Hi,
The two ground pins allow separate paths to the common
star point, see the application PCB in the chips datasheet.
The pins are not to be joined at the IC, they are for proper layout.
I still have no idea what is actually being discussed.
rgds, sreten.
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Signal goes into IN1 and IN2 (which have 1uf caps instead of .22uf)
Correct that signal and power grounds have separate pins, incorrect that they don't need to be connected. The amplifier won't turn on internally if they're not connected. Notice in the PCB and all Chinese models they're connected. Trust me, I had a hell of a time with the first PCB board I had made trying to figure out why the amp wouldn't turn on....
I'm still trying to understand..what you are doing,
Are you putting a resistor in line with the input Cap?
Because if you are where is the resistor grounding the input?
Ie a value from the input cap to ground..
If you just series wire a resistance into the cap you will "Hear" the resistor type.
(It will act like a tone control)
So I assume you have a resistance to ground with an input resistance creating a divider?
Regards
M. Gregg
Are you putting a resistor in line with the input Cap?
Because if you are where is the resistor grounding the input?
Ie a value from the input cap to ground..
If you just series wire a resistance into the cap you will "Hear" the resistor type.
(It will act like a tone control)
So I assume you have a resistance to ground with an input resistance creating a divider?
Regards
M. Gregg
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Here's another one, showing a switch to representing between straight wire and resistor, and where signal is connected. This is pretty f'ing simple, and I don't understand why you're all obsessed with the idea that something is wired wrong. I've been using the amp chip for over a year now, playing just fine, with multiple PCB's, many configurations on a Kmultiplier for power (including without), many input capacitors, etc, and the one thing that remains is the problem I'm talking about here (I thought it was just a one time thing with the Dale attenuator, but it's come up again).
http://www.diyaudio.com/forums/gallery/showfull.php?photo=12562
http://www.diyaudio.com/forums/gallery/showfull.php?photo=12562
They're in series, neither go to ground. And every single volume control would be a "tone control" by what you're saying - even though the SMD based ones don't change it like through hole resistors do. Refer to the picture. I tried the resistor as an experiment and I'm reporting the results because I thought they might be useful; it's not part of the amplifier.
The resistor in series with the input will create a tone control.
Try putting a 100K-1Meg from the input cap to ground..what effect does it have if any?
A digital volume control is a different issue..you have a driven output.
The issue you are getting is the series resistance in series with the cap<<<its that you are hearing.
And different resistors sound different even though nobody will accept it.
You are telling me you can hear the volume control well guess what you are correct..
And that is one of the problems with a passive volume control in series with a cable to a power amp.
The so called passive preamp..
If you had a buffer after the control you wouldn't hear the resistor any more..just how good the buffer is..
Regards
M. Gregg
Try putting a 100K-1Meg from the input cap to ground..what effect does it have if any?
A digital volume control is a different issue..you have a driven output.
The issue you are getting is the series resistance in series with the cap<<<its that you are hearing.
And different resistors sound different even though nobody will accept it.
You are telling me you can hear the volume control well guess what you are correct..
And that is one of the problems with a passive volume control in series with a cable to a power amp.
The so called passive preamp..
If you had a buffer after the control you wouldn't hear the resistor any more..just how good the buffer is..
Regards
M. Gregg
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If inserting or changing a resistor in series with the input changes the problem then HF instability is the likely cause. The extra resistance may be allowing more capacitive feedback from output to input. Or it could be some change in the wiring.
What is "digital volume"? A digitally switched attenuator, or that plus a buffer?
A picture would help. Show us what works. Show us what doesn't work.
What is "digital volume"? A digitally switched attenuator, or that plus a buffer?
A picture would help. Show us what works. Show us what doesn't work.
Any DAC with digital output, computers, etc. There is no schematic, it's just the source.
Gregg I appreciate what you're saying. Do you think it's possible to hear a RN55 to a SMD resistor be like the equivalent of putting your hands over your ears? My one thought as towards the big change in sound is that because the grounds are connected, something to do with the DC capacitors affects the changes in sound. People without OSCON's haven't reported the bass scenario, but do report a "tube like" sound in the higher ranges that is described similar to distortion (as if from tubes).
I'll try the resistor to ground when I can.
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Normally the sound will become more Warm as you increase the resistance in series with the input..
If you use a 1meg its very obvious..
Put a 1 meg Pot in series and vary it while listening..a carbon pot will sound different to a conductive plastic pot
A Takman REY MF will sound very warm..the Carbon version is almost sickly warm..YMMV
You will hear a reduction in Glare depending on resistor type. This is the standard MF bright harsh sound..that Carbon don't have.
The more transparent the equipment you have the more you will notice this..
You remember the carbon interconnects they made...think about it..it depends on the circuit configuration they are used on.
So now you know the effect of buffering a system..the sound of passives or should I say effect..
You now know that audiophools are hearing things and its all in there imagination..
Regards
M. Gregg
If you use a 1meg its very obvious..
Put a 1 meg Pot in series and vary it while listening..a carbon pot will sound different to a conductive plastic pot
A Takman REY MF will sound very warm..the Carbon version is almost sickly warm..YMMV
You will hear a reduction in Glare depending on resistor type. This is the standard MF bright harsh sound..that Carbon don't have.
The more transparent the equipment you have the more you will notice this..
You remember the carbon interconnects they made...think about it..it depends on the circuit configuration they are used on.
So now you know the effect of buffering a system..the sound of passives or should I say effect..
You now know that audiophools are hearing things and its all in there imagination..
Regards
M. Gregg
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No. Changing resistor technology would at most give a barely perceptible change in sound. I think you have capacitive feedback from the positive output to the input pin, which a low impedance source is preventing. Add a resistor and the feedback takes over. You need to review your layout and wiring.Destroyer OS. said:
That's what I thought, for the most part. However this is so strange and obvious that it's baffling.
It seems unrelated to distances between input and output cables/wires. The output wires are shielded inside the chassis, connected at one end (to star ground with all other grounds).
Funny thing is when the amp isn't having an issue, it's incredibly good. I thought this was isolated, but I guess it isn't.
As you can see feedback is internal, the output is balanced so they're connected to nothing at all. While what you're saying might well be, the differences in types of resistors is quiet odd! Perhaps now it has a lot to do with potentiometers being higher value. There isn't anything I can think of to do about that given the input impedance is set and adding resistance is bad.
+1
You shouldn't use shielded cables on speaker connections..it can make an amp unstable.
It was a favourite with guitar amps..using input cables as speaker interconnects it caused all sorts of problems.
Regards
M. Gregg
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Well, initially the shielded cables were a nice improvement. I'm trying to remember whether or not the initial problem became obvious before or after trying shielding.
I thought the balanced output might be a reason for some of the occurances with it thus far. I can try removing the shielding some time soon.
I see your point on how oscillations are easier. But I have to ask what makes them less of an issue for XLR?
I thought the balanced output might be a reason for some of the occurances with it thus far. I can try removing the shielding some time soon.
I see your point on how oscillations are easier. But I have to ask what makes them less of an issue for XLR?
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