low output moving coil preamp?

M

Mark Sellers

New Member
I've been using a Ortofon, SL15E MKii Cart. with my Carver C-1 preamp, this preamp has two phono stages and one is a low output moving coil with sound amplification on board. I upgraded to the Carver C-4000, this one does not have this option, and recommends to add on the Carver MCT Moving Coil Transformer, sounds great but they are not just lying around these days. Modern ones seem to be too cheap or too pricey, all of them seem to take the signal to line level to bypass the phono stage all together. It seems to me in my best interest to have one that works injunction with my phono stage. Any suggestions out there?
 
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Moving coil step-up transformers never take the signal to line level.
Yes, if your Carver preamp has only MM phono inputs and you want to use a LOMC cartridge you need either a step-up transformer or a head amp. No prizes for guessing whose products I would recommend.
 
Sorry, terminology issue, mostly what i found for quick satisfaction on amazon was independent phone stage to the line level to accommodate newer receivers out there without a phono stage, i gather. I have to refine my search, outside Amazon.
 
Perhaps I should have give more detailed advice, so here goes:
If you want to use a LOMC cartridge you could use an outboard phonostage which is LOMC compatible. The prices range from modest to very expensive. Or you could use your other preamp as just a phonostage as suggested by Blue Shadow in post #3.

If you want to use your MM phonostage you'll need some kind of step-up device. The obvious choice is a step-up transformer. There are quite a few step-up transformers available, but the problem you will have is the extremely low output voltage of the Ortofon SL15E mkii. If vinyl engine's database is to be believed the output voltage is only 0.015mV, which is insanely low. A lot of Ortofon's current cartridges have outputs of about 0.5mV, or 30 times more.
However, the figure quoted on vinyl engine is misleading. It's 0.015mV/cm/sec, so at 5cm/sec the output is 0.075mV. That isn't as bad, but it's still very low. For that cartridge you will need a step-up transformer with a high turns ratio of about 1:50. If I'm not mistaken, Ortofon used to sell step-up transformers with high ratios to match their cartridges. Locating one of those would be your best option. Of course there are other transformers which would work but you may struggle to find one with a turns ratio of 1:50, not least because so many manufacturers don't even tell you what the turns ratio is. I sell a SUT with a turns ratio of 1:20. It would work, but a higher ratio would be preferable.
http://www.rothwellaudioproducts.co.uk/html/mc_step-up_transformer.html
MCL.JPG


Your other option is to use a headamp. They're not as common as SUTs. In fact they're very rare. I sell one though.
http://www.rothwellaudioproducts.co.uk/html/headspace_mc_headamp.html
However, the extremely low output of your cartridge will still be a problem. Getting a good signal-to-noise ratio from a headamp when fed with such a low signal will be a challenge.

Out of interest, how does that cartridge perform with your previous preamp?
 
Wow, that is low! I would take rothwellaudios advice and find the matching step up transformer. At those super low voltages it's going to be hard to find an active stage that will be quiet enough.

BillWojo
 
rothwellaudio said:
If vinyl engine's database is to be believed...
Click to expand...
Sad to report that VE is not to be believed. It's a great resource, but I've found enough errors to make me doubt all its data. I mean instances where I have an NOS cartridge that's fairly rare, complete with its original documentation, and the specs disagree with VE. I have to assume those original specs are correct, and VE erroneous.

It's only happened a couple of times, but I'm only checking a few cartridges, and it's more than enough to raise doubts, in my mind at least — how am I to know if any given datum is correct or not?

Take the example of OP's Ortofon SL15E mkii. The output voltage, according to VE, is only 0.015mV, which rothwellaudio notes 'is insanely low". Did every single user of that cart buy a special Ortofon step-up with 1:50 turns? OP uses it with a Carver's internal MC section and it seems to be fine — is the Carver's MC preamp "insanely" powerful? If so, it wouldn't suit 99% of the MCs that owners use.

But I should ask OP, rather than speculate — @Mark Sellers Do you have to turn the volume all the way up, with the Carver? Is the 15E "insanely" noisy?
 
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BillWojo said:
At those super low voltages it's going to be hard to find an active stage that will be quiet enough.
Click to expand...

I have an Ortofon MC20 whose output is 70µV (0.07mV) I use a Crown DL-2 Phono Module "B" which has adjustable gain from 50-70dB. For this cartridge I have it cranked up to 70.

The Ortofon step up for this cartridge is the STM-72 plug in transformer. This unit has a 60:1 voltage ratio. These go for a c-note or a bit more. The head amp that ortofon made is the MCA-76 that had a 34 dB gain to phono input level.

So if looking for a phono amp for these cartridges, look for one that can do about 70dB to line level input.

Found the spec sheet for the SL-15EII. It is an extremely low output cartridge. SK-15 EII, II and Q.jpg

Seems folks use a 30db gain device to get into a phono mm stage to use the cartridge.
 
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The OP's C-1 preamp has 25dB gain prior to the phono stage gain of 35dB to tape output level for the moving coil input.
 
bimasta said:
Sad to report that VE is not to be believed. It's a great resource, but I've found enough errors to make me doubt all its data.
Click to expand...
Yes, I doubted that figure of 0.015mV when I saw it on VE so I looked for corroborating evidence and found the image which Blue Shadow posted in #9. The figure in the image appears to be the same as on VE, but it isn't - it's specified as "XmV per cm/s". That means it should be multipled by 5 to give the figure at 5cm/sec, which makes comparison with other cartridges more meaningful. Even then, it's a very low figure. It would appear that such low outputs were more common back in the 1970s (or whenever it was) and there was often a matching transformer sold along with the cartridge. These days such low outputs are rare.
Blue Shadow said:
I have an Ortofon MC20 whose output is 70µV (0.07mV) I use a Crown DL-2 Phono Module "B" which has adjustable gain from 50-70dB. For this cartridge I have it cranked up to 70.

The Ortofon step up for this cartridge is the STM-72 plug in transformer. This unit has a 60:1 voltage ratio. These go for a c-note or a bit more. The head amp that ortofon made is the MCA-76 that had a 34 dB gain to phono input level.

So if looking for a phono amp for these cartridges, look for one that can do about 70dB to line level input.

Found the spec sheet for the SL-15EII. It is an extremely low output cartridge. View attachment 1968899

Seems folks use a 30db gain device to get into a phono mm stage to use the cartridge.
Click to expand...
Those figures add plausibility to the notion that 0.015mV/cm/sec is indeed accurate for the SL15E mkii.
 
Exemplary research by Blue Shadow — I would have gotten a full scholarship to Harvard if I were that industrious in school. I'd just like to point out that, though the figure for the SL15E appears to be accurate, that doesn't make all figures on VE accurate. I've found enough mistakes there to call all its info into question — for me, anyway. It was a sad realization, as I'd taken VE as 'gospel', totally reliable.

When I can download manuals on VE, I trust those numbers. Our sleuth Blue Shadow found such numbers, an Ortofon spec-sheet, not on VE but on Canuck Audio Mart, verifying that the "insanely low" output was true.

But the tables in the VE databases — where does that data come from?
 
I have the original manual C-1 manual, "Phono 2 employs an additional 25 DB of linear gain (for a total of 60 DB to Tape output), designed especially for relatively low voltage output of moving coil cartridges. Input impedance is 39 ohms. The c-1 employs a built-in "pre-amplifier", but this design is free of the compromises usually associated with active gain at this stage" It goes on for another two paragraphs, the claim is step up transformers add noise, Carvers's stage does not. "the best step up up devise is no step up device at all, which is precisely the design approach used in the c-1". With that said, i think it sounds pretty good. I acquired this cart when i purchased a turntable at an estate sales three years back. Lucky my carver had this phono stage. It does take more volume then other line level devises, low to moderate volume its awesome, turn it up real loud, there is issues, but i attributed that to other issues, like vibration that i never bothered to trouble shoot because i just don't play that loud often.
 
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bimasta said:
though the figure for the SL15E appears to be accurate, that doesn't make all figures on VE accurate.
Click to expand...

Would never say that VE or HFE or Orion are correct. VE isn't bad but there are errors, gotta be with different spec sheets out there and folks just filling in the info, same for HFE but Orion, I preface or follow most info from that book with something like it came from orion and they are known to have errors.

VE would usually use their documents in the files to get the data for the databases. But who knows what really happens.
 
Blue Shadow said:
VE would usually use their documents in the files to get the data for the databases. But who knows what really happens.
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A lot of paid manpower required in searching through so many mountains of paper. I don't think it's feasible. I think some info is contributed by Users, well meaning, but inaccurate.
 
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Mark Sellers said:
... the claim is step up transformers add noise, Carvers's stage does not.
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That's just a claim from sales literature. Take it with a pinch of salt.
Anyway, Carver's onboard pre-preamp has 25dB gain. That's a bit on the low side for your Ortofon cartridge but it does the job. A step-up transformer with a turns ratio of 1:20 would give you just about the same amount of gain as that pre-preamp, so the MCL pictured above (post #6) used with your new MM Carver would perform similarly to the old MC Carver.
 
Mark Sellers said:
with my Carver C-1 preamp, this preamp has two phono stages and one is a low output moving coil with sound amplification on board. I upgraded to the Carver C-4000, this one does not have this option,
Click to expand...

The OM for the C-4000 says it has the same gain for phono as the C-1 allowing LOMC use on Phono 2. From the OM:
Clipboard01.jpg

Have you tried the SL into phono 2?
 
Only time a SUT will add noise is if it's not setup properly. Don't set it close to power cables or transformers, stuff like that. It's a passive device, it can't add anything. But it sure can sound good.
It's not easy to build quiet MC active stages, that's why really good ones tend to be expensive.

BillWojo
 
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