Goodmans Magnum and the Valve sound... - diyAudio
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Goodmans Magnum and the Valve sound...

Posted 30th September 2013 at 11:07 PM by hbc

To try to recreate the Magister experience I hooked up the Magnums to the little ECL86 amp mentioned previously. I was greeted again with enormous deep bass, but not as happy over all, a rather lumpy frequency response, and a big question, what's going on... So I hooked up my Hybrid amp and the Magnums sounded a bit more normal, but the bass was considerably reigned in, disappointingly.

I think the Magnums like being back against the wall, they seem happy there and the in room response is now quite civilised with a nice boom free sound and bass is only there when it should be.

Still confused, had the ECL86 on the bench to measure to try and find out what's up. The frequency response looks a bit rolled off to the bottom, so no help there, but the treble peak is looking quite promising, explaining the "prominent" treble. After some wriggling the little amp surrendered its output impedance, all be it with significant 50Hz artefacts.

The output impedance is mostly around 1.5 ohms, but below 80Hz starts rising up reaching over 60ohms at 20Hz.

So there it is, Speaker impedance interacting with feedback and output impedance. So the moral of this story, don't be fooled by the flat frequency amplitude response.

I am tempted to try tweaking the little amp to try to calm it down a little, but then again.

Images:

all scales are approximate,

Magnum frequency response driven by gain clone.
Magnum frequency response driven by ECL86 record player amp.
Magnum impedance plot.
ECL86 amp Amplitude response.
ECL86 amp output impedance.
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