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Old 29th March 2011, 08:45 AM   #21
amc184 is offline amc184  New Zealand
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I repaired an Arcam Alpha 1 integrated amp a while ago, these are almost identical to the Alpha 2 except for the case. One thing I came across is that if you remove or cut the two long wire links on the PCB that connect the pre-amp section to the power-amp section the input to the power-amp is left floating. The floating input will result in a high DC output. When you have the two separated you should temporarily solder a resistor between the power-amp input and ground.
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Old 29th March 2011, 08:59 AM   #22
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@jaycee:
I only tested for oscillation after powering up and not during - my bad. And you're right of course, something still seems to be amiss! On BOTH channels - this is SOOOO confusing!

I've owned this Amp from new from 1988. I would go along with ageing caps... but BOTH channels, at exactly the same time? That's just too much of a coincidence for me... but nevertheless I will check them (have use of a super-duper cap meter at work I can use for that).

@amc184:
Guess what I did! I think that in removing the input preamp stage to the power amp that yes, DC input offset resulting in this fault.... but what fault!!!
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Old 29th March 2011, 02:08 PM   #23
jaycee is offline jaycee  United Kingdom
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ahh... you will want to check all the small signal transistors then, including the LTP Q2, Q3 and it's current sink.

edit: these parts are so cheap, it might just be worthwhile shotgun replacing them.
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Old 30th March 2011, 11:11 AM   #24
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^ Might be an idea...

Also, I wonder if Arcam's ORIGNAL transistor drivers are DIFFERENT from stock transistors. The orignal transistors are marked AAR3055A and AAR2955A. I have replaced them with standard 2N3055 and 2N2955 devices.... I'm thinking (not a good thing ) that those original transistors may be specific to Arcam and may therefore have a lower gain.

Also, I have not matched the replacement transistors, I've just replaced the suspect devices with the only two devices I have to hand. I wonder how transistors are matched if I order say 10off of each...

Thanks again for your help everyone!
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Old 30th March 2011, 03:44 PM   #25
jaycee is offline jaycee  United Kingdom
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Probably remarked but I doubt they are in any way different to regular 3055/2955 devices
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Old 11th April 2012, 04:21 PM   #26
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I'd just like to say that this amp (Alpha II) sounds better than the Alpha 3 more musical I'm wondering if it could be down to the AAR2955Z / AAR3055Z outputs are they mosfet or bipolar?
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Old 11th April 2012, 04:26 PM   #27
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There are different version of the 2N3055/2N2955.

Most notably the H and E variants.

Why not talk to Matt at Arcam. He's very helpful.
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Old 11th April 2012, 04:42 PM   #28
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Quote:
Originally Posted by KatieandDad View Post
There are different version of the 2N3055/2N2955.

Most notably the H and E variants.

Why not talk to Matt at Arcam. He's very helpful.
thanks, I'm sure he is I don't have a problem with mine just like it's sound
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Old 20th January 2013, 08:08 PM   #29
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Hey everyone...sory for digging this topic...but was searching for a chead amp and i buy an old arcam alpha 2 for a very small price, but was listed with a fault...don't power up..but i give it a try...

maybe i receive it tomorrow...first thing that i will do is check the fuses....

underwurlde do you have any success with your repair?
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Old 30th January 2013, 10:53 AM   #30
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Already have the amp...so much burned resistances....:S anyone have the datasheets with values of the components...?
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