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barrows  
#1 Posted : Thursday, January 5, 2012 11:31:34 AM(UTC)
barrows

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I am building a B-III/IVY III DAC for a friend, using a Placid HD for powering the IVY III. On my Legato II I changed the power supply decoupling caps from 100 uF electrolytics to 100 nF films (Russ advised to use at least 100 nF of decoupling) because I figured with the shunt reg the large capacitance was unnecessary (low output impedance, very short wiring).
As the IVY III already has 100 nF film decoupling caps at the power input pins of the OPA 1632s, I am wondering if ommitting the electrolytic caps would be a good idea, considering, again, a shunt regulated power supply, and clse coupling (short wires). Or are the 100 uF electrolytics really advisable to keep?
barrows  
#2 Posted : Saturday, June 23, 2012 4:58:30 PM(UTC)
barrows

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No opinions or experience with eliminating the 100 uF electrolytics? I am going to use some shunt regulators which do not like to see a lot of C on their rails, neither do they need it.
In my Legoto II (with Supertex FETs) I just 0.1 uF films for decoupling with these regulators and the results are very good. Is there any reason I should not just go with the 0.1 uF already in place on the IVYIII and just omit the electrolytics?
Russ White  
#3 Posted : Sunday, June 24, 2012 1:17:23 AM(UTC)
Russ White

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It really comes down the the reg. Quite honestly no shunt regulator (no matter what the designer might tell you) can counter the effects of PCB parasitic impedance, to do that you need local decoupling.

I would leave the caps, unless it would make you regulator unstable.
barrows  
#4 Posted : Wednesday, June 27, 2012 3:25:42 PM(UTC)
barrows

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Thanks for offering your opinion Russ. These regulators can be configured different ways to accommodate different circuits, and they use sense wiring to, at least, account for the wiring impedance. My experience leads me to believe that these regulators, when powering analog gain/buffer circuit will result in the best sound when no electrolytic capacitors are used between the output of the regulator and the active parts of the circuit. Typically, the best config for the reg is with a zobel on its output consisting of a 4.7uF film cap and 1R. In this configuration the regulator generally will start to oscillate if it sees large amounts of C on its output: but this can be compensated for by damping the output of the regulator further: 47 uF across the output and another 47uF across the sense wires is usually enough to make it stable even in situations where there is considerable capacitance at the load end.

This IVYIII build is an experiment, to compare with my Legato. I think the IVYIII may drive my amplifier (15K input impedance per phase) a little better with its higher current capability and lower output impedance. So I will experiment with the onboard decoupling. I find that eliminating electrolytics close to the active circuitry can result in increased transparency and more apparent "speed". I'll start by leaving the e caps off.

BTW, I tried this with a build I did for a friend with the Placid HD, and the Placid HD was oscillating with the IVYIII without the 100uF caps in place, as soon as I added them it calmed down nicely.
Russ White  
#5 Posted : Thursday, June 28, 2012 12:05:35 AM(UTC)
Russ White

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Yes, that is because the Placid HD feedback loop is compensated for the capacitance at the load. You could very easily change this.

One thing you always much remember, even sense wires have parasitics. :)

There is no cheating fate. :)
barrows  
#6 Posted : Saturday, June 30, 2012 1:54:22 AM(UTC)
barrows

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Thanks Russ, understood... I'll try a few things...
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