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-   -   Simple ACTIVE I/V for TDA1543 (http://www.diyaudio.com/forums/digital-source/17226-simple-active-i-v-tda1543.html)

rbroer 2nd July 2003 09:16 AM

Simple ACTIVE I/V for TDA1543
 
2 Attachment(s)
IMHO passive I/V for the TDA1543 doesn't have the dynamics which are obtainable with an active stage.
I also noticed passive I/V is very sensitive to the load (preamp and cables).

Finally finshed some boards and put them in.
The I/V is similar to the one here:
http://www.diyaudio.com/forums/showt...simple+TDA1541

TDA1543 is still powered by 8V, bias pot has been removed from pin 7. Will try later with 6.1V and 5V.

NOTE: R6 is multiturn pot to set the Vc(Q3) DC level, I choose 10V

As I hoped, dynamics improved a lot compared to passive I/V.
It's got firm tight bass and sounds very transparent.

Compared to the TDA1541A-S1 with similar I/V this comes really close. The TDA1541A-S1 has more micro-detail, more texture to voices and instruments, but the TDA1543 sounds (surprisingly) more transparent and bass control is a bit tighter.
In fact my girlfriend prefers the TDA1543 now, thinks it's less irritating than the TDA1541A-S1 when the volume is up.

Application: Philips CD player, non-oversampling, Kwak-Clock similar to version 6/7, synchronous BCK reclocking with VHC logic, output caps are Audyn KpSn (Tin-Foil)

If somebody tries he/she could experiment to find the (soundwise) optimal voltage for the DAC's output, by changing the base voltage on Q3.

Enjoy,

jan.didden 2nd July 2003 09:32 AM

Rudolf,

I have a question. Since the DAC would ideally like to see 0 VDC at its output to minimize distortion, why not replace D3, D4 by a single diode-connected transistor. That will get the input offset very close to zero, especially if you give it the same current.

Jan Didden

Elso Kwak 2nd July 2003 09:35 AM

Simple Active IV for TDA1543
 
Hi Rudolf,
This is certainly something I am going to try too!
The difference in current supplied by the current source Q1 and the current sink Q4, is to compensate for the static current from the DAC?
What did you connect to Vref ?
I would also try a second common base connected transistor for Q3. (Fig. 12-9 page 235 in Low-Noise Electronic Design by Motchenbacher and Fischer.) "The CB-CB pair is useful as a wideband current amplifier."
;)

rbroer 2nd July 2003 09:56 AM

Janneman,
See the link for the TDA1541 I/V.
But now, this DAC's voltage compliance is NOT 0V, but 1.8V to Vdd-1.2V
That's why any voltage within that band will do.

Elso,
The Current source supplies the total of the current sink, DAC bias current and DC current through Riv to get some Vce(Q3).
I think pot R6 is like 60~80 ohms or so.
I must admit, the Vce(Q3) is a bit low. But the results are still very good.

I left Vref unconnected.
One might experiment connecting a capacitor to it to find out if there are audible differences.

My next I/V version will indeed have a cascode. I carefully noticed Jocko's hints. It will be a folded cascode with another current sink that's cascoded by a J111 fet. This one shall be DC coupled !
Then I will start using some better BJT's like 2SA1085E & 2SC2547E

Cheers,

fedde 2nd July 2003 10:00 AM

Thanks Rudolf for sharing !!!

What passive I/V configurations did you try? I just tried 2x2.17 k with 1.26 k reference and the dynamics are quite ok! The bass could be somewhat tighter though...

But this looks very interesting...

Fedde

fedde 2nd July 2003 10:09 AM

Quote:

Originally posted by rbroer

I left Vref unconnected.
One might experiment connecting a capacitor to it to find out if there are audible differences.

Seems risky to me. The input could be susceptible for noise now. And I think that a proper DC level helps for minimising the distortion level of the DAC. Just try attaching a pot...

Fedde

jan.didden 2nd July 2003 10:43 AM

Quote:

Originally posted by rbroer
Janneman,
See the link for the TDA1541 I/V.
But now, this DAC's voltage compliance is NOT 0V, but 1.8V to Vdd-1.2V
That's why any voltage within that band will do.
[snip]Cheers,


OK Rudolf, I didn't look at the link, that is indeed what I meant. But, beg pardon, in your latest diagram the input offset is shown as 2.4V, which is outside the 1.8 to -1.2 you quoted (which I have not verified, too lazy I'm afraid). Then again, although a compliance spec is given for operation within a (reasonable) linear range), ALL DACs I have seen work optimal with a zero offset into a zero impedance. Your call of course, just wondering why the change.

Jan Didden

rbroer 2nd July 2003 11:19 AM

Ok Jan,
one more try before I give up: ;)

TDA1543 voltage compliance is 1.8V to Vdd-1.2V
With a Vdd of 8V the voltage compliance is 1.8V ~ 6.8V
:nod:

So anywhere between will do.

This is why the TDA1543 is quite special and one can almost have 2Vrms output swing PASSIVE,
by carefully selecting Vdd, Rbias and Riv

I think Fred called this DAC a:
hybrid transconductance device with voltage feedback (about 2k open loop output Z,so not a true current out device)

:cool:

fedde 2nd July 2003 12:19 PM

Rudolf, what was the maximum I/V resistor you tried in the passive config ? Still no good dynamics !?

How high is the input impedance of the (pre-)amplifier you use !?

Fedde

jan.didden 2nd July 2003 12:40 PM

Quote:

Originally posted by rbroer
Ok Jan,
one more try before I give up: ;)

TDA1543 voltage compliance is 1.8V to Vdd-1.2V
With a Vdd of 8V the voltage compliance is 1.8V ~ 6.8V
:nod:

So anywhere between will do.

This is why the TDA1543 is quite special and one can almost have 2Vrms output swing PASSIVE,
by carefully selecting Vdd, Rbias and Riv

I think Fred called this DAC a:
hybrid transconductance device with voltage feedback (about 2k open loop output Z,so not a true current out device)

:cool:

OK yes, I mixed up those voltage levels. Seems you know what you're doing, still don't see why. But that's OK.

Jan Didden


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