Can anyone explain why this works (technically, it shouldn't)

[JimmyJet]

Hi all -- thought I'd ask here hoping someone would be able to give me a technical/scientific reason why a phono stage I just acquired works so well with my cartridge when the numbers say it technically should not work.

My Clearaudio MC cartridge has the following specs:
Output Voltage = 0.5mV
Impedance = 50 Ohms

My new phono stage, Line Magnetic LP-33, has the following specs:
Input Sensitivity MC: 1mV(H), 0.5mV(L)
Input Sensitivity MM: 6mV
Gain MC: 66dB(H), 72dB(L)
Gain MM: 50dB
Input Impedance MC: 100?(H), 47?(L)
Input Impedance MM: 50k?
Output Impedance: 10k?

The optimum gain for the output of my cart is around 56dB and loading should be in the 500 to 1000 ohms range. I had recently been using this cart with my McIntosh C-53 solid state preamp's built in phono stage with fixed gain at 60dB and the loading set at 1000 Ohms and it sounded great.

This Line Magnetic phono stage is tube driven and only has two settings (High/Low) for an MC cart as listed in above specs. After trying both settings, it was clear the Low setting sounded best, and in fact, it sounds fantastic! - much better than my McIntosh's solid state phono stage. But technically speaking, this new phono stage should sound horrible because at the low setting it's providing 72dB of gain which should be producing clipping and distortion. And with providing only 47 Ohms of resistance, it should sound muffled and lifeless. While I'm enjoying the sound, it really bugs me how these numbers can be so off but yielding such great sound.

The only numbers that line up between this phono stage and the cart is that both the cart's output voltage and the phono stage's input sensitivity are both 0.5mV, other than that, the numbers are way off. I'm wondering if the tubes interact differently with a MC cart than that of a solid state phono stage? (I would think this shouldn't be the case)

Anyway, I'm hoping someone here can explain why these "off" numbers are working so well.

--cheers!

 

[hongkongfoufou]

Hello,


Why do you say your cartridge technically should not work ?

For me , the numbers are excellent.

My Clearaudio MC cartridge has the following specs:
Output Voltage = 0.5mV
Impedance = 50 Ohms

My new phono stage, Line Magnetic LP-33, has the following specs:
Input Sensitivity MC: 1mV(H), 0.5mV(L)
Gain MC: 66dB(H), 72dB(L)
Input Impedance MC: 100?(H), 47?(L)
Output Impedance: 10k?

Best regards

 

[hongkongfoufou]

50 ohms is near 47?...

 

[DasguteOhr]

There is a step up transformer under the circuit board your pick-up is terminated with this load (marked red) i think it works pretty good P.S i think its a ear 834p clone with external power supply

 

[mtemur]

Looking at @DasguteOhr post you are loading the cartridge 180Ohms 68dB gain. That's not ideal but ok for a 0.5mV 50ohm cartridge. SUTs are more flexible in terms of loading.

If those specs shared by @DasguteOhr are wrong and your phono pre really loads the cartridge at 47ohm 72dB than;
- There is something tipped up in your setup. It could be tubes, phono, cables or another component that is amplifying lows and highs.
- When a 50ohm MC cartridge is loaded too low at 47ohm that attenuates output. It can no longer output 0.5mV but lower. That justifies 72dB gain. Additionally coils act like they got stiffer suspension and attenuates highs. Something in the RIAA circuit or another circuit can be non linear by amplifying highs more than it should and this attenuation just fixes it.
- Cartridge is not up to spec or another issue (deteriorated suspension, coils etc) is tipping up highs more than regular. MC cartridges normally have a rise at the end of frequency spectrum.

The cause of problem can be one or mix of those things.

 

[DasguteOhr]

Looking at @DasguteOhr post you are loading the cartridge 180Ohms 68dB gain. That's not ideal but ok for a 0.5mV 50ohm cartridge. SUTs are more flexible in terms of loading.

If those specs shared by @DasguteOhr are wrong and your phono pre really loads the cartridge at 47ohm 72dB than;
- There is something tipped up in your setup. It could be tubes, phono, cables or another component that is amplifying lows and highs.
- When a 50ohm MC cartridge is loaded too low at 47ohm that attenuates output. It can no longer output 0.5mV but lower. That justifies 72dB gain. Additionally coils act like they got stiffer suspension and attenuates highs. Something in the RIAA circuit or another circuit can be non linear by amplifying highs more than it should and this attenuation just fixes it.
- Cartridge is not up to spec or another issue (deteriorated suspension, coils etc) is tipping up highs more than regular. MC cartridges normally have a rise at the end of frequency spectrum.

The cause of problem can be one or mix of those things.

If you have a soldering iron and an ohm meter, swapping out the 51k resistor for a 68k resistor isn't a big deal. You'll get a fresher, airier sound and more liveliness if that's what you want. The circuit board and circuit is manageable. Follow the cable from mm input. This resistor should be connected to the board between signal and ground.

 

[JimmyJet]

There is a step up transformer under the circuit board your pick-up is terminated with this load (marked red) i think it works pretty good View attachment 115630 P.S i think its a ear 834p clone with external power supply

@DasguteOhr Thank you for posting that - I had no idea this unit was using a SUT... I'll try and find this article online and use google translate. This changes things and the specs look different. This may explain a lot. --cheers!

 

[JimmyJet]

Looking at @DasguteOhr post you are loading the cartridge 180Ohms 68dB gain. That's not ideal but ok for a 0.5mV 50ohm cartridge. SUTs are more flexible in terms of loading.

If those specs shared by @DasguteOhr are wrong and your phono pre really loads the cartridge at 47ohm 72dB than;
- There is something tipped up in your setup. It could be tubes, phono, cables or another component that is amplifying lows and highs.
- When a 50ohm MC cartridge is loaded too low at 47ohm that attenuates output. It can no longer output 0.5mV but lower. That justifies 72dB gain. Additionally coils act like they got stiffer suspension and attenuates highs. Something in the RIAA circuit or another circuit can be non linear by amplifying highs more than it should and this attenuation just fixes it.
- Cartridge is not up to spec or another issue (deteriorated suspension, coils etc) is tipping up highs more than regular. MC cartridges normally have a rise at the end of frequency spectrum.

The cause of problem can be one or mix of those things.

@mtemur Thanks for the updated spec of 180ohm 68dB gain - that's a bit better, but as you say, not ideal. (Curious at how you arrived at those figures.) The owner's manual never mentioned the use of SUTs and I read a review on Hifi-Advice in which the reviewer said the printed specs may be wrong because he was also used to higher loading with his cart, yet it worked with his as well.

So, both my Mac preamp and CA cart are only a few years old, and the 1000ohms @60dB I used on the Mac's built-in phono stage sounded great with this cart, so I don't think anything's amiss in my rig, but your second bullet point is interesting in that it helps me to understand better how loading works, so thanks. I actually purchased this unit for a second turntable I'm planning on setting up and it'll use a different cart which will be geared to the specs of the Line Magnetic phono stage. I just plugged it in to my current rig to see what would happen, and was quite surprised at how good it sounds and I'm probably just under the spell now of the tube magic which I realize I'm missing with my Mac's built-in. So, now I'll be on a mission researching for a tube phono stage that has more flexible gain and loading options to use with the CA cart. --cheers!

 

[mtemur]

(Curious at how you arrived at those figures.)

Check the picture posted by @DasguteOhr . it says 180/370 ohm and 48/68dB.

The owner's manual never mentioned the use of SUTs

Existence of only two (high and low) gain options made me think it has a SUT.

 

[JimmyJet]

Ok - mystery solved!

Thanks to @DasguteOhr & @mtemur, I found two German reviews linked from the Line Magnetic German website and they both allude to transformers being used in the bottom half of the case shielded away from the electronics above.

The other thing I figured out based on one of the articles is that LM is using the terms Low and High to refer not to the type of cart output you have, but rather how much stepping up you need, "...in the MC case, transformers are connected upstream. This means a maximum of 68 decibels, which is more than enough even for quiet MCs. The "MC Low" setting offers around ten decibels less if it's too much of a good thing."

So it looks like MC Low=58dB 370ohms and High=68dB 180ohms and this would explain why it works with my cart. On my Mac's phono stage, I had been using 60dB of gain and 400ohms (before I settled on 1000 for certain recordings) and 60dB/400ohms is very close to 58dB/370ohms.

Thanks guys for leading me to those articles and the other info you supplied. I can sleep nights again --cheers!