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?
In other words you think it´s so lousy it isn´t even worth considering😉 ?!
Personally I have the uttermost respect for Hagerman, that has the ability to "think outside the box".
Personally I have the uttermost respect for Hagerman, that has the ability to "think outside the box".
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.
Hej Per-Anders!
Think I am OK with the "manual" zero adjustment as proposed in the original schematic.
More concerned about how one should look at the passive I/V loading.
As you know, this is not my territory
!
Think I am OK with the "manual" zero adjustment as proposed in the original schematic.
More concerned about how one should look at the passive I/V loading.
As you know, this is not my territory
!
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.
Per-Anders!
Think you will have be more specific about "tweaking the two current generators".
Can´t see any servos in the original schematic. There is just I/V resistors to ground followed by two OPs.
Think you will have be more specific about "tweaking the two current generators".
Can´t see any servos in the original schematic. There is just I/V resistors to ground followed by two OPs.
Per-Anders!
Remember I am total novice in the digital/sand-department.
If it works without servos, why then add them?
My idea was that the RDC of the transformers should be the passive I/V-load. So in my ignorance I thought it was just to have the right value of RDC.....😉
Remember I am total novice in the digital/sand-department.
If it works without servos, why then add them?
My idea was that the RDC of the transformers should be the passive I/V-load. So in my ignorance I thought it was just to have the right value of RDC.....😉
revintage said:
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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