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Old 1st February 2013, 09:22 PM   #161
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Output impedance is still 4K; not comparable to Dado's circuit. Gain is 4. C8 and C4 should go to their respective rails as they decrease RF PSRR. How is THD with 25k source impedance?

For AC/step response a plain Bode plot is not very useful. Plot group delay by changing the right side scale or plot Tg(Vout). When this is smooth there will be no small-signal AC or step response anomalies.
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Old 1st February 2013, 09:26 PM   #162
dadod is offline dadod  Croatia
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Originally Posted by smms73 View Post
Using the "B" type of current mirror gives 0.000029%
The "A" type give 0.000125%

A good improvement.
I used "B" type CM in my TT amp. Here distortion is already so low that trying to make it lower adding more transistor in my opinion is not so good idea.
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Old 1st February 2013, 09:42 PM   #163
smms73 is offline smms73  Portugal
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Kean if i construct this, I intend to use the volume control in the output so I will use (10K) , followed by a buffer. A gain of 4 serves my needs . Are you sure about the PSRR ? By my experience this way is better, but i will give it a try. Thanks by the tips.
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Old 1st February 2013, 09:51 PM   #164
smms73 is offline smms73  Portugal
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Dado have you measure your circuit in real life ? Simulations are only as good as the models we use , i tend to use bc327 and bc337 because they give me results close to the reality, if you use the models 2sa1381c 2sc3503c from bob cordell you will have very good distortion results in sim , but not so good in reality.
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Old 1st February 2013, 10:03 PM   #165
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Quote:
Originally Posted by smms73 View Post
Using the "B" type of current mirror gives 0.000029%
The "A" type give 0.000125%

A good improvement.
But A and B perform the same when you have 220/75 degeneration. Do you know of a better way to increase gain?
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Old 1st February 2013, 10:06 PM   #166
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Early voltage changes with operating point. Some transistors even have a negative early voltage at specific operating points. So perhaps Cordell's model is a compromise. Furthermore, perhaps the 2SC3503 and KSC3503 are not very similar in this respect?
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Old 1st February 2013, 10:07 PM   #167
smms73 is offline smms73  Portugal
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curves from 2sc3503c from bob cordell (green) and bc327 (blue), if you use 2sc3503c in sim you will have much better results , but this transistor is very good , it has a hight early voltage and low noise, but low Hfe , i like it very much , but i think the models are not correct.
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Old 1st February 2013, 10:07 PM   #168
dadod is offline dadod  Croatia
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Quote:
Originally Posted by smms73 View Post
Dado have you measure your circuit in real life ? Simulations are only as good as the models we use , i tend to use bc327 and bc337 because they give me results close to the reality, if you use the models 2sa1381c 2sc3503c from bob cordell you will have very good distortion results in sim , but not so good in reality.
I did not measure my circuit just I've done some listening with temporary power supply.
Please post LTspice files with all models you use, and I can compare.
You said it is your best result wit current mirrors, or you meant with current conveyor?
Current mirrors convey a current from one side to other with very low distortion.
In my circuit its easy to get a gain of 4 and lower distortion with it.
Be careful with volume control at the output, it will change the gain(it's conveyor).
By the way have you red this thread from beginning, there som more circuit presented?
dado
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Old 1st February 2013, 10:13 PM   #169
smms73 is offline smms73  Portugal
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Kean I have ask Joachim to measure a pair of sanyo 2sc3503 and 2sa the result is here:

Mpp

Very good transistors.
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Old 1st February 2013, 10:19 PM   #170
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Or, short of that, you could use DMOS parts with a few volts of threshold in place of the bipolars. Unfortunately the low frequency noise will usually be higher, and the transconductance lower, compared to the bipolars. Candidates if used might be the ZVN3306 and ZPN3306.
Correction: should have typed ZVP3306 for the P channel part.
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