hafler 9300 transnova

[sakis]

here we go ....

hafler transova 9300 come in to my shop for a visit... problem was that one channel brakes down when the amp is hot works ok when cold

4 transistors per board inside 2xMPSA06 plus 2xMPSA56 exist inside per channel that actually overheat ....a bit .... noticed that this hafler is export version , more than ten years old, just about enough old when the voltage changed in europe from 220 to 240 volts .

many companies thought that will get away with it simply adding a sticker on the rear saying 240 volt

i cleaned up all the old ( boiled soldering ) cleaned up boards and then i thought to add a small heatsink for all 8 transistors of the amplifier .

it appears to work pefectly but please if there is any other suggestion i will be more than happy to listen since all the transitors are working but produce quiet a lot of heat for such a small device .

( finally the amp plays really fine but together with the 945 series tuner/preamlifier the result is very dissapointing , though the 945 preamp offers a hell of a lot of features but the sound result is almost poor especially if more than one active source is present in the preamp .... )

kind regards sakis

[sakis]

that is strange ...i thought that this post should be full of sugestions ...where is everybody ???

[kipman725]

did they actualy change the voltage? here in the uk we "changed" from 240VAC down to 230VAC but if you mesure the voltage at the wall it's still 240V. The tolerence is such that they just improved the regulation of the 240V to remain within the specified range.

[Enzo]

Link a schematic. I don;t see one on the Hafler site.

[eyoung]

Ditto... link us up a schematic, in the mean time use a variac and reduce the mains to spec... I do not think this will make a difference, it will give you a chance to check voltages on the board and to set bias at proper voltage.
keep on keeping on...

Regards, Elwood

[pliedtka]

I hope this helps

[pliedtka]

I sorry I can not help other way. I never got to listen to one of these, or see the insides, so I can't say what to expect from them.
Good luck...

[sakis]

been there allready ....al voltages except 24+24 volt coming from regulators are 7-10% up so this is an amplifier with sticker ( he he )

eventhough the trick with the heat sinks appears to operate very nicelly after the second day of tests i will also consider one click less bias ...

will see

thank you all for your time

[sakis]

the hafler is originally biassed at 260ma fairly ok id say ....lower it down to 210 ma stil the poor transitors are getting hot .... i dont see anything else damaged though i will check once more tomorow

looking from the past and the marks left on board from the transitors it seems that they been operating like that all life ...

i am going to keep watching and we will se

[Enzo]

Does the output stage bias really affect the current through those little MPSA's?

What current is flowing through THEM, that is what voltage is dropping across those 47 ohm resistors?

My eye was first drawn to the 2N7000. They fail a lot in certain guitar amps. If yours is getting leaky, might it not pull the bases of the MPSAs towards each other, turning them on harder?

Do both channels overheat similarly?

At proper idle spec, does crossover look good?