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In Reply to: It's all about the regulation posted by KurtP on April 29, 2007 at 12:08:09:
Does this mean that one have to choose voltage or current regulated,or is it possible to feed the circuit with both ?
So this power supply showing for the Karna ; http://www.nutshellhifi.com/Karna.gif ,is voltage regulated only?
Follow Ups:
You can only have one or the other. You could have a current LIMITED voltage regulator, but it's still voltage regulated. If your current output (which will vary in a VR supply) goes too high past a design spec, the output will drop, effectively limiting the current output.The Karna design uses shunt voltage regulation for the B+ driver stages, but does not regulate the filaments. It basically is a voltage supply, with regulation determined by the 120VAC of your house power. If your house power drops to 115V, all filament supplies will drop by the same percentage. So while it IS a voltage supply, it is not specifically regulated.
Technically, it has pretty good load regulation, but no line regulation. That is, as the load varies, the voltage will be fairly constant. As the line (house power) varies, the voltage will change.
FWIW, I am currently building a Raven preamp, and am debating between an Amity or Karna design. I can say this much, as a licensed PE with good knowledge in both power and electronic theory, the Karna is a VERY daunting design. It may look easy and simple on paper, but the actual build and attention to subtle grounding is critical. If you are having some of the questions you are posing, I would kindly and respectfully steer you away from building it. At a minimum, try a "tiny" Raven design first, to see how successful you are.
I will consider the build of Amity/Karna,but as you said it also look managable from looking at schematics.I just figured since it has been around for a while I could get help if I ran into problems,but I will now consider not building it.
Maybe a Raven,yes.
> Does this mean that one have to choose voltage or current regulatedThe vast majority of regulated filament supplies are voltage (not current) regulated. One good reason for this is that the filament supply usually feeds a number of tubes in parallel. With a current source, removing a tube (or having a filament open unexpectedly) will cause the supply to increase the voltage to all the other tubes. So, safe operation requires either a crowbar across the output of the current regulator or a separate current regulator for each tube. On the other hand, the downside to voltage regulators (and simple filament transformers) is the inrush current when the tube is cold. This can be minimized if steps are taken during the design of the regulator to provide a slower start.
One solution to supplying two tubes - e.g. a diff pair - with one current source is to wire them in series. So if you remove one tube you break the circuit.
> ...wire them in series.Yes, that's a good option, although it does make it more difficult to know which tube of the pair has failed. I have to say, my preference in all this is a voltage regulator (voltage source) with a current limiter, not merely a simple current regulator. I believe tubes are spec'd and designed for a specific filament voltage, and that the filament current listed for most is only an approximation provided for use in determining supply requirements. Regulating the tube to that current is unlikely to be what the manufacturer intended.
my preference in all this is a voltage regulator (voltage source) with a current limiter, not merely a simple current regulator. I believe tubes are spec'd and designed for a specific filament voltage, and that the filament current listed for most is only an approximation provided for use in determining supply requirements. Regulating the tube to that current is unlikely to be what the manufacturer intended.I used to think that, I even wrote an article in AudioEXpress on the topic.
After adding series chokes to my battery supplied filaments I'm thinking the current reg has benefits above and beyond lighting the things correctly. It looks as though extra impedance in the supply line is beneficial - whether it blocks hash getting in or out I can't say, but it seems to do something.
BTW you can get around the issue with current v voltage by making the current reg adjustable and setting it so that the voltage drop across the filament is correct.
I agree with those who say that the high impedance keeps the audio signal out of the power supply. The last thing i want is a good portion of my audio signal finding its way to ground though the filament supply.How did you size your chokes for your battery supply? I pretty much size it so the Z at 20hz matches the filament resistance and see what that looks like.
For the 71As I used a pair of existing chokes which were about 1H and had about the right DCR to drop nominal 6.3V to 5V. I added a common mode toroidal which tops up the DCR.For the 211s I bought some big transformers off the shelf, unstacked it, unwound the primary and added a new winding. The winding roughly matches the DCR of the existing secondary to give me almost 0.8 ohms as required to drop nominal 12.6 to 10V with the 3.25A draw of the 211 filament. I will add an air gap with paper between the Es and Is and put it on the DCR bridge to see what I get and use the same trick with the common mode toroidals as above.
I have only just sorted the recharging for the 211 batteries so they haven't been installed yet. I'm using laptop power supplies (15V) and a silicon bridge rectifier to achieve 13.8V, the laptop supplies are current limited at 6A so this should work a treat for the 65 Ah batteries.
I'm curious, being as you're using DC on the filaments, why aren't you using SS devices for isolation? This seems like a very inconvenient application for chokes given the frequencies and currents involved. I should probably add that I'm on the outside of the current rage for SS CCSs, but this particular use would seem much less likely to color the sound. The impedance ratio of desired to undesired signal paths would be extremely high with a SS CCS.
The original circuits used fairly high spec SS devices (LT108X series regs). With the 71As I moved from there to series / shunt regulation using discrete devices, from there to SLA batteries and from there to SLA batteries plus chokes. I felt that each step was a worthwhile improvement. With the 211s I'm in the process of jumping straight from first to last.I tried SS current reg but didn't like it, YMMV etc etc.
I tried SS current reg but didn't like itYou probably have some theory about the reason why. No?
I never tried batteries, probably should give them a go.
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