Skip to main content ↑ ↓

Notice

Please note that most of the software linked on this forum is likely to be safe to use. If you are unsure, feel free to ask in the relevant topics, or send a private message to an administrator or moderator. To help curb the problems of false positives, or in the event that you do find actual malware, you can contribute through the article linked here.
Topic: Question about amplifier DC voltage (Read 4763 times) previous topic - next topic
0 Members and 1 Guest are viewing this topic.

Question about amplifier DC voltage

I read an article about DC volatage at:
http://www.allegrosound.com/Fusing_AllegroSound.html
If an amplifier is leaking DC volatge, would this be a big problem to fix?

I am asking because I plan on buying an amplifier, and am considering
buying something used.

Thanks.

Question about amplifier DC voltage

Reply #1 –
This article seems to say that 50 mV bias in an amplifier's output is unacceptable (acceptable to some manufacturers but not good enough for the author.

The first reason given is that there will be power dissipated in the voice coil due to the 50 mV bias. This is true, but the amount of power dissipated into 8 ohms is 0.3 milliwatts, i.e. this is negligible.

The second reason is that this will bias the voice coil off center, so the maximum wattage will be decreased due to limited travel of the voice coil. Again this is true, but if the speaker is rated at 100 watts peak with no bias, 50 mV of bias will decrease the maximum wattage to 99.6 watts, again negligible.

My conclusion is that this guy is spreading fear, uncertainty and doubt so as to sell somethong.

Question about amplifier DC voltage

Reply #2 –
I agree.  Fear mongering.  Nicely articulated and backed up with the boring facts.  j/k


And btw - voice coil biasing used on purpose (which isn't what he's talking about) has some really awesome advantages...  like being able to control excursion (and know exactly where the driver should physically be based on modeling) without the distortion of a servo driver...  and also increasing the frequency response of the driver.

A father/son team from Florida (True Dimensional Sound) invented a technology that does just that, and it's now being licensed by a few companies, such as Harmon International (aka JBL) and available on the market.

Here's the patent for it...
http://www.google.com/patents?id=wpQGAAAAE...amp;as_maxy_is=

very very cool technology, imo.



(they also invented the technology behind several BBE circuits/algorithms)

Question about amplifier DC voltage

Reply #3 –
Thanks for replies.

So then, DC voltage leakage would not be something to be concerned with.

Thanks.

Question about amplifier DC voltage

Reply #4 –
Quote from: JFS on
Thanks for replies.

So then, DC voltage leakage would not be something to be concerned with.

Thanks.


I used to repair consumer stereo WAY back and even then with the comparatively primitive gear, only once did I run into an amp with a DC offset problem. In that case it was a damaged transistor that behaved as if it had a low value resistor across the emitter-collector terminals. Took a curve trace to pin that one down. Bottom line, its's a very rare problem. I've bought several old Technics receivers on eBay that are working  correctly and have no qualms about used gear.

G²

Question about amplifier DC voltage

Reply #5 –
Can DC voltage damage the speakers, or does this just affect sound?

Thanks.
 

Question about amplifier DC voltage

Reply #6 –
Quote from: JFS on
Can DC voltage damage the speakers, or does this just affect sound?

Thanks.

High enough DC voltage can do both, but we are not talking about millivolts or even a volt or two. I once damaged (destroyed) a speaker, but I accidentally applied 28 volts to it.

The only way an amplifier can damage a speaker or affect the sound is if it is broken.