DIY rotary DJ mixer

[efinque]

I don t know specifically of the mixer you are talking about or their functionnality but an aux and an insert are different things, this is independant from the level at which they work.
An aux is a parallel feed with an indepandant return which is mixed back to a bus. It usually have volume controls (individual sends, master sends then a fader to mix in the receiving buss).
An insert is a series feed, without volume controls as the reference levels is predetermined (pro or semipro line level or anything that please you) and it just need a on/off switch to be activated.

In your overall layout your isolator is in serie between your mix bus and your main output card, no need for an aux.
Same thing in your chanel if you want to include some processing in individual chanels.

An aux is interesting for external effects (mainly time related like reverbs, delay, chorus,... you name it) can sometimes be  used as more output or to make parralel treatment but i doubt you ll use them like this.

I've been lately using the channel sends from my Mackie D4 to a Macbook Pro running an instance of Traktor and Reaktor software in a live setup (you can check the in-depth article on the setup in my blog)

The send feeds a subharmonic synthesizer (edit : I programmed it a while ago, here's the thread on NI forum) which tracks frequencies from the program material and turns them into MIDI notes which are then again fed to a drum machine which has a built-in analog synthesizer which goes to a channel on the mixer.

EDIT : This basically allows me to blend basslines too... I can bring up a synthesized bassline and choose not to send the synth the track that's playing, basically blending the synthesized basslines on the fly..

EDIT 2 : as for the VU meters; I have an old JVC KD-A11 tape deck with sweet looking analog meters.. however I cleaned the playheads and calibrated it not too long ago (I use it for tape saturation) so I can't really justify using it as spare parts

 

[KrIVIUM2323]

Ok, that is nice you understand principle of an aux (and make creative use of it which i like).
Now let s take a look at v6 manual page 35. As you can see there is insert in chanel and main section (master mix).
From the overall diagram you posted your isolator could be inserted (hence the name) in the master section of the v6 and be another independent box, like the external one you already mentioned.
For this you need a switch and two 1606 and two 1646 overall cost of maybe 20 euros for almost the same benefit than a quad of transformers... i ll let you calcul the cost of transformers alone without driving electronic circuit...

Do you see what i mean?
You didn t include aux in your overlay so you are sure you could live without them?

 

[efinque]

Ok, that is nice you understand principle of an aux (and make creative use of it which i like).
Now let s take a look at v6 manual page 35. As you can see there is insert in chanel and main section (master mix).
From the overall diagram you posted your isolator could be inserted (hence the name) in the master section of the v6 and be another independent box, like the external one you already mentioned.
For this you need a switch and two 1606 and two 1646 overall cost of maybe 20 euros for almost the same benefit than a quad of transformers... i ll let you calcul the cost of transformers alone without driving electronic circuit...

Do you see what i mean?
You didn t include aux in your overlay so you are sure you could live without them?

I have no external effects processors to use in a DJ setup... live setup is another thing and it needs digital I/O from the software.

 

[KrIVIUM2323]

Ok so you plan to use the mixer only at home or for djing only duty?

 

[efinque]

Ok so you plan to use the mixer only at home or for djing only duty?

Well, seeing I play vinyl at home only that's the main purpose for a start.. I don't trust myself as an electronics engineer enough to play out with DIY mixer, maybe with a sound system (I've done that) because they are essentially in the more coarse end of the spectrum whereas electronics are much more intricate.

Mathematically speaking acoustics are much more elaborate in contrast to electronics..

But what about the internal wiring? I read there's the AWG system.. usually the small things play an important role too while people (like me) look at specs of a single component and forget the importance of other, smaller things. (edit : worst case scenario would be to forget to order the wires and substitute those with a standard audio/power cable.. I found some neat looking cloth-covered PVC wire which would have a certain wow-factor when showing the unit internals and I've seen it being used in some old devices, probably withstands soldering better too)

EDIT : also, would it be beneficial to match and make use of the crossover frequencies of the filter/EQ and the effective/usable frequency ranges of the speakers in a sound system?

EDIT 2 : The thing with speakers vs mixers is that sound systems are mainly designed for the audience whereas mixers are engineered to suit the needs of the DJ.. of course it's a joy to play on a good system (and demand one as a DJ) and to my surprise some audio-conscious partygoers are interested in the backline too. This puts some additional stress on the tools and the design which the DJ has to use to present the material the audience wants .

EDIT 3 : But of course I'd like to build it to professional standards.

 

[efinque]

Aight, I just ordered all the parts (or at least I think so..)

Let's hope for the best!

EDIT : Like 5 minutes ago I had money.. now I dont.

EDIT 2 : I can already tell that it's the aforementioned preamp kits, ALPS pots and Lundahl transformers.. I highly doubt it'll sound even half decent. I decided to scrap the isolator and the 3rd line channel for starters, instead I placed an order on a 3-band EQ.

EDIT 3 : I've never really thought about this but how does one get a mixer like this calibrated to "unity gain" or to 0dB?

 

[kooma]

Aight, I just ordered all the parts (or at least I think so..)

wow, that was fast, all the best with this project

did you order all that from analogmetric ?  are those generic chinese kits or is the quality better?

 

[efinque]

wow, that was fast, all the best with this project

did you order all that from analogmetric ?  are those generic chinese kits or is the quality better?

No the preamp kits and the headphone amp are from Velleman catalog.

EDIT : and thanks for the encouraging words!

 

[efinque]

Here's most of the parts... something to keep me busy while waiting for the rest of the stuff.

EDIT : I've had the flu so can't really do much about it for now... I'll get soldering once I've recovered.

EDIT 2 : I need to clear up some space for the project...

 

[efinque]

Despite the flu I couldn't keep my hands off the soldering iron so I assembled the mic pre and one of the RIAA preamps.

I'll post some pictures later

 

[efinque]

Here's the mic pre and the RIAA preamps :

 

[efinque]

How about the power supply to the boards? I have a 2x15VDC AC transformer, would I just run all the input modules in series from one output and power the EQ unit and the headphone amp from the other?

EDIT : despite the mic pre PCB print saying 12VDC the spec sheet states 10..30VDC

EDIT 2 : also,  where's the best place to connect the turntable ground wires? The reason I'm asking this is because some turntables have a modified ground (not mine though) Not that it would matter that much but I like to play it safe with these things..

 

[efinque]

I know this is purely an aesthetic but here's the knob layout (Colt lighter for scale)

EDIT : the EQ knobs will be a bit different looking though.. I actually forgot to place an order on those from one of the suppliers (there's actually 4 of them, 2 of which are based in my home country, one in Sweden/Germany and one in China) for more of an uniform look but I thought it'd be a nice detail if the EQ stood out a bit... this is just a prototype, if it performs well I might make a "commercial" version for installs but I highly doubt any of the venues that I know would want one (or if they did they'd get one from a reputable manufacturer)

EDIT 2 : I didn't take into consideration the customs fee though (I should've known because I've ordered stuff from abroad earlier, stupid me..)

EDIT 3 : I honestly have no idea how it'll perform... there's a slight hint seeing the PCBs are half the size of the original Bozak/Urei input cards and the fact that they're built from kits (edit : but stuff back in the 70's was very different I think). Although printing it out on a single PCB (or a few separate ones) would be a daunting task (it already feels like it tbh) but I guess I'll be happy to get it working in the first place.

EDIT 4 : Oops.. by accident I bought dual logs for the mic channel as well.. I already figured a workaround because I also ordered some extra RCA panel connectors so one could run an aux cord to it (switchable but I think it'd need a switch in general which I also forgot to order), this is due to the fact that I placed the order as 6 ch configuration and scaled it down to 5 and forgot to change the amount of some components (but I kinda saw that coming) I was also thinking a switchable, fixed frequency HPF on the mic channel but those are *very* rarely found in DJ mixers or booths (I can't think of a mixer that has a HPF in the mic channel but some have a 2-3 band EQ)

EDIT 5 : A power on indicator LED would've been cool too but I'm skeptical whether they withstand a 15V current.

EDIT 6 : And I'm not building one just because it's cheap.. there are a lot better designs on the market BUT there aren't many. I think the new Bozak AR-6 and Rane (it's tabletop and I'm looking for rack mount) are the only ones in production and the rest are either built to order, discontinued  or second-hand (I've seen a RLA serviced Bozak CMA-10-2DL go for 3k USD, and some ARS models for 5k upwards)

EDIT 7 : I have a hypothesis it'll be a "disco-smile" (term used by Bill Gibson in his Hal Leonard Recording Method : Mixing & Mastering, 2nd Edition book) type of mixer frequency response-wise (and to make up for some of the sound quality issues) due to certain components in action (I have zero knowledge of transformers but I believe they are a necessary evil to get balanced outputs and I've seen them in schematics) but I still think it needs a fancy project name

EDIT 8 : -removed-

EDIT 9 : I think I could've used 10K log pots too (now that I had a look at some old schematics)

 

[efinque]

I finished soldering all the input modules this morning.. the headphone amp, case and the transformers should be here by afternoon.

 

[efinque]

Here are the line preamps soldered.. there's also some soldering "rail" (I don't know if that's the correct word for it) I found from one of the suppliers which I thought could be used for tidying up the connections between the input modules and the potentiometers and also for some extra serviceability as well as summing to the outputs.

EDIT : Never mind the capacitors being a bit off place; it's because the holes weren't spaced wide enough apart from each other and I couldn't be bothered to bend the legs(there's also a risk of breaking one or both of them in doing so)

EDIT 2 : It shouldn't be too bad.. some of the opamps are TL072

 

[efinque]

Yet another question; wouldn't I need a summing mixer? I have some spare 10k/220k/1meg resistors from the Arduino kit.

EDIT : The transformers etc are delayed and will be here next week..

 

[efinque]

Here's the passive summing bus that goes from the channel pots to the main outputs.

As you can see I didn't bother using any resistors for it.

EDIT : Those are actually guitar strings linking the connectors.

 

[efinque]

Here's the summing stage assembled with 10k resistors.

I think the most noise issues will be in the grounding though. Nevermind the fancy tape assembly, I have to open it up at some point anyway..

EDIT : I also forgot to buy cable ties..  :-[

 

[efinque]

The transformers and the rack case... I'll get putting the thing together asap

 

[efinque]

Here's a top shot with the PSU,  all the input modules and a few potentiometers in place..