Magnetic cutting heads versus crystal

[ilium]

First off I'd like to say that I'm really new to all this and I'm thinking about building a record cutter.

With that said I have a question about magnetic cutters and after searching didn't find the answer I was looking for. So what is the main difference between a magnetic head and a crystal head. Both require an electromagnetic action to work?

I found mentions of at least one person who has built their own but I have not come across any DIY plans for doing so?

[emorritt]

Electromagnetic action only applies to magnetic heads. That is, heads that use a metal armature suspended somehow to allow it to move laterally and a coil of wire or two hooked up to an amplifier. Crystal heads rely on piezoelectric action. They're usually made from tourmaline or ceramic piezo elements. Years ago, the elements were made from rochelle salts that over time absorbed water and became unusable. If you find a crystal head, it usually requires rebuilding before it will work. Also, there is a big difference in how to drive either type of head. Magnetic heads can use the speaker output of an amplifier. Crystal heads require around 180 volts RMS to work, which means any recorder designed for a crystal head usually drives the head from the plate(s) of the output tube(s). You can't simply replace a dead crystal head with a magnetic one unless you want to smell the coils burning. You can use an output transformer to reduce the plate voltage in the recording circuit, but again, the type of drive mechanism is usually much different for a crystal head than a magnetic one. Typical crystal setups use a large tonearm with the cutter inside while magnetic machines have some sort of larger drive arm (like a Presto 75 or K recorder) or an overhead mechanism like a Presto 6N, Fairchild, RCA or other. Astatic did make a magnetic head compatible with small arm machines like the Recordio (I think it was called the M41), but again, if the machine was originally designed for a crystal head, you had to modify the circuit to accommodate the lower voltage magnetic head.

[ilium]

Okay thanks that's exactly the info I was looking for.

I've seen mention on here of a magnetic head where it appears the stylus is mounted and driven by a horseshoe shaped electromagnet. Though I didn't find much technical information about this kind of setup.

Other interesting setups I've noticed are using piezo speakers and transducers.

[45rpmdude]

im curious about this as well. but not too much info as specs and how to build one either..??

[emorritt]

There is a lot more to a magnetic cutter than just a magnet and stylus. The most simple is the Astatic M41, but the sound quality isn't very good. The larger (as you said "horseshoe magnet") heads sound better, depending on the design. Somewhere on this site (I think) is a tech brochure on the Presto 1D recorder that has some drawings that basically show how the head is constructed, but without giving away a lot of the design (for obvious reasons at the time). Magnetic cutters turn up on eBay a lot; whether you can get one for a reasonable price is another thing. The lower quality heads go for less than the known better quality units, and it sounds like one of those is where you might want to start.

[opcode66]

Not trying to hijack this thread. But, I figured I would mention that I plan to sell all plastic versions of my bladerunner head for less than $500. Most of the old mono heads that emorritt is referring to sell for quite a bit more than that on eBay.

[emorritt]

Todd; WOW less than $500?? Yes, I agree that even some of the crappy mono heads like Audak, Webster, etc. can pull inappropriate prices on eBay. But, as I say, eBay is a crazy place where crazy people pay crazy prices for fairly mundane items. They get caught up in the auction and they think they'll never see (fill in the blank) up for auction ever again. Like in my master's degree class on consumer behavior it's the "gotta have it" motivation. Once in a while I have seen some of the lower quality heads go for $200 or under, which might be what ilium is looking for. Good luck with your move to CA.