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JR149 impedance plot

sergeauckland

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I'm in the process of building a pair of GEC912+ amplifiers as a 'winter project'. These are EL84 ULPP amplifiers, but the output transformers are tapped for 4 and 16 ohms. No 8 ohm tap!

I'm intending to use them with my JR149 loudspeakers which are reputed to be a 'benign' 8 ohm load, whatever that means! I'm trying to work out whether to use the 4 ohm or 16 ohm taps, as into 8 ohms, the 4 ohm tap gives me less distortion but a lot less power, whilst the 16 ohm tap gives me somewhat more power but at higher distortion. All the specification for the JR149s say is 'suitable for 4-16 ohm outputs!

I've been looking on-line for reviews of the JR149 that include an impedance plot, but haven't been able to find anything. Does anyone here know what the impedance curve of the JR149 look like, so I can attempt to match with the best output tap? I could measure the impedance myself, but that's a faff to do if it's been published somewhere, so hope someone can help.

For those who like these things, here's a photo of the underneaths of the first amp being built.

912 build.jpg


With thanks

S.
 

DDF

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Nice speakers you've got there, they were responsible for getting me into hifi in the late 70s.
Below is the test report from Popular HiFi in 1976. Jim was playing on the wild side with a dead short at 10kHz.

I completely redesigned my pair a number of years back, with instructions and test results here, pretty well received here
The redesign is a big step forward in almost every way for not too much financial outlay but it does involve drilling the cabinet and may affect resale value.
They're limited in SPL which is helped quite a bit by careful crossing to a sub, but the redesign are still my main speakers and I've never tired of them.

1668117917443.png
 
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sergeauckland

sergeauckland

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Many thanks for that, exactly the sort of information I need. I think I'll run them from the 4ohm output and see if they go loud enough. They're in my study, and I sit only 1m away, so power may not be an issue.

S
 
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