Amplifier for new Rek O Kut Lathe Project

[cdslaten1s]

Hello all, I'm a newbie so please take it easy on me. I've done research for the past 3 years, had to travel 1300 miles on a failed attempt to pick up a lathe and have finally found one. The table and motor is working on the Rek o Kut. The cutter is a Mono M-12 and is at 5 ohms. Is this too low?

Also, I don't have the funds to buy a vintage tube amp right now but would like to run the sound to the cutting head from a computer. Now where I'm confused is what amplification system would work so I don't blow my cutter head? I would like to run the sound from a DAW so I can check levels etc. but out of my computer is where I'm stuck. Can I use my computer as the amplification system and then run a cable from my computer to an M Box and then use the left/right outputs to hook to the cutter head by using the left/right cables coming from the m box. Obviously this will take re-wiring. There is a picture here that shows my connections running out of the cutter head.

Or could I use a Zoom H6 which can control the output Voltage and how would that help/hurt the cutter head/sound on the disc?

Or would I also need an amp hooked to my computer to send the audio to before it goes to an M Box/Zoom H6 and then out to the cutter head? I have a tube guitar amplifier but am not sure if that would give a good sound quality. If I also need an amp, what modern day amps could you recommend that are reasonably priced?

Thank You all very much!!!!

[markrob]

Hi,

The cutter head is basically a speaker without a cone. So, you will need a power amp to drive the head. Is the 5 ohm figure you stated a DC resistance measurement you made using a digital multi-meter or is that the value stamped on the head? Either way, that should be fine to drive from a modern solid state amp. Anything that can output 10-100 watts into an 8 ohm load will work fine. To start, keep your levels on the low side until you get used to things. It would be a good idea to add a fast blow 1/2 amp fuse in line with the cutter head as protection. Once you gain some experience, you can drive harder and increase the fuse to maybe an amp or so. To determine a starting drive level, create a 1Khz sine wave tone in your DAW at a peak level of -15db below full scale. Feed this DAW to your power amp and measure the AC voltage right at the head terminals. Slowly bring up the volume until you read about 2.8 volts AC. Cut this test tone and see if you have decent level on playback. If you can, compare your cut with a standard test record with a 5cm/sec test tone, you will get a good idea if you head is in decent shape. It should be within a few db of the test record at that drive level. If it is, you are good to go. Otherwise, your head may need re-building.

Mark

[cdslaten1s]

Hi,

The cutter head is basically a speaker without a cone. So, you will need a power amp to drive the head. Is the 5 ohm figure you stated a DC resistance measurement you made using a digital multi-meter or is that the value stamped on the head? Either way, that should be fine to drive from a modern solid state amp. Anything that can output 10-100 watts into an 8 ohm load will work fine. To start, keep your levels on the low side until you get used to things. It would be a good idea to add a fast blow 1/2 amp fuse in line with the cutter head as protection. Once you gain some experience, you can drive harder and increase the fuse to maybe an amp or so. To determine a starting drive level, create a 1Khz sine wave tone in your DAW at a peak level of -15db below full scale. Feed this DAW to your power amp and measure the AC voltage right at the head terminals. Slowly bring up the volume until you read about 2.8 volts AC. Cut this test tone and see if you have decent level on playback. If you can, compare your cut with a standard test record with a 5cm/sec test tone, you will get a good idea if you head is in decent shape. It should be within a few db of the test record at that drive level. If it is, you are good to go. Otherwise, your head may need re-building.

Mark

Thanks for the reply. The 5ohm is the DC resistance measurement using a multi-meter. I have only referred to solid state amps pertaining to guitar amps. Would a 50 W tube guitar amp work as an amplifier to the cutting head? Or is there a specific trade name/category for the type of solid state amp that I need to use? So I test the AC voltage to the wires connected to the cutterhead after playback from the computer correct? Do you have any suggestions on how to add/install the fast blow 1/2 amp fuse to the cutterhead? And where you would add it? Thanks again!

[markrob]

Hi,

You could use a guitar amp if that is all you have. But I would start with a modern solid state amp. The fuse would go inline with one of the wires from the head that connect to the output of the amplifier. You would measure the voltage at the output of the amp (from the plus terminal to the minus).

Mark

[cdslaten1s]

Hi,

You could use a guitar amp if that is all you have. But I would start with a modern solid state amp. The fuse would go inline with one of the wires from the head that connect to the output of the amplifier. You would measure the voltage at the output of the amp (from the plus terminal to the minus).

Mark

Are these the fast blow 1/2 Amp fuse you were referring to? Is there a better one for audio? And by 1/2 do you mean .5?

https://www.amazon.com/Pack-500mA-Fast-AGC500mA-AGC500/dp/B00YHVHD6M/ref=sr_1_fkmr0_2?ie=UTF8&qid=1527104899&sr=8-2-fkmr0&keywords=fast+blow+1%2F2+amp+fuse+sound

Also when you referred to a modern solid state amp was this what you were referring to? Aka something to power computer speakers. My cutter head is running at 5 ohms and this supports 2-8 ohm speakers and has 100 W.

https://www.amazon.com/dp/B0071HZ5RI/ref=cm_sw_su_dp

Thank Again for all your help!!! My uncle is going to help me install the in line fuse once I had the exact one to use.

[markrob]

Hi,

The fuses are fine. The amp, not so much. Its meant to be powered by a car electrical system. It appears they provide an AC adapter, but its only rated for about 18 Watts. Might work to get started, but you would be better off with an AC mains powered amp with a decent power rating.

This one is at the bottom end of the range, but seems to have realistic specs and is not powered by a wall wort and can be run in bridged mode for more power (160 watts into 8 ohms):

https://www.parts-express.com/dayton-audio-apa102-class-d-stereo-60-wpc-amplifier-auto-on--300-591

It is a switching mode (class D) type amp, which is the reason its low in cost. But for what you are doing, it should be fine. Parts Express has good return policy in case it does not work for you.

Mark

[cdslaten1s]

Hi,

The fuses are fine. The amp, not so much. Its meant to be powered by a car electrical system. It appears they provide an AC adapter, but its only rated for about 18 Watts. Might work to get started, but you would be better off with an AC mains powered amp with a decent power rating.

This one is at the bottom end of the range, but seems to have realistic specs and is not powered by a wall wort and can be run in bridged mode for more power (160 watts into 8 ohms):

https://www.parts-express.com/dayton-audio-apa102-class-d-stereo-60-wpc-amplifier-auto-on--300-591

It is a switching mode (class D) type amp, which is the reason its low in cost. But for what you are doing, it should be fine. Parts Express has good return policy in case it does not work for you.

Mark

What do you think the best way to set up the amp you sent me is? From my understanding I would connect computer to RCA "interrupting main" on the back, and then run "Main Out" with RCA and connect each color to the in line fuse to the connection on the cutter head? I'm trying to cut mono so is there any specific way to do that with the connection as far as switches I would need to switch (i.e. Mono switch with Stereo and Bridged and below the "Auto On" Switch with Normal and Auto)? Or is the audio being sent already mono (once converted to mono in my DAW) and therefore the needle will cut mono and play through both speakers on playback? I'm calling them tomorrow morning when they open but you would understand the cutter head part more than anyone there I'm sure. Thanks as always and I promise I almost have this figured out.

[markrob]

Hi,

The RCA jacks are all line level inputs or outputs. The head needs to connect to the speaker binding posts. I would run the amp in bridged mono mode (see the manual for hookup instructions for bridged mode). You would connect the non-interrupting input to your computer. Turn off the auto power on feature. If your source material is stereo and you run Left and Right to the amp inputs, it will sum them to mono in bridged mode. The RCA jacks marked Main out are used to slave to another amplifier. It does not drive a speaker load.

I would recommend that before hook up the cutter head, you use a speaker to test out your setup. That will allow you to make sure your levels are right and that there is no distortion or excess noise.

Mark

[cdslaten1s]

Hi,

The RCA jacks are all line level inputs or outputs. The head needs to connect to the speaker binding posts. I would run the amp in bridged mono mode (see the manual for hookup instructions for bridged mode). You would connect the non-interrupting input to your computer. Turn off the auto power on feature. If your source material is stereo and you run Left and Right to the amp inputs, it will sum them to mono in bridged mode. The RCA jacks marked Main out are used to slave to another amplifier. It does not drive a speaker load.

I would recommend that before hook up the cutter head, you use a speaker to test out your setup. That will allow you to make sure your levels are right and that there is no distortion or excess noise.

Mark

I called them today and the tech guy said for bridged mode you would connect your wires from speaker to both positives on speaker A on the bridged output to send it out to a speaker. This same process would work for a mono cutting head if you could set up a speaker that way correct? I'm just running a mono track with Riaa/inverse riaa curve from my DAW so I wouldn't be sending a stereo track to the amp. Also since my cutter head is reading at 5 ohms, would the 8ohm on the bridged output cause any issues to anything? They have a sale going on right now as well so I'm glad you mentioned them. Thanks!

[markrob]

Hi,

That all sounds right. You probably only need to connect one RCA jack to the input as they sum L&R in mono mode. The 5 ohms you measured is the DC resistance. The actual impedance is higher for the cutter head. So you are probably fine with the bridged 8 ohm minimum per the amp specs.

Mark

[cdslaten1s]

Hi,

That all sounds right. You probably only need to connect one RCA jack to the input as they sum L&R in mono mode. The 5 ohms you measured is the DC resistance. The actual impedance is higher for the cutter head. So you are probably fine with the bridged 8 ohm minimum per the amp specs.

Mark

Would this 16 gauge speaker wire work to connect from bridged output to in line fuse? It says RATED 6-80 VOLTS 158 DEGREES FAHRENHEIT. Do I need to connect the speaker wire to a banana plug for the bridged output or can the speaker wire just go straight to the output bridge connection?

https://www.amazon.com/SPEAKER-STRANDED-COPPER-ENNIS-ELECTRONICS/dp/B06X6MG14K/ref=sr_1_13?ie=UTF8&qid=1527182754&sr=8-13&keywords=speaker+wire+16+gauge+25+feet

Thank you so much. If you ever make it through the Middle Tennessee area message me and my wife and I will take you out to lunch.

[markrob]

Hi,

The zip cord you picked looks fine. As far as jacks go, you should be fine either way. I like the direct connect option better. If you are using banana jacks, they can be easily knocked out of the binding posts. They are great if you need to disconnect often (e.g. in a PA setup). In that case get good quality jacks to avoid problems.

Mark

[cdslaten1s]

Hi,

The zip cord you picked looks fine. As far as jacks go, you should be fine either way. I like the direct connect option better. If you are using banana jacks, they can be easily knocked out of the binding posts. They are great if you need to disconnect often (e.g. in a PA setup). In that case get good quality jacks to avoid problems.

Mark

Awesome. Thank you again! Last question. What is the best lubricant for the feed screw and other parts that need lubrication on the lathe mechanisms, such as a lower weight on the consistency? I haven't found anything on here regarding if a specific lubricant is used for the lathe. Everything moves freely and I haven't seen any rust so far. I wouldn't mind cleaning the feed screw just to make everything nice and clean but don't know if there is a specific cleaning mechanism/material. Thanks Mark!!!

[nikc]

Hi cdslaten1s

Did you find that this worked? what volts did you get up to?

My cutter-head is also about 5 ohms. I have a 0.25 a fuse and have been having the input audio signal from a track about 3-4 volts.
(But i haven't tried the sine wave).
The fuse hasn't blown yet. My playback sound on the record isn't that loud so I am wanting to push the volume up, but worry blow the cutter-head.
The volume problem could be an issue with the magnets or something else in the head.

If it was DC and the volts are 4 and the ohms are 5, then you would think the fuse would blow.
But I'm guess as its AC then the impedance is not 5 ohms.

Best

Nik