Stax DA300

[thinkbad]

Hi

Is this circuit worth cloning ?
- or is it waste of time and money...

Comments please

cheers
JB

[thinkbad]

- 150W classA, good at driving electrostatics, what`s wrong with that...?

JB

[jacco vermeulen]

Try to really get 150 watts in class A out of that, it probably runs in A up to 50 watts or less.
Nothing wrong with cloning, unless you have the cash to clone a Stax DMA-X model, those were amazing.

[Mark A. Gulbrandsen]

Some Stax stuff was really nice stuff but I fear that most of the selling price was wrapprd up in the chassis they used as they were quite fancy.

Thanks for the schematic!! What was the rail voltage on this amp? And is this the complete schematic? I find the lack of output inductor interesting if this is the whole schematic. The outputs are very old stuff and the amp might work and sound alot better with newer devices in it.

Mark

[jacco vermeulen]

That is if the other part of the schematic is available too: the source of the feedback is missing in the diagram.

[thinkbad]

Rail voltage is +/- 90v, I know the transistors is obsolete but if the basic circuit is worth it one could use newer/better types.

A British amp maker claimed 70% of the manufacturing cost did go to chassis, big cooling fins and thick faceplates, otherwise customers refused to buy it !

JB

[jacco vermeulen]

Actually, the big succes numbers were the DA models, like the DA-50M and DA-100M.
Which were kinda small, as they employed heat pipes for cooling the output stage.

The big critters were the X1 and X2 models, of which i gathered very few have been sold.
In their price range the X2 has an outfit that is of the same standard as its competitors.
The X1 looked like a server computer, and imo not in accordance to what it cost. The insides were though.
I've only seen the X1, on sale in one of the fancy French audio palaces, not able to judge its qualities.
The X2 i did both see in the flesh, and heard it in action on Martin Logal CLS's.
The DA300 is from the early 70s, never seen one, but the stories are that it did have bragging rights when it comes to driving electrostats.
Even on ESL63s, which, for 70s and early 80s amplifiers, makes it prime beef. Krell KSA50 and KSA100 are also supposed to be members of that list.

Are you sure about that 90 volts ? Not peak to peak ?
Half would be nearly enough for the 150/8 of the Stax.
And 90 volts is way too high for the kind of output devices, the 2SA747 certainly is not up to rail voltages of such magnitude in a pushpull output stage. The circuit even has the Hfe number of some of the devices mentioned, as the output devices do not they must be low voltage types.

[Mark A. Gulbrandsen]

Here is the data for the outputs... Pretty old stuff and should be improved upon in a clone. I agree with Jacco that the rails were probably about half the devies ratings. They would not be very reliable at 90 volts!! I coulodn't read is the NPN'swere 2SC 1116 or 1118 on the photo so I posted the 1116.

2SA747: PNP / 120V / 10A / 100W / 15MHz

2SC1116: NPN 180V / 10A/ / 100W / 10MHz

Mark

[amplifierguru]

Hi Thinkbad,

It's rather ho-hum... nothing special. Nice FET cascode front end then downhill to a heavily slugged cascode Vas which will have characteristically poor +ve supply rejection, and then to matched multiple bipolar EF outputs. Itwould need to run Class A so your not listening to +ve supply AB commutation artefacts.

An expensive exercise and waste of power for little or no benefit- it's a dinosaur & should be left extinct.

Cheers,
Greg

[jacco vermeulen]

C104 is a 100V capacitor, between + and - rail ( top left corner)

For ugly picture lovers :