Reduce the audio volume on Tecsun PL-330

I found a method that does not require soldering at Baidu tieba. In FM mode, long press the number 7 key, then the display will show a blinking two digit number. Turning the volume knob will change the number and also the speaker loudness. Short press the 7 key to save the value.

===========================================

I have been using my new PL-330 radio everyday. I got annoyed by two things related to its digital volume control,

• It sets the volume to at least 10/30 for alarms, which is too loud for me.
  
• The lowest volume, 1/30, is too loud when I use earphones of low impedance.
  

So I opened the case to see if I can fix it. Immediately I saw a 16 pin chip. It is a CD1622CB, a clone of SONY's CXA1622 power amplifier.

According to CXA1622 datasheet (shown below), pin 14 controls the gain, i.e. the volume. The gain is greatest if pin 14 is connect to GND, and 0 if pin 14 is connected to pin 15.

On the PCB, a capacitor (labeled 1C25) sits between pin 14 and GND. I measured the voltage on pin 14 while I rotated the volume knob. The results matched the datasheet. I also shorted pin 14 and pin 15, the speaker got muted.

So to reduce the speaker volume, I need to raise the voltage on pin 14. This can be achieved by adding a suitable resistor between pin 14 and pin 15. I experimented with 4.7k, 10k, and 22k. I found 10k most suitable. So I soldered it on.

And now I can use a volume of 6/30 with earphones. And alarms are no longer annoying.

UPDATE

I found the volume levels were not granular enough after the resistor mod. So I removed the resistor and soldered an 1 Watt 20 Ohm resistor in series with the speaker.

Tecsun PL-330 Portable Radio Review

Tecsun released their latest PL-330 portable DSP receiver this summer. I acquired a Chinese version last week for $73.

The good,

• It is compact (139 x 85 x 26 mm) and lightweight (~220g).
• The build quality is good.
• I like the completely flat front surface.
  
• It supports AM synchronous detection and single side band demodulation.
• The easy tuning mode (ETM) has been improved to store shortwave results by clock time.
• You can sort the memory by frequency by long pressing the 0 button when powered off.
• It supports direct frequency entry.
• FM reception is very good.
• The power button is at the correct place and large enough.
• Tecsun finally introduced a tuning step button instead of relying on the user to rotation the tuning knob slowly for fine tuning.
• AM band has three bandwidths, 2.5, 3.5, and 9 kHz.
• AM SSB mode has 0.5, 1.2, 2.2, 3.0, 4.0 kHz bandwidths.
• The digital volume control allows different volume for alarms.
• It supports both 70 us and 50 us FM de-emphasis time constants.
  

The not so good,

• No air band support.
  
• I am not a fan of the tuning and volume knobs. I prefer the style on PL-380.
• MW and SW reception is average.
  
• No FM RDS although its DSP chip supports RDS decoding.
• Synchronous detection does not work well.
• The USB port is micro USB, not type C.
• No 6 kHz bandwidth for AM. 9kHz is too wide to be useful.
• Supports only one alarm clock.
• The snooze button is too small to be useful.
• LCD vertical view angle is small (less than ~90 degrees).
  

The bad,

• It uses the BL-5C lithium battery instead of two/three AA batteries. BL-5C holds less charge than two AA batteries. And it is hard to find good quality BL-5C batteries.
  
• An SSB reverse fine tuning bug was reported by Pawel Kita. (I did not verify.)
  
• It is difficult to operate in darkness. The buttons have a very short travel. The nine buttons on the right are too small. And the "5" button does not have a bump.
• It mutes very briefly while tuning like other DSP radios.
  

I also took it apart for some pictures. There is a connector hidden under the LCD. I guess it is for firmware update.

back

front

In conclusion, PL-330 is worth the ~$70 price. I hope Tecsun fix the small bug in the next firmware release. If you want air and NOAA weather bands, I would recommend CC Skywave SSB.