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Old 29th March 2005, 11:06 PM   #1
Gmorris is offline Gmorris  United States
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Question Purpose of Sonic Impact Input Cap?

Why does the SI need a high-pass filter? If I'm sure no DC is coming from my source, then I don't need a cap to block the DC, right? So the best input cap is no input cap, right? Is the cap necessary to adjust gain?

Thanks for any explanations and sorry if this has already been discussed...I couldn't find any info on it.
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Old 30th March 2005, 02:02 AM   #2
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Default Re: Purpose of Sonic Impact Input Cap?

Quote:
Originally posted by Gmorris
Why does the SI need a high-pass filter? If I'm sure no DC is coming from my source, then I don't need a cap to block the DC, right? So the best input cap is no input cap, right? Is the cap necessary to adjust gain?

Thanks for any explanations and sorry if this has already been discussed...I couldn't find any info on it.


The input cap is needed to block dc coming from the amp. There is a 2 - 3 volt bias on the input. This is needed to allow the push pull output and a single rail supply.
The standard cap is 0.33 ufd. This value needs to be raised to at least 1 ufd.
To answer yor question, it is needed.

George
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Old 30th March 2005, 11:36 AM   #3
Pano is offline Pano  United States
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George is precisely right.

It IS needed. The Sonic input caps is too small for full range audio, and probably of poor quality. Change it.
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Old 30th March 2005, 12:52 PM   #4
dgo is offline dgo  Netherlands
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Ok, so you guys say you NEED it replaced.

I don't understand. Is this purely reasoned from a technical point of view?

Or can you explain to me, what you're missing in the amps sound with the default cap?
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Old 30th March 2005, 01:24 PM   #5
UrSv is offline UrSv  Sweden
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The bass rolls off very early with the default size. It's down 3 dB at roughly 50 Hz already. Increasing it improves the low end response.
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Old 30th March 2005, 01:26 PM   #6
breez is offline breez  Finland
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-3dB at 50Hz? And the unmodded amp was praised everywhere with that response?
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Old 30th March 2005, 02:27 PM   #7
ohenry is offline ohenry  United States
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But it does so many things right...despite that shortcoming. Getting the bass corrected makes it worthy of high praise.

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Old 30th March 2005, 02:51 PM   #8
dgo is offline dgo  Netherlands
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Hmm, with such a loss, you should hear that...

I'm curious to know if that measurement is done using batteries powering the amp ? Insufficient power seems to be more of a logical reason for such a drop, which also has been reported by different sources to be the case with this amp.

I'm using a regulated PSU and I'm really not noticing that kind of a drop
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Old 30th March 2005, 03:28 PM   #9
Gmorris is offline Gmorris  United States
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So the dc is actually coming from the amp and not the source signal?

Replacing the input cap would seem to make the most noticable difference in sound but reports of people frying their amps makes me a bit nervous. I'm assuming the micro-caps and resistors make over-soldering more likely if one is not very careful. Does replacing the input cap have more or less potential of frying the amp or do all modifications have equal potential? I was thinking about using 24-ga wire as leads to fit in the holes for the original input cap....will 24ga fit?

Thanks again for any information.
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Old 30th March 2005, 04:52 PM   #10
ohenry is offline ohenry  United States
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Quote:
Originally posted by Gmorris
So the dc is actually coming from the amp and not the source signal?

Replacing the input cap would seem to make the most noticable difference in sound but reports of people frying their amps makes me a bit nervous. I'm assuming the micro-caps and resistors make over-soldering more likely if one is not very careful. Does replacing the input cap have more or less potential of frying the amp or do all modifications have equal potential? I was thinking about using 24-ga wire as leads to fit in the holes for the original input cap....will 24ga fit?

Thanks again for any information.
I didn't mod the SI board, but I did a tripath eval board and the input caps were surface mount, not through-hole design. So getting the Auricap leads soldered to the surface mount pads took magnification and patience. I'm thinking that the SI input caps are surface mount as well, but I could be wrong.
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