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Old 4th September 2012, 03:32 AM   #11
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Quote:
Originally Posted by lordvader View Post
I'll have a go at DC rectifing when I get a chance, but there are about a million options out there when it comes to regulation !
You might have a look at the datasheet for onsemi NCP NCV (Low Dropout Linear Regulator) to see if they might meet your needs. When I searched for 1a or higher LDO's there weren't many to choose from.
I guess this: NCV317BT, NCV317BTG Low drop out version of LM317

The difference between a 6.3vdc regulated output versus 9.2vdc unregulated input is less than 3v (maybe less than the necessary margin of some normal regulators) and thus I think you might need an LDO (low drop out) regulator so that it won't mistakenly turn off during normal mains power fluctuations. I'm not good with maths, so please double-check.
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Old 4th September 2012, 04:28 AM   #12
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Have a look at the LT1084 - 1086, the higher rated devices actually have slightly better drop out performance at moderate currents than the smaller ones do.

It would be preferable I think to find a transformer with 8V secondaries and rectify this with schottky diodes into an LT-1085 for example.

Even with the CCS I suspect the filtration in your supply is probably not sufficient, particularly as I have no clue as to what you are actually using. I would recommend investigating the Maida regulator that SY and others espouse as it will give you very stable and low noise DC - you really don't want a lot of variation here even with the CCS.

The Maida is a high voltage implementation of the LM317 with a high voltage transistor or fet that is configured to drop most of the voltage difference between the input and output of the supply - this so that the regulator never sees a voltage across it that exceeds its voltage rating.
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Old 4th September 2012, 04:54 AM   #13
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I'm liking all these suggestions !
For CCS, I'm using the KandK audio CCS.

I was thinking about using the Salas SSHV2 board to clean up the DC prior to the CCS (KandK seem to be offering one now too), but I'll think about the Madia reg too.
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Old 4th September 2012, 05:44 AM   #14
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I use the K And K CCS in my power amplifiers, and find they work quite well, but I have no idea of how high a PSRR they achieve in your circuit, even with 80dB or better (it's probably less) and a 1V low frequency variation on the raw supply this means something like 100uV could get through to be amplified by the following stage, where it might appear as several mV or more at the output of your phono stage.

The Salas HV shunt should be a very good solution to your issues - I've got one I'm going to use to power a future tube based I/V converter.
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Old 4th September 2012, 12:04 PM   #15
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Lordvader, it seems you have received a lot of good advice. The cure for your OP will probably be the HV regulator.
If you come back to the idea of a regulated DC heater supply, here are a few thoughts from when I did the same.
A rectified 6.3V will give 6.3*sqrt2 -2Uf. With a Shottky bridge that gives around 8.4V. Not to forget the ripple.
The LT LDOs are really nice. But I wanted to design something from components I had. I wanted a cheap and robust MOSFET as a pass element. It is hard to drive a Fet in the positive rail so I put in the gnd line. Used a reference, a PI and an error amp to drive it. The REF192 is probably a bit over the top, but that is what I had in the drawer. A TL431 would do nicely, I guess.
Here is the schematic and a photo of what it looks like on comfortably large pcb.
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Old 4th September 2012, 01:20 PM   #16
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Originally Posted by grommeteer View Post
With a Shottky bridge that gives around 8.4V.
Excellent idea, but a little bit of information is missing. Forward voltage drop pattern is a lot different between different models of Schottky and varies from 0.1v to about 3v. With the 6.3v heater circuit we don't want to drop voltage much. SO, for bridge rectifier, try the combination of "low voltage high current," such as MBR1035 or MBR1635, whereby the forward voltage drop chart looks much like a straight up wall and you won't get voltage loss.
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Old 4th September 2012, 04:14 PM   #17
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Daniel, good point. The SS36 I used was in the drawer. It drops about 0.35V and you can certainly do better than that.
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Old 5th September 2012, 02:23 PM   #18
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Hey all.

Though I'll upload a photo of the layout.
The only main difference is that the power to the top right CCS (red wire) goes over the heater wires (rather than under), and takes a more direct path (goes straight up, then left, rather than up, left, up).

The channel on the left (which happens to be the left channel), is particularly noisy, and there is buzzing in both channels (very noticable on my headphone amp, which has far too much gain). Originally I had a ground bus, which I replaced with the star arrangement you see here. Still there is buzz.

For the time being, I added a 220uF reservoir capacitor (near the bypass caps you can see on the right), and a 100uF decoupling cap near each CCS in the left channel (left the right channel alone for the time being, just wanted to hear what would happen). The reservoir cap, and decoupling has reduced noise a bit, but it's still there.
(haven't taken any measurements yet, will do that tomorrow).

Hopefully soon I can have a go with a HV regulator (if I rip out the bypass caps, I'll have heaps of space on the right side for a HV reg with heatsinks).
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Old 5th September 2012, 02:36 PM   #19
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Quote:
Originally Posted by grommeteer View Post
Daniel, good point. The SS36 I used was in the drawer. It drops about 0.35V and you can certainly do better than that.
Unlike the heater circuit, the shottky with the biggest voltage drop curve, the Fairchild Stealth, when combined with a CRC can be used for that "open sound rectifier" in the high voltage tube amp power section. That idea is not the exclusive territory of tube rectifiers. But solid state is a bit more needy and you will want to use RC's across the transformer's primary and secondary windings.

If there's transformer amperage to spare, it seems that the use of some bleeder resistors could send some high voltage low current peaks to ground. A turntable amp is probably not loading the power supply much, so modest bleeder resistors could be worth a try for wasting some power noise peaks. But, I'm not guaranteeing any benefit from bleeder resistors--only saying worth a try. For favorable proportion, you can put soft switch diode series with bleeder resistors since noise will fire up a diode about a third harder than clean DC, thus you can trick the bleeder resistors into wasting more noise than clean power. Also worth a try, but not effectiveness not guaranteed.
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Old 5th September 2012, 04:45 PM   #20
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Default Buzz?

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Originally Posted by lordvader View Post
. . . I'm carrying B+, 0V, earth. . .and there is buzzing in both channels (very noticable on my headphone amp, which has far too much gain). Originally I had a ground bus, which I replaced with the star arrangement you see here. Still there is buzz.. . .
Here's a briefing on the mostly likely cause of buzz: Ground Loop in your Hi-Fi? - Tricks and Techniques
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