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

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

Post: # 32838Unread post EpicenterBryan
Sun Dec 21, 2014 8:01 pm

dimi751 wrote: Great job Bryan and I also like this Track you playing Dimi
Thanks. That track was recorded on that very Protools system back in 2005. I didn't mix it, just recorded it. There is actually a DVD of the making of that CD. About a year after the fact I realized I shot enough video over the time we recorded it that I had enough to do a mini documentary.

Back then YouTube had resolution restrictions but here is a low res version of the recording of that song.

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

Post: # 32852Unread post dimi751
Mon Dec 22, 2014 5:46 pm

Hi bryan

thanks for the link cool video clip look like you guys had fun!

Is this song available on pressed vinyl ?

dimi

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

Post: # 32855Unread post EpicenterBryan
Mon Dec 22, 2014 10:32 pm

dimi751 wrote:Is this song available on pressed vinyl ?
No. But John is starting to get it. Perhaps we will do some specialty ones but hand crafted like "Pit Bull Blues" (a popular song on the net from another CD I recorded of his) on X-ray's from pet shelters or something crazy like that.

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

Post: # 32858Unread post EpicenterBryan
Mon Dec 22, 2014 11:03 pm

The number is in: 11.92 cm/s @1W?

Yes, and no.

I decided to take a crack at seeing what level the 1Khz signal was cut at for 1 watt input in terms of cm/s from my last video. I ran across a great post where Mark and Flow (among others) discuss using a phono cartridge to determine velocity.

http://lathetrolls.com/viewtopic.php?f=22&t=4612

I did a check of the level of the 1Khz signal I cut in the video at what I thought at the time was 1 watt input to the head using my Sure M97XE cartridge as the measurement transducer and the numbers didn’t make sense.

So I pulled out my 2 test records from CBS laboratories and the numbers jived with what would be expected. This is very interesting so I want to go into the details. I did the tests with the volt meter on the 0.1V scale. I measured the left channel from the cartridge; because that was the channel I used to measure the voltage (thus power) at the time of cutting the test shown in the last video.

Here are details about my cartridge:

Sure M97XE:
Specifications: 4.0mv output with 1Khz @5cm/s
Trackability at 1.25 g Tracking Force (cm/sec Peak Velocity): 1 kHz ... 44 cm/sec
So for each 1.0mv, it should translate to 1.25 cm/s

Test one:
CBS Stereophonic Frequency Test Record (STR100 - 1961) Band 1A Left Sweep
(starts with 1Khz at 0db – only used starting tone)
Result: 3.99mv (translates to 4.99 cm/s for Sure M97XE)

This agrees with what should be expected.
STR-100.jpg
Test two:
CBS Broadcast Test Record (STR 150 – 1963) Band 5B Lateral test, 1khz @ 5cm/s.
Result: 4.12mv (translates to 5.15 cm/s for Sure M97XE)

This agrees with what should be expected.
STR-150.jpg
Test three:
My test cut of 1khz at 1W from the disc in the last video.
Result: 9.54mv (translates to 11.92 cm/s for Sure M97XE)

WTF?

This is way too high!
GS 1K playback test.jpg
Well, remember me saying in the video while cutting the 1Khz test tone that it was around 2.82V for 1 watt into an 8 ohm load? That’s right, but it’s TWICE that going into a 4 ohm load! These drivers are 4 ohm and I KNEW THAT!!! 8 ohm is what the last drivers I was messing with were – NOT these drivers.

I had actually measured these drivers a month ago and found they were 4.7 ohm. And the data sheet says they are 4 ohm +/-15%. I even made my RC network for between the amp and drivers with a 4.7 ohm resister and a 2.0uf cap (really two 1.0uf in parallel because that’s what I had). I even did an NGPICE Online simulation of the network with a 2.0uf capacitor and a 4.7 Ohm load resistor. At some point I went into auto mode pilot mode and set the voltage for what the other drivers (from the other post) were and that was 2.8282V for an 8 ohm load - 2 watts, NOT 1 watt.
spice plot RC with 4.7R and 2.0C.jpg
So what does this tell us?

The reference I cut was WAY too high. And we all know the audio I cut was WAY too low as well as the test noise for generating the EQ curves.

1). It tells me I need to establish a 0db reference level first - now that I know my phono cartridge can be used to measure the result with some level of confidence.
2). It tells me this head does not need 2 watts to generate 0db grooves, at 5cm/s @1khz, and will not blow up with that much signal.
3). It tells me that I am not going crazy and with 2 watts input at 1Khz, this really does produce over 11cm/s – at unknown distortion, but is non destructive.

After Christmas, I’ll need to re-evaluate some of the test methods. Obviously I have to have the 0db reference drive level nailed. Then I need to address the need to apply the RIAA curve with it’s 20db gain at 20khz. I hate doing that in the digital domain because it means the 1Khz level is -20db relative to the peak which must be normalized to insure clipping doesn’t happen. Perhaps I use a -20db (in the digital realm) as the zero so it will match the -20db level of the same frequency of a RIAA compensated file on the same digital system and use that to set the 5cm/s level…

I’m sure Todd has gone through this. Tood has blown up several drivers as I recall. Perhaps that is why he is working on a VST plug in that not only does LF summing (to prevent vertical over modulation) but also has HF limiting (perhaps dealing with the 20db gain at 20khz).

You Lathe Trolls and mastering guys have complicated lives… I’m glad I’m just a newbie hobbyist. It makes it fun for me, but challenging to figure out the secret sauce.

Bryan
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opcode66
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Re: Project "Groove Scribe"- A DYI stereo 45/45 head.

Post: # 32861Unread post opcode66
Mon Dec 22, 2014 11:15 pm

I blew exactly 5 coils. One on its own in one of my early videos. And two sets thereafter. That's when I added the meter panel with fuses and RC network for R and L. 3d printed the panel. Perf board for the circuit with screw terminals for ins and outs. I use 1 amp fuses. My coils can take .8 amps continous before getting dangerous. They can take peaks of over 1 amp. Over 1 amp continous results in a spectacular death. I can run 40+ VAC peaks. Since using fuses, I've not blown any coils.

I'm primarily working on the VST because I want to pull the Neumann BSB Accelleration Limiters out of my amp rack fo cutting with my SX head. Each channel has 15 opamps. That's a lot of added noise. I want to build the protection into a VST and hard wire bypass the BSB's. The sooner the better since I'm starting to get more vinyl mastering business!
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Re: Project "Groove Scribe"- A DYI stereo 45/45 head.

Post: # 32867Unread post inspector77
Tue Dec 23, 2014 6:50 am

Thanks Brian! i have a question...the "stylusholder-pushrodconnector" need to rotate into the V spring or is fixed?.

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

Post: # 32870Unread post markrob
Tue Dec 23, 2014 11:13 am

Hi,

You can get a good idea of your distortion levels by using your spectrum analyzer software. On playback, you should be able to see all of the harmonic levels in relation to the fundamental. So, for example, if the second harmonic is down 40db from the fundamental, you are looking at 1% distortion (-40db = a ratio 100:1). First, you want to establish the distortion level of your pickup, so use the CBS test record. Since its recorded at 5cm/sec, you might want to see the pickup performance at a higher velocity. To do that playback the test record at 78 and the velocity level will increase by a factor of about 2.4 (or 45 for a factor of 1.4). So will the test frequency, but you'll get an idea of your baseline levels. By looking at the levels of the harmonics, you can draw some conclusions about the nature of the distortion. Odd harmonics are generated by symmetrical non-linearity. That is, the positive and negative excursions deviate in the same manner. Even harmonics suggest that one direction of motion behaves differently than the other.

As far as setting levels, I would try setting your reference 1Khz tone at -12 to -20 dbfs. Adjust your audio chain to produce 1 watt under these conditions at the head and lock the gains down. If you use an average reading meter (e.g. VU), this should be calibrated to read 0 when playing back this reference. For normal program source material, this gives you head room for short peaks. If you tend to cut modern heavily limited tracks, you would want to set closer to -12db or even higher (-10db??). Some experimentation will be required. Cut some program material that you have on vinyl and compare the playback of your cut against the professional, you'll get a good idea as to how you compare.

You can throw 400 watt peaks at the head with no problem as long as they are short in duration. Neumann went to a great deal of effort to protect the head from overload so it can run close to its thermal limits (also better cooling). In your case, you are running open loop, so you have to be much more conservative. I would not expect you to get close to the levels they are able to at the bandwidths they achieve. Low pass filtering your source material ahead of cutting will allow you to cut hotter at the expense of bandwidth.

Mark

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

Post: # 33078Unread post EpicenterBryan
Thu Jan 08, 2015 9:58 pm

inspector77 wrote:Thanks Brian! i have a question...the "stylusholder-pushrodconnector" need to rotate into the V spring or is fixed?.
Hi inspector, the V spring needs to be permanently attached to the end of the torque tube / stylus holder / push rod connection stuff ... but it also needs to be drilled through so the piano wire can connect behind the spring. In one of the photos, you may notice an extra segment of a larger carbon fiber tube that provides extra surface area for the tube to be glued to the spring.

I know this is hard to visualize. I have some stuff on order to mockup how the whole 45/45 system works for a YouTube video. It will demonstrate the mechanical movements required to make all this work. For demonstration purposes, the drivers will be represented by RC servos pushing and pulling rods connected to the torque tube. Stay tuned...

B

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

Post: # 33079Unread post EpicenterBryan
Thu Jan 08, 2015 10:26 pm

markrob wrote:Hi,

You can get a good idea of your distortion levels by using your spectrum analyzer software. On playback, you should be able to see all of the harmonic levels in relation to the fundamental. So, for example, if the second harmonic is down 40db from the fundamental, you are looking at 1% distortion (-40db = a ratio 100:1). First, you want to establish the distortion level of your pickup, so use the CBS test record. Since its recorded at 5cm/sec, you might want to see the pickup performance at a higher velocity. To do that playback the test record at 78 and the velocity level will increase by a factor of about 2.4 (or 45 for a factor of 1.4). So will the test frequency, but you'll get an idea of your baseline levels. By looking at the levels of the harmonics, you can draw some conclusions about the nature of the distortion. Odd harmonics are generated by symmetrical non-linearity. That is, the positive and negative excursions deviate in the same manner. Even harmonics suggest that one direction of motion behaves differently than the other.

As far as setting levels, I would try setting your reference 1Khz tone at -12 to -20 dbfs. Adjust your audio chain to produce 1 watt under these conditions at the head and lock the gains down. If you use an average reading meter (e.g. VU), this should be calibrated to read 0 when playing back this reference. For normal program source material, this gives you head room for short peaks. If you tend to cut modern heavily limited tracks, you would want to set closer to -12db or even higher (-10db??). Some experimentation will be required. Cut some program material that you have on vinyl and compare the playback of your cut against the professional, you'll get a good idea as to how you compare.

You can throw 400 watt peaks at the head with no problem as long as they are short in duration. Neumann went to a great deal of effort to protect the head from overload so it can run close to its thermal limits (also better cooling). In your case, you are running open loop, so you have to be much more conservative. I would not expect you to get close to the levels they are able to at the bandwidths they achieve. Low pass filtering your source material ahead of cutting will allow you to cut hotter at the expense of bandwidth.

Mark
Thanks for the great inputs like usual Mark.
I will go through all of them methodically and reference sections of this post as I plod through the next phase of testing.

FYI, I have not given up on feedback and want to get back to the other driver idea at some point as well. I also want to try out the eddy current sensors on this version if I can figure out how to cram sensor extensions in there some how. I still have not ordered a modulator / demodulator yet but will soon.

And Mark, I want to publicly note how much I appreciate you taking time to respond to my posts with such great ideas. An awesome example most people may not have noticed was the offer to send the white paper on measuring voice coil temperature. Having a guy like you who is willing to chime in with such hard to find and applicable information - Wait, I should say information I would never have thought about ... I truly do appreciate it Mark.

B

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

Post: # 33080Unread post EpicenterBryan
Thu Jan 08, 2015 10:49 pm

Some progress over the last few weeks of family related stuff and silence...

I did a mod to the left rear of the head so a swarf tube now clears. I also added connectors at the front to get the heater wire out (not used in this photo though). And I also added LED lighting inside the head. This sounds Juvenal but is a really nice addition for inspection of stylus angle and swarf tube clearance adjustment.
IMG_3210[1].JPG
B
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Re: Project "Groove Scribe"- A DYI stereo 45/45 head.

Post: # 33085Unread post recordboy
Thu Jan 08, 2015 11:46 pm

Bryan this is a wonderful thread to watch...

Your design is awazing. I love all the details too (coloured nuts/bolts, etc.). I Love the led idea too...

I was working on an exp. ov mine just last night (a soundscribe 5R) and put a 27 led light inside it to see better... Also was fitting a small old style flashlight lamp in the cutting head, to light that up too... So I am with you on those lights :) (maybe I am Juvenal).

Yr head looks like a NOS radio controlled gas airplane engine, it is REALLY cool...

Thanx for this thread, and best wishes...


-chees
Cheers,
recordboy

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

Post: # 33092Unread post inspector77
Fri Jan 09, 2015 5:23 am

EpicenterBryan wrote:
inspector77 wrote:Thanks Brian! i have a question...the "stylusholder-pushrodconnector" need to rotate into the V spring or is fixed?.
Hi inspector, the V spring needs to be permanently attached to the end of the torque tube / stylus holder / push rod connection stuff ... but it also needs to be drilled through so the piano wire can connect behind the spring. In one of the photos, you may notice an extra segment of a larger carbon fiber tube that provides extra surface area for the tube to be glued to the spring.

I know this is hard to visualize. I have some stuff on order to mockup how the whole 45/45 system works for a YouTube video. It will demonstrate the mechanical movements required to make all this work. For demonstration purposes, the drivers will be represented by RC servos pushing and pulling rods connected to the torque tube. Stay tuned...

B

Thanks Brian!

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

Post: # 33100Unread post opcode66
Fri Jan 09, 2015 2:44 pm

I can explain the V spring in two pictures.
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Re: Project "Groove Scribe"- A DYI stereo 45/45 head.

Post: # 33112Unread post inspector77
Sat Jan 10, 2015 4:44 am

opcode66 wrote:I can explain the V spring in two pictures.

So, the V spring must to have some flexibility, great photo Todd !

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

Post: # 33120Unread post opcode66
Sat Jan 10, 2015 3:31 pm

It is a spring. No???? :D
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Re: Project "Groove Scribe"- A DYI stereo 45/45 head.

Post: # 33362Unread post EpicenterBryan
Sat Jan 31, 2015 12:42 am

I had to take a break to make some progress on my Caruso Massimo build. All this stuff ends up being related... so be sure to check out the Caruso Massimo build from the start here:

http://lathetrolls.com/viewtopic.php?f=15&t=5462

I'm about to try out a crazy idea to add feedback to the "Groove Scribe" DIY head. The idea came to me when I was reading about Mark's testing of his V2 head when he used a phono cartridge to measure movement of one of his designs so he didn't need to cut actual grooves. Mark and I have exchanged a few E-mails about this since and he thinks it might have merit, so I think it's time to give it a try and make the idea public.
IMG_3274.JPG
So my idea is to cram a stereo cartridge inside the Groove Scribe head, above the torque tube, and have the stylus touch (and be glued) as close to the actual location of the cutting stylus as possible. The low level output of the cartridge should represent the movement of the cutting stylus. But there is a big unknown: When the cartridge is in the correct position but not physically connected to the torque tube, does it pick up magnetic fields from the movement of the drivers and by how much? This is a really important thing to know. If it picks up too much signal when not being physically connected it can't be used for feedback and this idea dies here....
IMG_3278.JPG
For this first test, I'm going to use a $25 Audio Technica AT3600. The specs are reasonable. If it works, great. If not I'm not out too much cash. I have one shot to try this once it's glued in place. It will require a custom 3D printed bracket to mount it. I will design the bracket so it will mount the cartridge without touching the torque tube for initial testing, then allow it to touch and be glued in place.

Now, for the preamplifier for the feedback cartridge...
I ran across a great little phono cartridge preamp on E-bay with RIAA compensation. It has quite the following on the web and the test results are quite good. I'll dig up some references if people are interested... But I made a little change to mine... I revised it so I could disable the RIAA compensation if I remove 2 jumpers. I'll be running a full test on the board with and without my changes, but I plan to use this board for my feedback from the Audio Technica AT3600 until I get my Caruso boards up and running.
IMG_3279.JPG
IMG_3280.JPG
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Re: Project "Groove Scribe"- A DYI stereo 45/45 head.

Post: # 33365Unread post markrob
Sat Jan 31, 2015 8:45 am

Hi,

I'll be interested to see how that works out. If you intend to use the output of the pickup in the feedback loop, you don't want to use an RIAA filter in the feedback path. It would make sense to have the RIAA in place so that you can monitor while cutting. So, you'll need two outputs from you preamp.

Mark

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

Post: # 33371Unread post opcode66
Sat Jan 31, 2015 7:00 pm

I built a switchable phono pre from parts and the caruso schematic. I wanted to have the exact same riaa implementation as is present there for feedback. What's in an off the shelf phono pre might not have the same curve exactly. All riaa eq curves are not equal...

Though I plan to use it for a pickup and not feedback. That way I can actually run a full calibration procedure.

Incidentally, this is how Souri does feedback. He uses a modified phono cartridge.
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Re: Project "Groove Scribe"- A DYI stereo 45/45 head.

Post: # 33396Unread post EpicenterBryan
Sun Feb 01, 2015 5:48 pm

markrob wrote:Hi,

I'll be interested to see how that works out. If you intend to use the output of the pickup in the feedback loop, you don't want to use an RIAA filter in the feedback path. It would make sense to have the RIAA in place so that you can monitor while cutting. So, you'll need two outputs from you preamp.
Mark
Mark, if I had RIAA pre-compensation already applied to the audio file, wouldn't I want an RIAA filter on the preamp for feedback summing? This is all until the last of my parts arrive for the Caruso boards... I may just use a mixer and invert the feedback in front of it.

Bryan

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

Post: # 33397Unread post EpicenterBryan
Sun Feb 01, 2015 5:52 pm

opcode66 wrote:All riaa eq curves are not equal... Incidentally, this is how Souri does feedback. He uses a modified phono cartridge.
You are correct sir. I spent some time today checking that preamp and it works remarkably well. I'll post some related stuff in the next post.
Do you or anyone have any more info or a photo of what Souri is doing? I've seen the name mentioned before but know nothing about what he is up to.

Bryan

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