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Old 31st January 2013, 08:32 PM   #141
dadod is offline dadod  Croatia
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Quote:
Originally Posted by smms73 View Post
I have download the ltspice file that you post , and have tested , there are alterations that i would like to propose, if you guys do not mind.
First is to lower the voltage , it does not make much sense that hight voltage, you will be ok with minus/plus 15 volts , less power waste. And less thermic problems with the circuit. Other is to change the mirrors transistors (bc550c) with bc327-40 and bc337-40, they should be better in dealing with the current that the circuit use, the distortion will be lower.

The 2sa1381 and 2sc3503 is a very good choice , but the cordell models are a bit to much optimist in respect to early voltage, so expect a litle more distortion in reality that with the simulation, but in the overall it seems a good circuit .

I use current sources instead of mirrors , I get even lower distortion that this circuit post here:

dac I/V convertion with very low distortion
Thanks for your suggestions.
I use higher power voltage to get distortion as low as possible with this circuit.
There is low voltage in this thread, simpler and, probably, good enough. One feature important to me was the possibility to drive 300 ohm headphones, not only to be line amp only. By the way, I don't thing that BC337-40 could lower allready very low distortion.
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Old 31st January 2013, 09:01 PM   #142
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The BC3x7 has a much larger die, so more thermal inertia and less thermal modulation. This is the theoretical basis for its improvement on quality. However it is much slower than the BC560C and while either of these will probably keep measured distortion pretty low, it was my experience in listening tests that the speed of the BC5xx is more important for a small-signal circuit.

At frequencies where R3 and R12 are bypassed, the effectiveness of the J1 CCS will not matter. At DC it will however.

For transient performance, compare the AC current through Q1 and Q2. Lower is always better. Multiply this current by the output impedance and you have a metric for the quality of regulator load response. With this metric you'd find that many regulators have fantastic output impedance but poor transient load response.

You need to consider inductance in absolute terms. Viewing output inductance against the backdrop of output resistance will just show you the proportion of the two. Compare the actual output inductance value to the real inductance of a cm of wire; how many virtual cm of wire does your regulator have?

Same for output resistance. How does it compare to the resistance of the PCB traces? How does the output resistance compare to the standard trace size used for carrying currents of this magnitude?
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Old 31st January 2013, 11:56 PM   #143
bcarso is offline bcarso  United States
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Originally Posted by dadod View Post
One think were I have my concern, jfet CCS between Q1 and Q2 bases. In the simulation it looks good, but does 1.3V is enough for 2SK170 to behavs as good CCS at 1.7mA??
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Old 1st February 2013, 12:09 AM   #144
smms73 is offline smms73  Portugal
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Originally Posted by keantoken View Post
Adapt your circuit to give similar Zin, Zout and gain and then we can toss boulders.

Early voltage of the A1381/C3503 should not matter if the Baxandall pairs do their job
ok, is fair , i will design a circuit similar to yours but with current sources instead of the mirrors , i like a good challenge .

Baxandall pair will lower distortion produced by the early voltage not eliminate it, the higher the early voltage of the transistor the better, try to swap the 2sa1381c and 2sc3503c with other model in the simulator, and you will see that the distortion increase.
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Old 1st February 2013, 12:14 AM   #145
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Can't right now. I'm cooking kraut burgers on my rocket grill and it consumes wood like a mad hatter.
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Old 1st February 2013, 12:16 AM   #146
smms73 is offline smms73  Portugal
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Quote:
Originally Posted by dadod View Post
Thanks for your suggestions.
I use higher power voltage to get distortion as low as possible with this circuit.
There is low voltage in this thread, simpler and, probably, good enough. One feature important to me was the possibility to drive 300 ohm headphones, not only to be line amp only. By the way, I don't thing that BC337-40 could lower allready very low distortion.
If you use lower voltage you will get the same distortion, because of the baxandall pair and the cascode at the input (test it ),

the bc550 with that current and voltage will be working in the knee voltage, if you use a bc327/337 you will have lower distortion (test in the ltspice), the bc327 have also a lower base spreading resistance than bc550 (lower noise)
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Old 1st February 2013, 12:25 AM   #147
smms73 is offline smms73  Portugal
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dadod , can you post the ltspice file of the power supply ? I would like to try it.
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Old 1st February 2013, 02:01 AM   #148
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Another reason to use the BC3x7 is that the low base resistance will contribute to better log conformance and thus better current mirror tracking. In theory. However the current mirror emitters already have over 27mV offset owing to the unequal degeneration and this will swamp out any Rb or thermal affects. Considering this discrepancy and that the circuit still performs as well as it does, I wonder if it will make any difference at all whether the BC5xx or BC3x7 are used. However it would be interesting to try and see.

Sometime I want to get hold of some SIP breakaway sockets; this way I can solder them in and keep plugging away with different transistors. I got some 20-pin DIP sockets already which allows for expedient prototyping.
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Old 1st February 2013, 09:15 AM   #149
dadod is offline dadod  Croatia
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Originally Posted by smms73 View Post
dadod , can you post the ltspice file of the power supply ? I would like to try it.
Here it is. Could you post spice models for BC337/40? In the zip file you'll find all models I am using.
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Old 1st February 2013, 09:19 AM   #150
dadod is offline dadod  Croatia
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Originally Posted by bcarso View Post
A slippery slope
It is simple to get that graph, but my question was about practical experience. I think that 2SK170 should be of GR type.
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