Radio to Speaker Box Conversion - Noise Problem

andyvp · 29th October 2012, 06:51 PM

I started a project that consists of gutting an old tube radio from the 50’s. I built a hard board box insert and mounted a 3” speaker.
I have a Kemo 18watt Mono amp that I wired through the old pot. I solder it all up and turn it on. I get distorted music and loud hiss. Switched pot works as it probably should.
To start trouble shooting I disconnect the amp from everything including pot to eliminate noise sources and reconnect to the power supply and 3.5 audio input (right channel only)

The result is there is audio but the loud hiss remains. Adjusting the volume at the source will turn the audio up or down but the hiss stays at the same level. At High volume the audio can almost drown it out.

What can I do to filter out this noise?
(btw this is my first electronics project like this so saying I’m a novice would be giving me to much credit)
Thanks in advance!

Parts list:
3” speaker
Specifications: • Power handling: 15 watts RMS/30 watts max
• VCdia: 3/4" • Impedance: 8 ohms • Re: 6.6 ohms
• Frequency range: 100-20,000 Hz • Fs: 106 Hz • SPL: 84.5 dB 1W/1m

Kemo M033N 18 Watt Universal Mono Amplifier Module
Specifications: • Operating voltage: 8 - 20 VDC • Current consumption < 800 mA
• Input sensitivity: < 80 mV • Compatible speakers: 4 - 16 ohm
• Output: maximum 18W into 4 ohms with 20V power supply • Frequency response: 40 - 20,000 Hz •

12 VDC 2A Switching Power Supply AC Adapter

3.5mm panel jack

Power plug

turk 182 · 3rd November 2012, 03:02 PM

have you tried bypassing the input line with a cap?
does the hiss go away or reduce if you connect the input lead to ground

andyvp · 11th November 2012, 10:11 PM

I switched to a different power supply with improved results. it's rated at 12VDC, 800mA. It reads 16 volts on the meter though.

The hiss is lower but still too loud. BUT it goes away completely when I touch ground. It sounds great so I would like to figure it out. The hiss also increases a lot when i get close to touching the + input line.

Any ideas?

turk 182 · 11th November 2012, 11:19 PM

well andy
you've already learned a few things.
first not all wallwarts /supplies are created equal your new one that helped with the noise probably has better filter caps then the first one.
secondly that noise problems can and will cause all kinds of troubles some of what you described might be helped by shielding

29th October 2012, 06:51 PM	#1
andyvp diyAudio Member Join Date: Oct 2012	Radio to Speaker Box Conversion - Noise Problem I started a project that consists of gutting an old tube radio from the 50’s. I built a hard board box insert and mounted a 3” speaker. I have a Kemo 18watt Mono amp that I wired through the old pot. I solder it all up and turn it on. I get distorted music and loud hiss. Switched pot works as it probably should. To start trouble shooting I disconnect the amp from everything including pot to eliminate noise sources and reconnect to the power supply and 3.5 audio input (right channel only) The result is there is audio but the loud hiss remains. Adjusting the volume at the source will turn the audio up or down but the hiss stays at the same level. At High volume the audio can almost drown it out. What can I do to filter out this noise? (btw this is my first electronics project like this so saying I’m a novice would be giving me to much credit) Thanks in advance! Parts list: 3” speaker Specifications: • Power handling: 15 watts RMS/30 watts max • VCdia: 3/4" • Impedance: 8 ohms • Re: 6.6 ohms • Frequency range: 100-20,000 Hz • Fs: 106 Hz • SPL: 84.5 dB 1W/1m Kemo M033N 18 Watt Universal Mono Amplifier Module Specifications: • Operating voltage: 8 - 20 VDC • Current consumption < 800 mA • Input sensitivity: < 80 mV • Compatible speakers: 4 - 16 ohm • Output: maximum 18W into 4 ohms with 20V power supply • Frequency response: 40 - 20,000 Hz • 12 VDC 2A Switching Power Supply AC Adapter 3.5mm panel jack Power plug

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3rd November 2012, 03:02 PM	#2
turk 182 diyAudio Member Join Date: Oct 2012	have you tried bypassing the input line with a cap? does the hiss go away or reduce if you connect the input lead to ground

11th November 2012, 10:11 PM	#3
andyvp diyAudio Member Join Date: Oct 2012	I switched to a different power supply with improved results. it's rated at 12VDC, 800mA. It reads 16 volts on the meter though. The hiss is lower but still too loud. BUT it goes away completely when I touch ground. It sounds great so I would like to figure it out. The hiss also increases a lot when i get close to touching the + input line. Any ideas?

11th November 2012, 11:19 PM	#4
turk 182 diyAudio Member Join Date: Oct 2012	well andy you've already learned a few things. first not all wallwarts /supplies are created equal your new one that helped with the noise probably has better filter caps then the first one. secondly that noise problems can and will cause all kinds of troubles some of what you described might be helped by shielding