The A.N.T. Audio Kora 3T Phono Stage circuit published. - diyAudio
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Old 17th October 2012, 01:57 PM   #1
x-pro is offline x-pro  United Kingdom
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Default The A.N.T. Audio Kora 3T Phono Stage circuit published.

As I've recently stopped production of the "Special Edition" version of the Kora 3T phono stage (the "Limited Edition" version is still available), I've uploaded a short history of its development and full circuit diagrams for both MM and MC versions at the "Special Edition" level. The Limited Edition MC version was awarded the "Phono stage of the year" title by Hi-Fi World magazine in 2009 and it is still the phono stage to beat, in my opinion. I will be happy to answer possible questions here.

Enjoy!

Alex
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Old 17th October 2012, 02:04 PM   #2
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Thank you very much for sharing it.

It looks like a very nice design. I will post more later.

Anyhow, please, also follow the thread MasterPiece and give a contribute to it if you feel like it ...

I know...I know....this is subliminal commercial.... what can I do?!

Thanks again for sharing!
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Old 17th October 2012, 06:47 PM   #3
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Quote:
Originally Posted by Stefanoo View Post
It looks like a very nice design. I will post more later.
Thank you! I've read a bit of your thread and found that you've said:

Quote:
Originally Posted by Stefanoo View Post
I have noticed that it is very hard to design an MC stage with enough gain with relative simple circuit (except for paradise) or at least with the different circuits we explored so far I am sure there are better ways out there I simply don't know them.
FYI, the MC version of the Kora 3T has gain 62dB at 1kHz - enough for all but the lowest output cartridges and referred to the input noise is about 100nV RMS (A-wtd). Not bad at all for such a simple circuit.

Cheers

Alex
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Old 17th October 2012, 07:04 PM   #4
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Quote:
Originally Posted by x-pro View Post
Thank you! I've read a bit of your thread and found that you've said:



FYI, the MC version of the Kora 3T has gain 62dB at 1kHz - enough for all but the lowest output cartridges and referred to the input noise is about 100nV RMS (A-wtd). Not bad at all for such a simple circuit.

Cheers

Alex
Yep I agree with you. I think it is a nice relative simple design.
However I meant to say to get enough gain with just one gainstage (actually two stages input and VAS) and get 62dB using only Jfets.
But eather way I am folding back to the two stage design as well.


Again thank you for sharing your design.
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Old 18th October 2012, 07:45 PM   #5
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Here are some measurement results for the Kora 3T MM SE - the frequency response using precision (<0.1% error) reverse RIAA and the distortion spectrum for 1kHz 1V RMS output. Both graphs are typical for production units.

Cheers

Alex

Click the image to open in full size.

Click the image to open in full size.

Last edited by x-pro; 18th October 2012 at 07:49 PM.
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Old 19th October 2012, 07:59 AM   #6
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G'day all, I'm glad to see this thread and it's quite timely too as hopefully I will take ownership of an ANT Kora 3T phono stage shortly.

I've been building some simple FET audio circuitry of late and they do sound 'nice'. Maybe it's 'euphonic' distortion perhaps but it is a joy to listen to! Regards, Felix.

Last edited by fap; 19th October 2012 at 08:00 AM. Reason: Spelling.
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Old 20th October 2012, 01:15 AM   #7
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Originally Posted by fap View Post
G'day all, I'm glad to see this thread and it's quite timely too as hopefully I will take ownership of an ANT Kora 3T phono stage shortly.

I've been building some simple FET audio circuitry of late and they do sound 'nice'. Maybe it's 'euphonic' distortion perhaps but it is a joy to listen to! Regards, Felix.
Hi Felix,

Apparently the parcel is already in Brisbane!



Cheers

Alex
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Old 20th October 2012, 01:34 AM   #8
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G'day mate, that's good to hear, alas within this country the postal services can be a mite slow especially getting up here in the north of Queensland!

I am really looking to comparing it against my beloved DIY ESP P06 phono stage which I regard as truly 'reference' quality.

If the ANT Kora 3T is better than the P06, that will be extremely impressive indeed! Regards, Felix.
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Old 20th October 2012, 03:01 AM   #9
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Hi Alex, nice simple elegant circuits as always. Why the BAV clamp bridge? Protecting the SIPMOS device's gate for hot plugging input abuse, or something different? I have some BSS135 for low dissipation position in HV cascode CCS use but never got to see about its intrinsic noise, what is the nVsqrtHz for its BSS139 bro? Mosfets are not famous for low noise, but some DMOS can be nice exceptions? Reminded me I am overdue for those BS170 switchers I got to test for audio use because I liked their 320mS gfs and 24pF Ciss. Enhancement mode though, they won't self bias.
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Old 20th October 2012, 02:25 PM   #10
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Quote:
Originally Posted by Salas View Post
Hi Alex, nice simple elegant circuits as always. Why the BAV clamp bridge? Protecting the SIPMOS device's gate for hot plugging input abuse, or something different? I have some BSS135 for low dissipation position in HV cascode CCS use but never got to see about its intrinsic noise, what is the nVsqrtHz for its BSS139 bro?
The diodes are for protection. I have no returns of faulty production units for 4 years of production.

The noise of the BSS139 according to my estimate is about 15-20nV/sqrtHz @ 1kHz or about the same as for the TL072 opamp. The A-wtd noise of the Kora 3T MM SE with 1kOhm source impedance is about -81dbA for 1V RMS output, as it has ~39dB gain at 1kHz it would be ~1uV A-wtd RMS referred to the input. The LE version has about a half of that noise but even for the SE as described the noise is never an issue in real life.

Cheers

Alex
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