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Removing / replacing output caps on a DAC
Removing / replacing output caps on a DAC
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Old 10th November 2017, 11:10 PM   #11
ig983 is offline ig983
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At the moment the first elements in the amp are two resistors 680ohm and 47K. I took out a cheap 100k pot and placed just two (higher quality) resistors to give me a fixed value and the rest of the volume is contolled digitally.

I hope this answers the input impedance question.
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Old 10th November 2017, 11:19 PM   #12
rayma is offline rayma  United States
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Quote:
Originally Posted by ig983 View Post
At the moment the first elements in the amp are two resistors 680ohm and 47K.
I took out a cheap 100k pot and placed just two (higher quality) resistors
IF a low end roll off at around 20Hz is ok, then you could make this work, especially if
the coupling capacitor is increased to 0.22uF or more. The R100 and R101 should be increased
to about 200k to minimize the bass roll off. If you could replace the 47k that you installed
in the amp with a higher value of 100k or more, that will also help. The same goes for
increasing R72 and R73 to about 200k. Is it a tube or transistor amplifier?

Last edited by rayma; 10th November 2017 at 11:30 PM.
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Old 10th November 2017, 11:30 PM   #13
ig983 is offline ig983
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This is a tube preamp / LM1875 chipamp hybrid.
I can change the 47k to 100k, no problem.
What levels of attenuation would that give me?
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Old 10th November 2017, 11:32 PM   #14
rayma is offline rayma  United States
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Quote:
Originally Posted by ig983 View Post
This is a tube preamp / LM1875 chipamp hybrid.
I can change the 47k to 100k, What levels of attenuation would that give me?
If you want an input attenuator on the amp, just scale up both input resistors
by the same factor to keep the same attenuation. I'd scale both up by around
a factor of four, from what you have now.
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Old 10th November 2017, 11:39 PM   #15
ig983 is offline ig983
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Meaning to keep more or less the attenuation of 680ohm and 47K I`d have to go with 1K3 and 100K.
Got it.
Rayma you`ve been such a help. Thank you so much
And thanks to wwenze and kaputt for their input
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Old 10th November 2017, 11:46 PM   #16
rayma is offline rayma  United States
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Originally Posted by ig983 View Post
Meaning to keep more or less the attenuation of 680ohm and 47K I`d have to go with 1K3 and 100K.
The amplifier input attenuation is only about -0.1dB, so the relative values aren't critical here.
I'd just use 1k and 200k.
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Old 10th November 2017, 11:51 PM   #17
ig983 is offline ig983
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Ok, I`ll go with that
Thank you
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Old 11th November 2017, 09:23 AM   #18
ig983 is offline ig983
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Rayma just one thing, tell me please do you know how the change in uF cap size and higher input impendance should affect the sound? Does it matter?
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Old 11th November 2017, 02:36 PM   #19
rayma is offline rayma  United States
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Originally Posted by ig983 View Post
Rayma just one thing, tell me please do you know how the change in uF cap size
and higher input impendance should affect the sound? Does it matter?
You can try that right now, before working on the DAC.
Just increase the 47k to 200k in both channels of the amp.
It will improve the bass response. There should be no downside.

The brand and type of capacitor will affect the sound more than
the uF value from changing say 0.1 to 0.22.

Last edited by rayma; 11th November 2017 at 02:38 PM.
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