Arcus Finest Class Amp 200

jlithen

Member
2009-11-20 8:57 pm
Vaasa
Hi all.

Thought I would share this amplifier project with all of you.
I just bought this beautiful integrated amp from a friend.

I was amazed by the number of inputs and amount of functions. Graphical display is nice, but of course gives the amp more of a blingbling look.

Sound wise it sounded bad. A bit harsh and not very detailed.
Then i noticed that it did not get warm at all.
So I opened it up and confirmed bias to be 0. Class B :)
Also distortion was several hundredths of a percent (odd harmonics measured) and I believe spec is 0.002%

I changed the 2.7k resistor next to the bias compensation transistor for a 10k pot and at slightly above 5kohm I had 18mA of bias and good distortion values. I then changed the pot back to a fixed resistor to increase reliability.

I did not yet listen to it. Now it warms up slightly. Bias is very stable. I have loaded amp for hours with 1W, it heats up but bias does not increase.

Amp is from early 2000s I think?
I e-mailed Arcus about this, but did not get any reply.
It is obviously made in Asia. Quite cheap capacitors et.c...but they have managed to pack a lot of amplifier in a slim and good looking enclosure.
I also measured all capacitors on power amp boards to be in good condition. One bad solder joint I had to fix.

Any one else have one and can confirm if it has (or has had) the same issue?
I believe bias pot missing is not a mistake, but do other amp 200's have some bias anyway?
Having to double the 2.7k resistor means many units may be operating in class-B. Of course a different set of transistors can work with different resistor values.

When my listening room is in order again I will do some serious listening and then probably sell the amp. I have too many anyway :)

Photos show left channel with trimmer and right channel with original resistor.
Measurement results speak for them selves.

You can find complete photos of the inside easily by googling or then ask me to take and upload some.
 

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