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In Reply to: RE: Ugly, it's a good thing you asked ahead of time posted by Ugly on October 09, 2014 at 06:34:43
Bipolar rails from 9 VAC?? That seems very little to work with, what 6 VDC per side? I had a +15-0-15 supply through a voltage balancer ?? for my phono stage. I replaced the whole thing with a +15 and -15 regulated supply. It was a somewhat well-regarded Black Cube stage. It really opened up the bass response after the mod.
Follow Ups:
I believe 12VAC -> 12Vrms 0-peak.
Measured a little tonight...
Mines actually putting out closer to 14Vrms 0-peak per my meter when it's unloaded. The regulated rails are sitting at right around + and - 18V.
I'd be happy just addressing the noise I'm seeing but better sound from other performance improvements would be great!
?? Does it have another transformer on the inside? 12 VAC will only get you about 18 VDC off of the first cap (1.414 * VAC = VDC) and so, to get 18 V regulated, it is not a normal regulator as it could be a low offset regulator and then how does it get -18v DC? Gasp, it could be a switching regulator??? Those are VERY bad.
Anyway, as I explained, a 1 Amp, 24 volt center-tapped transformer and very simple fixed voltage regulators and reasonable capacitor size, 3300 uF, 50V or so (I'm trying to recall) should get you to a pretty good power supply without having to go to the Belleson's. EBay will sell you regulators for $8 each. I tore up an old CD player and broke off the power supply section for mine. The circuits are really simple if you know how to use a soldering iron. The transformer is the most costly item for this and, probably, why you have to spend big bucks to get reasonable performance.
Xfmr regulation voltage depends on loading. I didn't measure but am guessing with the light loading this one sees it is sitting somewhere between it's no load voltage, the 14V I measured, and it's full load voltage of 12V. LDO's can be had with 0.1V drop and with 0.7V across what seems to be a half wave rectified circuit you only need18.8V from the tranny for 18V rails.If I do end up diying I'd most likely run with no regulation other than the transformer regulation but pump up filter capacitance so big ripple gets kept in the noise floor. What's even better than a really good reg? No reg at all.
Edits: 10/10/14 10/10/14 10/10/14
OK. I think it must be a typical voltage doubler, which makes sense, which means it is only getting half-wave rectified per rail, which is not as good as a center-tapped full wave circuit.
You should check the output rails compared to the input rails and see that there is, in fact, about 3 volts DC lower on the output side, which means they are standard regulators (+15volt and -15volt regulators are < $1 apiece).
Yes, the simplest mod is to just increase the cap size, maybe double it. I think having regulators is good, too as I find nothing wrong with them and they must be good as they are used in most audio circuits.
Still completely confused. It is good to take your measurements both before and AFTER the regulator to know what you are dealing with. Usually the ICs have VCC and GND pins that are easy to find, being the first and last pins. Having a spike AFTER the regulator doesn't seem very good to me -- but as I don't have a scope, I am not sure how the waveforms typically look. Usually, they just specify a ripple voltage %. So 5 mV for 15 volts is .03 %, which seems kind of high to me.
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