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Old 3rd October 2014, 12:40 PM   #1
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Default Hum issue in hpf circuit

Hi, this is a continuation of my thread for XO/HPF combo unit with associated PSU (see sig).
The PSU and XO sections are working fine - but I'm left with humming in HPF section. Nearby transformer is not the cause because the XO works splendidly.

Currently in doubt about how some parts of circuit are connected - For ease I've circled 3 doubts on below schematic with questions.
I hope its these that are causing the problem.
It is a relatively simple circuit.

Refer to schematic for numbering:
1. How should the filter resistors be orientated (I currently have them horizontally, this could be wrong).
2. How should the op-amp V+ and V- terminals be connected relative to the PSU?
3. As you can see i'm left with four unterminated 'commons', 2 are signal returns, and 2 from the hpf circuit - I don't know how to connect these or if they should be left like this.

Click the image to open in full size.

Thanks in advance
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Old 3rd October 2014, 01:16 PM   #2
AndrewT is offline AndrewT  Scotland
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I completed a 3way active speaker with 2ways in one box and a separate 1way for the bass only.

In the mid and treble box attached to the back of a small (5"+1" drivers) speaker I have a high pass filter and a bandpass filter as well as two chipamp channels & PSU. The Chassis is only 163x155x68mm, less that 1.7litres. It's all crammed in pretty tight.

I attached the input RCA directly to the chassis back panel. Expecting to have to change it after failed testing. But no measurable hum, no increased noise. It seemed to work !
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Old 3rd October 2014, 01:34 PM   #3
AndrewT is offline AndrewT  Scotland
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Forget about commons and grounds and other confusions.

EVERY signal is transmitted via a PAIR of wires. There are no exceptions.
Identify the pair of wires in every connection and twist them. solder at the 4 terminations.

The dual polarity PSU appears as an exception, but it is two 2wire connections where one wire carries the two return signals. We can return that signal as PSU Zero Volts. The two sets of 2wires becomes a twisted triplet.
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Last edited by AndrewT; 3rd October 2014 at 01:46 PM.
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Old 3rd October 2014, 04:42 PM   #4
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Hi andrew,
I was after instructions regarding how to connect up at 1,2&3...
You mention terminations but I cannot tell from what you wrote what to do exactly, still?
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Old 4th October 2014, 12:20 PM   #5
AndrewT is offline AndrewT  Scotland
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Quote:
Identify the pair of wires in every connection and twist them. solder at the 4 terminations.
Find the connection for the input signal.
It must be 2 (two) wires.
The two wires have four ends. Solder these four ends to the respective terminals.
The input socket gives you two terminals. The Receiver PCB has two input terminals. Solder to those four terminals.

Repeat for EVERY connection.
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Old 4th October 2014, 07:20 PM   #6
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https://www.google.com/url?sa=t&sour...TJXSy2MiayNZJw
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Old 4th October 2014, 07:27 PM   #7
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I would try going with balance inputs and ground as little as possible. Look up CMRR for great materials noise issues. The MC330079 is what crown audio uses but the opa op amps are better
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Old 4th October 2014, 07:38 PM   #8
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Old 5th October 2014, 08:12 PM   #9
AndrewT is offline AndrewT  Scotland
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The input to that section is a two wire connection. You must keep those two wires close coupled.

The output from that section is a two wire connection. You must keep those two wires close coupled.
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Old 6th October 2014, 03:56 PM   #10
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Andrew, you mean like this? (see attachment)
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