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MIDIBox Mixer - A PGAx311 Audio Mixer


lylehaze
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Hello all, i was thinking about the mixer last night, and i told me, if there is 4 output in a chanel board, i think it will be possible to have a 5.1 mixer.

2 normal output for left/right and the 2 other output (aux) for front and rear, and control the place of sound in space with a joystick?

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As far as I understand, 4.1 is a 5 speaker system.(4 + woofer), just as 5.1 is a 6 speaker system.

As it is now built, you could support "Quadraphonic" (kids, google it!).

Although it should be possible to build two stacks, and "gang" two channel boards (horizonitally) to the same input, then you'd have eight to work with, That gets a bit messy though.

I designed it to be as flexible as possible. Every day I hear new ideas that I never considered. Yesterday I was discussing how to use the "spare" op-amps on a channel board to build an audio compressor. A few days before, how to use these for a guitar effects chain.

I am REALLY looking forward to getting these into the hands of some of you crazy folks. :-)

I should add this:

This board was designed as a simple line mixer. It has lots of options that you are encouraged to play with, but in the end each user is responsible for making it work. If you follow the posted build, you will have a fine line mixer. Those who want something very different should consider starting with a regular mixer and experimenting from there. Too many changes at once can make troubleshooting difficult.

This is going to be a lot of fun.. ;-)

LyleHaze

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  • 2 months later...

So far, I have only built a 4 board version.

I am using it as a simple line mixer, combining eight stereo pairs.

I currently have the software configured for 16 channels, for testing purposes.

The board designs have not been released to the public. They will be carried

in SmashTV's webshop.  He has refined the design a bit, and I will announce

them here when they are ready for distribution.

If you'd like to build your own version, you can find all the circuit design details in the datasheet for the PGA4311. Available from Texas Instruments.

When I designed the set, I never thought anyone would build above a 16 channel set. Comments here indicate that some people may want more. I look forward to seeing how far they can be expanded. Since the hardware inputs are CMOS, I doubt we would need much more than a terminating resistor to get big fan-outs. The software will require re-writes for more than 16 channels, but the driver core should have no trouble with that.

Comments regarding expansion limits have been posted in the WIKI, and I'll add more details (including confirmation of expansion sizes achieved) as they become available.

Thanks for your interest, when the boards become available, I hope we'll get more people interested.

LyleHaze

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  • 5 months later...

Ok Lyle here are the photos as promised. PSU, Core + LCD are running so far, but i will have to change the transformer (11V secondary) as the regulator (with heat sink) gets hot. The LCD is a jumbo 2x20 and was already broke on delivery, but i got 15 more of the same type so i will change it when fitting the front face plate.

The housing is from an old panasonic encoder rack unit which i got from ebay (3 units for 6 euro). Its almost perfect for that type of project as i am trying to keep the differant sections seperated.

...as you can see there is so much room left inside, so i am wainting for all the channel boards;-D....the PGAs are already laying on my working desk....

IMGP1367.JPG

IMGP1367.JPG

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very nice..

Having the compartments in the case will be good for shielding, keeping the digital noise out of the analog signals. That display looks HUGE! Since you're making a mixer, I have a display question..

What do you get from character codes 0x10 to 0x18? (dec 16 to 24).

If you get vertical bars moving from left to right, you'll be able to use the graphic level display.

There's also a Db display that will work on all display types.

You CAN run the mixer software before connecting the PGA chips, if you want to check it out.

You may also connect a encoder if you make a DINX1 module (just one chip).

Looks like a great start.

LyleHaze

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Sasha: I will try do make my own boards, as its still not sure when lyles boards will show up on smashtv´s shop and am planning to build as many channels (at least 16 channel boards) as possible so it will be cheaper do make one or two big pcbs for all the PGA chips, as i wouldn´t be able to get all the 16 boards in the rack case with the pins stacking it.

But i am new in doing pcb layouts so please refer to lyles great artwork:-)

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Lyle: I only need two components more for the core modul to get it complete working, the 10mhz crystal and the Optocoupler. Right now only the backlight is working, the PIC is already flashed with the bootloader so when the core modul is working i will test the lcd concerning the 0*10 to 0*18 question.

The DIN modul is almost complete and i will connect it later this day. Since yesterday i am trying to make two little pcbs which will carry the 8 encoder (the cheap panasonic ones with push button and knob already contained). One big knob for quick patch browsing and the other seven encoder will later hopefully be assignable to channels...quick access to do things like ajust reverb and delay effect level, panning between the differant channels. I will post a concept how i want the unit to be working in the next days, its thought of beeing a mixer with about 12-14 channels containing guitar effect pedals on each channel or when doing stereo channels on each stereo side. The channels will be sent to outputs which will be connected to 2 guitar preamps(maybe output left preamp1 and output right preamp2 so i can fade between), routed back into the mixer channels 15(preamp1 return) and 16 (preamp2 return)which should be full mixer channels with effect sends, delay on effect1 and reverb on effect send 2. The delay and reverb effect must of course brought back into the mixer via two more stereo channels as the reverb and delay will be stereo effects. Now the effected signal will be going out from the mixer via a second stereo mainoutput which will feed the stereo power amplifier. So output1(stereo) for the 12-14 effectpedals which will be sent to the 2 preamps and output2/mainoutput stereo which will feed the poweramp.

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Right now i am about to do the regulator board which is intended to be placed in the same chamber like the transformator. As i wrote before i will have to change the transformator anyway as i only had an 11V secondary and the regulator on the core modul gets too hot with nothing more connected as the Display. I almost forgot that i will have to power the PGA chips too;-)...

...so Lyle: You wrote that powering the core and regulatorboard from the same powersupply is likely to get noise from the powersupply?? When i change the transformer to an , for example primary 230V and secondary 2x8V 2x500mA, leading the first coil with 8V to the core modul and the second coil with 8V to the regulatorboard(which will have the bridge rectifier on it), will this work and be save in terms of noise and stability?

...also...the 2 electrolytics behind the bridge rectifier are stated to be 2700uF or more. Wouldn´t be 2200uF also doable as i don´t have the 2700uF here on my working bench?

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@Orkspalter

as i wouldn´t be able to get all the 16 boards in the rack case with the pins stacking it.

The boards are sized to fit in a 1U case, no matter how many are stacked together. Each stack layer adds less than an inch to the total size, which then LAYS DOWN in the case. That's why I made the boards so narrow. Notice these boards are "mounted" with double sided tape.. it works great.

fetch.php?media=pga:stackpic.png

of course, my boards are not yet available, I can't fix that today.

The signal routing sounds pretty confusing, I'll be back to read more after breakfast and mowing the lawn. :-)

Using the same transformer should be fine.. just use separate 5 volt regulators for analog and digital. I think the two windings would be positive and negative, though the positive will also be feeding the digital stuff.

fetch.php?media=pga:txandbridge.gif

So in this picture.. both CT connect together (Ground), you'll feed both 7805s from +, and feed the 7905 from -.

2200 uf should be great, I always shoot a bit over on filter capacitors.

Have Fun,

LyleHaze

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OK, I finally had a chance to try and follow your signal path..

One thing you my want to change: You said that some of the mixer outputs would be going to the guitar preamps.

I think..

The channels will be sent to outputs which will be connected to 2 guitar preamps(maybe output left preamp1 and output right preamp2 so i can fade between), routed back into the mixer channels 15(preamp1 return) and 16 (preamp2 return)which should be full mixer channels with effect sends,

A "proper" guitar preamp will take a low level (high impedance) signal direct from the pickups, and will output a "line level" (low impedance) signal.

All the signal inside the mixer are line level. We can mix high impedance and balanced inputs only after converting them to line level. That's why the input sections are so configurable.

Taking an output of the mixer (line level, balanced or unbalanced) back to a preamp may not be what you intended.

As we talked about before.. getting your signal paths figured out will take some work.

I provide setup for a "line mixer" and a "Full Mixer" and you can mix and match those as desired.

Figuring out all the options for what you want might take a bit more work.

To review, for others just reading this thread:

A "line mixer" mixes a stereo pair (Left and Right) into the main Left and Right outputs, no effects.

You can handle two pairs per channel board. You'll use all four input sections, output to just A and B.

A "Full Mixer" takes a single input, and mixes it between Left, Right, Effects1 and Effects2. This requires a channel board for each input. You'll use just ONE input section, and all four outputs (ABCD)

Your may mix "line mixer" and "full mixer" boards in the same stack, and configure them by MIDI when you start the board up.

fetch.php?w=640&h=150&media=pga:barechanbrd.png

If you look closely at the "Channel Board" diagram, it has (up to) four input connectors, "-1+, -2+, -3+, -4+", up to four input sections,each with five points to configure them, four volume controls (inside the PGA chip), and four possible destinations to "mix" into. You wire the inputs and outputs as desired, and configure the rest with control change commands. All four mix destinations (A,B,C,D, usually left, right, FX1, and FX2) are usually ganged together by stackpins, but the user can separate them when building if you want.

Enough review. These are things I expect to be answering a lot of questions about, so I wanted to get it posted here. If there are suggestions to how I can make it more clear, speak up!

Have Fun,

LyleHaze

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