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Archive for November, 2010

19
Nov

iPatch Completed

As a musician and electronics buff it didn’t take long before I envisioned building a stompbox pedal switcher that actually provides proper true bypass as opposed to the stompbox pedal norm of FET bypass (that robs tone from the signal path).


A true bypass stompbox removes both the input and output from the guitars signal path and usually the pedal will advertise “TRUE” bypass. This isn’t completely true 100% of the time, but until you take the pedal apart to see how it’s wired, you can only go by what’s written on the packaging.

The common practice for an effects pedal (Line 6 or Boss for example) is to use FET circuitry that either routes the signal through to the “effect” or to the output. Unfortunately this form of bypass tends to diminish the tonal range because of the “bypass” circuitry.

Even pedals with a true bypass looking stomp switch can be misleading. For example, the switch will route the input signal to the output to bypass the effect, but will leave the pedals output stage connected to the output. Again, this will present a load to the signal and tone can and usually does suffer because of it.

The situation is compounded by the multi-pedal boards that guitarists use. Each pedal takes it’s toll on the ultimate sound and there’s no way to correct it after the fact.

I’d been using a VooDoo Labs Pedal Switcher for a few years and it’s great for studio or live work. It’s initially how I started testing pedals in their bypass state to see how badly they affected the tone. The results in some cases were quite astounding and I stopped buying pedals from some manufacturers because of my testing. However, the Pedal Switcher was limited to five pedals, had an odd ball MIDI sysex control setup that I didn’t like.

I’d also checked out other switchers, like the RockTron PatchMate 8. Which is a good unit, but isn’t all that programmer friendly. None the less it’s still an excellent unit.

When John announced the new version of the MSA-R, that was all the push I needed to decide to build my own. My design criteria was:

1. Input normal or buffered (makes up for long input cable loss)
2. Complete remove input and output signals from path
3. MIDI controlled (and easy to program)
4. Firmware upgradable

I selected the MSA-R as the brain, mainly because if I scrapped the whole project the R unit can be used for many other things. However, the MSA-R relays are only single pole and I needed to remove both input and output signals. Hence I required a DPDT relay setup.

I designed a relay PCB board, some driver transistors and LED output indicators. And then I happened to be searching for relays on eBay and came across a pre-built board solution:

DPDT Relay Boards

I viewed these as a cost effective solution that saved me the time and cost of building my own. I had no idea of the quality of the relays, but as it turns out, they are quite serviceable. Of course they aren’t the “gold plated” relays that some switchers use, but I ran some signal tests with my scope and they work good enough for my application.

I purchased four relay boards, unsoldered the LED’s and replaced them with pin headers that I could clip to for the front panel LED’s. I wanted the indicators on the front for relays for the audio, not the LED’s from the MSA-R.

Next was the input buffer. I’d originally bread boarded the thing on a piece of cardboard since it’s a very simple circuit. I was running off a battery but decided to run it off the 12VDC supply by wiring in 4 diodes in series to drop the voltage to 9.6. That worked perfectly, and audio scope tests showed no discernible audio noise. This really helps to make up a decent signal strength when you’re using those 20-25 ft guitar cables so the pedals have signal to work with.

Again, I was going to build a proper PCB and then I found the exact one on General Guitar Gadgets:

Input Buffer

Granted a little pricey for an unpopulated PCB, but it saved me the time of having to build it so I could work on other things.

Last was the multitude of 1/4″ input jacks. Rather than make a PCB and mount all the jacks, I chose the lug style to use and they also have switch capabilities (inserting a plug will interrupt the switch). While not Neutrik gold plated jacks, they work well and cost effective.

The toughest part to find was the 19″ 1U rack unit that was only 6″ deep. Plenty of 10’s and 12’s out there but 6″ ones are tough to find. The one I used is made of 18 gauge steel, after drilling it, I seriously wish it had been made from aluminum…

I run the iPatch from a 12VDC regulated wall wart and here’s what the completed project looks like:

And the rear:

I didn’t label the SEND and RETURN, because I wired it the same as a normalled patch bay. Send is the upper jack, return is the lower jack.

I decided to go with blue LED’s for the front panel so I had to change the relay board resistors to allow additional current, the blue LED’s, while only a 25 degree viewing angle are so bright (1200mcd) they light up the studio or stage. Significantly..

I also used a super bright yellow LED for the “act” LED on the MSA-R. Since it didn’t supply enough current, I used a PNP transistor to drive the “data” LED on the front panel.

Were I to add enhancements to this project, say for version 2, one area would be each channels input/output path.

At present, the signal flows from 1-8, if you turn on a channel that doesn’t have a SEND jack in it, the signal still passes through (the switches on the jacks allow this). If you want to rearrange your pedals, you have to unplug and change their order in the chain. To make the unit more versatile, a separate input, send, return, output would be the ultimate. A setup like this would allow you to use effects in parallel and the sound from this style setup is far different than a standard series setup (you then blend the effects signal with the raw signal). Or if you use multiple amps. Nice signal splitter.

Also with this setup, changing the signal path is merely moving the Out’s to In’s order with short patch cables. You could even add a buffer to each channel to further enhance the signal although this might invoke the law of diminishing returns…

One other area I plan to address is the lack of a MIDI Thru jack. There’s no room to put one on my chassis so I’m going to use the un-used pins of the OUT jack and built a custom MIDI cable for it. This way I can use my MIDI foot controller for the iPatch AND I can run any other devices by MIDI that I need to.

As for the name, I admit, I didn’t think of it myself. My bassist came up with the moniker when I first started talking about the idea and it just stuck…

18
Nov

iPatch Operational…

I finally finished off the iPatch (another Wabbit Wanch original name)…and it works like a dream. There’s still some bugs in the firmware, but since I don’t program the firmware, I’m just waiting on an update for it. I left the top off for the shot here:

iPatch Front High

The LED’s are plenty bright. I had some concern about them not being visible, where in fact I think I could use them for Laser Surgery…they light up the studio…

16
Nov

Programming my MSA

I got the latest MIDI control board from High Liquid and started programming it over the weekend. Today, I found several bugs in the firmware on the bug that will need to “adjusted”…and that will give me some time to finish off the rest of the build. Those empty holes in the back aren’t really supposed to be there…:-)

This is what it looks like on my test bench…

IMG_1712

6
Nov

Continuity…from the long ago past

Aside from working on iFCB’s Mackie Configuration, I was going through one of my old junk boxes today. Mainly looking for a wall wart supply for that cap meter I made yesterday. Of course, with a box of AC adapters collected over the last umpteen years, I was bound to have one, with the wrong end of course, I came across one of testers I used in the garage for many years.

Actually it stems back probably 30 years or more. I was building a dune buggy at the time, street legal of course and since it was from the ground up, there was no electrical system in it at all. Since a dune buggy doesn’t have all the bells and whistles of the modern cars electrical system, rolling your own from scratch really isn’t all that difficult. You got lighting, charging, starting and that’s about it. I made my own wiring harness, and if I remember right I found a wiring diagram for an early VW and based it on that.

So the required shot of the duner, when I first got it running and wried. I had a tow bar on the front initially but evenutally I built a proper bumper for it and it was 100% street legal. Drove it for three years through some of the coldest and snowy weather I ever seen (I’d built a heater in it of the stock j-tubes exhaust). That’s my son sitting in the front and driving with a vengeance..:-)

dune buggy4

Any way, the tester I found is one of the, I think, go no-go from Radio Shack, when Radio Shack was still Radio Shack (any one remember Allied Radio Shack; good you just dated yourself). Nothing fancy, just a pair of AAA’s and a grain of wheat bulb.

With mods 2

So with that in mind, I took it apart, took out the pathetic little light bulb, stuck in a 1000mcd green LED (3.2V) and a piezo buzzer. So even if you can’t see the LED, you can now hear it. I drilled a small hole in the case for the incredible stereophonic sound to escape (right)…Stuck it all back together and I’ll wager the wee beastie will be good for another 30 years…:-)

Continuity In Action

Oh if you look closely at the body it looks wrinkled. Apparently I never bothered taking the protective shrink wrap off the surface so it’s been on there since day one. And inside the case lid, it has cut outs for what looks like switches so I was thinking that at some point, they used the same case for a logic probe. Now one of those I have as well. Somewhere around here. I even set it aside so I wouldn’t lose it. Now if I could just remember where I put it so I wouldn’t lose it…

6
Nov

Capacitor Side Trip

Apart from writing some new routines into iFCB today, I decided to take a bit of a break and build a $14 capacitor meter. It’s claim to fame is that it can measure from 1pf to 500uf and with 1% accuracy.

If and when I get my Fluke multimeter I’ll be checking it against that, but this is was more of a fun project than something where I need any more than a ballpark number.

The Capacitor Tester kit is from Sparkfun electronics. They got all kinds of stuff but this caught my eye. Here is what the kit looks like, except the socket for the PIC brain chip wasn’t on there and not supplied. I used a couple of 14 sockets of my own to make the PIC socket.

Capacitor Kit

It takes a little while to put the thing together because, well, the instructions are exactly “Heathkit” style (if your memory goes back that far). Basically you get a BOM (bill of materials), a schematic in 4 point type, and that’s it. Fortunately, I can read schematic’s so the bigger issue is trying to figure out the value of those 1% metal film resistors they use. Lousy color code definition if you ask me.

But with an ohm meter you can figure it out. I did make some changes to the circuitry. I used better capacitors than what was supplied, and I took the 1K5 resistors that they use for the LED display and chucked them. I put in 270 ohm ones for a brighter display (one of the complaints of the board is the poor brightness of the display). My “hanger” where I build all this stuff is very well lit (like a drunk on a Friday night) so even with the added brightness the display was hard to see.

For power I used an 12VDC wall wart. Bad plan. Although the instructions says you can run it on 9-16VDC, you want to run it on 5.5 to 6VDC. Or the 5V regulator starts to cook…not good.

Assembled

Above you can see it assembled and sitting on some stand offs I had. The bottom right shows the cap being tested, bottom left shows the RS232 port where data can be sent if you want to.

It’s pretty easy to use. Zero it out, plug in a cap, wait. Watch for N, U or P and the value.

For example here’s a .1uf or 100nF cap being tested. You can see it’s 94.1nf so it’s not quite the 100nF that it should be. I checked a number of these caps and values ranged from 78nf to 98nf. Guess that’s within a range someplace…

100 nF Cap

When it comes to large electrolytic caps, you can test them too. Readings take a little longer. Here’s a 20uf being tested and it comes out at 18.2. Not half bad really…

20 uF cap

So, to make a long post longer, the cap meter works, and I think it’s well worth the $14. But I have to find a 5VDC wall wart for it and some decent clips… At least you can zero (or relative) it so you can subtract the capacitance from the leads.

4
Nov

iPatch Progress

Been a while since I wrote but I haven’t been inactive, I’ve largely been waiting on parts. Seems that the canoe that brings the parts from Asia is getting slower…

I picked up a simple buffer so that I can run the guitar plain, or buffered (so long guitar cables won’t affect the sound as much). I ran some test signals through the buffer and I have to admit that it cleans up the signal very nicely. I didn’t notice any problems anywhere within the range of a normal guitar (I didn’t test bass frequencies).

The circuit is quite simple, you could actually build the thing on a piece of cardboard:

iPatch.JPG

Now I got a little lazy and ordered the circuit board from General Guitar Gadgets for a few bucks. Mounted on a stand off and it’s good to go.

There are two input jacks on the back, one is for the raw guitar signal, the other jack connects to the input buffer. If you plug into the buffer, you can’t have a guitar in the unbuffered jack, because the buffer is taken out of the circuit when you do that.

The only thing different is that I used the 12VDC supply to run the buffer, but it only calls for 9VDC (battery). I used 4 diodes to drop the voltage to 9.6 and it works just peachy.

The MIDI brain has shipped and should be here next week sometime and then it’ll be a lot of programming to make it work with Moose. Until then I have to add some more I/O jacks and wiring on the relay boards.