2. analog
  3. 130529-1790

Can stepup transformer be used with an MC phono stage?

I just purchased an Electron Images MCP-1 phono preamp and it seems to be a VERY good phono preamp;  however, I'm realizing it doesn't have enough gain for my .2 mV output Dynavector.  Doing a little more research, it seems that the MCP-1 works well for cartridges down to .5mV of output.  Could I use a stepup transformer between my cartridge and the MC phono input of the MCP-1 without causing any damage to the phono preamp or other equipment in my system?  If so, what specifications should I be looking for in a stepup transformer?

Thanks in response for any responses and advice.
wcheng2
lewm
13,398 posts
 
Let's see: You added to my information by guessing at the value of the input resistor installed in the OP's particular product.  Your guess of 47K is one of the possibilities entertained in my post.  After that, everything you wrote is in agreement with my advice.  Yet you manage to be insulting despite all of that.  You're true to form.
wcheng2 OP
40 posts
 
Guys...thanks for your responses;  both are very helpful.  The input impedance should be 47k or open since the unit uses RCA loading plugs for load.  I have been listening to the Electron Images phono stage with my .2 mV output (6 ohms internal impedance) Dynavector DRT XV-1s cartridge.  It does work; however, I have to turn the volume on my preamp to about 3/4 of full output to get satisfying volume.  It also seems that the dynamics and bass are somewhat muted, which I think makes me want to turn the volume up even more.  With another phono preamp that had 55 dB of gain, I was at about 1/2 of full output to get satisfying volume and dynamics, so my assumption is that the Electron Images must be  55 dB or lower.  Let's say it is 50 dB...if I used a stepup tranny of 1:10, I think the gain would be 14 dB...so 14 + 50 = 64, which I assume shouldn't cause problems since I see many phono preamps with over 70 dB of gain.  And I would likely be okay with loading since 10 squared = 100 and 47,000/100 would be 470 ohms.  Am I way off base with my math?  I'm also wondering if I could use some kind of loading resistor in the RCA plug to bring the 470 ohms down to 100 ohms...
lewm
13,398 posts
 
Your math is good, and I'd say go for it. But you might want to double check on the load resistor value.  I do agree that the fact you have an RCA jack dedicated to adding an external load resistor suggests that the fixed value one is 47K.  Or "open".  You do want to know if it's open. Does the owners manual help?  Or just measure it.
tomwh
150 posts
 
Lundal has a sut that can run 5 /10/20 to 1.  If the loading plug thing is correct and you measure zero you have the cat by the tail.  Now you can do the easy math and try all kinds of values around the so called optimum value.

If you do not diy you can get ahold of the information from the manufacturer.  If you have the gain of the amp plus the load someone can get you into the ballpark.  If you try it without a sut and it sounds less than dynamic I would get a sut.

Enjoy the ride
Tom

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