Tecsun PL-606 Digital PLL Portable Radio + Electronic volume control hack

I did some searching on my own to get a perfect little pocket radio and this Tecsun PL-606 model gave me the perfect balance between price and performance. Granted there are other better models available that are twice more expensive which might have slight edge over longevity or have additional features But, overall I am happy with my “ultra-light” DXers portable radio.

PROS

• Highly sensitive receiver across the entire commercial bands (AM/FM/SW)
• Uses standard AAs or rechargeable. Excellent battery life! 
• Incorporates a [Ni-MH] 'built-in' Battery charger for the two AAs 
• Amber color Backlit LCD display, (Can be turned off to save battery)
• Very good sounding built-in speaker. Plenty loud for personal listening. Good fidelity.
• FM Stereo audio output via headphone jack! (mono mode by press of a button)

CONS (*)

• The electronic tuning knob jumps frequencies at random while tuning
• The tuning process temporarily mutes the sound which is super annoying!
• The electronic volume control is very low at level "3" and very high on level "4"
• There is some fair amount of audible hiss when using headphones at low volumes.

(*)The above mentioned CONs are 'fixable' to some extent especially the 'electronic volume' control oddity and audible hiss at very low volumes. I am not an electronics expert but I have some fair knowledge in this area. The audio amplifier IC CD1622CB which is actually a 'Chinese version' of SONY's CXA1622M used in this radio. That IC is designed to have a very high gain audio output to drive the built-in speaker and thereby the low volume hiss on headphone out. The noticeable 'low volume' audio hiss on headphones output can be eliminated by using a high impedance headphones (60 ohms or higher) or use a 'in-line' volume control type headphones to reduce the low volume hiss.

The irritating electronic volume control levels going from very low output at "3" and uncomfortably high on "4" does bother me as I listen to this radio in the night. I have hacked this radio so that I can now comfortably listen at low volumes without experiencing sudden jump in volume using headphones (See Below for the hack)

The hack is unconventional method but simple. Idea is to very slightly increase the voltage to Audio IC's pin14 to effectively control the audio output gain value and that should effectively shift the sudden jump in gain to higher value number on the digital display. The hack is to connect PIN 14 [VOL] of the The audio amplifier IC CD1622CB with Pin 9 [Vcc] with a high value resistor 1 Megaohm (MΩ) resistor. I used standard off-the-shelf 1/4 resistor but using smaller size SMD resistors is the best way to make it pretty. But hey it works!. 

Please note: This hack is tested only on Tecsun PL-606 while I understand various Tecsun radios use similar ICs. It depends on the DSP used in a particular model as that chip/IC provides the voltage to PIN 14 of CD1622CB to increase or decrease the volume level.

The other annoying 'soft-mute' of sound done by the DSP during the tuning process cannot be modified as far as my knowledge goes since I am not an expert programmer to change the code written onto the Silicon Labs Si4734 DSP chipset.

If anyone has ideas how to disable the 'soft-mute' please share your ideas in the comments section. 

If you want to get one of these from Amazon you can use this link below:

Tecsun PL-606 Digital PLL Portable Radio FM Stereo/LW/SW/MW DSP Receiver