First, there are now 6 audio input channels, 2 mono, 4 stereo. Each will have a TDA7418 audio processor as the channel strip EQ controlled by a central PIC chip.
 

The blue knobs aren't pots, they are rotary encoders, which have really come down in price. Why mess with dirty pots feeding ADC's and needing to rotate past the last position if the assignment of it changes?

These 6 knobs default to channel strip level for each input. But if a knob is pressed, that channel's Balance, Low, Midrange, High, and FX injection levels display on a course circle of LEDs around each "pot" !
A finer numerical representation will be displayed in the LED display while the pot is being turned.

One nice feature will be a set of 4 FX chips, PT2399 (analogue) that will output in stereo, a reverb, echo, combo range off of any channel. I plan to use some of my otherwise useless CDS cells pulled from scrapyard solar lights. These with PWM'ed LEDs have worked well in the past.

All of these signals will be mixed by op-amps into a stereo signal and fed into a final stage TDA7419 for final tuning, using a button up there to turn the "pots" below into the same controls for it. Mostly the output will only need initial tuning on-site, then the level, sub, and balance have been brought out as pots-->ADC.

  I have most of the circuitry/parts figured out, but there are a few "what-if's" I need to investigate, particularly with the live audio record thingy. Being able to record and play multiple samples that can also be called up from a MIDI sequence has always been a desire for me. Singing harmony with my own "oooo's and aaaah's" recorded at the start of the song, would be amazing, whether the audience new or not. I'm hyped on that one!   Now hopefully I can keep the box size down around 14" x 6" x 6" or less !

This Update: Feb 8th 2014

 I'm not so sure about those LEDS, compared to the round, retro look....but there are more of them which is a good thing...and I think they're easier on batteries.

 

March 17th Changes:  I realized that putting the Channel EQ controls on a separate panel made of PC board and epoxy would be a simpler way to go.  You may have noticed the panel has grown substantially. This is because I've decided to make the sequencer part of the unit. It was originally separate so I could use it in the studio etc, but the size of the box hasn't changed so it'd be pretty compact under the piano. I've also added a section for distortion and associated filters that will feed from the guitar strip, or ST1's right side. This way a second guitar and mic can be plugged into the pre-amp'ed ST1 but have only distortion on the guitar.  Audio looping records can be sequencer controlled, or from the panel using each strips level control.  Mic & Guitar inputs will have variable pre-amps, and ST1 will have a fixed gain pre-amp, although still controllable from that strip's inGain, and ST2 now has a mix amp with the recorders playback output, so the pre-amp light will be a mix light (during playback)

 Last but not least, there's now 3 MIDI outs on the panel, there's really 4, but that's exclusive to the on-board VS1053 synth board and MPX8 sample player (using out-of-range drum notes)
So if a real synth like my Korg or better drums etc is called for, the sequencer can have access to them. Hey! I forgot the headphone jack yet again on the new design :P

Because I order a lot of parts from China, I'm never exactly sure what I'm going to be getting until it arrives on the doorstep. Sometimes it's not as I'd imagined, I'm sure everyone has had that experience! Well such was the case with the encoder "pots". They are great quality-wise but the shafts on then looked a bit longer in the picture on eBay. As a result, I've had to re-think the whole lexan over aluminum idea, well at least for that part of the panel. The shafts are simply not long enough to go though the 1/8" lexan, then into a rather deep knob, which I also ordered at the same time. The SMD LEDs and the short shafts didn't work together as you can see in the "Methods" image to the right. I really had my heart set on using the laser printer to make a mask for the lettering, but it may not be so. Back to the stick-on letters or paint-pens. I wish I had a silk-screen setup, but unless I was going into production, it'd hardly be worth it.  Method 4 is the present consensus. There's something appealing about mounting tiny (really bright! ) white SMD LED's upside down so they poke light through a 3/64" hole while trying not to "melt" the black paint off of the other side of the board! Hmmm...                    Well we'll see how long this design lasts before I re-design it! Meanwhile, I'm slowly working on each section of the unit and the design all-in-all is starting to stabilize.
Update May 1st 2014   The boards for the encoder panel has been designed. The rest of the panel's size will be determined by this, then the exact size of the box from that.
Each encoder has 15 white SMD LED's around it to show the position of the "knob" that will change depending on the function of the panel at the time.  As mentioned above, I've made the decision to mount the tiny LEDs face down over a 3/64" hole. So this trace side view (top board) is looking up, that's why the lettering is backwards. The lettering will be lighted from a small board and a diffuser glued on after the epoxy is applied.  On each end of the board, you can see the vertical 8 LED level meters. These will stay exclusively meters, but the LED's around the knobs will become spectrum analyzer bars after no adjustments have been made for a while. I have 7 bands at my disposal from the Main Output's TDA7419, so I'll use the 6 lower. In an acoustic scenario, the 15 khz+ band is useless anyway.  The pads going around the knobs are commons for each set of LEDs. They can't go through the board as the other side will be visible on the panel!  It'll be sort of like knitting with a thin wire and the soldering iron.  The hole marker under each knob is for a standard 3 mm LED that will indicate the active Channel Strip when adjusting tone controls etc.  These LEDs will be mounted off of the lower board on stand offs. Headers on each end and in the middle will line up so it can be plugged right in. Headers off of the panel board must be "surface mounted" as holes shouldn't be drilled through!  The lower board is somewhat smaller so it can fit through the hole in the aluminum part of the panel.  The encoders will mount onto this board, hence the footprint for those, the the nut threaded onto the top board. This means the thickness of the top panel must be pretty accurate! These 6 nuts will be the support for the bottom board.  2 headers lead off of the lower board to connect to the mainPIC (Sequencer) board. These carry the encoder Up/Down/Button and common on one header, and serial data for all of the 240 LEDs on the panel.
Luckily, the 8x8 drivers only drive 8 LEDs at a time, so even if the 240 LEDs were all on, the draw could only be for 16 LED's, which at normal indoor brightness may be 40 mA or so. The 2 two LED driver chips, are the MAX7219. These chip are over 10 years old, but have become really popular on eBay for super cheap, probably because of the Arduino Revolution!  Completing the panel board is a 1 shot deal that I'm a bit nervous about. It must be drilled, masked over the lettering and painted black on the back side, have LED's mounted, have jumpers installed, then be well tested, all before siliconing aver the header pads and dipping it all in the epoxy..  It's important that the epoxy box be lightly siliconed and perfectly level as the panel must be completely submersed at least 1mm so the drilled holes don't create "dips" by the skinning effect. The silicone to the epoxy is like oil to water. It shouldn't bead up on the edges at all, in fact, I'm hoping it will angle down. That way the edge of the panel will be easier to finish.  I'll have to do it on one of my "good days" or it'll be an unfixable disaster! Maybe a scale test is in order with no board first...

 Update May 18th 2014:

  Here's the new and more or less final layout! It's stil within the size limits and has pretty much all of the elements required (I almost forgot the SD Card slot!)
The buttons may end up as home-made caps. I've been contemplating using the lathe to cut out some aluminum rod and polishing the ends. These would press against a standard PC mount button. I've printed this layout to scale and it's very close. The 1/4" and XLR socket spacings are accurate, allowing enough room for their cases.

  This layout is pretty close to the one above, but once re-sizing the panel to be large enough for the box size to accommodate the MPX-8, it looked kinda bare!
An LED display has been added for On-Tap sequencer functions. It'll count beats, show incoming MIDI notes etc. Not sure what else. Some important addition are the "User" knob, which can be programmed to control any function, even a MIDI out CC, the "Phones" knob to adjust headphones level, the phones socket, and a dedicated "SEL| encoder knob for the menu. Originally one of the knobs on the encoder board was to take this duty, but it seems kinda complicated that way.

 Oh! ...and the OLED display is seated lower into the panel so a magnifier can be used. This should make it more "viewable" (I hope!) You can see those yellow LEDs in there, I'm not sure why I did that, but as soon as I figure out why I'll let you know! A power switch on the panel is good, and a charge indicator. AUX 1 & 2 are now standard 1/4" sockets. These will feed to a stereo mix to share channels with the built-in synth, and the MPX-8. Finally, the large grommet in the lower right corner is for a curved cable tray to feed wires across the hinge from the lower box section.

 The scale is correct for the whole thing, with real components, so I'm pretty much ready to start cutting aluminum plate.

A cool trick I like to use for testing a scale during design (in Flash) is to use DIP IC spacing somewhere in the layout (this one has the encoder board which I used to scale the whole thing) and shrink it on the computer monitor until a real DIP plug matches the spacing. With a 40 pin chip, it's pretty accurate!   Then I proceed to place the actual parts, i.e. pots, sockets, LED display, etc., against the screen. It's amazing haw far one's perspective is when it comes to designing something "on screen". Things tend to end up too small.   As you can see, I've made the encoder board/panel. The PC board under the photo-sense is completely different than what I'm accustomed to. Instead of translucent green, it's nearly opaque yellow!! This board is so opaque that I couldn't tell it had finished etching while copper side down! Very unusual for MG chemicals.   Anyway, I've worked around it by utilizing some 5050 SMD LEDs to light the lettering (which now shows a third function!), put the original transparency over it, and taped it on to sharpen them up. I found that red/green (yellow) is great, red or green by itself is also nice, but blue is almost not noticeable at all. Blue with red makes a crimson kind of color though, so I will use it. ( RGB board not shown )   After soldering on the 106 white "pixel" LEDS, and testing them all, it was time to place the board in the epoxy box. Screws were used where each encoder hole will be drilled, mainly to make sure the board was flat. I must admit I was very nervous about doing this because any damage to the board would be extremely hard to fix with 1/8" of very hard epoxy over it!   As you can see, it came out not bad. My sloppy hand-drawn paint pen graphics aren't as good as the CG photo above, but it'll do. One disappointment I did have is some of the LED holes ended up with bubbles stuck inside them. Had I noticed this I would have popped them with a pin before the epoxy hardened.  Yo can see which ones (there are many) have bubbles as they're not as bright. The first circle is perfect.
It does affect the low level LED brightness, but when bright not so much. The bubbles are acting like little lenses that reflect the light outwards, into the side of the hole. Oh well, live and learn! The total thickness was of course too much for those bloody encoder shafts, as predicted, so I went with the contingency plan and routed them down using a dremel. One final kinda disappointment was the edges didn't run down as predicted, they went up. They had to be cut down. If I had to do this again, I would make the box oversized and cut it out. That way the edges would be relatively flat. I managed to "dig" out the contact points and connect headers. The LEDs all work! Yay!!  I'll post some more pics once I've finished populating the lower board. All in all I'm happy with it, it's tough and panel-ready!

Until Next time! Cheers, from Sandy

 

June 4th 2015 The box looks finished! Well almost! I know it's taken a while, but this is one huge project, much bigger than I ever thought. Anyway, over winter I designed and built the embedded synth, the distortionPIC board, the Sampler, and the Power Supply. The panel was done to take a break from the design of the other 14 boards that need to go into the SIAB. . . and here it is! Amazingly it looks pretty close to the CG rendition.>>>  The back of the aluminum panel had to be gouged thinner for the 1/4" sockets as they have almost no thread on them. The extra thickness of the pour-on epoxy made this absolutely necessary. I decided to glue on the tinted bezel (over the 7x5 LED matrix) before pouring. This has made a great finish with an almost concave lens effect. You can see that better in the unfinished image below.  The SD Card slot had to be cut before the epoxy completely set as it gets really really hard once finished (about 24 hours). The minor holes (up to .5") were backed with tape then drilled after as their edges won't be seen under nuts and knobs.  The larger holes, for the meter, LCD, MPX-8, and wire feed-through, were allowed to drip through, giving them a nice soft edge.
The button holes had to be carefully drilled (slightly over-sized) so not to damage the visible edges. everything else went in as expected. Some of the lettering I drew by hand, and others, the CH1,2 etc, were stick-on's I found at the dollar store. They were bright white, but the epoxy must've soaked into them a bit and made them darker. It was unintentional, but they look better and closer in colour to the silver lines I drew on. The hand-spun aluminum buttons I made also match so great!
In this photo it looks rather odd because the sky is reflecting off of the reflective epoxy finish. It's a bit of a pain to pour, but the finish is very tough. Minor scratches will actually fix themselves as it's always mildly fluid, or so I have found with my guitar.  Last but not least, the somewhat "tacky" words "Show in a Box" was with carvnivals in mind, you know, the chaser lights.. well whatever, I like it! The case closed is an unassuming wooden box. only the power socket and programming access panels give it away. I'm sure I'll be asked to shine shoes!

  Well that's pretty much it for the panel(s). I'll post some dark room shots/video once all the lights are blinking and the LCD display is in. (That'll be a while, Dec 2015?)

Cheers, Sandy *

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