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Old 3rd September 2001, 03:17 AM   #1
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I have used the LT1085/1033's in the past,
and they seem to be well regarded (even though
they are an aging design).

Are there better performing (for audio) single
chip regulators, or is the only other option
(which I am desperately trying to avoid) to
build a discrete regulator??

Thanks in advance,


Dan
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Old 4th September 2001, 02:36 AM   #2
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In my experience, both the 78xx and 79xx 3-pins regulators work great and are very cheap; the only donwside is the output current limited to 1A (after that, they just shut down). You might need a current booster with these to achieve the higher currents needed on amps...
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Old 4th September 2001, 08:03 AM   #3
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Better than the 78xx and 79xx regulators are the LM317T/K and LM337T/K three pin variable regulators. They can be used upto 37 volts input (HV version is 50v), deliver 1.5 amps and can be used in conjuction with transistors to boost their current output. Great for preamps and even input stages of power amplifiers. They are marginally costlier than the 78/79 types.
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Old 4th September 2001, 12:34 PM   #4
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Smile Linear Technologies

Linear Technologies are suppose to be the undisputed champs, but I can't remember the designation...I think LT1085 is one of the two. You can get them from Digi-Key. They cost more, but are worth it.

They were used by Corie Greenberg back when he reveiwed for Stereophile mag. He put together a buffered-passive preamp that's suppose to be real nice. (The issue also has an interview w/ Nelson Pass). A verion of it it sold in kit form from Micheal Percy. If you download his (.pdf) catalog, you can also find the LT IC's. No web site...search on his name.

I believe the power supply was created by Walt Jung, he's really good w/ IC circuits and regulators.

Vince

Man, I just re-read your post, I feel silly, sorry.


[Edited by vdi_nenna on 09-05-2001 at 02:51 PM]
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Old 5th September 2001, 02:43 AM   #5
hifiZen is offline hifiZen  Canada
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I've recently been considering power supplies much more carefully. I've come to the conclusion that mindlessly tossing the "best" IC regulator into your circuit is not always the best option. For instance, the cheap and slow 78xx and 79xx series regs may offer a certain measure of isolation to high frequency noise...

The main advantage of the expensive regs their better line/load regulation. So, if you need a precise DC voltage or a low impedence power source, they're good for that. Adjustable regs also provide a lower noise output than fixed voltage types. But, depending on your circuit's PSRR, you may not need the line/load regulation, and would be better off to focus on other aspects like providing a higher impedence between various sub-circuits to prevent interactions via the power supply. Remember: low impedence = good signal path.

The more I thought about it, the more attractive various methods of passive regulation became... not only because you can acheive a lower noise supply with passive components, but there are fewer frequency-related problems and a passive solution is also generally cheaper than complex active regulation schemes. As well, I think a large number of problems occur at higher frequencies where circuits can't adjust quickly enough to remain unaffected by the disturbance. Active regulators are just as incapable of effectively dealing with these frequencies, but passive schemes can work very, very well.

One device i'm using a lot more since I started doing lots of digital work is the ferrite bead. These little guys have basically zero impedence at DC, but will effectively block most of the high frequency junk which can cause insidious problems. Just be careful not to put too much current through them, or they will saturate. Another useful power supply device is the good 'ol pi-filter (remember your tube designs?). You don't need an inductor in there, just a resistor will do. Tack a cheapo fixed reg on there, and you've got a great supply (or preregulator).

Anyhow, when I need a good, stable DC voltage, I fish a LM317/LM337 out of the parts bin. They are 95% as good as the expensive LTs, which I no longer buy. If I'm really concerned about the performance, I'll invest the money I saved in better passive parts like larger capacitors, and I sleep soundly in the knowledge that I have a better power supply for less money...
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Old 7th September 2001, 06:29 PM   #6
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Question Where can you buy LT regs from now in UK?

I've been trying to source some LT regulators, but trying to get negative regulators at 3amps or above is proving to be more difficult than i first thought!

None of my regular suppliers stock them any more.

Any help greatly appreciated.
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Old 7th September 2001, 09:20 PM   #7
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a very effective way to boost the current capacity of an adjustable regulator is to add an external pass transistor... this way, you can have your 5-10 amps without shelling out the big bux, or chasing them down to the ends of the earth. Check out the datasheets for details...
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Old 7th September 2001, 11:29 PM   #8
paulb is offline paulb  Canada
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For a scalable way of adding external pass transistors to an IC voltage regulator, see Rod's Project 77 at:
http://www.sound.au.com/
His application is a fixed 13.8V supply, but it should be adaptable to a negative supply.
3 Amp negative regulators are not only hard to find, they're expensive! And then there's the heatsink.
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Old 7th September 2001, 11:57 PM   #9
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Dan,

Check out 'http://www.audiocom-uk.com/q_power.html'. These are pin compatable with a 78xx and 79xx regulator. They are basically high quality discrete regulators built on a PCB that plugs in where the monolithic regulator would. WARNING: These aren't cheap.

If you want to build your own, check out 'http://www.ednmag.com/ednmag/reg/199...97/01di_03.htm'. This is a Walter Jung design. It's VERY good.

Good luck.
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Old 8th September 2001, 04:15 AM   #10
hifiZen is offline hifiZen  Canada
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had to go here to read the article:
http://archives.e-insite.net/archive...97/01di_03.htm
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