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cicotte 18th November 2008 09:05 AM

Autocostruire Class-t-amp-2020 capless
Hi new to the forums diy audio newb here, seems like a great place for diy audio. I was wondering if i could get some help with my Autocostruire Class-t-amp-2020. I was trying to go input capless but i think I'm doing something wrong, am getting dc at the speakers "cones are moving in and stay there". These are the steps i took to go capless. Moved the input signal ground to the bias cap pin on the tripath chip put a jumper lead across the input caps so i could leave the caps on the board incase i wanted to go back to using them,the amp is powered by batteries the signal source is a theta pro prime dac. am i missing something here any help would be appreciated.

theAnonymous1 18th November 2008 01:25 PM

This might seem obvious, but have you checked the output of your DAC for DC offset? Have you also checked to see if there is any voltage from the amp input to the ground point at the biascap pin?

audiotux 18th November 2008 02:14 PM

Hi Cicotte ,

you need the cap !
The normal DC thingie (from the other
hifi components) is not
working here .
The T-Amp need the cap to
working correct !

Greetings from Germany

DcibeL 18th November 2008 03:24 PM

Re: Autocostruire Class-t-amp-2020 capless

Originally posted by cicotte
am i missing something here
You are missing two things:
-A multimeter
-The datasheet for the TA2020.

Read the datasheet thoroughly, you should notice that the inputs have 2.5V bias, thus a DC blocking cap is necessary.

Use the multimeter to determine where the DC is in your circuit, to know if you can remove a cap before you remove the cap, place DC at your speakers and melt the voice coil.

By placing your input ground at the BIASCAP pin, I believe you have grounded the 2.5V DC bias required for the chip to work.

kristleifur 18th November 2008 05:02 PM

@DcibeL and @audiotux,
the original poster is probably refring to the "capless" mod:
... for your reference.

DcibeL 18th November 2008 05:31 PM

Thanks for that kristleifur.

My points still stand...In regards to this thread, post 2:

Originally posted by theAnonymous1
You simply connect your source ground to the BIASCAP pin of the chip instead of the analog ground. This requires you to isolate the source ground and the power supply ground and Yeo does state that in the description.
Later on in that thread, post 28:

Originally posted by BWRX
If you're just going to remove the coupling caps you need to use a floating power supply for the T-amp so that you can connect the source ground to the biascap pin (which is at 2.5V with respect to the power ground).

cicotte 18th November 2008 06:09 PM

thanks for the help guys looks like i may have to stick to the input caps at least i used some junk speakers for testing. For now ill parallel some .22uf caps on the output to optimize the amp for 4 ohm speakers am using the amp to drive totem model one's, i know not the best amp for these speakers but i think it sounds better than my nait 3 and my listening level is usually low.

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