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.
@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!!!
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!!!
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.
edit: these parts are so cheap, it might just be worthwhile shotgun replacing them.
^ 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!
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!
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?
I'm wondering if it could be down to the AAR2955Z / AAR3055Z outputs are they mosfet or bipolar?
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.
Most notably the H and E variants.
Why not talk to Matt at Arcam. He's very helpful.
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?
maybe i receive it tomorrow...first thing that i will do is check the fuses....
underwurlde do you have any success with your repair?
Already have the amp...so much burned resistances....:S anyone have the datasheets with values of the components...?
- Status
- Not open for further replies.