Building a DJ mixer

liddokun

Member
2010-01-24 9:11 pm
Hello everyone,

I wasn't exactly sure which section to post this in, so I hope moderators can move it if it's in the wrong place.

I'm looking to start the planning to build a simple DJ mixer. I know that DJ mixers can be had for quite reasonable prices these days, but I figure if I'm going to be paying upwards of $1k for a mixer, I might as well build one myself and use good components, and strip it of some of the extra features I wouldn't need myself.

I have a pretty basic understanding of electronics; I've built a few amplifiers (Tube, solid state) as well as many guitar effects and other gadgets before, thus I don't think it's too ambitious of a project.

It would essentially be a two channel mixer with a crossfader to fade between the two turntable inputs, maybe an AUX input and a microphone input.

It would be RCA inputs into a phono preamp (also want to make this switchable between line in and phono in)-->EQ section-->crossfader-->master outputs

Do y'all have any links to good examples or schematics of those different blocks? e.g. phono preamp schematic, great EQ schematics.

I've got all the schematics from Rane and am trying to piece this together bit by bit and plan the design of this. Any help would be greatly appreciated.
 

Zero D

Member
2009-08-06 11:11 am
Hi, it all depends on what you want/need to include.

If you just require what you stated, then it won't be too complicated ;)

If you require any or all of the following, then it'll get progressively more indepth etc.

Tone controls

Headphone

Metering

I applaud your desire to do it, so i'll help you. Let me know EXACTLY what you want.
 
REally. A simple DJ mixer like that won't cost you anywhere near $1000.

Here is one for under $100, meets your specs too.
Numark M2 DJ Mixer | Musician's Friend

SOmething to consider too if you are actually DJ-ing. More and more offer USB ports. My DJs now carry their music in a computer. A port connects the mixer to the computer. Also some guys keep tunes in an iPod, and they make basicx DJ mixers with iPod jacks too.
 

liddokun

Member
2010-01-24 9:11 pm
Let me reiterate that I'm not looking for suggestions on buying a mixer. I understand there are plenty of mixers out there that have 99% of what I stated I'm looking for, but I'm looking to build one. "Save the trouble..." No, it's absolutely no trouble at all for me, actually.

What I want is to build a relatively simple DJ mixer with high quality components because I am a big audio geek (I'm sure most of us on this forum probably are anyways, so I hope I'm amongst friends).

@Enzo, there are audio interfaces that can serve that function, so it's all good on that aspect. Thanks for bringing it up though.

@Zero D: I'm looking to build a two channel mixer. Each channel will have a phono input and if possible, a line in (switchable). Each channel will have 3 band EQ, with EQ kill per band, and a gain control (pre EQ). One volume control per channel (post EQ). Crossfader between the two channels (it would be cool to learn how to implement other stuff to the crossfader like reverse crossfader or crossfader curvers, but I suppose that can come after). Ability to cue each channel (e.g. have a cue switch that will send the signal to the headphone when engaged, regardles of what the volume fader is set at for the channel).

Two sets of stereo outputs, one for monitors, one as master output. Balanced, if possible. Headphone output that can switch between what's being cue'd and the master mix.

Sound simple enough? I think it would be, it's just a matter of putting together the blocks for each section.

Any help would be greatly appreciated. I think it's definitely doable.
 

Zero D

Member
2009-08-06 11:11 am
Doable

Hi, OK now i know what you require. Also i'm pleased to hear you will be using Vinyl too :)

I would suggest having a GOOD look at the various projects in here ESP Projects Pages - DIY Audio and Electronics

Decide which you think is right for you, & then post back with the Project Numbers so i can check them. If you're not sure which you think are best etc, just say so & i'll offer my suggestions & guidance ;)

I built a Crossfader to add on to a mixer years ago, so that's not a problem for me to design in.

Are you going to design the PCB's for All/Any of these, and/or make the PCB's, or get them made ?

Or build on for eg Veroboard ?

Or hoping to buy kits of each block, or just the PCB's for them & use better components, & possibly upgrade the circuits ?

And of course you will need to Neatly drill out a suitable case for all the controls etc, & legend with something. Unless you are going to have the case professionaly made to your requirements ?

You didn't mention anything about metering, either PreFade or PostFade and/or output ? If so, i expect you want an LED type ?

Do you want an internal Power Supply, or external ?

Sure it's going to be a LOT of time/work, for everyone involved, but i presume you already understand/appreciate that.

Years ago i built a 4 channel stereo mixer with Bass/Treble on each input. 2 x Phono 1 x Jingle Machine 1 x Mic. Headphone monitoring on each channel. LED Metering. That was using a mix of transistors & IC's ! and it worked/sounded fine. These days i would use all quality IC's :)
 
I used to DJ and considered building my own rotory mixer a while ago. The reason i wanted to build one was because nobody was building a really high end mixer. There are many ways to approach this. I would recommend you start looking for DIY projects that fit what you need and piecing it together. When I was considering this I wanted to use aleph ono preamps for the turntable input and possible an aleph 1.7 for the preamp. Personally I was going to use rotory faders as I liked long smooth transitions in my mixes. I was going to skip the EQ as I was looking for the best SQ possible, you could always add an effects loop with an external EQ later.

I would like to point out you could make a regular mixer and use outboard phono preamps. Might make your lifer simpler.

After thinking about it for a long time I decided to mod the mixer I had to a rotary and call it a day. I don't DJ anymore professionally but I do play around with traktor and a vci-100.
 
I used to DJ and considered building my own rotory mixer a while ago.

I much prefer rotary pots.
I found the linear pots would collect dust and become scratchy quite quickly.
The rotary pots are enclosed and so dont catch as much dust.

On my Maplin disco I put the phono pre amp in the record decks, I needed power for the record decks so another mains connection for the pre amp was no problem.

I would be wary of using long leads from a phono pick up.
It really needs to be as short as possible to avoid picking up noise.

The Behringer mixer I mentioned really is top quality, they are broadcast quality.


BEHRINGER XENYX 502 ex- BBC 5 channel AUDIO MIXER + power supply.
 
Behringer and Numark don't give away schematics, and the market here is flooded with them that have bad pots. Having seen pictures, Numark has flat cable and surface mount parts inside, which is not suitable for modification IMHO.
I'd say look around for a Peavey disco mixer (has RIAA) or the jewel I found for $15 the Herald Electronics RA-88. The latter has hissy 4558 op amps and a stupid hummy power supply and power switch right next to the op amps (stupid), but the faceplate is beautiful stainless steel, the pots are outstanding, and the IC's are dip package so you can put in sockets and change them. (it needs bypass caps, too, I drilled holes in the pwb) The RA-88 is in a steel box too, so if you move to a wall transformer and delete the power switch you can get the hum out. I put toroid chokes on the power supply and caps to ground on the inputs, so the steel box excludes the noisy ******le CBer that beeps out Dixie as he drives by and lamp dimmer hash too. You could gut the whole PWB and just use the box, pots and faceplate for $15 and still be way ahead.
The disco version Peavey is rare but the common Unity mixer I have from them (no riaa) uses NJM4560's which are much less noisy than NJR4558 IMHO. Lots of rotary pots on a Unity line mixer. If you can't find a Herald or a Peavy disco mixer, you could take a Peavey Unity and change the gain on a couple of channels and insert some RIAA rolloff parts. Lot more fun than drilling D shaped holes in a faceplate.
 
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liddokun

Member
2010-01-24 9:11 pm
Hi, OK now i know what you require. Also i'm pleased to hear you will be using Vinyl too :)

Yes, I love vinyl!

I forgot to mention the metering part. Yes, some kind of metering pre-fader per channel, but after the gain control so I can visually match gain while mixing. Also a meter for L and R main/master output.

Microphone input (but not necessary if it proves too cumbersome to add), stereo pan for each channel. And if possible, the channel faders and crossfaders to be VCA so no audio actually passes through them.

I will look through those projects you linked. I'd like to avoid the wallwart as they're ugly. There's an electronics store near me that carries all sorts of Hammond transformers, I think an internal supply would be doable.

Lastly, I plan to design the PCB's myself after piecing together all the schematics, but have them made by someone else since I've never been able to really cleanly etch PCBs.
 
I will look through those projects you linked. I'd like to avoid the wallwart as they're ugly. There's an electronics store near me that carries all sorts of Hammond transformers, I think an internal supply would be doable.
In that case you need to design internal bulkheads and steel transformer wrappers to turn your enclosure into two steel boxes. One for the transformer, power switch, fuse, line filter and AC wiring, another for the DC wiring. See for example the dynakit PAS2 preamp which has the transformer wrapped in steel, and the bottom of the PWB enclosed in a separate steel bulkhead to keep AC fields away from the low level signals.
The wall transformer allowed me to reuse an existing steel box that violated all the proper rules of 120 VAC/25 mvac layout.
 

Zero D

Member
2009-08-06 11:11 am
@ liddokun

I had a feeling it would turn out to me more than just a "simple DJ mixer" :D

Yes, some kind of metering pre-fader per channel, but after the gain control so I can visually match gain while mixing. Also a meter for L and R main/master output.

So you want 2 sets of metering, or just switchable between inputs/output ?

Microphone input & stereo pan for each channel = No problem

And if possible, the channel faders and crossfaders to be VCA so no audio actually passes through them.

Well it's possible, but it's getting more & more away from your initial "simple" concept !

I will look through those projects you linked. I'd like to avoid the wallwart as they're ugly. There's an electronics store near me that carries all sorts of Hammond transformers, I think an internal supply would be doable.

OK

Lastly, I plan to design the PCB's myself after piecing together all the schematics, but have them made by someone else since I've never been able to really cleanly etch PCBs.

OK
 

liddokun

Member
2010-01-24 9:11 pm
@zero
I had a feeling it would turn out to me more than just a "simple DJ mixer" :D
Well I suppose simple relative to all the ones on the market these days with 3+ channels and all those bells and whistles. Haha


So you want 2 sets of metering, or just switchable between inputs/output ?
2 sets of metering would be nice, one for inputs of each channel and one for outputs.


Well it's possible, but it's getting more & more away from your initial "simple" concept !
I suppose that could be a good thing, right?

I looked at the projects page. I wasn't sure for all of the projects, but I've picked out some.

Headphone section: project number 24
For the phono preamp: project number 06
Balanced outputs: project number 51
For metering: project number 60
For mic input: project number 13 or 66 (depending on if I want balanced input or not..)

I suppose if I'm looking to include line inputs too, I'd need a preamp for that as well, which I could use project number 88 for. Would the phono preamps go before this preamp? Also, this preamp would feed the tone control section, or would the EQ section be added into the gain stages?


As for the other parts, I'm not particular sure which projects to look at. If an internal power supply gets too complicated, I'm not against using a wall adapter.

I think I hit most of the important bits here...all that's missing are the VCA circuits being used for line level controls and crossfader.
 

Zero D

Member
2009-08-06 11:11 am
Take a look at the screenie i've made, & confirm that it's what you are hoping for.

*

Headphone section: project number 24

Is more complicated than what you require, but project number 24 is essentially the same output wise & will be fine.

For the phono preamp: project number 06

I can design a better one for you ;)

Balanced outputs: project number 51

This is Much better - THAT Corporation 1606/1646 OutSmarts Balanced Line Driver ICs

For metering: project number 60

Fine, but best run from a 5 Volt supply, which can be incorporated into the main PS. VR1/VR2 would be Preset Potentiometers & once calibrated left alone.

For mic input: project number 13 or 66

This is Much better - THAT Corporation 1510-1512 Audio Preamplifier ICs

I suppose if I'm looking to include line inputs too, I'd need a preamp for that as well

Not a seperate one, as the Bass/Treble/Bal/Gain sections will take care of that. As they will be @ Line level.

Would the phono preamps go before this preamp? Also, this preamp would feed the tone control section, or would the EQ section be added into the gain stages?

See my screenie

If an internal power supply gets too complicated,

It won't be complicated, but it's better to feed the Audio & Headphone/Metering sections seperately, but from the same main PS.

I'm not against using a wall adapter.

You could, just to supply the low voltage AC to the internal DC PS.

I think I hit most of the important bits here...all that's missing are the VCA circuits being used for line level controls and crossfader.

VCA - THAT Corporation 2180-series Pre-trimmed Blackmer Voltage Controlled Amplifier ICs

Plus see my screenie, but quite frankly i don't think the Master Volume needs a VCA, as most of the time it will fixed. Also using a VCA to achieve FAST Xfades/Chops and/or Scratching, "might" not be advisable ! This is due to the delay in the control voltage changing the Actual audio level. Anyway, LOTS of Very good audio mixers use regular methods without problems. Not only that, but whatever option you choose WILL require the Xfader potentiometers to be renewed every now & then, depending on abuse !

For Bass/Treble you could use Project 97. But as it's inverting i'll need to invert the first OpAmp.

*

I would STRONGLY recommend that you take some time to study & get your head around ALL the above. There is a LOT more work involved in Actually putting this Altogether, & finally completing it. Not just the electronics, but the making/designing the PCB & case etc !

Just so realise, i've already spent a considerable amount of time searching/reading etc, & also compiling All this, together with making the screenie. So if you Really are serious about doing this, let's make some Music :)
 

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liddokun

Member
2010-01-24 9:11 pm
Very nice. I appreciate all the help ths far.

I will have a good long look at all the electronics involved. The screenie helps a lot. I don't need metering for the mic and aux in, so that'll be one less portion to design for this project. Most of these projects seem to run on +/- 15v...great!

I am serious about this project, although it will be a long and drawn out process partially because I'm learning as I go along, partially because I am trying to do it in my spare time, and partially because it will probably be the most money I'll ever spend on a project and I'm looking for a new job at the moment. But bear with me!

For the EQ section, possible to add a mid eq control?
 

Zero D

Member
2009-08-06 11:11 am
Very nice. I appreciate all the help ths far.

:)

I will have a good long look at all the electronics involved.

Good
The screenie helps a lot.

Thought it would ;)

You might not need metering for the mic, but if ever need to use the Aux, then it Will be beneficial, just as it will be for the other inputs. This is to match up the levels, along with any EQ variations you may make. Plus it ONLY means 2 extra to wires going to the source switch, so why not ! It's up to you though ?

Most of these projects seem to run on +/- 15v...great!

Yep :)

... I'm looking for a new job at the moment.

All the best with your search

But bear with me!

I'm bearing :D

For the EQ section, possible to add a mid eq control?

Yes, BUT, quite honestly in my experience with sound systems over the years, they do more harm than good. Unless you are playing through dreadfully designed etc speakers, it shouldn't be necessary to adjust the Mids. But again, it's up to you ?

You didn't remark on my VCA comments ?
 

liddokun

Member
2010-01-24 9:11 pm
That's right, I thought I was missing something in my reply! Yes, the master volume pot wouldn't need to be VCA controlled. I was hoping to get a second set of outputs to run into monitors, this would be as simple as tapping the output and giving it it's own volume control as well, correct?

As for crossfaders..I thought that most professional mixers use VCA circuits for their crossfader and channel faders as to prevent scratchy pots? I'm looking to get high quality optical or capacitance faders that are non-contact though.
 

Zero D

Member
2009-08-06 11:11 am
That's right, I thought I was missing something in my reply! Yes, the master volume pot wouldn't need to be VCA controlled. I was hoping to get a second set of outputs to run into monitors, this would be as simple as tapping the output and giving it it's own volume control as well, correct?

Correct ;)

As for crossfaders..I thought that most professional mixers use VCA circuits for their crossfader and channel faders as to prevent scratchy pots? I'm looking to get high quality optical or capacitance faders that are non-contact though.

A professional mixer can use VCA's, or not. It's the circuits & components & wiring etc that make it Pro, or not ! But naturally using good makes of pots is a Must :)

If there is no, or Very little DC on the faders/pots, & good quality ones are used, they won't be scratchy. VCA's by definition MUST use DC on the pots for the control voltage :D The main problem that causes pots to go scratchy etc, is wear & tear, especially as i mentioned earlier, with Lots of abuse. But it's your decision to make. When you've researched Exactly which make etc of faders you're thinking of using, post back with Links to their www's & i'll take a look.

Have you built ANY circuits before, if so what, & how did they perform ? Same with PCB's ?