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Old 14th March 2008, 12:39 AM   #11
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Quote:
Originally posted by Kevin_Murray
Running low impedance loads is a throw-back to the old days of car audio when only 12V was available and switching power supplies where for the rich.......................... In my opinion even 4 ohm speakers are dinosaurs.
WTF???

Since I can remember, for quite some time, most common car amps have 2 ohm channels so you have the option to bridge into a 4 ohm load!!!!!

Also, you may want the option to run 2 4 ohms speakers on each channel = 2 ohms/channel!

It has NOTHING to do with 12V.

16 or 8 ohms is more dinosaur because you have to use a high voltage mains powered amp and high voltage to get power, instead of having a heftier amp channel capable of pushing out some decent current into your speakers. Put a 4 ohm speaker on a wimpy 8 ohm channel, and you get distortion. Most lower ohm channels don't suffer so much when overloaded.
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Old 14th March 2008, 12:56 AM   #12
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To keep costs down, and make simpler...........I imagine a 4 channel amp with 8 output devices - 2 per channel.....600-800W....
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Old 14th March 2008, 01:19 AM   #13
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Quote:
Originally posted by EWorkshop1708


WTF???
<snip>
My apologies if my post came across as insulting. I'm not aware of "low ohm channels" though I am very familiar with electronics theory. I've also been around car audio for longer than I care to disclose.
What I meant was that high voltage/low current setups are more efficient than the opposite. The reason car audio has traditionally been low impedance is that there is not much voltage to begin with in a car. In a home or PA situation there is 120-240volts on tap and therefore designing an amp for higher impedances is an easier task. "Channel ohms" is not about machismo, rather it's about matching the impedance to the amp. An amp designed to operate into 8-16 ohms may have trouble with a 2 ohm load, but a "2kwatt" car audio amp would also struggle with PA speakers for example. Ohms law cannot be avoided.
I merely suggested changing the design philosophy of your system. I understand it wasn't well received but I meant no insult.
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Old 14th March 2008, 01:31 AM   #14
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Have you folks here had good luck and power handling with the smaller 0281 and similar variants in the TO247 package?

I've killed a 6V lead-acid battery with a MJL4302, by pulling too much current, and the transistor lived! Also they seem bulletproof in about anything I use them for. I use the PNP for battery chargers and the NPN for voltage regulators and fan speed controllers. They run cool and reliable and have lots of gain compared to most larger transistors.

Because they seem so tough, I'm tempted to push high power into speakers with a single pair and see how they do.

I remember when I was younger, I worked on an old Fisher amp using Toshiba Transistors 3281/1302 and it had 1 pair per channel @ 150W RMS per channel @ 8 ohms. Those are 150W transistors too, so they were being pushed to the limit. The On-Semi transistors seem much more rugged than the Toshiba.
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Old 14th March 2008, 01:40 AM   #15
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Besides amps, have any of you here used the OnSemi audio transistors for purposes other than audio?
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Old 14th March 2008, 01:57 AM   #16
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One thing I forgot to mention is if you incorporate source (emitter) resistors into your amp you can then run a VA current limiting scheme. Even if you only use a single output pair per amp. This will protect your output transistors no matter what the load impedance.
I'm not experienced with the ON Semi devices but I have an amp design which uses the IRF 9240/240 FETs to great success. They are extremely robust and I used current limiting to boot.
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Old 14th March 2008, 04:45 PM   #17
wg_ski is offline wg_ski  United States
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Quote:
Originally posted by EWorkshop1708

Besides amps, have any of you here used the OnSemi audio transistors for purposes other than audio?

Does the 2N3773 count ? Used in three of my amps, and more other applications than I can recall. You can't blow those very easily either. It's just real tough getting prime 2N6609's anymore.
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Old 14th March 2008, 04:55 PM   #18
ilimzn is offline ilimzn  Croatia
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Quote:
Originally posted by Kevin_Murray
I'm not experienced with the ON Semi devices but I have an amp design which uses the IRF 9240/240 FETs to great success. They are extremely robust and I used current limiting to boot.
That does not count as MOSFETs do not have secondary breakdown limitations, which BJTs do, and which in fact prevent full power dissipation at higher C-E voltages.
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Old 14th March 2008, 05:01 PM   #19
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I think that Onsemi's BTJ are very "conservative" rated...

They usually can take much more than rated - especially the 4281 and 21194 with their opposite

The only "Onsemi's" that I have blow up in the last 2 years are the counterfeits
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Old 14th March 2008, 05:11 PM   #20
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Quote:
Originally posted by ilimzn

That does not count as MOSFETs do not have secondary breakdown limitations, which BJTs do, and which in fact prevent full power dissipation at higher C-E voltages.
I'm not sure what you mean by "does not count". Are you saying that current limiting is pointless with mosfets because they do not have the same SOA as bipolar transistors?
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