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Old 10th July 2002, 04:47 PM   #11
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Default Substitute 78xx 79xx with YOUR fine Regulator

rbroer

You ask if you should make PCB with your circuit.
Why not make it possible to fit in 78xx and 79xx positions.
make a 20-25x60 mm PCB with 3 pins at one short end.
Then you could substitute any of those ICs
with your regulator.

I have seen such small PCBs
used for Dual OPamp -substitute, using 2 Hi Quality single OPamps.

A sort of of "piggy-back" construction.

If you need more Current you could also use an TO126 Transistor
as an output-buffer, and include it in feedback-loop.

That would take some of the pressure off the OP.

Glad for your sake, that janneman liked your design.
He is surely right is his judgement!

gromanswe
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Old 10th July 2002, 05:36 PM   #12
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Question Regulators

Hi James.
I don't like guessing- I never play in the lottery- but my best guess is:
purple= TL431
red= LM317
blue/light blue= LT1086
Apart from the noise issue one should consider carefull the application of the regulator whether it be digital audio, analog audio; line or MC phono or a clock supply.
Rudolf came with the large cap mod 6800F on the KWAK-CLOCK supply. Though very sceptical about this I tried it and it improved the sound! With such a large cap one should be carefull for the large inrush current and check if your rugulator can take it. Actually I am using 10000F. A TL431 with a BC550C transistor wouldn't live long this way, I believe. LT1086 or LM317 can take it. How the AD811 reacts to the clock and the large cap I don't know for sure. I tried once a LT1021-5 and a OP27 or AD817 opamp in the scheme like proposed by Rudolf and was not impressed by the result sonically.
I am still not convinced that low noise supply= low jitter/ low phase noise
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Old 10th July 2002, 07:31 PM   #13
rbroer is offline rbroer  Netherlands
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Up till now I've been using TL431's used as local regulators for DACs like TDA1541, Kwak Clock etc. Local bypassing with electrolyte and 805 smd duet of 10nF and 100nF of different ceramics.
I like the idea of decoupling the various supplies by the inherent use of series impedances, be it resistors or current sources.
They are easy to implement as well and have inherent current limiting. The decoupling also limits the "fighting each other" (potential) problem, which will occur with multiple regulators being fed from the same raw supply or pre-regulated supply.
Maybe they're too noisy for a high gain preamp, but so far I've not heard audible noise problems.
What I don't like about them is you need to know the maximum current draw for the circuit one is powering, this means measuring all the time since datasheets are not always correct (for example the max current draw for TDA1543).

I am hoping to get some feedback from people having tried various regulators for divers applications.
For the circuit posted and tested I have some initial doubts about PSRR at higher frequencies etc.

I like to keep things cheap and simple, so try to avoid esoteric parts, but spend space and money on (simple) individual regulators with very local bypassing, ground planes etc.

So will such an opamp approach give better sonics than using a TL431 shunt regulator when connected to the Analog power supply of a dac chip ?

And for ALW, a TL431 used as a filtered reference shouldn't be a problem ?

Rudolf.
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Old 10th July 2002, 09:18 PM   #14
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Default Low power reg etc

Hi Rudolf,

How's the new government coming along in the Netherlands??

Seriously now: I have trouble following your logic on the supply architecture. Why would they 'fight each other'? They run from a common raw supply, and there may well be some load-variation-caused-noise reflected from an output to the (common) input, but that will (hopefully) be blocked by the input rejection of the other regulators.

I would never use series impedance decoupling. I know Philips used it a lot in earlier CD players, which sounded awfull (well, OK could have been coincidence). Think about it: you go to all this trouble to design a supply with zero output impedance and therefore zero variation with load variation, very low noise etc, then ruin it by a series impedance. That will surely give you load dependent supply variations where you don't want them. Or am I missing something?

Cheers, Jan Didden
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Old 11th July 2002, 12:20 AM   #15
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As per the nice colored graphs of noise response vs. frequency response, the graph for the 431 is not valid for the whole frequency range on this forum thread. In the circuit that was suggested, the 431 output goes through an RC circuit which will limit the frequency range of the noise response of the 431. However, the noise of those resistors and capacitors can absolutely be an issue. Input current noise in the op-amp will result in a voltage noise when it flows back into the RC.

I would look very carefully at the noise spectra of the whole circuit and specifically look very carefully at the noise contribution of the RC filter between the reference and the op-amp. You may find that better filtering in front of the reference with no RC between the reference and the op-amp results in an overall lower noise circuit. When you do this, you may also want to consider some of the better references that are now on the market that have far superior noise and power supply rejection characteristics w.r.t. the 431. Unless you are planning on commercializing this, the small added cost of a better reference is warranted.

What do you plan to drive with this op-amp? If it is digital, it is virtually a given that you will have capacitive load as you will need decoupling capacitors close to the digital circuity no matter how good your regulator. You may find that a resistor at the output of the op-amp but inside the feedback loop gives you better overall performance. Not having the resistor there may result in faster overall settling, but you will likely have ringing which is probably worse than giving up some bandwidth.

Alvaius
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Old 11th July 2002, 12:45 AM   #16
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W.R.T. does low noise = low jitter\phase noise, I can state, unequivocally, from years of analog\digital experience in communications systems, video, audio, etc. that absolutely it does, with conditions.

The condition is, what is that bandwidth of that noise and what types of circuits am I exposing it to?

I could take a 1V pk-pk sine wave at 60Hz, ride that on top of a 5V digital supply, and contribute absolutely no audibly perceptable jitter to many simple digital circuits, i.e gates, buffers, etc. Heck, it may make no difference at 1 MHz. This is all assuming good high frequency decoupling of course. If that sine wave was at 100MHz then that is a whole different story. The transitions for many logic family are so fast and the edge speeds are so fast, that low frequency power supply variatians do not cause huge jitter issues. Now if I did the same thing to a PLL, which is an analog circuit, then that 60Hz wave could do a lot, the 1 MHz would drive it crazy, and the 100MHz may go unnoticed as it would be completely filtered out [implementation dependant]. And the existence of a PLL is not always obvious. Some DACs multiply the frequency internally.

All circuits are analog at some level. Digital circuits, by their nature, often have inherent filtering of low frequencies. Analog circuits often have inherent filtering of high frequencies. When in doubt, assume nothing and experiment, but only after thinking out absolutely all the causes and effects of your circuit.

I designed a very large system imaging system many years ago. The largest contributor of noise in the A\D conversion was jitter of the sampling clock caused by noise injection through the power supply into the digital timing circuitry. That noise injection was caused by switch mode power supplies sitting in another rack 20 feet away. In theory both systems were fully isolated from each other. It is not hard to see why $300 power cords can improve your audio. However, I find that $3.00 of 8 guage battery cable ran between the chassis of your equipment and $5.00 shielded power cords works just as well... but that is for another forum which I think I will start.....
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Old 11th July 2002, 11:47 AM   #17
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Default Low power etc

Alvaius,

I agree 100& with what you write. This is a very comprehensive account showing clearly that you cannot whip together an application-sheet circuit and expect it to be optimal for your particular requirement. Power supplies really are systems that need to be considered as systems regarding noise, bandwidth, Zout etc. In fact, reading your account I cannot escape the conclusion that a high performance power supply is not that different from a high performanbce power amplifier in term of issues and aspects!

I own a couple of 1970's Sony power amps, some of which have switching power supplies, some are class D switching throughout. This was quite revolutionary at the time, engineered like HF equipment. Interestingly, many people who have heard them commented on the excellent sound they produce, until I show them pictures of the output waveforms with all the switching noise and spikes...! One of the amps has a broken supply, which I am going to replace with commercially available switching supply modules. They will undoubtedly measure better, but it will be interesting to see if the perceived sound quality changes.


Cheers, Jan Didden
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Old 11th July 2002, 03:56 PM   #18
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What Janneman states is exactly how I feel about it right now.
There are most probably different requirements for power supplies depending on what you're powering.

Up till now I've been using individual TL431's setup as shunt regulators for powering low power devices. They are fed from raw supplies.

For example a DAC&IV stage I use has individual TL431's for DAC analog supply, digital supply, the pos&neg rail of I/V & output stage and the clock circuit.

Now I do like the results, but I may be able to improve sound and here's where I need the experts on this forum.

So I would appriciate suggestions, or have people telling me I'm completely on the wrong track...

A "gut feeling" tells me the analog supplies for DAC and I/V stage might benefit from lower noise supply, clock might be fed from better supply as well, digital should be ok with these TL431's.

Life is too short to try all power supply permutations myself; this board is a great place for sharing experiences and knowledge and I've found a lot of useful info already.

alvaius,
can you tell us which references are better than a TL431 ? I've seen the LM329 but that's not 2.5V
After some searching I found the datasheet for TLV431 shows a input noise vs freq diagram. TLV431 has ca. 210nV/SqrtHz between 100Hz and 100kHz, whereas the LM329 has ca. 75nV/SqrtHz zener noise.

Regards Rudolf.
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Old 11th July 2002, 04:11 PM   #19
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Default Hello rudolf.

If I should chose a device,
where the budget is not so important,
my favourite is this one.

It has Noise 1.5 uV p-p at 2.5V
temp koef 2.5ppm/C where TL431 has 50.0
can be supplied 8-36 Volts
Can drive/SINK 15 mA
Have pins for NR=noisereduction cap
and TRIM referensvoltage
Is also availeble in 4.096 V and 5.00 V
SO8 or DIL8

http://pdfserv.maxim-ic.com/arpdf/MAX6225-MAX6250.pdf

That must be a darn good referens!

Groman
good sometimes. sometimes not
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Old 11th July 2002, 05:02 PM   #20
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Default Another one, 5dB better PSRR

http://www.thaler.com/thcpdf/vre3050.pdf

groman
searching the net
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