This is probably too basic to be interesting for most people around here, but I have a number of devices I'm feeding into a 100W power amp (all from their headphone out jacks) driving a set of speakers for my home audio system and I'm having trouble getting the relative levels of all these devices balanced.
My TV, a couple different MP3 players, and a computer all seem to have different headphone out levels, so one might be turned way up and others down or in the middle for me to hear them at a similar volume.
So the goal is to have the amp's volume static and control the volume on the individual devices using their remotes. Ideally, having the volume somewhere in the middle on all the devices would result in roughly the same volume overall.
The Amp is has auto-sensing and will turn itself on only when there's a signal, so made to be stashed in a closet and forgotten.
Anyway, I think I need something to boost the low signals and attenuate the high ones. I was looking around and found some options and would like to know if anyone here can tell me if one would work or if they have a better solution. Below are the things I found but not sure if they are appropriate to what I'm going for. Thanks for any advice.
DC Input 12V 2 Channel Stereo Power Amplifier Module Kit 1W Based on TDA2822M | eBay
Low Voltage Audio Stereo Amplifier Module Based on NJM2073D | eBay
My TV, a couple different MP3 players, and a computer all seem to have different headphone out levels, so one might be turned way up and others down or in the middle for me to hear them at a similar volume.
So the goal is to have the amp's volume static and control the volume on the individual devices using their remotes. Ideally, having the volume somewhere in the middle on all the devices would result in roughly the same volume overall.
The Amp is has auto-sensing and will turn itself on only when there's a signal, so made to be stashed in a closet and forgotten.
Anyway, I think I need something to boost the low signals and attenuate the high ones. I was looking around and found some options and would like to know if anyone here can tell me if one would work or if they have a better solution. Below are the things I found but not sure if they are appropriate to what I'm going for. Thanks for any advice.
DC Input 12V 2 Channel Stereo Power Amplifier Module Kit 1W Based on TDA2822M | eBay
Low Voltage Audio Stereo Amplifier Module Based on NJM2073D | eBay
Isn't that what you have now? Not sure I understand.
Anyhow, the links you provided are for small low-voltage power amps; that won't work*.
The only solutions I'm aware of are 1) an automatic gain control (AGC) circuit, 2) a compressor/expander circuit, or 3) a multi-input preamp with each input individually processed to equalize the output level.
*"Won't work" may be too extreme. They could be used as a variation of #3 above. Less than ideal, but they could be used as preamps for the sources with lowest output. Some, like the TV and computer, should be capable of level matching without additional circuitry.
Yeah, that was poorly worded.
What I meant to say is that the goal is the set the volume control on the power amp once, stick it somewhere out of sight, and control volume using the volume controls on the individual devices.
Each device seems to have fairly different gain levels coming out of their headphone jacks and I would like to be able to compensate for that to even them out a bit.
What I'm describing is basically mixer, with controls to boost or cut each stereo channel to what would be a good strong headphone out level for probably 4 devices.
I hope that's more clear. Thanks again.
What I meant to say is that the goal is the set the volume control on the power amp once, stick it somewhere out of sight, and control volume using the volume controls on the individual devices.
Each device seems to have fairly different gain levels coming out of their headphone jacks and I would like to be able to compensate for that to even them out a bit.
What I'm describing is basically mixer, with controls to boost or cut each stereo channel to what would be a good strong headphone out level for probably 4 devices.
I hope that's more clear. Thanks again.
I dug around the forums a bit more and found this , which seems like someone with a similar issue using small transformers to get the impedance corrected to get a better signal to the power amp.
So, if I use this transformer solution to correct the impedances of each device, will that level out the different signals going into the power amp or do I still need a way to adjust the level of each stereo channel with a pot in the signal chain after the transformers?
I get that the impedance of the headphone outputs need to better match the amp's input and that will give me a stronger signal, but I don't know if that will correct the difference in volumes between the devices or just give me better sound but still very different volumes when I switch between them.
So, if I use this transformer solution to correct the impedances of each device, will that level out the different signals going into the power amp or do I still need a way to adjust the level of each stereo channel with a pot in the signal chain after the transformers?
I get that the impedance of the headphone outputs need to better match the amp's input and that will give me a stronger signal, but I don't know if that will correct the difference in volumes between the devices or just give me better sound but still very different volumes when I switch between them.
It isn't just the impedances (which to me is questionable and/or confusing, eg. there are plenty of low output impedance preamps driving high input impedance amps) but the voltage across those impedances.
If you connect a pair of those transformers to each source device, you'll still have the large difference in signal strength. You'll only have shifted it all to another level.
DIY solution... an op amp for each device output channel, with the op amp gain adjusted for each device so all outputs are more or less equal, i.e. #3 above. Use op amps that are stable at low gains because you won't need much. Of course the device with the strongest output signal doesn't really need to be tweaked - it can be the target level for the other outputs. Or you could buy preamps to do the same thing.
If you connect a pair of those transformers to each source device, you'll still have the large difference in signal strength. You'll only have shifted it all to another level.
DIY solution... an op amp for each device output channel, with the op amp gain adjusted for each device so all outputs are more or less equal, i.e. #3 above. Use op amps that are stable at low gains because you won't need much. Of course the device with the strongest output signal doesn't really need to be tweaked - it can be the target level for the other outputs. Or you could buy preamps to do the same thing.
If you look at E-Bay item --- 121196799893 --- This is such a pre-amp. Use one per input.
All you then need to do is feed each output via a 2K2 resistor to the input of the power amp. Ideally you also need a 2K2 then between the commoned resistors coming in and 0V.
This is known as a summing circuit, just connecting all the pre's together wont work satisfactorally.
If you google "summing amplifier" you will see the way this works...Op Amp Summing Amplifier
All you then need to do is feed each output via a 2K2 resistor to the input of the power amp. Ideally you also need a 2K2 then between the commoned resistors coming in and 0V.
This is known as a summing circuit, just connecting all the pre's together wont work satisfactorally.
If you google "summing amplifier" you will see the way this works...Op Amp Summing Amplifier
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It's a lot less fun, but this might be an easy off-the-shelf solution, and probably cheaper.
I figured I would end up getting 4 kits like katieanddad's ebay suggestion and then do the summing circuit exactly as described but maybe not worth the effort. Or maybe I can still do the impedance thing and be able to get my hands dirty after all. If I do, would it best to add those transistors to each stereo channel before the mixer or just do it to the summed stereo channel after the mixer before the amp?
I figured I would end up getting 4 kits like katieanddad's ebay suggestion and then do the summing circuit exactly as described but maybe not worth the effort. Or maybe I can still do the impedance thing and be able to get my hands dirty after all. If I do, would it best to add those transistors to each stereo channel before the mixer or just do it to the summed stereo channel after the mixer before the amp?
As a lot less fun off-the-shelf solution, 3 of those Rolls mixers will do the job.
A very good DIY solution (#3 again) could be built for half that price, or less.
FWIW, a "mixer" isn't really what you need, unless the plan includes playing more than one source at a time. Though the circuit is virtually the same, the function you need is isolation of the four variable stereo outputs. This could be achieved with a 4-position switch.
A very good DIY solution (#3 again) could be built for half that price, or less.
FWIW, a "mixer" isn't really what you need, unless the plan includes playing more than one source at a time. Though the circuit is virtually the same, the function you need is isolation of the four variable stereo outputs. This could be achieved with a 4-position switch.
I like the idea of your #3 better than buying an off-the-shelf solution, way more fun, but I'm not sure what that circuit looks like. I tried a search of "multi-input preamp" but didn't find anything appropriate on diyaudio so far. Do you have an example or link, or a better search term I could use to search it?
I'll keep looking in the meantime. Thanks!
I'll keep looking in the meantime. Thanks!
Here's a couple of examples. The first is adapted from an old Radio Electronics article, "Op Amp Audio Applications", and the second is from "An Applications Guide for Op Amps," National Semiconductor (now Texas Instruments) Application Note 20.
The first circuit I chose because it illustrates fairly obviously the circuit function.
The second is perhaps a little more technical, but shows that there's almost always more than one way to put components together for a desired effect. V1, V2, & V3 are the signal voltage sources. This circuit also includes the summing formula for determining Vout, -R4(V1/R1 + V2/R2 + V3/R3). With just one source supplying a signal, the formula simplifies to Vout = -R4(Vn/Rn). So Rn can be determined for each Vn input to provide a consistent Vout.
Search terms "summing" and/or "mixer" and "circuit" should return lots of results here and on the web.
The first circuit I chose because it illustrates fairly obviously the circuit function.
The second is perhaps a little more technical, but shows that there's almost always more than one way to put components together for a desired effect. V1, V2, & V3 are the signal voltage sources. This circuit also includes the summing formula for determining Vout, -R4(V1/R1 + V2/R2 + V3/R3). With just one source supplying a signal, the formula simplifies to Vout = -R4(Vn/Rn). So Rn can be determined for each Vn input to provide a consistent Vout.
Search terms "summing" and/or "mixer" and "circuit" should return lots of results here and on the web.
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I've been thinking about this post, and in doing so have made a 180° to conclude it is mostly correct.
The OP says,
IOW, the OP wants to vary the gain level coming out to the power amp from various devices, but also wants the power amp output to be evened out among them!
My solutions list is reduced to #1 and #2 only.
I may be slow, but I did get there...
And it ain't so bad when looking back to see the pack.I may be slow, but I did get there...
I think #3 still sounds closer to what I'm after. I don't need to even anything out dynamically after the devices such as with a compressor, and don't need anything to adjust itself automatically. Each device can just be leveled relative to the others one time to have their various gain differences evened out. Once that happens, the preamp should be able to just do what it does.
Hello again, what I wanted to say is, that high gain amplifiers mostly do not need much voltage to be very loud. If there are more than one sources it can occur, that they are sometimes really loud and others are weak. If you want to control the volume of each unit by itself and not use a pre or passive solution that fits for all units at full speed, why not see every unit as a separate problem. I would not use resistors or so, even buffered. See what every unit has as output voltage and think of placing a transformer between the source an amp as reducer for example. Besides you will not have problems with impedance matching and galvanic separation. I hope you understand. Best
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