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Old 25th November 2012, 09:25 AM   #8621
RCruz is offline RCruz  Switzerland
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Quote:
Originally Posted by buzzforb View Post
RCruz, Could you point me to the schematic that you are working with.
Simplistic NJFET RIAA

Quote:
Originally Posted by Salas View Post
Its in conjunction with how fast the PSU settles and how fast the bias in the input JFET(s) settles. Could speed up if it was a BIB powering.

It would need enough modifications for 369s. I already posted a 57dB using just one. Which is same noise as with 2xK170 with an advantage in the mids to lows 1/F area though. Two would make it too strong for your carts. VGeorge hit on fakes on first try sourcing on ebay he told me.
It seems quite easy looking at the schematic: Simplistic NJFET RIAA

Maybe changing R13 and R2.....

PS: Thank you Vgeorge
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Last edited by RCruz; 25th November 2012 at 09:28 AM.
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Old 25th November 2012, 09:28 AM   #8622
AndrewT is offline AndrewT  Scotland
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Would a "test" version of one (not stereo) of these circuits be a good way of identifying good low noise versions of the 2sk170 ready for assembling the first stage of the stereo versions?

Which version would be more selective in identifying the slightly noisier jFETs to be put into the second stage, or not to be used at all?
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Old 25th November 2012, 09:30 AM   #8623
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post8621 link1 took me to post8601 !!!
post8621 link2 took me to post8601 !!!

Both links took me to the same wrong post !!!!!!
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Old 25th November 2012, 09:34 AM   #8624
RCruz is offline RCruz  Switzerland
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Quote:
Originally Posted by AndrewT View Post
Would a "test" version of one (not stereo) of these circuits be a good way of identifying good low noise versions of the 2sk170 ready for assembling the first stage of the stereo versions?

Which version would be more selective in identifying the slightly noisier jFETs to be put into the second stage, or not to be used at all?
Maybe for noise only.... of course other aspects like sounstage width and imagery could not be evaluated and these are the strongests points of thiese designs.
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Old 25th November 2012, 09:36 AM   #8625
RCruz is offline RCruz  Switzerland
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Originally Posted by AndrewT View Post
post8621 link1 took me to post8601 !!!
post8621 link2 took me to post8601 !!!

Both links took me to the same wrong post !!!!!!
Both work fine here

Look for #8368 and #8011
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Old 25th November 2012, 09:37 AM   #8626
AndrewT is offline AndrewT  Scotland
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Simplistic NJFET RIAA

post8368 has no sch and no link
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Last edited by AndrewT; 25th November 2012 at 09:39 AM.
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Old 25th November 2012, 09:39 AM   #8627
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Perfect
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Old 25th November 2012, 09:43 AM   #8628
AndrewT is offline AndrewT  Scotland
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Maybe for noise only.... of course other aspects like sounstage width and imagery could not be evaluated and these are the strongests points of thiese designs.
I am talking about noise selection.

Many report that the K170 and F862 have different noise.

For a high gain Riaa stage maybe the noisy jFETs should not be used in the first stage.

If this is the case, then we should be selecting out the noisy devices so that they don't get used in the first stage.

Then we can fine tune the gains/EQ to get the final sound required.
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Old 25th November 2012, 10:13 AM   #8629
RCruz is offline RCruz  Switzerland
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I believe it is a good idea to compare ifferent types of jfets for the input, but as using different jfets with different transcondutances would need also different values for Rs and other parts, I do not know if it would be conclusive.

Anyway, I never detected differences in noise using 2SK170BL. In my builds I believe the differences in noise come principaly from the value and type of Rs used.

In this case, using two k170 in parallel with much lower Rs really made the difference.... This 60dB build is even lower noise than the bjt build I did previously.
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Old 25th November 2012, 10:22 AM   #8630
Salas is offline Salas  Greece
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The folded cascode first stage can give times hundred. If enclosed in copper shielding and better be powered by floating means, maybe a battery array, so to even isolate the ground it refers to, it could do for amplifying the equivalent input noise of JFETs for a handy nVrtHz characterization jig.
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