chip amp for line arrays

[zhar]

i have a wonderful set of NSB line arrays that i have set up in a bi-amped configuration.

i have been looking into building some chip amps for some time. the only problem is that i have read that chip amps dont like dificult loads. my line arrays are running around 98-100db so power isnt really a problem, but i have read that they will be a very high inductance load. is that a problem?

the chip i am planning on using is the lm3887 and i am planning to get a SMPS to drive them. and as i am biamped, i will need to build 4 of them.

if you know of anyone who has done a set up like this before, please point me in their direction.

As always, thanks for your advice in advance

Zhar

[Spasticteapot]

Originally posted by zhar
i have a wonderful set of NSB line arrays that i have set up in a bi-amped configuration.

i have been looking into building some chip amps for some time. the only problem is that i have read that chip amps dont like dificult loads. my line arrays are running around 98-100db so power isnt really a problem, but i have read that they will be a very high inductance load. is that a problem?

the chip i am planning on using is the lm3887 and i am planning to get a SMPS to drive them. and as i am biamped, i will need to build 4 of them.

if you know of anyone who has done a set up like this before, please point me in their direction.

As always, thanks for your advice in advance

Zhar

There's the absolute overlill solution.

Use one side of a LM4780 for every four or so drivers. This would also make EQing them a bit easier.

Alternately, you could sell me a few drivers off of each side .

[zhar]

that sounds like it would be an awsome project to do, but i jsut dont have the expertise/time/money to come up with a setup like that.

although it does appeal to the overkill freak in me

[exipnos]

Hi Zhar,

NSB line arrays, biamped . I have a couple of boxes of NSBs waiting for me to start a similar project. Could you tell us more about your line arrays? Maybe in the speaker forum or PM directly?

Cheers,

Exipnos

[Spasticteapot]

Actually, it might not be as hard as you might think. LM4780's are cheap, and when both halves are run in parallel (they're essentially dual LM3886s), they can drive 2 ohms.

The more drivers you have in paralell, the lower the inductance. (It goes up when you run them in series, of course.)

If the NSBs are 8 ohms, I'd put them into paralell sets of four, each run by a 4780. Alternately, do a series-parallel array; I'm pretty sure (if I remember my math right) that a 2-series by 4-parallel group would actually have half the normal inductance overall, while still being drivable by a single LM3886.

If you have 16 per side, you could use 2 LM4780's, with one half of each LM4780 for the top 8 drivers per channel, and the other half for the bottom. Inductance should be roughly 1/2 that of a normal driver, I think, and 4 ohms is ideal for a LM3886/LM4780 - plus, you can adjust the top and bottom halves seperately.

For the power supply, I'd reccomend a humongous transformer. If 2 LM4780s are used, 330va is an absolute minimum, with 400va being a bit safer and 500 + VA being ideal if you want to run 'em hot.

[Fenris]

I'm working on a similar arrangement right now. 16 NSBs in a 4 x 4 series/parallel open baffle arrangement, 7 Dayton planars in a 3/4 power taper and two Peerles 8" DVC woofers with a Linkwitz transform. Actively crossed at 125 and 3000 Hz, IIRC. It uses 8 3886 boards from BrianGT and four power supplies. The 4 x 4 NSB arrangement means that you have the same resistance and inductance overall as a single NSB - not a particularly difficult load to drive. Make sure your 3886 has a zobel and you should be fine.

I haven't touched my amp in about 5 months. I've finished the case, inputs, volume controls (master, tweeter, and woofer), crossovers, Linkwitz transform, PSUs, amps, and speaker terminals. I only have to sort out the 120 VAC stuff - soft start and Bulgin power switch. But that has to wait since I'm overseas for the next month.

Here's a picture of the line array:
http://img.photobucket.com/albums/v3...tanis/line.jpg
and the back:
http://img.photobucket.com/albums/v3...anis/line3.jpg
and the side:
http://img.photobucket.com/albums/v3...anis/line5.jpg