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Increase input impedance
Increase input impedance
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Old 21st March 2018, 06:23 AM   #1
nzlowie is offline nzlowie  Australia
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Default Increase input impedance

Hi all

For my active horns I want to run 2 amps feed from the one DAC, each amp has an input impedance of 10k this means that the combined load maybe too great on my DAC. I want to include a passive volume control in the mix, if I feed the DAC into the volume pot, say 20k that would be a constant load on the DAC, yea? The output of the pot (wiper) would then go to both amps or should I have a dual gang pot where 1 wiper goes to each amp?

Appreciate your thoughts and other possible solutions.

Cheers Dave
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Old 21st March 2018, 07:32 AM   #2
jan.didden is offline jan.didden  Europe
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Two comments:

I do not know of any DAC that has a problem with 5k load. It's not that heavy.

Second, if you add a pot and want a 'good feel' to the settings, the rule of thumb is that the pot impedance is 5 to 10x lower than the load. That means a pot of say 1k to 2k, which makes the load on the DAC much heavier.

So if you don't need the pot, don't use it and just use the DAC and power amps as is, no problem!


BTW A pot is not a constant load to the DAC, the load depends on the pot setting. The impedance the DAC 'sees' is the top part of the pot, plus the parallel impedance of the bottom part of the pot and the load. So the total depends on the post settings and is not constant.

Jan
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Last edited by jan.didden; 21st March 2018 at 07:34 AM.
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Old 21st March 2018, 07:39 AM   #3
nzlowie is offline nzlowie  Australia
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Thanks for the good explanation of the pot loading.
Might just give it a go feeding directly into the amps.

Cheers
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Old 21st March 2018, 07:57 AM   #4
jan.didden is offline jan.didden  Europe
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Yes, if your DAC has some sort of volume control I would check that out first. It's very easy to pack too much gain in a chain that you then have to throttle back and that is generally not good for the signal to noise ratio.

Jan
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Linear Audio pubs and articles . The SilentSwitcher now at diyaudio store SilentSwitcher. Keeping in touch with SY.
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