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Old 28th August 2012, 02:23 PM   #401
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Quote:
Originally Posted by Joachim Gerhard View Post
Another problem solved, i know where the hum came from.... shame on me....again a stupid mistake but i will not tell you...
do you know the difference between a smart man and a wise man?
The smart man learns from his own mistakes...
The wise man learns from the mistakes of others.
Please let us be a litle bit wiser and tell us the mistake.
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Old 28th August 2012, 03:03 PM   #402
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I made some grounding wires that where not connected to ground but to a sensitive part of the circuit. It played some music though so i got confused. Know it is super clean.
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Old 28th August 2012, 03:35 PM   #403
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This is the idle per transistor so the input stage draws ca. 32mA in total.
The simulation of your circuit gives 8ma for each at 12v. the values for resistances you post is the ones that you use?
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Old 28th August 2012, 03:39 PM   #404
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Yes, i reduced the 5kOhm to 2kOhm.
I have the circuit in the system to listen so i can not measure again at the moment.
I will measure tonight.
The original measurements where done with 12V floating.
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Old 28th August 2012, 04:01 PM   #405
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That's alright Joachim, don't worry.

I have been thinking about the ground path, and i think the best is for you to connect the shield of the MC cartridge directly to the bases of the drivers transistores and then a connection to the star ground.

what do you think?
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Old 28th August 2012, 04:12 PM   #406
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some pnp transistors curves.
The BD140 have the best curves, but the gais is lower than the rest.
The biss transistor (0,5 Amp) have the better Hfe.
The BC328 is from a old stock.
the bc337-40 that i test have the same gain as bc550c , i test 5 of them and the hfe was similar.

The npn transistor all have better curves than pnp, the bd140 and bd139 are the ones with the most similar curves.

the BD140 and bBC328 where test with 50uA Ib steps the biss and bc560c with 10uA

the scales are horizontal 1 volt/cm Vertical 5mA /cm
Attached Images
File Type: jpg bc328.jpg (214.8 KB, 234 views)
File Type: jpg bc560c.jpg (226.5 KB, 228 views)
File Type: jpg bd140.jpg (187.5 KB, 218 views)
File Type: jpg biss.jpg (252.3 KB, 213 views)
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Old 28th August 2012, 04:29 PM   #407
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Originally Posted by smms73 View Post
That's alright Joachim, don't worry.

I have been thinking about the ground path, and i think the best is for you to connect the shield of the MC cartridge directly to the bases of the drivers transistores and then a connection to the star ground.

what do you think?
I've always thought that the best approach to very low level audio signals like MC cartridges was to use a balanced line between the cartridge and the head amp. I did this over 20 years ago. It works fantastic.
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Old 28th August 2012, 05:35 PM   #408
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I had some guests and we listened. I am really overwhelmed.
I am planning now to build the circuit more tidy and with a matching RIAA.
Do you think about a balanced input ? One pin of the cartridge to the input, one pin to the bases and the ground as a shield ?
I will now put the I/U into the lab and measure currents and voltages.
The BD140 looks really good.
What could also work well is the KSC3503 / KSA1381 combination.
2SC3601 / 2SA1407 is even better. Very fast and Rbee`in the 2 Ohm region.
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Old 28th August 2012, 05:56 PM   #409
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The 2sc3601 is a fantastic transistor, but the 2sa1407 is very different.
see the datasheet curves.

I think the old BD140 and BD139 are very linear and truly complementar.
And i bet the Rbb are also low.
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Old 28th August 2012, 05:57 PM   #410
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I measured the voltages again. Now ca.90mV ( plus-minus 2mV ) develop over each 5.1 Ohm emitter resistor and 30 ohm base stopper. The voltages of the version with the collectors on the input shows even more similar values on all resistors as before.
The idle current is about two times higher as in the simulation you did.
By the way 5.57V develop over the positive 2kOhm resistor and 5.67V over the negative.
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