Crossover for Naim

[KIERANPHILLIPS]

I am starting to design an active crossover to work with naim 42.5 and a pair of 90.2's.
The speakers are tannoy m1's @ 2.5KHz 12dB per octave.
Any last second advice on op-amps or any other areas?

Regards
Kieran

[Geoff]

Kieran

There are many options for op-amps etc, by why not go discrete and use the Naim Naxo circuit. Details can be found here:

http://www.neilmcbride.co.uk/naxocircuits.html

Geoff

[KIERANPHILLIPS]

Thanks for the link.I have decided to use op-amps because there are less conections and simple to write a report on compared to tranys.
I am now interested in what you said and if I am sold the idea i will continue with it.If i made the trany one i could make a dedicated PSU and use it on other naim kit????

[GRollins]

Kieran,
A discrete crossover circuit need not be particularly complicated. A Sallen-Key circuit using followers has minimum parts and minimum connections.

Grey

[Hedlund]

Geoff,
thanks for that link.
Looks like a very interesting circuit worth to take a closer look at.
Interesting way Naim connected the transistors, haven't seen anything like it before.

Janne

[KIERANPHILLIPS]

Ok what order is it and are the 2 groups of four tranys replacing op-amps??I admit I am leaning towards making it but i need to make it 2.5kHz and understand it a bit more.I can handle electronics so throw it at me

[Geoff]

Kiernan

If you redraw the schematics in a more traditional layout form you will find them easier to understand. In each set of four transistors, one ZTX384 and the ZTX214 form a compound pair emitter follower, with a constant current source made from the other two ZTZ384.

The first set of four transistors and associated components is a unity gain input buffer. This is followed by a passive 6dB/8ve filter stage and a 12dB/8ve active filter utilising the second set of four transistors in place of an op-amp.

The crossovers are therefore 3rd order 18dB/8ve and have been designed primarily for use with Naim SBL and Linn Kan speakers but I see no reason why they should not work well with other two-way designs. A search on the Naim site might elicit more information regarding the use of the Naxo crossover.

Geoff

[KIERANPHILLIPS]

Geoff

Thank you I will try and dig out more info and take on the challenge (then again I am half way down a very nice red wine).Joking apart It makes sence to use the circuits due to the fact it is designed for Naim, all I might do is put the regs in the same box and see if I can upgrade any parts.

Nice wine

[jam]

Kieran

Naim uses a cross-coupled buffer used extensively in video circuits, an improved version is used by Levinson. The circit can be improved by current sourceing the emitters of the input pair.
Another approach is to use two complementary j-fets which simplifies the circuit down two active devices per buffer.

Jam

[ALW]

Hi there again,

The ZTX384 / 214 combination is often known as a complementary or series feedback pair.

A hunt through some electronics books should help you understand it, it's a little more complex than just a follower, owing to the feedback, but it's not too difficult.

It offers exceptionally good linearity for a simple circuit.

Jam's comments are interesting - may take a look at this.

Andy