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Old 19th October 2011, 03:06 PM   #581
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Quote:
Originally Posted by coolhead View Post
Look at Salas post no 544, it is explained in there.
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Old 19th October 2011, 03:22 PM   #582
NicMac is offline NicMac  Italy
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Quote:
Originally Posted by Backbones View Post
I'm putting together a split rail -25V-0-+25V for the BA-3 front end which draws per channel 50mA.
I'll go for a 23Vac output per secondary winding rated at 500mA. This should account for voltage drop acrss diodes and headroom for the regulator.
I might as well go for the 3.9 ohm 5W R101 (overkill here perhaps).
10000uF 63V on C105.
Dummy load should be 500ohms for each of the rails at 3W.
Comments please.
Chris
I'm also planning for this use of the BiB.
Which components have you chosen to set the voltage?
I'm planning for a more reasonable current draw (say 200 mA) to limit dissipation, but I still have to estimate the best combinations of LED's and R101 for this draw at this voltage.
Will you be using plastic or electrolytic filter caps for the BiB in this application?
Cheers,
Nic
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Old 19th October 2011, 03:32 PM   #583
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I'll go for the polypropylene 4.7uF caps 63V WIMA MKS4 at C102,C202 and at the output C103 and 203. I've already used these and they sound great.
5K trimmer with R103 R203 1.8Kohm and two red LEDs.
Unless Salas tells me different.
It may be that I should go for 8.2 ohms for R101, R301 and three green LEDs.
Chris
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Old 19th October 2011, 03:48 PM   #584
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Quote:
Originally Posted by NicMac View Post
I'm planning for a more reasonable current draw (say 200 mA) to limit dissipation, but I still have to estimate the best combinations of LED's and R101 for this draw at this voltage.
Cheers,
Nic
Salas suggests adding 150mA to your current draw needs so you are up to 350mA. Look that up on the graph above and you will get a Vgs of about 5V.
If you have about 1.9V drop across the three green LEDs you have a total drop of 5.7V. Voltage across the R101 is 5.7-5=0.7. I=V/R so 0.7/3.9=179mA. If you add another LED though it will be 2.6/3.9=666mA.
Chris
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Old 19th October 2011, 03:54 PM   #585
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Over 0.48A Salas manual said 4 LEDs or stronger 3 LEDs.

Last edited by merlin el mago; 19th October 2011 at 04:01 PM.
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Old 19th October 2011, 04:05 PM   #586
NicMac is offline NicMac  Italy
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Quote:
Originally Posted by Backbones View Post
Salas suggests adding 150mA to your current draw needs so you are up to 350mA. Look that up on the graph above and you will get a Vgs of about 5V.
If you have about 1.9V drop across the three green LEDs you have a total drop of 5.7V. Voltage across the R101 is 5.7-5=0.7. I=V/R so 0.7/3.9=179mA. If you add another LED though it will be 2.6/3.9=666mA.
Chris
BA-3 front-end draw = 50 mA + 150 mA spare current = 200 mA total current
3x green LEDs = 6.3V - (Vgs @ 0.2A = 4.2V) = 2.1V => R=2.1V/0.2A = 10.5R
My green LEDs are 2.1V while the red and yellow are very similar and both 1.9V.....
Cheers,
Nic
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Old 19th October 2011, 04:09 PM   #587
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Looks good. You can always add another LED if you run out of current.
Those caps were polyester not polypropylene as I previously wrote.
Are you mounting the BA-3 front end in a separate chassis?
Chris

Last edited by Backbones; 19th October 2011 at 04:11 PM.
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Old 19th October 2011, 08:21 PM   #588
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by Backbones View Post
I'm putting together a split rail -25V-0-+25V for the BA-3 front end which draws per channel 50mA.
I'll go for a 23Vac output per secondary winding rated at 500mA.
It's another of my guesses, but 30+30Vac seems better for +-25Vdc.
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Old 19th October 2011, 08:47 PM   #589
NicMac is offline NicMac  Italy
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Quote:
Originally Posted by Backbones View Post
Are you mounting the BA-3 front end in a separate chassis?
Chris
Yes - as I do not have an output stage ready

I will actually be doing a balanced BA-3 (BBA-3) as all the rest of my system is balanced.

In place of these approximations for choosing the right R101 et al. I will get myself a couple of 3W 20R "trim-pots" to experimentally determine the right value for R101

As a balanced load is easy on the supplies I may even reduce the shunt current further - in fact using a shunt regulator is probably an overshoot. Does the, already minimal, BiB noise go up or down with increased current?

Cheers,
Nic
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Old 19th October 2011, 09:02 PM   #590
Salas is offline Salas  Greece
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Use at least 100mA more than your load demand, its for keeping the output impedance of the regs low. The more the spare current, the more subtly dynamic the result will be. Precision in the set current isn't much of a concern when there is much to spare. Regarding noise, that comes from the voltage creating shunt part more so than from the constant current feeding part. Since such a reg was not worsening the noise floor of phono stages, I don't think there is a noise concern in the power amp driver stage signal level. Use 220uF electrolytic capacitor in the voltage set rectangular frame section to filter noise better as discussed in the guide, if a priority. Here is an analyzer result for PSU noise in a next of kin Mezmerize DCB1 supply with just 100uF filtering, to have an idea of the noise scale such a topology is capable of. Thanks to Spanish member Ramallo. The rails are AC coupled to the lab grade audio analyzer's input. You can see the hum peaks at 50Hz & 100Hz above the reg's noise floor in the full preamp layout and connections, and the rise in the flicker noise region towards 0Hz (including analyzer's own). 1/f (flicker) is strongly further suppressed with up to 1000uF if for digital clocks where it counts more. But won't help the tone for full range audio IMHO.
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