DC-DC converter to get +-12V to feed the ouput opamps in DAC2000 - diyAudio
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Old 21st January 2004, 08:16 PM   #1
Ryssen is offline Ryssen  Sweden
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Default DC-DC converter to get +-12V to feed the ouput opamps in DAC2000

I have a 7,2v accumulator,and if I use the IC MAX743 DC-DC converter to get +-12V to feed the ouput opamps in DAC2000,
Will the switch frekv. diturb the audio output?

MAX 743:http://www.maxim-ic.com/quick_view2...._pk/1344/ln/en
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Old 21st January 2004, 09:28 PM   #2
mcs is offline mcs  Denmark
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You could also considder using a standard DC-DC converter. Like this one from Elfa: http://www.elfa.se/elfa/produkter/dk/2017321.htm

But either method will probably cause noise, so a metal shielding can will probably be a good idea. You should probably also add extra voltage regulators to remove noise/ripple after the converter...

Best regards,

Mikkel C. Simonsen
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Old 21st January 2004, 09:37 PM   #3
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You maybe don't want this advice but:

You could use 2 accumulators or even better, a decent transformer with a decent linear supply.

Don't expect much from switchers, they loose from linear supplies in terms of noise and they radiate RF in most cases ( certainly DIY switchers I might add ). Very hard to get them quiet and knowing that they will practically never be as quiet as good linear supplies I gave up trying.
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Old 21st January 2004, 10:14 PM   #4
Benjlv is offline Benjlv  United States
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could you explain your desired application a little more. I may be able to recommend another solution.

in general the inductor based power converters throw a lot of eletromagnetic noise around as a part of their function. This creates noise and thats no good. So unless you are able to keep the circuit away from the DAC or shield it very throughaly i would suggest finding another solution.
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Old 21st January 2004, 10:45 PM   #5
Ryssen is offline Ryssen  Sweden
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I have a 7,2Volt accumulator and charger in my CD player that powers all +5v
in the cd(Pioneer pds 904)I have removed the trafo for +-12v,as
I have been using a tubeoutput stage,now I am building a Ext. DAC2000.I thought of powering the output ICīs in the DAC with
the 7,2v, but the opamps will not run on single + power(or will
they?)I thougt if I used a +- converter I got +- 12volts,and even
+- 5volts for the Dacīs.So the 7,2volts is in the cd player,what if I
put the converter in a shielded box?
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Old 21st January 2004, 10:54 PM   #6
hifi is offline hifi  Sweden
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Does the dac need to be portalbe or why the desire to have it powered frome one 7,2v battery?
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Old 21st January 2004, 11:02 PM   #7
mcs is offline mcs  Denmark
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Quote:
Originally posted by Benjlv
could you explain your desired application a little more. I may be able to recommend another solution.
I have another application but the same problem, so I would like to hear your recommendations. My application is an SSM2019 mic. pre. that needs +/-12V or so. I need to power it from a 6V battery, so I was also planning a DC/DC converter. But if you have better ideas?

Best regards,

Mikkel C. Simonsen
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Old 21st January 2004, 11:10 PM   #8
Ryssen is offline Ryssen  Sweden
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Quote:
Does the dac need to be portalbe
No,I thougt I got cleaner DC from battery,when I already have it in my CD player.Or whats your solution?
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Old 21st January 2004, 11:22 PM   #9
hifi is offline hifi  Sweden
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"No,I thougt I got cleaner DC from battery,when I already have it in my CD player.Or whats your solution?"

No you wonīt a simple linear supply will most likely give a much better result,

Why not just get 2pcs of lead batteries?

/micke
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Old 21st January 2004, 11:36 PM   #10
V/IR is offline V/IR  United Kingdom
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A DC/DC converter in a mic. amp is a real challange - but they used in professional phantom 48v boosters.

The biggest two problems are (1) the fast transients that you get with most modern current-mode switching regulators (2) the HF magnetic leakage from the switching inductor.

The fast transients can be dealt with by slugging the inductor switching with a capacitor this will affect the eff% of the converter but will help the transients. Using magnetically shielded inductors will reduce noise. Best would be to mount the DC/DC in the far corner of the enclosure in it's own electrically screened box with PI feed-thru filters on the inputs and outputs.

The other approach that gives a good noise figure and *no* inductor is the charge-pump. These are simple to build and will run at a fixed freq. AND duty cycle; you will need to re-regulate the outputs on these supplies - this would be great for +/-12V from 6V.
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