P901
Member
After repeated individual requests for information this is a post to outline the modifications to the "7001X" ( for experimental).
This unit has had all the phono sections removed.
Circuitry is locked into Synthesizer Surround with all unused associated switching and wiring removed.
(Much of the original 28ga stranded factory wiring has been replaced with 18ga solid copper done in a squared off point to point style, photo will follow).
(The circuit path through all the selector switches was quite convoluted, no doubt causing some degree of loss).
High/Low Filter section removed with the Matrix Board 4 channel output wiring directly connected to the Tone Board section, (through the necessary remaining 10k resistor and a .1uf Poly inserted in the line to extend the Bass)
This had the added benefit of increasing the gain to the Tone Board (pre-amp) and then onto the Driver board. This translates to quite noticeably increased power output.
Unit has been completely recapped with Panasonic FC series electrolytics, and all original polyester or mylar caps have been replaced with Panasonic P-series Polypropylenes.
Decided against the extra expense of "audiophile" grade caps such as Nichicon Muse Series or Auricaps since the ESR numbers etc. were so close as to not have realistic net resolution value with the vintage Sansui circuit topology.
(I know, I know, every absolute statement can be debated).
Resistors R-41 through R-44 on the Tone Control Board were changed from 12k to 10k which allows more Bass signal to pass through the Bass control caps. Can you say warm Sansui sound? In concert with the original vintage Sansui factory wound iron core transformer rather than a generic toroidal transformer as Sansui started to do with some of their later units. With lovely rich deep tight thunderous Bass and more than enough mid/high having never been lost.
Power supply caps were upgraded to Panasonic AA-series computer grade caps from the original Chemi-Con 63v 10000us to 100v 18000uf.
The residual AC ripple went from 180mvac with the Chemi-cons to 9mvac with the Panasonic AA`s !! (To be fair the Chemi-cons were 25 years old but a set of fresh Panasonic Industrial Grade caps of equivalent numbers yielded 125mvac. These were finally swapped out for the AA`s.
However the next unit I do may use the Nichincon Muse KZ`s. Same price but (just about insignificant) better numbers.
An added piece of information, if anyone should happen to blow an Audio Frequency driver transistor on the Driver Boards, the 2SA706-3.
You will find the 2SA-706-3 a bit hard to find since they have been obsolete for quite a while and they now run about 12$ apiece !!!
An upgrade substitute is the 2SA1535AR-ND from Digi-Key at about 97 cents each !! Better numbers. The only downside is that two of the pins need to be carefully bent to transpose the Base and Emitter. Takes about 2 seconds and slip a piece of 3mm heat shrink over one of the pins.
Amplifier case is powdercoated Satin Black, dial lamps have been coated with dark green lamp lacquer to mellow the glow. The "4" indicator has had a halogen lamp with a quarter watt more power to make is stand out.
Photos of the finished unit and internal modifications will follow.
andrew
This unit has had all the phono sections removed.
Circuitry is locked into Synthesizer Surround with all unused associated switching and wiring removed.
(Much of the original 28ga stranded factory wiring has been replaced with 18ga solid copper done in a squared off point to point style, photo will follow).
(The circuit path through all the selector switches was quite convoluted, no doubt causing some degree of loss).
High/Low Filter section removed with the Matrix Board 4 channel output wiring directly connected to the Tone Board section, (through the necessary remaining 10k resistor and a .1uf Poly inserted in the line to extend the Bass)
This had the added benefit of increasing the gain to the Tone Board (pre-amp) and then onto the Driver board. This translates to quite noticeably increased power output.
Unit has been completely recapped with Panasonic FC series electrolytics, and all original polyester or mylar caps have been replaced with Panasonic P-series Polypropylenes.
Decided against the extra expense of "audiophile" grade caps such as Nichicon Muse Series or Auricaps since the ESR numbers etc. were so close as to not have realistic net resolution value with the vintage Sansui circuit topology.
(I know, I know, every absolute statement can be debated).
Resistors R-41 through R-44 on the Tone Control Board were changed from 12k to 10k which allows more Bass signal to pass through the Bass control caps. Can you say warm Sansui sound? In concert with the original vintage Sansui factory wound iron core transformer rather than a generic toroidal transformer as Sansui started to do with some of their later units. With lovely rich deep tight thunderous Bass and more than enough mid/high having never been lost.
Power supply caps were upgraded to Panasonic AA-series computer grade caps from the original Chemi-Con 63v 10000us to 100v 18000uf.
The residual AC ripple went from 180mvac with the Chemi-cons to 9mvac with the Panasonic AA`s !! (To be fair the Chemi-cons were 25 years old but a set of fresh Panasonic Industrial Grade caps of equivalent numbers yielded 125mvac. These were finally swapped out for the AA`s.
However the next unit I do may use the Nichincon Muse KZ`s. Same price but (just about insignificant) better numbers.
An added piece of information, if anyone should happen to blow an Audio Frequency driver transistor on the Driver Boards, the 2SA706-3.
You will find the 2SA-706-3 a bit hard to find since they have been obsolete for quite a while and they now run about 12$ apiece !!!
An upgrade substitute is the 2SA1535AR-ND from Digi-Key at about 97 cents each !! Better numbers. The only downside is that two of the pins need to be carefully bent to transpose the Base and Emitter. Takes about 2 seconds and slip a piece of 3mm heat shrink over one of the pins.
Amplifier case is powdercoated Satin Black, dial lamps have been coated with dark green lamp lacquer to mellow the glow. The "4" indicator has had a halogen lamp with a quarter watt more power to make is stand out.
Photos of the finished unit and internal modifications will follow.
andrew