Let’s say you’re building a passive preamp, whether it be a typical attenuator or maybe an autoformer, and you wanted two inputs, one for a cd player and a tuner - and one output for a power amp. Really basic, right?
Keeping it really basic, let’s say you don’t want to include a source selector switch. You could have one pair of input jacks on the preamp and plug in the CDP interconnects when listening to cd’s, and unplug those and plug in the tuner’s interconnects when listening to the tuner. Or just have one pair of interconnects and swap one end back and forth between sources, while keeping the other end permanently connected to the preamp. Kinda of a hassle, but I’m sure there are some that do this.
Are there other ways to handle the two sources without the use of a selector switch? What about having two pairs of input jacks (one for each source) and have them both wired to the volume pot? Since you would be listening to one source at a time, would the fact that the other input jack being wired to the volume pot (with no signal input of course) have any detrimental effects? Would there be any capacitance issues?
Keeping it really basic, let’s say you don’t want to include a source selector switch. You could have one pair of input jacks on the preamp and plug in the CDP interconnects when listening to cd’s, and unplug those and plug in the tuner’s interconnects when listening to the tuner. Or just have one pair of interconnects and swap one end back and forth between sources, while keeping the other end permanently connected to the preamp. Kinda of a hassle, but I’m sure there are some that do this.
Are there other ways to handle the two sources without the use of a selector switch? What about having two pairs of input jacks (one for each source) and have them both wired to the volume pot? Since you would be listening to one source at a time, would the fact that the other input jack being wired to the volume pot (with no signal input of course) have any detrimental effects? Would there be any capacitance issues?
So effectively with the two sources in parallel? It depends on how the output of the unused source behaves when it is off. For example, when it has a muting relay straight across its output, that will short-circuit the output of the source you want to listen to.
When you keep the CD player on while listening to the radio, just with no CD playing, the tuner output will be loaded by the quite low output impedance of the CD player, causing signal loss, possibly gross distortion and probably some weird behaviour in the bass.
You could try 2.2 kohm or so resistors between the inputs and the potmeter, each input getting its own resistor. That might work, or it might not.
When you keep the CD player on while listening to the radio, just with no CD playing, the tuner output will be loaded by the quite low output impedance of the CD player, causing signal loss, possibly gross distortion and probably some weird behaviour in the bass.
You could try 2.2 kohm or so resistors between the inputs and the potmeter, each input getting its own resistor. That might work, or it might not.
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People build amplication into their mixers for a reason. Paralleling outputs can cause tiny volume through the resistors, or without resistors the two sources can damage each other. Passive preamps with multiple inputs require cable swaps, resistors reducing each source, a selector switch, or source damage.
Good selector switches have become hard to buy with the movement of all production to a source of lies and counterfeits. "Gold plate" now means maybe a millionth of an inch, except in retail jewelry where FTC regulation actually means anything. I have moved on to powered mixers, where good op amps and PCBs can still be purchased.
Good selector switches have become hard to buy with the movement of all production to a source of lies and counterfeits. "Gold plate" now means maybe a millionth of an inch, except in retail jewelry where FTC regulation actually means anything. I have moved on to powered mixers, where good op amps and PCBs can still be purchased.