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Old 11th December 2009, 11:30 AM   #1
webby is offline webby  United Kingdom
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Smile Need a MC phono stage, do i need a pre as well?

Hi All,
I need some advice please, i have looked through the forums for phono stages, and am now more confused than ever.
I have Just built a Tubelab Simple SE amp, i'm over the moon with it. But the weakest link is now the phonostage. I have a Cambridge audio 640p, not bad, but i would like a tube based design that will do justice to my Audio Technica at33ptg MC cartridge. This output's 0.5mv, so i have a few questions;

The Simplse has plenty of gain, so will it benefit from using a tube pre&Phono, or is the pre unnecessary? Something like the 12B4 coffeedj is working on?

Or should i save money and build just a phonostage, and which one?
Maybe the Tubecad Tetra, has anyone tried this model?

Is it better to use tubes with enough gain, i can leave out step up transformers? or other way round.

I would like to save money if possible, but not compromise on sound quality too much. Budget is about $250.
Please let me know what you think, i am itching to know!
Many Thanks
Ian
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Old 11th December 2009, 04:39 PM   #2
kevinkr is offline kevinkr  United States
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I think building a tube phono stage to function with a 0.5mV MC cartridge for $250 is going to be a bit tight.

Going the tube route with this cartridge output level is going to require a transformer - a pair of good ones could well exceed your entire budget.

SY has a design that is due to be published shortly that should interest you, transformers will probably be required from the perspective of providing adequate gain.

If you are a consumate bargain hunter and frequent electronic flea markets and hamfests (not sure what British hams call their flea markets) you might find at least some of the parts cheaply enough.

Build a phono stage with enough gain and you will not need a separate line stage. (Again pointing to the use of transformers..)
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Old 11th December 2009, 11:52 PM   #3
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Kevin has made 2 important points: you don't need a line stage, as the Simple SE has control over the listening volume and a budget of approx. $250 is extremely tight.

About 65 dB. of NET gain are needed with a 500 μV. LOMC cartridge. Due to cost, SUTs are out and you can't get satisfactory noise performance employing 100% tubed circuitry. IMO, the only option is tube/SS hybrid circuitry. Allen Wright's hybrid cascode will provide sufficient 1st block gain. Follow with "all in 1" passive RIAA EQ and a MOSFET buffered 2nd gain block.

A single ElectroHarmonix (EH) 6922 will do quite nicely at the top of the hybrid cascode, for both channels. You can appropriate the 2nd gain block and buffer circuitry from the schematic I've uploaded, but that is 1 option among many.
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Old 12th December 2009, 12:04 AM   #4
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last tubecad phono plus cinemag ...
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Old 12th December 2009, 12:11 PM   #5
webby is offline webby  United Kingdom
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Thanks very much for your input, i see that i will have to spend more money on this project. The whole point is to get good performance out of my cartridge, and if that requires a bigger budget to achieve this, fine. Might as well do it properly.
I don't want the phonostage to be a limiting factor in my system.
I will look out for SY's design, any thoughts on the Tubecad Tetra?
I see the cinemag step ups are not too expensive, but are they the right choice for a highish end phonostage.
Many Thanks
Ian
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Old 12th December 2009, 01:00 PM   #6
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Ian,

By all accounts, CineMag makes good stuff. However, shipping costs from California will be substantial. You can get excellent SUTs manufactured in the UK. Sowter and Stevens/Billington are obvious candidates.

Allen Wright's stuff is very much HIGH END. Check his site out. The matched pair of JFETs needed to execute the hybrid cascode 1st gain block cost 25.
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Old 21st December 2009, 12:00 PM   #7
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Default Tubecad's Tetra All in One

I just finished the Tubecad "Tetra All In One".
Some "tube rolling", "capactor rolling" and listening tests this weekend

It's a very very good phono amplifier for MM, The best I listened to so far (I havent llistened to that many though), but not enough for MC. You also need a transformer.
I use 12AX7 and 12AT7 as combo per channel. To be more exact I use the last two NOS Telefunken ECC803S I had left, from a sleeve of five from the beginning. The other three I sold on Ebay for more then 1000$ together

Second stage is NOS Telefunken ECC81.

I just bought the PCB from John Broskie (Tubecad). Very high quality, very thick and lots of room for big PIO capacitors if you want to.
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Old 21st December 2009, 03:41 PM   #8
Jaap is offline Jaap  Netherlands
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Talking give yourself a christmas present

Quote:
Originally Posted by Eli Duttman View Post

Allen Wright's stuff is very much HIGH END. Check his site out. The matched pair of JFETs needed to execute the hybrid cascode 1st gain block cost 25.
This guy matched 2SK369-V for sale is selling those 2sk369-V JFETS for a lot less
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Old 23rd December 2009, 10:04 AM   #9
webby is offline webby  United Kingdom
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Hello All,
Thank you for the replies, all very useful.
The Tetra/ SUT option sounds good, but i have had a good read of SY's thread. This sounds very promising, but way over my head technically. I am hoping there might be some sort of group buy / kit for it, or PCB at least. I dont have the ability to just read the circuit diagram and build it.
I just want to have a good phono stage, better then the CA640P. Not worried if it is a tube based design anymore.
Many Thanks
Ian
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