Hi,
Looks like it turned out nicely!
I've attached a pdf of the schematic for my amp. I am using an off the shelf amplifier board with a TI TPA3118 chip. Its a 50 Watt unit. You can get instantaneous peaks up to 100 Watts. There are several sources for these boards. Here is one:
https://www.amazon.com/dp/B07Q6RGVHQ
The design is a bit unusual. I wanted to see if I could avoid using a power supply 24Vdc at 2-3A and run with a much smaller supply. I did this because the head can't take more than 3 Watts continuous power. But you need 100 Watt very short duration peaks to get the head moving at high frequencies. So my Idea was to have a bank of energy storage capacitors on the amplifier DC bus charged to 24Vdc. A 10 ohm 1/2W resistor limits the charging current such that only a few watts can be pulled or the voltage will sag. So, you can use a very low power supply of a couple of watts and still get high peak power to the head. The additional components are in place to allow the capacitor bank to charge up to 24 Volts slowly on powerup so that the inrush current is limited. This limit is set by a 75 ohm resistor. Once the bus is at voltage, a MOSFET switches on and removes the 75 ohm resistor out of the circuit. It works well and adds some protection for the head if you drive it too hard. I'm not sure its worth the effort since 24Vdc 2A wall wart supplies are pretty low cost these days. But feel free to use it if you like. You could really just use the amplifier module off the shelf with a suitable supply and be off and running.
Mark
Hacking The Teenage Engineering PO-80
Moderators: piaptk, tragwag, Steve E., Aussie0zborn
Re: Hacking The Teenage Engineering PO-80
You do not have the required permissions to view the files attached to this post.
-
kugelblitz
- Posts: 40
- Joined: Thu Oct 07, 2021 6:16 am
- Contact:
Re: Hacking The Teenage Engineering PO-80
thanks for the info and tip towards a good module.
i wondered what those huge capacitors in your video were for - makes your circuit look like it really means business
i wondered what those huge capacitors in your video were for - makes your circuit look like it really means business
-
kugelblitz
- Posts: 40
- Joined: Thu Oct 07, 2021 6:16 am
- Contact:
Re: Hacking The Teenage Engineering PO-80
i just realized your removable stylus holder is aimed towards cones, i have a tungsten embossing stylus from epos, not easy to get it straight with the flat-side of the stylus a 1/4 turn from the screws 
funny how these things are so obvious when it's all printed out (for me at least), but hard to spot when looking at the stl files
guess i'll have to print it out again with the bottom hole turned a 1/4 turn as well
funny how these things are so obvious when it's all printed out (for me at least), but hard to spot when looking at the stl files
guess i'll have to print it out again with the bottom hole turned a 1/4 turn as well
You do not have the required permissions to view the files attached to this post.
Re: Hacking The Teenage Engineering PO-80
Hi,
Here is a version with an extra hole on the side of the pivot. Due to the pivot hole, I could only fit one setscrew on this side. I think it should work out fine.
Here is a version with an extra hole on the side of the pivot. Due to the pivot hole, I could only fit one setscrew on this side. I think it should work out fine.
You do not have the required permissions to view the files attached to this post.
-
kugelblitz
- Posts: 40
- Joined: Thu Oct 07, 2021 6:16 am
- Contact:
Re: Hacking The Teenage Engineering PO-80
wow, now that's what i call service!
thank a lot!!
thank a lot!!
Re: Hacking The Teenage Engineering PO-80
Hi Mark, Looking at your platter, how do you decouple the original lower mounting point part (with the screws which attach to the plastic case) from the original? or what is the mounting method in your case please? I'm having serious issues with my original platter not spinning freely and cannot work out how to get it to behave itself! but interested in the way in which you reuse or don't the existing parts
Re: Hacking The Teenage Engineering PO-80
Hi,
You might have a tolerance issue between the bottom white pulley and the platter. The shaft of the white pulley has a key slot that engages the platter. The metal center pin is also keyed and should be a bit shorter than the surface of the white pulley. When you add the keyed overhead pulley and screw that into the metal center pin, the entire assembly is locked to the to bearing upper and lower surfaces.
If you disassemble everything make sure both bearing are not binding. Then, lay the platter in place, it should rest on the inner bearing race and spin freely.
Now add the white pulley and align it to the platter via the key slot and see if this pair can rotate freely. If it binds in this state, remove the platter and make sure the white pully rotates freely on its own.
Drop the metal center pin from the platter side and check that there is a slight (~1mm) indent where the overhead pulley will attach. If it is proud of the surface, you might need to add some shim washers to the metal center pin on the platter side to move the pin up.
I added a metal stiffener to my base to reduce the flex. I don't think this can work with the stock platter as it sits too low and would hit the stiffener.
You might have a tolerance issue between the bottom white pulley and the platter. The shaft of the white pulley has a key slot that engages the platter. The metal center pin is also keyed and should be a bit shorter than the surface of the white pulley. When you add the keyed overhead pulley and screw that into the metal center pin, the entire assembly is locked to the to bearing upper and lower surfaces.
If you disassemble everything make sure both bearing are not binding. Then, lay the platter in place, it should rest on the inner bearing race and spin freely.
Now add the white pulley and align it to the platter via the key slot and see if this pair can rotate freely. If it binds in this state, remove the platter and make sure the white pully rotates freely on its own.
Drop the metal center pin from the platter side and check that there is a slight (~1mm) indent where the overhead pulley will attach. If it is proud of the surface, you might need to add some shim washers to the metal center pin on the platter side to move the pin up.
I added a metal stiffener to my base to reduce the flex. I don't think this can work with the stock platter as it sits too low and would hit the stiffener.
You do not have the required permissions to view the files attached to this post.
Re: Hacking The Teenage Engineering PO-80
Many thanks Mark, that's really helpful! I've never had the bottom part fully apart, looks a bit different to your image - made up of two bearings plus a locking plate with screws and an outer drive rim for the belt plus the pulley for the overhead. Maybe a revision or difference between the gakken/PO-80? or yours shows a mod already? It's weird as disassembly and reassembly fixes it briefly and then it returns to binding. I'll try with a shim
Re: Hacking The Teenage Engineering PO-80
Hi,
Next time you have things apart, post a picture. There may well be a difference.
Mark
Next time you have things apart, post a picture. There may well be a difference.
Mark
Re: Hacking The Teenage Engineering PO-80
Really cool stuff Mark! Gonna pick up one of the Gakken ones to fool around with while I continue to looks at diy lathes and how I want to go about mine (those linear rails are expensive especially in Canada!) I have a few 3d printers (both resin and fdm) as well as a bunch of spare printer parts im hoping to recycle into a lathe (smooth rods, lead screws, linear bearings etc). I figure since im completely new to the art that the Gakken would be a good learning tool without breaking the bank. I was kinda disappointed in what I saw in youtube reviews about the Gakken/PO-80 until I found this thread. Thanks for all the work you've done!
Re: Hacking The Teenage Engineering PO-80
Hi,
Should be a good primer before you get into the big build. Let me know if you have any questions.
Mark
Should be a good primer before you get into the big build. Let me know if you have any questions.
Mark
Re: Hacking The Teenage Engineering PO-80
Super travail 
Re: Hacking The Teenage Engineering PO-80
Hi Everyone,
I have an update to my 7" platter mod. One of the big issues was getting the platter to run true. I tried various solutions involving some sort of post processing to the 3D print to get the top face of the platter to run without up and down run out. Some methods worked ok, but are not very practical for people without the ability for make a special tool. I had an idea to use three 2-56 set screws to contact the face of the bearing to allow trimming of the run out so that the plater can be trued up. This seems to work well for me. Attached is a new STL for the platter with pilot holes for tapping to 2-56 or the nearest metric set screw. You can see what I did with this photo and a short video of the platter adjusted via the set screw.
You adjust by first setting the screws so they just sticking out from the bottom of the platter. Assemble the platter and pulley without any belts attached. Pick a fixed reference point on the base and slowly spin the platter and note the set screw at the lowest point of the run out. Adjust the screw to raise the platter to remove the run out. There is some interaction and you may need to take a few adjustments to get it running true. The center hole is about 6mm and you may need to open it up so the metal shaft runs freely. You also should make sure that the two upper surfaces of the white teeth of the lower platter do not contact the upper face of upper platter. You can see this if you assemble the platter without the metal shaft and check for a slight gap as you look in the hole. If there is contact made, you can raise the platter a bit by turning all of the 3 sets screw the same number of turns. The idea is to make sure that only the 3 setscrew determine the plane of the platter referenced to the bearing surface. Note that if you already have this printed, you might be able to modify it by carefully drilling and tapping the 3 holes.
Hope this makes sense.
Mark
I have an update to my 7" platter mod. One of the big issues was getting the platter to run true. I tried various solutions involving some sort of post processing to the 3D print to get the top face of the platter to run without up and down run out. Some methods worked ok, but are not very practical for people without the ability for make a special tool. I had an idea to use three 2-56 set screws to contact the face of the bearing to allow trimming of the run out so that the plater can be trued up. This seems to work well for me. Attached is a new STL for the platter with pilot holes for tapping to 2-56 or the nearest metric set screw. You can see what I did with this photo and a short video of the platter adjusted via the set screw.
You adjust by first setting the screws so they just sticking out from the bottom of the platter. Assemble the platter and pulley without any belts attached. Pick a fixed reference point on the base and slowly spin the platter and note the set screw at the lowest point of the run out. Adjust the screw to raise the platter to remove the run out. There is some interaction and you may need to take a few adjustments to get it running true. The center hole is about 6mm and you may need to open it up so the metal shaft runs freely. You also should make sure that the two upper surfaces of the white teeth of the lower platter do not contact the upper face of upper platter. You can see this if you assemble the platter without the metal shaft and check for a slight gap as you look in the hole. If there is contact made, you can raise the platter a bit by turning all of the 3 sets screw the same number of turns. The idea is to make sure that only the 3 setscrew determine the plane of the platter referenced to the bearing surface. Note that if you already have this printed, you might be able to modify it by carefully drilling and tapping the 3 holes.
Hope this makes sense.
Mark
You do not have the required permissions to view the files attached to this post.
Re: Hacking The Teenage Engineering PO-80
Hi Mark
and thanks so much for this update, this is wicked and will make it much easier for a simpleton like me to it install as I was struggling to get the old one to spin true.
Outstanding work Mark and thanks for taking the time to revise the platter.
Gonna fire up my vyper and get this printed out ASAP, how long do the set screws need be?
and thanks so much for this update, this is wicked and will make it much easier for a simpleton like me to it install as I was struggling to get the old one to spin true.
Outstanding work Mark and thanks for taking the time to revise the platter.
Gonna fire up my vyper and get this printed out ASAP, how long do the set screws need be?
Re: Hacking The Teenage Engineering PO-80
Hi,
The screws don't need to be very long. I only had 1/8" long 2-56 setscrews here and they worked fine. Once you get them so they just protrude from the surface, you are not moving them much higher. One turn is probably quite a bit of adjustment. A small change in height at the center of the platter results in a large change at the edge. As it stands, there is not much meat in the plastic for the threads. I think I can now add some diameter to that part of the design since it is not in contact with the bearing anymore. If you print it and find that its too close for comfort, let me know and I'll update the file.
Mark
The screws don't need to be very long. I only had 1/8" long 2-56 setscrews here and they worked fine. Once you get them so they just protrude from the surface, you are not moving them much higher. One turn is probably quite a bit of adjustment. A small change in height at the center of the platter results in a large change at the edge. As it stands, there is not much meat in the plastic for the threads. I think I can now add some diameter to that part of the design since it is not in contact with the bearing anymore. If you print it and find that its too close for comfort, let me know and I'll update the file.
Mark
Re: Hacking The Teenage Engineering PO-80
Excellent, thanks for the detailed instructions Mark. I have my platter done but the set screws are gonna take a little while to get here.markrob wrote: ↑Fri May 03, 2024 10:37 amHi,
The screws don't need to be very long. I only had 1/8" long 2-56 setscrews here and they worked fine. Once you get them so they just protrude from the surface, you are not moving them much higher. One turn is probably quite a bit of adjustment. A small change in height at the center of the platter results in a large change at the edge. As it stands, there is not much meat in the plastic for the threads. I think I can now add some diameter to that part of the design since it is not in contact with the bearing anymore. If you print it and find that its too close for comfort, let me know and I'll update the file.
Mark
Once again thanks for your continued time and effort for working on this. Hugely appreciated sir.
Re: Hacking The Teenage Engineering PO-80
Got my Gakken in last week, haven't started modifying it as I need to purchase an exciter/driver and build/buy an amp as well. But I think I finally got my first "acceptable" embossing after making a whole bunch of coasters.
Test cut link
- I 3d printed a little adapter for the CD's to fit properly on a turntable spindle.
- I give them a buff with some turtle wax (not sure if you do any prep to yours Mark)
- I gave the recording needle a slight angle by sticking a 2nd CD underneath.
- Inverse RIAA curve that's built into Audacity.
- merged the left and right channels into a mono track.
Test cut link
- I 3d printed a little adapter for the CD's to fit properly on a turntable spindle.
- I give them a buff with some turtle wax (not sure if you do any prep to yours Mark)
- I gave the recording needle a slight angle by sticking a 2nd CD underneath.
- Inverse RIAA curve that's built into Audacity.
- merged the left and right channels into a mono track.
Re: Hacking The Teenage Engineering PO-80
Would the 8ohm version of those exciters be efficient with a volume boost or should I really use the 4ohm ones? (They have the 8ohm version on amazon but not the 4ohm)
Re: Hacking The Teenage Engineering PO-80
Hi Estacaco,
8 ohm is fine as long as you have an amp that can drive enough power into the head. The driver can only handle about 3 watts on a continuous basis. But, to cut a decent levels you could need 50-100 watts for short duration peaks to cut the high frequencies. When using an amp with that much power make sure to fuse the head with a 1/2A fast blow. Maybe even start with a 1/4A fuse until you get the hang of things. If you are buying drivers, I would pick up a few since they are pretty cheap.
Mark
8 ohm is fine as long as you have an amp that can drive enough power into the head. The driver can only handle about 3 watts on a continuous basis. But, to cut a decent levels you could need 50-100 watts for short duration peaks to cut the high frequencies. When using an amp with that much power make sure to fuse the head with a 1/2A fast blow. Maybe even start with a 1/4A fuse until you get the hang of things. If you are buying drivers, I would pick up a few since they are pretty cheap.
Mark
Re: Hacking The Teenage Engineering PO-80
Thanks markrob, I'll pull the trigger on a few of those then and look at getting probably a 100w amp to drive them. I first watched a bunch of Youtube reviews on the machine and it all sounded pretty bad. I found your thread and it inspired me to pick one up anyways after seeing what you were able to get out of it, Even without mods this thread and boards in general have gotten me better than anything I saw in those reviews.