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Restoration of an A&R Arcam Alpha Amplifier

Discussion in 'British Audio' started by slimecity, Nov 19, 2018.

  1. slimecity

    slimecity Super Member

    Messages:
    3,079
    Location:
    New Zealand
    This is the second one of these I have worked on. The first one i got was a simple flipper - so I did a simple recap, not expecting much in the way of results - but I was pleasantly surprised. These amps came out in the late 80's and went thru several iterations. Starting with this one (assuming its not an Alpha "plus", but I dont think it is).

    I offered to help a friend upgrade this amp if he wrote a review on my hobbyist repair facebook page. Im only charging him parts cost.

    I thought I'd write this up as many people are quite quick to dismiss this amp. I think this amp is on a similar level to the NAD 3020 - they were everywhere at one point and critics were loving both of them - however both of these amps are at a stage now where they need overhauls to sound and operate at their best.

    The panels are easily removable from the top and bottom and the amp is very basically assembled. Fairly cheap parts are used - the speaker fuse holders can also lose their tops - but unbelievably - I found some replacement entire units at my local Jaycar - that was totally unexpected.

    The stock caps are actually Rubycon - so they arent too bad. I replaced what I had onhand (1uf x 2 by the volume pot, and also 6 x 22uF). This didnt really result in much sound improvement - that didnt really happen until the 9 or so 10uF caps throughout were replaced. All caps were panasonic except for Silmics adjacent to the volume pot.

    Powersupply caps were upgraded from 6800 to 10000 CDE types and bypassed with 5uF film caps. All these changes resulted in the sound becoming fuller and less thin and "shrill."Heatsink compound was refreshed - these outputs dont actually get very warm at all. They are TIP 2955 & 3055.

    I also briefly experimented with rolling the opamps. I thought I would leave the NE5532 in there as they dont have a terrible reputation and the recommended subs were a bit harder to source here in NZ. The old TL071 however was sounding like it needed to be rolled. The TL2071 is a modern uprated JFET opamp that is a drop-in replacement for the 2 of these units in this amp.

    Once these were changed I got a lot more bass & detail, and the soundstage was a bit fuller, and less shrill.

    I am one of those nutty believers in cap break-in so I think after a few more hours this thing will just sound better and better.

    After all the work - you are left with a fairly low-power amp that leaves an impression of having a lot of "space" in the sound. My view is this could be attributed to the 4 x 1N5403 diodes in the rectifier (rather than the one usual bridge). It is fun and punchy to listen to, and detailed. The bass is adequate on my test speakers, the mids are subdued but good. Im still waiting for the treble to get a bit less "splashy" and that could happen over a bit more time. Plus there is a 7815 and 7915 providing the 15V supply, and I know these could also easily be upgraded to "quieter" devices doing the same job.

    Overall this is worth doing - if you get hold of one of these - dont judge it until you have at least done the above (very straightforward) work on it. In my view, its well worth it.....

    Other (more technical) peeps may have some other thoughts on other things that could be done to these little amps too.

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