Project "Groove Scribe"- A DYI stereo 45/45 head.

[Bahndahn]

Damn, this sounds great!!!! Excellent choice of program material to show off the dynamic range and stereo coherence. This version of your head sounds sufficiently suited for professional recording!

It's hard to know whether you will keep working on this or not, but for now I think you deserve to hear: You've done it!

[EpicenterBryan]

Great work! I think you nailed it!

Thanks Mark. Those mechanical changes sure made a difference to the channel separation!

It's hard to know whether you will keep working on this or not...

Well, I have a few more things to try related to FB and the EQ within the FB loop but the head with these drivers is locked down and done! Just too big and clunky. Something based on what was learned is possible...

Below is the response of the left channel with no feedback or EQ in the FB loop, and about the best I can do with some FB applied and some EQ inside the FB loop. I had to sacrifice some HF response to keep things stable.

Left Driver.jpg

Here is the same for the right driver:

Right Driver.jpg

The big issue is that with no EQ in the FB loop I can only apply a certain amount of FB before it wants to run away at 4K or so. With some EQ tweaks in the FB loop I can apply more FB, and then it wants to run away at a higher frequency and on and on until I have used the only few bands on my analog parametric EQ's. So, I still plan to make the mods I mentioned some time back to my parametric EQ's so I have more bands that can be adjusted up in the problem areas.

But I also want to try one other thing: I'm going to make a mod to the Caruso boards so I can insert a Low Pass filter before the input to the final summer on the Caruso boards. I'm thinking the corner frequency will be above the main resonance so basically nothing above 4Khz actually goes to the FB summer. That's the first region where my FB really goes unstable. But then I would apply parametric EQ to deal with the rest in the upper region. The FB monitor path I will leave as is, so I will still see the full impact of FB adjustment and also EQ adjustment between Caruso Massimo and the amp, but only changes in EQ below 4Khz (really, I only need a little on the bottom end) will actually go to the summer. The other parametric EQ changes will insert after the summer. Sort of a partial FB system - only to the point of non-stability and the rest dealt with like an open loop head.

Why is this necessary? I'm not convinced that the shielding is working well enough at high frequencies. Remember, I had to add 12mm plastic spacers after we ran the magnet FEMM simulations. I did cover the plastic with alternating MU metal and copper ... but who knows.

One final thing I want to check is if the main bolts holding the head to the body are non-magnetic. I'm pretty sure they were stainless steel. But not all stainless is non-magnetic so I may try to find some threaded brass to replace them. Likewise, the X-Spring plastic adapters are held in with machine screws. I'm pretty sure they are magnetic and I didn't think about that. And finally, although the FB wires are twisted and connected to other twisted wires - I had to route them on the outer edge of the head for space issues. I wonder if I should try to shield them with some copper tape.

...but for now I think you deserve to hear: You've done it!

I've done something for sure, and I like it! Not sure if I've done all that I can do but I thank you for the kind words. I'm very happy to hear the mechanics are working correctly now. I'm not going to do too much more on this one, but we all learned several lessons having to do with insuring drivers can only move in and out at exactly 45 degrees in all planes. We also learned the importance of the Vertical Cutting Angle as it relates to channel separation. All these lessons can be applied to other drivers and other head designs.

Yes, I do have a few more things to try out but now that the channel separation issue is resolved. I'm much happier that the time resulted in things learned. Even though all these discoveries have obviously been made long ago, they all feel new.

Sex is like having your cutting head actually scribe a groove in stereo for the first time! (Get it - Groove Scribe) Now for a flashback from 1978 to tie it all together.

https://www.youtube.com/watch?v=qHDy_b33cCQ


Bryan

[Sillitoe]

Nice work Bryan!

[EpicenterBryan]

I should also mention something about the audio used. It was from a session from 2003 where we were experimenting with different microphones and placement to capture a specific sound for a totally different song. This sound check had nothing to do with the final tracks in other songs from that session. But it was something I could come up with that had some channel separation and some dynamics.

I also need to say that I used Todd's "Dr. Cuts" VST plug in and Audacity to sum all frequencies below 400hz to mono before cutting the test cut. Thank you Todd for making "Dr. Cuts" available!

Here is a link to Todd's site where you can get the "Dr. Cuts" VST plug in...

http://www.deepgroovesmastering.com/dr_cuts.aspx

[socialroots]

Greetings from Taiwan Bryan, just wanna thank you for being so dedicated to the groovescribe project, and mostly for being so kind as to share openly all your triumphs and failures , so that someone like me who is not an experienced electronics guy can have the chance to get myself the basics of how cutterheads are designed, ive been reading your posts pretty much everyday since you took the challenge upon yourself to conquer and explore the limits of those off the shelf tweeters. The knowledge that ive gained is priceless, and gives me great confidence to be able to overcome any possible problems that could arrise from my old Audax head.
Thanks so much , and congrats on achieving such great results in STEREO!
Patrick

[EpicenterBryan]

...just wanna thank you for being so dedicated to the groovescribe project, and mostly for being so kind as to share openly all your triumphs and failures ...

Thanks Patrick. I'm getting ready for the final testing... Had to make a few new mounting adapters to make it easier to mount and dismount the head, and also the brackets for my counter balance setup on the lathe. Since the head is so heavy, the counter balance is needed. It had to be reworked a bit since I made that for the plastic version.

Also, spent a bit of time getting a tone arm setup so I can speed up the level settings and such for the next round of testing on groove scribe (and also the yet to be named project).

See this thread:
http://lathetrolls.com/viewtopic.php?f=15&t=6655

OK, so although I have not decided on a name for the next project, I'm going to share a photo and a little (very little) detail about this one until I have some data...

Get this... The brass trim is there only for decoration and was not planned in advance. The way I figure it, if it doesn't work worth a crap it should still look good, and I had some trim I could add.

It's a little inside joke I like to inject when I can. The story goes like this... 30+ years ago one of my friends in College who was a mechanical engineering student, had an interview with the Lucas Films model shop. He felt totally dejected when the interviewer said "remember, it doesn't have to work - it just needs to look cool". Ever since, my motto has been this... "It needs to work, but it also needs to look cool". I like my version better!

Anyway, here is a sneak peak at an OrtoFon inspired rocking bridge like prototype - yet to be named in a new post.

MarkRob will get where this is going... Yes, those crazy angles are intentional. The stylus will actually interact with the recording surface at 90 degrees.

IMG_4786[1].JPG

The first check about 3 weeks ago was interesting but I discovered superglue got into one of the drivers and froze it solid. I did get modulation on one groove wall as seen on a microscope so that was encouraging. More details on this new project later. And yes, it has been rebuilt since and is ready for a new test... It will use a Neumann 320 stylus.

Bryan