A good rear end

There is rumour of a 500 series source component. That may be available at the time you consider a 552 - in which case I would say to go for the 500 series source.

Andrew

Andrew Randle
Currently in the "Linn Binn"

For some reason I appear to be attracting a reputation of having as much of a disposable income as Donald Trump.

This is not the case because I am only a public servant.

Buying the 552 will all but squander my pocket money for this year, so a 500 as well, would sink me into the depths of poverty.

It has to be one or the other, not both.

Hence the purchase of either a pair of 250's or 135's may allow me to buy a 552 later in the year.

Regards

Mick

Whether this is better than using a pair of 135s is arguable, I suspect 'yes' in theory. It's presumably cheaper to buy a single 250 (possibly used to match the age of your existing one?) than to sell a 250 and buy a pair of 135s.

It's also possible to use a single channel of a 250 as though it were a 135.

Personally I would dump the Isobariks and take my two 250s and some of the 7 or 8 thousand that a preamp upgrade will cost and go with active SBLs and then change to the new speaker.

Paul

Your Isobariks have two identical crossovers in each speaker. (I know this because I was considering buying them off David myself!) One feeds the front-firing units, the other the internal bass and upward-firing units. Using two 250s to drive each of these crossovers independently means that the 250s see a much easier load -- average 8 Ohms, with attendent improvements.

Theere's a bit of re-wiring to be done but Martin Payne has posted excellent Pics and instructions on the thread 'PMS briks and crossovers'

Hope this helps,

Tim

Thanks for the response but I am still confused.

Is there any advantage in using 2 x 250's as apposed to 2 x 135's.

Many thanks

Mick

AS you have commented you need to open up the back end to benefit from what you have at the front and middle at the moment.

Arrange a private trip to Salisbury and get to listen to a 500 in your type of system

Derek

quote:

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Originally posted by Mick Parry:
Is there any advantage in using 2 x 250's as apposed to 2 x 135's.

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Mick,

the Isobarik is famously an extremely difficult speaker to drive.

A 'normal' speaker will have an 8 ohm load. For an 8 volt drive signal (which will pretty much determine the volume level), this speaker will draw 1 amp of current, and therefore 8 watts of power.

The Isobarik is two 8 ohm speakers wired in parallel (as described above). This halves the impedance to 4 ohms, and that 8 volt of signal will now draw 2 amps, and therefore 16 watts.

Indeed, the Isobarik can make things much more difficult than this. Under certain types of music drive, the speaker can momentarily drop to 1.7 ohms. That same 8 volts of signal will now draw 4.7 amps of current, and nearly 38 watts of power - for much the same volume level.

Thus, very heavy demands are placed on the power amp, as large amounts of current (power) are required to drive the speaker. The Naim amps were never really designed to cope with this (although they do manage very well). See:-

quote:

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Date: 1-Dec-98 16:17
Author: julian vereker
Subject: shut down

Some of the Shahinian speakers have an impedance that falls to 0.9 Ohm at 13kHz (if my memory serves) if not, it was very low anyway.

This is sufficiently low to trip the power supplies in the 250 and 135 when playing Techno and other music with high levels of high frequencies, we spent some while (10 or so years ago) to help Dick (Shaninian) to fix this, but he didn't much care for the sonic result, so they still do this so far as I know.

When I designed the amps, 8 Ohms was the norm, 4 Ohms was an occasional thing, the idea of less than this bought severe approbation from the technical reviewers and so I didn't think to design for a continuous 'short circuit'.

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(At least the Brik doesn't go anywhere near 0.9 ohms!)

Splitting the crossover and using one NAP250 to drive each speaker, the amp has a much easier time than is normally the case. Each channel of the 250 sees a 'nominal' 8 ohm load with a minimum of 3.4 ohms, and that 8 volt signal now only draws 19 watts of power. This is basically within the design intentions of the amp, as described.

Some basic specs. The NAP135 can supply a maximum power of 500VA (for a brief instant). The NAP250's two channels can supply 400VA each, so in total each speaker can call on 800VA of power in reserve.

Of course, the 135 has fans to help it when the volume gets very loud, and an amp does sound worse when it gets hot. However, the NAP250 is sharing the load across two halves of the amp, so it should not get so hot.

When I did this myself with 4x135s I found it to be a huge upgrade from 2x135s. The sound really opened out, bass was much tighter and the whole sound seemed less constrained.

Of course the 135 is a big upgrade from a NAP250, so I can't comment which is the biggest upgrade in practice - but you don't have to sell your current amp in the process.

If you do end up with another NAP250, it's worth mentioning that you would get some benefit from a minor change to the wiring scheme of the 52-to-250 leads. With the standard leads each amp will drive half of one speaker and half of the other. With modified leads, one amp can drive the two halves of the left speaker, and the other the right speaker. One of the NANA guys (?? DD ??) recently described this as a much better configuration for bi-amping.

cheers, Martin

Thanks for all that, I am still not certain why some people use 2 x 250's instead of 135's.

My Briks are 1986 and have a XLR connector, does that have any impact on the choice of amp.

Regards

Mick

Maybe not when you introduce likely resale value into the equation.

quote:

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Buying the 552 will all but squander my pocket money for this year, so a 500 as well, would sink me into the depths of poverty.

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No No Mick, I mean that later this year when you're in a position to buy, the 500 series source may be available. If that is the case then you're probably better buying the 500 series source before the 552, the 52 will be more than capable of coping with it.

Andrew

Andrew Randle
Currently in the "Linn Binn"

quote:

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Originally posted by Mick Parry:
My Briks are 1986 and have a XLR connector, does that have any impact on the choice of amp.

Regards

Mick

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Mick,

My Briks are of similar vintage and configuration to yours. I believe the crossovers are located in the isobarik chamber. I presume there are separate runs of cable from both to the xlr? Would also be interested to hear from anyone who has bi-wired/activated these.

Regards,

Willy.

FWIW I doubt that Mr Mick listens loudly enough to be needed extravagant power. I wonder how often his son causes 250 shutdown?

Paul

Go for a 500 - you know it makes sense...:)

Regards,
Frank.
All opinions are my own and do not reflect the opinion of any organisations I work for, except where this is stated explicitly.

But am I better of with 52 and 500

or

552 and 250 or 135

See my dilemma

I cannot yet go for 552 and 500

Regards

Mick

You just better hope they don't come up with a new CDP too soon or you will be completely screwed!

cheers

Matthew

PS you could wait until May and then get a demo comparing them

Keep the CDS2; buy a 552; sell the 250 and buy a pair of Dynavector HX1.2s; keep the Briks or sell them and buy a pair of Shahinian Diapasons.

Why not at least feign interest with your local dealer and home dem this system? If you do may I come round for tea?

Alex

After all:

1. Before the 552, the 52 was the bees knees.
2. The 500's improvement over the 250 is staggering (even with a 52:), especially due to its extra drive with more difficult loads such as Briks.

I guess it depends on just how itchy your feet are. If you can live with the poor crumbs you've got at the moment , you could wait until your dealer has a 552 run in. Then you could do the direct comparison - 52/500 versus 552/250. Once your dealer has a good idea of how big the difference is (rather than the short blast at the Bristol show), they'll be able to advise you on which route is the more sensible (???).

Regards,
Frank.
All opinions are my own and do not reflect the opinion of any organisations I work for, except where this is stated explicitly.

quote:

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Originally posted by Mick Parry:
Martin

My Briks are 1986 and have a XLR connector, does that have any impact on the choice of amp.

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Mick,

I guess it does have some impact, because you will only be able to use two amps if you are prepared to have the speakers opened up, and re-wired with two sets of inputs.

This will not be quite as easy as it was with mine, as they are not designed to be opened up. You will need to remove the bass drivers in order to re-wire the crossovers.

Suspect this is something you're not going to be up for...

quote:

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Thanks for all that, I am still not certain why some people use 2 x 250's instead of 135's.

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To paraphrase what I said above - the Isobarik is a tortuous load for anything short of a NAP500.

By dividing the speaker into halves, the amplifiers' job is dramatically eased. This may outweigh the improvements to be had from 135s.

cheers, Martin

Does that mean I have to stay with my single 250.

Regards

Mick

The question is, where do you want to end up? If you're sticking with Isobariks then you need to be looking at active configurations, that's a lot of boxes. You need to add a Supercap, SNAXO and have three stereo or six mono power amps.

I'm an active advocate, especially with complex three way loudspeakers like the Isobarik. A power amp that works well into a single drive unit is much less challenging than one that works will into a passive crossover and six drive units.

Paul

There are a lot of people using 500s with 52s! Who knows how long it will be before the 552 is out. You can't be sick of the 52 already???

Thanks for the replies but I am still not certain of what I can and cannot do.

To recap, I have a pair of 1986 Briks with a XLR connector powered by a single 250.

Simple question is this

Will I get an improvement if I fit either a pair of 250's or 135's and is one type better than the other.

I have no intention of messing about with any internal wiring.

Many thanks

Mick

Thanks for that and may I assume that your Briks had the single XLR connector at the back.

Thanks

Mick