Amplifier Distortion, DC-Offset, and You!

I have a Meridian plate amplifier that powers an active M10 speaker system.
DC offset measures very high .1v on the mid amp, .76v on the tweeter amp and 11.5v on the bass amp.
The bass amp shut down by way of a thermal switch and I didn't wait for the mid/tweet to follow suit.
Is it possible this amplifier(s) was designed to be measured and adjusted with a speaker/dummy load?

EDIT: I think the amplifier is an "inverting" amp if this might shed some light, thanks
EDIT 11 volts not watts on the bass amp:sigh:
 
Last edited:
My Soundcraftsmen MA5002 reads A +180mv B +188mv after warming up, a little more when cold.
It's not adjustable so clearly I have some work to do.
 
And I have a question regarding this measurement... On the Pioneer QX-949a I measured above, if I have only the A channel on and measure the DC voltage across the B speaker connection then I get ~50 mV rather than the ~5 mV I get with the channel turned on. Why am I measuring a voltage when the channel is off? This could very well be a very simple thing, just don't know much about these things except how to plug them in but I'm learning!
 
Can't trust a DMM reading with an open-ended lead. That's 'null' territory. 'Does not count'. Like dividing by zero.
 
Bias and DC offset adjustment,heatsink temperature.

I adjusted my marantz 2385's Bias & offset after it stabilized but the heatsink was still cold, I had no problem dialing it in, I checked the offset again after the heatsink was warmed up, the DC offset had increased to 25mv on both channels. Should the heatsink be room temperature or fully warmed up before making these adjustments? Is it normal for Bias and DC offset to change with heatsink temp? The manual says nothing about temperature.:no:.
 
I like to see where these values are after a good hour or so. And yes, both of these values fluctuate with temperature.
 
EchoWars said:
I like to see where these values are after a good hour or so. And yes, both of these values fluctuate with temperature.
Click to expand...

Thanks EchoWars, This time I let it warm up for 2 hours before making adjustments. When i adjusted the bias & DC offset the first time, the ambient temperature was 65 degrees fahrenheit, so I think it was a little cold for adjusting.
I have one more question, if you don't mind, If the offset adjusts to 0mv +~- 1mv and the trim pots are near center, would there be any other reason to change the differential pair? Or should I leave it the hell alone? :scratch2:
 
+/- 1 mV meterering error

a +/1 mV error could easily be simply the DVM you're using or just how solidly the probes are making contact with the test points/speaker outputs. Most importantly - 1mV( or is it three if you consider a range of +1 ,O and -1 ?) simply won't be audible. Avoiding OCD behaviors with this stuff is important. ALL of us who have repaired enough stuff have had the experience of pulling something apart to repair a straightforward problem and then spending many "entertaining" hours chasing the problem(s) created as part of the original repair.Enjoy the Marantz.
 
"Avoiding OCD behaviors with this stuff is important."
I agree,:yes: I just recapped the driver board with silmic II's and Panasonic films, that's why I was looking at these adjustments, I hear a lot about changing the differential pair, so I don't what to miss anything :no: So far, this receiver with a recapped power supply & amp driver board sounds sWeeeeeeeeeeeEET :music:
 
Criterion Mark VII Receiver Bias reading @ 200mv
Left -73 +/- 2
Right -75 +/- 2
Could not get either to stop fluctuating even after 15 minutes.

Are seriously high negative numbers a cause for concern even though they are close? I read some posts about negative numbers in this thread until my head hurt!
Should I have used the next higher 2V setting as I have read on other threads here?
Thanks
 
Just bought a new R-S700 yamaha to replace an older unit with less power. Just for the heck of it I checked the offset.

Left channel .2 mv
right channel 14.0 mv

Question is, should I be concerned at all at the difference between channels when new?
 
Just finished recapping my Luxman R117 including the big power caps (10000uf/160v) and I'm at -2.8mv Right and -8.7mv Left. This baby sounds most excellent!:thmbsp:
 
macgolf said:
Criterion Mark VII Receiver Bias reading @ 200mv
Left -73 +/- 2
Right -75 +/- 2
Could not get either to stop fluctuating even after 15 minutes.

Are seriously high negative numbers a cause for concern even though they are close? I read some posts about negative numbers in this thread until my head hurt!
Should I have used the next higher 2V setting as I have read on other threads here?
Thanks
Click to expand...
According to Echowars original post, 75mV is high, I am a greenhorn but the way I under stand it, there is a negative voltage and a positive voltage so if the offset is not dead on 0mV it can only be + or -



"50 - 85mV: Something is certainly amiss, and while this is not enough to put your speakers or equipment in jeopardy, the amp is running nowhere near where it should. I'd venture to guess that most of the DC-coupled amps that are in use by forum members here fall into this range."
 
I have an old AKAI that reads left 8mv, right 21mv.

Any cause for concern for the difference between channels?

Great info btw :thmbsp::thmbsp:
 
Great thread and tested my JVC AX-Z1010TN.

Idle current:

10.5mV on the Left channel.
10.4mV on the right.
The manual states 10mV.

DC offset measured across the speaker terminals is;-
-0.9mV on the Left output
-1.5mV on the Right output
 
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