Amp for Coaxial speaker with active crossover

[partyjups]

Hi I have bought 5 Beyma 12" coaxial speakers (beyma 12cx)

And I want to build 5 active speakers for PA /monitor use.

I have some amp chips - Lm3875tf, lm3886tf, opa549t, tda7294

already, but im ready to seek for diferent types if any better ?

What type will do the job best ? any comments welcome

If theres a particuler circuit that to be recormemtet I'll be happy to know.

I have thought about running 2 chips in bridge mode for the bas coil. and a single chip to run the horn coil. is this a good way to do it ?

Since it´s o 8 ohm speaker i hope the bridge mode wont get to hot. with a propper heatsink.

I already have passive crossovers but would it be better to make 2 ways active crossovers insted ?

I hope that some one will help a bit. since i have only build a few chip amp using lm3886 before.

Thanks jeppe c dk. sorry my bad english

[testlab]

You may want to try doing something with the new National LM4702 amp driver chip. Then all you have to do is scale your output transistors for the particular driver.

[ThorstenL]

Konnichiwa,

Originally posted by partyjups
Hi I have bought 5 Beyma 12" coaxial speakers (beyma 12cx)

And I want to build 5 active speakers for PA /monitor use.

I have some amp chips - Lm3875tf, lm3886tf, opa549t, tda7294

already, but im ready to seek for diferent types if any better ?

Given the Amp's will be driven rather hard I'd suggest bridge/parallel LM3886 for the woofer section and a single LM3875 for the HF driver.

What is worth doing in this kind of speaker is to have a suitable limiter per driver that is fed with a signal derived from a circuit that approximates long therm thermal handling (using peak voltage with a long integration interval will give away some during long sustained tones, but will keep the drivers safe, true RMS is better) as well as checking the LF excursion and amplifier clipping. The Limiter should then operate to reduce the input signal to the driver/amplifier combo if:

a) The Amplifier clips.
b) The Driver is driven by low frequencies past safe excursion.
c) The long term thermal power handling of the driver is exceeded.

For a) the ESP "sound impairment monitor" circuit is a good choice to detect clipping, for b) a 2nd order lowpass with peak detector is fine, for c) a true RMS detector chip is ideal, otherwise a peak detector (which in effect derates the system to 0.7 on sinewaves).

The limiter in the simplest principle can be a simple transistor or FET, a VCA or (best sound) a Photoresistor/LED combo.

Sayonara

[partyjups]

Hi thanks for replying. I don't think I will go for a limiter ... I know it's smart to protect the speaker but, it's myself that are using them for a duo mainly for vocal, so I think it's a bit to much to add limiters.

The speakers are rated 100 rms 8 ohm. so I will try out with a bridge lm4780 for bass driver, and see how well it goes before I deside to parralel. or chose a diffrent design maybe the driver chip.

I will propperly need fan cooling to keep the chip cold.

have anybody tryed with a cpu headsink with fan ? If posible running fan at less than full speed to avoid noise.

thanks