MC Load Resistance

Dertonarm, the use of the word 'feedback' in your posts above either has a new meaning for the term or else the term is misapplied (language issue). My theory is the latter right now.

There is an ideal loading for any inductive audio device wherein the device does not exhibit either ringing/overshoot (under-damped) or excessive rounding (overdamped).

This can be accomplished with or without a stepup transformer.

Loading can be used as a sort of tone control but is ill-advised, but sometimes very difficult to set up otherwise if the right equipment is not available (which is a 'scope and a squarewave generator). With the test equipment, the inductive device (cartridge) can be 'rung' by the square wave and the resulting waveform displayed on the scope. Without loading ringing will be observed. A load in parallel with the output of the device will cause the ringing to decrease- there will be some point where the ringing will cease altogether.

If loaded excessively, the corners of the square wave will be rounded. The debate about where critical damping lies centers around whether or not any overshoot is allowed (I tend to go for a slight amount). At this point the loading value will be only slightly higher- often the difference of only a few ohms.

A transformer can complicate the matter as the transformer can ring also. In addition, the load on the secondary will be 'transformed' by the transformer to a load on the cartridge, so if you are loading the secondary this must be taken into account. Jensen transformers has published a chart of how this is done with their transformers (they make some excellent SUTs BTW).
http://www.jensen-transformers.com/design/MC_Table.zip

Dertonarm, I'm not familiar with any MC unit that actually loads correctly at 10 ohms! I imagine that the results might sound like the application of excessive negative feedback, but it is *not* in fact feedback.

Even though the Jensen transformers are some of the best (we offer then as an option), I've yet to hear a situation where they actually sound *better* in all regards. Usually, they help a lot with noise, but the best I've heard over the years, time and time again, they rob the signal of detail and 'air', as well as bass impact.

The exception to that is if the MC signal by itself is too low for the phono stage, then the transformer is a benefit; actually *adding* impact, reducing noise (and thus revealing detail). So from your posts above, is it simply that the phono section you are using falls into that category?

Allen, a peak past 'audibility' will have effects not unlike a tube without grid stoppers, exhibiting oscillation; IOW it can behave as if there is excessive ultrasonic energy. This can cause some preamps (not all) to exhibit excessive ticks and pops (in addition to brightness), due to the various instabilities introduced. The effect on the cartridge is easily measured, and without loading often there is more 'air' but when you examine it on the scope you will find that the 'air' is mostly just ringing (distortion).

This is why critical damping is such a nice value to achieve- you get out the the transducer just the signal, without additional 'commentary'. I suspect many cartridge distributors don't listen to any cartridge for very long so it might be that they don't bother, but they are simply missing bet, that's all.

Lewm, FWIW in working with the Jensens we notice more degradation when they are set for the higher stepup ratios and almost none at the lowest stepup. (Jensens have multiple windings that allow a variety of combinations for different stepup ratios.) The lowest possible is usually sufficient for most preamps (1:4). While I don't agree with Dertonearm (the effects of the transformer degradation are easily heard, at least on our gear), his recommendations otherwise corroborate what we have found.

A slight bit closer to topic... Dertonearm, your description of the difference between hybrid and all-tube cascode is very similar to how I would have described it.

There are a number of manufacturers that use semiconductors right at the input of their otherwise 'all tube' preamps. I feel they loose that last bit of natural detail, so I go for the tubes, although there is a little more noise. Despite that, I win back the detail that the semiconductors seem to loose.

In the last 2 years, we added a new CCS circuit that is able reject noise from the power supply while maintaining precise current for the differential cascode gain stage. This reduced noise, increased bandwidth, increased gain and reduced distortion all at once. The RIAA spec works out to 0.15mV; so with good tubes in the unit I've found no need for transformers.

We have offered the Jensen SUT as an option for years, but with the introduction of this circuit no-one has installed that option. We do run into noise issues on occasion- we have found that the vast majority of NOS tubes (that occasionally get installed by end users) are simply not quiet enough to do the job. However there is an ample supply of new tubes.

I have yet to find a transformer of any variety or application that does not have a sonic footprint, be it SUT, line, interstage or output. There are of course advantages- gain and isolation being two, but if a simple circuit can be devised to bypass the need for a transformer, then greater transparency is the immediate reward.

From a previous post I am asked to assume that you have one of the most neutral systems in the world; however I exhort you to consider that if you have heard a particular piece by a particular manufacturer, please keep in mind that we manufacturers are often doing our best to make improvements over the years and are often quite successful at that. So you would be doing any manufacturer and yourself a disfavor by 'assuming' that since you heard a unit five or ten years ago, that you thus 'know' what that product sounds like today.