Active FETs vs. Step-up phono stage designs

Dan_ed,
Everyone's opinion is more than welcomed :)
Your comment about optimization is one of the issues that I was thinking of as well. It seemed to me it would pose a bit of a challenge in designing a phono stage that utilized step-up transformers rather than FETs.

I have it from a good source that Fremer's review of the Chinook is coming out, I believe, in the next issue of Stereophile. It should be an interesting read.

One challenge facing designers who wish to use solid state these days is the rapidly dissappearing discrete transistor. Good low noise parts (both bipolar and FET) are becoming harder and harder to find, because the mass market electronics industry is moving to integrated circuits soley. That means OP amps at the minimum, with other mass market parts incorporating analog audio into LSI and VLSI parts. I-Phones, I-pads, MP3 players have no need of discrete semis. If there is no volume or demand, there is no product. High end audio demand is not even on the map.

I have trying to procure a discrete transistor hybrid class A operational amplifier that is used in the professional microphone amp industry. The manufacturer tells me the parts he has used as low noise input transistors have been discontinued by the manufacturers so he is scrambling to find replacements.

Ironicly, a technology long considered obsolete (tubes) seems to have better support from a parts perspective than discrete semis.

I am a solid state biased designer, as I don't care for coupling caps and transformers in the audio chain if they can be avoided.

Dear DHL, The late Allen Wright told me much the same thing about the scarcity of high quality discrete transistors that he experienced in building his two phono stages, FPV and RTP. I was implementing a hybrid dual differential cascode input stage in my own phono stage, and AW advised me to try the MAT02 bipolar for the bottom active element in the cascode. With some effort I finally found some, and I bought a bunch, just in case. But when I asked AW why he was not using that part in the RTP3C (or whatever), he said he could not afford to risk it because of the difficulty in obtaining a stockpile for production and future repairs. The MAT02 had already been discontinued at that time. As I understand it opamps and other ICs are also constantly being discontinued in favor of newer types that offer some real or imagined advantage.

Lewm:

I think that part MAT02 is the same part I was refering to. As the older analog device producers get aquired by larger companies, many of these parts get lost in the shuffle, unless the customer starts screaming. Couple that with the fact that fabs for discretes are becoming more expensive to maintain...not even the Chinese want to make discretes. Large power transistors are still available, but small signal are getting tougher to find.

Suprisingly, many of the early op amps are still available, probably due to replacement requirements in military and industrial equipment. All the late 70's TL070 and 080 series are still with us, as are the the very first 741s. But special parts from Burr Brown and PMI have dissappeared.

The MAT02 certainly lives up to AW's opinion of it in the context of my preamp. I have two extra pairs, just in case. (As you know, the MAT02 is a dual section device, so one of them suffices for each balanced channel, and the section matching in terms of transconductance, etc, is way better than one could hope for in a dual section tube, plus it stays that way over time.) Everything else downstream is tubes.