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Resolving power.

Posted by Al Sekela (A) on November 14, 2006 at 17:44:52

In Reply to: Ping Al Sekela posted by CometCKO on November 13, 2006 at 08:04:38:

This is an area where there are vast differences in audio components, but no convenient specification. The usual specs such as signal-to-noise ratio do not address the amp's ability to resolve the finest details present in the input signal with real-world speakers.

Resolving power is limited by a number of different design and construction issues. Mechanical vibration is an obvious one. Crossover distortion is present in any linear amp that gets in to Class B operation. Sometimes the distortion is disguised as a subtle degradation in output impedance as the output voltage crosses zero. The details of the feedback scheme are important in how this manifests itself. Even the mechanical construction of things like resistors can affect the resolving power of the amp.

The InnerSound amp is Class A-B, but runs at very low standby power. This means it goes into Class B operation after the signal exceeds a couple of watts. I believe this is the primary limiter of resolution in the amp once the obvious chassis vibration issues have been addressed. The Gilmore amps have much better resolving power than even the tweaked InnerSound, and produce better bass with Maggies as well.

I've also heard the Gilmore amps on Horning Alkibiades and Dali Helicon 800 speakers, which are 99- and 89-dB efficient (respectively), cone-driver box speakers. Both systems sounded better with the Gilmores than with their existing tube / SS amps. Resolution was better in both cases.

Also, be aware that the amp is single-ended inside. The XLR connectors are there for convenience, as the input impedances on the two phases are not the same. Pin 2 to pin 1 is high impedance, but pin 3 to pin 1 is lower. This will degrade the performance of any truly balanced source. If you use single-ended source then you should be OK. The InnerSound is a good amp at the used amp price level, but is not competitive with the Gilmores at the new prices.

If you are buying a late production Mark I, be sure to check the dropping resistor for the front panel pilot lamp. It is to the left of center at the front of the main circuit board visible when you take the top off (with front of amp facing you). Some amps were made with under-sized resistors and have charred circuit boards under the resistor. Be sure the charring does not extend to the B+ area on the board if you find it, and replace the resistor with a larger one.

This post is made possible by the generous support of people like you and our sponsors:

Kimber Kable

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