Burble. Uhm... You would probably get a getter answer from someone else but...
http://www.ti.com/lit/ug/slou441/slou441.pdf
Piccy Figure 6) page 18) Input impedance to the amplifiers is 10K. Set it up single ended and use a 10K log pot. Not sure which way up things would go and it might be an anti-log pot but wiper to input on the RCA. Top to your source. Bottom to ground on the RCA.
Audio Taper...
What are Audio Taper Potentiometers?
I mention the input impedance because that will likely modify the response.
Attachments
Not via jumpers...
http://www.ti.com/lit/ug/slou441/slou441.pdf
Piccy is Figure 6) on Page 18). R8 and R41 set the gain (With R7 and R42) for the SE/DIF amplifiers. Input impedance is set by R7 and R42. Gain is R8/R7 and R41/R42.
Gain as supplied is unity. Change R8 and R41 to 20K for a gain of 2. You can do similar with R7/R42 but it changes the input impedance. 20K would give a gain of 1/2.
Don't go mad.
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Attachments
The TPA3255 intrinsic gain is 21.5dB (11.88x). With post filter feedback (PFFB), it is 15.93dB. The Chinese EVM copies that boost the gain with the input buffers are doing so at the expense of more noise and distortion and perhaps risking stability.
http://www.ti.com/lit/an/slaa788a/slaa788a.pdf
A proper preamp that can drive about 2.7Vrms (in SE mode) is needed to make a 21.5dB amp hit a maximum of 90Vpp to clip. In BTL balanced drive, the preamp needs only half of this since there are two legs, each 180deg in phase apart.
If running PFFB with 15.93dB (6.26x) of gain is going to require a preamp that can 5.08Vrms (in SE) or 2.54Vrms in balanced drive to have the BTL amp reach clip.
http://www.ti.com/lit/an/slaa788a/slaa788a.pdf
A proper preamp that can drive about 2.7Vrms (in SE mode) is needed to make a 21.5dB amp hit a maximum of 90Vpp to clip. In BTL balanced drive, the preamp needs only half of this since there are two legs, each 180deg in phase apart.
If running PFFB with 15.93dB (6.26x) of gain is going to require a preamp that can 5.08Vrms (in SE) or 2.54Vrms in balanced drive to have the BTL amp reach clip.
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You can drive an amp with 28dB gain with your phone. Let's say you want to run your 8ohm speakers at 100w for a backyard party. Can your phone's little 3.5mm dongle headphone out do this?
Power = Vrms^2 / Impedance solve for voltage needed we get Vrms = sqrt(Power x Impedance) = sqrt(100W x 8ohms) = 28.3Vrms Output.
28dB of gain is 10^(28/20)=25.1x (25.1 times)
Gain = Vout/Vin solve for Vin = Vout / Gain
Vin = 28.3Vrms / 25.1 = 1.13Vrms
So your source needs to be able to drive a 10kohm load to 1.13Vrms (or 3.2Vpp).
Most portable sources can do this. Your phone may or may not be able to but you know what you need now.
Power = Vrms^2 / Impedance solve for voltage needed we get Vrms = sqrt(Power x Impedance) = sqrt(100W x 8ohms) = 28.3Vrms Output.
28dB of gain is 10^(28/20)=25.1x (25.1 times)
Gain = Vout/Vin solve for Vin = Vout / Gain
Vin = 28.3Vrms / 25.1 = 1.13Vrms
So your source needs to be able to drive a 10kohm load to 1.13Vrms (or 3.2Vpp).
Most portable sources can do this. Your phone may or may not be able to but you know what you need now.
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