Does my phono stage have sufficient gain?

I am considering a ZYX UNIverse for my Granham Phantom Mkii/VPI TNT Mk IV rig. I use the EAR MC-4 SUT with a tube phono stage run in MM mode. I would prefer the LOMC UNIverse at 0.24mV output and 4 ohm internal impedance from what I have heard and read.

Do I have enough gain? Here my reasoning:

* EAR MC-4 SUT has four taps. Using the 3 ohm tap is 30x input or 7.2mV; I have been told that each 10x of an SUT roughly equates to 20 dB, so 30x equals 60 dB??? There is a 6 ohm tap at 24x (or 48 db???)
* The MM mode of my tube phone stage provides 37 dB gain
* My line stage using XLR out is 18 dB

Am I thinking clearly?

Hi Brent,

That's not quite correct. A 10x increase in voltage does equate to 20db, but an additional 10x increase would correspond to an overall increase of 100x, which in turn would correspond to an additional 20db, making 40db in total. 60db corresponds to a voltage gain of 1000. So the 10x increases you are referring to are multiplied in terms of voltage, but added in terms of db.

Voltage ratios convert to db based on the formula 20log(V1/V2).

In this case the 3 ohm tap of the SUT, providing 30x voltage gain, would provide a gain of 20log30 = 29.5db. The phono stage provides 37db, and the line stage 18db. So the total gain ahead of the power amp is 84.5db, or 16,788x, resulting in 16,788 x 0.24 mv = just over 4 volts, into what I presume is the balanced input of your power amp. That's probably ok, assuming your power amp's sensitivity is not highly unusual, but hopefully the power amp sensitivity is specified to require significantly less than 4 volts input to reach its full output power, or else you might find yourself having to operate the volume control closer to its maximum setting than is preferable.

Of course as we've discussed in other threads your choice of SUT gain will also be a factor in the load impedance that the cartridge sees.

The other thing to consider is the possibility of having too much gain, and consequently overloading either the phono stage or the preamp input circuits. I'm just about certain that won't be a problem even with a 30x stepup, but it's probably worth checking against the overload specs for the phono stage output and the preamp input. 37db gain applied to 7.2mv results in 0.5 volts at the phono stage output and the line stage input.

Overloading of the line stage output and the power amp input certainly will not occur, because those points are "after" the volume control.

Best regards,
-- Al
As always Al, thanks for the education.

ZYX did not use the industry standard test record when they measured that .24mv output spec. A LO ZYX's output using the industry standard record is ~1.41x higher, so ~.34mv.

Redoing the calculation above for .~34mv yields ~5.7 volts before the power amp inputs, which presumably is sufficient.

Whether the 3 ohm tap on the EAR will provide a suitable impedance for a LO UNIverse is a whole other question. If not, frequency balance in the highs may be off.

More generally, the EAR and Sonic Frontiers phono and line stages are not really capable of reproducing everything a UNIverse will send them. Not saying it won't sound great, it probably will, but be aware that you'll still be missing quite a bit. To that extent this is a slightly risky choice of upgrades.

OTOH, the remaining UNIVerses are such a bargain it's hard to resist, even though upgrading your phono and line amplification before attempting a top tier cartridge would normally be preferable. But top tier phono and line amplification would cost at least 3X the price of a UNIverse, so this might be a good time to break that "rule".

Thanx, Dougdeacon. Ths impedance issue is a concern. Using the 3 ohm tap on the MC-4 and the stock 47.7K ohm impedance of my phono stage, the load impedance would be about 53 ohms = 47,700/(30^2) - low for the UNIverse. Might not be a good fit.

I appreciate the advice and candor. My Sonic Frontiers phono stage has been completely re-built by Bill Thalmann and the EAR MC-4 is a well-regarded SUT, or at least I thought. While I am fairly pleased with the results of this combo, I will certainly consider your thoughts. My Clearaudio Stradivari was slightly less than the UNIverse, but not by much.

The Sonic Frontiers Line 3 line stage comment did surprise me a bit. I have never had anyone suggest upgrading the Line 3 unless I had $10k plus on hand. I sent it back to Chris Johnson for a comprehensive update and mod using premium parts, so we are not talking a stock, 10 year old unit. Obviously, I like the SF sound and I thought a Line 3 was a well-regarded line stage - able to hold its own with most line stages out there. My "price of admission" to a top-tier line stage was reduced by buying a cream puff unit used and using Chris to mod.

Again, I appreciate your candor.

It sounds like you might get by with using the 24:1 tap, which would give the ZYX a more favorable (i.e., higher) input impedance. Failing that you can replace the load resistance on the SUT secondary (the 47K resistor in parallel with phono input) with a larger value one. If you go to 100K ohms, your cartridge will see about 100R via the 30:1 taps, which is at least in a better ballpark. (I don't know what is considered ideal for the LO ZYX.) The point is that you have more flexibility than you realize. Any typical amplifier will have an input sensitivity for full output of less than 2V. Of course, there are exceptions.
I missed the fact that you've had your SF gear upgraded. Very sorry. Of course I withdraw everything I said about it since I haven't heard yours. Higher quality caps and power supply improvements would, IME with other preamps, make a dramatic difference.

That said, $10K+ is indeed the price of admission to the 2 or 3 best phono/line stages I've heard, and even that doesn't necessarily get you there. Not that you need to spend more, I just meant that I've heard many $10K and even $20K preamps that DON'T get you there. Your buy quality used and upgrade path makes great sense to me.

Unfortunately, with SUT's, about the only way to know if a particular LOMC will mate well is to try. You could always adust impedance with resistors either on the primary, the secondary or both. That's a lengthy process needing many resistors of many types to find the optimal setup. Been there, did that, much prefer the ease and sound quality from my high gain LOMC section. YMMV of course, especially with something as complex as impedance matching with an SUT.
Thanks, Dougdeacon. I hope I didn't sound "prickly" in my response. I ALWAYS like critical input - only way to improve.

Yes, Bill Thalmann and Chris Johnson did wonderful work: completely re-wired with Teflon di-electric solid core Ag, Teflon V-caps, re-built the PS and the rectification, NOS Mullards, Mills hand wound resistors - I could go on.

Modding is very controversial. I am a fan - buy a well-regarded cream puff unit used and have the mod work done by a well-established pro. This brings the price of admission to top flight gear down quite a bit. Now, I understand that I will likely loose the mod investment IF I sell - a big if. But, even if I sell, there is no way I could have had this level of gear in my system for my budget.

Bill in particular is SOOO knowledgeable about tube equipment. I simply could not believe the sound of the phono stage after I got it back.

Chris Johnson even keeps enhancing the proprietary parts found within his Line series of line stages and Power series of amps - the last series of line stages and amps SF made prior to selling the company to Paradigm. So, for example, inside my Line 3 audio unit, the remote control and the selector button "chips" in the unit were replaced. In addition, there are three separate, independent power supplies with three separate transformers in the PS unit of the Line 3: one for left, one for right and one for the "housekeeping" functions, such as input selection, LEDs, remote control, etc. Each was seprately re-built.

The downside of my phono stage mod IMHO is the lack of flexibility - I cannot easily change impendance by simply moving a knob or a dial like the Manley Steelhead or EAR 324. My EAR MC-4 does require careful matching and the UNIverse may not be a viable candidate. My Strat is a great match and if I wanted to move to the Lyra line (which I heard is wonderful with a Phantom), the Skala and Titan appear solid, as well.

Anyway, I do appreciate the candor - good listening.