My Numark PT01 portable turntable project

[JeffS7444]

During the pandemic, I built up a audiophile-ish Numark PT01 Scratch with the following upgrades:

Jesse Dean Designs JDDPA tonearm + MM phono preamp
Audio Technica AT95E cartridge
Vistaton replacement speaker

As a portable record player suitable for even the best vinyls, I felt the project was a success. But what I wasn't so comfy about was that I had around $300 sunk into what was pretty much a toy for me, and there was still the battery issue to be dealt with: I've experienced leakage problems even with brand-new alkaline D cells.

Then I checked out this video, and was impressed by how XjunkieNL had managed to accomplish pretty much the same thing, but with a cheaper PT01, and the stock tonearm. So I recovered most of my misspent money by reselling the newly-built PT01 Scratch, and just recently, scored a secondhand PT01 USB (same thing as the Scratch, minus black/red accents and mix switch, which I never used) for $40, shipped, and thus began my latest, lower-cost turntable build.

XjunkieNL offers his tonearm modification CAD files for non-commercial uses, but figured I'd try my hand at creating my own, and ended up going a bit further:

Left to right:

• Cover plate for stock counterweight cavity which formerly housed a pot-metal part, but which I've now stuffed with tungsten putty, which packs more mass.
• Expanded counterweight outer shell, which gives me a lot more room for said putty, but without interfering with the turntable cover or movement of the tonearm.
• Tonearm vertical stop, because I don't need to have the stylus crashing onto the top of the plinth
• Adapter block for Audio Technica AT3600 cartridge. Unlike XjunkieNL, I opted to trim away the mounting points for the original ceramic cartridge, and simply cement the body of the cartridge into place. Figured it was unlikely that I'd care to revert to original ceramic cartridge, while market value of an AT3600 body is minimal, as most of the $$ is in the stylus.

 

[JeffS7444]

And with the addition of a Talentcell YB1203000 battery (about 23 USD, shipped), and Jesse Dean JDDPHOPRE (19.99 + SH) the initial phase of the project was complete:

And and this point it, uh, mostly played, at least at 33-1/3 rpm. No doubt the aged belt is part of the problem, but the real surprise was what I discovered when attempting to power the turntable using an external 12 v battery via the 12 v power connector.

 

[JeffS7444]

The analog electronics are pretty straightforward, but it always helps to have a schematic (attached), in this case, by a member of digitalvertigo.co.uk.

Bihari Designs' battery mod seems pretty straightforward by connecting a 12 volt lithium battery to the unregulated internal battery terminals, though that approach has it's own challenges, including the need to reach inside the battery compartment to access the battery's power switch, and this is a must, because the battery's internal power regulation circuitry and LED indicators will otherwise drain the battery.

Another possibility would be to use rechargeable 1.5 V lithium AA cells + D adapter shells in the stock battery compartment. With a claimed 3000 mAh capacity, there ought to be plenty of capacity for a day's music listening.

As far as connecting an external battery via the 12 volt input: Despite staring at what is obviously a full wave bridge rectifier, it seems it dawned on neither myself nor the creator of said schematic that it's really designed for AC, not DC! No biggie, but when you attempt to plug in a battery putting out 12.2 VDC, you get almost 1 volt of voltage drop through the rectifiers, and with the turntable motor at full stall, and circuit drawing 150 mA, I was seeing another ~ 4 volt drop across R2 (27 ohms), so by the time it reached the 7809 regulator, that original 12 volt input had been reduced to ~7 volts: Not so good for a 9 volt fixed regulator. My solution was to replace R2 with a jumper, which raised the 7809's input voltage to 11 volts, and allowed the regulator to regulate: Rock-steady 9 V output - perfect.

 

[JeffS7444]

Cost-wise, taking shipping and sales tax into consideration, this latest build comes in at less than 1/2 the cost of my previous PT01 Scratch build, and solves my battery gripes.

And in case anyone is wondering about upgrading the stock speaker: I never did a real comparison between original part and oft-recommended Vistaton replacement, but recalled being underwhelmed by the change. So at least for now, the stock part stays.

 

[keith24]

The analog electronics are pretty straightforward, but it always helps to have a schematic (attached), in this case, by a member of digitalvertigo.co.uk.

Bihari Designs' battery mod seems pretty straightforward by connecting a 12 volt lithium battery to the unregulated internal battery terminals, though that approach has it's own challenges, including the need to reach inside the battery compartment to access the battery's power switch, and this is a must, because the battery's internal power regulation circuitry and LED indicators will otherwise drain the battery.

Another possibility would be to use rechargeable 1.5 V lithium AA cells + D adapter shells in the stock battery compartment. With a claimed 3000 mAh capacity, there ought to be plenty of capacity for a day's music listening.

As far as connecting an external battery via the 12 volt input: Despite staring at what is obviously a full wave bridge rectifier, it seems it dawned on neither myself nor the creator of said schematic that it's really designed for AC, not DC! No biggie, but when you attempt to plug in a battery putting out 12.2 VDC, you get almost 1 volt of voltage drop through the rectifiers, and with the turntable motor at full stall, and circuit drawing 150 mA, I was seeing another ~ 4 volt drop across R2 (27 ohms), so by the time it reached the 7809 regulator, that original 12 volt input had been reduced to ~7 volts: Not so good for a 9 volt fixed regulator. My solution was to replace R2 with a jumper, which raised the 7809's input voltage to 11 volts, and allowed the regulator to regulate: Rock-steady 9 V output - perfect.

I also replaced the resistor with a jumper with my pt01 a few months ago and bypassed the rectifier so the 7809 gets 12v, also when unplugging and plugging the 12v input jack the solder joint broke and the power light turned off when i twist the jack it came back on so i soldered a wire from the jack to the adjacent trace.

 

[JeffS7444]

I also replaced the resistor with a jumper with my pt01 a few months ago and bypassed the rectifier so the 7809 gets 12v, also when unplugging and plugging the 12v input jack the solder joint broke and the power light turned off when i twist the jack it came back on so i soldered a wire from the jack to the adjacent trace.

I opted to keep the bridge rectifier, guessing that my battery's LVCO would kick in long before output voltage fell below ~10 volts. I also like the added level of protection it offers against reverse polarity or AC input.

 

[DeLaw]

Has anyone had motor noise after installing a preamp v4 by Bihari. I also installed a Bihari Tonearm QRM . I’ve checked all grounds and other connections. This happens with battery or plug in. I also tried a DDPHOPRE PORTABLE TURNTABLE PHONO PREAMP KIT and get the same motor noise. Disconnected the motor and it was gone. It’s hard to here with the speaker but with headphones it gets loud and also it is heard through USB to computer. No support though Bihari and only found one post asking with no response. Would appreciate help, Thanks

 

[JeffS7444]

Has anyone had motor noise after installing a preamp v4 by Bihari. I also installed a Bihari Tonearm QRM . I’ve checked all grounds and other connections. This happens with battery or plug in. I also tried a DDPHOPRE PORTABLE TURNTABLE PHONO PREAMP KIT and get the same motor noise. Disconnected the motor and it was gone. It’s hard to here with the speaker but with headphones it gets loud and also it is heard through USB to computer. No support though Bihari and only found one post asking with no response. Would appreciate help, Thanks

A classic fix for such motor noise is to solder a small ceramic capacitor across the + and - leads of the motor. 330 pF? 680 pF? I'd try whatever I already had on hand. If soldering isn't an option, a "wire glue" type product might be worth a try, though I haven't tried this myself.

 

[DeLaw]

I'll need to look to see if I have any. I did do a quick check for the motor voltage and got 2.7 volts. Don't know if that makes a difference.

Found a 470pf and a 330pf. I will try that sometime today.

 

[JeffS7444]

I'll need to look to see if I have any. I did do a quick check for the motor voltage and got 2.7 volts. Don't know if that makes a difference.

That sounds about right.

 

[DeLaw]

Tried both 470pf and a 330pf. No change in noise. Even jump from + motor to - chassis. No change.

 

[DeLaw]

That sounds about right.

So JeffS7444. Do you have a hum noise when using headphones and you start your turntable platter spinning with volume all the way up and not setting the needle on a record?

​

 

[JeffS7444]

So JeffS7444. Do you have a hum noise when using headphones and you start your turntable platter spinning with volume all the way up and not setting the needle on a record?

Nope, but I am running off of batteries, not AC, and I am using JDDPRE, and have no experience with the Bihari.

BTW, I have confirmed that the capacitor trick works like a charm, in fact, when I cleared the factory solder blobs away, I discovered an extra set of capacitor-sized holes. I used a 220 pF, 100 volt part, because for some reason, I had just a onesie in that value, and what else am I going to do with just a single tiny capacitor? Motor noise is completely gone, and with headphones and volume cranked to max, I hear just a faint bit of white noise, but your headphones and hearing may be more sensitive.

 

[JeffS7444]

Just remembered something which could cause hum: Line input jack. Best to turn the level down if not using it.

 

[DeLaw]

I used a 330 pF, 50 volt part with the Bihari. I do have a JDDPRE. I will try and to find that value and see if it works. I also grounded the tone arm wit a separate
wire to the ground where the ring like wire touches the turntable platform. That stop noise from the tone arm. I also use batteries 6 D cell rechargeable. That make
no difference. Thanks for the help.

 

[JeffS7444]

Replacement belt from AliExpress vendor 41CD has arrived. Folded length of 154 mm works great, and at 1.51 USD, I can't argue about the price.

 

[DeLaw]

Found that putting internal D batteries was causing a lot more hum than plug in on the side. At volume 3 mark it is very hard to hear and using line out to computer. Recording is now doable. Removed the USB board. That is junk and for recording there was no bass. Line out sounds good. I might try a outboard battery to see if that is better. Also have a 220pf 50v on the motor but that is not changing anything.

 

[JeffS7444]

Found that putting internal D batteries was causing a lot more hum than plug in on the side. At volume 3 mark it is very hard to hear and using line out to computer. Recording is now doable. Removed the USB board. That is junk and for recording there was no bass. Line out sounds good. I might try a outboard battery to see if that is better. Also have a 220pf 50v on the motor but that is not changing anything.

By any chance, did you relubricate the turntable's platter bearing using some ordinary grease? Some turntable bearings require use of conductive grease, which the stock lubricant is. Not sure why it should make a difference, considering that most of the platter is made of plastic, but apparently it does.

 

[DeLaw]

This is a new turntable. It is well greased. I have got the noise down to accessible levels to do what I need. Thanks.