Audio cliping with NJM2755 input selector

smartroad · 8th February 2020, 10:22 AM

Hi all!

I have been building my own mini amplifier system and ran out of inputs. I decided to use an NJM2755 4 to 1 stereo audio switch to increase my input availability.

I have done a test circuit with it, following the application circuit diagram in the datasheet to start. The device works very well when switching. However I have found that with my CD player, Minidisc and DAT the audio is being clipped at higher volumes, only my tape cassette doesn't clip but I think that is more as tape cant get loud enough! I can't figure out why it is distorting. It is being supplied with the required nominal 9V.

I am asking on the off chance anyone has any experience on using this chip (NJM2755 | NJM2755V | 4-Input / 1-Output Stereo Audio Selector)

Here is my amp that I have made and it is feeding into: Customizable 20W Amplifier | Hackaday.io

smartroad · 8th February 2020, 12:28 PM

I'm an idiot! I was trying to figure out where in the system the audio was distorting. I discovered that when I connected the CD player directly to the amplifier (missing out the tone controller in my amp) then the audio was crystal clear. I then connected the CD player to one of the inputs on my amp and the distortion was there again. So it isn't the NJM chip causing the issues.

I figured out that the problem was the way I have setup the various volume controls. The main volume is controlled using the amp boards built in control. However the TDA selector and tone chip also has a volume control. Long story short, I had set that volume to high and THAT was causing the distortion

.

On the bright side I've updated the firmware to break out that setting so I can adjust if needed in the future without re-compiling!

Lesson here for me, methodically diagnose the problem first and don't jump to conclusions!!

Thmr · 24th January 2021, 01:01 PM

Quote:

Originally Posted by smartroad

Hi all!

I have been building my own mini amplifier system and ran out of inputs. I decided to use an NJM2755 4 to 1 stereo audio switch to increase my input availability.

I have done a test circuit with it, following the application circuit diagram in the datasheet to start. The device works very well when switching. However I have found that with my CD player, Minidisc and DAT the audio is being clipped at higher volumes, only my tape cassette doesn't clip but I think that is more as tape cant get loud enough! I can't figure out why it is distorting. It is being supplied with the required nominal 9V.

I am asking on the off chance anyone has any experience on using this chip (NJM2755 | NJM2755V | 4-Input / 1-Output Stereo Audio Selector)

Here is my amp that I have made and it is feeding into: Customizable 20W Amplifier | Hackaday.io

Hello dear smartroad, I will be very grateful if you explain in more detail or run a diagram on how you have implemented the control of the inputs of NJM2755.

davidsrsb · 24th January 2021, 03:29 PM

Make sure you run the NJM2755 at 9V supply. It will work at 5V, but clip easily.

Thmr · 12:01 PM

Hi, after some research I found this NJM2755 binding scheme involving PIC16F88. My question is is this a working circuit, and should the PIC16F88 be programmed? Regards.

Thmr · 2nd February 2021, 12:25 PM

i-매거진

Thmr · 2nd February 2021, 12:36 PM

Quote:

Originally Posted by Thmr

Hi, after some research I found this NJM2755 binding scheme involving PIC16F88. My question is is this a working circuit, and should the PIC16F88 be programmed? Regards.

The site with the scheme is Korean, in the post above

Mark Tillotson · 2nd February 2021, 09:12 PM

Any microcontroller needs programming. It wouldn't be hard to switch the device with
a rotary switch though, the 1µF/100k circuit used in the datasheet to reduce pops seems a
good idea.

8th February 2020, 10:22 AM	#1
smartroad diyAudio Member Join Date: Feb 2020	Audio cliping with NJM2755 input selector Hi all! I have been building my own mini amplifier system and ran out of inputs. I decided to use an NJM2755 4 to 1 stereo audio switch to increase my input availability. I have done a test circuit with it, following the application circuit diagram in the datasheet to start. The device works very well when switching. However I have found that with my CD player, Minidisc and DAT the audio is being clipped at higher volumes, only my tape cassette doesn't clip but I think that is more as tape cant get loud enough! I can't figure out why it is distorting. It is being supplied with the required nominal 9V. I am asking on the off chance anyone has any experience on using this chip (NJM2755 \| NJM2755V \| 4-Input / 1-Output Stereo Audio Selector) Here is my amp that I have made and it is feeding into: Customizable 20W Amplifier \| Hackaday.io

2nd February 2021, 11:33 AM	#5
Thmr diyAudio Member Join Date: Jan 2021	Hi, after some research I found this NJM2755 binding scheme involving PIC16F88. My question is is this a working circuit, and should the PIC16F88 be programmed? Regards. Last edited by Thmr; 2nd February 2021 at 12:01 PM.

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8th February 2020, 12:28 PM	#2
smartroad diyAudio Member Join Date: Feb 2020	I'm an idiot! I was trying to figure out where in the system the audio was distorting. I discovered that when I connected the CD player directly to the amplifier (missing out the tone controller in my amp) then the audio was crystal clear. I then connected the CD player to one of the inputs on my amp and the distortion was there again. So it isn't the NJM chip causing the issues. I figured out that the problem was the way I have setup the various volume controls. The main volume is controlled using the amp boards built in control. However the TDA selector and tone chip also has a volume control. Long story short, I had set that volume to high and THAT was causing the distortion . On the bright side I've updated the firmware to break out that setting so I can adjust if needed in the future without re-compiling! Lesson here for me, methodically diagnose the problem first and don't jump to conclusions!!

24th January 2021, 03:29 PM	#4
davidsrsb diyAudio Member Join Date: Dec 2005 Location: Kuala Lumpur	Make sure you run the NJM2755 at 9V supply. It will work at 5V, but clip easily.

2nd February 2021, 12:25 PM	#6
Thmr diyAudio Member Join Date: Jan 2021	i-매거진

2nd February 2021, 09:12 PM	#8
Mark Tillotson diyAudio Member Join Date: May 2018 Location: Cambridge UK	Any microcontroller needs programming. It wouldn't be hard to switch the device with a rotary switch though, the 1µF/100k circuit used in the datasheet to reduce pops seems a good idea.