Galu, Intesting, it was hard to find pictures online of what it looked like so I took a best guess. Is yours spring loaded or is there twist CAM?
I like the finish. I have a lathe and if I could figure out a way to mount the one I made I might be able to skim the surface for a better finish. Or I could ruin it by mistake..... might leave it the way it is for now.
Arch, Thank you! To be honest I'm just getting into records and only have a few new manufactured records from a few Syth artists. I bought a 45 of "House of the Rising Sun" just to test it. I don't really plan on getting any 45's but I know if I didn't fix it it would bug me every time I saw it.
Krivium, Thankfully the SL-7 is easier to override than the SL-10. I just flick a slider and it'll accept any record. I've got quick a few translucent records so this is very convenient. Still a similar problem, if the settings are wrong the needle and the bed will become best friends. Some thing to be said for a "cruder" mechanical button.
Small update. I accidentally ordered mismatched RCA jacks on Digikey.... Right now I'm waiting for the second order to arrive. Needed to make an order for another project anyways so no big loss.
I like the finish. I have a lathe and if I could figure out a way to mount the one I made I might be able to skim the surface for a better finish. Or I could ruin it by mistake..... might leave it the way it is for now.
Arch, Thank you! To be honest I'm just getting into records and only have a few new manufactured records from a few Syth artists. I bought a 45 of "House of the Rising Sun" just to test it. I don't really plan on getting any 45's but I know if I didn't fix it it would bug me every time I saw it.
Krivium, Thankfully the SL-7 is easier to override than the SL-10. I just flick a slider and it'll accept any record. I've got quick a few translucent records so this is very convenient. Still a similar problem, if the settings are wrong the needle and the bed will become best friends. Some thing to be said for a "cruder" mechanical button.
Small update. I accidentally ordered mismatched RCA jacks on Digikey.... Right now I'm waiting for the second order to arrive. Needed to make an order for another project anyways so no big loss.
This the current state of the 3D printed cover. I used a cheaper spool to make prints to test the fit, hence the weird colors. The printer is currently acting up and I'm waiting for a new part in the mail. Should come some time next week. Note the dual color print with the second color used for labels. Not really needed but if you have a dual head printer it's fun to put it to work.
I had an idea and idea's are dangerous things. What if I could use this machine to play 78's? I have a wind up machine in the mail and it would be nice to digitize any 78's I buy. Especially since the steel needles are a bit "rough". The tracking force is too low on the SL-7, it needs to be 2-3 grams for the p mount 78 needles I found. I suspect this could be solved with just some weight added to the cartridge, not a big deal. The bigger problem is the machine won't spin that fast and I was unable to find any speed mods for this machine.
Well that's not a good start. I cracked open the machine to see if any thing caught my eye. I did find a few Technics branded chips. In an effort to learn more about the chips I googled the part numbers and found zero useful information, except that the SL 1200 uses the same chips. The SL 1200 has a pitch control slider..... So how does the SL 1200 with the same/similar parts change play back speed?
Turns out the SL 1200 has an extra two chips that work with the pitch slider. However the clock chip is still the same chip. So how is the pitch circuitry controlling the clock chip? Thankfully both these turntables have service manuals complete with block diagrams. The SL-7 is on the left with the SL 1200 on the right. Notice that the pitch control chip only connects to the clock chip with 2 wire. On the SL-7 those same two wires simply loops back to the chip. The pitch chip is modifying the signal some how.
I was puzzled at first trying to figure out what the pitch chip was doing. I think the lower part of the diagram represents a phase locked loop. It's using the main signal as a reference and using it to generate a new one at a slightly higher or lower frequency. I suspect that it's a clock of some sort. Lets check it out on the scope. I'll be measuring the loop back that exists on the SL-7.
It's just a ~260 KHz square wave! Makes sense since the signal is a ~4MHz crystal divided by 16 as indicated in the block diagram. Now I have a very important question, if I cut the trace and use a signal generator instead can I make the turntable spin faster? Lets find out!
I soldered on wires to the back side of the chip to help record the wave form and input a new one. These wires are small enough I can snake them out the back of the unit. I set it back up and used a signal generator to create and square wave and successes! If I increase the frequency it spins faster! An input signal of about 610Khz gets me to around 78 rpm. I need to build a board to generate a signal and some how find a way to signal to that board to put the unit into 78 mode. I've got quite a bit to think about but I've proved it's possible.
I had an idea and idea's are dangerous things. What if I could use this machine to play 78's? I have a wind up machine in the mail and it would be nice to digitize any 78's I buy. Especially since the steel needles are a bit "rough". The tracking force is too low on the SL-7, it needs to be 2-3 grams for the p mount 78 needles I found. I suspect this could be solved with just some weight added to the cartridge, not a big deal. The bigger problem is the machine won't spin that fast and I was unable to find any speed mods for this machine.
Well that's not a good start. I cracked open the machine to see if any thing caught my eye. I did find a few Technics branded chips. In an effort to learn more about the chips I googled the part numbers and found zero useful information, except that the SL 1200 uses the same chips. The SL 1200 has a pitch control slider..... So how does the SL 1200 with the same/similar parts change play back speed?
Turns out the SL 1200 has an extra two chips that work with the pitch slider. However the clock chip is still the same chip. So how is the pitch circuitry controlling the clock chip? Thankfully both these turntables have service manuals complete with block diagrams. The SL-7 is on the left with the SL 1200 on the right. Notice that the pitch control chip only connects to the clock chip with 2 wire. On the SL-7 those same two wires simply loops back to the chip. The pitch chip is modifying the signal some how.
I was puzzled at first trying to figure out what the pitch chip was doing. I think the lower part of the diagram represents a phase locked loop. It's using the main signal as a reference and using it to generate a new one at a slightly higher or lower frequency. I suspect that it's a clock of some sort. Lets check it out on the scope. I'll be measuring the loop back that exists on the SL-7.
It's just a ~260 KHz square wave! Makes sense since the signal is a ~4MHz crystal divided by 16 as indicated in the block diagram. Now I have a very important question, if I cut the trace and use a signal generator instead can I make the turntable spin faster? Lets find out!
I soldered on wires to the back side of the chip to help record the wave form and input a new one. These wires are small enough I can snake them out the back of the unit. I set it back up and used a signal generator to create and square wave and successes! If I increase the frequency it spins faster! An input signal of about 610Khz gets me to around 78 rpm. I need to build a board to generate a signal and some how find a way to signal to that board to put the unit into 78 mode. I've got quite a bit to think about but I've proved it's possible.
There you go! 78rpm stylii for P-Mount cartridges! I would never have associated them! 😎
P-Mount Phono Cartridge | Turntable Needles
P-Mount Phono Cartridge | Turntable Needles
Thanks that's very usefull. I've found a few other options to consider as well.
The tracking force for the first one seems too good to be true. Every thing I've read on 78's indicates that they need high tracking force so I'll take it with a grain of salt. The grado seems a bit pricey for a 78 stylus. Would a 78 really benefit from a higher quality stylus? Does 3 mil vs 2.55 mil mater for tip diameter? I suspect the answer vary's depending on the condition of the record.
Right now I'm leaning towards either the BN78RPM or the Ortofon stylus due to price.
There is the one your found the, BN78RPM for 47$ 1.25g - 1.5 grams tracking force with a tip diameter of 3mil.
Grado makes one for 90$. The 78C with 2.5g of tracking force with a tip diameter of 3mil.
Ortofon also makes a 78 rpm stylus I could put on the Ortofon cart I have. It needs 1.75g - 2.25g of tracking force. It's 62$. It's tip diameter is 2.55 mil.
Grado makes one for 90$. The 78C with 2.5g of tracking force with a tip diameter of 3mil.
Ortofon also makes a 78 rpm stylus I could put on the Ortofon cart I have. It needs 1.75g - 2.25g of tracking force. It's 62$. It's tip diameter is 2.55 mil.
The tracking force for the first one seems too good to be true. Every thing I've read on 78's indicates that they need high tracking force so I'll take it with a grain of salt. The grado seems a bit pricey for a 78 stylus. Would a 78 really benefit from a higher quality stylus? Does 3 mil vs 2.55 mil mater for tip diameter? I suspect the answer vary's depending on the condition of the record.
Right now I'm leaning towards either the BN78RPM or the Ortofon stylus due to price.
I know I'm raising the dead, but did you ever finalize your back panel? Would you share the stl file?
The motor in the SL-10 is different to the SL-7. The SL-10 motor is similar to the SL1200, whereas the SL-7 motor is a coreless design. Better, in my opinion.
Hi, could you please share with me CAD design of thr 45rpm adaptor? My plan is to print it on 3D printer. I can share the design with community if successful.Galu, Thank you! It's nice to have the core action of the machine working again.
This angle shows how it works. The three holes are for springs to hold the outer ring in place. The original uses one wide spring but I was not able to find that spring for a reasonable price. The spring stores I looked at had a 40$ minimum order. I used 3 smaller readily available springs from Mc Master Carr.
This inner ring is one of the more complicated parts I've machined. The tool paths really were a mess and I had to go back and redo them a few times. I don't work with ABS much either so this was a learning experience. For this part I used 3 tools and thus 2 tool changes during the machining process.
This is the outer ring being milled out on my CNC. The CNC really does make a huge mess but thankfully plastic produces heavier chips and the mess is limited just to the CNC. MDF on the other hand is nasty and coats the whole basement in dust. I came close to running out of ABS stock but ended up with just enough.
Here's the final part with springs fitted! The two parts interlock together nicely. Now I simply need to wait for my 15/32 TAP to arrive later today.
