Very good , I should also mention , highend amps dont have a lean restrained sound...
Hi Terry, Yes its in a case with the safety earth connected, and the -ve cap banks grounded via an earth loop breaker. I've wired it up the way I described to you in another recent thread.
Hi Wayne, Well that's how some (but not all) "high end" amps sound to me. Whenever I've make that observation the salesman/owner has usually come to its defense claiming that's the natural sound, without over-emphasis or distortion. My P3A - build detailed in another thread - sounds a little "lean" too. Anyway I'm very impressed with the MKIII so far.
Hi Wayne, Well that's how some (but not all) "high end" amps sound to me. Whenever I've make that observation the salesman/owner has usually come to its defense claiming that's the natural sound, without over-emphasis or distortion. My P3A - build detailed in another thread - sounds a little "lean" too. Anyway I'm very impressed with the MKIII so far.
this is confusing.
The amplifier with an open input is usually noisy. A mixture of hum and buzz and white noise. This can be anywhere from 1mVac to 20mVac.
The amplifier with an open interconnect plugged in will be about the same or slightly worse.
The amplifier with a shorted input should be <0.1mVac Even a dummy input load of 100r or 200r will be expected to give a similar output noise.
This is what Canon has just confirmed.
Still4,
confirm what you have measured?
I did. I checked several times to be sure since I knew you would question my results. With either of my preamps plugged in I read 7.0mVac on each channel and I hear a low hum. With nothing plugged in the hum goes away and the output drops to 0.1mVac. I didn't try shorting the input to see if it would drop further.
On the DVM I have 3.5 mv. Looking at the garbage on the scope there is a mixture of 120 hz peaks and noise. The p-p value is 70 mv with the peaks being the 120 hz. By comparison my ancient BGW amp with an E frame trafo measures under 10 mv peak on the scope and unmeasurable on the DVM. All measurement are with the source and speakers connected. BTW my main reservoir caps are off the board with smaller 4700uf caps on the board.
Hi Terry -
I think the hum isn't there when there is no input connected because you have broken the ground loop that circulates from the left channel ground up through the input cable shield across the common source grounds and back to the right channel ground. I'm going to try inserting a small resistor in series with one input cable shield to see if that has an effect on the hum level. The question is what's the source of that ground current.
Steve
0.1mVac is very good for an open input. Very few Power Amps are this good.
most depend on a lowish Source Impedance/Resistance to give a low noise figure.
However, 7mVac is very bad for the pre-amp connected.
If these preamps have no hum on their outputs then it is a ground loop due to interference current circulating around the interconnects.
Does the hum go lower, when only one channel is connected?
Does it change when you swap channels?
Hi Ranchu,
I hope you are still following this thread. I am very interested in your wiring scheme for this amp. I just can't seem to get rid of the last bit of hum. Everything I have tried past what I've already done, makes it worse. I don't think it is a loop as the hum is the same whether one channel is plugged or both. One channel is slightly worse than the other but not much. I have tried several different sources and all do the same thing. I really like the sound of this amp so I would really like to get it working properly.
Thanks, Terry
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