dac I/V convertion with very low distortion - Page 25

Shinja · 18th August 2012, 08:11 AM

I understood the "base current" of driver transistor swing due to the current swing of 5k ohm resistor.
I misunderstood again ,sorry.

Shinja · 18th August 2012, 09:31 AM

not so good...

smms73 · 18th August 2012, 11:50 AM

Quote:

Originally Posted by Joachim Gerhard

Yes, the circuit i build makes some trouble. I have one or two ideas to try though.
I will publish what i have at the moment. Maybe somebody has an idea how it can be made to work.

Joachim,
maybe the problem is the dc offset , try connect 2 batteries like this image.

smms73 · 18th August 2012, 11:58 AM

Quote:

Originally Posted by Shinja

not so good...

I think Q3 and Q2 have very low Vce

Joachim Gerhard · 18th August 2012, 12:21 PM

I will try post post 243.

dirkwright · 18th August 2012, 01:15 PM

This one sim's with THD of 0.0007%. S/N is 135dB. Just a tweek here and a tweek there. No big deal. 1mA in and 1.41Vrms out.

Joachim Gerhard · 18th August 2012, 01:39 PM

I wonder why my build did not work so far. I use different resistors from dirk but it is basically the same. i will do some research soon.

Joachim Gerhard · 18th August 2012, 02:28 PM

I tried the version with the two batteries. Again no luck. What i can see is oszillation.

tankcircuitnoise · 18th August 2012, 03:27 PM

And 1 nanosecond edges will upset operating conditions.

The nonlinearity of bipolars (I do like bipolars, carefully used),

Ie Delta_Vbe
1mA -------
2.718mA +0.026 volt
1/2.718mA -0.026 volt

may show the distortion issue. Boosting Vbe by .026v will almost triple Ie.
Reducing Vbe by .025v reduces Ie by approx 70%.

That is
1mA--baseline bias
2.718mA at +26mv
0.39mA at -26mV

That's a big positive response, versus weak negative response.
Lots of 2nd harmonic.

tank

Joachim Gerhard · 18th August 2012, 04:05 PM

I will try a bandwidth limiting.

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18th August 2012, 08:11 AM	#241
Shinja diyAudio Member Join Date: Jul 2008	I understood the "base current" of driver transistor swing due to the current swing of 5k ohm resistor. I misunderstood again ,sorry.

18th August 2012, 12:21 PM	#245
Joachim Gerhard diyAudio Member Join Date: Mar 2009	I will try post post 243.

18th August 2012, 01:39 PM	#247
Joachim Gerhard diyAudio Member Join Date: Mar 2009	I wonder why my build did not work so far. I use different resistors from dirk but it is basically the same. i will do some research soon.

18th August 2012, 02:28 PM	#248
Joachim Gerhard diyAudio Member Join Date: Mar 2009	I tried the version with the two batteries. Again no luck. What i can see is oszillation.

18th August 2012, 03:27 PM	#249
tankcircuitnoise diyAudio Member Join Date: Jan 2012	And 1 nanosecond edges will upset operating conditions. The nonlinearity of bipolars (I do like bipolars, carefully used), Ie Delta_Vbe 1mA ------- 2.718mA +0.026 volt 1/2.718mA -0.026 volt may show the distortion issue. Boosting Vbe by .026v will almost triple Ie. Reducing Vbe by .025v reduces Ie by approx 70%. That is 1mA--baseline bias 2.718mA at +26mv 0.39mA at -26mV That's a big positive response, versus weak negative response. Lots of 2nd harmonic. tank

18th August 2012, 04:05 PM	#250
Joachim Gerhard diyAudio Member Join Date: Mar 2009	I will try a bandwidth limiting.