Sansui TU-9900 Resistors upgrade


Nounours Nounours <nounours18200@...>
 

Hi,
I read in the Sansui TU-9900 section of FMTunerInfo.com that "The factory resistors should be construed as much less than optimal, in a lot of performance areas. Those KOA/Speer SP series are very, very nice as replacements, even on the audio side."
Does this means that the author recommends to use the KOA SP serie (nowdays replaced by the SPR serie if I am correct) instead of the KOA Metal Film resistors ? 

I ask this question because most of the time, people recommend Metal Film instead of Carbon resistors...

Thank you for your reply,


John Carpanini
 

Hi NounoursX2,

 The salient point of the observation was that IMO & based on having done 3 9900s the OEM resistors were all to often out of spec.  The power supply was particularly problematic, heat maybe??.  The KOA SPR series work very well in that application, are very quiet and were designed to be used in a power circuit.  The fact that they are also pretty good in the signal path was just the cherry on top.

When using metal films, & given my druthers i try to use the Vishay/Dale CMF series in the signal path. These are literally MilSpec parts without the MilSpec markings.  Lately I've been playing with the Vishay Beyschlag  MBA/SMA 0204, MBB/SMA 0207, MBE/SMA 0414 - Professional series which seem quite nice. I feel that there is a slight difference in SQ between the CF & MF resistors.

If you want to see some pictures, Look here:

https://groups.io/g/FMtuners/photosearch?p=created%2C%2C%2C20%2C2%2C0%2C0&q=tu+9900

There's some good shots of the PS and the rest of the boards.  Have Fun,

Regards
JohnC


Radu Bogdan Dicher
 

John,
I second your choice of Vishay CMF/RN resistors. Have not tried the Beyschlags, though from a quick glance over at Mouser, they seem extremely inexpensive, even in high precision flavor. 

Technically, it seems the RN/RL is the mil-spec version of the CMF (which is "global/industrial" type), though I agree - they're likely the exact same resistor inside with different scribbles on them. When "mil-spec'd," they seem to derate them to lower handled power at a given temperature (though not on the same sheet, so I'm not very sure what that's about). 

I did notice though, at least at Mouser, I tend to find the RN cheaper than the CMF for a given value. They have the added nuisance of the weird value markings, but once you get used to the aspect, no biggie. The CMFs typically have very normal, spelled out values with no coding whatsoever, so that's just a bit easier on the eyes. 

I personally prefer any alphanumeric markings to color coding any day of the week. 

Radu.  

Virus-free. www.avg.com


On Mon, May 3, 2021 at 5:57 PM John Carpanini <jacarp@...> wrote:
Hi NounoursX2,

 The salient point of the observation was that IMO & based on having done 3 9900s the OEM resistors were all to often out of spec.  The power supply was particularly problematic, heat maybe??.  The KOA SPR series work very well in that application, are very quiet and were designed to be used in a power circuit.  The fact that they are also pretty good in the signal path was just the cherry on top.

When using metal films, & given my druthers i try to use the Vishay/Dale CMF series in the signal path. These are literally MilSpec parts without the MilSpec markings.  Lately I've been playing with the Vishay Beyschlag  MBA/SMA 0204, MBB/SMA 0207, MBE/SMA 0414 - Professional series which seem quite nice. I feel that there is a slight difference in SQ between the CF & MF resistors.

If you want to see some pictures, Look here:

https://groups.io/g/FMtuners/photosearch?p=created%2C%2C%2C20%2C2%2C0%2C0&q=tu+9900

There's some good shots of the PS and the rest of the boards.  Have Fun,

Regards
JohnC


John Carpanini
 

On Mon, May 3, 2021 at 10:28 PM, Radu Bogdan Dicher wrote:
the RN/RL is the mil-spec version of the CMF (which is "global/industrial" type), though I agree - they're likely the exact same resistor inside with different scribbles on them. When "mil-spec'd," they seem to derate them to lower handled power at a given temperature (though not on the same sheet, so I'm not very sure what that's about). 
 
Hi Radu,

Not to belabor the issue but they are indeed identical except for the marking.  That fact is even documented on the CMF Industrial datasheet "Notes" section, quoted below:

" (Except for marking, the Industrial and Military versions are exactly the same)."

Regards
JohnC


Nounours Nounours <nounours18200@...>
 

I have  made a lot of work on the TU-9900, look at my restoration work here: https://www.threshold-lovers.com/2019/02/07/sansui-tu-9900/ and use the bottom right "Translate" button to get it in English.

I have changed all the resistors in the Power Supply: I had used the TAKMAN Metal resistors and made all the other upgrades recommended by FMTunerinfo on this P.S. board.

The resistors on the FM board F-2524 have also been replaced by TAKMAN Metal resistors, known to be excellent.

My question relates more on the SQ difference between Carbon resistors and Metal Film resistors: what kind to you prefer in the P.S. locations and in the Signal locations ?

@John Carpanini:
I see on your photos that you have also changed the TA7136P operational amps: this is an upgrade that I still have to do. I already have designed and received the PCB adaptors , exactly the same than yours with a place for a capacitor (47µF probably).
Have you used the OPA604 or another Opamp ? and more important are there any surrouding parts that need to be replaced in order to use perform this opamp upgrade  ?