Thoughts on reduction of 2nd order harmonic distortion - diyAudio
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Old 24th May 2015, 11:53 PM   #1
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Default Thoughts on reduction of 2nd order harmonic distortion

Hi guys,

What kind of ideas do you have for reducing this on an input of an amplifier (that has 1uf input caps on signal)? On one hand it's a bit tubey, but the positive affects appear they may shift around in the frequency they affect. Perhaps the reason is the chipamp is dependent on signal ground being connected to power ground; ANYTHING in-between so far has resulted is catastrophes noises.

One suggestions has been a 470pf to ground, for infrasonics.

Other thoughts?
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Old 25th May 2015, 04:25 AM   #2
Jay is offline Jay  Indonesia
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You might get no or little answer if your question is not clear.

2nd order HD is determined by the amplifier overall design. The 1uF input cap is added to protect DC. This cap determines the lowest frequency the amplifier will be able to pass, and usually it is designed around a maximum of 10Hz (if you want to lower the frequency you can increase may be to 2uF).

Of course, cap has it's own distortion. To lower this you can use MKP, may be a good quality one. But Non-polar electrolytic is also fine.

470pF to ground is an input HF filter. It is usually needed to avoid oscillation. The better the amplifier design (and real implementation and usage) the lower capacitance you need here. For a good one, maximum is I think 270pF. You might need more if your amp is prone to oscillation due to (1) the amplifier design itself (2) PCB trace, cabling, etc (3) speaker cable capacitance.

Grounding is another complex issue. Usually it relates to hum. I don't understand what catastrophic noises you were talking about.
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Old 25th May 2015, 04:28 AM   #3
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I'm looking for reduction on the incoming, not within the amp. The amp seems sensitive to it.
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Old 25th May 2015, 06:04 AM   #4
Jay is offline Jay  Indonesia
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What do you mean by incoming distortion?

An amplifier has an input impedance (Zin). This Zin will affect distortion of the previous amplifier (preamp or CD player). The Zin is slightly affected by the input resistor. But this (Zin and input resistor) is part of the amplifier design. It could be also affected by potentiometer, depends on your implementation of the volume control (passively, or actively within a preamp).

You were talking about "noise". When did you hear the excessive noise? Is it not oscillation? Nor hum? You may also check the power supply, it may need more regulation or capacitance (some amplifiers need it more than others).
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Old 25th May 2015, 07:25 AM   #5
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Separating signal ground from power ground creates massive noise, but may also be the link for problems with distortion from volume control pieces.

SMD resistor volume controls and digital ones interact just fine. Any resistors inline cause a total loss of balance and you end up with tons of bass and poor qualities otherwise. This occurs no matter what caps are used.

The worst is Dale resistors, but potentiometers seem to be bad, too.
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Old 25th May 2015, 08:25 AM   #6
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by Destroyer OS. View Post
................... Any resistors inline cause a total loss of balance and you end up with tons of bass and poor qualities otherwise. .................
I think understand what you are posting, but I don't believe what you have posted.
Am I misunderstanding what you are concluding?
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Old 25th May 2015, 09:21 AM   #7
DF96 is offline DF96  England
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I don't understand the OP's question. What is "incoming" distortion? I don't understand his subsequent attempts to explain his thinking.
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Old 25th May 2015, 10:09 AM   #8
Jay is offline Jay  Indonesia
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Quote:
Originally Posted by Destroyer OS. View Post
Any resistors inline cause a total loss of balance and you end up with tons of bass
If you put a resistor in series with the input (i.e. you connect to the amp through a resistor) you have to make sure the resistance is correct. Too big, (in combination with cap connected to ground) it will pass low frequency more than expected.

Did you measure the resistance? You need to measure two resistors, one the series resistor, another the "shunt" resistor.
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Old 25th May 2015, 04:19 PM   #9
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Currently there is no bypass to ground, that's just an idea.

The problem really comes from attenuators of different types. One will sound great, another is very, very off. The differences are not seen when the amp is substituted. Both with 20k attenuators.
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Old 25th May 2015, 05:56 PM   #10
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Who is the manufacturer and what is the type number of this amplifier?
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