by Bob Latino Thu Aug 20, 2009 4:14 pm
Kevco,
The ST-70 II just never caught on like the original 70 did. Maybe by 1990 audiophiles were too into solid state amps or maybe, as the reviewer mentioned, the sound quality just didn't have the "magic" of the original 70. At the end of the review he mentions that he "really can't recommend the Panor (ST-70 II)".
One of the reason's is that the driver circuit is similar to the old 70 but uses a 6GH8A pentode/triode in place of the 7199 found on the original '70. The sound quality is about the same as the 7199 but the 6GH8A is more easily sourced than the now "extinct" 7199 tube.
Another issue I have with this amp is that they use bandwidth limiting filters on the input to reduce the overall bandwidth in an attempt to counteract non linearities in the design of the driver circuit. In other words because the driver circuit can't respond properly to very low and very high frequencies at high volume levels - well Jeez - we'll just filter those frequencies out ! When you use an RC filter system, as is done on this amp, you introduce phase irregularities into the amp. This will usually translate into reduced soundstage depth and width and hazy placement of individual instruments in the soundstage.
Rather than deal with the compromises in the ST-70 II, you are better off to pick up an original ST-70 and simply replace the driver board with a high quality modern all triode design driver board like the VTA driver board. This driver board is flat from 17 Hz to 30,000 Hz at rated output and doesn't resort to the use of bandwidth limiting filters.
Bob