Balanced or unbalanced phono stage with MM cart

Does it make sense to go balanced with MM cart?

I use Ortofon Super OM 20 with Technics 1200 turntable (current is Elliott Sound P06 phono stage). I think it's reasonable to make an attempt and set a theoretical goal of squeezing 95-98% sound quality out of my MM playback system. I look to other DIY phono stages and start again with the fundamental question:

that last 1-2% -- not necessary for me.

So with that in mind, would going balanced and getting a balanced phono stage for MM front end bring substantial benefits, aside from chasing that 1-2%?
 
Unbalanced vinyl playback setup require some jumping through hoops to get right, but once that is done, they can work quite well. I struggle to think of anything that would massively benefit from having input CMRR... perhaps static pickup from the record, but even that could be taken care of by a suitable brush (I also had the idea of a thin but stiff piece of wire as a "lightning rod" attached to the tonearm that floats over the surface ahead of the cartridge).

I think given your goal, you'd be better off just giving the headshell contacts a cleaning and tweaking your P06, including optimum input capacitance to match the rest of your wiring (looks like most recommendations for the OM20 are for 250-300 pF total, so that would be maybe 100 pF, 150 pF tops in the phono preamp for most people). P06 is a basically solid circuit that could benefit from some polishing. Thankfully, most of that can be done with component value changes and tacking on a few extra components:
1. U1 & U2 feedback networks are inexplicably high in impedance, worsening noise performance. It matters little for U2, but I would downsize R3-R5 by a factor of 10 and upsize C1 accordingly, C2 maybe a little less. (C2 should ideally be a low leakage / bipolar type, and really, 47 µF would be just fine. With the modest signal levels there, a cap would have to be extremely crummy to cause appreciable distortion. It just shouldn't be one thing: microphonic.)
2. Input filtering is too simplistic and series resistance a bit high. Would suggest maybe 1-3 mH in series with 330 ohms ahead of CL, and another 330-470 ohms for R2.
3. Another slight improvement in noise is gained by swapping out U1 for an NJM2068. Estimated total ~5 dB - at least at low frequencies; it would probably be down to ~2 dB by 1 kHz for your cartridge.
4. Unless your +/-15V supply is notably low-noise (e.g. LM317/337 with 10µ ADJ pin capacitor), RC pre-filter both rails with e.g. 100 ohms and 220 µF each, ahead of the board.
 
Stephan,

Is the benefit of fully balanced phono stage more effective with MC cart?

Thank you for the detailed list of P06 modifications. To be honest, I am a novice and would not be able to modify my P06 without a complete description of parts and values, although I can kind of see what you are suggesting.

Idea: maybe you can create a better phono circuit with a board for DIY assembly. I'd build your design! On the other hand if you know of a better phono board or kit, please let me know, I'll do my best to build it and can share my findings on the sonic qualities.

Another finding:
Akitika phono stage uses "electronic cooling" with a Miller loop to reduce noise.
Phono Preamp
www.akitika.com/documents/SchematicPhonoPreampRevB4.pdf

Does this technique work and if so why other DIY phono stages skip on it?

Thanks!
 

billshurv

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2014-03-01 11:53 pm
I'm building a balanced MM stage, Actually two of them. Mainly because I can. There are a number of designs published on here that can be used some with PCBs available. There is one gotcha with MMs which is that the case is usually connected to one of the gnd pins. ideally you would tease that off and ground the case seperately from the wiring.



Regarding the question on electronic cooling. Yes it does make a small difference, but generally not worth the bother. There is one case where it does, which Bob Cordell found when designing his vinylTrak preamp. This is because Bob was using cartridge loading to produce the HF pole. This is an interesting technique as, by using the cartridge to make an L-R filter you get the first order roll-off RIAA needs and bypass all the problems with capacitance. BUT you get a significant noise penalty from this. electrically cooled loads are beneficial in this case. I have not seen anyone try a balanced cooled load though!
 
An MM or MC cartridge is essentially a floating source, so it is neither balanced nor unbalanced. You can connect it either way. In practice most cartridge wiring uses a pseudo-balanced form: shielded twisted pair connect to an unbalanced input. This is a good compromise - given the floating source. The twisted cable rejects magnetic interference, while the shield rejects electric field interference. Other things being equal, an unbalanced input will generate less noise than a balanced input - but record surface noise will usually be greater anyway. There seems little point in going for a balanced input; it adds complication but offers nothing in return.

For a microphone (also a floating source), where cables are typically much longer and signal levels typically much lower, the best compromise is a balanced input. For local interconnects the best compromise is unbalanced, except where ground loops push you towards balanced.
 

billshurv

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2014-03-01 11:53 pm
With a current mode input balanced actually generates less noise. But it's way down in willy waving territory. I would suggest in commercial gear STP fo is the exception rather than the norm. My SME came with STP as the stock cable but every other turntable I have personally seen in the last 30 years didn't. Would be interesting to see what the actual percentages were each way.



I don't think anyone has ever tried to measure CM and DM pickup by a phono cartridge. That might be interesting to see.
 

6L6

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2010-10-22 6:43 pm
Denver, Colorado
The single best reference concerning balanced phono that I've read exists on this very site - His Master's Noise: A Thoroughly Modern Tube Phono Preamp

Read that a few times, don't worry about the math, SY explains things in layman's terms very well.

In your setup I would suggest that your limit is currently the phono preamp - I've build and used a P06, it is quite nice, better than many, but there is absolutely room for improvement. sgrossklass' suggestions are very good and worth doing. Or build something with much better performance.

Lastly, there are a few modifications you can make to your SL-1200 that are astounding benefits, much more than you'd expect. (but it proves that the TT is a mechanical device first and foremost...)


Change the mat to cork or a material like the Herbies mat or the Acromat.

Rest the stock feet on something more compliant - Vibrapods or sorbathane, or repack the feet with Isonoe feet.

Re-wire the tonearm. SL-1200 Tonearm rewire

Make the PSU outboard. Technics SL-1200 DC Power Supply

The SL-1200 responds incredibly well to mods, and the price/performance ratio is absolutely astonishing.
 
Hi Guys,

>>I'm intrigued by "95-98% sound quality" - does that mean "5%--2% distortion"?

Heh :) Not distortion. I meant, of what's theoretically possible in the realm of DIY phono set up based round a Technics 1200 and an Ortofon MM cart. It' s a vague statement but since I don't want to go into tubes yet, I'd like your input on improving what I have, namely going BALANCED and if it's worthwhile. This may lead to a different phono stage and that ok.

To me - "95-98% sound quality" is making a reasonable effort to improve the sound, after which point the improvements are negligible. Example: if you have a hard time perceiving the improvement in sound -- NOT reasonable going any further.
Another example: if it is no longer obvious to a good phono stage designer on what to improve here, there is no reason to proceed. No nitpicking.

>>His Master's Noise: A Thoroughly Modern Tube Phono Preamp. Yes, but this is an MC phono pre amp. So would going trough a transformer bring equal benefits in the context of MM phono?

This brings me to the "The Equal Opportunity" MM phono. Here, SY states, and I quote "So, ideally, we would run our cartridge balanced, have a balanced input, and a preamp with high common mode rejection (CMR)."

  • Firstly, this is a tube design and I would not be able to tackle it without any support and it seems that there is no support on it.

  • Secondly, SY states "ideally". Ok, but has anyone converted their MM to balanced and found the improvements substantial?


6L6,

>> Or build something with much better performance.
Can you please PM me what would be better than the Elliott P06?
JLTI design?

I did all the mods to my SL-1200, save for the external power supply.


to everyone: thanks for the responces!
Herman
 

6L6

Moderator
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2010-10-22 6:43 pm
Denver, Colorado
Do the external PSU. Single biggest improvement to the SL-1200.

As for better phono, essentially anything in DIY land that's available. Muffsy, Pearl 2 (amazing), Salas Simplisric Folded (which is outstanding), Yaniger 'Equal opportunity", RJM Emerald, Aikido Phono, etc... Phonostage is a component that has a very large impact on the sound.
 

6L6

Moderator
Paid Member
2010-10-22 6:43 pm
Denver, Colorado
Of those that I've built (P06, Muffsy, Bugle 2, Pearl 1, Pearl 2, Salas, Steve Bench RIAA 4, as well as His Master's Noise, Equal Opportunity, and Aikido in various stages of complete, and one or two others that are escaping memory at the moment...) ) The performance of the P06 is at the beginning of that range. This is not to say that it's bad, on the contrary, it's quite nice, performs well, and I very much enjoyed it.
 

billshurv

Member
Paid Member
2014-03-01 11:53 pm
Of those that I've built (P06, Muffsy, Bugle 2, Pearl 1, Pearl 2, Salas, Steve Bench RIAA 4, as well as His Master's Noise, Equal Opportunity, and Aikido in various stages of complete, and one or two others that are escaping memory at the moment...) )


And I thought I had too many phono stage on the go!


Even when I have mine running I will not be in a position to comment on the benefits of balanced operation other than grounding one leg of the input and seeing if I can tell the difference.
 
Ok, I think I can do the modifications per sgrossklass, if someone can clarify a few point for me.

Downsize R3-R5. I am literally decreasing R3 to 1k, R4 to 18K and R5 to 470ohm? yes?
Upsize C1 to what value? "Accordingly" means how?
Upsize C2 to 47uF?

Input filtering is confusing me a bit:
I add 1-3mH inductor and 330ohm between the input and R2?
R2 is increased from 2.2k to 2.6k?

I understand the rest and my power supply is the Silent Switcher.

With your help and explanation of how to arrive at specific values of the above listed mods, I can do this.

Thanks.
 
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6L6

Moderator
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2010-10-22 6:43 pm
Denver, Colorado
sgrossklass - to verify, this is the schematic you are refering ?

p06-f1.gif