Batery powered DIY CNC phono stage

[sachu888]

They are for DC blocking, so don't play any long if I switch off. Big electrolyte caps in power filter store current. You can experience some time of play time in PassB1 and DCB1 as both draw very minimal current and can play 2 -3 mins( in very low volume) after switching off.

Regards
Sachin

 

[jls001]

@Sachin : on the CNC, do we need to populate the slot marked "33pF"? Or can we leave it blank? Is this for inserting capacitive loading of our choice? Thanks in advance. It's been such a long time since I assembled CNC that I've forgotten it. That's the problem with my need-based learning.

 

[sachu888]

You can leave it blank or experiment with capacitive loading.
Not necessary to solder anything there.

Regards
Sachin

 

[jls001]

Another CNC build completed today. Thanks, Sachin for the troubleshooting help. As usual I had problem with the CAT 6 wire I favour for internal wiring. One channel refused to sing. Repeated troubleshooting didn't yield results, so in frustration I rewired it using another wire, and it works fine now. Now playing with a Shure M97xE. This one is for fellow forumer Shafic.

Question for M97xE users: is the best impedance setting 62k or 33k? I remember vaguely that 47K is not the best for this cart. Using 33k right now. Will try 62k later.

 

[reignofchaos]

When I had one I used 47k after trying both 62 and 33. 62 though appealing on first listen sounds a bit unnatural and 33 sounds absolutely dead boring. Try varying the capacitance between 200 and 300 pf.

 

[jls001]

Duplicate post - deleted

 

[sachu888]

Re: Battery powered DIY CNC phono stage

Shure recommends 250pf to 300pf total capacitive loading. Since you are using low capacitance cables, try some 68-100pf additional loading. It sounds best at 250pf total loading.

Regards
Sachin

 

[jls001]

When I had one I used 47k after trying both 62 and 33. 62 though appealing on first listen sounds a bit unnatural and 33 sounds absolutely dead boring. Try varying the capacitance between 200 and 300 pf.

Thanks, RoC. Will try 47K.

 

[jls001]

Re: Battery powered DIY CNC phono stage

Shure recommends 250pf to 300pf total capacitive loading. Since you are using low capacitance cables, try some 68-100pf additional loading. It sounds best at 250pf total loading.

Regards
Sachin

May be I'll fit screw type terminal blocks on the capacitance loading point so that the owner can screw on desired capacitor. I'll check my parts bin if I have the correct value cap. I think he will eventually use an M44-7 cart.

 

[omishra]

Joshua, I used that 97xe with 270pF total loading achieved with extra 68PF along 47K resistance load. 62K was too bright to my taste. m44-7 will need 350-400pF loading.
Hey one alcheapo opamp socket, cut its one leg socket and mount it there. I have pics somewhere in this thread itself.

 

[jls001]

Joshua, I used that 97xe with 270pF total loading achieved with extra 68PF along 47K resistance load. 62K was too bright to my taste. m44-7 will need 350-400pF loading.
Hey one alcheapo opamp socket, cut its one leg socket and mount it there. I have pics somewhere in this thread itself.

I fitted a 5 mm terminal block. The PCB holes were quite small and are obviously not meant to accept the pins of the terminal blocks so I had a hard time. I carefully filed the legs till they have slimmed down enough to fit. I should have known about the opamp socket - if do have them in my parts bin.

And thanks for the heads up on cap loading for M44-7. Can I assume about 50-60 pF for the tone arm's internal wiring, add about 120 pF for TT to phono preamp (1.25m Toyo RG 174 coax cable)? So probably around 200-250pF cap will be needed?

 

[sachu888]

50-60pf seems to low for tonrarm wiring of vintage tt.You will also need to consider capacitance of internal wiring.

Regards
Sachin

 

[omishra]

I have capacitance meter with my DMM. With Amazon Video Cable as Phono cable I measured total ~187-195pF for tonearm and RCA cable, after removing headshell. so add another 5pf for headshell and 5pf for preamp internal. It works like that.

 

[jls001]

Even my theoretical estimate above is approximately 170-180pF. Adding 5 pF for cartridge leads, it adds up to nearly 200. So 350 -200 = about 150. Or we can also try 400 - 200. Or go with the arithmetic mean of the two numbers

 

[sachu888]

Re: Battery powered DIY CNC phono stage

Capacitance won't make much difference in M44 IMO . It has a very high output, almost double than most of the mom carts.

Regards
Sachin

 

[sachu888]

I have capacitance meter with my DMM. With Amazon Video Cable as Phono cable I measured total ~187-195pF for tonearm and RCA cable, after removing headshell. so add another 5pf for headshell and 5pf for preamp internal. It works like that.

Om,
Which tonearm did you measure? I asked this because, as far as I know you did internal rewire of SL1210 with Cardas, and your Rega tonearm comes with Isokinetic wires. Both Cardas and Isokinetic has very low capacitance. Amazon Basic Video component cable is also very low C. I don't think Shafic will need additional Capacitance(or very little) if he is on stock tonearm wiring and RCA.

Regards,
Sachin

 

[reubensm]

Re: Battery powered DIY CNC phono stage

Capacitance won't make much difference in M44 IMO . It has a very high output, almost double than most of the mom carts.

Regards
Sachin

Yes, thought so. Earlier I've tried different capacitance settings on my brother's NAD 3020A (it has a phono capacitance switch on the rear panel) but noticed there is not much difference between them while using the M44-7. However when using the stock Technics cart, there was noticable differences between the settings.

 

[jls001]

I guess M44-7 makes life easier

 

[omishra]

Om,
Which tonearm did you measure? I asked this because, as far as I know you did internal rewire of SL1210 with Cardas, and your Rega tonearm comes with Isokinetic wires. Both Cardas and Isokinetic has very low capacitance. Amazon Basic Video component cable is also very low C. I don't think Shafic will need additional Capacitance(or very little) if he is on stock tonearm wiring and RCA.

Regards,
Sachin

I measured it with my Technics 1200 MKII. For Thorens I have Denon DL-103R cart. So I did not bother to measure capacitance of my Isokinetik cable.

 

[Record Player]

Pssst, sshhhh...me CNC and DCB1 will be up on the rig soon.