DIY Moving Coil phonostage

[jls001]

Please use 1/4 watt Metal film resisters with 1% tolerance.

1% will be possible only when I have time to visit Lamington Road. For now, I will have to make to with usual 10%. Thanks for the advice on 750K. Will buy that as well.

Opamp rolling is still far away. First I need to give it decent housing and probably buy a pair of rechargeable batteries to keep as spares.

Some WIP pictures:

It's still a mess as you can see. For inputs and outputs I have used thin coax cables terminated in female RCAs.

By jls001 at 2012-08-29


This is the underbelly:

By jls001 at 2012-08-29

 

[sachu888]

Looks very neat,Joshua.You can use 750 ohms resisters which I sent you with CNC MM kit.You can also solder PCb terminals for swapping resisters which I sent you with this kit.

Regards,
Sachin

 

[omishra]

Congratulations! It is neat build.

PS : didn't expect this to sound half this good. Otherwise I would have completed it long, long back.

This is the myth I am out for breaking. Please try well regulated and well filtered PS. You wont feel the difference as many of my friends doing it.

 

[jls001]

Made these changes:
A) R1 and R9 changed to 39 ohms
B) R2 and R10 are 630 ohms - the nearest value to 750 recommended by sachu. Bought 330 too in case I want put them in series with the 630 to get near 1000.
C) 1.55 uF capacitor changed to 2.55 uF.
D) 75k ohms resistor changed to 200k.

Again no sound. This is becoming a bad habit. Checked batteries and found one has drained completely. I did not disconnect this battery when I left for work this morning. I disconnected only one battery thinking that is sufficient to open the circuit. Apparently it's not. I'm spinning CDs while the batteries recharge.

 

[sachu888]

Made these changes:
A) R1 and R9 changed to 39 ohms
B) R2 and R10 are 630 ohms - the nearest value to 750 recommended by sachu. Bought 330 too in case I want put them in series with the 630 to get near 1000.
C) 1.55 uF capacitor changed to 2.55 uF.
D) 75k ohms resistor changed to 200k.

Again no sound. This is becoming a bad habit. Checked batteries and found one has drained completely. I did not disconnect this battery when I left for work this morning. I disconnected only one battery thinking that is sufficient to open the circuit. Apparently it's not. I'm spinning CDs while the batteries recharge.

Are you not using DPDT toggle switch for ON/Off.I have used cheap 10 rs batteries in the past and they provided Approx 36 mins of playing time.I have now upgraded to a well filtered Power supply designed by Omishra.

Regards,
Sachin

 

[jls001]

Are you not using DPDT toggle switch for ON/Off.I have used cheap 10 rs batteries in the past and they provided Approx 36 mins of playing time.I have now upgraded to a well filtered Power supply designed by Omishra.

Regards,
Sachin

I did buy the switch but haven't used it as my setup is still at 'proof of concept' stage with all sorts of wires hanging about. A big mistake.

I guess the PS from Om is the logical way forward.

By the way I opened up the packages for SSP and the CNC but couldn't find the terminal blocks. No worries, I will get them when I go to Lamington Road. I asked the guy from whom I picked up the resistors this evening. To his credit, he knew what it was.

And thanks a million for the 2.55uF caps and the 200k resistors. Until I actually got down to rigging up the circuit I didn't understand the significance though you have posted it on this thread, and even informed me by mail.

We live, we learn something new every day.

 

[sachu888]

You will need 7.5mm pitch spacing PCB wire terminals.You can see them here
http://www.hifivision.com/phono-turntables/24051-diy-moving-coil-phonostage-11.html

Regards,
Sachin

 

[jls001]

You will need 7.5mm pitch spacing PCB wire terminals.You can see them here
http://www.hifivision.com/phono-tur...I have a feeling it will open up and bloom:).

 

[jls001]

Yes Om has designed a well filtered power supply for preamp applications.It uses R core transformer.I myself running CNC on it.

@Sachin/Om: is the OPS available as kit for me to buy? Also, is the transformer toroidal, C Core or R core? What is best for this application? I know a guy in Mumbai who wound the toroids for my (still incomplete) MyRef C. I don't know if he winds other types but I think he will. I guess I will need at least two OPS as I surely plan to complete the CNC build as well (getting myself some better MMs). And also complete the SSP sometime in the future.

Thanks in advance.

 

[sachu888]

@Sachin/Om: is the OPS available as kit for me to buy? Also, is the transformer toroidal, C Core or R core? What is best for this application? I know a guy in Mumbai who wound the toroids for my (still incomplete) MyRef C. I don't know if he winds other types but I think he will. I guess I will need at least two OPS as I surely plan to complete the CNC build as well (getting myself some better MMs). And also complete the SSP sometime in the future.

Thanks in advance.

Hi Joshua,
R-core is the best for this application and its available cheap. You can run bothe ther Phonostage and SSP with one Power supply.Will PM you details.You can see OPS in action here http://www.audiokarma.org/forums/showthread.php?t=456732

Regards,
Sachin

 

[omishra]

@Sachin/Om: is the OPS available as kit for me to buy? Also, is the transformer toroidal, C Core or R core? What is best for this application? I know a guy in Mumbai who wound the toroids for my (still incomplete) MyRef C. I don't know if he winds other types but I think he will. I guess I will need at least two OPS as I surely plan to complete the CNC build as well (getting myself some better MMs). And also complete the SSP sometime in the future.

Thanks in advance.

For low power, low noise I suggest r-core as this will get less noise transfer from mains. Also on the primary side mains wire use ferrite bead (same which you see on VGA/HDMI cable). Because these OPAMP could work beyond audible range, so we need to stop their unwanted service.

BTW if you make one PS with 3-pin terminals them you can use both boards. I am not finding pictures now, somebody please point out.

Edit got it:

http://www.hifivision.com/phono-turntables/24051-diy-moving-coil-phonostage-12.html#post355550

http://www.hifivision.com/phono-turntables/24051-diy-moving-coil-phonostage-11.html#post345968

 

[jls001]

For low power, low noise I suggest r-core as this will get less noise transfer from mains. Also on the primary side mains wire use ferrite bead (same which you see on VGA/HDMI cable). Because these OPAMP could work beyond audible range, so we need to stop their unwanted service.

BTW if you make one PS with 3-pin terminals them you can use both boards. I am not finding pictures now, somebody please point out.

Thanks for the info about R Core.

I am not clear about "3-pin terminal" and "both boards".

 

[omishra]

Thanks for the info about R Core.

I am not clear about "3-pin terminal" and "both boards".

If you see attached links then one PS which as male part of pin on wire and female part of pin on each of phono. 2 boards mean 2 phono boards boxed separately. Also you can revert to battery if you wish.

 

[jls001]

Went to Lamington Road today. Got the terminal blocks I needed, and all the resistors I will need for all my MCs but couldn't get the LME 49990 opamp. Did get the 2134 though, asking 600 each which I thought was too costly so didn't buy.

The terminal blocks and new resistors are now in circuit. Spinning Grieg Concerto in A Minor right now.

 

[jls001]

@sachu: I bought an extra pair of 9V rechargeables for the Hypnotoad. Now I know why the previous ones didn't play that long - I didn't charge them long enough as per the instructions in the packing

The new ones I bought are to be charged for 15 hours at 25 mA. My charger does 35 mA so I guess 12 hours odd is about right.

Smart Alec that I am, I don't know the figures for the old one as I threw away the blister pack without reading the instructions.

Anyway, all parts for OPS are purchased and ready for assembly, except cab.

 

[sachu888]

Ops would be better than those 9V rechargeables.2134 performs little better above +/-12.BTW there is a great review from a hard core Tube user member here Here It Is: The All Singing All Dancing HTMCPS - Page 16 - AudioKarma.org Home Audio Stereo Discussion Forums

Regards,
Sachin

 

[jls001]

@Om/Sachu: I'm soldering the OPS right now and I'm stumped by the polarity of 0.1uF, 50V capacitors (9 are there in total). The board doesn't have an indication of the polarity. Drawing also doesn't have. What I have bought are electrolytic type of 0.1uF, 50V. The space on the board for these caps is way too narrow for what I bought. Should these be film types?

Thanks in advance.

 

[omishra]

@Om/Sachu: I'm soldering the OPS right now and I'm stumped by the polarity of 0.1uF, 50V capacitors (9 are there in total). The board doesn't have an indication of the polarity. Drawing also doesn't have. What I have bought are electrolytic type of 0.1uF, 50V. The space on the board for these caps is way too narrow for what I bought. Should these be film types?

Thanks in advance.

These are polyester or ceramic caps, do not have polarity. Ask for box type 0.1,50V with 5mm lead spacing.

 

[jls001]

These are polyester or ceramic caps, do not have polarity. Ask for box type 0.1,50V with 5mm lead spacing.

OK. Will need to buy polyester type then. Was hoping to rig it up tonight. No chance now.

 

[omishra]

OK. Will need to buy polyester type then. Was hoping to rig it up tonight. No chance now.

No problem, still you can power on the board and use it. Only issue is you may have to live with some power noise if any. You can put these 0.1uF caps later on. Those add immunity from power noise as well as regulator noise.