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Old 4th February 2012, 04:51 PM   #5141
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Just going through pre orders i think i can buy 1000 2SJ74 and they are gone in a minute.
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Old 4th February 2012, 04:54 PM   #5142
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Quote:
Originally Posted by Joachim Gerhard View Post
For a balanced volume control i like configuration B, of cause without the input transformer. It is a shunt and does not have problems at higher frequencies. I use a shunt volume control too in my system and it sounds more transparent then the standard configuration A.
I'm not sure if I get how config B works. If the wiper pot is near 0R, we certainly need a beefy driver stage, no?

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Old 4th February 2012, 05:04 PM   #5143
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It depends on the resistors before the pot. I use 5kOhm in my system without problem. The 0R potion is rare anyway. The system has to be optimized so that most of the listening happen in the middle position of the pot and when we use a 20kOhm for example the input resistance will be higher then the 5kOhm series resistors anyway most of the time. In my system, at the volume i listen most i have around 10kOhm input resistance.
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Old 4th February 2012, 05:48 PM   #5144
RCruz is offline RCruz  Switzerland
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Just to be sure before I solder the parts in the heatsink, I would like a confirmation on my layout of transistors....
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Old 4th February 2012, 06:00 PM   #5145
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Ricardo, Frans can answer that. As far as i can see a lot of TO220 BJTs and Enhancement MosFets will work here. Japanese Transistors can have other Pin Out though.
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Old 4th February 2012, 06:06 PM   #5146
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Sampler, there are other ways to setup a J-Fet based balanced input stage. Here are two of them. You can also modify the second schematic ( Claudio ) for non feedback by simply connecting the sources to ground. I think that your solution is optimum though from the standpoint of distortion because it is balanced AND differential.
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File Type: gif b_pre_04.gif (31.6 KB, 240 views)
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File Type: pdf Claudio INA Sampler.pdf (148.8 KB, 72 views)
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Old 4th February 2012, 06:24 PM   #5147
sampler is offline sampler  Lithuania
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Sorry Joachim, it was too late to edit that nonsense, it's in parallel. This balanced stuff starts to confuse hell out of me. Ok, this is one version of bjt masterpiece. Lot's of gain, 0.5mV form your titan would give about 1Vrms out. Numbers look extremely good. I adopted MiiB's auto biasing, but servoing this thing is not so straight forward as we have common emitters between branches, so correcting offset on one side gives some effect on the other, but 2 servos should manage this. Still working on fet version. Can't figure out what would be the best way to servo it. Can't touch fet sources with low impedance as it spoils cmrr quite badly, so looking for other alternatives.
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Old 4th February 2012, 06:43 PM   #5148
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That is a masterpiece when i just look at it, awesome !!!
I just talked to MiiB. He is in Boston. He comes back on wednesday and may find a servo solution.
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Old 4th February 2012, 06:52 PM   #5149
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That is the way JC does the servo in the Vendetta.
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Old 4th February 2012, 07:33 PM   #5150
sampler is offline sampler  Lithuania
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And I believe it works so well for couple reasons. Low gain off stage resulting in low feed through, and what gets to sources acts only as feedback. AD711 and good integrating cap doesn't spoil things. But I mentioned that we cant touch fet sources as whole common mode rejection happens there. Even 1M to anywhere starts to spoil it. I will sleep on it. If nothing comes out, it will be your call after all. We can put your strange servo to mirrors.
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File Type: png cmrr_2.PNG (22.3 KB, 216 views)
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