DIY Volume Control for Line Levels

[Torea]

Hey all,

Until I have the funds for a nice motorized fader unit (like the Faderport), I'm interested in making my own attenuator box with faders. I'd like to have it made for the outputs of my Saffire Pro 40, so that I can use the fader box to ride the faders. I've been working with tube amps for a while now, but haven't so far ventured into transistor/op amp stuff. Obviously, there are better products for just this much and yada yada but I enjoy making stuff on my own.

Is this kind of box feasible? Feasible to make?

I was looking for information on the topic and I found this page. Could I take their op amp design from the second circuit (no input pot) and use it for each channel? Would the TL072 be a good opamp for this? Also, would the resistor values for stay the same for a line level input?



I'm trying to learn about audio circuits so any explanations or reasoning for solutions would be very very much appreciated.
Thanks for the help!


[IMG]******//www.all-electric.com/schematic/simp_mix.gif[/IMG]

[Torea]

Anybody?... Please?...

[a zombie]

I don't know how much help this will be but I'll try to help you out...

Since the faderport is only $120 or so, I'd say it probably doesn't make much sense. The cost of the box, jacks, faders, opamps and power supply could easily eat up $120, let alone the time it would take you to design and build the whole thing.

It would be a learning experience, but when you're done all you would have the worlds simplest, boring 8-channel mixer.

It's worth asking yourself these questions:

Could you really do all your fader ridding in one pass with no automation?

Can you mix a song with 8 faders?

Do you want to 10 A/D conversions to your mix?

Don't get me wrong though, I am all for DIY, but with your setup it makes more sense to save up for the faderport since you will be able to write automation and perfect your mix without any degradation in quality.

that's my 2¢

[Torea]

Originally Posted by a zombie

I don't know how much help this will be but I'll try to help you out...

Since the faderport is only $120 or so, I'd say it probably doesn't make much sense. The cost of the box, jacks, faders, opamps and power supply could easily eat up $120, let alone the time it would take you to design and build the whole thing.

It would be a learning experience, but when you're done all you would have the worlds simplest, boring 8-channel mixer.

It's worth asking yourself these questions:

Could you really do all your fader ridding in one pass with no automation?

Can you mix a song with 8 faders?

Do you want to 10 A/D conversions to your mix?

Don't get me wrong though, I am all for DIY, but with your setup it makes more sense to save up for the faderport since you will be able to write automation and perfect your mix without any degradation in quality.

that's my 2¢

I absolutely agree with what you say. My biggest issue is that I don't have as much recording/mixing coming my way these days, but I'm trying to learn more electronics since I'm getting more of that work (mostly with old tube amps). I can't really justify spending a lot on a mixer. I wish I had a year or two ago. But I get parts orders all the time, I can spare a few bucks here and there to accumulate parts.

I'd be fine working with just 2 faders, I already have jacks and can make the box pretty easily since I have the tools for that. Would it be feasible to make this circuit with low enough noise (aka not using parts at the bottom of the line) to be usable, but still be affordable? Or would it pretty much be an entire waste of time? If it is, I understand. I just like getting my hands dirty and like learning by building, especially when I can use what I built.

[a zombie]

I think I get what you mean.

So you more just want faders that you can buss tracks through one at a time, that makes sense.

I'm not sure exactly how it is normally done, but I think it would be a de balancing stage -> an attenuator (a 104mm fader would be nice) -> then you would run it into a gain stage, just a simple opamp gainstage -> and then into a balancing circuit.

This might be a bit pricey, but this is what I would try to do... in this order

(this might not be great advice, so some of the pro's here should check me on this)

1) input de-balancing stage (not sure what you'd use here, nicest would be a transformer)
2) fader
3) inverting gain stage with 2520 style opamp. ($17 gar2520 kit) gives you say 12db of gain.
4) Output Transformer 2623 or 2503, to balance the signal and invert the phase back to normal

This would also give you some sexy api console tone too

[Torea]

Originally Posted by a zombie

I think I get what you mean.

So you more just want faders that you can buss tracks through one at a time, that makes sense.

I'm not sure exactly how it is normally done, but I think it would be a de balancing stage -> an attenuator (a 104mm fader would be nice) -> then you would run it into a gain stage, just a simple opamp gainstage -> and then into a balancing circuit.

This might be a bit pricey, but this is what I would try to do... in this order

(this might not be great advice, so some of the pro's here should check me on this)

1) input de-balancing stage (not sure what you'd use here, nicest would be a transformer)
2) fader
3) inverting gain stage with 2520 style opamp. ($17 gar2520 kit) gives you say 12db of gain.
4) Output Transformer 2623 or 2503, to balance the signal and invert the phase back to normal

This would also give you some sexy api console tone too

Exactly. I just want to send individual tracks or busses, just to get used to riding the fader. That way, if I do end up doing more of this stuff, I'll have a better feel for the faders. Who knows, if I get to that level, maybe I'll be able to afford a big motorized console, instead of just one fader


That looks pretty cool. Do I need a de-balancing stage? I thought the Pro40 had unbalanced 1/4" outputs. Is it necessary to balance the signal going back into the interface?

Thanks for the help!

[a zombie]

you could do unbalanced ins and outs I would think. The reason for the output transformer is a) the sound and b) you can use a single discrete opamp as an inverting amplifier (the simplest way to use the opamp)

Obviously if you are going for cheap, then you wouldn't want to buy spendy transformers and there is no point in using cheap ones. You also wouln't need a discrete opamp.

Hopefully someone here can point you in the right direction with some schematics of a simple fader with gain circuit.

[Torea]

Originally Posted by a zombie

you could do unbalanced ins and outs I would think. The reason for the output transformer is a) the sound and b) you can use a single discrete opamp as an inverting amplifier (the simplest way to use the opamp)

Obviously if you are going for cheap, then you wouldn't want to buy spendy transformers and there is no point in using cheap ones. You also wouln't need a discrete opamp.

Hopefully someone here can point you in the right direction with some schematics of a simple fader with gain circuit.

I'm definitely tempted by the method you suggested. I'll have to see if I can afford it. I'd like something cheaper but this method seems like a good option.

Hopefully someone else will have a slightly cheaper suggestion