Arjen Helder TA2024 MKII Feedback Resistors

[johnviera]

Arjen Helder told me to replace the existing 100K feedback resistors with 50K. He said it would improve the output when using an iPod as the input source. The iPod seems to output around 2.84mV. Do you agree with this mod?

Can I solder a 100K in parallel and get the same result? These resistors look tiny and I don't think I could pull off the desolder and replace process.

Where are these located on the PCB? My best guess is circled in the image below.

thanks.

[nigelwright7557]

You would need to replace the resistor, you cant put one in parallel.

The output of of an ipod is quite high but definitely not line level, or mine certainly isnt.
The effect of the 100k would be to double the gain.

[Saturnus]

Originally Posted by johnviera

Arjen Helder told me to replace the existing 100K feedback resistors with 50K. He said it would improve the output when using an iPod as the input source. The iPod seems to output around 2.84mV. Do you agree with this mod?

You must have got that mixed up. Pretty sure he would suggest replacing the existing 50K ohm feedback resistors with 100K ones to increase input sensitivity.

[vacuphile]

@Saturnus,

And indeed, in that case, you could not solve the issue with soldering a resistor in parallel,

vac

[johnviera]

You are correct. I have my tech data mixed up. Going crazy over here.

here is the exact reply:

Hi there john,

As far as I know it will not be at the maximal volume, but this can be changed by replacing the feedback resistors with a 40K Ohms one instead of 20K.

This doubles the gain of the amplifier.

Greetings!

Arjen Helder

>

[johnviera]

I have measured the board and found four 20K resistors. I have emailed Arjen about which is which. How many feedback resistors are there??? Two? Right?

[Saturnus]

There's 2 feedback resistors and 2 input resistors. In this case they are all 20K ohm then.

Changing the feedback resistor to 40K ohm will indeed double the input sensitivity but not enough for your iPod. You need to have a roughly x5 difference between input resistors and feedback resistors for that, eg. 20K ohm input resistors and 100K ohm feedback resistors.

[johnviera]

Aren't you using an MP3 player as the input device for the boominator? How do you regulate the input/output level to achieve max output?

>

[Saturnus]

Originally Posted by johnviera

Aren't you using an MP3 player as the input device for the boominator? How do you regulate the input/output level to achieve max output?

Yup. And the way I described above. Keep Rin to Rfb ratio at around 1:5.

Examples of most commonly used combinations:

Rin : Rfb = 15K : 82K

(for extremely low output devices like Sony Walkman and some smartphones. The lower input resistor boost the output of the media players headphone output)

Rin : Rfb = 22K : 100K

(for very low output devices like Ipod/Iphone and most smartphones)