DIAMOND DIFFERENTIAL INPUT POWER AMPLIFIER EBay kit

[janusz]

This is very true, Forr,

This particular amp has two patents (self regulating VAS current and something else if I remember correctly) but the drawback was that this amp (and possibly other Sansui amps as well) operated on the verge of stability. I never had any Sansui equipment and I am not really familiar with their designs. Simply when I saw this kit on EBay I decided to check the net for similar designs before deciding whether to buy it or not and found this Sansui.

cheers,

 

[carlmart]

I'm looking forward the assembly of this kit. It looks very interesting.

Perhaps a DC servo might allow eliminating the NFB capacitor.

 

[Dave S]

There is no NFB cap. Matched JFET input and trimming is used instead of a servo.

 

[carlmart]

There is no NFB cap. Matched JFET input and trimming is used instead of a servo.

Yes, there is an NFB cap, from RF2/1K to ground. No value is specified though.

Matching N and P JFets at the input might be a serious problem to accomplish a stable, no-DC output.

In any case, if you have DC protection might be worth trying.

 

[forr]

Hi Janusz,
I you can afford some Sansui vintage, you may like it. They were well built and very nice to look at. For example, I love my tuner TU555 (excellent sound too), here are some pictures
sansui tu555 - Recherche Google

 

[janusz]

Attention,
the most recent simulation with Beta24 of the DDInput amp showed that R16=220 with W2 and R28 out of the circuit. Or R16 in parallel with W2 and R28 should be set to 220.

Has anyone already finished building this amp?

cheers,

 

[tvi]

The Real Sansui still exists but only in Japan they sold the name in all the other territories.

sansui-jpn

 

[marchel]

I 'm interested with this amp too, Waiting for your results.

 

[carlmart]

It's now 40 days since this topic started. Has anyone got to any results with the kit?

Does anyone know which commercial amp this project clones? It was established it's not the Sansui. So what is it?

 

[poler]

We all know Sansui is good; however we are more interested in this kit, has anyone tested it? how does it sound?

 

[carlmart]

This topic doesn't seem to go forward.

No assemblers yet?

 

[carlmart]

I got into the game and bought this kit.

Will make some mods to it, hopefully to improve it.

Now let's wait for the kit to arrive.

 

[dinamic1]

At last.🙂...the amp is finished....sounds great...had some problems with fake devices..sorry for the delay.

 

[breweryfr]

Hi dinamic1,

After all, do you recommend Tubehunter for his kit ?
You mentioned fake devices, could you give us more details ?

 

[janusz]

Hi,

The same question as above - which parts were fakes?
Very nice looking case.
Hve you done any measurements on it? What offset do you have and what bias?

cheers,

 

[dinamic1]

Fakes were output devices (ON-Semi NJW3281...)...the emitter resistors bad quality too...once replaced the unit works fine..two buyers are available: Tubeshunter and Jimsaudio..Tubeshunter don´t send any information..and the boards are different too from different suppliers...Good luck.

 

[janusz]

How did you find out they were fakes? Did you check Hfe at high currents? I have tested hfe at currents from 10uA to 20mA and these which I got were pretty linear. Did not test them at higher currents.
Where did you get quality non-inductive resistors?
cheers,

 

[dinamic1]

Well,first of all most of devices from ebay are fake...this is well known..mine exploded litterally with only 50V. per rail..sent photos to On-semi and they confirm this ones were fakes.
My resistors are buyed from an ebay supplyer.

 

[dinamic1]

Janusz l forgot to answer your questions about measurements..dc offset about 2mv..bias 1omv across 0.22ohm resistors..

 

[john curl]

It is a little on the low side. 15-22mV is usually optimum, IF the heatsink can support it.