A good rear end
Posted by: Mick P on 06 March 2002
I want to improve my rear end at minimal cost because I would like a 552 later in the year.
I currently have a single 250 firing into a pair of briks and I am fairly happy with the sound.
I know that some people use 2 x 250's instead of the more normal 135's.
Is there a reason for this.
Regards
Mick
the 2*250 question...
Normally you would have: either a) a pair of 135's, each seeing a hefty load that is a Brik, on each amplifier, =or= b) a pair of 250's run mono, like 135's (AKA 125's), =or= c) a single 250, which as you know is a little less muscular than a 135, seeing a helty brik load on each of its channels, all competing for the current from a single power supply....
what they are saying is: d) if you use two 250's, there may be some benefit over using two 135's. The reason is that with some small modification to the 'Brik's x-over arrangement, to whit:
2 pairs of 250's, with each channel driving a x-over, and hence each amplifier channel seeing an 8 ohm effective load.
That is - in a normal situ, 8ohm speaker, one on each channel, all happy as most amps well happy driving 8 ohm load. Replace normal speaker in this situ with Brik, (which has effectively 2 whole 8 Ohm x-overs and two whole speaker systems in each box, totalling a bloody tough load for mere-mortal amp, let alone muscular Naim amp)... and said amp turns a little wheezy.
SO - by separating the two "systems" within each brik cabinet, and assigning each to a respective channel of the pair of 250's (run in parallel from your preamp PSU) you gain the benefit of less wheezy action... QED the Brik's hefty load diminished for each channel working of a pair of 250's.
Please note, I have neither heard nor tried this config - have just tried to explain the concept (after reading the posts) as you still seem confused. I hope this somewhat wordy explaination helps clarify it for you.
Rico - SM/Mullet Audio
PS - to surmise - with internal messing of Brik wiring completely off the agenda, your best option for more beef into the Briks, short of a 500, is a pair of 135's.
I am now much clearer and I may go for a set of 135's as a stop gap for the 500.
My main quandry was in using 250's which now seems a non starter.
Many thanks
Mick
quote:
I am now much clearer and I may go for a set of 135's
This worked well for me; I replaced a 250 (driving old xlr-socket briks) with 135s last year. Despite the miniscule nominal power increase, the extra power supplies in the 135s seem to make a significant difference. Although I get the fans whirring on a regular basis, it's only at outragous volumes that the 135s start to seem unsettled. They never shut off, peter out, or do the other annoying things the 250 would regularly do into this load.
quote:
Originally posted by Mick Parry:
To recap, I have a pair of 1986 Briks with a XLR connector powered by a single 250.[snip]
I have no intention of messing about with any internal wiring.
Mick,
OK, to confirm - 2x250s are out of the question. Your choices are now a pair of 135s or a 500.
quote:
Mick, this was the advice I too received from dealers when trying to sort out the same conundrum a couple of years back. i.e. Pair of 135s better than bi-amped (non-active) 250s.
and
quote:
I don't have Briks, but monsters of a different ilk...but the principle is much the same if you're only considering passive operation of the Briks or without surgery.
The principle is NOT the same.
The correct comparison is not between one passive amp on the bass and another on the treble. It relates to driving two complete speakers off one amp, or having separate amps for separate speakers.
cheers, Martin
quote:
Originally posted by Nick Lees:
Well, I'm confused then, and apologise if I've mislead Mick. I thought you could only do what you're suggesting with surgery and that he'd ruled surgery out.
Nick,
sorry, you are indeed correct. Mick has ruled this option out, as some surgery would be involved.
However, the "standard" bi-amping method is one amp on the bass & another on the treble. This is often discouraged, as it appears not to work as well as upgrading from 1x250 to 2x135s.
This is not the case with the doubled-up amping of the Isobarik, as each amp is driving a complete "speaker", consisting of a full-range crossover & one bass, one mid & one treble driver.
cheers, Martin