Running LOMC with MM (47K) loading

Larry,  200 ohms would be fine for most LOMC cartridges that have an internal resistance of 20 ohms or less, but there are some exceptional LOMC cartridges that have a higher internal resistance and will be affected by 200 ohms as a standard.  I think you know this, but I thought it ought to be pointed out to those who might not. By the same criterion, I don't think one can say that 125 or 150 ohms is "universal".  Once you go below a critical value, where the load R becomes much less than 10X the internal resistance of the coils, you start to roll off the top end of the frequency response and to lose signal voltage to ground.  Like you say, if the cartridge is too bright, it's best to tame it by some other method, IMO.

Pindac,  I apologize if my earlier post seemed overbearing.  I do respect that each of us has a slightly different "taste" in SQ, for want of a better phrase.  What I assumed is that your phono stage was designed to provide what we commonly think of as MM levels of gain (anywhere from 39db to less than 50db), when using an ECC83, i.e., your phono stage was designed around the ECC83 input.  I assumed or guessed that into that ECC83 input tube socket, you are now using an ECC81.  This substitution would "work", but it would not be optimal for operation of the ECC81 (too little current, mainly), and as you know, there would be a significant penalty to overall gain of the phono stage.  With such a phono stage using the ECC81, it is not at all surprising that you found it worked best with a SUT.  In fact, if my conception of your phono is correct, I am surprised it works at all with an ECC81, when you use any typical LOMC cartridge, unless there is a second gain stage following the RIAA filter section.  (I guess I also misunderstood you to say originally that you far preferred the ECC81/SUT configuration to no SUT; I now understand you to say that you like the sound both ways but that the character is different, not surprisingly.)  Anyway, unless you are using a linestage with inordinate amounts of gain, into an amplifier with very high input sensitivity for full output, driving very efficent speakers, or some combination of these, it is no wonder you need to twist the VC fully over to achieve satisfactory sound pressure levels.  So, first question, was your phono stage designed FOR the ECC81 as input tube, once you inter-acted with the designer, or for the ECC83?  For slightly less gain in an MM stage, compared to the ECC83, many people use the 5751, which pops right in to an ECC83 design and is in between the ECC83 and ECC81 in terms of gain.

Pindac, What are you saying?  Seems you are saying that if gain is insufficient, then your cartridge doesn't sound its best.  Which is almost certainly true. Clearly, the ECC81 (also known as 12AT7) substitution produced overall phono gain that was not adequate, but it would help to know what was the tube type for which the phono stage was designed. Just because it is so commonly used in phono stages, I am going to guess it was the ECC83 (also known as 12AX7).  If you did sub a ECC81 for a ECC83, it is no wonder that didn't work well.  The ECC83 has over twice the gain of an ECC81, and also the latter tube requires more plate current than an ECC83 to sound its best.  So you loaded the dice against the ECC81.  If you then added a SUT to the input of the ECC81, perhaps that worked better, because you restored the missing gain.  (I think you are also saying you run an LOMC cartridge into an MM phono stage, implying a stage with not more than 50db of gain and probably less, even when the input tube is the one for which the circuit was designed, plus or minus a SUT.) Other things, like phono input load impedance also change when you add or subtract a SUT, and that too affects SQ.

audioguy, There is nothing sacred about 47K ohms; it's become the standard for MM cartridges by default.  In fact, many have found that at least some MM and MI cartridges sound best with even less of a load, like 100K ohms.  ("Less of a load" means higher load resistance, and vice-versa.) Likewise, there is no rule that says you cannot try loading an MC cartridge very lightly, with the 47K option if your preamplifier provides for it. (In many cases, the needed gain for LOMC in a phono stage is achieved by using a SUT.  With a SUT, it may not be possible to achieve a load resistance as high as 47K, if the SUT is connected to an MM input with a 47K resistance load a priori, because of the effect of the transformer on the load seen by the cartridge.)  You noted that the manufacturer of your Hana recommends "greater than 400 ohms".  That certainly allows for ANY load R above 400 ohms. Which means there is no penalty associated with much lighter loading.  What Artemis refers to is the concept that loads much below 47K on an MC, like 400 ohms on the Hana, are mostly for the benefit of the phono stage circuit. I will let Atma-sphere or anyone else explain that in better detail. 


Wow, that's big news, to learn that the VTPH2A is out of production and not to be replaced.