Arcam Alpha 10 - Service

[enkidu78]

Hi

I'm not sure if this is the right section but i'd really appreciate some help.

I own a 12 year old Arcam Alpha 10 and am extremely interested in servicing it. One of the channels seems a bit quieter and its just not quite as good as it was. Upon first inspection one of the main capacitors has a bit bulge on the top. Its a 63v 10,000uf alc10a103df063 bhc.

I'm fine with soldering new parts on boards just need advice as to what to change ie resisters, other caps etc.

I downloaded a service manual which goes into loads of detail from hifi engine.


Please help

[Mooly]

I had a quick look at the manual. Seems there are two versions, a power amp and an integrated. Which is yours ?

Caps with a bulge. If the actual aluminium can is bulging then it needs replacing. If it's a plastic sleeve or plastic disc on top of the cap it could well be OK. Photo maybe
What is the voltage across the cap ? Anything approacing 60 volts at correct mains input voltage and it's marginal and a higher voltage cap should be fitted.

Quieter on one channel... you need to be sure! That would take seconds to check with an oscilloscope and signal generator but I'm guessing you don't have one.
I see there is a gain switch on each channel on the power amp. Is that OK... not intermitant contacts etc.

If you have a test CD with a lowish test tone on it (say between 100 to 1 khz) you could measure the AC voltage across each speaker and compare left and right. All the signal switching and processing is "electronic" in the preamp so unlikely there is a real problem here.

[enkidu78]

Thanks for the reply, its the integrated amp.

I've not actually tested the cap but the one next to it looks fine. It does however have a sleave. I will take a picture tonight and post for an update.

Is it ok to just measure the voltage on the cap with a multimetre?

The gain switch is for the amp rather than per channel to turn it into a power amp.

I will also test the AC voltage on each speaker, I will find a test CD.

[Mooly]

Just measure on DC volts anywhere convenient that the cap connects to. On the bridge rectifier might be easiest if you can't get to the underside of PCB easily.

[enkidu78]

Ok here's some pictures of my amp insides...

Sorry for the bad quality its the lower cap on this picture











Its hard to take a pic of the bulge but you can see the sleave is different than the identical cap next to it.

[enkidu78]

What advice would you give as to the cap replacement, like for like or an upgrade?

Also the main resistors are gold band but would you recommend any upgrades for these?

[Mooly]

Hard to say looking at it... I have seen caps like that many times before and it's not always a problem. The real check would be to compare the ripple on each with an oscilloscope.

If you want to replace them there are a few things to consider,

The size and spacing of the leads
Is the working voltage of the originals sufficient ? Did you measure the DC voltage to see if they are running to close to there limits ?

Try and get 105 degree C rated caps but it's not the end of the world if you can only get 85 C.

I wouldn't touch any of the resistors. You won't gain anything.

[Andy5112405]

Many of these caps have a plastic jacket. If the bulge can be popped back without too much effort you are probably barking up the wrong tree..

[Andy5112405]

Arcams are well built, using reasonable components in a well designed circuit.

Every manufacturer though works to a consumer budget. You could build a Lada to Rolls Royce Specs but no-one would buy it, because it is a Lada.

Arcam can only command a certain area of the market, allbeit be very good, their reputation cannot command the £100K prices of the big boys.

To this end, they have to make compromises. How much you want to pay to correct these compromises, is up to you.

I spent £500 upgrading an Arcam AVR280 and the difference was stunning. This was predominantly down to capacitors being replaced along with a few signal level Op-Amps.

My Mark Levinson Clone, the DIY700 however, knocks socks off the modified Arcam.

How often have you heard, you cant build a palace in Tooting, but you could build a brothel in Knightsbridge.

[enkidu78]

Originally Posted by Mooly

Hard to say looking at it... I have seen caps like that many times before and it's not always a problem. The real check would be to compare the ripple on each with an oscilloscope.

If you want to replace them there are a few things to consider,

The size and spacing of the leads
Is the working voltage of the originals sufficient ? Did you measure the DC voltage to see if they are running to close to there limits ?

Try and get 105 degree C rated caps but it's not the end of the world if you can only get 85 C.

I wouldn't touch any of the resistors. You won't gain anything.

Couldn't really see a point in which to measure the voltage, seems like it might be a board out job.

What make of cap would you get that'll be an upgrade? Would I just match the 63 volt cap providing its not too close to the limit 10,000uf with the legs the same spacing?