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Zener+Voltage follower
Zener+Voltage follower
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Old 12th August 2017, 03:12 PM   #91
Elvee is offline Elvee  Belgium
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Originally Posted by kinku View Post
Thanks Elvee! How does it look now?
Phew! this time, everything looks about right -don't touch anything now-, at a later stage, the 1Meg resistors could be replaced with 10, or even 22Meg, to scrape half a dB of rejection, and D7 D10 can be ordinary 1N4148, they will perform as well and may ease the startup
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Is there any advantage/issue with using B vs C devices?
For most transistors, but especially T2 Q5, a lower β will mean a lower Early effect, and a better hum rejection: use preferentially B types, and even A types if you can find them
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Old 12th August 2017, 03:25 PM   #92
Mark Johnson is offline Mark Johnson  United States
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Zener+Voltage follower
Why not increase R2 & R8 (post 87) if your number-one priority is preventing zener diode noise from reaching the output?

Or, if instead your number-one priority is preventing unwanted AC garbage on the +12V input, from reaching the output ... why not consume some of that (12V - 6V) = 6 volts of headroom by using an LDO preregulator? It'll give you an additional 75dB of input rejection.
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Old 12th August 2017, 04:14 PM   #93
Kay Pirinha is offline Kay Pirinha  Germany
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Originally Posted by kinku View Post
I was planning to use dual secondary ( 9-0-9)V transformer with two bridge rectifiers to do this. If I can just use either 0-9 V or a single bridge with 18V and make a bipolar supply +/-6V it will be better in terms of cost. Is it possible?
9-0-9 Vac, i.e. a center tapped secondary winding, won't work with two rectifier bridges. Simply use one. The center tap will be the return for both the negative in- and output of the positive andfor the positive one for the negative half of your arrangement. Sounds complicated, but isn't .

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Old 12th August 2017, 05:09 PM   #94
kinku is offline kinku  United States
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Sorry ,it is not a center tap ,it is a transformer with 9-0,0-9 seconadries.
Yes it was a challenge.Thank you all. Elvee, made all recommended changes.
There is more.Please see the complete schematic.To reduce the size going with CRC instead of CLC.
Mark give me an example of LDO pre regulator,google not returning much results.
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Old 12th August 2017, 06:13 PM   #95
Mark Johnson is offline Mark Johnson  United States
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Zener+Voltage follower
See post #43 in this thread, especially its attachments.

LDO = Low Drop Out

An LDO regulator works fine when the difference between Vout and Vin is small. The one in post #43 is spec'd to work great for Vout as high as (Vin - 600 millivolts).

So ... you could put it upstream of your post #94 circuit. Now your circuit gets 11.4V input instead of 12V; whoop de doo. Your input rejection increases by 75 dB (5600X) which you may find desirable.

PREcede your circuit with a REGULATOR ... voila, PRE-REGULATOR.
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Old 12th August 2017, 06:50 PM   #96
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by kinku View Post
Sorry ,it is not a center tap ,it is a transformer with 9-0,0-9 seconadries.
Yes it was a challenge.Thank you all. Elvee, made all recommended changes.
There is more.Please see the complete schematic.
It looks fine now. Note that C7 C8 and probably C5 C6 are completely dispensable: at best, they will do nothing, and at worst they will introduce unwanted resonances, albeit at frequencies that probably don't matter too much.
Have a look at the impedance curves of parallel combinations here, you will understand why:
Paper-in-Oil Capacitors
For C5 C6, if they are at the POL, they might be justified and do some good.
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Old 12th August 2017, 07:59 PM   #97
kinku is offline kinku  United States
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Thanks Elvee. I would remove those caps.
You mentioned for C5and C6 if they are POL ,what is POL?
Mark , can you recommend a LDO device that I can use? Search returning so many devices and not sure which one to pick.
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Old 12th August 2017, 09:21 PM   #98
Mark Johnson is offline Mark Johnson  United States
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What part number appears at the very top of the attachment in post #43??
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Old 12th August 2017, 10:02 PM   #99
kinku is offline kinku  United States
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Gotcha,LM2941.Do I need a positive and Negative regulator for bipolar supply?
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Old 13th August 2017, 12:51 AM   #100
kinku is offline kinku  United States
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Mark, if PSRR is the purpose why LDO as pre regulator ,seems like low drop out is not an issue here as I am droping voltage from 11.7 to say 7V.Or is it because their inherent low noise properties?

Last edited by kinku; 13th August 2017 at 01:08 AM.
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