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Gain requirements: Ultra LOMC cartridges

davstev

davstev

Well-Known Member
Hi all,

In the past, I've used a selection of MM and MC cartridges. However, just recently, for cheap I acquired an ultra low output MC, a MC-20 by ortofon, and it needs a re-tip. The output is super low: 0.07mV. (This is the MK1 version, with the purple/blue body, circa 1980, much lower than the popular MC-20 Super). For this reason, I may be considering not only re-tipping, but also... will my current preamp be able to provide enough gain, or am I into a whole new kettle of fish, whereby I would also need to look into a costly new SUT or phono pre with more gain?

I used the Voltage Gain Calculator on VE, and it was interesting. I put the values in- .07mV output w/ 32db gain (highest gain setting for my current phono pre), and the output was 2.79mV. This is pretty close to the low end of a typical MM cart....going into my MM phono stage.

Is this a sufficient enough amount of gain? What is the ideal amount of gain for such a low output MC?

As I consider whether to retip I need to consider 1) what the performance potential of this cartridge is vs. the cost of retipping, and also 2) Whether I am getting in over my head with now needing to purchase a new high-end preamp with more gain than my 32db has currently. Wondering if it's all worth the cost.

Thanks for any input.
David
 
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Calling @Mister Pig

Mister Pig can give you some insight on these ultra low gain carts as well as recommendations on a retip as he has just went through all of this with two of his.


Audiofreak71
 
I have one of theses as well and have a shibata cantilever i plan to re tip it with, just have gotten around to it.

But I think it may need an SUT to help it out.

Look for any Denon SUT and it probably might be enough to go to your MC input. Then you can try the different settings for gain on that.

Athanasios
 
I was just noting that the Ortofon MCA-76 is supposedly the head amp made for the MC-20 mk1. It has 34dB of gain. My Denon HA-500 is 32.6 dB of gain. Basically the same.

In terms of input impedance, the MCA-76 has 75ohms and the HA-500 has 100ohms. Not sure exactly how this input impedance has an effect, but they are not wildly dissimilar either.
 
And SUT don't need to be expensive, especially if you can make a hot solder joint. Slagles were $350 a pair
 
I'm not a TT guy, but calculating voltages and gain stuff isn't really contingent on that.

Hoping I might learn something here, but right at the minute I don't see how you get much volume out of anything at that rate.

0.07mV +32dB phono pre gain = 2.8mV (0.0028 volt).

2.8mV + 20dB pre amp gain (and I think that's generous) = 28mV (0.028 volt)

28mV + 30dB power amp gain (again, generous, I think) = 0.89V

0.89V = is 0.1 watt to an 8 ohm speaker

What am I missing here how that's actually supposed to work out?
 
The Accuphase would be fine if you used a step-up transformer with the Ortofon, without it you aren't going to have enough gain....the phono section sensitivity is for 2 - 6 mV cartridges, the 0.07mV is just not enough.

.
 
The Slider said:
How long ago? The basic transformers on the Intact Audio site are listed at $900 a pair.
Click to expand...
A guess would be 2 years ago. Basic mic transformers. I bought 2 pair.

Edit: just looked at his site. Prices have more than doubled, just like everything else. Looks like he copied my procedure for potting too. He used to use a PVC tube cut in half. Those can are $100 a copy. I' used beeswax for potting.
 
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whoaru99 said:
I'm not a TT guy, but calculating voltages and gain stuff isn't really contingent on that.

Hoping I might learn something here, but right at the minute I don't see how you get much volume out of anything at that rate.

0.07mV +32dB phono pre gain = 2.8mV (0.0028 volt).

2.8mV + 20dB pre amp gain (and I think that's generous) = 28mV (0.028 volt)

28mV + 30dB power amp gain (again, generous, I think) = 0.89V

0.89V = is 0.1 watt to an 8 ohm speaker

What am I missing here how that's actually supposed to work out?
Click to expand...

OP here. Just thought I would pipe in here because I just discovered that my head amp offers 32db of gain and my MM phono stage in my preamp offers 60db gain. Will this suffice? One way to tell... once I get the retip done on the MC-20...:)
 
RickB said:
The Accuphase would be fine if you used a step-up transformer with the Ortofon, without it you aren't going to have enough gain....the phono section sensitivity is for 2 - 6 mV cartridges, the 0.07mV is just not enough.

.
Click to expand...
Yes, I will run it though my HA-500 Denon headamp first, for 32db of gain, then into the Accuphase C-200 for 60db of gain (according to the specs in the C-200 manual). Thinking this will be enough... hopefully?
 
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davstev said:
OP here. Just thought I would pipe in here because I just discovered that my head amp offers 32db of gain and my MM phono stage in my preamp offers 60db gain. Will this suffice? One way to tell... once I get the retip done on the MC-20...:)
Click to expand...

So... what things are strung together in that scenario and what's the gain of each?

Name and model number from start all the way though power amp might be helpful.
 
whoaru99 said:
I'm not a TT guy, but calculating voltages and gain stuff isn't really contingent on that.

Hoping I might learn something here, but right at the minute I don't see how you get much volume out of anything at that rate.

0.07mV +32dB phono pre gain = 2.8mV (0.0028 volt).

2.8mV + 20dB pre amp gain (and I think that's generous) = 28mV (0.028 volt)

28mV + 30dB power amp gain (again, generous, I think) = 0.89V

0.89V = is 0.1 watt to an 8 ohm speaker

What am I missing here how that's actually supposed to work out?
Click to expand...
And why I leave calcs to the smart ones.
 
As the conversation develops it looks like the missing link is a SUT or equivalent to get the LOMC output up to a more reasonable level, or the 60dB gain that came up just a bit ago.

So, if we redo it and throw 60dB gain in the mix from C-200 whatever that is...

0.07mV +32dB phono head amp = 2.8mV (0.0028 volt).

2.8mV + 60dB MM pre amp gain (C-200?) = 2800mV (2.8 volt)

2.8V + 30dB power amp gain (again, generous, I think) = 88.5V

88.5V = is 980 watts to an 8 ohm speaker

Obviously, even if the amp would have 30dB gain doesn't inherently mean you can get 980 watts out of it. Gain and power aren't the same, I just played it out without having his actual amplifier gain and power capability.

The salient point is that there is a WHOLE lot more output with that 60dB factored in, and if all that is correct then you'd have up to 2.8V pre out which should be enough or more than enough to drive most amps to full rated output, if so inclined.
 
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I dont think the MM is the right phono stage to use. Use the head amp with the MC stage in your pre . I think it will clip using the MM section.

@rothwellaudio is needed here for answers to this issue.

nashou
 
whoaru99 said:
As the conversation develops it looks like the missing link is a SUT or equivalent to get the LOMC output up to a more reasonable level, or the 60dB gain that came up just a bit ago.

So, if we redo it and throw 60dB gain in the mix from C-200 whatever that is...

0.07mV +32dB phono head amp = 2.8mV (0.0028 volt).

2.8mV + 60dB MM pre amp gain (C-200?) = 2800mV (2.8 volt)

2.8V + 30dB power amp gain (again, generous, I think) = 88.5V

88.5V = is 980 watts to an 8 ohm speaker

Obviously, even if the amp would have 30dB gain doesn't inherently mean you can get 980 watts out of it. Gain and power aren't the same, I just played it out without having his actual amplifier gain and power capability.

The salient point is that there is a WHOLE lot more output with that 60dB factored in, and if all that is correct then you'd have up to 2.8V pre out which should be enough or more than enough to drive most amps to full rated output, if so inclined.
Click to expand...
The Accuphase C-200 is spec'd at 40dB gain for the phono stage (2mV sensitivity on phono, 200mV sensitivity on high level inputs). It has a volume control on the inputs to allow stepping it down to around 30dB. So either 64dB or 72dB total gain with HA-500, and with option to reduce it further with volume controls on phono input.
 
Nashou66 said:
I dont think the MM is the right phono stage to use. Use the head amp with the MC stage in your pre . I think it will clip using the MM section.
Click to expand...

Unfortunately my Accuphase C-200 preamp doesn't have a MC stage, only MM.
 
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the other trick you get with a step-up is the loading calcs. 32db would be a voltage ratio of 1:39.8 so 0.1 mv in gets you 3.98mv out.
The impedance ratio is a square of that, or 1:1584

assuming we're working into a typical 47k MM phono stage, what the cartridge would "see" is 29.7 ohms.

whether thats right for your cart or not I have no clue.
 
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