Can I use a SUT or head amp with my 60dB Coph Nia MC phono preamp?


Since I use a passive preamp, I am running into low gain issues with my .4mV MC cartridge (Denon DL-301 MkII) and my Coph Nia phono preamp.  The Coph Nia is marketed as a MC phono stage, with a fixed gain of 60dB.  It does have adjustable loading, however, with one of the settings being 47kohm.  So my question is whether it would be possible to use a SUT with this phono stage, and if so, what would the recommended spec be for it?  Or would I be able to use a MC head amp with adjustable gain, such as the Rothwell Headspace (with 4 gain settings between 10dB and 27dB)?  I know there are other head amps out there as well, I just use that one as an example.  

I appreciate the input and education!

Tom
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A SUT really isn't designed to be used with a high gain phono preamp such as yours. I'm not familiar with your phono stage, but it's likely it will be overloaded if you put a SUT in front of it. A better approach would be to use a higher gain phono cartridge, an active line stage, and/or a higher gain phono stage. You're trying to make something work using parts not intended to be used together.
If you set the load resistance to 47K, there is no real reason you cannot use a SUT with your phono preamplifier, provided, as CLeeds mentions, the phono input will not be overloaded. However, I am not sure from what you’ve written that you really need a SUT, because with 60 db gain, it is not immediately obvious to me that you do not have adequate gain for a 0.4mV cartridge output, on paper at least. (Is the "0.4mV" based on a velocity of 3.54cm/sec, the old standard, or 5cm/sec?) I’ve never heard of the Coph Nia, but perhaps you should consult the manufacturer. Be aware of the effect of the SUT on impedance, if you go down that road. Which is why I say you would want to set the input load to 47K; SUTs like to see that resistance on the secondary side. Likewise, you could also use a "head amp", assuming by that you refer to an outboard active gain stage designed to be inserted between the cartridge and the phono input. But at most, you only need a few db additional gain, if what you have seems insufficient, and if the cause can be determined to be lack of phono gain.  

Check to see if there is an impedance matching problem between the output of the Coph Nia and the passive attenuator or between the passive attenuator and your amplifier. Also, check the input sensitivity of your amplifier. (These are other causes of that "lack of gain" feeling.)

It’s defintely a lack of gain issue between the .4mV Denon and the 60dB Coph Nia, when used with the passive pre. The amp I’m using is a First Pass J2. I have plenty of gain with the passive pre when I use my DAC/CDP combo, it’s just a phono stage issue. It’s not that it won’t get loud, as I can get to about 91dB-93dB at my listening position at full throttle. But that’s just not enough with some recordings (think Zeppelin or Floyd). In most cases it’s fine, albeit I have to turn the volume knobs (it’s a dual mono passive) up quite a way.

I should’ve left off the SUT comment, as I pretty much knew I wouldn’t be able to go that route. I was more curious about a head amp with adjustable gain, since some of those can go down to a 10dB or so gain.
I would contact Rothwell also, he is very helpful and perhaps
could even mod a low output version to your requirements.

He often chimes in on technical matters on another site and
if he thinks you should go another route he will say so.



Interesting, tlarwa.  Some of the First series of Pass amplifiers, good though they are, do have a relatively high input sensitivity, which is to say that most amplifiers are driven to full output by about 1V input or less, but I think some of those First Watt designs require more input voltage.  You might look up the characteristic of the J2.  This would be no problem with the typical CDP, which puts out 2V, easily.  So it could be a combination of high-ish input sensitivity of the amplifier, marginal phono stage gain, and the fact that your system lacks the typical boost in overall gain usually provided by an active linestage.

I just looked it up; the J2 requires 1.4V for full output of 20W.  This is a rather high and fits my prediction above. You don't mention what speakers you are driving, but that would enter into the equation, as well.  If you've got 100 ohm sensitive speakers then my analysis may fall apart, since you are then using around 1-2W at most.
I've always been curious about the First Watt series; I bet the J2 is a great sounding amplifier.
By the way, if your phono can make 60db of gain, that's equivalent to a 1000-fold gain in voltage.  If the cartridge is making 0.4mV at the standard stylus velocity, the output of the phono stage is 0.4V.  With many if not most amplifiers, this would be sufficient to drive the amplifier at least close to its full output, and stylus velocity gets much higher (faster = more voltage) during musical transients.  So, I think it's the combination of factors I outlined above that leads to your sense of lack of adequate gain from the phono.
Lewm, I'm driving Klipsch Cornwalls.  My listening position is about 9 feet back.  Line I said before, I can get to the low 90's, which is typically fine.  But I'd like to have more in reserve when I need it.  I'll probably just replace the Coph Nia at some point.  There are a lot more cartridge choices in the .3-.5mV range than in the 1mV range, and I don't really want to be limited by that.  If I had a phono stage that had 66dB - 70dB (or a little more) of gain I'm sure I'd be fine.  I know there are some quality dual mono designs (which the Coph Nia is) out there that get into higher gains like that.  

The alternate cure is to use an active linestage.  That typically adds 10 to 25 db of gain, and you'd be good to go.  The Cornwalls are ultra-sensitive, to be sure.
You might even talk to Nelson Pass. He may be able to suggest a way to increase the input sensitivity of the J2.  He's always tinkering with his designs.  That would be a lot cheaper than buying a new phono stage, most likely.  In the price range where the Coph Nia once lived, you might consider the iPhono2.  For $500 it may be a bargain.