Spectral input impedance and MIT IC impedance switch?

[acousticsguru]

This is my first post on this forum, please be kind!

I have little doubt this has been discussed before, but I was unable to find the answer via Advanced Search:

Has anyone ever measured their Spectral power amp's input impedance? I was told (= straight from the horse's mouth) they're all the same. In other words, they're all supposed to be 10k?. However, according to independent measurements (e.g. German audio magazine reviews) the input impedances vary from model to model (e.g. 35k? for the 200S, 101k? for the 100S etc.).

I own Spectral amps from different generations (including Class A, i.e. reaching way back), and am currently experimenting with the impedance switch of the MIT Oracle Matrix 50 interconnect (why anyone would say it sounds "lean" is a mystery to me, by the way, and mine's only been burned in for 100 hours so far).

To cut a long story short: I'd be curious to hear what impedance settings fellow Spectral users prefer in their system? My guess is, since audiophiles are a curious bunch, setting it to "Low" without even trying the other options is a no-go, especially since it's partly a matter of system synergy, and no doubt also personal taste/preference.

So, what conclusions have you reached for your system?

Greetings from Switzerland, David.

 

[zztop7]

Greetings to Switzerland,
Just a greetings & welcome; do not have your component answers.

zz.

 

[ack]

Welcome. Best to call the factory. I don't think anyone has but what's in the manuals and web site. It's also "questionable" how the magazines measure impedance - any details?

 

[acousticsguru]

Greetings to Switzerland,
Just a greetings & welcome; do not have your component answers.

zz.

Thanks for the welcome! Must admit I'm confused by the latter, sorry to say I'm not a native speaker.

Welcome. Best to call the factory. I don't think anyone has but what's in the manuals and web site. It's also "questionable" how the magazines measure impedance - any details?

Thanks! The factory is whom I was referring to ("straight from the horse's mouth"). As to those audio magazines, no details on how they measure.

Regarding my other question, I seem to remember (browsing via the Search engine) you're using the same interconnect, if memory serves with a DMA-260S (again, e.g. Hifi&Records measures 35 versus the official 10 kOhms) - have you tried setting the impedance to something other than "Low"?

(Having said that, both the official and independent measuring are covered by MIT's "Low" setting, and I know the amp, presumably "Low" is what sounds best regardless.)

Greetings from Switzerland, David.

 

[ack]

Don't forget, Spectral had those "Universal" versions of amps, usually marked with an 'S', but not all- marked as such were (e.g. the 150S was, as was the 160S; and perhaps the 250S ??? not sure about 200S) - and they had in fact higher input impedance to make them compatible with more preamp choices. So perhaps both Spectral and the magazines are correct, and the only difference would be in the question you asked of Spectral. I think the truth is really in the manuals; for example, my 360s claim a 10kohm impedance, but the 200S clearly says: Impedance: 10K in parallel with 100pF - that makes a huge difference of what the actual overall impedance is. Therefore, again, I would question what and how the magazines measure, including that perhaps they may have not paid close attention to the finely-written manual (aka RTFM )

 

[acousticsguru]

Don't forget, Spectral had those "Universal" versions of amps, usually marked with an 'S', but not all- marked as such were (e.g. the 150S was, as was the 160S; and perhaps the 250S ??? not sure about 200S) - and they had in fact higher input impedance to make them compatible with more preamp choices. So perhaps both Spectral and the magazines are correct, and the only difference would be in the question you asked of Spectral. I think the truth is really in the manuals; for example, my 360s claim a 10kohm impedance, but the 200S clearly says: Impedance: 10K in parallel with 100pF - that makes a huge difference of what the actual overall impedance is. Therefore, again, I would question what and how the magazines measure, including that perhaps they may have not paid close attention to the finely-written manual (aka RTFM )

I believe you mean the so-called "Studio Universal" models (nothing to do with the "S" behind the number, note "Studio Universal" is always marked in large letters on the front plate, if not illuminated). Can't speak for those as I have never seen (except on pics) nor auditioned one. There were Studio Universal versions of the DMA-150S, the DMA-160 and the DMA-250S that I know of for sure. Very few Studio Universals have made it to Europe, so few that I wondered at one time whether they're exclusive to the U.S. market. I have never seen one of them reviewed anywhere, certainly not in German audio magazines, where there have only been a handful Spectral reviews in total that I know of in the last thirty years. I've always been curious how Studio Universal versions compare to the respective standard models (my former Spectral dealer claimed they're no good, but I doubt he's ever seen nor tried one). Are Studio Universal Spectrals such a niche product in the U.S., too?

As to "RTFM", I can only guess when it comes to professional reviewers. What I do know is that it's against the professional honor of electronics engineers to ever consult, let alone read a manual.

Greetings from Switzerland, David.

 

[acousticsguru]

One thing I can add to this discussion (short of answering my own question) is that not all my Spectral amps sound right with the "Low" setting on the Oracle Matrix 50 impedance switch. Needless to say, this only confirms my suspicion that the input impedance cannot be identical for all models. But still investigating the matter, no interest in spreading rumors. Just to say, the switch is proving more useful than I'd anticipated.

Greetings from Switzerland, David.

 

[ack]

Well informed dealers explain this weird naming and numbering scheme with Studio Universal amps best. For example, take a look at http://www.goodwinshighend.com/manufacturers/spectral_audio/spectral_audio2.htm and you will see the following (notice the universal 150S, 160S, 360S and 250S amps - these were only "universal" versions, their counterparts didn't have the 'S'; and moreover, there are S versions of other amps, like the 100S, not branded as universal):

[h=4]Ø DMA-100S stereo power amplifier[/h] [h=4]Ø DMA-150 stereo power amplifier[/h] [h=4]Ø DMA-150 Series II stereo power amplifier[/h] [h=4]Ø DMA-150S Universal stereo power amplifier[/h] [h=4]Ø DMA-180 stereo power amplifier (1992)[/h] [h=4]Ø DMA-180 Series II stereo power amplifier[/h] [h=4]Ø DMA-360 mono power amplifier (1999)[/h] [h=4]Ø DMA-360S Universal mono power amplifier[/h] Ø DMA-160S Universal stereo power amplifier

Ø DMA-250 power stereo amplifier
Ø DMA-250S Universal stereo power amplifier
Ø DMA-100S Series 2 stereo power amplifier



Another example is http://www.spectralaudio.com/dma-160s.htm (and you won't find a non-universal 160S).

They were all allegedly inferior and were primarily sold for home theater systems. They have long been discontinued, and I hear for good.

 

[acousticsguru]

They were all allegedly inferior and were primarily sold for home theater systems. They have long been discontinued, and I hear for good.

Good to know, thanks! - I'd considered buying a Studio Universal as "work tool", if I'd ever come across a reasonably priced 230 VAC model (which, as mentioned earlier, I never have).

Greetings from Switzerland, David.