PGA2311 based (remote) volume control
So I replaced the 10K input resistors with 220K bleeder resistors. The 220 Ohm series resistors in the input circuit where replaced by 220uF bipolar capacitors, this might look as overkill, but to keep the distortion of the capacitors low, you have to reduce the AC voltage across the cap. And I put all the decoupling capacitors in place, according to the datasheet. The resistors in the output where replaced by 150 Ohm. The unit measured and performed ok, this unit was programmed for 1dB steps, which worked very good. Also you could select three sources. Which makes it a preamp. The only thing which wasn't there was a balance control.
A general remark about the PGA2311 chip, it will only give very low distortion when it is used with high level signals, high levels compared with the Quad standard of 500mV for their power amp inputs and pre amp outputs.
So to get minimum distortion, the levels between the Quad equipment must be raised. So the output of the preamp must increase, but more importantly the input sensitivity of the power amp must be set lower. The PGA2311 based unit performs at his best when the 0dB setting means full living room volume.
Then the last check. I bought a PGA2311 PA chip from our regular supplier and placed it in the unit...........The distortion and noise went slightly up! So the chip supplied was a real PGA2311 PA. Very good indeed!
- Very good casing and mechanical work.
- Electronic modules were perfectly built.
- Price quality ratio.
- Remote controled.
- Ad some form of manual, real or downloadable.
- Follow the advice in the datasheet from the manufacturer about decoupling.
- Redesign the input and output circuit to make it a real world preamp.