Removing the LPF

Sure 2024 – Signal Line Modification Part 1

SuretrichipThe Sure Electronics TA2024 Amplifier impressed on my first inspection although suffered from Poor DC offset and a slightly dull sound. This is the second modification I have made which is aimed at improving the top end sound of the amp.

Again credits for this modification must go to Audio 1st at diyaudio.com. He posted on the 11th of December 07 this modification. Since then many have tried it and reported improvements. Recently I joined this group of hobbyists.

Like the DC offset modification that I have detailed in a previous article, this is a simple modification to complete.

sure_signalside

The Sure amplifier has on the signal line a low pass filter (C3 and C24 for left and right channels), its purpose is to filter out high frequency junk from the signal line leaving the amplifier with the lower frequency Audio signal.

Unfortunately it would appear that Sure have been a little aggressive with the cut off point of the filter. Thus the filter is reducing the high end frequencies in the audible frequency range.

The solution is simple. Remove the two capacitors that connect the signal line to ground. These capacitors are the low pass filter. Their removal will stop the throttling of the higher audio frequencies. Fans of T class amplifiers like the crisp top detailed top end that Tripath chips give. It seems a shame that Sure decided to remove this signature sound from their version.

 

SureC3C24ampoutboxAnyway, let’s get on with the Mod.


First of all, the Capacitors that we are looking for here are labelled C3 and C24 on the schematic. They have values of 100nf. Like in the DC modification, locating them on the Sure Tripath TA2024 PCB is very simple. You can see them in the top corners, very near the inputs of the boards.


To remove them, various methods are available to the hobbyists, namely:

  • Using a standard solder iron
  • Destroying them
  • Using a Hot Air SMT solder station.

In the previous article, these methods are described in more detail. Needless to say, I used my KADA 852D SMT solder station to remove these caps. Advantages here are neatness, reversibility of the modification, speed and ease.

The caps were removed easily, though one thing that I would recommend when doing this. The capacitors are very close to the (fairly cheap) RCA inputs that are supplied on the PCB. On the first side that I modified, the heated airflow, though not melting, seemed to deform the plastic insulation from inside the RCA connector. Making the Test RCA lead fit inside was difficult afterwards. On the second occasion I left the RCA lead in the plug as I did the modification. Having the male plug inside stopped the plug being difficult to insert afterwards.

Trying out the amplifier after the modification, it was obvious straight away that removal of capacitors C3 and C24 has made a significant change to the sound. The top end of the audio frequencies is where I hear it. The sound is far clearer, brighter and more detailed than before. The overall sound is improved as well, the music sounding more balanced, if thinner in the mid range than before.

I will be completing this mod with all of my test amplifiers before comparing further modifications.

Next I will be examining the effects on the sound by tinkering with the power supply lines to the amplifier. Expect an article soon.