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Power supply ripple - how much is too much?
Power supply ripple - how much is too much?
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Old 8th March 2018, 05:12 PM   #1
matherp is offline matherp  United Kingdom
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Default Power supply ripple - how much is too much?

Just starting to design my first SE amp probably based on RH84 rev2

I'm using Duncan's PSU Designer II to model the power supply and LTSpice for the amp.

At the moment my power supply design (2-pole RC) is showing approximately 0.1V of 100Hz ripple when on load (100mA).

Is this a reasonable level to aim for or do I need to do better (more expensive)

Thanks

Last edited by matherp; 8th March 2018 at 05:19 PM.
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Old 8th March 2018, 05:37 PM   #2
nigelwright7557 is offline nigelwright7557  United Kingdom
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Probably ok for an output stage but I would be using further decoupling on the front end and phase splitter.
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Old 8th March 2018, 06:05 PM   #3
Lingwendil is online now Lingwendil  United States
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Power supply ripple - how much is too much?
Split one of your existing RC stages in half, making it into two RC stages (each "R" half the resistance of the original, same value capacitors though is fine) for some additional filtering, and give it a listen.

With an SE output stage, and on efficient speakers 0.1V of ripple may be audible at near field, or in a very quiet listening space.
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Old 8th March 2018, 06:06 PM   #4
matherp is offline matherp  United Kingdom
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Thanks Nigel

There is another 10K into 100uF in the design going to the 22K anode resistor of the 12AT7 which according to the model reduces ripple to that to less than 1mV so that bit looks OK.

I'm intending to use a separate 6.3V transformer and semiconductor bridge rectified 1:1 isolating transformer. That will allow me to use a PIC powered by the 6.3V supply to switch the first HT resistor into circuit once a high value bleed resistor has very slowly brought up the HT rail. This should give a nice soft start for the valves and avoid any high power across the first HT resistor.

So soft start is 10K into 470uF followed by 68R into 470uF. Once the PIC senses the HT rail is above 290V it will then switch a 22R resistor in place of the 10K one.

If my calcs are correct this will give an HT rail of 104mA at 312VDC with ripple of 0.06V
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Old 8th March 2018, 06:22 PM   #5
waltube is offline waltube  Italy
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which is your ratio on OT trafo?
In every case it iseems to be high.
Try ti use a L of , p.e., 20H 160mA each channel ( from Hammond) it is much better than C-R-C stage and you lost less voltage


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Old 8th March 2018, 06:39 PM   #6
matherp is offline matherp  United Kingdom
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Quote:
Try ti use a L of , p.e., 20H 160mA each channel ( from Hammond) it is much better than C-R-C stage and you lost less voltage
Yes but first try is intended to be budget. Total cost for the PSU in my approach is much less than 1 choke

The output transformer I'm looking at is tapped for 5k or 7K to 8ohm. The current through the 5K models as 48mA for one channel
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Old 8th March 2018, 06:52 PM   #7
waltube is offline waltube  Italy
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Please don't save money on supply.



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Old 8th March 2018, 06:58 PM   #8
Lingwendil is online now Lingwendil  United States
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Power supply ripple - how much is too much?
Add another resistor/cap, or grab a $15 choke if it truly bothers you. Or build a Mosfet ripple filter (cheap, easy, very effective, $5USD will make one that is dead silent and that will be much more cost effective than any choke of four times the cost) and be done with it. A crappy PSU makes a good amplifier circuit sound crappy.
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Old 8th March 2018, 07:04 PM   #9
waltube is offline waltube  Italy
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A Mosfet ripple filter is a good idea.


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Old 8th March 2018, 07:13 PM   #10
Lingwendil is online now Lingwendil  United States
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Power supply ripple - how much is too much?
I run this in my 6sn7 push pull, change that preceding resistor to a smaller value, and may be increase the 12k resistance to a 18~22k for more headroom. Easy build, parts are cheap. Dead silent, even with 97dB/w speakers. Much more cost effective than a choke, and no stray magnetic fields to fool with. Nice little soft start feature too.

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