Hello!
I come from a tube amp building / repairing background and have taken notice of you trolls and your clandestine activities.
I have read the excellent newb intro post and decided that my probable course of action will not be spending my time refurbing a recordio ( or something similar ) nor do I have a spare 5k plus to toss at a "real machine". Well...I do but I don't.
So I'll learn the hard way and build "something". I'm a glutton for punishment.
Here are few questions that I am aware are silly ( and likely lazy ) but here we go.
I've noticed cutting heads with two speaker / transducer elements on them. Are those stereo heads or are the elements wired out of phase to increase cutting power ( in push / pull )?
Why does it take so much power to drive the head? I saw a recommended 200W per side!! I have two 40 watt mono blocks I built ( kind of modified Williamsons) laying around that need a purpose.
Now here are few that will drive you to get the pitchforks out...
I have about 100 junk records slated for target practice. For science I got the orbital sander out with a few different auto body grits and blanked a few of them out. Then I buffed them and put a little turtle wax on them and I must say they look quite good. I assume they are PVC? Am I on a fools errand here?
Lastly ( I'm done I swear! ):
I have a few old turntables in my bonepile that are idler driven. Will these possibly have enough torque to do something reasonably useful or is a bigger motor needed?
If you are still with me thanks. If this seems fun please play along.
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Mold_motel
- Posts: 1
- Joined: Sat Apr 13, 2024 12:37 pm
Re: A few sub noob questions regarding...well everything.
Hi,
The two driver heads are indeed typically stereo, but they can cut mono if you feed them a mono signal. They are in fact wired in reverse polarity so that if you feed them an identical signal on both drivers, you get a lateral cut mono groove cut. If you wired them with the same polarity, they would cut a vertical "hill and dale" groove like the old Edison cylinders were cut. If you think about the vector addition of the two drivers, this will become clear.
For moving coil heads, the average power required to cut is typically low (1-10 watts). However, you need a tremendous amount of peak power to accelerate the moving mass of the cutting elements at high frequencies. There are two reasons for this. One it the amount of high frequency boost applied via the RIAA recording curve. The second reason is the roll-off of the open loop response of the head above its main resonance. This is typically in the 500 - 2000 hz range and falls off at -6db/oct (-20db/decade). All told, you are looking at needing 30-40db of overall boost at 20 Khz. You can get away with less power if you are willing to lower the bandwidth and/or reduce the volume of the cut. I would note that moving iron heads like the Presto 1D require much less power because the coils do not move and can contain more turn and higher mass and can generate more force per amp. They are also stiffer and their main resonance is 4Khz and higher.
There are many sources for blanks for reasonable prices. Given that you need a good surface, I would not waste time trying to recycle old records. There are also lots of better DIY materials to do some cutting on. For example CD's, plastic plates, and old laser disks.
Many of the old rim drive tables will have plenty of torque for cutting. For reference, a stock SL-1200 is just able to function. You should be able to get started with a decent rim drive TT.
Hope this makes sense.
Mark
The two driver heads are indeed typically stereo, but they can cut mono if you feed them a mono signal. They are in fact wired in reverse polarity so that if you feed them an identical signal on both drivers, you get a lateral cut mono groove cut. If you wired them with the same polarity, they would cut a vertical "hill and dale" groove like the old Edison cylinders were cut. If you think about the vector addition of the two drivers, this will become clear.
For moving coil heads, the average power required to cut is typically low (1-10 watts). However, you need a tremendous amount of peak power to accelerate the moving mass of the cutting elements at high frequencies. There are two reasons for this. One it the amount of high frequency boost applied via the RIAA recording curve. The second reason is the roll-off of the open loop response of the head above its main resonance. This is typically in the 500 - 2000 hz range and falls off at -6db/oct (-20db/decade). All told, you are looking at needing 30-40db of overall boost at 20 Khz. You can get away with less power if you are willing to lower the bandwidth and/or reduce the volume of the cut. I would note that moving iron heads like the Presto 1D require much less power because the coils do not move and can contain more turn and higher mass and can generate more force per amp. They are also stiffer and their main resonance is 4Khz and higher.
There are many sources for blanks for reasonable prices. Given that you need a good surface, I would not waste time trying to recycle old records. There are also lots of better DIY materials to do some cutting on. For example CD's, plastic plates, and old laser disks.
Many of the old rim drive tables will have plenty of torque for cutting. For reference, a stock SL-1200 is just able to function. You should be able to get started with a decent rim drive TT.
Hope this makes sense.
Mark