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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, 07:55 PM   #11
kodabmx is offline kodabmx  Canada
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Nice, Lingwendil. I might have to try that although I usually attack the problem with more capacitance This is indeed cheaper than using more caps, even if they are cheap Chinese ones. How much of a heatsink does that MOSFET need?
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Old 8th March 2018, 08:47 PM   #12
Lingwendil is offline Lingwendil  United States
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Power supply ripple - how much is too much?
On my particular use, its just a few degrees above ambient with a small 1"x1"x2" (one of these, actually) or so sink, but I'm yanking maybe 50mA total through it, with maybe a 10~12 volt drop across the Fet. For higher current use I would want to drop maybe 10% of the voltage supplied through it for safe margins, but less would work well on a class A design like the circuit the OP is using.

I've been meaning to bolt it straight to my chassis, but need to strip some paint so I can mount it. I think page six of my 6SN7 thread is where GoatGuy and I were riffing back and forth on the basics for it.
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Old 8th March 2018, 09:04 PM   #13
TonyTecson is offline TonyTecson  Philippines
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Power supply ripple - how much is too much?
Quote:
Originally Posted by matherp View Post
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
at a plate voltage of say 300 volts, will 0.1v ripple matter that much? i hardly think it will...
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Old 9th March 2018, 01:27 PM   #14
pl802 is offline pl802  United Kingdom
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Power supply filters - sim results-diyaudio
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Old 9th March 2018, 02:46 PM   #15
kylej1050 is offline kylej1050  United States
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Quote:
Originally Posted by Lingwendil View Post
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.
I had to simulate and build that regulator to convince myself it would work but I'll be a monkey's uncle if a handful of parts worth less than a couple bucks does in fact do an excellent job. So much for my usual standby of an LM317 zener protected regulator with a high voltage parallel pass transistor.
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Old 9th March 2018, 02:50 PM   #16
Lingwendil is offline Lingwendil  United States
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Power supply ripple - how much is too much?
Quote:
Originally Posted by kylej1050 View Post
I had to simulate and build that regulator to convince myself it would work but I'll be a monkey's uncle if a handful of parts worth less than a couple bucks does in fact do an excellent job. So much for my usual standby of an LM317 zener protected regulator with a high voltage parallel pass transistor.
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Old 11th March 2018, 04:29 AM   #17
PRR is offline PRR  United States
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Quote:
Originally Posted by matherp View Post
...approximately 0.1V of 100Hz ripple ... Is this a reasonable level to aim for or do I need to do better (more expensive)....
It is cheaper to do some thinking and figuring before you open your wallet.

What is the power supply rejection ratio (PSRR) of a "SE amp"? It depends; Pentodes are much better than triodes. But I will assume triode.

We usually ballpark the tube's plate resistance (rp) and then use a 2X-to-5X rule of thumb to get a load impedance. 2X is more power, 5X is less THD, though the 2X amp may play soft as clean as the 5X amp. Let's take 3X.

So for tube of rp=2K, we use 6K load.

The ripple splits as in any resistor voltage divider. 1/4 across the 2K, 3/4 across the 6K.

We will hear the ripple in the 6K. So call it 75mV. (Peak? RMS? Peak-to-peak??)

That is divided-down by the transformer ratio. 6K:8 is 750:1 impedance, 27:1 voltage. Call it 2.8mV at the 8 Ohm side.

This is (too conveniently!) 1/1000 of the 2.8V (1 Watt) we use for rating speakers. Say your speakers are 90dB SPL at 1W at 100Hz in a room-size space.

1/1000 of voltage is 60dB. So that makes 30dB SPL of ripple in the room.

Is this low enough? I've heard worse. Due to Fletcher-Munson, 30dB SPL at 100Hz is not real audible. I would worry more about your higher harmonics. However you say 2-stage filter, and that will *tend* to cut the higher harmonics quickly (more info needed).

Personally I would plan (leave space for) another 20dB (10:1) drop of ripple, because I know I would note 30dB SPL at 120Hz when I put my head in the speaker. I don't demand no-buzz with my ear on the grille, but it is nice.
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Old 11th March 2018, 08:54 PM   #18
stocktrader200 is offline stocktrader200  Canada
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the FET in the cct will need a gate protect zener. the output will be noise free.
I used a 2N5551 to silence ripple feeding a 6922 stage.

Last edited by stocktrader200; 11th March 2018 at 09:23 PM.
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Old 11th March 2018, 09:28 PM   #19
stocktrader200 is offline stocktrader200  Canada
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I do demand no noise as the amp is capable of 100db s/n relative to 1 watt and the tube is driving the amp through the tone stack. The heaters are also at + 22v.
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Old 11th March 2018, 09:32 PM   #20
Lingwendil is offline Lingwendil  United States
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Power supply ripple - how much is too much?
Quote:
Originally Posted by stocktrader200 View Post
the FET in the cct will need a gate protect zener. the output will be noise free.
I used a 2N5551 to silence ripple feeding a 6922 stage.
I've got one included on my PCB, I'm so used to using them that I don't draw them anymore. They are just "assumed" to be there.

Anything from 12-15 volts will usually work.
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