Found Jim Hagermans old Jimdac in another thread:
http://www.hagtech.com/pdf/jimdac.pdf
With a clever arrangement the 1543s outputs are without offset and fineadjustable to zero. Suits me fine as I want to use (nonDC amorphous core) transformers directly at the DACS output.
Any comments on the zero offset arrangement?
http://www.hagtech.com/pdf/jimdac.pdf
With a clever arrangement the 1543s outputs are without offset and fineadjustable to zero. Suits me fine as I want to use (nonDC amorphous core) transformers directly at the DACS output.
Any comments on the zero offset arrangement?
Take a closer look!
The TDA1543 is fed with +/-2,5VDC making the output 0V.
Zero DC-offset adjustment is with Vref resistor.
The digital input is therefor "level translated", see schematic!
My idea was to feed it with +/-4V and skip the output filters and OPs. As my output transformers can take no DC at all this must be a possible way to fix it.
My concern is how to look at the output loading as there will be no DC-current through the I/V-resistor, only AC?
The TDA1543 is fed with +/-2,5VDC making the output 0V.
Zero DC-offset adjustment is with Vref resistor.
The digital input is therefor "level translated", see schematic!
My idea was to feed it with +/-4V and skip the output filters and OPs. As my output transformers can take no DC at all this must be a possible way to fix it.
My concern is how to look at the output loading as there will be no DC-current through the I/V-resistor, only AC?
I'm sure you can attach a DC-servo from the output and to the regulator. The servo tweaks the +-2.5 voltage. It should be possible.
If you'll have a floating 5 volt supply and to that you'll add a virtual ground (with an opamp) which is controlled from the output of the dac.
If you'll have a floating 5 volt supply and to that you'll add a virtual ground (with an opamp) which is controlled from the output of the dac.
Check this DC-servo. It's the same idea.
http://www.ibiblio.org/tkan/audio/dynahi.html
This servo is tweaking the two current generators.
http://www.tangentsoft.net/audio/ppa/
The PPA has a "ground channel". You'll need almost the same.
http://www.ibiblio.org/tkan/audio/dynahi.html
This servo is tweaking the two current generators.
http://www.tangentsoft.net/audio/ppa/
The PPA has a "ground channel". You'll need almost the same.
revintage said:Take a closer look!
The TDA1543 is fed with +/-2,5VDC making the output 0V.
Zero DC-offset adjustment is with Vref resistor.
The digital input is therefor "level translated", see schematic!
My idea was to feed it with +/-4V and skip the output filters and OPs. As my output transformers can take no DC at all this must be a possible way to fix it.
My concern is how to look at the output loading as there will be no DC-current through the I/V-resistor, only AC?
Sorry Lars, I totally overlooked the dual supply for the TDA1543.
I am not sure the offset will be low enough for IV-transformers. Probably the Sowter 8347 can take it; the 9762 not!
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