hifisonix

Hifisonix X-Altra MC/MM RIAA Phono EQ Preamp

Written by

bonsai

in

The X-Altra MC/MM phono preamp, whether bought as a completed unit or DIY built, delivers the ultimate performance with respect to noise, overload, and RIAA conformance, placing it among the very best available anywhere at any price.

In 2021, the design was featured in audioXpress, a leading audio industry publication based in the US. Part 1 and part 2 of the article can be downloaded from the audioXpress website here: – 

You Can DIY! X-Altra MC-MM RIAA EQ Preamp – Part 1 | audioXpress

You Can DIY! X-Altra MC-MM RIAA EQ Preamp – Part 2 | audioXpress

Here is a 27-minute YouTube video describing the X-Altra MC/MM preamp design

Click here for a set of very high quality THP DS SS PCBs

Click here to link to the BOM and other supplementary materials hosted on the audioXpress website

Note carefully: only use the BOM dated September 2024.

Click on this link if you’d prefer to buy a fully assembled and tested X-Altra MC/MM preamplifier

If you have any questions, or require technical support with your build, contact me via the comments section below or email me at bonsai(at)hifisonix.com (replace the (at) with @)

There is also a diyAudio thread about this preamplifier here :-

Bonsai’s X-Altra MC/MM Phono Preamp | diyAudio

Filter switch wiringDownload

Click here for the user manual for the X-Altra MC/MM

The PCB set offered to build this preamp is designed to work with the Modushop Galaxy Maggiorato GX287 230 x 170 mm 10mm front panel housing. The main analog board with the black, gold flashed and silk-screened rear panel attached, slides into the housing from the rear and is then held in place by 4 x M4 x 10mm retaining screws on the rear panel.

The table below allows you to get an idea of how noisy a MC preamp is given the cartridge coil resistance and the amplifier input referred noise. Once you have the number off the table, use the following formula to calculate the S/N Ratio: 20 log [(Rdg*144)/Cartoutput] where Rdg is the reading from the table and Cartoutput is the MC cartridge output in Volts.  It is clear from this table that the X-Altra MC/MM is in a league of its own in terms of thermal noise (and overload capability).

For the X-Altra, the measured equivalent input thermal noise resistance is 1.4 Ohms, so its ABOVE the 2 Ohm row, but we will use the 2 Ohm row since it is close enough. The figures in RED show the expected X-Altra preamp S/N ratio for a 200uV output cartridge. The ‘A’ weighted figures will be about 4 dB better than those shown.



Some photos of the completed preamplifier, along with my Michel Gyro SE are shown below.

 

 

 

Comments

11 responses to “Hifisonix X-Altra MC/MM RIAA Phono EQ Preamp”

  1. admin avatar
    admin

    Thierry,

    These are available at 2%. This will still give good RIAA conformance, but if you can buy 10 off and select to 1% that will be better. Note, any 0805 NP0/COG 35V and higher will work in this position.

    https://www.mouser.co.uk/ProductDetail/Murata-Electronics/GCM2195C1H123GA16D?qs=QzBtWTOodeWUxWAHZ4NdVw%3D%3D

    Regards

    Andrew

  2. admin avatar
    admin

    Hello Thierry,

    let me check to see if I can find and equivalent for you – I’ll come back shortly.

    rgds

    Andrew

  3. Thierry Vitale avatar
    Thierry Vitale

    Hello

    I’m about to order the PCB kit and had a look at the Bom. I see that the 4 x 12 nF caps (GRM2195C1H123FA01D #12) are absolutly unavailable anywhere and the #8 are supposed to arrive in mid June.
    Is there a way to find them or is there an equivalent ?

    Thank you
    Best

  4. Bonsai avatar
    Bonsai

    Thank you Joost.

    Yes, the headroom is for RIAA encoded signals. However, good overload recovery with RIAA signals also helps with non encoded signals like clicks (lot of HF content) and warp and arm resonance (LF). Stereophile has reviewed commercial phono preamps with only 6-9 dB O/load capability at HF, and one recent product was less than 3 dB. This is not enough in my view and most sensible practitioners would agree.

  5. Joost Plugge avatar
    Joost Plugge

    Hello Andrew,

    I read the articles in Audio Xpress, very good! You mentioned the headroom of 31.5dB across the audio band, although not clear in the text, not to me anyway, I think you mean for signals that are RIAA coded, not for siganls that appear after the cutting process like warped and eccentric records, cracks and plops and so on. This is relevant because most of the discussion about headroom concerns this type of signals.

  6. Bonsai avatar
    Bonsai

    Hello Matej.

    The S/N improvement over an NE5534A with a MM cartridge connected approaches 5 dB which is significant.

    Certainly vinyl surface noise is much higher than the preamp stage.

    The X-Altra MC/MM provides SOTA performance levels for very reasonable cost and provided a great design challenge. Similarly performing solid state vinyl preamps sell for more than $2000.

  7. Matej avatar
    Matej

    Hi,

    congratulations on great design and making it to real product!
    I like low noise designs, but I like simple solutions too.

    In a real world of vinyl records I would say we can get S/N about 60dB(A).
    If this is true, why just not use NE5534 instead of (unobtainable) FETs at front-end?
    I am asking from practical point of view (I completely understand engineering challenge of building the best phono pre-amp). Do we need discrete solutions (for MM)? I mean good PSU and well designed RIAA should do, right?

    Best,
    Matej

  8. Raph avatar
    Raph

    I was coming back randomly to your site and found your answer. I’m glad that a magazine decided to publish your work, although I guess that it will be hard to find here in France 😉
    Your photos look great, I’ll come back here to read your updates.
    Thanks for sharing your PCB manufacturer and one more time thank you for the nx-amp which I enjoy nearly every day.

    Take care,
    Raph

  9. Bonsai avatar
    Bonsai

    For PCB manufacture, I use ‘PCB Cart’ who are based in China. I found the quality very good.

    Rgds

    Andrew

  10. Bonsai avatar
    Bonsai

    Hello Ralph,

    I’m still doing some work on the preamp. I have been approached to potentially have it printed in a magazine, so once development is completed, I will submit it to see if they want it. If not, it will go up here on the Hifisonix website.

    I’ll keep everyone updated on the X-Altra page

    Rgds

    Andrew

  11. Raph (blacknoz) avatar
    Raph (blacknoz)

    Hi Andrew,

    Hope you are doing well.

    I love your nx-amp and would definitely like to build this RIAA.
    If you go for a group buy, just ping me, I’m in 🙂
    I’ll mix it with the Doug Self pre from Linear audio #5 I just finished last month and which sounds great with the nx-amp (at least to my ears).

    Best,
    Raph
    P.S. if I may, would you share / recommend a PCB supplier for small audio projects as I am trying to design some at the moment?

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