Alpair 7.3 Impedance Matching - diyAudio
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Old 8th May 2013, 10:36 AM   #1
xtaljo is offline xtaljo  United Kingdom
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Default Alpair 7.3 Impedance Matching

I have Alpair 7.3s drivers in Frugal-Horn 3 enclosures powered by a pair of diy SE (Mullard) valve amps (3.5 watts per channel). Should the Alpair 7.3s be connected to the 4 or 8 ohms taps on the output transformers? The published impedance of the Alpairs is 5.4 ohms.

The present connection is to the 8 ohm tap and switching to 4 ohms will be a re-soldering job.

Sorry if this has been covered before.
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Old 8th May 2013, 02:31 PM   #2
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The 8 ohm tap. That impedance is the DCR for deisgn purposes and is in the typical range for 8 ohm speakers.
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Old 8th May 2013, 02:36 PM   #3
Octavia is offline Octavia  United States
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And by the way - how do you like the sound of the 7.3 Frugal Horns with your flea watt amp?
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Old 8th May 2013, 03:36 PM   #4
xtaljo is offline xtaljo  United Kingdom
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My Mullard 3+3s are very sensitive and would not take kindly to being described as 'flea watt'!!!

Seriously they sound great and there is plenty of power for a medium sized room (15' x 17'). On some vocals they are almost too bright for my (ancient) ears but superb for chamber music, piano etc.

Glad 8 ohms is right the iron can stay in the cupboard. Many thanks.
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Old 8th May 2013, 03:53 PM   #5
Octavia is offline Octavia  United States
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Great to know. I've been looking at some low powered single ended EL84 amps. A friend bought the Tecon (alas out of production now) marvelous sounding amp really.
I am seriously thinking of trying something similar with one of the Alpairs. Just not sure if it will be one of the 7.3's or possibly the 10.3 or 10p. And then there is the question of the frugal horn or something else. Decisions, decisions.
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Old 8th May 2013, 04:54 PM   #6
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Along these same lines I switched my Jolida 202BRC over from the 8 ohm to 4 ohm setting driving the Alpair 7's

I thought it was OK to drive 8 ohm off a 4 ohm setting but not the other way around. It could be me but I detect an improvement on 4 ohm.
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Old 8th May 2013, 05:40 PM   #7
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if i recall, it is ok to use a lower tap but not a higher tap. Something to do with giving a more gradual curve into overdrive, rather than a sharp transition. It works for guitar amps...
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Old 8th May 2013, 06:34 PM   #8
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Again, from what I understand/read the amp will work much harder if it is 8 ohms driving a 4 ohm speaker and 4 ohms to an 8 ohm speaker will see less resistance.
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Old 8th May 2013, 06:54 PM   #9
chrisb is offline chrisb  Canada
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xtaljo - how many hours playing time on the drivers? It has certainly been mentioned before, but they don't fully open-up / settle in until after at least several hundred

Octavia - save yourself the dilemma of decision making, and build one of every design available at the time for all the drivers you have in mind.

I'm only half kidding - as the combination of my and Dave's living rooms demonstrates, it sometimes feels like I've taken that approach myself.

Seriously, I'd be inclined to await the 10P and further down the road, the 8s. As big a fan as I am of Mark's metals, there's something about paper. If the 12Ps didn't need such impractically large boxes for my situation, I'd have pulled the trigger on those already - but even the MarKen12T is larger than I could get away with.
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Old 9th May 2013, 07:28 AM   #10
xtaljo is offline xtaljo  United Kingdom
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Chrisb - I ran the Alpair 7.3s for several hundred hours at low volumes and I have now had them about 5 months, I should think they are well run in now.

I wonder if the the slightly edgy vocals I sometimes hear are due to poor recordings and/or this might be a feature of metal cones. Using the -6db limiter on Foobar software helps considerably and so to a lesser extent does a notch filter centred on about 2.5KHz using the Foobar equalizer. Others might find the 'brightness' attractive. The issue is most acute when playing CDs (on an
Audiolab 8200). Use of the sharp roll off filter on the Audiolab produces a very slight softening of tone.
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