Deep Grooves Mastering - Opcode66 Transducer Project

[opcode66]

Reading current dissipation and estimating temperature is more accurate than actually measuring the actual local temperature of he coil??? I disagree. I am going to implement something else here. If it is wrong or not as effective, so be it. I've never made a circuit that employed a thermister before. It would be a handy thing to know how to do. Would also relate to another project with a friend. Oscillator temperature stabilization for analog modular synth stuff.

Regarding the SEL's, my main improvement will be an arcless, snubberless relay. No bleed when the relay is opened. That means nothing is heard of sent through the head when the Oper light is not green and the the head is up.

I will get to feedback. This is only week #2. Give me some more time. While we're on the topic, I'd be glad to use one of your pre-amp boards for testing feedback on this head once I'm far enough along.

Regarding self repair. That is exactly why the transducers are modular. They will have dsub pins on one end. The pins will fit into reciprocal dsub sockets in the cutterhead body. If you blow a coil you can just pull out the transducer card. And then replace it with a spare for that channel that I will supply with every cutterhead. Zero downtime. As long as you don't blow two coils in a row.

Plenty of cutters get fantastic results with the dynamic version of the vinyl recorder. i'm not saying that I won't include feedback. What I am saying is that it's not a feature I'm particularly focused on at the moment.

I appreciate your interest and your comments Flo. Thank you. I am willing to send a completed head to you for inspection once I feel the project has come far enough to justify that.

[markrob]

Hi,

Yes it is much better than your proposed solution. The circuit uses the temperature coefficient of copper (about 4000ppm/degree C) in a bridge circuit to measure the change in voice coil resistance vs. temperature. For copper, the curve is quite linear in the range being measured. If you try to do this using a thermistor, you will run into several problems that will make your reading suspect.

1. You are only measuring at one point on the voice coil.
2. There will be some error due to inability to make good contact the with the coil due to thermal resistance from thermistor to the wire.
3. Response time is much slower depending on the size of the thermistor.
4. Adding the thermistor adds moving mass to your system.
5. Not sure how you introduce the thermistor into the magnetic circuit without affecting the gap or the geometry of the coil.
6. You have to have very small wire gauge leads that will be subject to breakage due mechanical fatigue and/or stress.

On the other hand using the voice coil resistance only gives you the average temperature of the entire coil. If there are local hot spots due to variations in the wire or thermal resistance from wire to bobbin to ambient or other temperature gradients, they could be averaged out and yield a lower number than the worst case.

Mark

Mark

[opcode66]

Well, I'm leaving room for them. A combined approach might be good.

My intention is for them to sit very close to the coils. But, not be a part of the actual coil or bobbin. Since my magnet is very small and is in the middle of the bobbin, I have room around the outside of the coil. My intention was to put a thermister pointing at the coil and housed within the outer cover of the transducer.

The wire gauge is very small, yes. It was selected specifically. I won't comment on why. Suffice it to say, my transducer will be easily changed out. So, no worries about longevity.

For your viewing pleasure. Test #3 of project codenamed "Bladerunner"

[studiorp]

With this coil, how many watt for channel you can obtain ?

[markrob]

Hi Todd,

The head is coming together nicely!

One thing you are be able to do is that I would never have the opportunity to check is to compare the stiffness of your head to the Neumann. You should be able to determine how much force it takes to deflect the stylus of you head as compared to the Neumann. Even a simple finger test like are doing in the video will give a lot of info. Do this with the head disconnected from any amplifier. This will give a you good feel for the required spring. If you have a s scope, you can get an idea of the system resonance by connecting the drive coil to the vertical input of the scope and tapping the torque tube. You should see a damped sine wave at the system resonance. If you don't have a scope a PC sound card mic or line input should work as well. It will also tell you have well damped the resonance is. Faster decay time indicates better damping. If you see no damped sine, then the head is overdamped (which should be a good thing), and you won't be able to determine the resonance this way. I suspect plastic will have better damping properties than metal as it typically doesn't ring like a bell when tapped.

Are you planning to test the head open loop or with feedback?

On the thermistor front, it costs nothing to make provision for it, so why not. If it is not in intimate contact with the coil, the thermistor is really only reading the local ambient temperature. You can make an argument that this is related to the average coil temperature, but you will have to perform some experiments to develop exactly what that relationship is. Once you move away from contact with the coil the response time will be made even longer as you now have to wait for thermal mass in the sensing region to reach temperature.

Mark

[opcode66]

I am now fully convinced that I am in error regarding the thermisters. They have been removed from the design. Thanks to Markrob and Flo for setting me straight. The wire lead holes are now being re-purposed. I will add LED lighting and a Pin Hole video camera so you can illuminate the cutting area and see the stylus tip via the camera.

[opcode66]

No progress to report today. I've been printing upgraded parts for the 3d printer. And, I've been tweaking the design of a few parts. I should have some more progress tomorrow. Soon, I'll start another thread. I think I've diverge far beyond the initial Transducer Project.

[recordboy]

I am so completely, and utterly inspired!!! Thanx Todd!!!



p.s. I use that same sony amp... It's pretty damn fabulous








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

[opcode66]

I only use that Somy amp for bench tests. When I actually do test cuts I am using a QSC GX3. It is very similar to the power amplifier in the neumann amp rack, but lower signal to noise ratio.

[recordboy]

I'm Way far from that point indeed XD

That sony is the top amp I own ATM (for sure going to uprate at some point)...

I'm pretty poor

Yet working on that too X)

[45rpmdude]

we do not all have helium cooling.

[45rpmdude]

Not all of us have helium cooling..

[opcode66]

Huh? Ok. Well, if you are using a Neumann cutterhead and are cutting loud and are not using helium you are prematurely aging your drive coils.

This thread is quite old now. Have a look here for the most recent developments http://lathetrolls.com/viewtopic.php?f=15&t=5250&start=160