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
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
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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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.
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.
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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
Equal resistors will always give you -6dB regardless of their value.
That's because the voltage is exactly halved, and 20 x LOG ( 1/2 ) = - 6.02.
The output impedance will then be 2k.
What output impedance would be the best?
We don't know the dac's values ore the preamp values. Only the headphones that are 32Ohm.
Can I measure with my multimeter?
Would -6db and output impendance 2k be o.k.?
How I reduce to -12db?
We don't know the dac's values ore the preamp values. Only the headphones that are 32Ohm.
Can I measure with my multimeter?
Would -6db and output impendance 2k be o.k.?
How I reduce to -12db?
Lower output impedance is better, but keep the total load on the op amp more than
the rated minimum load for the op amp. More than 2k should be ok.
For -12 dB, you have -12 = 20 x LOG (loss), which means the loss is 0.25.
Then the series resistor could be 3k and the shunt could be 1k. The output impedance would be 750 Ohms.
The 3k ( actually 3.01k) and 1k are standard values of 1% resistors.
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