Feedback on vintage mono heads and other heavy mods

[jesusfwrl]

I have been repairing and modifying vintage mono heads for a while now and have been experimenting with different feedback concept modification.
This involves new coil formers, different winding configurations and changes to the mechanical damping systems. I have had very good results on a variety of different heads up to now, with a few different feedback arrangements, I will be presenting some of these under this thread.

I am writing a thorough technical paper, description of the procedures and measurements as well as the theory behind it and the mathematics to predict the results, which will be published at a later date. Until then, I will not go much into the technical side of things as it is really too much to write it twice. This is an initial presentation of the work and I will keep on updating. Many of these techniques were the result of the Research & Development effort that has been going into the Agnew Analog stereophonic cutter head.
For updates on this project, please subscribe to the Agnew Analog newsletter: https://agnewanalog.com/contact-us.html

I shall begin with the Neumann MS-52HA:

https://agnewanalog.com/blog/neumann-ms-52h-cutter-head-with-feedback-repair-and-hot-mods.html

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This arrived with a fried coil and a broken stylus mount. It was decided to modify it with a new coil arrangement with feedback.

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The winding setup in action:

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The result is stunning. If anyone wants to hear an A/B comparison, source vs cut, please let me know and I will send the files.

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The performance is still limited at HF by the moving mass being high, but the usual limitations/non-linearities inherent in moving iron transducers are compensated for, to an impressive extent.

A new stylus mount was machined for a Transco 320/Adamant NSH-2 stylus shank and a special head mount adapter (Agnew Analog Reference Instrument Type 1416) was designed, which allows Neumann heads to be fitted to Presto/Rek-O-Kut/Fairchild/etc lathes with 2-screw heads mounts:

https://agnewanalog.com/blog/fitting-a-neumann-cutter-head-to-a-presto-lathe.html

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This head is now with a fellow lathe troll in California, being put to good use. Check out his work here: https://10shun.bandcamp.com

More to follow soon!

[Jccc]

As the owner of this cutting head i can say the Jesus work is Ace.

Really good quality work with solid materials used.

i really highly recommend Agnew Analog for repairs and custom modifications to any record cutting lathe.

[Soulbear]

Really good quality work with solid materials used.

i really highly recommend Agnew Analog for repairs and custom modifications to any record cutting lathe.

Audax R5-Test.jpg

As a "Fellow Beneficiary" of this type of "Modification/Updating" in my case with an Audax R5, I can only concur with JCCC. I also really highly recommend Agnew Analog for repairs and custom modifications to anything related to Recording Cutterheads and Cutting Lathes! Soulbear

[socialroots]

Yes,yes,yes! Was always wondering about how much better my shiny likkle Audax head could get if it were to be updated wit some new tech n materials,Jesus thanx fe looking out for us that stil use th poormans cutting tools!
Tenshun,when i saw that Neumanm head,somehow i knew it was yours,just like when i saw that fairchild head at one time up for sale in Australia.just wanna know one ting,what the f*#ck do you do to your heads that u have yet another styli mount problem!!!? Turntablism tricks while cutting?
Jesus,ive always known bout the another stateside service,always thought of him to be quit talanted n capable as well,but the vibes just didnt rub me the right way.
Im very glad for all the big ups thats been going you n Sabine way as of late....well deserved. Makes me think about some wise words of advice that i picked up during lifes troddings," work on your reputation until your reputation works for you".
For someone so talented and wise n respectful,youve always left me with a feeling that your one very humble person. All the best to you and your loved ones during this holiday season.
Maximum respect,
Patrick

[socialroots]

Soulbear,what ever happened to your ugly duckling? Seasons greeting out your way as well,keep the vibes warm inna England.
Maximum respect,
Patrick
P.s i ve always been quite envious of your vinly collection.
If you ever come across some Volt 45 releases of the the Mad Lads,at decent price do link me up,i wanna make a special altar in my cutting room for them,Julius n John were good friends n mentors in my musical journey,and have all passed away as of late. Not to many of that generation left,hardest part of ageing is seeing everyone else leave.Merry xmas soul breddah!

[Jccc]

Tenshun,when i saw that Neumanm head,somehow i knew it was yours,just like when i saw that fairchild head at one time up for sale in Australia.just wanna know one ting,what the f*#ck do you do to your heads that u have yet another styli mount problem!!!? Turntablism tricks while cutting?

Hey Socialroots,

the old stylus mount that Len Horowitz made for me back in the day was not good. it was off center and would keep falling off making it unstable and hard to maintain if changing needles.

The new stylus adaptor that Jesus made is way more stable and robust. It seems to be planted in there which i really like and the cutting results have improved along with the modification he applied to rewinding of the coil.

[jesusfwrl]

Thank you so much for your kind words, Jcc, Soulbear and Patric/Socialroots!

The Audax head will be up next!

Patrick, I find all disk recording technology, from ancient to modern, truly fascinating. I still really enjoy cutting with vintage mono heads and trying to figure out their secrets.
Considering how long ago these were made, I am blown away by how good they can sound and by the potential for improvement that many of them offer!

Besides, it is essential to fully understand the work of others before us and how we got to where we are now, if we are to stand any chance of taking things further. This applies to all fields of science, technology, engineering, philosophy, etc. These heads were just as important as the latest generation of stereophonic heads, in the development of the art and science of disk recording.

They are a valuable part of our cultural and technological heritage and I'm glad to see and hear them in active use!

Happy holidays and happy cutting!

[socialroots]

Thank you so much for your kind words, Jcc, Soulbear and Patric/Socialroots!



Besides, it is essential to fully understand the work of others before us and how we got to where we are now, if we are to stand any chance of taking things further. This applies to all fields of science, technology, engineering, philosophy, etc. These heads were just as important as the latest generation of stereophonic heads, in the development of the art and science of disk recording.

They are a valuable part of our cultural and technological heritage and I'm glad to see and hear them in active use!

Happy holidays and happy cutting!

Jesus,so true,past n present in harmony will produce a well balanced future.
Dig not just your work but your vibes as well!
Have a nice holiday the both of you!
Maximum respect,
Patrick

P.S, Tenshun,digging your work as of late,still waitin on your Asian tour,seen?
Feliz Navidad y prospero ano carnalito!

[jesusfwrl]

As promised, here is Soulbear's Audax R-56A, the modified feedback version of the Audax R-56:

https://agnewanalog.com/blog/rebuilding-an-audax-r-56-cutter-head-with-feedback.html

R1.JPG

The concept is very similar to what was done with Jccc's Neumann Ms-52HA, but with the Audax head being a different design, all the calculations had to be done from scratch to design a new coil assembly.

R7.JPG

The original damping material had turned into a combination of jelly and dust, so the type and amount of damping was also taken into account. Less mechanical damping was used, letting the feedback do the job instead. The damping material I have used is known to not change properties with age, having a remarkably long service life in industrial applications.

R6.JPG

More soon!

[socialroots]

Jesus,i think im gonna fry my coils just so i have a urgent reason to send it over to Greece! This upgrade looks way to good fe be true,im way exited just thinking bout it !
maximum respect,
Patrick

[EposLab]

Jesus,i think im gonna fry my coils

..not a good idea but keep in mind : For best Fries, Always use Extra Virgin Olive Oil

BTW my Presto 1-D (rebuild and moded by Jesus - posted at his blog) sounds superb!
..I cannot wait to use his new Stereo Cutter Head!

[jesusfwrl]

Happy New Year, lathe trolls!

Many thanks, Social Roots! No need to fry the head, I can modify another one for you!

Next one to show is the Presto 1-D, modified in similar ways to become a Presto 1-DA.

https://agnewanalog.com/blog/presto-1-d-cutter-head-feedback-modification.html

There is almost always a long delay between us doing something and actually writing about it, not enough hours in the day.

This mod was done several months ago, last year! We get Presto 1-C and 1-D heads in for repair quite often.

monoHeads.JPG

This 1-D arrived with fried coils as usual. It was decided to modify it with feedback.

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This time you can see detailed photographs of machining new coil formers, drilling miniature holes in them, winding the coils, etc.

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This Presto 1-DA is now at Epos Labs in Greece, cutting some nice records on a Rek-O-Kut lathe:
https://agnewanalog.com/blog/a-fashionable-rek-o-kut-lathe-cabinet.html

https://www.lathetrolls.com/viewtopic.php?t=8482

There are a lot of measurements involved in all this, as well as important procedures during the disassembly and reassembly of the heads and the magnetic circuit in particular, which are not shown yet.

I have been building a head measurement system, consisting of a transducer to measure flux density, a transducer to track stylus velocity, a spectrum analyzer, a swept sine wave oscillator and a noise generator, with which I can measure important parameters of the heads. I am now in the process of adding a pen recorder to this setup, to be able to print out frequency response plots and so on. I also do test cuts and play back on a calibrated reference reproducer, which you can read about here:

https://agnewanalog.com/blog/accurate-record-reproduction-thorens-td160-sme-3009-and-van-den-hul-mc-two.html

There are of course also oscilloscopes, a function generator, various meters, resistance/capacitance bridges, a few precision scales, measurement microscopes, calipers, micrometers and so on, on the bench.

This way I am collecting and archiving a lot of data about the performance and parameters of different cutter heads and doing a lot of comparisons, also before and after any modifications.

More soon!

[EposLab]

Happy New Year, lathe trolls!

There are a lot of measurements involved in all this, as well as important procedures during the disassembly and reassembly of the heads and the magnetic circuit in particular, which are not shown yet.

I have been building a head measurement system, consisting of a transducer to measure flux density, a transducer to track stylus velocity, a spectrum analyzer, a swept sine wave oscillator and a noise generator, with which I can measure important parameters of the heads. I am now in the process of adding a pen recorder to this setup, to be able to print out frequency response plots and so on. I also do test cuts and play back on a calibrated reference reproducer, which you can read about here:

There are of course also oscilloscopes, a function generator, various meters, resistance/capacitance bridges, a few precision scales, measurement microscopes, calipers, micrometers and so on, on the bench.

This way I am collecting and archiving a lot of data about the performance and parameters of different cutter heads and doing a lot of comparisons, also before and after any modifications.

all these some may call it just a "professional repair job", I call it "state-of-the-art repair/upgrade work" (or even better a "perfect repair/upgrade procedure"?!?!)!

[markrob]

Hi,

Those bobbins look super! Do you have any concerns using aluminum as it relates to eddy current losses. On speaker voice coils, I usually see a gap provided to help kill the eddy currents. Is that not an issue here?

Mark

[dubcutter89]

I had the same concern coming up my mind, and I guess this is what the claimed "feedback" should be... nice machining work though

[Fela Borbone]

It can help reduce inductance, as a shorted turn. As is stationary is not as harmfull as in movil coil former.

[jesusfwrl]

Markrob, dubcutter89 and Fela Borbone, many thanks.

As Fela Borbone correctly points out, a metallic bobbin is a shorted turn, so it does have an effect on the operation of the transducer system. Being stationary, as opposed to the coil former on a moving coil transducer, the effect is quite different. The fact that it is not a moving coil transducer, but a moving iron system, makes it even more different.

The bobbins could also be made gapped (I tried this as well), but then it would be an open turn rather than a shorted turn, with a different effect on the system.

These effects are not really eddy-current losses, which also occur to some extent regardless of bobbin material. This is why Presto used a laminated pole construction, to deal with the eddy-current effects at the pole pieces, where there is no complete "turn".

There is a lot more to it, I will be publishing a detailed analysis of the system and the feedback implementation in due course. For now, I will just say that if the effect of the shorted turn is calculated into the design, an aluminum bobbin can work very well. But it is not as simple as just using aluminum instead of plastic, with the same coil wound on top.

There are several benefits to using an aluminum bobbin, including but not limited to various electromagnetic effects. There is a massive thermal benefit, with the bobbin aiding in heat dissipation, and a stability benefit which permits more accurate winding and as such, the use of more demanding winding configurations.

I do not intend to keep any of this secret for very long, it will all be published soon, in hope that others will draw inspiration and develop these concepts further.

More soon!

[markrob]

Hi,

Thanks to both Fela and Jesus, for the explanation. Looking forward to seeing your results. Thanks for sharing.

Mark

[Fela Borbone]

Thanks to you too! Can't wait to read these papers, an know about this stereo head.