Arcam Alpha One upgrade

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ash_dac

Member
Joined 2005
markk02474 said:
Assuming you bypass the tone controls.....:

Leave Z301 alone (it adjusts the amp's DC voltage offset to 0V).
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Hi,

I haven't seen a NE5532 used as a dc servo. Not 100% sure it's the right part for the job.

Is the dc servo there so the IRF540 MOSFET's didn't need to be matched during production ?

Not too sure about the use of ultrafast rectifier UF5403 in the power supply.
 
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markk02474

Member
Joined 2006
Malefoda said:
I've already removed the DC blocking caps from CDP, it seems they put this everywhere! Is it really useless?
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"They're everywhere!" is true. These capacitors can help around volume, balance, and tone potentiometers if there is a DC offset. The DC offset makes the potentiometers noisy. Also, if some part fails in a way that DC voltage is applied to the signal path, they protect the speakers from a large excursion and possibly burning out. Often there is a small DC offset in hundredths of a volt that is inconsequential.

Amplifiers have additional protection to keep them from amplifying DC - turning hundredths of a volt into volts. This is gain, and there is often a filter to reduce gain at very low frequencies, ie. 0Hz, or DC. This filtering is usually done with a capacitor in the 100's of uF range. Other times a DC servo circuit is used. I think your amp has both! C27, bypassed by C25. So, C27 would be a candidate for replacement with a Black Gate. I'm not sure what LK18 is though. Its possible that some versions have the caps and no servo, while other versions have the link and servo. The link would probably mean having gain at DC and better bass.
 
Malefoda

Malefoda

Member
Joined 2006
rx7france.com
2x3 caps removed and bypassed, LM4562 at preamp and did not resist the temptation of upgarding the 4560 for OPA2132 at the tone control: before from direct/tone there was a diffrence mainly of volume, now of "sound behaviour" : Burr Brown stuff sounds "loudness" like : rich bass. But I like more the crystal clear LM4562. The amp get more benefit from the upgraded CDP, and yes better bass. Maybe a bit hard on high mids, I'll let the LM4562 burn in some. I think I have some Elna RJH (no BG...) to upgrade C27.
 
Malefoda

Malefoda

Member
Joined 2006
rx7france.com
Hi there!
I've get some big caps, but I think this is not an audiophile brand.
The specs are the ones from the bigger Arcam Alpha 7, 10.000u and 50V.
Any idea about these? They seems small according to the specs... Useless? My small Rubycons ZL for my Sansui Tuner wich are far smaller are far heavier! I think these caps are worth garbage...
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Thanks!
 
Malefoda

Malefoda

Member
Joined 2006
rx7france.com
Hi :)
It sounds great but has a flaw : when play loud, bass fade and overall music becomes hard.
Whatever, the sound is now more relaxed and balanced with the LM4562 and the DC caps removed and upgarded ones.
I'm happy e,ough to leave it in its state as it'll be used for main living room very soon, no more on the music room.
Thanks for helping !
 
Malefoda

Malefoda

Member
Joined 2006
rx7france.com
Yes Mark that's what I have been told to me by the CD63 fellowship.
Ok for me right no, this will be used as " background " music system, in the living rooms.
My new integrated amp will replace this one -rated 100W vs 35W for this tiny Arcam-.
If some wanna have a look to the one to come:
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An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.


The last word to say thank you for your great support here, especially Mark in this case. My amp will have a second life now. Merry Xmas!

And the upgraded caps are Elna RJH 220uF 25V bypassed with 100n PPS.
 
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