Alpair 7.3 Impedance Matching

[xtaljo]

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.

 

[fastbike1]

The 8 ohm tap. That impedance is the DCR for deisgn purposes and is in the typical range for 8 ohm speakers.

 

[Octavia]

And by the way - how do you like the sound of the 7.3 Frugal Horns with your flea watt amp?

 

[xtaljo]

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.

 

[Octavia]

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.

 

[scaleautoart]

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.

 

[mondogenerator]

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...

 

[scaleautoart]

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.

 

[chrisb]

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.

 

[xtaljo]

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.

 

[Octavia]

Chrisb, my place is a jungle of speakers too just not all of them with Mark's drivers. Yes those 10p's certainly have my interest too, that little dimple ala the SB tweeter design might just have the magic for me. Still awaiting spec's and design ideas. I'd love it if either the 10p or 10.3 might fit right into one of PE's curved boxes, we'll see.

 

[scaleautoart]

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.

I would think it's the recordings. I get no "edgy" vocals in my set up and I have good sources. I find the Alpairs very smooth...and I only have a bit over 50 hours on them.

 

[chrisb]

+2 on recordings likely being the culprit -

The only all metal coned widebanders that I've ever found unlistenable on any material were one of the cheap MCM 5"( or so), as implemented in some DIY Bottlehead Straight 8s - at least 10yrs ago.

Now, metal domed tweeters, or Fostex FE138ESR - that's another story

I have much more experience with the smaller Alpair metals ( 6M & 7s) than the 10s or original 12Ms - both of the former are very detailed, and definitely not as "forgiving" as the papers that I've heard ( EL70 / A6P, A12P ).