Ideal bias setting for high current 303's

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02-Mar-2019 07:41 PM

PeteUK

PeteUK

Posts: 15

I've got 2 paralleled 303's, and I'm looking for views on the best setting for bias after adding extra diodes at MR105 and 106. Any ideas?
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04-Mar-2019 08:43 AM

EJP

EJP

Posts: 1676

Higher current capability doesn't have anything to do with the correct bias setting. You should still aim for what it says in the Quad service manual. However in practice it is easier to do this by measuring thevoltage across pins 4 and 6 and aiming for about 7.5mV, or lower if it runs away. Take your time doing this, it takes minutes to settle after each tweak.
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04-Mar-2019 05:51 PM

PeteUK

PeteUK

Posts: 15

That's great, thanks EJP.
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16-Apr-2019 09:51 AM

jackdelang UK

jackdelang UK

Posts: 16

hi pete,

just purchased another 303 so I  have 2 quad 303's. bypass any pre-amp and pull audio through a dacmag 100 straight to one 303 - i intended to split the feed in two which should indirectly attenuate (good)    i was planning to buy 2 more ditton 44's to have 4 in total. Would u be able to advise me as you mention yours 'in parrallel' -  I'm going to service 1 of the amps  with a DADA kit  now - bar the crappy no-name power caps that were bundled in this kit. 

Also, some setup advise in regards to using both amps together.

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15-Nov-2019 08:05 PM

PeteUK

PeteUK

Posts: 15

I just followed the Quad info "Quad 303 Monoblock Instructions" in the downloads section of this site.

Parallel is the easiest option. Speaker impedance is important. You will find that with higher impedance the power output may not be as much as you were hoping!

The really big difference comes from the rock steady stereo image and elbow room obtained by each channel being isolated and having its own power supply.

I built the adjustment pot into a small enclosure. All in all very worthwhile, cheap and easy to do.


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