Passively Tri-Amping Isobariks

Posted by: Tim Danaher on 11 May 2003

Hello All,

I've decided to have a go at passively tri-amping my Isobariks, since the RFI problems with the NAXO are driving me nuts.

I've spoken to Naim, they said no problems (tri-wiring is what they don't like) and my HiCap has the requisite 3 unpowered 4-pin sockets to feed the 3 250s.

Question is, do I need to do anything to the crossovers in the Isobariks? These are the late, in-stand, 4-ohm jobbies. There are two pairs of three short, soldered links on the board and two pairs of three longer ones. The shorter ones are labelled 'Single Wire Input'. Do these need to be cut/de-soldered?

Thanks In Advance,

Cheers,

Tim
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Posted on: 11 May 2003 by Paul Ranson
You'll need to remove the links from the 'single wire input' to the other inputs, to separate the crossover into three distinct sections. It should be fairly obvious from the three sets of input sockets.

I don't know what the wiring looks like on your crossovers, on the set I have the links are underneath, but this may be a consequence of modification. Perhaps you could post a photo if it isn't clear?

After you've removed the links it is probably a good idea to test for shorts across each input, and between each input and the others.

Paul
Posted on: 11 May 2003 by Tim Danaher
Thanks, Paul

We've tried to de-solder them...no way will they come off! So, we're going in with tin snips...

Cheers,

Tim
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Posted on: 12 May 2003 by Tim Danaher
Thanks, Mark

Have done the snipping...now have passively tri-amped Isobariks. Naim said they'd need to look at and service the NAXO, which isn't an option for me at the moment (money!)

Actually, I was having other problems with the active set-up, namely tweeters intermittently producing loads of distortion, and a lack of any real bass weight. I loved the 'hear-through' naturalness of the active set-up, though.

Passive tri-amping is a big change -- loads more control and oomph and detail, and the sound seems to have divorced itself completely from the speakers (imaging - surely not!) but I'm missing the lquid, euphonic treble of the single, passive 250. Sounds a bit peaky to me now -- like someone's turned the treble up.

Why, oh why, did I sell my 135s? Frown

Cheers,

Tim
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Posted on: 12 May 2003 by Tim Danaher
Mark --

Thanks for the suggestions -- actually, I've been down most of the routes you mention...I think I'm starting to lose the will to live...

NAXO fiddling: been there, done that...setting it to level (as per factory markings) -- reduced bass. Turning up the bass in the NAXO -- boomier bass.

125s -- have done this as well, but without the internal snipping (Ron Toolsie reccommended this route). Yes, sounded fine. I just felt I had to try the passive tri-amp route.

As regards the 125s, what if I get a set of XLR cables made up in a dedicated Left channel/Right channel pair (only one signal pin active in each)? This would have the same effect, but without the internal wire cutting, wouldn't it?

Anyway, many thanks again for your input.

Cheers,

Tim
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Posted on: 12 May 2003 by Tim Danaher
quote:
Originally posted by Mark Russell:

Re the trebble distortion, maybe the 250 you are using on the highs needs some attention. Either that, or the it is your NAXO.



The 250 for the treble has just come back from a full service at Salisbury...so it must be the NAXO.

quote:

How long have you been having these sorts of problems?


Since I got the third 250 (S/H). That's the one that's been serviced now. Previously I was using 135s on the treble -- no RFI/distortion, but I don't think this was ideal from a system balance point of view. The character of the amps was too different, IMO. Hence flogging the 135s and buying the third 250 and trousering the change...I haven't moved house or the system. The thing that really gets me is that radio reception here is terrible, but the NAXO seems to be making a good job of it!

Cheers,

Tim
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Os nid Campagnolo yw hi, dyw hi ddim yn werth ei marcho...