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How can I get my amp down to 2 ohms?

#41
premiumplus said:
... "Pro-level gear" includes high end tube amps? I have yet to see a tube amplifier that has overcurrent/short circuit protection circuitry.
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HaHa - No I wouldn't. Some tube amps actually have shorting 1/4" jacks - so if you forget to plug in a speaker they don't destroy themselves.

Most of the amps that do have protection circuits are solid state, and the protection circuits won't always detect a fault in time to avoid catastrophic failure.
Just my experience as a seasoned bench tech, and EE. YMMV!
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My Mileage does vary.

It's like a Q-tip in the ear - when you hit resistance stop.
if you hear unplanned distortion - turn down.
 
#42
This discussion has specifically addressed class AB/G/H amps, these (specific) issues are not present in class D amps and there are completely different class D failure mechanisms that must be considered. Class D amps have weaknesses and vulnerabilities too, but generally they are quite different due to the switching (non-linear) nature. I have designed products using both types of amplifier, and have studied in detail the various issues common to each type of amplifier. It kind of makes sense as I'm after all and amplifier designer.

When you have designed for the general market for as long as I have, and seen what people can do to even a very well designed amplifer, you would understand better why we put protection circuits in amps, and why we can't always predict some of the most incredibly stupid things that can be done to cause them to fail.

Protection circiuts, like seatbelts, are not 100% successful 100% of the time. They are a vast improvement in most cases though and do help in the survivability in the case of an "accident".
 
#43
If the USER is the accident (like driving a load lower than designed) just because they are nieve enough to believe that safety circuits should make up for lack of forsight.....?
If the amp is designed for 4ohm min or 2ohm min and the user exceeds that design, they also exceed the design of the safety circuit! People REALLY need to start thinking again, it is really a wonderful thing to do IMHO.
 
#47
Quite some dramatizations in this thread.
But judging by how many players get confused by loads I can guess plenty play with unsuitable loads with no problems. Otherwise there'd be even more protection to amps added. While it's under warranty there wouldn't be a way for a manufacturer to tell the amp was abuse by a wrong load or failed for general device problems. They'd fix it.

Plenty of public information out there amplifier protection circuits.
Invalid Link Removed
Link Removed
http://www.yamaha.com/yamahavgn/CDA/ContentDetail/WrappedTextDetail.html?CNTID=48555&CTID=227500

Plenty of published papers.

Plenty of car metaphors. Never driver over the speed limit because that is what the department of transportation deemed safe for the road you're traveling on.

Within reasonable limits, like reasonable speed limits, I don't worry too much about it. And I've never had a ticket.
 
#48
I hope you realize seamonkey, that the articles you posted are gross oversimplifications of the real world and also include major errors and omissions. They are essentially feel-good pieces that don't relate much of the tradeoffs involved in developing protection circuits. Not one of the articles mentions the SOA curve shift that occurs when the transistors heat up. This is a HUGE variable that is often ignored.

I repeat, in theory protection circuits should work 100%. In practice, they don't. Most responsible manufacturers recognize this and do their best to support a customer who does manage to slip through the protection cracks. That's a good incentive for not releasing poorly designed products IMO.
 
#51
Why is it that when highly regarded amplifier engineers, designers, and repair professionals reply with tech answers based on years of experience as well as solid engineering facts, there is always some kid who has to have the last word and be the expert?

Where is the Talk Bass for grown ups, professionals, and others with credentials?
This reminds me of some mortorcycle forums that became invite only just so solid restoration and engineering information could be exchanged without driving people away.
 
#52
seamonkey said:
I appreciate that, thanks.
I do think that ESP Link Removed is a great honest resource.
They of course do sell products so some opinions may be weighted.
If there's something you feel is incorrect you'll find the author is willing to listen.
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Actually, I agree it's probably one of the best explainations out there, but it's oversimplified. Now in Rod's defense, adding all the real meat and potatoes to the to explaination would make it long, boring and difficult to read. It is a very complex subject with difficult and ill-defined math and variables that don't stay still long enough to solve. I hate moving variables... ;)

I specifically disagree with his comment that most big power linear amps are MOSFET (I would say that maybe 5-10% are), and that MOSFETS don't require any more protection than gate clamps (which are similar to single slope VI limiters). While MOSFETS do not suffer from second breakdown (one of the details that MUST be considered when designing a Bipolar output stage), the SOA still consists of considerably more than a straight line from a practical standpoint. Especially when thermal issues are accounted for.
 

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