Phono Transfer System 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.
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mediatechnology
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Re: Phono Transfer System Construction Information

Post by mediatechnology » Wed Nov 20, 2019 6:50 pm

Maybe you should consider using J2 and modifying the range from +3, 0 -3 to something else. (+4, 0 -4?)

It should be relatively click-less that way.
https://ka-electronics.com

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billshurv
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Re: Phono Transfer System Construction Information

Post by billshurv » Thu Nov 21, 2019 5:43 pm

That was plan B when I realised plan A was stupid (switching gain on MC board) and If you switch in a parallel resistance that gives you what you need. I'm just having a risk averse moment as, come next year I will need a visa to go and fix it! He is known to change cartridges 2 or 3 times an evening.

I don;t like throwing away gain but sometime you have to be pragmatic.

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mediatechnology
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Re: Phono Transfer System Construction Information

Post by mediatechnology » Thu Nov 21, 2019 5:46 pm

I'm just having a risk averse moment as, come next year I will need a visa to go and fix it!
Your client is off the island and on the continent?
https://ka-electronics.com

"States Ordered To Fraudulently Inflate COVID-19 Cases 15 Times Actual Rate"
https://banned.video/watch?id=5efab695672706002f367a0a
"Plandemic/Doctors In Black" https://proaudiodesignforum.com/content/Plandemic.mp4

billshurv
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Re: Phono Transfer System Construction Information

Post by billshurv » Thu Nov 21, 2019 6:21 pm

Not so much a client as a friend. I figured having someone to encourage me would accelerate the completion of my set as well*. He's paying for the parts and labour will be bartered for some spare cartridges he has.

*At least that was the theory. Life has a way of getting in the way :)

billshurv
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Re: Phono Transfer System Construction Information

Post by billshurv » Sun Dec 15, 2019 6:24 pm

No Progress in last few weeks due to other comittments, but my PCM4222 EVM has arrived so I can integrate that. As well as giving me galvanic isolation it will allow me to offend all those sensitive souls who think digitising a vinyl signal will rob it of some magic. Happy days :)

billshurv
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Re: Phono Transfer System Construction Information

Post by billshurv » Thu Dec 26, 2019 7:06 pm

Wife away with kids for a couple of days so time to crack on. And first dumb question. How did you intend the shield drive to be setup for remote switching of gain? I'll just be switching between A&B on the first build.

brianroth
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Re: Phono Transfer System Construction Information

Post by brianroth » Tue Jun 09, 2020 7:06 pm

I have a potential idea to use the line level portion of the system for an unusual application.

Background. Several years ago, Chad Kassem (owner of Acoustic Sounds here in Salina, KS) bought the Neumann lathes and all of the related custom electronics from the estate of Doug Sax along with the Mastering Lab "brand". Everything was shipped from CA to KS, and a variety of outside experts have been bringing it back online. I initially knew nearly zero about cutting lacquers, and am still a mere babe in the woods. But, I'm the guy who chases down problems within the barely documented custom electronic systems, which are largely vacuum tube based.

There is one feature that Sax never implemented, but more than a few of the various guys through here say is important to have.... the ability to monitor the RIAA equalized signal that drives the cutting head. That is the very last point before the stylus cuts the groove. The lacquer cutting guys call that "feedback monitoring", which was initially confusing to me since there is also a feedback signal going from the cutting head back to the amplifier. It's just a matter of jargon that I'm learning!

In this case, the custom cutting amplifier is all tube (with a very handsome Peerless output xfmr on each channel). Each channel uses a pair of 6550's which should produce around 100 Watts into an 8 Ohm load. I seem to recall someone telling me the Neumann cutting head provides a 6 Ohm load, but whatever.

In addition to the connector which feeds wiring to the cutting head there are two unbalanced (TS) 1/4" phone jacks paralleled across the Peeerless xfmr secondaries. That seems to be the ideal place to "sample" the RIAA equalized signal. Those jacks are currently unused.

Back of the napkin calculations tell me that the maximum voltage will be in the vicinity of 25-28 VRMS.

Rather that wiring a 10000000 dB (lol) pad between those phone jacks and the input of a typical phono preamp, my thought is to construct a minimally populated version of Wayne's line level RIAA board. I know a small-ish pad will be required to tame the signal down a bit before feeding into the card. I like the available trimmer pots on the card which will allow level matching for A/B comparisons between amplifier in and out.

Just musing on this possible solution. Perhaps Paul may also have some comments.

Thanks!

Bri
Professional audio and video systems design/installation/maintenance.
www.BrianRoth.com

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JR.
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Re: Phono Transfer System Construction Information

Post by JR. » Wed Jun 10, 2020 8:32 am

I am not the mastering guy around here (although my dad was a recording engineer back in the 50s and probably did some).

I do know a little about RIAA playback EQ... it is basically a low pass filter with gain incorporating rolloff poles at 3180usec and 75 usec, with a zero thrown in at 318 usec. If you use google you can probably find a passive RIAA network schemo.... I vaguely recall at least one would be esoteric phono preamp back in the day using flat gain stages around a completely passive RIAA EQ. Since you don't need the gain stages you might just use the passive RIAA EQ portion by itself.

My last phono preamp (to end all preamps) decades ago, used a flat open loop front end gain stage feeding the 75 usec roll off LPF, followed by an active gain stage with the rest of the RIAA EQ. My preamp before that one (I designed a lot of preamps) had a flat front end gain stage (30dB?) followed by active RIAA EQ (again with more gain).

Good luck I hear vinyl is coming back... :lol:

JR
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

brianroth
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Re: Phono Transfer System Construction Information

Post by brianroth » Wed Jun 10, 2020 12:11 pm

It looks to me that Wayne has a "paint by number" kit which should simplify the work required to set up that monitoring path.

Bri
Professional audio and video systems design/installation/maintenance.
www.BrianRoth.com

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JR.
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Re: Phono Transfer System Construction Information

Post by JR. » Thu Jun 11, 2020 8:00 am

OK never mind....

JR
Don't only half-ass tune your drums. Visit https://circularscience.com to hear what properly "cleared" drums sound like.

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