Developing a Regulated Dual Rail Power Supply For FirstWatt Amps - Page 3 - diyAudio
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Old 14th May 2016, 11:40 AM   #21
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Instead of a cap I could put a 24V battery in parallel with the output as another thing to try
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Old 14th May 2016, 12:10 PM   #22
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Default Modified circuit to give flat 25mOhm output impedance

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Output impedance

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Old 14th May 2016, 10:16 PM   #23
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For reference, for the stock ccrcc supply (15000u, 15000u, 0.12 Ohms, 15000u, 15000u) here is the impedance.
I don't know if I am just super anal about this (maybe just a bloody storm in a teacup) but I don't like the rising impedance response below 100Hz where there is a lot of bass energy.


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Old 14th May 2016, 11:45 PM   #24
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If the amplifier dissipates 180 watts during operation, as the Firstwatt F6's owners manual states, and if the raw unregulated supplys are ± 30 volts as shown in the simulation files here, then the DC bias current is about 3 amps. The amp is rated for 50W into 4 ohms so that's an RMS output current of 3.5 amps and a peak output current of ± 5 amps. The PSU idles at 3A and is occasionally called upon to deliver 5A.

If the amplifier drives a full size square wave into a 4 ohm load, the output current of the PSU switches between 1 amp (it's a class A design so the current never falls to zero) and 5 amps. Delta-Current is 4 amps. If the PSU output impedance is 25 milliohms then the ripple on the "regulated" supply is 25*4 = 100 millivolts. Multiply this by the amplifier's PSRR, which is unlikely to be enormous for these kinds of common source amplifiers with very modest amounts of global feedback, and you get the equivalent input signal that a 100mV ripple on the "regulated" supply produces. Have your engineer run the numbers and see if she's pleased.
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Old 14th May 2016, 11:55 PM   #25
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Quote:
Originally Posted by Mark Johnson View Post

If the PSU output impedance is 25 milliohms then the ripple on the "regulated" supply is 25*4 = 100 millivolts. Multiply this by the amplifier's PSRR, which is unlikely to be enormous for these kinds of common source amplifiers with very modest amounts of global feedback, and you get the equivalent input signal that a 100mV ripple on the "regulated" supply produces. Have your engineer run the numbers and see if she's pleased.
Yes I understand all that but it's a lot better than 100mOhms of the stock supply.

What suggestions would you make following the KISS principle?
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Old 15th May 2016, 12:11 AM   #26
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If I throw 200000uF at the output I get 17mOhms at 20Hz

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Old 15th May 2016, 12:27 AM   #27
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I'll put together a proper linear regulated supply just to keep our options open.

If we are going to do this seriously, we should explore all options I suppose.
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Old 15th May 2016, 12:49 AM   #28
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How much is the dropoutvoltage?
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Old 15th May 2016, 12:55 AM   #29
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Quote:
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How much is the dropoutvoltage?
For regulated about 4V
For unregulated capacitance multiplier about 1V
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Old 15th May 2016, 01:32 AM   #30
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Default My First Attempt of A SIMPLE Discrete Linear Regulated Supply

Ok you better be bloody happy with this you bastards.

Output impedance less than 1mOhm.

I'll post the schematic later. I have to go out now.

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