In that case, if there is a tap on the OPT to give a load match to 3
ohms, the Rout without NFB will be 1 ohm, and loads below 4ohms nominal
will be tolerated OK.

The impedence of the speakers is around 3 ohms. So as you say you
figure for a low ohm tap on the secondary. I'm getting good sound with
a PPP 6S4A amp with a nominal 8k a-a into 4 ohms, which works out just
about OK. Sounds fine. My brother uses a Nagra VPA 845 PP valve amp,
which sounds great. A friend uses a KT88 amp with feedback. That works
too. All of us have Caliper Sigs, though my friend just upgraded to
Duettas. Drool.


25Watts class AB1 is easy from 300B and if speaker sensitivity is above
88dB/W/M, sound is OK but the higher the sensitivity the better.

Apogees are what, about 85db - something like that.

What's so great about ribbons though?

Have you heard the big Apogees? They're now built down under.
http://www.apogeeacoustics.com/index.html

Are you anywhere near Queensland's "sunshine coast"?

Andy

Andy Evans wrote:

In that case, if there is a tap on the OPT to give a load match to 3
ohms, the Rout without NFB will be 1 ohm, and loads below 4ohms nominal
will be tolerated OK.

The impedence of the speakers is around 3 ohms. So as you say you
figure for a low ohm tap on the secondary. I'm getting good sound with
a PPP 6S4A amp with a nominal 8k a-a into 4 ohms, which works out just
about OK. Sounds fine. My brother uses a Nagra VPA 845 PP valve amp,
which sounds great. A friend uses a KT88 amp with feedback. That works
too. All of us have Caliper Sigs, though my friend just upgraded to
Duettas. Drool.


25Watts class AB1 is easy from 300B and if speaker sensitivity is above
88dB/W/M, sound is OK but the higher the sensitivity the better.

Apogees are what, about 85db - something like that.


With 85dB its getting a bit hard to drive and I'd like to have 50W
available....

What's so great about ribbons though?

Have you heard the big Apogees? They're now built down under.
http://www.apogeeacoustics.com/index.html

I wasn't aware of that.

There is another ribbon company, Ambience on the sth coast NSW.

Are you anywhere near Queensland's "sunshine coast"?

No, I'm in Canberra, 300km sthwest of Sydney.

I prefer really well done dynamic cones and domes.

Patrick Turner.

Andy

In article
,
Andy
Evans wrote:

In that case, if there is a tap on the OPT to give a load match to 3
ohms, the Rout without NFB will be 1 ohm, and loads below 4ohms
nominal will be tolerated OK.

The impedence of the speakers is around 3 ohms. So as you say you figure
for a low ohm tap on the secondary. I'm getting good sound with a PPP
6S4A amp with a nominal 8k a-a into 4 ohms, which works out just about
OK. Sounds fine. My brother uses a Nagra VPA 845 PP valve amp, which
sounds great. A friend uses a KT88 amp with feedback. That works too.
All of us have Caliper Sigs, though my friend just upgraded to Duettas.
Drool.


25Watts class AB1 is easy from 300B and if speaker sensitivity is
above 88dB/W/M, sound is OK but the higher the sensitivity the better.

Apogees are what, about 85db - something like that.

I suspect that may be rather 'optimistic'. :-) If you look at something
like MCs review of the Apogee Caliper in HFN (1986) he reported a 2.86V
sensitivity of just 80dB. Very different to needing 88dB or more! If my
memory isn't playing me false, some other Apogees had even lower
efficiencies and/or impedances.

If you then factor in what Patrick went over (although that wasn't the
actual point of my previous comment which actually took what he
described for granted) you may find an even lower effective sensitivity
for reasons I assume are now obvious! :-)

Slainte,

Jim

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