7001x

[P901]

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

 

[P901]

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)
This had the added benefit of increasing the gain to the Tone Board and then onto the Driver board. This translates to 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.
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. With 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.
An added piece of information, if anyone should happen to blow an AF driver transistor on the Driver Boards, the 2SA706-3.
You will find the 2SA706-3 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

 

[P901]

Internal photo of the "7001X", showing the direct wiring, upgraded power supply caps.
The four colored wires on the Tone Control Board are the direct connections from the Tone Board to the Driver Boards. This is the direct bypass of the High/Low Filter section.
Gain was significantly increased without sending the signal through the filters.
Any change that is needed, (not much with CD`s), is easily accomplished by the Bass/Treble control.
The CD-4 phono section has been removed, unit is used for CD and FM only.

andrew

 

[P901]

Recapped Matrix and Phase control boards.

The most noticeable change after the recap was the increase in clarity and the loss of the "clumsy" steering of the phase control.
Signals now shift from channel to channel in a much more fluid fashion.
Where before some recordings would have the music "pop" or "ping-pong" from channel to channel the effect is now very smooth and blended.
Again, all Panasonic FC electrolytics and P-series polypropylenes used throughout the unit.

andrew

 

[P901]

Recapped Driver Boards.

I have taken in a few of these boards for repair and I have discovered that the AF Driver transistor, the 2SA706-3 rather difficult to locate, cost ~$12 when they are available, probably obsolete for many years.
A readily available substitute is the 2SA1535AR-ND from Digi-key at .96 cents each! Better numbers and the only downside is that the Base and Emitter pins need to be bent to swap places, simple.

andrew

 

[P901]

Recapped Tone Board.

Changing the resistors R-41 through R-44 from 12k ohms to 10k ohms will send more Bass frequency signal current through the section to the Driver Boards.
Richens and deepens the Bass, easy to do, cost about 2.00$
Be aware that Sansui factory silkscreening is in some cases wrong.
For example, on this particular board there were two resistors marked R-42!!
Just follow the schematic to an associated component to insure you have the correct resistor.
(This board also had two transistors marked TR-09 , and of course there is only one).
Note the silkscreened rectangular area to the left end of the board. This is the location of the "Loudness" control. The control has been removed and hard bypassed with jumpers.
Never turned the thing off anyway so why run signal through all those contacts?
andrew

 

[P901]

Photo of the upgraded filter caps.
Original caps were Chemi-con 10000uf 63v.
The replacements are Panasonic AA computer grade, 18000uf 100v.
For the next restoration the Nichicon Muse series 12000uf 100v will be used.
The Panasonic AA`s are very nice but large and they do work the transformer a bit.
(Plenty of steam for the Bass transients though!!).

andrew

 

[proufo]

Hello Andrew.

Lovely work, and very generous of you to share it.

If I got this right, this unit is used only for deriving four channels from stereo sources, right?

I plan to do a clean up of the innards of my SQ-W, to turn it into a much simpler line-in/line-out SQ decoder. Your work is a great guideline and inspiring too.

Thanks again.

 

[P901]

Modified 7001.

See previous posts for additional internal photos.

andrew

 

[P901]

Hello Andrew.

Lovely work, and very generous of you to share it.

If I got this right, this unit is used only for deriving four channels from stereo sources, right?

I plan to do a clean up of the innards of my SQ-W, to turn it into a much simpler line-in/line-out SQ decoder. Your work is a great guideline and inspiring too.

Thanks again.

Good evening proufo !

Yes, this unit has been hard bypassed and locked into the "Synthsizer Surround Mode" only.
I can appreciate your interest in "cleaning" up your SQ unit, and as a confession I must admit to be influenced by some of the "minimalist" approaches to electronics that I have seen on other websites.
A future plan is to build a set of 4 monoblock OpAmps with the Matrix board grafted in to retain the Quadraphonic separation since I do enjoy the effect.
Ultra minimalist amps with only 9 internal components per amp and a total signal path measured in millimeters.

andrew

 

[proufo]

I have taken in a few of these boards for repair and I have discovered that the AF Driver transistor, the 2SA706-3 rather difficult to locate, cost ~$12 when they are available, probably obsolete for many years.
A readily available substitute is the 2SA1535AR-ND from Digi-key at .96 cents each! Better numbers and the only downside is that the Base and Emitter pins need to be bent to swap places, simple.

Hello again Andrew.

The SQ-W has only six transistors outside of the decoder boards. Might be cheap to upgrade. I don't dare to touch the decoder boards.

Are there newer substitutes, with better specs/sound for 2SC900(F) and 2SC828(T)?

Also, both my SQ-W and my 4DD-5 have caps at the line-outputs, 4.7 uF. Is it safe to remove them if the pre-amp line-inputs have caps too? What if the preamp doesn't have caps?

Thanks in advance and sorry for the bother.

 

[proufo]

I plan to do a clean up of the innards of my SQ-W, to turn it into a much simpler line-in/line-out SQ decoder.

Hello to all.

Today I did the first steps towards this. I removed the wiring related to the 4-ch discrete input, the tape monitor circuit, and some others. The plan is to have an SQ decoder, with two line outputs and four line outputs and no more.

Some curious things about the SQ-W:

1) The rear channels both is SQ mode and in 4-ch discrete mode (external) are attenuated. In the user manual Lafayette suggests the rear speakers to be placed to the side and a little to the back, just like in current 5.1 arrangements.

2) There are four resistors right our of the function selector that are not in the board, but in series with point to point wiring. This may indicate that at one point they intended to put level controls. As it will have the space formerly occupied by the volume control and the function selector, I plan to put a pair of stereo pots for front and rear level.

Next step is to remove the volume pots and the function selector.

Regards.

Note: I have the choice of removing the volume pots leaving the connection open, or shorting the connection and getting a second line-level output with inverse phase relative to the other. What would you do?

 

[P901]

Hello to all.


Good evening Mr. Roufogalis,

In response to your question regarding the removal of the 4.7uf caps.

Without the schematic of your particular units in hand it would be difficult for me to express an opinion.
I could suggest that you set up the unit(s) on your work bench with a reference source and speakers and try removing the caps or changing their values. Of course with a schematic I can basically predict which direction any change I make will go, the test is to see how much of a change and if it has shifted in a direction I like.
It is safe enough to shift the values of some of these components in the signal path as long as your unit has a good protector circuit as these Sansui units do.
Regarding your question on the transistors.
What I do is go to a website, for example, American Semiconductors, do a search and find the operating parameter numbers for the original transistor and then find one in the Digi-Key catalogue that has better numbers.
Working voltage, inverse voltage, current carrying capacity and very important, slew rate. Higher voltage per second on the slew rate basically means a faster "action" on the semiconductor.
Sometimes you are lucky to find one that has the same pin out configuration but it is not too much trouble to carefully bend the pins into the required place.

andrew

 

[proufo]

In response to your question regarding the removal of the 4.7uf caps.

Without the schematic of your particular units in hand it would be difficult for me to express an opinion.
I could suggest that you set up the unit(s) on your work bench with a reference source and speakers and try removing the caps or changing their values. Of course with a schematic I can basically predict which direction any change I make will go, the test is to see how much of a change and if it has shifted in a direction I like.
It is safe enough to shift the values of some of these components in the signal path as long as your unit has a good protector circuit as these Sansui units do.
Regarding your question on the transistors.
What I do is go to a website, for example, American Semiconductors, do a search and find the operating parameter numbers for the original transistor and then find one in the Digi-Key catalogue that has better numbers.
Working voltage, inverse voltage, current carrying capacity and very important, slew rate. Higher voltage per second on the slew rate basically means a faster "action" on the semiconductor.
Sometimes you are lucky to find one that has the same pin out configuration but it is not too much trouble to carefully bend the pins into the required place.

andrew

Thanks Andrew for the additional tips.

I removed a lot of wiring from my SQ-W and my 4DD-5 during the weekend. Tomorrow I'll go to an acquaintace's to use his suction desolder to remove more superfluous components from both.

Best regards and thanks again.

 

[P901]

Good evening Mr. Roufougalis,

If you have the ability and time to do so would you mind posting a picture of your work with a short outline of the modifications and components chosen?
I think it would be helpful to other members who may wish to embark on this segment of the pastime.
Thanks, andrew

 

[proufo]

Good evening Mr. Roufougalis,

If you have the ability and time to do so would you mind posting a picture of your work with a short outline of the modifications and components chosen?
I think it would be helpful to other members who may wish to embark on this segment of the pastime.
Thanks, andrew

Hello Andrew.

Sure I will. Sadly I don't have a digital camera so I was not able to photograph the work done when the gumption rush hit, prompted by your mod.

But I will post eventually what I can re pictures, and a full description.

BTW, is there a place in the forum to host this?

Best regards.

 

[P901]

Good evening,

Regarding the place to "host" this type of discussion, all I can say is that I contacted Jon, the moderator, when I wanted to post my photos and he moved my posts to the hardware segment of the forum.

Jon was also quite helpful in "resizing" my photos to the required file size.
Try as I might I could not reduce them to fit within the necessary limits.

Hope this helps. I am interested in modifications and simplifications to circuitry. Suppose it goes back to some philosophical ideal of locating the "essence" of these units.

I did put forth the question a few months ago regarding the often seen phrase, "warm Sansui sound". I was looking to engage a discussion of suitably experienced people in trying to determine the actual reason for the particular qualities of the sound produced by the Sansui gear. Was it the style of circuit architecture, a unique chemistry utilized in the production of the capacitors, or the wide thick copper band that wraps the core of the heavy iron transformer ?
During the modification of the 7001X the goal was to remove every component that was not necessary to play a CD or engage the FM radio.
Then the introduction of fresh caps, electrolytic and poly`s probably had the effect of bringing the original circuit architecture as close to the intended ideal of the factory engineers.
Of course much discussion is made on other forums regarding the sonic qualities of different caps, speakers, power cords, pure DC battery power supplies, etc. that it might be difficult to put your finger on one particular feature of the Sansui that makes the sound so many people prefer.
Looking forward to the photos of your work.
Take care, andrew

 

[proufo]

Hello to all.

I'm making the parts list for the recapping of my 4DD-5.

I wonder if Panasonic FC Series capacitors qualify as low-leakage. There are several orange-color caps in the demod that need to be LL.

Maybe all current caps are low-leakage.

Thanks in advance.

 

[Scottmoose]

Good evening,

Regarding the place to "host" this type of discussion, all I can say is that I contacted Jon, the moderator, when I wanted to post my photos and he moved my posts to the hardware segment of the forum.

Jon was also quite helpful in "resizing" my photos to the required file size.
Try as I might I could not reduce them to fit within the necessary limits.

Hope this helps. I am interested in modifications and simplifications to circuitry. Suppose it goes back to some philosophical ideal of locating the "essence" of these units.

I did put forth the question a few months ago regarding the often seen phrase, "warm Sansui sound". I was looking to engage a discussion of suitably experienced people in trying to determine the actual reason for the particular qualities of the sound produced by the Sansui gear. Was it the style of circuit architecture, a unique chemistry utilized in the production of the capacitors, or the wide thick copper band that wraps the core of the heavy iron transformer ?
During the modification of the 7001X the goal was to remove every component that was not necessary to play a CD or engage the FM radio.
Then the introduction of fresh caps, electrolytic and poly`s probably had the effect of bringing the original circuit architecture as close to the intended ideal of the factory engineers.
Of course much discussion is made on other forums regarding the sonic qualities of different caps, speakers, power cords, pure DC battery power supplies, etc. that it might be difficult to put your finger on one particular feature of the Sansui that makes the sound so many people prefer.
Looking forward to the photos of your work.
Take care, andrew

My bet is that it's the transformers that produce that effect. Circuit topography, components like caps and the signal processing of the x01 series all have a role, but in the case of equipment like this, it'll be the transformer that has the greatest overall infulence upon the style of sound produced. Especially as this characteristic seems to hold true across the Sansui range, be it stereo or quad amp / reciever.
For eg., valves are often described as 'warm, smooth, slow' etc. They aren't necessarily any of these things, and it isn't the valves that produce this effect in some of the less-well engineered amps of that kind, but poor output transformers. Others can make a Naim cower for mercy, because they have properly wound and designed transformers in their output stage, and these by definition have a similar effect upon solid-state -something which in my view many manufactuerers of solid-state amps have either ignored or have forgotten for far too long.
Other thoughts?
Scott