Xotic EP-Booster  [traced]

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Re: Xotic EP-Booster

Postby jsrfo » 12 Apr 2010, 03:19

I just got my EP Booster done and in an enclosure. I built it first on a breadboard, and then on a generic PCB type board. I tested it out and it works and sounds great but has a couple of issues

There is a slight pop when I hit the stomp switch. It has a much smaller resistor than I have used in other builds on the LED. Any suggestions on how to get rid of that?

I used the bill of materials found in a couple locations on this thread, and the potentiometer recommended doesn't seem to really roll the boost on. It doesn't add much boost from 0 to about half, and then the boost can be rolled in nicely. Any way to correct that?

Finally, this thing can be a bit hissy and noisy. I suppose I need to isolate things better inside the box, since it didn't do this when it was just a bunch of wires and board?

This is only my third build. I built a tube screamer variation and a Klon Centaur from PCB's bought on line. Those went together without a hitch and work very well. This EP booster was my first "scratch build", and it, too sounds great, but I am just not sure how to clean this up and tweak things listed above.

This is a bit addictive. I really haven't played much guitar since I have been working on these boxes.

Thanks in advance for the help.
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Re: Xotic EP-Booster

Postby Greg » 12 Apr 2010, 05:40

jsrfo

I would suggest that:
1. a 1N4148 is not the best choice for a Polarity Protection Diode and you're better using a 1N400X.
2. The placement of the LED circuit would be improved (from a switching noise perspective) by connecting the 33K resistor on the other side of the Protection Diode (battery + side).

The original effect has a slight pop also when switched and I suspect the 4.7uf cap that's tacked on is a band aid for the noise.
It also causes the LED to flash very brightly when switched before glowing at a lower level of brightness.

It should have plenty of volume on tap, even at lower settings, and yes it'll be noisy if it's un-boxed..
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Re: Xotic EP-Booster

Postby jsrfo » 12 Apr 2010, 11:22

Sorry, I kinda was a little backward on my post.

I did not use the same layout for the LED. I moved it all to the switch, instead of coming off the input line. I actually used a 3PDT switch, and got this slick little PCB from small bear that solders to the back of it. I used something like a really low value 400-500 ohm resistor on it. It would be a simple matter to put in a capacitor the same as the EP circuit shows.

Again, my booster uses a 10k linear taper pot, and I am getting very little boost on the first half of the rotation, so do I need to change the pot to audio taper or add something to the circuit somewhere, change a ground resistor value?

As for the noise, I may just have something loose in the box or maybe a cold solder joint on a jack. I need to look at that.

As for the diode change, being new at this, what can I expect that to do? I am slowly learning but right now I have more of an assembler mentality rather than a designer mentality.

Thanks
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Re: Xotic EP-Booster

Postby Greg » 12 Apr 2010, 11:54

Where in the circuit did you take the power for the LED ?

Sorry I didn't pick up on the fact that you used a different pot. The original uses a reverse audio taper pot, so yes the gain will come on much more slowly with a linear pot.
The 'C' pots aren't too hard to find.

The diode won't change anything sound wise.. it just offers better Polarity Protection in the event of a mishap.. that's all that diode is for.
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Re: Xotic EP-Booster

Postby jsrfo » 12 Apr 2010, 12:30

Thanks again, I'll look for the reverse audio taper pot or put one on my next order.

Any suggestions for the slight pop when the stomp switch is depressed? I could change resistor values higher, or put that capacitor across it.

As I do more of this, things become more apparent, but it's a pretty steep learning curve.
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Re: Xotic EP-Booster

Postby Greg » 12 Apr 2010, 13:10

again..

Greg_G wrote:Where in the circuit did you take the power for the LED ?



This may have an effect.. also the way you've wired the 3PDT can have an effect on switching noise.
It's best to ground the input when the effect is bypassed (check out the wiring diagrams at tonepad.com).
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Re: Xotic EP-Booster

Postby jsrfo » 12 Apr 2010, 22:52

I have the LED being powered straight from the power input to the board. I went over circuit, and the wiring looks proper otherwise. Is that a bad place to take the power from? The two PCB pedals I built had a lug for the LED +. This is the first one I did on my own, and I did it the same way, with the exception that I pulled power from the 9V into the board.

I could not get that LED to work the way the EP booster circuit was drawn, so I just moved it to what I knew. I also omitted the capacitor on that LED, and am wondering if that has something to do with it.

The pot and the noise, I can fix. Thanks for the help with the popping noise.
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Re: Xotic EP-Booster

Postby jsrfo » 13 Apr 2010, 18:10

Thanks for your help. I got it pretty much all sorted out. Basically I had some of the wiring ass backwards on the battery/DC jack, and two solder joints were found broken on the board.

No pop, no hiss. Just waiting for the 10KC pot.

The booster works really nicely, otherwise. I find that it is on more than off.

One question, should this booster also add a bit of overdrive? With the amp on a clean setting, if I crank the boost up, I can get a bit of break up to the sound. It's actually kind of nice, but I was thinking that this booster was more clean, and it surprised me a little bit. It's nothing like the tubescreamer or Klon I previously built, though, and really expands the sound of the amp nicely.
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Re: Xotic EP-Booster

Postby Greg » 14 Apr 2010, 01:12

No problem... I'm glad you got it sorted.

As far as the overdrive... I said I first heard this that it sounded to me like it was clipping, and posted some 'scope pics on page 3 to confirm that.. so yes it does add distortion at higher settings and with higher output pickups.
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Re: Xotic EP-Booster

Postby jonahstepro » 19 Apr 2010, 20:20

Curious if someone can post up a wiring diagram for this, how it connects to the jacks and switch and pot. thanks
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Re: Xotic EP-Booster

Postby jsrfo » 22 Apr 2010, 15:44

I'm wondering if anyone who has made a board for the EP Booster has any for sale. I built one on a generic PCB, and it works great. Well, actually the second one worked great. I'd like to do another one on a good PCB, but don't have the knowledge or equipment to do one. It's one great littel box for sure.

As for the wiring of the Pot, jacks, and switch, there are generic schemes for that on this site and elsewhere that are extremely helpful. One note, on my build, I removed the indicating LED portion from the circuit shown on this thread, and put it onto the 3PDT switch. Smallbear sells a nice little PCB for a dollar that fits the back of the switch, and makes wiring very easy for the jacks, LED, etc.
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Re: Xotic EP-Booster

Postby Greg » 22 Apr 2010, 23:50

jsrfo wrote:Are you sure that the Fatpants is the same circuit? It looks completely different than the circuits and part values that Elrengofa, Theo, or Moska have posted here. There are a million ways to skin the cat, so to speak, so it may be an equivalent circuit, but I didn't look that deep into it.

I used Elrengofa's circuit, breadboarded it, and then basically handwired it onto a RadioShack generic board. Compared to my friend's original, there isn't much difference to note, if any at all.

Anyway, the real one and my version are just great little devices. Glad the forum enabled me to build one.


Nope.. that's not the EP Booster circuit from the schematic and discussion in this thread.
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Re: Xotic EP-Booster

Postby Jack Deville » 23 Apr 2010, 00:11

Why is a 1N400x a superior alternative to a 1N914/1N4148 for polarity protection?
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Re: Xotic EP-Booster

Postby Greg » 23 Apr 2010, 11:48

Jack Deville wrote:Why is a 1N400x a superior alternative to a 1N914/1N4148 for polarity protection?


Probably none in this configuration, but obviously it has a higher current rating when placed from input to ground...
I forgot that in this one it was used in series.
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Re: Xotic EP-Booster

Postby Tube2stomp » 29 Apr 2010, 14:19

[smilie=a_hrm.gif] Do you guys use load lines to see how SS gain devices behaves?
I draw them for circuits floating around to try and learn what's going on... and many times I end up like this >>> :shock: :scratch: [smilie=a_hrm.gif]
What also I don't understand is that (at least) jfets are not very constant, checking VGSoff and saturation for same part numbers gives values that are all over the places, so how can any one design a firm circuit if every other jfet will behave in a different way there?

Tubes don't sound the same with every B+ rail and in a specific rail voltage they REALLY don't sound the same with every load (which effect how much current goes thru them).
I don't even remember reading here remarks on sound of SS parts with regard to current/voltage thru them... other then headroom related.

I don't think I'll ever "understand" SS :?
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Re: Xotic EP-Booster

Postby MullisMan » 01 May 2010, 17:39

I made a custom PCB for this boost and wired everything up, the only problem I had is that the PCB wouldn't fit in my enclosure, so I used a dremel tool to file down the edges. Was this a stupid move? I mounted everything inside but when I engage the pedal it works for about 15 seconds, then the sound starts to just fade and finally farts out. It's almost as if it's shorting, as sometimes when I touch the PCB to the enclosure it will work, other times it won't. Extremely confusing for me. I even worried that I had heated the two transistors up too much and that was causing the sound to die, but I'm pretty confident that's not the case. Any ideas on why this is happening or has anybody else had the same problem?

Here is a gut shot and a picture of the PCB that I had to file down:
Image
Image
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Re: Xotic EP-Booster

Postby Steven_M » 01 May 2010, 20:06

Hold it up to the light and see if you cut any traces.

Do you know if your layout works?
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Re: Xotic EP-Booster

Postby MullisMan » 01 May 2010, 20:19

I'm using the layout from this thread, the one with the PDF titled EPA Booster. I believe some people have built and verified it. I didn't actually cut into any traces when I filed it down, however I can see some copper colored material along the edges that I filed, maybe some copper from the layers and this is interfering?
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Re: Xotic EP-Booster

Postby Steven_M » 01 May 2010, 20:25

MullisMan wrote:I'm using the layout from this thread, the one with the PDF titled EPA Booster. I believe some people have built and verified it. I didn't actually cut into any traces when I filed it down, however I can see some copper colored material along the edges that I filed, maybe some copper from the layers and this is interfering?


Yeah the copper on the edge of the board showing under soldermask, if that touches the case it would cause problems. Unless it's the ground trace. Perhaps you could post voltages and someone might be able to help a little better.
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Re: Xotic EP-Booster

Postby MullisMan » 01 May 2010, 22:52

Sure thing.

I checked the voltages, and i'm getting 9 volts up until the 2N5088 transistor. I'm getting in the millivolt to nothing at all there. Like I said before, with the sound coming through at first and then slowly fading out the two transistors were the first thing I thought of. I'm fairly proficient at soldering though and I've done other builds with J201's just fine. Are the 2N5088's known to be very sensitive to heat? I checked each pin on the 2N5088 and i'm getting that same millivolt reading which keeps varying. I'll post a picture of the Eagle layout I did. I just tried to make it a little smaller with the resistor placement. Q2 is the 2N5088 transistor in the layout.

Image

I checked the datasheet for the 2N5088 and the orientation I used in the layout is correct. I guess I could take the 2N5088 out and flip it around just for kicks.
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