[sdiy] "Zerolytics"

Harry hbissell at wowway.com
Fri May 8 22:02:08 CEST 2020


I think the resistance helps you here... The trouble is that when power is suddenly applied the capacitor is a very low impedance (low ESR) you you can get a hell-roaring current flowing in theinductance of the cables, which then overshoots to an unexpected degree.  If you were using 22uF I'd guess you only went with maybe 25V, and you can shoot way over that on a transient basis.
A lytic will have much higher ESR, the initial current rush is much less, the voltage does not spike as far... 
If you are using ceramics you need a much higher voltage rating, 100V would not be out of the question. Now buy THAT in a 22uF ceramic and you will be back to lytics in no time...
H^) harry
----- Original Message -----
From: mark verbos <markverbos at gmail.com>
To: ColinMuirDorward <colindorward at gmail.com>
Cc: Richie Burnett <rburnett at richieburnett.co.uk>, synth-diy at synth-diy.org
Sent: Fri, 08 May 2020 12:26:59 -0400 (EDT)
Subject: Re: [sdiy] "Zerolytics"

I tried it. I put 22uF 1206 ceramic caps as the “big” on the inlets of power on my first Eurorack modules. Everything worked out great in my shop. Then people started showing up with all kinds of leakage and noise. Turns out they were using horribly cheap power supplies, many of which use a 12 volt dc wallwart with no regulation and a CHEAP dc-dc converter to make an unregulated -12 rail. Then they run the whole system power through a ribbon cable with as much as 1Ω of resistance between the supply and the last module on the ribbon. I switched to 150uF 16v tantalums that work GREAT, except that some of them spontaneously explode ( I think this is power supply related too ie high voltage transients from unregulated or over voltage protected SMPS). Now I’m back to electrolytics.  :(MarkOn May 8, 2020, at 6:15 AM, ColinMuirDorward <colindorward at gmail.com> wrote:I'm wondering, is anyone using ceramic 10uf at the power inlet of their synth modules?Is there a good reason why it never occurred to me to try this out before?I enjoy that the electrolytics look like proud little sentinels, but if an smd robot can deploy an equally effective 0805 ceramic, all the better.On Wed, May 6, 2020 at 12:41 PM Richie Burnett <rburnett at richieburnett.co.uk> wrote:>>> At work we have many high-end powered studio monitors.  They're getting
>>> up there in age and they start to hum louder and louder.
>>> Guess what fixes the problem?  New capacitors in the power supply.
>>
>> It *might* work because new caps would reduce mains ripple compared to
>> old ones. Hopefully! Otherwise what’s the point?!
>
> Well, sure, so there would be an emphasis on the second harmonic in that
> hum? ;)
Usually mains hum on supply rails is at twice the supply frequency because
most people use full-wave rectification these days.  So in the UK, the
fundamental of the hum would be at 100Hz, with harmonics at 200, 300, 400
etc...
> Then again, I’m curious why that would cause (or not) a sound - would the
> current load on the transformer be that different?
I'd imagine that high ESR in the smoothing caps of the PSU causes excessive
ripple on the supply rails to the power amp.  And this makes it's way to the
loudspeaker due to poor Power Supply Rejection Ratio (PSRR) of the power
amplifier.
>> But I know what you mean. I’ve got an old toroidal transformer on the
>> back of my desk running a test supply. You can tell by how loud it hums
>> how much work it’s doing. Plugging in any circuit with a short on it
>> produces a decently loud hum, and you know somethings up and to unplug it
>> right away. It’s actually quite handy as a basic sanity check!
When there is a heavy load on the secondary (like a short-circuit!) you get
greater forces between the primary and secondary windings because their
magnetic fields interact.  That can make transformer "growl" under load
because the force is modulated at twice the supply frequency and makes
things vibrate.  A small 30V/1A old-fashioned linear Thurlby power supply
I've got on my desk does this.  In fact you can *just* feel the vibration
through the desk when you get up near full load ;-)  Often transformers are
dipped in a coating to stop windings and laminations from vibrating and
making annoying humming/buzzing sounds.
-Richie, 
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