Phono Transfer System Construction Information

Construction information for DIY projects, including the MS Mid Side Matrix, Width Controller, Phono Transfer System, Insert Switcher and the Dual Class-A Amplifier. You can post your baby pictures here.
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mediatechnology
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Flat Moving Magnet Preamp New Layout with Gain Header

Post by mediatechnology » Mon Apr 02, 2018 4:33 pm

I have just received a new layout for the Flat Moving Magnet Preamp for the Phono Transfer System.

The new board is identical electrically and mechanically to the original with the exception of the addition of a 6 pin Gain header. There is also a minor expansion of the ground plane "keep out" area under the dual op amps.

The additional pins have connections for driven shields (thanks JR!) to minimize cable capacitance when external gain switching is used. The external gain can be either a DPDT switch to alternate between preset A and B gains, or it can be configured to switch Rgain for stepped gain control.

Molex "CGrid-III" housings mate with the header to allow external connections or on-board jumper shunts.
I'll post an image of the gain cables once I receive my ultra-miniature Mogami console cable.

Image
Flat Balanced Input Moving Magnet Preamp

Image
Flat Balanced Input Moving Magnet Preamp

I also did a Common Mode Rejection test.

Rsource is 1 KΩ per leg matched within about 0.5Ω.
The gain is +22 dB so the measured CMRR numbers, referred to the input, are 22 dB better than shown.
Sweeps are done with Cterm = 0, 50, 100 and 200 pF. (150 pF not shown).

Image

The top trace is the right channel output with the input differentially driven at -44 dBu and with 22 dB gain.
(The right channel does not provide any reference for the left channel and should be ignored.)

The bottom traces are the left channel CMRR with the input driven at 0 dBu through 1KΩ resistors matched within 0.5Ω.
The left channel differential gain is 22 dB.
The CMRR at 60 Hz, referred to the input, is about 96 dB.

There is, as expected, some effect of Ctermination on CMRR. The best combinations at HF are with J3 open where the CMRR at 20 kHz is still a respectable 70 dB.
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FMMP 26 Layout Mating Connectors

Post by mediatechnology » Wed Apr 11, 2018 7:22 am

I updated the Flat Phono Preamp Bill-of-Materials for the FMMP_26 layout: https://www.mouser.com/ProjectManager/P ... 557eba35fd

This BOM adds 2X 6 pin headers.

BOM for Mating connectors. Includes 6P Centigrid-III housing, pins and additional 3 pin headers to mate with the Phoenix connectors: https://www.mouser.com/ProjectManager/P ... 5d68f4a431

The Centigrid housing and pins are for off-board gain switching.
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Flat Moving Magnet Phono Preamp Test Pads

Post by mediatechnology » Wed May 02, 2018 4:27 pm

These are the pads and common mode networks I used to test the Flat Moving Magnet Preamp.

The Differential test pad has 40 dB attenuation and can be driven from an unbalanced generator.
For the Common Mode test network I matched the resistors to about 0.1Ω using a Kelvin-connected LCR bridge.
With a regular DVM and clean leads matching to about an Ohm should be possible.

Image
Pads and common mode networks used to test the Flat Moving Magnet Preamp.
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Epicenter Brian's Phono Transfer System Build

Post by mediatechnology » Sun Jun 03, 2018 2:23 pm

Epicenter Brian's monster PTS build: https://www.lathetrolls.com/viewtopic.p ... 92&p=46788

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quattro64
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Re: Phono Transfer System Construction Information

Post by quattro64 » Sat Jun 30, 2018 5:39 pm

I noticed on the schematic for flat phono that the R4, R5 are optional? Just wondering what the purpose of these Rs are? I've currently placed some 500R prps in those spots, should I just jump them instead?

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Re: Phono Transfer System Construction Information

Post by mediatechnology » Sat Jun 30, 2018 10:46 pm

You can jump them to 0Ω if you'd like.

R4 and R5, along with C3, provide some added RFI protection if needed.
I usually use 100Ω and find that common mode rejection actually measures better with them than without. (When J3 is open.)
I'm not exactly sure why, but it is very consistent.
500Ω is on the high side.
They do add some source resistance so the choice is up to you.

Checkout the figure on page 8 of Jensen pdf here: viewtopic.php?f=12&t=932
It may provide all of us a clue.
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quattro64
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Re: Phono Transfer System Construction Information

Post by quattro64 » Sun Jul 01, 2018 10:24 am

ok, thanks!

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Re: Phono Transfer System Construction Information

Post by mediatechnology » Sun Jul 01, 2018 4:39 pm

Good luck with your project.
Please post some baby pictures when you finish building it and thanks for visiting us!
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quattro64
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Re: Phono Transfer System Construction Information

Post by quattro64 » Sat Jul 07, 2018 3:22 pm

I definitely will, in a couple of weeks or so, thanks again.

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mediatechnology
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Re: Phono Transfer System Construction Information

Post by mediatechnology » Tue Dec 11, 2018 5:11 pm

Topic bump.

Update December 11, 2018. Updated RIAA EQ Monitor Switcher assembly instructions with test procedures: https://proaudiodesignforum.com/images/ ... 121118.pdf
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