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Old 22nd July 2004, 10:56 PM   #1
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Default transformer coupled TDA1547 differential mode

Hi..
i'm thinking about to do the final tweak in my marantz CD10, after tweaking power supplies and clock i would like to redo the output stage and remove the many ne5532 and 5534 replacing with a transformer or with a fet stage...
the problems are many...
1) I would like to bypass the embedded opamp in the tda1547 (as you can see in this link... not appeared for the first time in this forum http://digilander.libero.it/paeng/a__tda1547_tweak.htm ) and in this case the current on out is very low, if i will use this sot1 (1:1.. 1:2) i have to do an amplification stage for having 2vpp on out.
2) the cd10 have two tda1547 in differential mode, and i want to mantain this characteristic.
3) I have to out unbalanced... my amps are all umbalanced...
4) I would like to do a very simple stage...

I have seen also other transformer like the sowter 9055 (http://www.sowter.co.uk/dacs.htm) but my experience are all in digital electronic... i really need an help... an idea, a similar schematic to view....
I've seen on a post, some months ago, the project of D1 stage (but unfortunately not for differential dac and umbalanced out)... there is some of the people that have realized this stage on tda1547 who wants to tell me the final results with this???

thanks in advance for help
bye to all
DoctorWho70
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Old 23rd July 2004, 08:10 AM   #2
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Why would you want to do this tweak? The TDA1547 is a bipolar integrated circuit (not CMOS), so it has reasonable quality internal opamps. If at all, I would use a discrete active current to voltage converter, e.g. discrete opamp or at least a discrete transistor circuit that keeps its input at 0 V.

Using resistors as converters means the current output is not kept at 0 V, and this will certainly degrade the linearity of the switched capacitor current source.

Also, I am concerned about nonlinear input current into the unused op-amp. I the noninverting input is left open, it may start switching wildly. It may be better to connect this input to one of the rails to obtain a defined state.
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