DC-DC converter to get +-12V to feed the ouput opamps in DAC2000

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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.
 
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.
 
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 IC´s 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 Dac´s.So the 7,2volts is in the cd player,what if I
put the converter in a shielded box?
 
Benjlv said:
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
 
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.
 
V/IR said:
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.

The Linear Technology LT1054 looks like a posibility. The datasheet includes a circuit for a 5V to +/-12V converter - the current is limited to 25mA, but that may be enough. I guess there aren't any higher power versions available?

With the 7.2V supply the original poster has available, I guess a regulated +/-12V supply using one LT1054 should be possible...

Best regards,

Mikkel C. Simonsen
 
The LT1054 would work, but maybe difficult to obtain and limited in the Iout possible.

Charge pumps are very easy to build and I would advocate building one from discretes and a 555 timer. Regulation can be done with a linear regulator after the event - unlike switched DC/DC you do not need active control on the charge pump. Anyone using a DAC could generate the charge pump drive signal from the LRCK (44.1KHz), no async. noise.

We designed a product awhile back that needed -1v to -3v to bias an LCD display; from recollection we had a spare microcontroller pin and ended up using this with a couple of diodes (BAS16) and small capacitors to get this supply - I guess it probably didn't cost more than $0.08

It might be interesting to design an 'audiophile' DC/DC converter...
 
Anyone using a DAC could generate the charge pump drive signal from the LRCK (44.1KHz), no async. noise.
How is this done?The power konsumption of 4 OPA627 is 28mA
Max,maybee if i built 2 of these.One for 2 OPA627,or AD8610.And I wonder if the relays for switching between the 2 filter sections is realy nessesery?And it says on the schema for the LT 1054 that
max voltage is 15volts can I use 7,2Volts for the +- 12v schema
instead of 5v as it says on the schema?Meny questions.:confused:
 

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