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Old 23rd April 2011, 07:18 PM   #501
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Quote:
Originally Posted by ThorstenL View Post
And work is the curse of the drinking (and music listening and shagging) class, to which I definitly should be a-counted...

Anyone needs a consultant?

Ciao T
I saw a picture of you and your wife on the web, everyone should be so lucky. You could charge a lot more for that consulting than mere audio.
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Old 23rd April 2011, 10:07 PM   #502
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Sorry Bappe, nobody seems to be interested in a BUILDABLE, quality phono front end.
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Old 24th April 2011, 12:34 AM   #503
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Quote:
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Sorry Bappe, nobody seems to be interested in a BUILDABLE, quality phono front end.
You're not listening. This is about all we are talking about. Using what we can get now.
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Old 24th April 2011, 12:45 AM   #504
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2SJ74 devices are difficult to get. Yes, there are a few around here. However, WE find them almost impossible to get in quantity, and we would like to avoid them in less critical designs, JUST LIKE THE JC-3. Why do you think that we used IC's? However, there is a 'loophole' that I would like to explore. This is: What about JUST N channel Toshiba or equivalent devices? They are quiet, still available and not too expensive, YET! This could have made the JC-3 even better. That is why I am attempting to discuss topologies like you use in IC design, but in discrete.
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Old 24th April 2011, 09:37 AM   #505
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Hard to get 2Sj74? Nope, easy. In DIY quantaties.

Here's my take on a "VendettaRevA" in Retin style. SNR is 75 dB rel 500uVrms 20-20kHz unweighted. Good enough, IMO. Gain is 64 dB. I remade the

DCservos a bit and I use OPA627 as DC servo OPamp.

I use Zetex ZVP/ZVN3310 at a failry high idle current instead of the original MOSFETs.

The 2nd stage in the first amp-stage is now made outof BJT:S running at around 20mA.





Quote:
Originally Posted by john curl View Post
2SJ74 devices are difficult to get. Yes, there are a few around here. However, WE find them almost impossible to get in quantity, and we would like to avoid them in less critical designs, JUST LIKE THE JC-3. Why do you think that we used IC's? However, there is a 'loophole' that I would like to explore. This is: What about JUST N channel Toshiba or equivalent devices? They are quiet, still available and not too expensive, YET! This could have made the JC-3 even better. That is why I am attempting to discuss topologies like you use in IC design, but in discrete.
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Old 24th April 2011, 10:05 AM   #506
MiiB is offline MiiB  Denmark
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would it harm to take the first servo out.. and instead capacitor couple..in order to get too much varped record filtered out a bit..

Last edited by MiiB; 24th April 2011 at 10:09 AM.
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Old 24th April 2011, 11:31 AM   #507
RCruz is offline RCruz  Switzerland
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Quote:
Originally Posted by ThorstenL View Post
Building stuff is hard work.

And work is the curse of the drinking (and music listening and shagging) class, to which I definitly should be a-counted...
Indeed
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Old 24th April 2011, 01:26 PM   #508
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Quote:
Originally Posted by john curl View Post
2SJ74 devices are difficult to get. Yes, there are a few around here. However, WE find them almost impossible to get in quantity, and we would like to avoid them in less critical designs, JUST LIKE THE JC-3. Why do you think that we used IC's? However, there is a 'loophole' that I would like to explore. This is: What about JUST N channel Toshiba or equivalent devices? They are quiet, still available and not too expensive, YET! This could have made the JC-3 even better. That is why I am attempting to discuss topologies like you use in IC design, but in discrete.
Good point, John. I have advocated the use of N-channel-only phono input stages all along, for both MC and MM designs. The LSK389 is a good part.

Cheers,
Bob
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Old 24th April 2011, 01:34 PM   #509
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Quote:
Originally Posted by MiiB View Post
would it harm to take the first servo out.. and instead capacitor couple..in order to get too much varped record filtered out a bit..
It is not necessary to take the servo out and put in a coupling capacitor to achieve some LF rolloff to deal with warp. A properly-designed DC servo can be made to provide the desired first-order LF frequency response cut. Just remember that the DC servo is really in the audio path, and should be constructed with audio-grade components. It is part of the whole system. This is especially true when it is being used as a filtering function in the subsonic audio range.

Significantly, you can design the DC servo with an additional pole in its feedback path to achieve a second-order subsonic filter response if desired.

Cheers,
Bob
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Old 24th April 2011, 01:40 PM   #510
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John,

For a slight shift in direction. In the past I have mentioned when using IC's I prefer to not use the same voltage for both rails. I take it in the JC3 both rails run at the same voltage?

My other new trick is in RC shunt filters. Instead of having the R go to signal common, I find you can use 2R x 2 with one going to each rail. Same filter action different resistor result. Of course it can be "voiced" with an additional wye resistor to signal common.

Now of course everyone knows there is no difference in those changes as long as the resistors sum to the same value, but of course there is a real difference!

ES
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