Hacking The Teenage Engineering PO-80

[markrob]

Hi,

You will need a ton of high frequency boost to get the performance I was getting. Also, you should not use a full IRIAA curve in your signal path as this will kill the lows. Only some slight boost below 50 hz is needed as the head already has the required response from its resonance (about 800Hz in my case) and below. Just do the IRIAA boost starting at 2122hz. You will still need to damp out the head resonance and apply additional high frequency boost to counteract the normal roll-off this type of head has. In total, you might require as much as 30-40 dB of boost at 10Khz to flatten the response. This is why you need such a large amount of peak power. The average will be in the 1-3 watt range, but you will need peaks in excess of 100 watts to get the head moving at high frequencies. You will need to reduce your levels to keep your amp from clipping on the peaks. If you have more power available, you will be able to cut hotter, but just make sure you don't exceed 3 watts long term average.

I removed the adhesive on the driver an used CA to make sure the bond was solid. I've never tested using the 3M adhesive supplied on the driver as I was afraid it might be too rubbery and decouple at high frequencies. That may not be true and would be a time saver if it turns out it bonds well.

If a friction fit to the stylus works and there is no lost motion or buzzing that is great! It will make it easy to change out the stylus.

Mark

[ton]

Unfortunately I can’t take advantage of the software you wrote, I’m on a mac. I’ve experimented with a few cuts and have learned a lot each time.

Next I’ll send a sine through it with various settings and take some readings to calibrate as best I can with compensating EQ. Surprised to learn a boost as big as 30db is required and that explains a lot. Today I read about RIAA. Thank you for sharing all of this. I’ve learned so much because of this thread.

[Kat]

Any major differences between this and the original Gakken?

[CutR]

I've installed markrob's modified head and done a few test cuts into a newly acquired 100W amp and i must say this head compared to the stock one is like night and day for me. I'm really surprised at the frequency response of this head. For example on a particular track that i have cut a number of times already with the stock head, certain elements of the track are just not there or are very faint. Even with harsh EQing the problem still persists. So for a quick test i cut this same track flat, with only just the bass cut and nothing boosted. Upon playback i was shocked to hear all elements of the track were present and in fact the overall sound was a bit toppy and needed a little roll off would you believe. I've yet to cut any other tracks with this head but so far I'm very happy with it. A BIG BIG thanks to markrob fantastic work mate

[markrob]

Hi,

I'm glad this is working out for you. I've been working to improve and add some features. Most important is the ability to add replaceable styli that can be purchased from vendors like Mike at recordlatheparts.com. I've found that cutting off the short length of the stylus that extends past the driver removes some resonances in the 10Khz range (don't try this in place). I've also had good results adding some damping material to the area near the spring clips. I'm using kids silicone putty ear plugs as the damping material. It is very formable and does not harden or dry out and is removable. The downside of adding the damping is that you lose a bit of sensitivity but get a smoother response. The removable version is still a work in progress and you will need a SLA resin based 3D printer to make the adaptor or have to send it out for fab. Same is true for the new piece that attaches to the driver as the details are too fine for a typical FDM printer. I've also discovered that its a pain to remove and replace the driver if it fails. The connection terminals get hung up on the cutout on the arm. I can muscle it out, but its not too easy. Some filing in that area will make this easier.

Here is a shot of the two mods with the standard stylus

PO80 Head mod.jpg

Here is a shot of the prototype removable stylus

PO80 Removable Stylus.jpg

[CutR]

Great work markrob, looking forward to hearing how it sounds with the embossing stylus.

[concreteutopia]

Hi Markrob- Were you able to upgrade the stylus and do you have any stl files for the attachment? thanks!

Hi,

I'm glad this is working out for you. I've been working to improve and add some features. Most important is the ability to add replaceable styli that can be purchased from vendors like Mike at recordlatheparts.com. I've found that cutting off the short length of the stylus that extends past the driver removes some resonances in the 10Khz range (don't try this in place). I've also had good results adding some damping material to the area near the spring clips. I'm using kids silicone putty ear plugs as the damping material. It is very formable and does not harden or dry out and is removable. The downside of adding the damping is that you lose a bit of sensitivity but get a smoother response. The removable version is still a work in progress and you will need a SLA resin based 3D printer to make the adaptor or have to send it out for fab. Same is true for the new piece that attaches to the driver as the details are too fine for a typical FDM printer. I've also discovered that its a pain to remove and replace the driver if it fails. The connection terminals get hung up on the cutout on the arm. I can muscle it out, but its not too easy. Some filing in that area will make this easier.

Here is a shot of the two mods with the standard stylus
PO80 Head mod.jpg

Here is a shot of the prototype removable stylus
PO80 Removable Stylus.jpg

[markrob]

Hi,

See the attached files for my latest versions. I have two coupler STL files. One has a thicker base. I've been experimenting to see if I can reduce some of the resonances and I think the thicker is a bit stiffer. It does add some mass however. Feel free to experiment. That coupler should be tapped for a 0-80 (or similar size metric) screw thread.

The removable holder should be tapped for 2-56 (or metric equivalent) threads.

IIRC, the shaft between the two pieces is 1/16" or 1.5mm. I used aluminum rod to keep the mass down. I used CA glue to fasten the shaft to the removable holder.

You may need to cut the shank of the embossing stylus to length.

Removable Stylus Holder STL Files.zip

Let me know if you want the Fusion 360 files or need some help.

Mark

[concreteutopia]

Thanks, do you have any photos of it?

Hi,

See the attached files for my latest versions. I have two coupler STL files. One has a thicker base. I've been experimenting to see if I can reduce some of the resonances and I think the thicker is a bit stiffer. It does add some mass however. Feel free to experiment. That coupler should be tapped for a 0-80 (or similar size metric) screw thread.

The removable holder should be tapped for 2-56 (or metric equivalent) threads.

IIRC, the shaft between the two pieces is 1/16" or 1.5mm. I used aluminum rod to keep the mass down. I used CA glue to fasten the shaft to the removable holder.

You may need to cut the shank of the embossing stylus to length.

Removable Stylus Holder STL Files.zip

Let me know if you want the Fusion 360 files or need some help.

Mark

[markrob]

Hi,

Its shown in the photo of the head just above my post with the files. You can also load the STL files into your 3D printer or CAD program to view in more detail. These will need to be printed in a MLCD resin printer. The details are too small for an FDM print.

Mark

[CutR]

Hi Mark,

Did you use any lube when you did the tapping, I tried using a M2 self tapping screw but my parts breaking, I got 4 bits done in Rigid 10K Resin now i only have 1 left

[markrob]

Hi,

I did not use any tapping fluid, but I did go very slowly with the tap. The resin prints are pretty brittle. I'm still very much on a learning curve with my resin printer. If you have the correct tap drill for an M2, did you try running that through by hand with a small chuck prior to tapping? It might just clear out some material and make it easier to tap. I would avoid a self tapping screw and go with tapped thread. Fluid might not be a bad idea. I'm just not sure what to use in case it would react badly with the resin. Maybe WD40 since it mostly evaporates.

Mark

[CutR]

Hi Mark,

Yea i have the correct tap drill for an M2, although silly me having never tapped anything before i started off using the drill instead of by hand.
The self-tapping screws i have seem to work ok with FDM prints but this resin is something different. My came back from the printers very chalk-like which leaves some powdery residue on my fingertips. I've got one more part left so i think I'm gonna go with the 2-56 you initially suggested and use a proper tap and T wrench this time and see how it goes.

[markrob]

Hi,

Go slow and back the tap out every few turns. I ran the tap through to the hole on the opposite side. Then I blew out some of the powdery residue and ran it through again. Hope it works out for you.

Mark

[CutR]

Hi,

Go slow and back the tap out every few turns. I ran the tap through to the hole on the opposite side. Then I blew out some of the powdery residue and ran it through again. Hope it works out for you.

Mark

Duly noted, Thanks markrob. On side note i have finally added another motor to control the overhead independently from the turntable. I now able to do lead in/outs, inside to outside cuts which is cool. I now can listen to what I'm cutting in real-time using the playback tonearm, I've also noticed that i can run the motor quite slow, even slower than the standard speed from the reduction gearing which is yielding increased recording time on the disc. Big shout to mrd who helped me a lot with this

[mrd]

Hi,

Go slow and back the tap out every few turns. I ran the tap through to the hole on the opposite side. Then I blew out some of the powdery residue and ran it through again. Hope it works out for you.

Mark

Duly noted, Thanks markrob. On side note i have finally added another motor to control the overhead independently from the turntable. I now able to do lead in/outs, inside to outside cuts which is cool. I now can listen to what I'm cutting in real-time using the playback tonearm, I've also noticed that i can run the motor quite slow, even slower than the standard speed from the reduction gearing which is yielding increased recording time on the disc. Big shout to mrd who helped me a lot with this

Oh nice, glad you got it sorted!

[Skwoz821]

Hi,

I'm glad this is working out for you. I've been working to improve and add some features. Most important is the ability to add replaceable styli that can be purchased from vendors like Mike at recordlatheparts.com. I've found that cutting off the short length of the stylus that extends past the driver removes some resonances in the 10Khz range (don't try this in place). I've also had good results adding some damping material to the area near the spring clips. I'm using kids silicone putty ear plugs as the damping material. It is very formable and does not harden or dry out and is removable. The downside of adding the damping is that you lose a bit of sensitivity but get a smoother response. The removable version is still a work in progress and you will need a SLA resin based 3D printer to make the adaptor or have to send it out for fab. Same is true for the new piece that attaches to the driver as the details are too fine for a typical FDM printer. I've also discovered that its a pain to remove and replace the driver if it fails. The connection terminals get hung up on the cutout on the arm. I can muscle it out, but its not too easy. Some filing in that area will make this easier.

Here is a shot of the two mods with the standard stylus
PO80 Head mod.jpg

Here is a shot of the prototype removable stylus
PO80 Removable Stylus.jpg

Hey, I ordered your STL files!
About to get a sapphire stylus from RecordLatheParts.com, should I get the Long, Short or Thin Shank stylus??

[markrob]

Hi,

I would go with the long shank and cut it down to size. The short shank is probably closer to the correct length, I think it's better to have extra just in case.

Mark

[Skwoz821]

Awesome, cheers, MarkRob!

Also, might you have an MP3 of how the sapphire sounds?

[Skwoz821]

All right, I got everything set up.
However, when I went to make a record, it was making a terrible squealing sound.
I immediately lifted the stylus.
I’m guessing the angle is off, but I’m too afraid to experiment and possibly damage my new stylus.

I was curious if you could offer any insight.
Thank you for your time!