Acurus A250 and starground

mondialfan said:
modern On-semi clones of those Toshiba parts called MJL1302/MJL3281. Some people have said they think the On-Semi parts sound better than the Toshiba's.
Click to expand...

Not to interrupt.. I do like the sound of the original once.
Just curious; have you ever heard the On-semi, Mondialfan?? I've never heard them...
 
I am just trying to learn so i did not know how to do it properly. There is a1/2 inch gap by C2 and the heatsink i used the solder iron and pull each leg of the C2 at a time then place the other one in and solder it in. Maybe it was bridged but i don't think solder iron was dropped in to the board.
 
Thanks.... It plays absolutely fantastic. I think the guy who measured it made some mistakes, course both channels sounds great to my ears?!
The THD+N is also lower then published..! It has come to my knowledge that he measured my Acurus A250 with signals through his preamp!
:eek2:
 
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KNielsen said:
Thanks.... It plays absolutely fantastic. I think the guy who measured it made some mistakes, course both channels sounds great to my ears?!
The THD+N is also lower then published.. actually at least 0.07% lower! It has come to my knowledge that he measured my Acurus A250 with signals from his preamp!
:eek2:
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What mica film size did you use for the output transistors? Could you give me a link Thank you
 
KNielsen said:
Not to interrupt.. I do like the sound of the original once.
Just curious; have you ever heard the On-semi, Mondialfan?? I've never heard them...
Click to expand...

I have heard the On-Semi devices but couldn't tell a distinct difference. Maybe my old ears are not sensitive enough.
 
IMG_20190224_142939.jpg

Been fixing left channel today that did show some odd figures on the scope.

To be honest, I can't hear any difference after I swapped C13/14 that I thought was faulty.. and they wasn't (a multimeter showed perfect 220pf on both the old micas that I pulled out today!) Also rechecked every component again for the x20 time, also passed to the mV!

Until I find someone who could measure this amplifier again (I cannot reach the guy who did the first test), I'll have to live with the sound I got now and say to myself that everything I just fine..
course it sounds absolutely amazing!!:beerchug:

I do think it's because he did these test without a dummy load that we see these figures. - And forgot to do a matching test on right channel so we could establish if it were so.. mistakes can happen, I'm just glad he wanted to help when I needed it:)

Regards
 
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BTW: flicker led...

Is there any way to restore the led in the power switch?

Both my A250's flicker. The modded one isn't that bad right now, but it'll come..

I have been able to take the switch apart, no problem, but didn't know what to order (led replacement ect...)

Thanks
 
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KNielsen said:
BTW: flicker led...

Is there any way to restore the led in the power switch?

Both my A250's flicker. The modded one isn't that bad right now, but it'll come..

I have been able to take the switch apart, no problem, but didn't know what to order (led replacement ect...)

Thanks
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You can swap out the original neon lamp inside of the switch for a T1 LED however you must disconnect the power to the lamp from the mains AC and feed it off the transformer secondaries. I remove the original lamp and resistor from the switch and install just the LED inside of the switch. A new wire harness with a half wave rectification circuit should be used to feed the LED power from the transformer secondaries. I usually integrate a 1n4004 diode and a current limiting resistor into the new wire harness that powers the LED. I do this for all of the Gen 1 Acurus amps that I work on.
 
So.... Finally! I can officially tell that this amplifier is finished.

Left channel is fixed.

At 1khz we weren't able to separate the testcurve form the amplifiercurve on the scope. So job done! :)

At 10khz the impulsecurve started to show on the scope, but it were in such a matter that it really is nothing:beerchug::banana:

Rais/fall time approx ~900ns on both channels.

Cheers and thanks for all the help. This thread has been a great support throughout and all the way! Thanks

NB: I sold my Dali Diva and bought a pair of Sonus Faber Venere 3.0 today. Hope they arrive pretty soon:p
 
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KNielsen said:
I would suggest as minimum a Dim Bulp Tester as Mondialfan mentioned when powering up first time :)
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Hi everyone
I got my A250 working again I’m hooking it in the DBT with 100w light bulb when I turn the volume louder the light bulb get brighter is it normal or something is not right?
 
The DBT is just for initial testing. Do not connect a preamp or signal to the amp while connected to the DBT. Once you've verified that the bulb dims after starting the amp with no signal and you have minimal DC offset on the outputs then you're ready to take it off the DBT and set the DC bias then give it a test with either an analyzer or connect it to a set of "test" speakers. I say test speakers because I'd not connect it right away to my expensive speakers just in case something goes wrong. Let it play on the test speakers for a period of time and then you're ready to move it into your listening area.
 
Thank you Mondialfan
I put the R20 of 10k ohm in as on the schematic shown and the DBT was bright then i measured the R20 in the working channel it showed 1k ohm so i replaced R20 with 1k ohm and the DBT was not bright up what value should be used and would you please show me how to measure and set DC bias thank you for helping.
 
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