I want to start by saying thanks for those who responded.
I’m attempting to build my first speaker setup. I have chose the TDA7850 IC due to its simplicity and have concerns about multiple audios sources.
I’m planning on adding a Bluetooth module, 3.5mm jack, and an iPod connector since I have it lying around.
My question is how do I handle the different audio voltages. For instance if I feed the 3.5mm input and have the volume set at a particular level, when connecting Bluetooth wouldn’t the volume level change if it has lower or higher input voltages?
How would I handle this? I’ve stumbled across Automatic Gain Control so would this be a viable option? Or does anyone else have a recommendation?
I’m attempting to build my first speaker setup. I have chose the TDA7850 IC due to its simplicity and have concerns about multiple audios sources.
I’m planning on adding a Bluetooth module, 3.5mm jack, and an iPod connector since I have it lying around.
My question is how do I handle the different audio voltages. For instance if I feed the 3.5mm input and have the volume set at a particular level, when connecting Bluetooth wouldn’t the volume level change if it has lower or higher input voltages?
How would I handle this? I’ve stumbled across Automatic Gain Control so would this be a viable option? Or does anyone else have a recommendation?
Found an old HEATHKIT ss RECEIVER in the Goodwill bin, which had a board underneath with two CTS level trimmer potentiometers, handling L&R, for each input. So get some trimpots, mount them to a perfboard, wire them up to your inputs. They dont have to be "audio taper" or anything special. With solid state audio sources, I suppose any value from 10K to 250K would work, though which value is best to "load the source" may be debatable here.
A typical preamp has two sensitivity levels. About -50dBm for the RIAA phono and microphone inputs, and about -20dBm for all "line level" inputs. A headphone jack is a bit higher than most line level devices but because it is much lower impedance, the voltage is not drastically different, and a headphone signal has its own volume control. This will require about 10dB adjustment of the volume control, but this is not much on an audio taper pot. The volume control is late in the pre-amp chain, usually the last thing. This is so that pre-amp noise is reduced with the music. This means that the earlier stages must have the headroom to handle unattenuated inputs. Typical signal stages can handle +20dBm so this is not usually a problem.
Well, no. It makes sense to reduce the higher levels to match the lower. Because running a signal through a potentiometer - a resistor divider - is less of a signal molestation than running it through an amplifier - any amplifier. Heck, some even believe running a signal through a certain type of wire molests it - hence the "cable wars" and all the endless discussion therein.
So for several inputs, all running simultaneously, with a selector switch that you want to go across all of them and have each sound about the same loudness, it's best to reduce the signal of the louder input to match that of the quietest. Versus amplify all the quieter to match the loudest. The only exception would be if the quietest doest allow the amplifier to go to full volume, then you have to amplify it to be able to do so. Just, in case you want to play something from that source really loud.
Not necessarily true, depends on the value of the potentiometer, stray reactances, noise floor. The lowest distortion opamps are able to exceed the linearity of a cheap log-taper carbon track pot I suspect too. Linear taper pots cancel out voltage coefficient to first order and can be very performant, admittedly. However you need gain somewhere and placing it before the pot risks headroom limitation issues on strong sources, placing it after risks noise issues on weaker sources.
An active volume control doesn't have to compromise noise performance / headroom, since it avoids the situations where a signal is both attenuated and amplified, in other words the the best all-round performer isn't just a pot in a signal path, its a pot with feedback wrapped around it... The Baxandall approach is hard to beat for all-round performance when well implemented.
And for a practical example nearly every small personal music player or phone has much lower output than can drive typical power amps to full output.
I appreciate everybody’s input. I have a test circuit with a lm386 and my placing various resistors between the audio source and volume pot allowed me to control the input voltage. I’m waiting on the Bluetooth module and actual IC to get here so I can do measurements and adjust accordingly.
Just out of curiosity could something like a summing amplifier be used? I have some knowledge of it and have been researching everyday on different topics. Just wondering if you guys have tried this.
Just out of curiosity could something like a summing amplifier be used? I have some knowledge of it and have been researching everyday on different topics. Just wondering if you guys have tried this.
Yeah, but if two sources are on simultaneously, you'll hear both. I suppose that could be managed by turning everything off, except the one you want to listen to. Versus an input selector switch.
As Frank Zappa once suggested. I couldnt do it. I guess I'm just not open minded enough...