Do I need a sut?


I purchased an Ortofon MC2000 cart from a fellow A'Goner, it is very low output .05mV, my phono pre is a Herron VTPH-2 which has 69db of gain and my pre is a Herron VTSP-3a(r02) 14db gain.
The cart sounds wonderful, but with such a low gain I have to turn up the volume by quite a lot. If I had, another source at that volume, I wouldn't be able to stand it. With the volume turned up so high I get a fair amount of noise between tracks. 
Should I be looking at an sut or just live with it the way it is? I found an Ortofon at a decent price, it has 24db of gain. Would that be ok to go into the mc input on the VTPH-2? The mm gain is 48db, if I plugged it in there I would only gain 3db(if I'm doing my math correctly) I will also be contacting Keith, but I thought I would ask here too.
Thanks
Jeff
jdodmead
Regarding the adequacy of 76 db of SUT + phono stage gain, that is 7 db more than the OP presently has. For a typical rotary volume control, which when viewed as a clock dial can be adjusted between limits of say 6:30 or 7 o’clock at min and 5 or 5:30 o’clock at max, and is used in the upper half of its range, a 7 db difference probably corresponds to a bit more than 45 degrees of rotation. For example, see the dial calibrations shown in this photo, although the photo is of an MFA passive (not active) preamp.

So **if** the volume control on the OP’s Herron preamp has similar rotational limits (approximately 6:30 or 7 o’clock and 5 or 5:30 o’clock or so) he should be able to approximately judge the effects on noise level of 7 db of additional gain by reducing the volume control setting by a bit more than 45 degrees, and seeing how that change in setting affects noise levels when no music is playing.

Also, I agree with Folkfreak that it in general it would be wise to assure that the combination of cartridge output rating, SUT gain, phono stage gain, and line stage gain is adequate to drive the power amp to full power. Even if the most power that is ever used is say half of the amp’s capability, that would only be 3 db less than full power. So if full power can’t be obtained even with the volume control at max (which is the position at which the preamp will provide its rated gain), 3 db less than full power may not be attainable at any volume control setting either. And regarding the KAB calculator, it can be important to note that the calculations of phono stage gain which it provides are based on boosting the cartridge’s rated output to only 325 mv.

Regards,
-- Al

My amps are Herron M1A mono's
Output Power150 watts @ 8 ohms, 275 watts @ 4 ohms (measurements at 1 khz)
Gain24 db
Input impedance220k Ohms

150 watts into 8 ohms corresponds to about 34.6 volts. 24 db less than that is about 2.18 volts. 2.18 volts divided by 0.05 mv is a voltage multiplication of 43,600 times, which is about 93 db.

So to be able to drive the amp to full power when the cartridge provides its rated output you need a total of 93 db of gain between the cartridge and the input to the power amp. For that to be accomplished with the MM section of the phono stage providing 48 db and the line stage preamp providing 14 db, the SUT would have to provide 31 db (or more). Exactly mid-way between the value Hdm suggested and the value Folkfreak suggested :-)

Regards,
-- Al
There are in and out ground lugs on the XG-5, would I be ok if I just went straight to the Herron phono pre with the output ground from the turntable? 

Thanks
Jeff