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Old 20th October 2012, 04:42 PM   #11
Salas is offline Salas  Greece
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That bridge reminds current input overload protection circuitry in good DMMs. But they don't use fast ones there like you do for catching fast gate threatening transients, their job is just to route away the current from the shunt reference resistors until the HRC fuses heat up enough to blow.

15-20nVrtHz hmm... not bad for a Mosfet, still 15-20 times higher than what a K170 can do, but the Mosfet's gFS gives you ample gain for single stage. Min. noise goal is not a can't do without, priorities contention area, its MM after all. Its still your SRPP but with passive RIAA and output left inverted, yes? What subjective parameter the bias trimmer changes that has enough impact so you gave it as an externally accessible feature to the user in some versions?
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Old 20th October 2012, 05:26 PM   #12
x-pro is offline x-pro  United Kingdom
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Quote:
Originally Posted by Salas View Post
Its still your SRPP but with passive RIAA and output left inverted, yes?
Yes.

Quote:
Originally Posted by Salas View Post
What subjective parameter the bias trimmer changes that has enough impact so you gave it as an externally accessible feature to the user in some versions?
The biasing changes sound in a way that makes it more natural, the sound stage opens and everything snaps to focus. I had to provide it as an external control as I've found that the precise point is cartridge and set-up dependant. The operating point change alters the transfer characteristic and the "best" point from the generator can be set by the least residue in the multi-tone IMD measurement. However as any cartridge has it's own non-linearities (and these depend on the cartridge setup, tracking weight, VTA etc.) a slight deviation from that point can actually provide a better sound in a particular set-up.

Cheers

Alex
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Old 20th October 2012, 09:44 PM   #13
Salas is offline Salas  Greece
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Thanks for the detailed answer. Is it also fitting the concept of the sweet spot mutual error cancellation philosophy again as with ''tuned'' CCS Jfet loading lets say?
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Old 20th October 2012, 09:50 PM   #14
x-pro is offline x-pro  United Kingdom
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Quote:
Originally Posted by Salas View Post
Thanks for the detailed answer. Is it also fitting the concept of the sweet spot mutual error cancellation philosophy again as with ''tuned'' CCS Jfet loading lets say?
Yes .

Cheers

Alex
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Old 21st October 2012, 09:36 AM   #15
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Hi Alex

Thanks for your interesting thread.
And congratulations on the best phono-pre award !

I see your phono-pre was tested by 'Inverse RIAA'.
I am interested in making a 'reference' network at present.
I have looked at various 'takes' on Inverse RIAA.
All but 1 seen so far, remain for me, less than convincingly accurate ( or just plain crazy ! ).

I'm guessing you have your own 'take' on Inverse RIAA for your testing.
Perhaps you have adopted your own referance network.

Would you have any general comments to make about Inverse RIAA.
Perhaps you have a schematic of your own network, you might post.

Cheers

Si.
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Old 21st October 2012, 10:34 AM   #16
x-pro is offline x-pro  United Kingdom
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I'm using the standard version:

Click the image to open in full size.

Cheers

Alex

Last edited by x-pro; 21st October 2012 at 10:36 AM.
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Old 21st October 2012, 09:13 PM   #17
Nanook is offline Nanook  Canada
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Default Differences between the Special vs Limited?

As the title says. I'm seeking a phono stage that can be easily configured for MC and MM with adjustable loading capabilities. Curious about the differences in the two stages.
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Old 21st October 2012, 10:16 PM   #18
x-pro is offline x-pro  United Kingdom
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As the title says. I'm seeking a phono stage that can be easily configured for MC and MM with adjustable loading capabilities. Curious about the differences in the two stages.
The Kora 3T circuit can be easily adapted to have an adjustable cartridge load thought I personally prefer not to have any additional switching on the input so I usually just solder in whatever load is required.

The most important difference between the SE and the LE versions is in the type of FETs used - LE uses a completely different type of FETs with about 6-7dB lower noise. Also there are differences in the quality of passive components used and their matching. All passive components for the LE version are matched to 0.1% between channels, output capacitors are Black Gate and premium resistors are used in several positions. That is all I can say as the LE is still a production item.

Cheers

Alex

Here is a noise floor comparison between the Kora 3T MM SE and MM LE units I've done some while ago.

Click the image to open in full size.

Last edited by x-pro; 21st October 2012 at 10:18 PM.
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Old 22nd October 2012, 02:20 AM   #19
andyr is offline andyr  Australia
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The Kora 3T circuit can be easily adapted to have an adjustable cartridge load though I personally prefer not to have any additional switching on the input so I usually just solder in whatever load is required.
You do not need switching to implement externally-adjustable cartridge load, Alex. This feature is essential, IMO - however, IME switches at these very low signal levels degrade the sound (compared to if they were not there).

What I do is have a parallel pair of inputs RCAs - so the phono cable goes in one pair and "loaded" plugs go in the other. Best to make the default input load 100K (instead of 47K) in this instance.

Regards,

Andy
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Old 22nd October 2012, 02:31 AM   #20
x-pro is offline x-pro  United Kingdom
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Quote:
Originally Posted by andyr View Post
You do not need switching to implement externally-adjustable cartridge load, Alex. This feature is essential, IMO - however, IME switches at these very low signal levels degrade the sound (compared to if they were not there).

What I do is have a parallel pair of inputs RCAs - so the phono cable goes in one pair and "loaded" plugs go in the other. Best to make the default input load 100K (instead of 47K) in this instance.

Regards,

Andy
Hi Andy,

Yes, I know about that approach too . However I still prefer a properly soldered load at these signal levels.

Cheers,

Alex

Last edited by x-pro; 22nd October 2012 at 02:34 AM.
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