results speak for themselves as seen below.
Although it should go without saying, all controls have been cleaned however, we don’t mean by the standard that some consider where one sprays a bunch of cleaner at the device insitu and as a result, all over everything around the device L … We Completely remove all the devices and break them down to a point where the contact points can be properly serviced. We finish the treatment off with lubricant refresh (Where applicable) and direct application of d100 / F5 where appropriate for long life and noise free operation.
DC Offset and bias were calibrated as per Sansui Specification
Performance testing was done with fixed loads of 4 and 8 ohms.
The Power was calculated in the Pavg method = ‘RMS’, see reference wiki at;
https://en.wikipedia.org/wiki/Audio_power
After all Modifications, the tests show a better than factory spec is now achieved.
Each Channel was tested for maximum achievable output for less than 0.1% THD, the results of the tests represent the associated Oscillograms below.
At 8 Ohms the Modified AU-7700 produces 64 Watts per channel with less than 0.065% THD
At 4 Ohms the Modified AU-7700 produces 93 Watts per channel with less than 0.85% THD
DC Offset Left Channel = 0.003v
DC Offset Right Channel = 0.0045v
Bias Current Left = 45mv (After 30 mins of operation)
Bias Current Right = 45mv (After 30 mins of operation)
In order to insure reliability, we break in our amplifiers for at least 2 weeks, in this case 30 days.
The amp was ‘burnedin’ using various source material being supplied by a Denon MC (H.O.) Cartridge driving Magnepan speakers (4 ohm). The Maggies are notoriously power hungry and the 7700 drove them with finesse and detail throughout their frequency range to SPL well within the realm of ‘Authenticity’.
Running A/B testing against a stock Yamaha CA-!000, rated at 75 Watts / Channel, was a win for the AU-7700 especially noticed was a better defined low end and very smooth, honest representation, of the source material in general as opposed to a more sterile sound from the Yammie.
The phono section of this amp is very special and a soundstage with much greater depth and definition was observed. There are phono only pre-amps costing twice the asking price of this amp that would get a run for their money against the modified AU-7700.
Every piece we restore has a story to tell us. Of note for this piece is the face plate cosmetics, it is about a 6/10 due to some pitting of the aluminum that is visible in the pictures. The Davies style selector knobs are not original but we found them to be a good fit for the size and style required to maintain the ‘original look’.
Shipped with care, double boxed with custom crate and documentation covering the restoration as well as the Owners Manual
All work guaranteed for 12 months parts and labor, customer pays shipping.
