about transformer for 290E

[shensc127]

Sorry! I am new in Altec, one more question. Altec recommends the 15045-A (70.7V version) for 290E, but it's hard to find. Is it possible to use 15067 for 290E?
Thanks!

[Todd W. White]

Why do you think you need a transformer for the 290?

[shensc127]

I am planning a bi-amp A5 system. I would like to use a 6C45(1W) amp for 290E+Beyma 21F at a 1st order xover, so I think that the 290E should be protected by transformer. The other purpose is for impedance match.

[cclark65]

I think the transformers you are talking about are meant only to be used with a distributed sound system, where lots of drivers will be driven by 1 amp with a 70v tap on it.
To bi-amp, you don't need anything really, just cross it over at the right frequency. If you are concerned about protecting the drivers, then put a non-polarized capacitor of the proper value inline with it. However, I run a PA system really hard with the drivers hooked directly to the amps, and have only once blown a diaphragm, otherwise they are all stress related failures. (The blown one was a very stupid mistake also, I hooked the horn driver up to the wrong connector, and put 1200 watts of subwoofer through it...that was a $150 dollar mistake!)

[shensc127]

I appreciated that you make me clear completely! I believe simple is the best. I think that there is no need to have a crossover for 290E, and I will just make a 2nd order xover for 515 at 260Hz.

[shensc127]

Thank for the helpful information. I try to describe my system with poor english!
I have no any active crossover in my system. My DAC has two pairs of signal output(6V) with VR, and connects directly to two power amplifiers(one is 1W tube amp and the other one is 25W A-class solid amp). Of course, they also have VR. The tube amp is for 290E + suppertweeter+ capacitor, and the solid amp is for 515+ 2nd crossover. I found that the 290E+311-60 could down to around 260Hz, mybe 300Hz will be better! Let's why I wonder whether it should be protected with transformer or not?

[shensc127]

An additional Remark, due to room space limitation, I used bass reflex enclosure for 515.

[cclark65]

you definitely want to crossover the horn driver, with an electronic crossover before the amp. When you bi-amp, you will drive each speaker and horn with a different amp, or different channel of an amp. One of the channels only gets the frequencies for the woofer, the other channel only gets the frequencies for the tweeter. You will probably want to go no lower than 300 for it though, and I would suggest 500 or so probably.

[cclark65]

Here is a pretty intense article about bi-amping
http://sound.westhost.com/bi-amp.htm

[cclark65]

If you do not have electronic crossover, then you will definitely need to put a capacitor inline with the 290, otherwise it will get frequencies to low for it to handle. I know of no other way besides electronic crossover or capacitor to eliminate the low frequencies.

Here is a very simple calculator for determining the capacitor you need.

http://www.the12volt.com/caraudio/crosscalc.asp

According to this, for 260Hz, you will need a 76.5uF cap. This however will only create a 6db slow, still allowing possibly dangerous low frequencies to your speaker. You might want to consider making it a 2nd or 3rd order to get a 12 or 18db slope. The closer you cross it over to the lowest possible frequency, the sharper you want it to cut off the lows.