The simplistic Salas low voltage shunt regulator - Page 580 - diyAudio
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Old 1st March 2013, 09:00 AM   #5791
Salas is offline Salas  Greece
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Haven't used that there, so you are on your own. See it does not oscillate.
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Old 2nd March 2013, 11:06 AM   #5792
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Nick up to what frequency should we check for oscillations? And what coupling should we use in the scope? DC?AC?GND?
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Old 2nd March 2013, 07:28 PM   #5793
vgeorge is offline vgeorge  Greece
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Use AC and make a sweep up to the full frequency of your scope.
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Old 2nd March 2013, 07:48 PM   #5794
Salas is offline Salas  Greece
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If something "rings" it will do it between 2-6MHz usually from a couple of times I have seen it in wrongly made ones some friends brought to me to debug. If the scope has high bandwidth it can bring in environmentally born stuff also and we should know what is what. I would start with the probe at 1X where its naturally slow and the system noise is best on the screen. If clear I would go 10X and sweep across. First with the scope in 20MHz limit mode. Sure oscillation has a sinewave profile sometimes even perfect in shape or about and 20mV-200mV amplitude from what I have seen on those problematic p2p builds. Other stuff can be much lower frequency periodic "spikes" from digital equipment interacting with the rail and can be fought with extra 100uF across the sense lines and/or 0.1R resistor in series on the force line.
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Old 6th March 2013, 08:13 PM   #5795
RollE2k is offline RollE2k  Sweden
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Salas: I know you posted somewhere how it was possible to modify a positive supply pcb to negative, with only some simple changes.
I've been searching, but haven't found it this time, can you re-post or redirect me to the post?

Edit: ok found it in the SSLV1.1 thread.. in THIS post. :-)

Last edited by RollE2k; 6th March 2013 at 08:20 PM.
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Old 6th March 2013, 08:40 PM   #5796
Salas is offline Salas  Greece
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Old 7th March 2013, 05:12 AM   #5797
nezbleu is offline nezbleu  Canada
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I am building a phono preamp board which requires +/-15V supplies, which I intend to provide from a SSLV power supply. I also want to experiment with a Salas RIAA phono preamp. Those seem to require a single-ended supply on the order of 20-30V. I would like to use one transformer, some rectifiers, and some capacitors for the initial "primary" supply. I would like to be able to move some wires around to switch from +/-15V to +25V(ish). The SSLV boards conveniently come in triplets, a +/- pair and an extra positive regulator.

So my question: Would a 2*15V transformer be a good choice for this? Lower? Higher? I am assuming the shunt will operate at no more than 300mA, probably more like 200mA
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Old 7th March 2013, 05:32 AM   #5798
Salas is offline Salas  Greece
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The latest folded cascode MC phono version requires +35V. For the MM +28V. For choosing a transformer with single secondary or double secondary to wire them in series follow the rules of thumb VAC=~VDCout and VA>=VAC*(3*ICCS).
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Old 9th March 2013, 02:26 AM   #5799
nezbleu is offline nezbleu  Canada
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Quote:
Originally Posted by Salas View Post
The latest folded cascode MC phono version requires +35V... follow the rules of thumb VAC=~VDCout and VA>=VAC*(3*ICCS).
So if I am considering at some point to build the folded MC version (I don't even have a MC cart, just thinking about the future) my transformer should have AC out on the order of 36V, so a 2x18V secondary would be OK. If I use that transformer to feed a BiB to get a +/-15V supply for the other preamp I'm working on, is that going to be a problem? I presume the regulator is going to have to dump a bit of voltage and run hot for a given current. Maybe some heavy-duty resistors will be in order to step the voltage down. One nice thing about the Salas shunt is the current consumption is predictable and consistent!
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Old 9th March 2013, 04:44 AM   #5800
Salas is offline Salas  Greece
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Only a matter of wasting your extra energy to heat in clever RC passive filter manner as you wrote, or just dumping it on the input Mosfet sink. Not a huge deal when at the 200mA mark or about. Just roughly calculate the thermal design before you start. Being the wattage of the RC's R element or the capacity of the sink.
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