[Toka]

I tried searching to no avail...so no heat if its been asked before.   

Anyone know the input capacitance on the phono stage for the Ultra preamps? Looking to hit about 150-180pF total and its the only missing number I need...thanks!

[avahifi]

Actually its in the 20-40 pF range or less, just that of a few inches of the input shielded cable.

By the way, adding capacitance to get flat measured response from a phono cartridge is a bad idea.  All this does is generate a large underdamped above audio peak in the response and the nature of resonators is to resonate.  You can't hear it, but electronics and tweeters can, and they don't like it.

The whole idea is to shore up the frequency response of a cartridge that does not cut it without a big fat treble boost.  You would not buy speakers that way, why phono cartridges?

We discussed this in detail in Audio Basics many years ago.  The issues and math is still there for you to research.

One of the things we have always liked about standard Grado cartridges was that their coil inductance was so low that any resonance caused by the interaction with cable capacitance was way way out of band (about 60 KHz, and relatively minor).  Their frequency response was natural, not puffed up by a fake resonant peak.

Regards,

Frank Van Alstine

[Toka]

Thanks Frank! This is a subject I've only just started digging into...and just like you said in that Audio Basics article, I don't think reviewers (of any stature) take such things into consideration at all! Even all these years later. 

The cartridge I was looking at (Audio-Technica AT150MLX) has a coil inductance of 350mH...using the calculator on the Hagerman website http://www.hagtech.com/loading.html (and using a 'best case' total capacitance figure of 60pF...very do-able), I get a resonant freq. of 34.7kHz...would that still be considered in the 'danger zone'?

I like that cart because its affordable, tracks anything all night and day, and the micro-line stylus (which I can replace in-home) rides deep enough to make old vinyl sound new again...I had tried some lower-end Grado's in the past but couldn't deal with some tracking issues (granted, I never tried a Longhorn...). Plus, honestly, they had a bit more of a 'house' sound that I would prefer...but again, they weren't the top dogs in the line. I don't want to deal with step-up transformers or anything like that, so perhaps my choices are limited in that regard. I'm by no means 'locked' on the AT but so far it fits my needs the best of the models I've checked out thus far.

Anyway, I appreciate your input/advice on the matter! 

[avahifi]

Just ask yourself the question, "will my preamp, power amp, and tweeters like a 35kHz resonant peak dumped into them?"  I think not.

The goal, a cartridge that has wide band flat response without resorting to a high frequency peak to make it look flat, and of course a preamp that protects everything else down stream by not passing HF garbage.

Try the Longhorn bar, its free, it works.

Regards,

Frank Van Alstine

[Toka]

Thanks Frank, I'll keep looking (and try the Longhorn, of course)!

One last thing...when you say a preamp should not pass HF garbage, what would the limit be on an Ultra preamp? 60kHz? Would the high/low filter help at all with the above example? Just looking for some lines on the playing field...

[rlee8394]

I believe all AVA designs, not just the Ultra, filter out all ultrasonic and out of band garbage at the preamp input before it reaches the gain stage in the preamp. This in theory would limit the high end frequency to around 20 kHz or so. The idea is to limit the input to just the "audio frequencies" thereby keeping the rest of the crap out of your system. I think this philosophy is applied to all AVA products. Frank, correct me if I'm wrong on this.

[Toka]

Good point/question...anyone?