m00dawg
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Texas

I'm back at it again working on yet another ArduinoBoy design. After realizing that a rackmount ArduinoBoy doesn't work well in live applications, I've decided to try making a stomp-box style ruggized thing while also adding some features to reduce all the crap I have to take to a live show.

So the plan is to combine an ArduinoBoy, PISS BOX-like design, and a Balun into one box. The schematic is basically done, though untested. But one problem I've run into is whether or not to use a transformer for the balun and what type. The PISS uses what appears to be something close to the Xicon 42T series. Seems to work well, but it does attenuate the bass and requires more EQ. For noise rejection, that's not a big deal since you'd just run the empty channel through the tranny. For a balun, however, that's a problem. I looked at using bigger tranny's from Hammond MFG, but their working range is from 200Hz - 15kHz which represents a cut in bass that would have to be brought back in with EQ. Anything larger and both the cost and complexity go up to the point it's not practical (from what I found so far).

An active balun would offer much better frequency repsonse, but it wouldn't be isolated. That means ground loops could become a problem if the box is powered by an external wall supply requiring an isolation transformer anyway. Likewise, using a 9V battery may get tricky because an active driver needs a balanced circuit (so +/- 4.5V) and the Arduino needs +5V.

Yet another option I have read about but don't now quite so much about is to effectively do something of both by driving the tranny with more power, boosting the input side to help keep a more flat response. That fixes the isolation issues, but still requires an external power supply.

So I said all that to say, both, if anyone had thoughts on the above considerations (say if isolation is really an issue for most applications) and if there was anything else that might be convenient to have in a box like this?

egr
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Abandoned on Fire

Interesting plan!  The "data side" of your device, the arduino, will require power regardless so you may be more pleased in the long run if you just go ahead and make the other sections active.

basspuddle
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washington

what does a balun do? i've never heard of one.

m00dawg
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Texas

@egr

Yes, in fact I was seeing if I even had enough room for a bipolar supply and a line driver. The seems to be the case so far, though I'm not done routing just yet. The GB won't be the only thing I would need to isolate in cases where isolation was really necessary, so for that, using a rackmount Ebtech would probably be good enough. Of course, along those same lines, I guess I could argue as to whether I needed a balanced output at all.

@basspuddle

A balun is a circuit the converts an unbalanced signal to balanced or visa-versa. So basically on the output side, there would be an XLR or 1/4" TRS jack you could plug into a mixer. It's not really required, but makes the box more stage friendly and would allow running longer cabling without near as much loss in signal quality.

basspuddle
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washington

cool.

m00dawg
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Texas

Hmm so I really like the active approach. One problem is I don't know what the output impedance is for the Pro-Sound mod and that could be one reason why there is a big bass drop-off when using a tranny. If I go active, I think I can do both the inversion (noise rejection) and balancing without needing a tranny at all for anything (though the output won't be isolated, obviously).

The problem is, I don't think a voltage divider is gonna cut it since there is too much draw on the positive rail. I could simply require dual power supplies, but that seems kinda dumb. I want the box to be as integrated as possible.

The plan is to try one of the tranny's from HammondMFG, which seem a bit larger, to see if they end up offering more low end. Since I don't know what the impedance is from the GameBoy, I'm going to just get a 1:1 and hope that'll do the trick. Open to suggestions if anyone has ideas on a bipolar PSU that can tolerate higher load on the positive side.

m00dawg
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Texas

Well here is what I came up with. For now, I am calling it the GigBoy:

Note that air wire is intentional as there are two ground planes. I did it this way because both sides are grounded to the GameBoy and I haven't figured out how best to do that to avoid a ground loop.

Still a work in progress as things need to be tested, measured, etc. I need to make a simple control surface board for the LEDs and button for instance. I am fairly happy with it so far. I do wish I could have figured out a way to house a 9V battery in the thing, but a bigger enclosure would be needed and the cost increase didn't seem worth it. Similarly, an active circuit for the balanced out would have likely provided better sound but the power solution just didn't seem worth it.

On that note, though, I suspect the transformer will still attenuate some bass (still need to test that), so for cases where that cannot be compensated for and balanced output isn't needed, I added jumpers to switch it to an unbalanced out and avoid the output transformer entirely.

Feedback certainly welcome! I haven't decided on which open hardware license to use, but I plan on using one with it and, like my other designs, will make the board layouts and schematics available.

m00dawg
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Texas

As an update, EDCOR makes a combination summing and balancing transformer so I'm checking with them to see if inverting one of the inputs is possible. If so, it means those two tranny's turn into one. EDCOR also has much better specs and for way cheaper. The downside is availability is sometimes an issue, but is probably worth it.

m00dawg
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Texas

EDCOR came back and suggested this as a means to accomplish the both goals using a single transformer. In practice, I'm not sure how well it will work, so I am going to buy one and give it a go before changing the above design.

I am cautiously optimistic, however! The only downside is that using a single transformer like this means that it cannot be bypassed like the current design (so as not to color the sound more than the noise rejection). So it'll have to sound good, but the spec sheet indicates 20Hz-20kHz and I've read good things about EDCOR so I think it's worth a shot.

m00dawg
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Texas

As another update, I got the EDCOR tranny. It didn't work quite as I thought it would, but in the process, I think I found a better way - hook the L and R signals as the outer taps of the input side and use the center-tap as ground. This creates a difference signal. As with the PISSBox, play all the content on one channel and, BAM, noise reduction. It has the added benefit of not needing a passive mixer which seemed to be causing some harmonics from what I could tell. The EDCOR transformers are much larger than the one used on the PISS but, as a result, they sound pretty good - only a very marginal loss in bass from what I could tell. The output side is also balanced so two birds, meet one stone.

The caveat is that the speaker volume on the GB is noticeably attenuated. I rarely use it when hooked up to a mixer or my sound-card so no big, but I think that indicates an impedance mismatch in the GB and input side of the transformer. I was using a 600:600 Ohm transformer. But since the output seems unaffected, so long as it's not a risk to the GB itself, it's a non-issue. I'm just not sure if it is indeed a risk or not.

Any thoughts there? Apart from that, the box is coming together nicely and, if this works, it's basically ready to be prototyped.

egr
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Abandoned on Fire
m00dawg wrote:

As another update, I got the EDCOR tranny. It didn't work quite as I thought it would, but in the process, I think I found a better way - hook the L and R signals as the outer taps of the input side and use the center-tap as ground. This creates a difference signal. As with the PISSBox, play all the content on one channel and, BAM, noise reduction. It has the added benefit of not needing a passive mixer which seemed to be causing some harmonics from what I could tell. The EDCOR transformers are much larger than the one used on the PISS but, as a result, they sound pretty good - only a very marginal loss in bass from what I could tell. The output side is also balanced so two birds, meet one stone.

Nicely done!  The PISSbox "mixer" does indeed have some odd behavior, will try to address this in future revisions.  Just how big is this transformer you're using?

m00dawg
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Texas
egr wrote:

Nicely done!  The PISSbox "mixer" does indeed have some odd behavior, will try to address this in future revisions.  Just how big is this transformer you're using?

I think a different type/rating on the resistors may help? The mixer I setup while testing the EDCOR had the same problem, though I couldn't really hear a noticeable problem when using my GB test song.

The EDCOR I'm looking at is perhaps as big as the whole PISSBox smile I plan on using the 1455K1201 from HammondMFG (http://www.hammondmfg.com/1455.htm), which should fit both the PC and PCW line of transformers from EDCOR. Specifically this one is the one I'll likely go with, though I may try a 2:1 or 4:1 so see if that fixes the speaker funkiness on the GB. Since I'm having to send both channels to the tranny, I needed something a bigger to keep that bass response up. For the price, the EDCOR I tested (the 600:600:600) did an amazing job so I think it should be good to go.

I should probably setup some sort of test to verify the balanced circuit works well for longer cable runs. Don't have great means to do that, but I guess I can connect all the XLR cabling I have and make the longest cable possible and measure that high frequency rolloff with an unbalanced and balanced output and compare.

I may also change the design a bit for how the LEDs work on the ArduinoBoy side. I'm trying to avoid using extra boards which means all my I/O has to be on the bottom board in the enclosure and there isn't enough room for 6 LEDs. I'm thinking 2 tri-colors or perhaps 3 standard colors and doing sort of a binary count kinda thing to determine the modes. Smaller detail though (I plan on having headers on the board itself for folks wanting to do something else).

m00dawg
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Texas

Still waiting on those EDCORs hmm but I have been playing with the on I do have and I've grown more impressed at the noise rejection abilities of the thing. It doesn't look like much, but here is basically an ugly prototype before the prototype:

The board at the top is my ShieldBoy and the yellow protoboard is the noise rejection circuit. That's basically all there would be to the StageBox. The aluminum enclosure came in along with some samples of the audio jacks I will likely use. Waiting to have the board fabbed until I can measure the EDCORs just to make sure. Still am pondering the LED situation as well.

Alley Beach
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clovis CA

dope! super sick man! smile

m00dawg
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Texas

EDCOR transformers finally came in WHEE! I've also been thinking about the LED and button situation. I'm not pondering using DIP switches to set the mode and doing away with the button altogether. Then I'd only have 1, maybe 2 LEDs (BPM and, optionally power). The DIP switches would not require reading from EEPROM and there won't be any external switch to switch the mode (say if you accidentally kicked the button during a show or something).

I've been using the above pictured solution for a while now and I have to say, the extra iron is well worth it in terms of noise rejection performance. It's very good.

m00dawg
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Texas

I finally finished the thing! Works quite well, though I'm still working on adding a few features. The DIP switches aren't even being used right now, and the LED doesn't blink how I'd like. I also need to get the side panels cut still. However, it currently functions in the way I needed it and does a damn good job of it.

The rest of the photos are on our Facebook page (https://www.facebook.com/VictimCache) and I also have a GitHub repository for this here:

https://github.com/m00dawg/stageboy

The project isn't "complete" but it is functional at this stage so be mindful if you want to trudge on ahead and build it.