DIY rotary DJ mixer

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Added RCA inputs and a mic channel fader:

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Added a summing bus and wired stereo channel pots.

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Tapatalk hasn't been working for me so here's a pic of the build so far :



And a close-up of the master EQ section I finished today :

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Wired the headphone out today and tested the stereo channels.. both are functional as well as the PFL and the EQ. The EQ sounds fantastic! It's got a crossover frequency at around 120Hz according to my calculations.

The downside is I used too high resistance potentiometers so only about 1/4 of the taper is useable (tested with a smartphone output jack)

EDIT : I've yet to wire the main outs.. other than that it's finished.

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Wired the master outs, it's done now as far as soldering goes :



Also labeled the front panel :

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Looks cool, yea.. that's similar to my first DJ mixer which I built myself too. Except, if I understand how you did it.. the main output is totally passive, the only amp is for the headphones. But on mine, I had a simple 1 transistor amp on the master output, and two transistor amp for the headphones (It was a mono mixer.. because I was using it for an AM radio station).

I think it would look really good with old school Dymo labels for everything, instead of the marker. Would make it look like it was from some old school 1970's disco

Like this but real...
http://imagegenerator.fuzzimo.com/embossedlabels/

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Looks cool, yea.. that's similar to my first DJ mixer which I built myself too. Except, if I understand how you did it.. the main output is totally passive, the only amp is for the headphones.

Thanks! It's passive without a headphone amp so only good for home mixing I guess. I was thinking of adding a HP amp though.

But on mine, I had a simple 1 transistor amp on the master output, and two transistor amp for the headphones (It was a mono mixer.. because I was using it for an AM radio station).

Was this to make the headphone out louder?

I think it would look really good with old school Dymo labels for everything, instead of the marker. Would make it look like it was from some old school 1970's disco

Yeah the marker doesn't look very professional. I think we have a Dymo at work (or a similar machine iirc)

EDIT : I was also thinking of making an all-passive version of the first 3RU mixer.

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Was this to make the headphone out louder?

Yes, but more important, it prevents the headphone setting from interfering with the master output. When totally passive, switching the headphones in and out or changing their volume causes changes to the master output volume, but having an amp prevents that.

And the reason for having an amp stage on the master output was to allow me to use a larger resistor in the summing network.. so that reduces the interaction between one channel input and another (turning the gain up and down on input #1 doesn't change the level of input #2). And this also allows the loads on the output to change without audible interaction, so for example I could have my transmitter connected to the output, a tap to my headphone selector, and another to my monitor selector/volume.. and when these selections were changed it wouldn't alter the on-air level.

I think we have a Dymo at work (or a similar machine iirc)

Yea we use a Brother P-Touch and have many different kinds of tape we can put in it.. different colors (or clear), different sizes.. even have shrink tubing that can go in the P-Touch, to make wire labels, which is cool. Dymo makes a machine that is just like that.. a modern one. But the one I was suggesting is the OLD Dymo.. from 50 years ago.. they still sell it. It doesn't use electronics to make the label at all, it;s totally mechanical and the labels of that type have become iconic . It's not slick looking at all, but a cool vintage vibe... Like this:

https://www.amazon.com/DYMO-Organize...0000AQOD3?th=1

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Yes, but more important, it prevents the headphone setting from interfering with the master output. When totally passive, switching the headphones in and out or changing their volume causes changes to the volume, but having an amp prevents that.

Good point, as I never tested the mixer with speakers and both inputs at full volume (only to find turning the cue switch makes a pop like in my first build, which had preamps)

And the reason for having an amp stage on the master output was to allow me to use a larger resistor in the summing network.. so that reduces the interaction between one channel input and another (turning the gain up and down on input #1 doesn't change the level of input #2).

There's something wrong if the circuit does this.. but there's a solution right? And that is to use either active summing or output buffering?

And this also allows the loads on the output to change without audible interaction, so for example I could have my transmitter connected to the output, a tap to my headphone selector, and another to my monitor selector/volume.. and when these selections were changed it wouldn't alter the on-air level.

So the total load determines the output level? I know this is a problem in DIY projects like mine..

Yea we use a Brother P-Touch and have many different kinds of tape we can put in it.. different colors (or clear), different sizes.. even have shrink tubing that can go in the P-Touch, to make wire labels, which is cool. Dymo makes a machine that is just like that.. a modern one. But the one I was suggesting is the OLD Dymo.. from 50 years ago.. they still sell it. It doesn't use electronics to make the label at all, it;s totally mechanical and the labels of that type have become iconic . It's not slick looking at all, but a cool vintage vibe...

The shrink tube sounds cool.. didn't know about that.

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There's something wrong if the circuit does this.. but there's a solution right? And that is to use either active summing or output buffering?
So the total load determines the output level? I know this is a problem in DIY projects like mine..

Yes, basically, if you do passive summing, the degree of isolation between channels is determined by the ratio of the potentiometer value by the value of the summing resistor. So if you use a relatively low value potentiometer, eg. 10k, and a relativelt high summing resistor value.. eg, 100-200k or higher.. you will have very little interaction. The problem being that if you put let's say a typical load on the output.. let's say 47K, you will experience a noticeable drop in level. If you put a low impedance load such as headphones you'll drop the output to almost nothing. The solution is to put an amplifier with a high impedance input and low impedance output.. and then from there you connect your various loads. With an output impedance of let's say 100ohms from your buffer, and let's say your headphone amp has an input impedance much higher than that.. let's say 47k as the absolute minimum.. then you can switch the headphone amp in and out without it being noticed.