UGS-DC offset

[Josip_Del]

OK one question about UGS – preamp it works great but dc offset varies from 0 to 5, 6 mV. Should I put a cap on output or what and what value? MY amp doesn’t have input cap.

[AndrewT]

Hi,
is the Power amp DC coupled?
What is the DC gain?
Multiply that gain by the worst case output offset of the pre-amp.
Is that output offset acceptable?

You have a number of solutions, I don't think you can do nothing.

a.) Insert a DC blocking cap at the power amp input, so that external offsets can't pass through.
b.) Insert a DC blocking cap in the Power amp feedback circuit to reduce DC gain to 1.
c.) Add a DC servo to the pre-amp.
d.) Add a DC detect to activate an input mute on the Power amp input.
e.) Add a DC servo to the Power amplifier.
f.) Add a DC detect to activate a speaker isolation relay/switch.

[analog_sa]

Originally Posted by Josip_Del

MY amp doesn’t have input cap.

What is really important is what is the gain of your power amp at DC. The absence of a cap is not really an issue if the dc gain is 1 but may not be pleasant if the dc gain is the same as the ac gain. Have you measured the dc at the speaker output?

[Josip_Del]

Dc offset of amp is 4 mV one channel and 8 mV other, It is symasym AAK 1.4. and on Pass amp it is 30 and 35 mV.

[analog_sa]

Is that with the preamp connected?


Looking at your amp it doesn't seem small input dc would be a problem. No need for an input cap.

[Josip_Del]

No, without preamp, just amp

[Josip_Del]

Can I insert a blocking cap at preamp output, instead at amp input?

[analog_sa]

Of course. But have you measured the offset with a preamp? Why give up performance?

[Josip_Del]

Offset with UGS is slightly higher but nothing to worry about. But I worry. Could I put a cap I don't know 47nF or 2,2uf, 10uF?

[analog_sa]

Originally Posted by Josip_Del

Could I put a cap I don't know 47nF or 2,2uf, 10uF?

Sure.