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How to reduce dac output gain?
How to reduce dac output gain?
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Old 31st May 2015, 09:40 PM   #1
dacster is offline dacster  Europe
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Default How to reduce dac output gain?

Hi

My AK4495 has an LME49860 opamp.

The output gain is to high for my tube preamp.
Any idea how to reduce the output gain?

Are opamps with lover amplification and good sound available?

Thanks in advance

cheers

dacster
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Old 31st May 2015, 11:12 PM   #2
abraxalito is offline abraxalito  United Kingdom
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The opamp's gain does not determine the signal gain in your circuit, rather resistors do. If your DAC has this application schematic from the datasheet, then you'd need to increase the '1.5k' resistors connected to the DAC's output pins. You'll also need to decrease the capacitors proportionately.
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Old 1st June 2015, 12:01 AM   #3
dacster is offline dacster  Europe
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Thanks. I will check my dac's circuit diagram.

What do you think about rca input attenuators?
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Old 1st June 2015, 12:03 AM   #4
abraxalito is offline abraxalito  United Kingdom
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They might work, depending on the impedance. Have any links to specific ones?
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Old 1st June 2015, 12:30 AM   #5
rayma is offline rayma  United States
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Quote:
Originally Posted by dacster View Post
Any idea how to reduce the output gain?
A couple of resistors at the output forming an L-pad (totaling between 2k and 10k) would be fine.
For example, two 2k resistors would have an output impedance of 1k, and attenuate by 6dB.
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Old 1st June 2015, 12:41 AM   #7
dacster is offline dacster  Europe
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Quote:
Originally Posted by rayma View Post
A couple of resistors at the output forming an L-pad (totaling between 2k and 10k) would be fine.
For example, two 2k resistors would have an output impedance of 1k, and attenuate by 6dB.
What type is the best? Should they be low tolerance and matched?
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Old 1st June 2015, 01:00 AM   #8
rayma is offline rayma  United States
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Originally Posted by dacster View Post
What type is the best? Should they be low tolerance and matched?
These should be 1% metal film, 1/4 to 1/2 watt. Dale RN60 or RN65 are good.
You can match them between channels if you want, but any channel imbalance due to tolerances will be very slight.
The most it could be with 1% resistors is 0.34dB. Usually, with a typical spread of 1% resistors, it would be about half that.

Of course, you can make the two resistors unequal, to have a value of attenuation other than 6dB.
For example, if the series R is 4k and the shunt R is 2k, the atttenustion is 9.6dB.

The output resistors will not affect the op amp's operation. Just make sure the total load on the op amp
is higher in resistance than the minimum load specified for it.

Last edited by rayma; 1st June 2015 at 01:03 AM.
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Old 1st June 2015, 03:07 AM   #9
abraxalito is offline abraxalito  United Kingdom
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Quote:
Originally Posted by dacster View Post
No data is provided regarding what resistor values they're using. They'll work as attenuators for sure but might compromise your SQ. Modding the 1.5k resistors and caps around the LME opamp will likely sound better
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Old 1st June 2015, 04:25 PM   #10
dacster is offline dacster  Europe
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If I use two 4K resistors in each L pad, what attenuation I will get?
 

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