DIY High or Low Ouput Moving Coil Phono Stage

After giving up on Comet Supply sending me my Denon DL-301mk2 anytime soon I decided to go ahead and build the clone, the Phonoclone 3. I had bought the PCB's from RJM the man who made a copy of the Phono Cube a four thousand dollar zero input impedance moving coil phono stage & PSU.

I hoped that since it will "only" work with moving coil carts it would also work with high output moving coil carts like my Benz Micro Ace since they have similar coil structures to the low output ones.

Zero input impedance is achieved by connecting the cart to the inverting or negative input side of the first op amp. Being obsessed with battery power I decided to see if it will run properly on them as most of the design is on a very low noise PSU. I just wanted the part that makes music.

This simplified the process no end so I designed a PCB and etched it earlier this week. I got the parts and using the suggested OPA27GP op amps, which are very cheap, and stacked plastic caps with metal film resistors to see if it would work. Very few parts, very cheap to build.

It has a very tight RIAA tolerance and I got more of the 8 x 1nf caps I needed and measured them, I only used ones less than 1%. Which turned out to be most that I ordered.

R1 is the same as the internal resistance of your moving coil cart, easy to work out. R2 is the gain resistor, I used 300ohms for this which should give me a gain over 42db with this cart. These resistors must be tailored to suit the cart you are using, for a Denon DL-301mk2, R1 is 33ohms and R2 is 850ohms with gives 58db. I have a gain calculator from RJM the man who copied the Phono Cube which gives the value for any cart.

Finished putting it all together today and double checked everything, connected it up to see if it would work.

It worked first time, I was struck by how low the noise is, I have reduced the gain a lot but if this is any indication it should be extremely quiet with LOMC carts. I added a 0.1uf poly cap to each of the 8 x 100uf filtering caps, they certainly didn't hurt anything. To give you an idea it's much quieter than my modded 640P's and they are very quiet. With battery power you don't have to worry about hum for a start.

Right out of the blocks I knew this is going to be good VERY good, it bowled me over with the definition and smoothness on the first track which was Because by The Beatles off the Love album. I could easily hear the fly buzzing back and forth. The bass response and separation was second to none I have heard, Elanor Rigby sounded better than I have ever heard.

I kept thinking this thing is not even broken in yet, it can't be this good, those op amps are cheap as well. I called my wife she couldn't believe it either. It has a slightly warm yet detailed and very open sound, the music just flows out. If it has faults I can't find any at the moment, it just sounds like vinyl should.

It's probably the best I have heard and is very easy to build.

Here's a pic, I am going to get a nice case tomorrow for it, this thing is a keeper.

I must have one!!!!

Toad! I must hear this for myself.

Bill.

Big Bill said:

Toad! I must hear this for myself.


Bill.

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I would be both rapt and stoked to have one as well!

Fasterdamnit said:

I would be both rapt and stoked to have one as well!

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Times three!!

Very interesting Toad.

Moderation note: no buying&selling in the open forums guys. Thanks.

It uses single circuit op amps so each channel is totally independent.

Here's a rave review of the Phono Cube.

... simply the best
Fantastic, unmatched, fascinating, impressive... In a word, absolutely superior! Regardless of whether jazz, rock, ethno or classical accords were pressed in the vinyl grooves, regardless of whether dealing with small or big, vocal or instrumental, silent or loud listening, with Phono Cube as preamplifier stage in my system everything sounded better than ever. And here one should conclude the review because words are not enough to describe the whole of the sound, least to express the subtlest details and emotions that unfolded widely and manifestly in front of me and filled my room through Phono Cube. One should say simply and without any hesitation that Phono Cube produced in my system the best sound I have ever heard at home and brought it closer to the rare ecstatic experiences I had while sitting in front of several best and excellently tuned systems in the world, i.e. the Phono Cube is unparalleled not only as the best phono stage I have ever used but also as the best individual piece of audio gear, regardless of the type, ever being a part of my system. And there were many of them... This would be the end of the tes(x)t. However, to make perfectly clear what sort of audio gem we are dealing with, I will try to put in words as detailed as possible everything that was going on within the walls of my room.
Phono Cube is, undoubtedly, a phono preamplifier that brought me closest to the ideal of live music so far. It is one of the rare devices used as a paragon for all other and that sets new audio standards, pushing the limits of the possible beyond the imaginable up to the present date. Above all, Phono Cube contributed to making the sound coming from the turntable essentially neutral and transparent. Its absolute noiselessness and thus practically physical absence, enabled a piece of music to be as it really is: with all its strengths and weaknesses. The sound was neutral because all the veils obscuring the finest musical details were lifted, because nothing remained hidden and covered, because not a single trace of parasitic resonance and the related coloration, which is usually considered to be an inherent and unavoidable weakness of the phono preamplifiers, could be perceived, because there were no any admixtures that would add additional character to the sound. Transparent because nothing hindered clear and full insight into the integrity of the intricate musical fabric as well as into the configuration of the orchestral body interpreting it. Nothing less worth mentioning is the purity of the sound and absence of any, even the minor distortions. Everything seemed absolutely natural and exactly as it should be. It is therefore fascinating how one simply stops feeling the need for asking oneself "how?", "why?", "from where?", and starts taking what one hears for granted, laying on the same level something that is in its essence "unnatural" with the live sound experienced in a real surroundings and with actual people who play genuine instruments, simply and easily believing that live musicians are in front of him, and not a pile of electronic components molded into a more or less harmonious audio chain, dreaming only about how everything could sound even better if one would have the one, actually non-existing, ideal audio system that would exploit all the capabilities of Phono Cube to the fullest level.

http://www.sakurasystems.com/reviews/reviews9.html

Now that is one heck of a review.

You can accomplish the same thing using single channel SMD chips on adapters and using them in the dual circuit sockets. Probably one reason I so like the LME49990's in the mix. We need to have a shoot out!

I cant stand anymore!

Your killing me Phillip!!!! :cry:

Fasterdamnit said:

Now that is one heck of a review.

You can accomplish the same thing using single channel SMD chips on adapters and using them in the dual circuit sockets. Probably one reason I so like the LME49990's in the mix. We need to have a shoot out!

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The op amps are only $3.05 each, and the secret is the inverted zero input impedance. Here's what the makers say:

Input impedance 0 ohm
Most of currently available phono equalizers are designed to amplify the voltage that appears at both ends of a resistor when a current generated by the cartridge is carried to the ground through this resistor. Our Phonocube has a unique and original circuitry ( with input impedance of 0 ohm), which enables all of the current generated by the cartridge to flow directly into the amplifying circuit.

http://www.sakurasystems.com/products/47phono.html

And that's what it sounds like, the music just flowing out, it doesn't sound bright, dull, forward, laid back it just sounds right.

Of course I'm in on this one as well, I have a Dyna PAT-4 carcass awaiting a dual-purpose phono stage and one of the e-Bay servo line preamp modules to power and back it up.
Check your Bartertown LOMC thread.

Here is one channel of the PCB's I bought, everything inside the red box is the super regulated power supply, it's the majority of the circuit. By using batteries we cut out all of those parts. The music part is on the left side of the red box. It's a very simple circuit but it works unbelievably well.

Simple is GOOD!!

Another great find and implementation, Phillip.

I think it will work nicely with my Hagerman Bugle power supply! :yes:

If this is another build opportunity, I'm in!

dodog said:

If this is another build opportunity, I'm in!

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This reminds me of the Blues Brothers, "Putting the band back together".

Why do you have 4, 1nf caps??
There is one per channel on the original schematic and PCB.

Check your PM Phillip, now I see you've got the Burr-Browns in there already. Go for it!

Fasterdamnit said:

Why do you have 4, 1nf caps??
There is one per channel on the original schematic and PCB.

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There is one in C1 and three in parallel in C2.

The original schematic has been updated a few times, this is the latest one I have, and the value of R7 has been changed to 68k since then, which is what I used.

R6 you can see is now 768k and not 750k as in the original parts list to accommodate the change in C2 from 2.9nf to 3.0nf for the RIAA section.

Ah,
You did not go with the originally recommended .68nf+2.2nf. Wima has them in pulse film, 2.5%. Do you know why it was changed? 2.88nf is closer to the 2.90nf originally spec'ed for the RIAA curve.

Fasterdamnit said:

Ah,
You did not go with the originally recommended .68nf+2.2nf. Wima has them in pulse film, 2.5%. Do you know why it was changed? 2.88nf is closer to the 2.90nf originally spec'ed for the RIAA curve.

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See my edit above about R6 which was changed to bring it back in line. You can see how simple this design is.