Make sense of this amp test.

[butterMilk 10+ year member]

In this link there is a ''simple'' procedure for testing amps for distortion. Its doesn't quite make sense to me, can anybody simplify this procedure (steps 1 through 7).

Phoenix Gold Phorum • View topic - Amplifier Distortion and DC-Offset Info

Or is this not for car audio?

Click to read more...

 

[Shroomic 10+ year member]

"As a semi-poll, I'd like to see those on this board whip out their multimeters and take a look at the DC that is being presented to the speakers. This means..

1. Speakers disconnected (or connect the meter to the 'B' speakers and set the front panel speaker control accordingly)

2. Input set to an unusued position (not Phono)

3. Volume control at minimum.

4. Balance in center

5. Tone controls either defeated or set to mid position

6. Set your meter to read DC, and set to a low scale (300mV scale is common) Connect directly to the Pos and Neg of the speaker terminals

7. Give the amp 10 minutes to settle. Report back...I'd like to see how healthy all these old amps are."

To me it sounds like he wants you to unplug your sub, turn down the mids and highs. Leave the volume on 1(Maybe 0 to check for distortion constantly present in the amp?) with all eq and bass boost off, fader centered. Leave meter hooked up in the speaker terminals on amp and watch the voltage.

Step 6 is more knowing how to use and read a DMM, Im sure theres a guide on here somewhere if you need it.

 

[butterMilk 10+ year member]

So i guess it is as simple as it looks.

1. disconnect all speakers from the amp being tested

2. set head unit to aux

3. set volume low… would that be anywhere under 10 ish?

4. balance is centre

5. put the equalizer at centre positions

6. meter set to DC. Connect pos and neg to speaker terminals (and leave them there for 10 mins?). Check left and right channels? One right after the other?

 

[Shroomic 10+ year member]

its measuring minute numbers so I would think 0-1. It says min which is usually 1 or off.

 

[bbeljefe]

His technical stuff is correct but the rest is the primary reason why I had to jump ship in the home audio industry.

For example, a quote:

"The guy I bought this from was well-meaning, but did not know how to listen subjectively."

Uh... doesn't know how to listen subjectively? Really? So that's what audio excellence is boiled down to.... subjective experiences? FFS... "I like chocolate ice cream" is subjective. "Blue is the best color" is subjective. "Blondes have more fun" is subjective.

How the fawk can anyone not listen subjectively? To argue that a person can't listen subjectively is to argue that that person can't have an opinion.

Of course, I'm sure he meant to use the word objective, which absolutely cannot apply to audio sound quality..... EVER.

In the end, it's lame attempt at being a yuppie sound magazine reviewer that's rife with spelling and grammatical errors.

Oh and, did I mention that this kind of crap is the reason why I bailed on the home theater/hifi business? Maybe he should have used a $3,000.00 pair of interconnects. I'm sure that would have made the sound more "warm and tube like" even though the amp had a bad FET.

/rant

 

[butterMilk 10+ year member]

His technical stuff is correct but the rest is the primary reason why I had to jump ship in the home audio industry.
For example, a quote:

"The guy I bought this from was well-meaning, but did not know how to listen subjectively."

Uh... doesn't know how to listen subjectively? Really? So that's what audio excellence is boiled down to.... subjective experiences? FFS... "I like chocolate ice cream" is subjective. "Blue is the best color" is subjective. "Blondes have more fun" is subjective.

How the fawk can anyone not listen subjectively? To argue that a person can't listen subjectively is to argue that that person can't have an opinion.

Of course, I'm sure he meant to use the word objective, which absolutely cannot apply to audio sound quality..... EVER.

In the end, it's lame attempt at being a yuppie sound magazine reviewer that's rife with spelling and grammatical errors.

Oh and, did I mention that this kind of crap is the reason why I bailed on the home theater/hifi business? Maybe he should have used a $3,000.00 pair of interconnects. I'm sure that would have made the sound more "warm and tube like" even though the amp had a bad FET.

/rant

So would you say this is a accurate way to test if there is something wrong with a amp?

 

[bbeljefe]

So would you say this is a accurate way to test if there is something wrong with a amp?

Yeah, if there's DC voltage present on the outputs with no source signal, there is a problem.

 

[Jepalan]

No mystery. It is testing for 'DC Offset". Just one of many things you can check on your amp. If your DC offset is too high, it is time to get the amp serviced.

Here is the original wiki-how How to Measure DC Offset: 5 Steps - wikiHow

Too much DC offset (generally more than 100mV) is bad, bad, bad for your system & can blow speakers pre-maturely.

This is not a measure of audio distortion.