Simple Audio Splitter with NE5534

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b1gtuna
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Simple Audio Splitter with NE5534

Post by b1gtuna » Sun Aug 09, 2015 1:18 pm

Hello everyone, first and foremost, I am glad to be part of this forum. And this is my first post!

I have multiple receivers (headphones, speakers etc). I generally don't like plugging them in and out, so I am working on this amplified audio splitter.
Please keep in mind that I have no knowledge of prior audio electrical engineering, so everything I have done could be flat-out wrong!

I designed the PCB using Altium Circuit Maker. If you are using Circuit Maker, and would like to take a look at my design, please let me know.
I would like to post a direct link to the project, but I haven't figured out how to do that yet. For others, I have attached a PDF file of schematic, and the layout.

I ordered the PCB from OSHPark. And populated the parts myself at home. Here is the link to my project - https://oshpark.com/shared_projects/V7Yweifv

Then I connected +12V and -12V power from my old computer power supply. I checked the voltage. They seem pretty good at ~+-12v.

And then there is no sound!! I noticed it gets fairly hot to touch when I plug in the audio jack from my iPod. Until I plug it in, NE5534 remains pretty cold.

I need to look at the datasheet of NE5534 again and check my work. In the mean time, can anyone take a look at my design, and see if there is anything obviously wrong?
I just need some sort of audio output. At the moment, quality is not my concern.

Thank you!
rsz_20150808_011450.jpg
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rsz_20150808_235304.jpg
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mediatechnology
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Re: Simple Audio Splitter with NE5534

Post by mediatechnology » Sun Aug 09, 2015 2:22 pm

Thanks for joining us. The board looks nice.

If the board was routed from this schematic it may be hard to make all the corrections on the PCB.

WRT the schematic the biggest problem I see are the supply connections around pin 4 of the 5534.
The polarity is wrong should be -12V. The cap polarity is also backwards. Check that everywhere.
It also has pin 4, V- shorted to the inverting input and the feedback resistor.
The 5534 is likely feeding DC out its inputs.

There are also problems with the non-inverting input.
It has no DC bias path to ground and should have a coupling capacitor in series with the input with a resistor to ground on both sides.
The second channel has no build-out resistors like the first.

Redraw that and then we can have a second look.
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b1gtuna
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Re: Simple Audio Splitter with NE5534

Post by b1gtuna » Sun Aug 09, 2015 3:30 pm

mediatechnology wrote:Thanks for joining us. The board looks nice.

If the board was routed from this schematic it may be hard to make all the corrections on the PCB.

WRT the schematic the biggest problem I see are the supply connections around pin 4 of the 5534.
The polarity is wrong should be -12V. The cap polarity is also backwards. Check that everywhere.
It also has pin 4, V- shorted to the inverting input and the feedback resistor.
The 5534 is likely feeding DC out its inputs.

There are also problems with the non-inverting input.
It has no DC bias path to ground and should have a coupling capacitor in series with the input with a resistor to ground on both sides.
The second channel has no build-out resistors like the first.

Redraw that and then we can have a second look.
Wow thank you very much for a prompt and thorough explanation of all the things I screwed up!
I will report back with a new schematic. Should have done that before I ordered the PCB.
Got overly excited =(

b1gtuna
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Re: Simple Audio Splitter with NE5534

Post by b1gtuna » Sun Aug 09, 2015 3:41 pm

One thing I would like to clarify. The capacitors have negative end connected to GND. Is that what you were referring to in regards to reversed polarity?
Much appreciated.

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mediatechnology
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Re: Simple Audio Splitter with NE5534

Post by mediatechnology » Sun Aug 09, 2015 5:33 pm

The power supply bypass for the negative supply should have it's positive end grounded.
It looked like you had pin 4 connected to +12V - it should go to -12V.
The bypass for pin 4, V-, should connect to the - end of the cap.
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b1gtuna
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Re: Simple Audio Splitter with NE5534

Post by b1gtuna » Sun Aug 09, 2015 11:16 pm

mediatechnology wrote:The power supply bypass for the negative supply should have it's positive end grounded.
It looked like you had pin 4 connected to +12V - it should go to -12V.
The bypass for pin 4, V-, should connect to the - end of the cap.
Doh, that makes a perfect sense now. Thank you for your patience.
I am correcting my design at the moment. Mostly done. Just have to get my head wrapped around dc bias current in the input.

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Re: Simple Audio Splitter with NE5534

Post by b1gtuna » Sun Aug 09, 2015 11:40 pm

mediatechnology wrote: There are also problems with the non-inverting input.
It has no DC bias path to ground and should have a coupling capacitor in series with the input with a resistor to ground on both sides.
Ok, I did a little bit of reading on coupling capacitor. At the input we need an AC coupling capacitor to remove any dc bias voltage from the audio source.
As I see it, it is a high pass filter. And we need a return path of the dc bias voltage, which is provided by the resistor placed after the high pass filter.

b1gtuna
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Re: Simple Audio Splitter with NE5534

Post by b1gtuna » Sun Aug 09, 2015 11:57 pm

Ok here is my updated schematic.

I have addressed these issues:
  • 1. Added missing resistors at the output on the 2nd channel (R14, R15, R16)
    2. Added an AC coupling capacitor (C11/C10) along with resistors for dc path(R6/R1).
    3. Negative DC input no longer being fed back to non-inverting input
    4. Corrected polarity of the capacitor (C8/C4) on negative DC input.
Things to do:
  • 1. I have not figured out how to select a value for the AC coupling capacitors (C11/C10)
    2. Replace R3/R2 and R8/R7 with a proper potentiometer.
Thanks a bunch.
Attachments
AudioSplitter.PDF
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mediatechnology
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Re: Simple Audio Splitter with NE5534

Post by mediatechnology » Mon Aug 10, 2015 7:01 am

I have not figured out how to select a value for the AC coupling capacitors (C11/C10)
The cuttoff frequency, Fc, (3dB point) is 1/(2piRC).
You can use this calculator here to check your work: http://www.muzique.com/schem/filter.htm

I corrected the schematic for you.
You might want to add compensation caps to 5534 P5 and P8 if you eventually need them.
I would use just one pair of 100 uF bypass and put 4X 100 nF (0.1 uF) to bypass each IC.
Attachments
Buffer_Stage_Corrected_081015_1.jpg
Corrected buffer stage.
Buffer_Stage_Corrected_081015_1.jpg (51.31 KiB) Viewed 18870 times
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Covidland (The Movie) Part 1: Lockdown https://banned.video/watch?id=615f96b3aa816336dbd21792

A voice-over with Orson Welles: "What Is It That You Want?": https://waynekirkwood.com/content/Orson ... u_Want.mp3
Americas Frontline Doctors Lawsuit Motion For Preliminary Injunction Of Covid-19 Vaccine Emergency Use Authorization: https://waynekirkwood.com/images/pdf/Am ... zation.pdf

b1gtuna
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Re: Simple Audio Splitter with NE5534

Post by b1gtuna » Tue Aug 11, 2015 9:23 pm

Almost done with my schematics. Thanks for making corrections and posting the image. Thanks!

The RC filter has a cut-off frequency at 159.2Hz. This is using the values you have suggested (10kOhm and 0.1uF).
Am I correct to understand this as any frequency below 159.2Hz will be filtered out?

In other words, it is a high pass filter that filters everything below 159Hz?

Thank you very much. When I am done with this project, I should send you a board as an appreciation.

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