|Sure TA2024 DC offset Mod|
In the last article we looked at the Sure TA2024 amplifier boards, fresh from their box. Amongst the issues identified is that the Sure boards have an issue with DC offset. This article shows how with a very quick modification the DC offset of the boards can be improved upon.
Sure Tripath amplifier chips from other manufacturers are not normally reported as having DC offset problems, so why does the Sure board exhibit these issues.
Looking at the Schematic, the Sure board differs from that of other manufacturers by the inclusion of a resistor network. Resistors R3 and R16 connect this network to the inputs of the amplifier.
Audio 1st at DiyAudio identified that removing these resistors from the board was all that was required in order to reduce the dc offset back to normal levels.
Let's locate these on the Sure Tripath boards.
Looking at the board we can see that all the resistors and capacitors that can be seen on the left hand side of Sure’s schematic are conveniently grouped to the left of the Tripath 2024 chip. All that we have to do is to remove the resistors marked in the picture.
Obviously these resistors are surface mount devices, and rather tiny as well. There are a number of options that can be used to remove these resistors
Standard soldering irons can be used to remove Surface mount components. The problem that we face in doing this is in heating the pads up on both sides. I have seen double tipped soldering irons that are design ed for this very purpose, but at around £50 I don’t think these make good value for money. I suppose if you do own two soldering irons, with one in each hand you could use this.
Alternatively, and this will be made easier due to the very small size of the resistors on this board you could use a standard iron. If you melt a glob of fresh solder over the whole resistor, the solder itself will transfer the heat to both pads of the resistor. Using a sideways swipe with the iron should then lift the resistor away from the pads. You can wipe the resistor off the iron tip then with your wet sponge.
The destruction method.
Whilst not a neat way of doing this modification, another route to take that involves no soldering tools at all, is to simply crush the offending resistors. A set of snips can be used for this purpose, though I am sure that the imaginative use of other tools could also be employed
Using a hot air solder station.
Having just received a Kada 852D solder station this month, of course this would be my first chance to do something useful with it. I used the smallest nozzle and set the temperature to 300c and the airflow to low.
After lifting half a pad I realised that the best method for me in doing this was:
Grip the resistor with a pair of hooked tweezers.
Apply the heat flow to the resistor.
Whilst doing so, gently twist the resistor.
When you see a little movement on the resistor, hold the airflow for a second or two longer before sliding the resistor off of the pads and then lift it away from the PCB.
The results are impressive.
You can see from the table that all of the high figures for DC offset have been reduced considerably. Note however, that on the final amplifier, which already had a low DC offset, the resistor bridge was presumably working as Sure had intended it. Disconnecting the resistor bridge from the amplifier in this case had a negative effect.
I would suggest that anyone buying the Sure TA2024 Amplifier considers the DC voltage modification as their first step in the amplifiers modification diet. For the little work that is involved, the results speak for themselves. Sound wise nothing changes with this modification. This is purely to protect the speakers.
A step further.
I have seen others who have further reduced the DC output of the amplifier, by installing a variable resistor onto the pads that have been left. Then the resistor value can be altered until near zero DC offset is achieved.
In this later article, DC Offset Mod II, I successfully reduce the DC offset from the Sure Tripath TA2024 based amplifier module to zero!