Phono stage question

crn3371

Well-Known Member
With regards to a MC phono stage, how much are you missing out on by not having adjustable loading? The internal MC stage on my Anthem STR Integrated has adjustable gain and multiple EQ curves to choose from, but loading for MC is fixed at 100 ohms. How much of a disadvantage is that vs a stage with adjustable loading?
 
Really depends on the cartridge you plan to use. Some are VERY load-sensitive, others less so.
 
My Valab LCR-1 has both variable gain and loading for MC's via DIP switches under the box. I find I prefer the results I get using a quality SUT and the phono on its lowest gain settings and loading on 47k. Go figure right?

I just find that irrespective of the phono stage used, higher gain settings with MC stages just sound a bit thin compared to using a SUT. Likewise different SUT all have different sound signatures, just as different carts and RCA cables do. Waiting for my latest acquisition to arrive now: A Hashimoto HM-3 SUT.
 
I rotate between about six different LOMCs, all different recommended loads. Normally I just use a SUT into 47K, either tube and SS, and it sounds fine. I've read other posts by smart people, like mjw21a above, that say the same thing. I have another SS preamp with an active MC stage fixed at 100 ohm like yours, and it sounds fine, though I prefer tubes. I have one cart with a very annoying peaky treble. I have a tube phono-only preamp lets me load it down as low as 10 ohms, and that fixes the treble — but everything else suffers.

I think loading may be crucial to getting the absolute best out of a cart, but short of that its importance is vastly overrated and only drives me nuts. But then again, I'm lazy... I even think matching a cart's compliance exactly to a tonearm's eff mass is overrated.
 
I use a PS Audio GCPH that has some selections for impedance but the lowest is 100 ohms. My main cartridge (Monster Alpha 2) should be loaded at about 20-40 ohms, so I rigged up a way to put a resistor across (in parallel) with the cartridge coil on the output of my turntable. After much experimentation I decided that it sounds virtually identical with a 100 ohm load (via the phono pre) as it does when adding a resistor to bring the "load" down to roughly 30 ohms. I've also found that the bass is a bit tighter using the PS Audio at 100ohms than it is at the variety of lower impedance levels that I have tried. I'm sure that this is dependent upon the phono pre one uses - as I found different results with the phono stage on my previous pre-amp. Like mjw21a (post #3) I have found that using an SUT and keeping the phono stage at the lowest gain setting, seems to give the "best" sound. Currently I'm very pleased with the sound I'm getting with the GCPH on high gain with 100 ohm loading, but would like to try a really HQ SUT sometime - just hard to justify the expense when it is already sounding sooooo good.
 
I believe the importance of the "correct" load impedance for a LOMC cartridge is vastly overstated. Most manufacturers don't actually specify an optimum load impedance, just a minimum load impedance. In the wider world of audio electronics it is considered normal that the load impedance should be much higher than the source impedance - the source impedance being the resistance of the cartridge's coils in this case. A factor of 1:10 is usually considered high enough, and with most LOMCs having a coil resistance of approximately 10 ohms a load impedance of 100 ohms satisfies that 1:10 rule. Coils also have inductance as well as resistance but the inductance is usually so low in an LOMC that it is negligible.
I find I prefer the results I get using a quality SUT and the phono on its lowest gain settings and loading on 47k.
Yes, many people have found the same. I'm only surprised that there aren't more people using the SUT-plus-mm phonostage option.
My main cartridge (Monster Alpha 2) should be loaded at about 20-40 ohms, so I rigged up a way to put a resistor across (in parallel) with the cartridge coil on the output of my turntable. After much experimentation I decided that it sounds virtually identical with a 100 ohm load (via the phono pre) as it does when adding a resistor to bring the "load" down to roughly 30 ohms.
I think many manufacturers specify a load impedance for their cartridges because people expect to see that kind of information and they don't want to say "it doesn't really matter that much". The manufacturers who specify only a minimum impedance come close to admitting it doesn't really matter that much.
I'm not surprised your cartridge sounds identical with 30 ohm loading and 100 ohm loading.
I have one cart with a very annoying peaky treble. I have a tube phono-only preamp lets me load it down as low as 10 ohms, and that fixes the treble — but everything else suffers.
Yes, when the load impedance gets down really low - say less than 3x the coil impedance - the overall output will drop but maybe the treble will drop a bit more than everything else. Possibly better than a low resistance load would be a high capacitance load. There's thread about just that here on the forum.
http://audiokarma.org/forums/index.php?threads/lomc-treble-peak-capacitor-cure.838117/
Of course, you already know about that thread - you started it :thumbsup:

Anyway, to answer the OP, I don't think you're missing out on very much.
 
You're a wealth of information rothwellaudio :)
I don't want to embarrass the man, but I also like his apparent lack of ego — e.g. "And don't call me an expert again :biggrin:" in the FR1 thread — and his willingness to recommend products other than his own. He wants to help, not sell. I guess that makes him a really lousy salesman...
 
Yes, many people have found the same. I'm only surprised that there aren't more people using the SUT-plus-mm phonostage option.

I think that cost is the most important factor in that - transformers (usually) cost a lot more than electronics, so head amps (or MC stages) can be built for a much lower price (comparatively) than SUT's.

After all, if you've already got a phono stage, and the power supply for that, it doesn't cost much extra to add a few extra transistors/op-amps/resistors/capacitors/switches etc, to get some extra gain.
 
The Anthem being at 100 ohms is really in the most common range for a lot of lomc carts. I'm very lucky to have 2 very good phono stages (ARC Ref Phono 2SE and a Manley Steelhead), both of which have many settings for MC. With my setup, 100 ohms works very well, and since the ARC has a remote, I can be totally lazy and switch impedance on the fly to see the differences. Funny thing is, both of them have some form of transformer included in the MC section rather than something like an additional gain stage.

As an aside, when I upgraded my Oracle Delphi, I spent some time with Jacques R at Oracle discussing a few things. At the tie I had my Sumiko Pearwood Celebration cartridge on the table and he was quite emphatic that the cartridge sounded better loaded at 1000 ohms. I've tried it both ways (and other settings in between) and there is a difference (100 ohms = little more dark and mid-rangey, 1000 ohms is a little more detailed and airy) and frankly I'm not really sure which I prefer. Think it depends on what beverage I'm having at the time.

If you're still interested in other settings, call or email Anthem (they are quite helpful) and see if they have any provision for any custom setting (via additional resistors etc).
 
think many manufacturers specify a load impedance for their cartridges because people expect to see that kind of information and they don't want to say "it doesn't really matter that much". The manufacturers who specify only a minimum impedance come close to admitting it doesn't really matter that much.
Rothwell nails two important points here, IMO. The obvious point is about LOMCs and the over-emphasis that precise loading is crucial.

The broader point is that this afflicts the whole audiophile headspace. Over-emphasis on minor things inflated into "crucial". If you don't have the precisely correct this or that, you're not hearing music. If you don't have or do this or that, you're either ignorant or a fool. If you do and have the correct this or that, and don't hear a difference (a "crucial" difference) you don't have "golden ears" — you're a "tin-ear", as contemptible as a "tinhorn" was in the Wild West.

It's a great way to sell thisses and thats.
 
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