A lot of Cross-talk occuring.
..... and may be a clue as to how you get so much power line freqs/harmonics into the amp as well.
THx-RNMarsh
I think he's saying he had plugs that are inline and do loading... as in for MC inputs.
Not that he shorted one channel and looked at the other, that one having music coming out.
Without a look at the layout, only you can figure out the problems if they are related to layout related issues.
I'm entirely unclear on what Andrew T asserted. The paralleled caps reduce capacitive Z at HF. The added series inductance has to be minimal given the size of the caps, and in the case of ceramic caps, nil.
_-_-
Not that he shorted one channel and looked at the other, that one having music coming out.
Without a look at the layout, only you can figure out the problems if they are related to layout related issues.
I'm entirely unclear on what Andrew T asserted. The paralleled caps reduce capacitive Z at HF. The added series inductance has to be minimal given the size of the caps, and in the case of ceramic caps, nil.
_-_-
The amp was completely disconnected from the active crossover at the time.
The crossover was muted. The sound was *full range*.
The 470R resistor on the "shorting plugs" was inducing the voltage from some radiated source... The preamp (DCB1) is input into a bunch of behringer stuff (SRC/DEQ and DCX2496) that are used to triamp a set of speakers.
The DCB1 also has a ground loop breaker in it ( ie diodes and resistor from zero volt line to safety earth) , as does the phono section.
There is no noise when the plug is not inserted.
I hope to reacquire my camera this weekend.
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Ah... new information.
this is in a triamped system...
has the amp been tested free and clear of the "system"??
this is in a triamped system...
has the amp been tested free and clear of the "system"??
No, he said the xover was in bypass, if I understood.
But perhaps I do not understand, and it was physically separated...
My main question is if he disconnected the amp from the "system" in the previous tests or not.
_-_-
But perhaps I do not understand, and it was physically separated...
My main question is if he disconnected the amp from the "system" in the previous tests or not.
_-_-
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Not starting a fight, but:
"The amp was completely disconnected from the active crossover at the time. The crossover was muted. The sound was *full range*."
"The amp was completely disconnected from the active crossover at the time. The crossover was muted. The sound was *full range*."
Yeah, that was the weirdest thing... the amp was just sitting there attached to a pair of 15" low mids with these plugs in the RCAs. The crossover was muted (DCX2496) and I dropped the needle with intent to unmute and listen. You see, I had forgotten to plug the F5T back into the crossover.
I was TOTALLY shocked that I could easily hear the LP on the low mid units...
Does this mean that the ground is being modulated?
That would indicate a problem with either the phono or the DCB1 grounding. I am going to measure both on the QA400 at some point, as well as with the scope.
Or, is there EMI being rectified by the 470 ohm "shorting plugs"? I guess the first test is to actually short the inputs to the amp circuit ground and forget about using that 470ohm resistor in the plugs.
I was TOTALLY shocked that I could easily hear the LP on the low mid units...
Does this mean that the ground is being modulated?
That would indicate a problem with either the phono or the DCB1 grounding. I am going to measure both on the QA400 at some point, as well as with the scope.
Or, is there EMI being rectified by the 470 ohm "shorting plugs"? I guess the first test is to actually short the inputs to the amp circuit ground and forget about using that 470ohm resistor in the plugs.
Ok, that ought to be impossible.
First step is to replicate the situation.
Assuming it happens again, then turn off, sequentially all of the other gear except for the preamp and the F5...
I see no way that the signal can travel through the air to ur amp, unless it is rectifying what is essentially RF being broadcast. But that's somewhat unlikely.
There would be no way to modulate the ground if there is only ONE connection to a ground on the F5 - which would be the power cord. There could be a signal riding on the ground, but that would have to be (again) like RF, and the ground like an antenna, since there is no loop for current to flow.
Otoh, if those are diodes and not 470 ohm resistors...
_-_-
Dick Moore, later today, high noon, 50 paces, leaky caps. 😀
First step is to replicate the situation.
Assuming it happens again, then turn off, sequentially all of the other gear except for the preamp and the F5...
I see no way that the signal can travel through the air to ur amp, unless it is rectifying what is essentially RF being broadcast. But that's somewhat unlikely.
There would be no way to modulate the ground if there is only ONE connection to a ground on the F5 - which would be the power cord. There could be a signal riding on the ground, but that would have to be (again) like RF, and the ground like an antenna, since there is no loop for current to flow.
Otoh, if those are diodes and not 470 ohm resistors...
_-_-
Dick Moore, later today, high noon, 50 paces, leaky caps. 😀
I will try to replicate once I put the amp back together. I was stunned to see it.
I'm in the midst of twisting and figuring out how to snub it
I'm in the midst of twisting and figuring out how to snub it
BigE, there is nothing to "snub" until you determine where your problems are coming from in the first place...
...I'd suggest doing more diagnostic work first.
For example, open the path through the resistor to the second cap section.
Look at the voltage and current at the first cap.
It is trivial to look at the current going to the subsequent caps since you already have resistors between the sections. So look at the voltage and current waveforms for each section.
Is the unwanted waveform(s) decreasing or increasing as you move toward the end of the filter bank?
With the first resistor opened, what happens to the waveform??
@Dick Moore ---> changed my mind, noisy transistors, midnight, full moon...
...I'd suggest doing more diagnostic work first.
For example, open the path through the resistor to the second cap section.
Look at the voltage and current at the first cap.
It is trivial to look at the current going to the subsequent caps since you already have resistors between the sections. So look at the voltage and current waveforms for each section.
Is the unwanted waveform(s) decreasing or increasing as you move toward the end of the filter bank?
With the first resistor opened, what happens to the waveform??
@Dick Moore ---> changed my mind, noisy transistors, midnight, full moon...
I just wanted to try snubbing, I felt that may remove some of the other noise, like all the high order harmonics or 60 Hz.... 120 being missing....
I will reassemble and post, likely after I recover from tomorrow's surgery.
I will reassemble and post, likely after I recover from tomorrow's surgery.
ouch! don't mess with it after surgery! ur brain will be flowing with strange stuff!!
anyhow instead of snubbing the thing, try just diss'ing it? maybe tell it off! 😛
anyhow instead of snubbing the thing, try just diss'ing it? maybe tell it off! 😛
I was out for 45 minutes or so. Light General anaesthetic. The Doc is very positive that the tests will be positive. Phew!
I can't lift anything for awhile, so getting that 50+ pound transformer back into the case will have to wait.
The purpose of snubbing was to see if it would have any impact on what appear to be harmonics of the diode bridge operation. That "grass" in the graphs from the distortion analyzer.
So, while I recuperate, not much is going to happen -- maybe clean up the workbench?
I can't lift anything for awhile, so getting that 50+ pound transformer back into the case will have to wait.
The purpose of snubbing was to see if it would have any impact on what appear to be harmonics of the diode bridge operation. That "grass" in the graphs from the distortion analyzer.
So, while I recuperate, not much is going to happen -- maybe clean up the workbench?
Not sure, but I think that you might prefer negative results if the test was trying to detect something bad?
So the doc could be positive that it will be negative or negative that it will be positive? 😀
So the doc could be positive that it will be negative or negative that it will be positive? 😀
Ha ha! He is strongly suggesting negative results for a malignancy test.
I want to lower the "grass". I'm thinking that if the snubbing fails, a CLC might do the trick.
I want to lower the "grass". I'm thinking that if the snubbing fails, a CLC might do the trick.
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BTW: in discussing grounding, I found this diagram on post three of the following thread:
http://www.diyaudio.com/forums/chip-amps/265751-lm3886-grounding-am-i-doing-right.html#post4140755
Notice how there is no "Zero volt line" exiting the capacitor bank... All grounds are refered to the same point.
Is this preferred to one where the zero volt line extends across the amp from the cap bank?
http://www.diyaudio.com/forums/chip-amps/265751-lm3886-grounding-am-i-doing-right.html#post4140755
Notice how there is no "Zero volt line" exiting the capacitor bank... All grounds are refered to the same point.
Is this preferred to one where the zero volt line extends across the amp from the cap bank?
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