Spectral DMA-90 questions...

[john65b]

Hello all,

Read up on the Spectral DMA-90 requiring special cables to prevent oscillation and frying the output devices...can anyone confirm this to be true? I remember some of the the Naim amps needing special speaker cables, as these cables completed the Zobel circuit (?).

Anyway, if so, can anyone offer up the impedance / inductance / capacitance of the "correct" speaker cables? Would it be worthwhile to try to "match" (as best as I can) these parameters for safe operation of the amp?

 

[Nelson Pass]

If you have cables with a low characteristic impedance then you want to consider a Zobel network at the speaker end. Typical values are 10 Ohms in series with .1 uF. This damps out high frequencies reflected back to the amplifier.

 

[adason]

Perhaps you can ask Spectral about their own speaker cable. Looks like anaconda just swallowed capybara and now is digesting.
http://www.spectralaudio.com/Spectral MIT Cables/Speaker Cables/Spectral MIT Speaker Cables.htm

 

[john65b]

Ha, how often does a one of my questions get answered by an Audio Legend...sorry, no offense adason 🙂

My Quad ESL-2805 appears to have a Zobel already...

EDIT - whoops, thats not a Zobel...in parallel, and not across the outputs

EDIT EDIT - a pic of outputs with coil / resistor across output...doesn't this serve same purpose as Zobel, preventing reflected HF back to amp?

 

[huggygood]

Perhaps you can ask Spectral about their own speaker cable. Looks like anaconda just swallowed capybara and now is digesting.
http://www.spectralaudio.com/Spectral MIT Cables/Speaker Cables/Spectral MIT Speaker Cables.htm

yeah 🤣🤣🤣🤣

 

[Mark Johnson]

If you have cables with a low characteristic impedance then you want to consider a Zobel network at the speaker end.

Matthew Polk (a familiar name to diyAudio readers of a certain age) patented this Zobel network decades ago -- the patent expired pre-Y2K. He recommended 6.2 ohms in series with 0.05 microfarads. Images below.

_

 

[john65b]

Hmm, I see that writeup indicate that tube amps (with Output transformers) do not need the Zobel? I remember seeing Zobel across speaker outs in a tube amp - cannot remember which one....

 

[ALTAFIDELIDAD]

Hello, good afternoon. Can anyone provide me with a schematic for the Spectral DMA-90? Thanks in advance.
I have a lot of technical information, so if anyone needs it, please contact me.