Too Much Awesome (Boneyard with JFET input buffer)

[mgwhit]

Here's my MadBean Boneyard in a remarkably flaw-free Mammoth Vintage Orangle Sparkle Translucent 1590BB.  The Bypass footswitch operates a red LED on the left, the Gain footswitch switches between Crunch (Green LED) and Crush (Blue LED) modes on the right.  The toggle switch is for symmetric or asymmetric clipping, and is just a DPDT On/On with either a jumper or another red LED for D4.  I did a half-gain mod (R5=100R, C5=1u), as I thought full gain was just too much.  I also included the low-pass filter on the output, as this is a very bright circuit.



I gotta admit, I love how this came out.  I'm happy with the look, and I'm thrilled with the sound.  Haven't used it in a rehearsal setting yet, but I plan to give it a spin later this week.

I'll post the gut shot and some gruesome details a little later this morning.

[mgwhit]

Now the ugly bits.  As some of you may know, a few weeks back there were several threads about a high pitched whine in the new Boneyard PCB.  I breadboarded the circuit at maximum gain and didn't have any whine.  So I built the board (half-gain, as above) and mounted it in a spare 1590BB that I had laying around -- still no whine.  Finally, my sparkly orange 1590BB arrived, I transferred it to that...and WHINE CITY.

I was  pretty upset and, frankly, embarrassed.  I had made a lot of posts saying that I hadn't had the problem that EVERYBODY was having, and now here it was.  I only had the whine in bridge-pickup-only postion and even then, only with my tone knob at about 100%.  The only thing I can think is that maybe I had the tone rolled off a bit when I was testing it in the other enclosure..  (Like I said, it's a trebly circuit, and I do tend to roll back the tone on my tele when I use it.)  I had tested the breadboarded circuit for a couple of weeks and at maximum gain, so I'm pretty sure the circuit itself is sound, but I may have only tested the finished, but not fully housed board for an hour or so.

Luckily, several other people had done a lot of work on fixing the whine.  Based on reports that a grounded shield between R1/C1 and R4/C4 had diminished the noise, I wondered if the parallel components from the high gain stage feedback loop and the input might be causing the problem.  I actually lifted the input of R1 and moved it to the same input pad as the pull-down resistor (effectively standing it up and making it perpendicular to R4), but that didn't fix it.  So then I bent C1 down away from C4 and over the top of RPD, but that didn't fix it.

I also remembered that some people had reported that placing another effect in front of the Boneyard effectively killed the whine, so I placed my BOSS TU-2 tuner in-line and...BINGO!  Whine gone!  The always-on BOSS buffer effectively killed it.  This was great news because I always have the buffered tuner at the front of my chain, but I still wanted the effect to work okay by itself, so I decided to add a buffer to the circuit input.

I spent several days reading about and breadboarding buffers.  Beavis, Jack Orman, etc.  I originally built a Klon buffer, which I liked just fine, but I eventually settled on a JFET buffer using a 2n5457.  I moved it over to a Radio Shack board, crammed it into the space I was originally going to use for a battery, clipped and reattached some wires et voilà:

[jimmybjj]

Now that's a build report. Great job inside and out! I'll give the boneyard a go with your improvements. If you don't mind can you post a schematic of the buffer you used. Is there any particular reason you choose the JFET? Could you hear a substantial difference in the different buffers?

[mgwhit]

I kinda combined one of Jack Orman's designs with the General Guitar Gadgets JFET buffer (which is probably based on Jack's to begin with).  I changed the input cap (C1) to 220n and the output cap (C2) to 4.7u as I thought the stock GGG values were affecting the lows a little bit.

I went with the JFET version just because I thought it was simpler.  It takes a tiny smidge of gain (and maybe a bit of treble) off the signal, and I thought that was fine in this circuit.  I think the differences in all the buffers I built came down to the following:

• IC's get you closer to unity gain than JFETS or BJT's.
• Make sure you design to get the input and output impedances you want.
• Adjust caps to taste.

I also wondered about noise tolerance, especially since this was going to sit in front of a high gain circuit, but I didn't notice any significant noise from any of the buffers I tried.  I even used a tantalum cap on C2 and didn't hear anything bad, but then again my ears are pretty shot.  The gain loss from the JFET (as compared to the IC) made it difficult to A/B.  It was slight, but definitely noticeable.  And of course once you roll off the gain a bit, it's more noticeable in the treble, so there's a temptation to think that there's less treble in the JFET circuit.  I dunno.  Maybe there is, but it certainly didn't hurt the Boneyard.

I went back and forth between an MPF102 (R4=3k3) and a 2N5457 (R4=10K).  In the end I thought the 2N5457 was a bit more transparent, but honestly that might have just been a gain difference.

I also did a crap job of visualizing how my buffer board was going to sit in my enclosure.  I would've laid it out a bit differently if I would've gotten that straight in my head first before I started soldering.

The insides of this thing certainly leave something to be desired, but I was just happy I didn't scratch up the outside with all the disassembly and reassembly.

[DutchMF]

Looks fantastic!!! I'll be shure to follow your advice when I finally get to boxing up my Boneyard. And, like you, I have a buffered pedal at the beginning of my FX chain (Korg DT10 tuner), so it'll probably work out fine. Thanks so much for all your troubles in making this work!!!

Paul

[bigrigg]

Great job figuring out the buffer and whine dealio.  Awesome name for the pedal and your advice too.
Thanks

[gtr2]

Sweet!  Great name.  Love the color as well.

Josh

[mgwhit]

Thanks, everyone.  Here's a direct shot of the front.



Notice how uneven the knobs are.  It's keeping me up nights. 

[midwayfair]

Great build report! Not every day I learn that much from looking at the pretty pictures.

Thanks, too, for the really thorough explanation of the buffer.

[pickdropper]

Yeah, great build report.  I'll keep all of that in mind when I ever get around to boxing up my Boneyard.

That orange sparkle looks fantastic.  I wish I had ordered one of those when I placed a Mammoth order the other day.

The built itself looks good, too.  I like the labeling you do on your pedals.  Simple, but effective.

[pryde]

Awesome job mgwhit. Love the finish and layout. Glad you found a method to deal with the squeel.

Thanks again for all your help with my Boneyard build as well! Long live the Boneyard 

[k.rock!]

Dude this looks great! I love it...I'm curious if the buffer by itself would take care of the whine completely without altering the original circuit.

I'm also curious about the older Boneyard layout...I know a few people were reporting whine with the older as well but I've built 2 (one with the first version and another with the new version) and I had to whine problem like the ones I got with the new...

This is circuit is such a mystery that I love it haha I'm intrigued by it...we'll get it down people!

-K

[mgwhit]

Thanks, Kaleb.  Your original demo was what turned me on to this circuit in the first place!

All of the buffer circuits I tried killed the whine dead before I even touched the components on the board: BOSS pedal, Klon IC buffer (with several op-amps), and JFET buffers with 2N5457 or MPF102.  An IC buffer like the Klon preserves the most gain and is probably the most transparent.  I wired mine up so that it is only inline when the effect is switched on.  The pedal is still true bypass, although you could choose to wire it either way.

I don't know if the buffers work because they roll off some extreme high end or because the lower impedance renders the input less susceptible to cross-over.  I assume the latter, but I am not an EE, and only barely know what I'm talking about.  I only monkeyed with R1 and C1 after I knew I had a workable buffer solution available.

I should add that the input buffer is not necessarily the solution to fixing this board, but it is certainly a solution.

[Strider0007]

Hi all, I'm new to this forum but I've been following a few threads and this one in particular as I have also built this pedal for myself recently. I used the original a few months ago and I loved it so I waned to make me this one.
Now I love how this pedal sounds but I have also run into the high pitch whine problem. I noticed that moving or touching dome of the wiring killed the whine. So I suspect it might be a layout problem. I let a friend of mine borrow it for two weeks and told him to roll off the treble in his guitar to temporarily cure it. I will work on it as soon as I get it back.
I don't know if you guys noticed that this pedal already has an input buffer according to the schematics. So it might be just a matter of adding a small bypass capacitor(47p or so) at the input or at different stages. I'll try some theories I have and post my findings. Usually high gain circuits as this should have a very short gain loop, so it might be the traces on the PCB as well contributing. If input and output traces are too close, that will cause all the feed back or oscillations.

Well sorry for the extra long first post. I just want to give something back to this great forum where I have learned so many different things.

[mgwhit]

Hi all, I'm new to this forum but I've been following a few threads and this one in particular as I have also built this pedal for myself recently. I used the original a few months ago and I loved it so I waned to make me this one.
Now I love how this pedal sounds but I have also run into the high pitch whine problem. I noticed that moving or touching dome of the wiring killed the whine. So I suspect it might be a layout problem. I let a friend of mine borrow it for two weeks and told him to roll off the treble in his guitar to temporarily cure it. I will work on it as soon as I get it back.

This has received a lot of discussion in another thread (or two).  I'm not sure what you mean by "dome of the wiring", but another builder noticed that running a grounded shield between R4/C4 and R1/C1 killed off a good deal of the whine.  My own attempts to reroute R1 didn't seem to make much of a difference.

I don't know if you guys noticed that this pedal already has an input buffer according to the schematics. So it might be just a matter of adding a small bypass capacitor(47p or so) at the input or at different stages. I'll try some theories I have and post my findings. Usually high gain circuits as this should have a very short gain loop, so it might be the traces on the PCB as well contributing. If input and output traces are too close, that will cause all the feed back or oscillations.

Yeah, the buffer I added is totally redundant to the circuit itself, but I think the on-board input buffer (IC1B) might be where the whine is leaking in in the first place.  I agree with you about a low value cap to ground potentially working -- especially since a little treble roll-off on the guitar seems to fix it -- but at the time I wanted to get a known good solution in place fast.   A well designed low-pass filter would certainly be less intrusive than my solution.  My pedal is temporarily on someone else's board, so I'll leave that as an exercise for someone else.

Well sorry for the extra long first post. I just want to give something back to this great forum where I have learned so many different things.

Always good to have another person working on it.  Welcome to the forum!