"Brother Singer" Cutterhead

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sifis1983
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"Brother Singer" Cutterhead

Post: # 45082Unread post sifis1983
Tue Dec 06, 2016 12:48 pm

Hi again trolls,

Well, after many efforts, I've just finish this cutterhead, that I call it "Brother Singer".
brother singer.jpg
The body is printed by PLA plastic, designed in a simple 3D application.
The V spring and the torque tube is made also with PLA. The V spring is 1mm thick and the torque tube is approximately 5,5mm thick.
Drivers are 4ohm and can carry 10watt (RMS) and/or 20 watt (MAX).
The push rods are 1mm thick copper wire and they have a plastic support for the attachment in the drivers.
A guitar string is attached in the back of the torque tube to the body.

All the elements are glued, except the drivers and the V spring.

The stylus I will use is the 3rd one, of these : http://www.ebay.co.uk/itm/Record-lathe-cutter-presto-record-in-stylus-needle-styli-rek-o-kut-recorder/282085271275

The stylus has a 25-27 degrees angle from the vertical axis.



So, before put it in my lathe for my first test cut, I will need some information.

1st. The whole construction of the head has a 350-400gramars, weight. Is this ok for embossing in polycarbonate plastic? Do I need to have a counterbalance?

2nd. What kind of amp should I use? I see that many people here, use amplifiers with a lot of watts (300-400 watt). Is it necessary to have a "big" amplifier for the head? And if yes, is there no problem, of destroying the drivers?
Also, someone suggest me a cheap class D amplifier. I have read that the class D amplifiers, converts the analog signal into pulses and then with a lowpass filter at the end of the circuitry, returns to analog. So, what about if I will try a class D amp with, let's say 20 watt power? Is this enough to have a good response for the high frequency range and low noise? Is this "pulse" conversion, deteriorate the motion of the stylus?

3rd newbie query. Do I have to connect the wires of the drivers, the one in a normal way, and the other one, in inverse polarity? Is this critical, to have the one driver push and the other pull? If I connect them without inverse polarity, would I have an extreme vertical motion of the stylus?

That's all for now, any comments, suggestions and information are welcome.
Sifis
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markrob
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Re: "Brother Singer" Cutterhead

Post: # 45084Unread post markrob
Tue Dec 06, 2016 3:05 pm

Hi,

You need the extra power to make the head work at the higher frequencies. The head would smoke if you tried to run anything more that a few watts through it on a constant basis. But you need the extra power for short bursts of time to make the moving mass accelerate.

Class D amps should work fine and will give you lots of power at high efficiency at a lower cost per watt.

One of the drivers needs to be connected in reverse as compared to the other. This allows the stylus to move laterally when fed with a mono signal. If you do not reverse the polarity, the stylus would move vertically in response to a mono signal.

You will find that you need extreme amounts of EQ to make the head response flat along with adding in the required RIAA EQ. As much as 30-40 db of boost at the upper end of the spectrum (that should give some idea on the need for power). If your head is not "text book" in its response, you will need even more EQ. How well the head is designed will determine how far you can push the bandwidth and how loud you will be able to cut.

Hope that helps some.

Mark

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sifis1983
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Re: "Brother Singer" Cutterhead

Post: # 45097Unread post sifis1983
Wed Dec 07, 2016 7:54 am

Hi again,

Thanks for you information Mark.

I know that I need much power to achieve high frequency acceleration of the stylus.
What do you mean saying that I will smoke my head if I run through it, a few watts on a constant basis?
What does this "constant basis" means?

Do you suggest me to start with something like 50watt amp for example? and if not have enough power to try a "bigger" amp?
Or should I try a bigger amp first ?

What do you say for something like this one : http://www.ebay.co.uk/itm/TDA7492-2x50W-HIFI-D-Class-Digital-Amplifier-Board-Amplificador-Radiador-TE398-/192009471721?hash=item2cb4a806e9:g:dwYAAOSwUEVYEOVY


Concerning the connectivity of the drivers, I think I have to try to emboss stereo signal.
But if I have, let's say for example, a stereo sine 440Hz signal that is identical in both channels, does it means that I will have big vertical motion, if I connect them normal, without reverse polarity in one of the drivers?

Thank you,
Sifis

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markrob
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Re: "Brother Singer" Cutterhead

Post: # 45098Unread post markrob
Wed Dec 07, 2016 9:34 am

Hi,

My comment on power handling was meant to indicate that the drivers are only rated for 10 Watts RMS. If you apply more power than this over a long time the drives will pop. How long depends on several factors (previous conditions, applied power, thermal mass of the driver, ability of the driver to dissipate heat to the environment, and max allowable voice coil temperature, etc.). Having 400 watts at your disposal opens you up to the possibility of quickly smoking the driver if you make an error. Keep an eye out for Todd's Neumann style approach to driver protection. This method measures the actual voice coil temperature and shuts down the driver before things get out of hand.

Aside from thermal failure, you can also damage the drivers mechanically by forcing them beyond their limits.

If you connect the drivers with the same polarity and apply a sine wave to both, the stylus will move vertically. You want it to move laterally to be compatible with a standard playback system.

Mark

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sifis1983
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Re: "Brother Singer" Cutterhead

Post: # 45643Unread post sifis1983
Thu Jan 19, 2017 10:45 am

Hi,

My cutterhead was too heavy for the embossing in polycarbonate. So, I build a counterbalance like this one that you can see in the picture.
The idea for the counterbalance is taken from EpicenterBryan, with a Γ shaped pulley mechanism, with a guitar string at the pulleys and about 150grams counterweight at the back.
The downforce weight now, is about 200grams.
counterbalance.jpg
I 've just made a cut with my "Brother Singer" cutterhead. The source is a stereo output of my macbook, just to see what happens in the grooves.

I have a Inter M amplifier rated at 150W @ 4Ohm - stereo. I can't use it at the moment because I have no protection circuit.
As I can see from others here, there are many options to choose for protection of their cutterhead.

Mark, I suppose that you mean the Mantra Head Protection Circuit, of Todd.
Beacause of my poor knowledge of electronics, I can't build something like that. :?

Also, I see that other guys here use just fast blow fuses for protection.
Ciuens new Lathe machine indicates : RC network and protection fuses.

So, I need information of how can I build - connect fuses or some simple circuit to try my Inter M Power Amplifier.

Anyway, the signal that I fed my cutterhead is a white noise first, then it is tone sweep from 50Hz to 7Khz, after that is 1Khz tone only Left channel, then 1Khz only right channel, then 1Khz both channels and at the end a part of a .wav file of James Brown's Payback track :D
Here is the file in mp3 with iRIAA plug in processed:
white noise + 50-7K sweep + 1k tones + Payback.mp3
(of course I didn't use the mp3 to emboss, but I upload it in mp3 just for posting it here)

The result is this file (in mp3 again):
embossing test noise sweep tones payback.mp3
Well, as you can hear, too much surface noise (no heat applied, only some polish with Turtle Wax), too low signal, too weak high frequencies and there is too much harmonic distortion in 300Hz-700hz and some distortion in 1,9Khz.
Also, there is no stereo separation at all. The Left 1K signal is lower than the Right :? . (maybe some bad wire connection to the drivers)

So, I know that my drivers has resonant frequency at 530Hz. I suppose that's why there is too much harmonic distortion in 300Hz-700Hz. Especially in 400-550Hz. Also there in 1Khz tones I can see that there is little distortion, that I suppose became from my cutterhead design. Am I right here?

Do you believe that these "errors" can be fixed with a corrective EQ, if I have more power in my drivers?
I try to emboss the same audio file, with a corrective EQ, but the signal is extremely low to have a result.

Here is a picture of the grooves in the sweep part of the file:
grooves sweep.jpg

Also, I have another query about the stereo separation of the embossed signal.
Well, my cutterhead is built according this amazing video from EpicenterBryan: https://www.youtube.com/watch?v=s62GfJEr6PI
My two drivers are connected in difference polarity. Is that means that I try to emboss a stereo signal in "mono" way?

I'm sure that I miss something here. I can't understand why there is no stereo separation at all.

Anyway, I'm waiting for a sapphire needle at the moment and I will order some PVC blanks to see what happens with that, but I will post it when I have some new tests.

The thing I need mostly to know now, is about the Power amplifier connection, to my 10W at 4Ohm drivers.

Bryan, Marc, Ciuens, Sillitoe, Grooveguy, Todd, Soulbear, PLEASE I NEED HELP HERE! :roll: :roll: :roll:

Any suggestions, comments or advices are welcome.

Sifis
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CountMoogle
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Re: "Brother Singer" Cutterhead

Post: # 45645Unread post CountMoogle
Thu Jan 19, 2017 11:46 am

I too can't wait for a reply.
By the way Sifis, what drivers are you using?

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markrob
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Re: "Brother Singer" Cutterhead

Post: # 45647Unread post markrob
Thu Jan 19, 2017 12:44 pm

Hi,

Nice first start. Some comments:

1. You will have to add corrective EQ (quite a bit) in addition to RIAA. This would be true if your head was "textbook". You might need as much as 20-30 db of high frequency boost to flatten the response. You will also have to notch out the resonances.
2. What drive level were your cuts made at? The noise floor is swamping the high frequencies.
3. It would be better to test using lacquers and a sapphire cutting stylus to start if you can afford the cost. Embossing has builtin limitations to how far you can push the high frequencies. You cuts will be lower in noise as well.
4. A fuse is fine for protection to start. Just make sure you monitor your cutting levels at the driver and you you should be fine.
5. To see if your separation is at issue, just cut with one driver connected and check the playback. That way, you eliminate and problems with your audio chain.

Mark

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tape
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Re: "Brother Singer" Cutterhead

Post: # 45670Unread post tape
Fri Jan 20, 2017 8:45 am

About stereo: Embossing can only be mono, never stereo

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sifis1983
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Re: "Brother Singer" Cutterhead

Post: # 45684Unread post sifis1983
Sat Jan 21, 2017 3:50 pm

Hi,

CountMoogie, the drivers that I'm using are dayton audio bct2-45.

Mark,
1: I will try to add some corrective EQ, when I will be able to emboss with more power in my drivers. There is no reason to try it now, because the signal in the previous test cut, is very very low.
2. I don't know what the level is. I ve just connect the output of a macbook straight to the drivers. I ve made a measurement with a voltmeter and I see that there are 0.35 volts in white noise part. (I suppose that is very low). I don't have any db meter at the moment.
3. Ok, perfect! But I will try PVC, not lacquers. Anyway, I will try it soon.
4. My main problem now, as you understand, is to have an amplified signal in the drivers. As I can see, Todd insists to have circuit breaker with high quality relays, instead of fuses, like professional lathes. At the moment I'm not able to make something like this. So, I will try to connect 2 fuses for my drivers as you told me. I don't know what fuses to choose. I ve just read this thread http://www.lathetrolls.com/viewtopic.php?f=1&t=6845&p=44330&hilit=fuses#p44330

According to Soulbear calculations, I do this, for my head. 10W/4ohm = root 2,5 = 1,58A. Is this calculation correct?

If my amp is 150W at 4Ohm and the drivers 10W at 4ohm, what kind of fuse I should choose? 1,58A is correct? and what about the type? Fast blow, medium, standard?
I don't expect to give me a specific answer to this, but a little help of your electronic knowledge is welcome.

5. I made a test with only the one driver connected. No result. Same signal in both channels again.

Maybe tape, is right. Embossing is not for stereo?

Sifis

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Soulbear
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Re: "Brother Singer" Cutterhead

Post: # 45710Unread post Soulbear
Mon Jan 23, 2017 9:27 am

sifis1983 wrote:According to Soulbear calculations, I do this, for my head. 10W/4ohm = root 2,5 = 1,58A. Is this calculation correct?

Bollocks, of course it's correct!!!!!! Don't ask in future :twisted: :twisted: :twisted: :twisted:

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markrob
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Re: "Brother Singer" Cutterhead

Post: # 45714Unread post markrob
Mon Jan 23, 2017 1:09 pm

Hi,

Not sure why Soulbear is so upset with you. His calcs are correct, but you should probably select a much smaller fuse to protect the driver. I would start with 1/2A fast blow fuses and a move up from there as you gain more experience.

Todd is not insisting you use an electronic protection circuit. He is just offering it as a higher end, more reliable way to protect the driver. If implemented correctly, it will allow you to run closer to the driver power limits without fear of smoking them. Not sure its needed in your case since you are using "off the shelf" drivers that are easy to purchase and, from the looks of your design, easy to replace. If you pop a few in the name of experimentation, it will not be the end of the world.

If you go by voltage measurement, the formula becomes: V = Sqrt(P x R). So for a 4 ohm driver at 1 watt (a good starting point) you would need 2 volts RMS at the head. That would result in a current of about 1/2 amp.

I don't have any experience trying to emboss stereo, but it makes sense that it might be tricky. The grooves are U rather than V shaped and the playback stylus tends to ride on one wall. I seem to recall some here have had success embossing stereo. Maybe they can weigh in.

Mark

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sifis1983
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Re: "Brother Singer" Cutterhead

Post: # 45759Unread post sifis1983
Tue Jan 24, 2017 1:45 pm

Hi,

Soulbear, I can't understand why you are upset, either. I had only ask others if your calculation is right. I appreciate that you gave me these numbers. I really do. I'm just trying to have opinions from other people here. No offence.

The word "insist" is wrong about Todd's circuit breaker (sorry for my poor english). "Offer" is a good word about his suggestion.

Anyway, I will try some fast blow fuse to my drivers.
But, Mark why you suggest me to start with 1 watt and 2 volt RMS in my head?

Something I do for my previous test, is to connect a multimeter to the output of my macbook, to see what Volts it will show.
It shows about 0.25 Volts, in the "white noise" part.

I make two more tests:
In the first one I connect only the one driver of my head with a cheap mono 18W amp, to see what is happening. The amplifier has unbalanced inputs. The audio file is the same as the previous one (noise + sweep + 1K tone + payback track) with iRIAA. The source now is from a focusrite saffire and the 18W amp. I can't measure the level that reaches the driver. I have only connect a multimeter to amplifier's output to see the volts. (see pic)
multimeter.jpg
I set the amp volume potentiometer, in the middle. As you can see, it shows 3.04 volts at white noise part.
The result is this one :
emboss noise + sweep + tone + payback 18W amp (1 driver).mp3
I think there is a progress here, but not that much.
The sweep tone part has extreme resonance at 400-600Hz. The 1khz tone is has something like "vibrato" and I don't know where it comes from.
Also, the harmonic distortion in 1Khz is bigger. :?

Here is a pic of the grooves in "1Khz tone" part
1khz tone with 18W Kemo Amp.jpg

Then, I try to add some corrective EQ. This is the same as the above test, but with iRIAA + a quick adjustment in a corrective EQ.
The Multimeter shows now 1,55V at the "white noise" part, and it reaches 4,5Volt approximately, in the peak of the sweep part. (at 6-7Khz).
The potentiometer of the amp is steady at the middle, as before.
Also, I must say that I reduce the level from the source (at the pc) because it clipped. The reduce was about 10dB in noise part and about 5dB in the rest of the audio file.

Here is the result:
emboss noise + sweep + tone + payback 18W amp iRIAA + corrective EQ.mp3
Extremely low signal, especially in noise part. There is some better frequency response, but what about the level?


So, anyway maybe these tests are meaningless. I don't know if this multimeter in the amplifier output, shows something that matters. What do you believe?

That's why I'm asking if this 2Volt RMS that you suggest me to start, would be enough for my cuts?

Anyway, I would like to thank you again for you help and I will try my "bigger" amp in a few days and I will try to upload a video.

Regards,
Sifis

P.S. : The stereo is tottaly meaningless here. As you can see and hear, with only the 1 driver connected, there is the same signal in both channels.
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markrob
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Re: "Brother Singer" Cutterhead

Post: # 45764Unread post markrob
Tue Jan 24, 2017 2:24 pm

Hi,

You should not do a sweep with RIAA applied. The high frequency boost relative to 1Khz is too much. If you use white noise that is processed with RIAA you will not damage your driver. The voltage measurement in that case is the integrated average of all frequencies. So if you measure 2 volts RMS, the total power to the head is limited to 1 watt. That is not true if you set the level of your sweep at 1Khz. At 10 Khz, for example, the signal would be almost 14db higher (almost 20 X the power!). I suggested you start at 1 watt to be conservative. You can increase that up to about 6 volts RMS (about 9 watts), but be careful.

If you want to do sweeps, the best bet is to build or modify a phono preamp so that the RIAA is disabled. That way you can feed the head a constant voltage sweep at specified power level and be assured that you won't exceed its rating. If the playback preamp has no RIAA then it will represent the true velocity response of the head.

The physics of a moving coil head results in a main system resonance that you must deal with. Due to construction problems, you may have additional resonances that will also need to be taken care of. Note that below resonance, the response of a moving coil head rises at 6 db/octave. Beyond resonance, it falls at -6db/octave. This also must be accounted for in addition to application of RIAA. A textbook moving coil head has a open loop velocity response that looks like an upside down "V".

Mark

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Gus
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Re: "Brother Singer" Cutterhead

Post: # 45770Unread post Gus
Tue Jan 24, 2017 2:49 pm

Excuse me for the Greeks guys

Γεια σου Sifi, ακριβώς για αυτό τον λόγο θα χρειαστείς ένα ενισχυτή όχι στα 18w αλλά πολύ μεγαλύτερο γύρω στα 150w για να έχεις ένα σωστό ηχητικό αποτέλεσμα(hi-fidelity) σε τόσο χαμηλά watt δεν θα περάσουν ούτε οι υψηλές συχνότητες ούτε η ένταση θα είναι ίδια με ένα δίσκο βινυλίου του εμπορίου .Επίσης είναι πολύ καλύτερα να χρησιμοποιήσεις ένα πραγματικό (hardware) ισοσταθμιστη καθώς επίσης και ένα riaa μετατροπέα,σε αυτή την περίπτωση ψάχνεις για τον caruso preamp του Flo http://vinylike.de/index.php/carusopreamp/ επίσης μπορείς να φτιάξεις ένα παθητικό riaa με λίγα και φθηνά υλικά ψάξε εδώ μέσα θα βρεις κάποια σχέδια.Μην περιμένεις όμως να έχεις εκπληκτικά αποτελέσματα με την τεχνική του embossing είναι χαμηλής πιστότητας έτσι κι αλλιώς, ρίξε μια ματιά και άκου κάποια δείγματα μέσα από το site του γκουρού Peter King που ασχολείται εδώ και 30 χρόνια με την τεχνική του embossing
http://peterkinglathecutrecords.co.nz/mastering.htm
Γεια καλό ήχο η κοπή PVC με διαμάντι είναι μονόδρομος... ακριβή αλλά με πολύ καλά αποτελέσματα.
Σχετικά με το βιμπράτο που γράφεις δεν είναι τίποτα άλλο από το wow του πικ-απ σου, δυστυχώς τα Technics mk ii έχουν μοτέρ χαμηλής ροπής και το embossing θέλει αρκετή ροπή το Technicks sp 10 mk2 είναι μονόδρομος .
Τέλος θα πρέπει να είσαι σίγουρος ό,τι η κεφαλή σου είναι σωστά φτιαγμένη.
Ελπίζω να βοήθησα λίγο.

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sifis1983
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Re: "Brother Singer" Cutterhead

Post: # 46555Unread post sifis1983
Sat Apr 01, 2017 10:37 am

Hi,

Well, the last days i've made a lot of tests with different combinations of my cutterhead.
Firstly, I have now a sapphire stylus and PVC blanks from myshank.
The big difference is that I cut the plastic (not emboss).
I have to tell that I have no suction machine for the swarf, and I'm just trying to push the swarf away with a paintbrush. :shock:

So, I printed a combined V spring with tube, with a thinner "V" (0.7mm approximately). (see pic)
This way I thought that I can achieve less stiffness to the whole mechanism of the head.
vspring + torque tube.jpg
The first try, was to add some 3d printed plastic piece for pushrod, to my drivers. I screw them over the metal piece of the driver. (see pic).
At the end of this plastic, I glue a 2mm brass rod, and then I attach them to holes of my tube. I'm not glue the brass rods in the tube. I just push them to fit by force. I do this because I want to easily change and try different pushrod mechanisms. However, I don't know if this way of connection of the brass rod to the tube, is a benefit for good stiffness of the whole mechanism.
plastic pushrods.jpg
cutterhead v.2.jpg
With the help of Wim (Knop Lathe), I did some tests with the above version of the head, but I understand that I had to much mass to move and therefore I was need to much power. I try to cut with max power of my amp (150W @ 4ohm) but the signal on the record was too low, because of the EQ I make, to compensate the frequency response. (+30db approximately in high frequencies). I have to say that with this built of the head I have a peak resonance in 530Hz approximately, and too much harmonic distortion in the 1Khz tones. (the signal chain is not clipped anywhere).



Now I'm trying to have a different way of the design of the head. I remove the previous plastics from the drivers and I just add a nylon screw in the M5 hole and then I glue a brass rod to the top of the nylon screw. The connection to the tube is also the same as the previous design (I push them to fit by force). This way I thought, that I will have less mass to move. (see pic)
cutterhead nylon screw + brass pushrod.jpg
I don't know how much mass I have this way, because I can't measure the pieces of the construction. I should buy a weigh scale... :roll:

CONTINUE IN THE NEXT POST
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sifis1983
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Re: "Brother Singer" Cutterhead

Post: # 46556Unread post sifis1983
Sat Apr 01, 2017 11:10 am

CONTINUE FROM THE PREVIOUS POST

The signal I cut is: white noise + 1Khz tone on both channels + 1k only right + 1k only left + song, without any EQ, straight to the disc. The result was better than before.
In the white noise part, the frequency response is look like this:
f response noise NO RIAA (screw pushrods).png
You can listen this cut here:
white noise NO RIAA screw pushrod.mp3
As you can see the resonance frequency now is at about 450Hz. Markrob says in another post :
"Consider the system resonance. There are two variable parameters that determine the resonance point. The moving mass and stiffness (or compliance) of the suspension. If you want to raise the resonance point, you can either decrease mass or increase stiffness or some combination of both"

So, I can't understand what I'm doing wrong here. I believe that I was decrease the mass, but the resonance point is lower than before. :roll:


Anyway, I try to compensate this response with Fabfilter EQ. The result is this one:
white noise fab6 + 6.1.mp3
The above cut, has 2 fabfilter in series (to achieve a flat response), a HF limiter at 7khz and above. I don't measure any output levels. I can only say that my amp was set at 3 o'clock.

Also, I have to say that I have some skips and some "wow" vibration, but I think that there is no enough torque from my Technics SL1200 mk2. :(
Or maybe this is because that I don't have any suction mechanism for the swarf.

In the "tones" part of the audio, I can see that there is a slight harmonic distortion in only one channel. Also, if I try to cut louder signal than this, the harmonic distortion at 1Khz is getting bigger... This make me think that there is something wrong in my construction, but I don't know what it is.... :(

Any comments or advices are welcome...

Regards,
Sifis
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markrob
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Re: "Brother Singer" Cutterhead

Post: # 46557Unread post markrob
Sat Apr 01, 2017 11:41 am

Hi,

You probably did lower the mass of your coupling parts a bit, that driver has a pretty high moving mass to start with. I took some measurements some time ago. Below are what I was able to determine.

T/S Parameters for Parts Express Driver BCT-2

Re = 3.28 ohms
Le = 388 uH
Fs = 529 Hz
Mms = 8.31 g (8.31 e-03 Kg)
Cms = .0109 mm/N (10.9 e-06 m/N)
BL = 4.32 N/A (Tm)
Impedance at 1Khz = 4 ohms
Max power 10 W rms

Coil former .540g
stiffener (minus rivets) 2.06g
Threaded pusher 2.24g
Spider 2.87g
Coil Wire 1.41g
Total 8.85g 6.61g (minus pusher)

Aprox 17' of Metric 2.0 (32 ga AWG) gage wire wound on 4 layers of 5mm length
Aluminum Coil former diameter 28mm

So your changes may not have much effect on the overall moving mass given the baseline mass of the stock head.. The frequency response plot looks pretty good. The results above 10K may be the noise floor limit. To check cut some silence before you noise and see if it intersects with your noise plot. You just may not be able to get much level out of the head before you run into power limits.

You may want to look at removing the metal spider assembly (see above) from the voice coil (not so easy) and mounting a lighter 3D printed version. Bryan did that on his build.

Getting a milligram scale is well worth it. I have this model:

https://www.amazon.com/American-Weigh-GEMINI-20-Portable-MilliGram/dp/B0012TDNAM


Hope that helps a bit.

Mark

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sifis1983
Posts: 67
Joined: Fri Feb 10, 2012 3:55 am

Re: "Brother Singer" Cutterhead

Post: # 46561Unread post sifis1983
Sun Apr 02, 2017 8:19 am

Hi,

Thank you mark! Of course your info helps, as always... :D

I remove the "spider" assembly of the drivers.
spider remove.jpg
Then I try to glue the 3D printed part over the coil former but it doesn't fit with accuracy.
I test it, to see how it sounds. The 1kHz sine wave, was very distorted. Something like a square wave.
I think this is because the plastic doesn't fit exactly over the former of the coil.
Do you have any suggestions how to mount the plastic?

Anyway, I will print tomorrow some other plastics with bigger bottom radius, to try again.
Also, I order a digital weigh scale with 0.01 resolution. 8)

Regards,
Sifis
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TheCrates
Posts: 80
Joined: Wed Jan 18, 2017 12:39 pm

Re: "Brother Singer" Cutterhead

Post: # 46565Unread post TheCrates
Sun Apr 02, 2017 1:49 pm

Cant help you with this one, but well done, hang in Sifis!

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markrob
Posts: 1623
Joined: Wed Nov 28, 2007 1:14 am
Location: Philadelphia Area

Re: "Brother Singer" Cutterhead

Post: # 46567Unread post markrob
Sun Apr 02, 2017 2:50 pm

Hi,

Nice job removing the voice coils. When you fabricate a lower mass replacement for the stock spider, you have to make sure that the coil is centered and well bonded to it. Another issue that can crop up is that you may lose high frequency response if you have too much flex between the voice coil drive point and your center coupling rod. If that is not very stiff it will flex like hitting a drum and create a secondary resonance with a sharp drop in response beyond that point. So you may end up trading one problem for another. A cone shape might make more sense here. Looking forward to seeing how you progress.

Mark

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