Testing output on MC2255

saltpeter

saltpeter

New Member
I just received a well used 2255 and would like to know how to test the output.
Initial test with a signal generator and no speakers connected shows the meter on the right channel to be much lower.

Is this an accurate enough test, or should I use a multi-meter and test the output connectors with the speakers connected?
 
Last edited:
You'll need the following:

Sine generator
Oscilloscope
Distortion Detector
Resistive load bank

Or something like an Audio Precision.
 
To properly test output and calibrate the meters you need a 8 ohm load box with sufficient heat soak capabilities, a signal generator and a appropriate meter that will read voltages accurately across the audio spectrum not just around 60 hz.

Typically those last two needs are satisfied with a distortion analyzer.
 
I'd like to check the amp output for even power on both channels, if the meters aren't calibrated that is ok for now.
I only have a signal generator on the iphone with a cable that has RCA jacks.
I was going to connect the phone signal to the 2255 inputs, then check the speaker terminals for voltage.
That won't test the output at the terminals properly?
 
You need to use load at the output terminal of your MC2255 ;
Use the same value (8 ohm) and terminal plug (8 ohm) if you wish a precise result
Don't forget that meter are used for indication purposes only
using signal generator with iphone is not serious measurement
 
clinic-audio said:
You need to use load at the output terminal of your MC2255 ;
Use the same value (8 ohm) and terminal plug (8 ohm) if you wish a precise result
Don't forget that meter are used for indication purposes only
using signal generator with iphone is not serious measurement
Click to expand...


Thanks, I am planning to connect the speakers for load, and then measure the 8 ohm terminals.
I had an idea this would not be a precise result, but I am hoping it is ok for my purpose.
I'm just wanting to see that the output is of reasonably similar strength in both channels.
 
Bad idea. Most speakers cannot handle pure sine waves at any power level to speak of. You could very easily cook the mids, tweeters, crossover components, or some combination thereof.

Given the age of the amplifier, you’ll be time and money ahead having it brought back to spec by a qualified technician.
 
Thanks, I am planning to connect the speakers for load, and then measure the 8 ohm terminals.

We don't use speakers as load , the reason is simple . When we check a powerfull amp we don't disturb our neighbour !
Use 8 ohm loads , it is much better for your speakers !
 
damacman said:
Bad idea. Most speakers cannot handle pure sine waves at any power level to speak of. You could very easily cook the mids, tweeters, crossover components, or some combination thereof.

Given the age of the amplifier, you’ll be time and money ahead having it brought back to spec by a qualified technician.
Click to expand...

ok thanks, this might not be happening then. :eek:

Would a pink noise generator be safe for the speakers?
 
op may be looking to do something similar to this setup -
37751383786_c3827bc741_c.jpg

Dummy 8ohm loads from Parts Express - B&K signal generator and a DMM.

37799411201_89962cfb70_c.jpg

and help from an EE that knows how to do this and calculate power based on output voltage.
 
Sure, give it a whirl. But it won't work. Ohm's Law, as written, applies to DC Circuits whereas your MC2255 creates AC at its output. Furthermore, the impedance of a loudspeaker varies based on frequency, so any calculation you would perform would be like measuring wind with a tape measure.

I know that we're not giving you the answer you're looking for but there really is no easy way to do this. Is there a reason that you're opposed to having this service performed by a qualified individual that does have the necessary test equipment? The old saying, "You rarely save money by saving money" surely applies here. You have in your possession a former top of the line McIntosh power amplifier which is incredibly complex. It'd be a shame to cause damage to it in this fashion.
 
clinic-audio said:
You need to use load at the output terminal of your MC2255 ;
Use the same value (8 ohm) and terminal plug (8 ohm) if you wish a precise result
Don't forget that meter are used for indication purposes only
using signal generator with iphone is not serious measurement
Click to expand...

Bingo.
 
So I won't be testing the output terminals myself, thanks for the words of caution.
If there were a local (SF Bay Area) technician I would go there. I am loathe to ship the unit right now.
 
saltpeter said:
So I won't be testing the output terminals myself, thanks for the words of caution.
If there were a local (SF Bay Area) technician I would go there. I am loathe to ship the unit right now.
Click to expand...
Actually, this has been discussed here extensively. Let's solicit input from @4-2-7 and @gmc . You may also search the Mc forum here for SF Bay tech. Man, you got my mouth watering for some fresh seafood from Sausalito ...
 
saltpeter said:
If there were a local (SF Bay Area) technician I would go there.
Click to expand...

damacman said:
You may also search the Mc forum here for SF Bay tech.
Click to expand...
Yeah I think there is a thread going somewhere, maybe the mac forum for local techs.
House of Music recommended L&M to me a year ago to take my MC275 to and they worked under the mac warranty but are now closed for good due to retirement.

House of Music SF
A sleek shop offering top-of-the-line speakers & sound systems, plus repair & installation services.
Address: 410 Harriet St, San Francisco, CA 94103
Phone: (415) 255-0888
 
4-2-7 said:
Yeah I think there is a thread going somewhere, maybe the mac forum for local techs.
House of Music recommended L&M to me a year ago to take my MC275 to and they worked under the mac warranty but are now closed for good due to retirement.

House of Music SF
A sleek shop offering top-of-the-line speakers & sound systems, plus repair & installation services.
Address: 410 Harriet St, San Francisco, CA 94103
Phone: (415) 255-0888
Click to expand...


SF and Berkeley used to be meccas of hi fidelity sales and service.
Now, I wouldn't let most of the available "techs" near my boombox. :cool:
 
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