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Old 30th April 2020, 10:19 PM   #8731
Variac is online now Variac  Costa Rica
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And perhaps if the preamp is 2nd order forward you might want a bit less in the power amp and as you’ve mentioned the speaker impedance curve affects things too. Fun to try it different ways and see what works best for your preference and your system. I agree it is hard to predict.
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Old 30th April 2020, 11:31 PM   #8732
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What comes before and after play a significant role. It is a system.

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Old 8th May 2020, 07:39 PM   #8733
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Default Sbooster vs. Meanwell

Would using an Sbooster power supply improve ACA performance over the Meanwell power supply? Has anyone tried other power supplies and found improved performance?

Thanks,

John
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Old 30th May 2020, 06:33 PM   #8734
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Default Input capacitor C3

Hello,

Maybe someone already asked this question, I was not able to find an answer however so if it's asked previously I apologize.

I was wondering if I could place a 15uf cap on C3 instead of 10uf? Currently it's stocked with an 10uf audyn cap plus (very nice cap). I came across a good deal for two 15uf jantzen silver z caps so I couldn't help but wonder if I could throw those in.

Cheerz
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Old 30th May 2020, 06:46 PM   #8735
Mooly is offline Mooly  United Kingdom
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Simple and quick answer is 'yes'. The larger value shifts the peak in the ACA's low frequency response a little but since this is around 1Hz its way below the audio band.
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Old 30th May 2020, 07:05 PM   #8736
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Alright thank you! I've known this was the case for my gainclone lm3886. I didn't know this design however and since the positive output is connected to ground I thought I'd ask before smoke magically appears.
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Old 30th May 2020, 07:09 PM   #8737
Mooly is offline Mooly  United Kingdom
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It won't let any magic smoke out

The peak in the response is caused by the two time constants of input AC coupling and AC speaker coupling. This shows 10 and 15uF for comparison.
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Old 30th May 2020, 07:15 PM   #8738
JorenC is offline JorenC
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I see. Thanks for making things visual. The graph however suggests that since the rolloff is so low in the audio band that C3 can be much lower to obtain for example a roll off at let's say 10Hz. This makes me wonder why Nelson choose the 10uf value
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Old 30th May 2020, 07:28 PM   #8739
Mark Johnson is offline Mark Johnson  United States
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JorenC you're not looking at the correct curve on the plot. Look at the DOTTED curve.
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Old 31st May 2020, 06:57 AM   #8740
Mooly is offline Mooly  United Kingdom
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Quote:
Originally Posted by JorenC View Post
I see. Thanks for making things visual. The graph however suggests that since the rolloff is so low in the audio band that C3 can be much lower to obtain for example a roll off at let's say 10Hz. This makes me wonder why Nelson choose the 10uf value
I would like to think it's because its the most suitable vs cost effective part for the job

Physically large parts like caps have a much greater chance of pickup of stray radiated noise and hash, particularly when used in high impedance locations such as C3 here. This is a 0.047uF cap

If you go smaller in value then you push the point at which the input vs output phase difference becomes a factor (the dotted line). It is 180 degrees (right hand scale) out of phase over the audio band because the amp inverts.

At low frequency the phase shift increases.

This amp behaves differently to most because the AC feedback is taken from after the speaker coupling cap. So the amp tries to increase the output voltage (before the cap) to compensate as frequency falls. That means a small value cap would increase the probability of clipping at LF.
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