Transfer Filter / Neumann HT75 Replacement Construction Information

Construction information for DIY projects, including the MS Mid Side Matrix, Elliptic Equalizer, Mastering Console, Phono Transfer System, Insert Switcher and the Dual Class-A Amplifier. You can post your baby pictures here.
Gold
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Re: Transfer Filter / Neumann HT75 Replacement

Post by Gold »

mediatechnology wrote: Thu Feb 25, 2021 7:37 pm Yes, that's about as close to 16 kHz as we can get on the LPF with E6-series capacitors.
Great. I’ve never measured the HT75’s. I hope I’m not coming across as nit picking. I’m trying to learn. Do the same component tolerances account for the roll off being -14dB at an octave out instead of -18dB?
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mediatechnology
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Re: Transfer Filter / Neumann HT75 Replacement

Post by mediatechnology »

I measured the slope on mine at 18 dB/octave.
My reference points were a little farther outside the pass band than 2xFc and Fc/2.
Its a Butterworth alignment so the initial rolloff isn't as steep as the outer skirts.
Gold
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Re: Transfer Filter / Neumann HT75 Replacement

Post by Gold »

I fixed the response of Pre B LPF. It was all of my own doing as usual. Yesterday I fixed the Pre B HPF section which of course wasn't broken...

I took another look at it today. I had the 680p and the 10n capacitor positions swapped on the right channel. Now it matches to a few hundredths of a dB like most of the rest of them.
Gold
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Re: Transfer Filter / Neumann HT75 Replacement

Post by Gold »

It's done. It of course took much longer than I thought. That's kind of a good thing. If I accurately could estimate time I probably wouldn't have started in the first place.

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The faceplates are getting neater. This one has some mistakes but I'm happy with the overall look. I did the stripe down the middle on the micro mill. It's the first time I've tried something like this. I like the way it looks.

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There is a lot of wiring. There are separate power supplies for Preview and Modulation. This is all eight channels.

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The power distribution is done with these DIN rail terminal blocks. I had to diode isolate the Relay Common's so they didn't talk to each other through the return path. Luckily I've been through that already and knew what to do.

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Installed in the console. Now it's time to master a record and cut a couple of sides.

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mediatechnology
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Re: Transfer Filter / Neumann HT75 Replacement

Post by mediatechnology »

Now it's time to master a record and cut a couple of sides.
Yea!
Gold
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Re: Transfer Filter / Neumann HT75 Replacement

Post by Gold »

I can't thank you enough Wayne. You saved my butt. The console sounds better already.
Gold
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Re: Transfer Filter / Neumann HT75 Replacement

Post by Gold »

A2F3D050-EA45-429C-B511-5A3453844346.jpeg
Here is a second Transfer Filter unit for Shaker Desk. It also includes the Stereo Width Controller. The LRS-1 was an early version of the Stereo Widener that added an insert on the side chain. The sidechain insert isn’t being used so the LRS-1 and the Compact Widener are functionally identical.

The previous photos were hosted on my old website. I haven’t recreated them on the new site.

This is eight channels for the A/B path Shaker Desk lacquer mastering console. Modulation A L/R, Preview A L/R, Modulation B L/R and Preview B L/R.

This unit has the same 3 pole filters as the EE unit located below it. The frequencies on this unit are HPF 20Hz, 30Hz and LPF 20K Hz, 18K Hz. All capacitors were hand matched to within 1%. All resistors were matched to 0.1%. I used Wima MKP for the HPF and TDK C0G for the LPF. I’ve been liking C0G in filter and EQ’s. They aren’t as soft focus as polystyrene but they have a very clear and non fatiguing sound.

I always forget how long hand wiring takes. Lucky for me as I probably wouldn’t start if I actually remembered.
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mediatechnology
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Re: Transfer Filter / Neumann HT75 Replacement

Post by mediatechnology »

Nice!
Love seeing lacing cord. Reminds me of my Dad and growing up around airplanes.
Very neat work Paul.
Gold
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Re: Transfer Filter / Neumann HT75 Replacement

Post by Gold »

Thanks Wayne! I like lacing cord for in chassis wiring because it’s soft. With cable ties it’s easy to scratch or cut yourself when everything is a tight fit. I don’t do it like the Navy manual says but you really need to set up a jig to do it that way. I’m winging it when I make these. I use it like you would use a cable tie.
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Re: Transfer Filter / Neumann HT75 Replacement

Post by emrr »

Yes, love seeing lacing! Great work on the system!
Best,

Doug Williams
Electromagnetic Radiation Recorders
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