One of Spectral's claims to fame is the very wide audio bandwidth of their components
chuck03054@yahoo.com -- Sun, 02/22/2009 - 15:53
One of Spectral's claims to fame is the very wide audio bandwidth of their components, which is of course good for phase and transient response. However, the repeated Spectral warnings of circuit instability when connected through anything other than MIT "network" cables seem counterintuitive to me. So what is the point of designing wide bandwidth circuits with insufficient gain/phase stability margins only to have them "stabilized" by low pass/bandpass filtered cables like those offered by MIT or Transparent cable? Isn't that a bit disingenuous ?
I've heard Spectral amplifiers before and they were truly peerless and represent the creme de la creme in HighEnd audio. However, less than candid and truthful marketing will hurt their business in the long run.
Petre
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Spectral is probably among the least marketing-driven audio companies out there.
But I think the purpose of advocating MIT is a) that Spectral knows MIT works and b) Spectral is trying to have users avoid cables that actively introduce rf into the system (i.e. antennae).
Spectral is not just "among the least marketing-driven audio companies" it is absolutely the least marketing-driven audio company. My understanding is that they use very high-speed circuits (3MHz) to maximize certain performance attributes of the circuits, particularly transient behavior. This includes not just slew rate (how fast it can swing a voltage, measured in volts per microsecond), but how quickly the circuit "recovers" after amplifying a transient signal. The audio transient heats the transistor and it takes a finite time for the transistor to return to its nominal temperature. Spectral calls this a "thermal tail," a time during which the transistor's characteristics change and affects the sound.
Another reason Spectral recommends MIT cable is that the consider an audio system a single piece of engineering that happens to reside in several chassis. The interface between those components shouldn't be left to chance, in their view.
See my review with Spectral's Richard Fryer and Keith Johnson in the February, 2009 issue for more on their design approach.
Hi Robert,
Thank you for your reply.
MIT and Transparent cables use filters ( probably all pass together with low pass filters ) in their cable designs.
The stated need for Spectral to operate without going into "potential" oscillations
only with "networked" cables implies that their amplifiers need their bandwidths to be reduced by these
cables. Wouldn't that defeat the purpose of using wide bandwidth circuit design only to have it
throttled back by bandwidth limiting cables?
I recall Harry Pearson's previous review of Spectral amplifiers where he was very nervous of mating them
with Nordost cables, which are very widebandwidth designs, the polar opposite of narrow bandwidth
MIT and Transparent. offerings.
( I own both MIT and Nordost cables myself )
With regards,
Petre
Spectral amplifiers do not have the common output inductor that helps prevent oscillations, that being left to the network in the cable, so it will be "closer" to the load - whatever that buys Spectral. As such, I feel HP's position back then in 2000 was simply wrong, as was his friend's from which he borrowed the amps. As far as interconnects go, the amps do not feature the common input choke either, that being left to the cable again. If you look at it from a system-design point of view, all the necessary parts are there, just in different places, and considering that research shows that spectra of certain musical instruments extend up to at least 102kHz (http://www.its.caltech.edu/~boyk/spectra/spectra.htm), limiting bandwidth to 800kHz with the filters leaves plenty of room for phase interactions, while still protecting the circuitry... Then again, I am not an engineer...
Thank you very much for such an insightful explanations.
Thank you very much for such an insightful explanation.
Thank you very much for such an insightful explanation.
If I am not mistaken, I think MIT cables used to be manufactured by the Transparent people before they had a fall out and Transparent was formed as a separate entity.
In the Manufacturer comments, Bruce Brisson does take a swipe at Nordost "Cables that are advertised as being fast .. are the worst offenders when it comes to these series-resonance problems .."
I suppose different philosophies here and a different set of compromises.
I use both Nordost and Transparent in my own system