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Old 29th June 2004, 01:38 PM   #1
diyAudio Member
Join Date: Dec 2003
Location: brussels
Default 2a3 or otl on an fullrange coral

hello guys, it's me again,

still haven't made up my mind,
soon i will have an coral flat8 or maybe a beta8

i'm gonna build an amp. Now what is best ?
i don't need a lot of juice, since the driver is 95db/m and i live as a student in a very small place and don't like loud music (for example mahler symphony doesn't has to be realistic loud, otherwise the neighbours go crazy)

So if power is not an issue, with 4 watt i can go, (or otherwise an pp2a3 if ineed more) ; the otl : power won't be a problem, but i don't want it to use as a central heating, so not to much tubes in the endstage. i think of an 6c33; otl amps are said to be good if there is only an resister load, and the absent of filters, well that's what i'm gonna build. I also skip the expensive transfo's

any comments guys
(i have red the large otl archieves: good god a lot of info)
thanx already guys
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Old 29th June 2004, 11:57 PM   #2
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Join Date: Aug 2002
Location: Belgium

Re OTL, I'm afraid that when all is said and done they'll end up being even more expensive than a SE (probably) or PP 2A3 (most likely).

Before you know it you'll have at least 25W of music power from a OTL but the heaters of the power tubes are still going to make the meter run like crazy.
Let's face it, OTLs just are about the least efficient tube amps you can think of.

A 2A3 can be had for about the same price as a 6C33 but you'll need two of each per channel for PP.

A PP 2A3 would be my choice for your speakers and budget as they're actually "easier" to do right than a SE would be IMO.
They'd also be alot cheaper to run than any PP OTL of comparable output power and the OPT for a PP 2A3 (Zprim say 6K) won't break the bank.
Another advantage is that you really don't need a global FB loop to match the outputstage' impedance to the speakers, with some local FB distortion is still acceptably low.

With an OTL the main chunk of the money ends up in the powersupplies and powerxfmr(s) which often benefit from being overrated and should be of the best quality.

Last point to consider is that the top end of the Coral doesn't reach very high up in frequency (if these are the same Japanese Corals I once knew) , so much of the open, airy sound of the OTLs may be lost when the Corals are run as a FR unit.
At least I think it would...

So, my vote goes for the PP 2A3 as first choice, second place would be the OTL.

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Old 30th June 2004, 01:27 AM   #3
diyAudio Member
Join Date: Dec 2003
Location: brussels
thanx frank,

i was already looking at the scheme of thorsten who posted here on the net though it wasn't push pull,

i was also afraid that the powersupply would break the bank of an otl.

I have had contact with ae-europe, a very friendly guy who told me that he had 2 power transformer, 2 chokes, 2 output transformer (0.05 plates) for 270 euro, this package was developed for a SE 2a3. fine material i think. Still the SE in the link still makes up a small 550euro and for a student damn much money.

I heard the problem of the corals too, some people do find indeed that they don't go all the way up, others don't, probably i'll think you are right, well : i like a lot of "high" , so if that is missing, i will have to put an supertweeter with it.

i have an old PP el84, maybe i do first something with that but the previous owner has don weird things with it. or maybe i use the output transfomers. i'll think about it, well : my wallet
thanx a lot already
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Old 1st July 2004, 12:49 AM   #4
diyAudio Senior Member
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Join Date: Aug 2002
Location: Belgium

Regarding the OPTs, chokes and other iron, have you considered the Lundahls as offered by Auquablue in Antwerp?

I haven't compared prices but as far as Lundahl goes, they have great OPTs and benny Glass of Aquablue is selling them at the best price I've ever seen....besides it's not too far from Brussels either.

i have an old PP el84, maybe i do first something with that but the previous owner has don weird things with it.
If you know what make it was, chances are I either have the schematic for it or can find it....
Failing that I could probably fix it anyway, PP EL84 amps are usually pretty straightforward designs.

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Old 5th July 2004, 02:30 AM   #5
diyAudio Member
Join Date: Dec 2003
Location: brussels
well actually it is this piece of hardware.

does anybody know this transfo?

i have put a conclusion at the end of the topic.

i have also emaild with diyparadiso; he's a nice guy, but i think the lundahl are more expensive, but not much.

thanx a lot
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Old 5th July 2004, 04:50 AM   #6
karma is offline karma  Canada
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Join Date: Feb 2003
Location: hamilton,ontario
that old trio amp you have has nice power.and sound i have a trio
just a different model. i lost a tube a month ago so im rebuilding

will look better when the plate is flush with the wood
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