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Idling current in Rega Mira 1, 2 or 3
Idling current in Rega Mira 1, 2 or 3
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Old 19th July 2011, 10:49 PM   #1
2N6658 is offline 2N6658
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Default Idling current in Rega Mira 1, 2 or 3

Hello,

I'm looking for the idling current of the final stage of the Rega's amplifiers Mira (it's the same final stage for Mira1, 2 and 3).
If anybody has a Mira and can juste give me the tension on the two big white emitter resistors it would be very nice.

Thank's.

EG
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Old 29th November 2011, 11:38 PM   #2
mashley_nad is offline mashley_nad  Australia
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It should probably be about 20mA, and if your R5,6,7 and 8 are 0.22 ohm, then the voltage would be 4.4 mV; 5mV would give 23mA.

Out of interest, what value did you settle on?
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Old 2nd December 2011, 09:30 AM   #3
2N6658 is offline 2N6658
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Hello,

Thanks a lot for your answer!

R are 0,22ohm, I ajust the voltage at 4,4mV after 1 hour, and it's still at this value after 2 hours.
In fact there was a problem on one chanel, and I had to change the two Power Transistors. But I was not sure that the biais of the other channel was good, in fact it was (4,4mV).

Do you have a Mira? Which model?
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Old 10th February 2012, 04:39 AM   #4
mashley_nad is offline mashley_nad  Australia
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Default Mira

Sorry for the late posting.

I do have a Mira - a clamshell, the main PCB says "ver 2" so I assume it's a Mk II. tested in 1998. I bought it after my last post.

It has an electromechanical rotary switch for remote control input switching - works OK, but they forgot to add muting circuitry to silence the inputs you're passing over.

When I got it one channel ran very hot - the 'OK' channel was biased at 7ma, so I set the hot channel to that, and it has worked OK.
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Last edited by mashley_nad; 10th February 2012 at 04:44 AM. Reason: typo
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Old 11th February 2012, 01:40 AM   #5
mashley_nad is offline mashley_nad  Australia
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Just heard from a guy who works at Rega that the bias should be 2.5 mv (across the 0.22 ohm emitter resistors) so about 11 ma it seems!
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Old 17th March 2012, 04:05 AM   #6
mashley_nad is offline mashley_nad  Australia
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Info for Clamshell Maia (Mira minus the preamp) from Rega:

Setting up the Maia’s Quiescent Current.


Before any changes can be made, please make sure the amplifier is “cold”, ambient temperature of 20 C - 25 C and switched off!

Equipment:


1x Mutli-meter (DVM)
1x Trimmer
2x Crocodile clips.

Open the lid of the Maia, and locate the potentiometers in the power stage, turn them fully anti-clockwise and then adjust according to the following procedure.


Turn on the amp and wait for the relay to click over.


Attach the crocodile clips to the right hand output resistors on test points TP1 and TP3.


Switch DVM to read mV’s, it should be reading nothing! Then turn potentiometer until the DVM reads 2.5mV tolerance of +/- 0.1mV. - Don’t take too long doing this as the left side amp is starting to warm up too!


Now attach the crocodile clips to the left hand output resistors on test points TP4 and TP6.


Then turn left hand potentiometer until the DVM reads 2.5mV tolerance of +/- 0.1mV.


Now leave amp on for 15 minutes to stabilise.


Check the voltages on both channels, they should read between 6.5mV – 7.5mV, if they don’t then re-adjust to correct voltage. – This reading is dependant on ambient temperature so may vary!


Leave amp for another 5 minutes to stabilise if adjusted then recheck voltages again.


If all is ok then replace the lid and panels.
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NAD C730, NAD C541i, Denon DR-M14HX, NextWave DAB-390; NAD 7100, NAD 5000; Rega (clamshell): Mira II, Planet II, Radio R.
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Old 29th September 2017, 08:20 PM   #7
mashley_nad is offline mashley_nad  Australia
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The attached pic shows the two emitter restores across which the bias voltage should be read.
Attached Images
File Type: jpg mira interior edited.JPG (807.4 KB, 46 views)
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Old 30th September 2017, 11:20 AM   #8
2N6658 is offline 2N6658
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Hello,

Thank you. But the think important for me was the voltage, I know very well how to mesure the bias across emitter resistors.

Any way this amplifier has been sold.

Best regards.


2N6658
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Old 2nd October 2017, 12:53 PM   #9
Bohuweno is offline Bohuweno
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Quote:
Originally Posted by 2N6658 View Post
Thank you. But the think important for me was the voltage, I know very well how to mesure the bias across emitter resistors.

Any way this amplifier has been sold.

Mashley_nad has kindly been assisting me (by PM) in running the test and adjustment procedure covered in this thread. I asked for clarification, which is why the picture has been added here. I realize it's an old thread, however the information is very useful to other owners of this equipment, and if you look around online, there is very little if any similar information available for this model. As well as that, where people working on other amplifiers and audio equipment often have the service manual to work with, that's not the case with Rega units.

Last edited by Bohuweno; 2nd October 2017 at 01:00 PM.
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