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Old 7th November 2012, 05:42 PM   #1
domolo is offline domolo  Italy
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Default Help for Rega biasing value

Hallo everybody,

I'm searching for the mV value to reach on the emitter resistor on a Rega Luna (1997) clamshell 40watt to get a proper biasing.

On Rega.co.uk/service there's no info on this amplifier.

I can't find any REGA mail address either
And in Italy (where I live) the service center won't give any help, they will suggest me to ship them the amplifier.
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Old 7th November 2012, 06:16 PM   #2
Mooly is offline Mooly  United Kingdom
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The correct bias will depend on the type of output stage, bjt or FET, EF or CFP configuration etc so without a lot more info its impossible to advise really.
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Old 7th November 2012, 06:24 PM   #3
domolo is offline domolo  Italy
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Hi Mooly I'm just searching for the idling current value.
Usually service manuals provide a mV value across an emitter resistor that have to be set up through a trim pot.

I spotted the values for the MIRA, the MAYA and others REGA Amp, but I can't find the value for the Luna.
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Old 22nd December 2012, 02:17 AM   #4
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The Luna is basically just the Mira without remote control. For the Mira, according to Rega, the bias should be 2.5 mv (across the 0.22 ohm emitter resistors) so about 10-11 ma should be about right.
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Old 22nd December 2012, 02:30 AM   #5
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Not many DMMs will be accurate enough to read 2.5 mV with any confidence.
It would be better to read across both resistors and set bias to 5 mV.
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Old 22nd December 2012, 09:20 AM   #6
domolo is offline domolo  Italy
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The Rega Luna uses two pair 2SA1186/2SC2837 SANKEN I'm not sure the Mira uses the same output devices...

I think the ELEX is similiar than the Mira.
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Old 22nd December 2012, 08:04 PM   #7
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You are right domolo - I just checked the Elex circuit diagram and it uses 2SA1186/2SC2837 while Mira (2000) uses 2SC3519/2SA1386.

However, there won't be a lot of difference in this; just try a bias of ~ 10ma to start with (2.2mV over 2.2 ohm) and see how it goes. I had an Elex with similar issue.

BTW do you have the Luna curcuit diagram?
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Old 22nd December 2012, 09:25 PM   #8
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Just a further note: in the Elex, the output stage emitter resistors are 0.47 ohm, so 10ma would give 4.7mV across them.

Are the Luna's 0.47 ohm too?

BTW There's a guy from Rega who posts on PinkFishMedia: Paul Darwin. It was he who gave me the correct bias for the Mira.
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Old 22nd December 2012, 09:34 PM   #9
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Correction to earlier post: 10ma gives 2.2 mV across 0.22 ohm ( not 2.2 ohm).
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Old 22nd December 2012, 11:16 PM   #10
domolo is offline domolo  Italy
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Hi Mashley,
I haven't the Luna diagram, I simply look at the output circuit and I see several things in common with the Elex. At the moment I'm using 100mA bias current. I've look at the datasheet and it seems the devices can handle such a current. The Rega get hotter but I can still keep my hand in contact under the transistor, below the clamshell (with the unit weights on my hand) without feeling pain at all. I choose an high value to have the channels as close as possible in biasing: my DMM give good reading only at the end of the scale. I don't notice clipping but I'm preatty sure several distortion in higher armonics can occur with such a idling current. The amp pulled toward a class A biasing has a more "live sound", but it loose that british "elegant feeling". I've replaced the 4x4700uF caps with 4x10000 Cornell Doublier, those are large cans with an high ripple current, the improvement has been outstanding 40.000uF is the maximum value that the 153VA trasformer can handle, over this sizing the bass becomes boomy and its control becomes poor. I wonder if I ever will find a 250VA transormer slim enough to replace the one in this slim clamshell.
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