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Acurus A250 and starground

My first post, just changed the original 23,000mfd 85vdc caps to Klement 36,000mfd 100vdc caps, and now have 85.5-85.6 volts on both rails. Checked for dc at the speaker terminals and I have 3.4mv on the left channel, 45mv on the right channel. The amp was working fine before changing caps, I did not check for dc before changing them - my bad. I have a schematic but no volt/ohm test points or chart, any help or pointers would be appreciated.
 
Nothing sounds out of the ordinary there....
3.4mV and 45mV of DC offset are within tolerance. 45mV is getting a touch on the high side, but is still acceptable. This offset is almost certainly unchanged even with the primary capacitor replacement.

Is this an A200?
 
mondialfan said:
Nothing sounds out of the ordinary there....
3.4mV and 45mV of DC offset are within tolerance. 45mV is getting a touch on the high side, but is still acceptable. This offset is almost certainly unchanged even with the primary capacitor replacement.

Is this an A200?
Click to expand...
Just curious, why A200 like you ask?

Regards
 
Spend approx 4 hours on this one today..... The chassis was made earlier this week, only the heatsinks were cleaned today and started soldering the PCB's.
Only thing missing is the silver mica's and the added decoupling caps.

Sun is shining in Denmark, so better get outside while I have the chance:)

Pics are shown as I progressed.

IMG_20200530_112452.jpg IMG_20200530_120840.jpg IMG_20200530_145821_Bokeh.jpg
 
mondialfan said:
The finished amp looks great. Nice work!
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Thanks. To be honest, it's an awful lot of work and I think the 2x36.000uf combo comes pretty close to this build, except for bette left/right separation on this one (to my ears that is)...
Anyway all went well and turned out pretty good.
 
Listening to my A200 (Gen2) again this evening... I'd better get my PCB-build finished for my A250.. The sound from the A200 is far more balanced, a such good potential. Sounds good
 
I have an amplifier where the left channel reads roughly 3mV on all NPN emitters and two PNP reads 3mV, but the last two reads 6mV!??
There are new insulation pads and thermal paste.

The amp haven't been hooked up to speakers yet, just measuring at startup. DC-offset is fine at 10mV

All emitters are .5ohm spot on.
Is this a sign of two possible bad PNP powertransistors?
It's normal with a bit of variation throughout the powertransistors, but I think a 3mV jump on the emitters is a bit more then I normally read

Regards
 
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Really hard to say. Possibly abnormally low Vbe on those transistors. It is also very likely that your meter is not that accurate at extremely low resistances < 1ohm.

For a quick test try turning the bias up to say 15 - 20mV and see how large of a difference exists at that setting. Is it still 3 - 4 mV? If so I wouldn't worry about it. If the difference gets much larger then you may want to look into it. Don't leave the bias at that high setting or else your amp will overheat.
 
mondialfan said:
Really hard to say. Possibly abnormally low Vbe on those transistors. It is also very likely that your meter is not that accurate at extremely low resistances < 1ohm.

For a quick test try turning the bias up to say 15 - 20mV and see how large of a difference exists at that setting. Is it still 3 - 4 mV? If so I wouldn't worry about it. If the difference gets much larger then you may want to look into it. Don't leave the bias at that high setting or else your amp will overheat.
Click to expand...
The amp has been hooked up and played quite hard. New readings surgest that it's not an issue, as BIAS claimed equally on all transistors, still with a 3mV difference. No issues with heat and DC is rock steady. I'll leave it for now
 
I hate to be the naysayer, but I see some equipment for sale that says "New in Box" and if they actually show pictures of the unit its typically anything but new. In fact most of the time it's well used, scratches, dings, etc. I'd be surprised if this was actually new and unused.
 
It's quite here. Still working with Acurus, so just posting a pic while desoldering components on two amps I'm working on. Both in for a psudo-dual-mono makeover.
I've done quite a few A250's so far and more one it's way. Still looking forward to my first meeting with a A150 or DIA-model. They are just not that popular in Denmark and rarely on the usedmarked here..
IMG_20200812_205344.jpg
Regards
 
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