Boneyard grounding issue?

[CK1]

It seems the highest value I can use for R1 is about 14k before it starts squealing again.  But I can tell that I'm still losing some highs, otherwise this would have solved it outright.  Is there somewhere else in the circuit where I could make up some of the highs?

[shawnee]

If you want to get the gain down some and still keep the same tone you can raise R5 to 100 ohms and change C5 to a 1uF cap. You can go even further and try 220 ohms with a 470nF cap. I would put R1 and R2 back to stock first. I also think shielded wire on the input and output is a must with single coils.

[CK1]

I should say that I've tried this with both single coils and humbuckers, and it's actually worse with humbuckers due to the increase in input level (as far as I can tell).  If I'm desperate, I may try switching out R5 and C5, so thanks for the reminder about that.

[shawnee]

Do you have a Klon type pedal handy? Run it in front and the buffer will help tame the noise quite a bit.

[CK1]

No Klon, but I do have some buffered pedals, so I can try that tomorrow.  That may help some of the inherent noise of this type of high-gain pedal, but I don't expect it to do much to the other squealing which seems to be related to input impedance. 

[shawnee]

I would also use the lowest value gain pots that you can (and still get the gain that you want). I like a pretty low amount of grit on the crunch side and got good results from a 25k. The larger the pot the more gain and bass you will pass and it seems to sound less and less like an amp to me. Anything you do to reduce gain will help with squeal. I have been working with this circuit for months now and will post some findings, mods, and personal preferences soon.

[CK1]

OK, now this is really interesting.

I still have R1 removed, and nothing in it's place at the moment.  So, I decided to try shawnee's suggestion of using a buffered circuit in front of the pedal (I have a Keeley-modded DS-1 that fits the bill) and the squeal is gone with no apparent loss of highs!  One thing that surprised me is that the distortion level wasn't as high as I expected it to be (with everything all the way up, it was still fairly open-sounding).  Going to probably replace R1 with a 1M as per the doc, and then see if it still feels the same.  I might actually try to increase the gain with some combination of R5, C5, and the pot itself if I feel like I need more grit.

So, even though I said this a number of times already, just want to reiterate that I have used both single coils and humbuckers to try this, and found that an unbuffered signal will squeal when in medium to high gain settings regardless of my guitar (unless I use active pickups).  My pots, clipping diodes, etc., are all the values listed on the Boneyard pdf. 

[madbean]

Yeah, the low impedance output of the buffer is essentially taking the place of your jimmy on the pull-down resistor. You don't have a loss of highs because the buffer retains them. When you were using a low value pulldown instead, you kill input volume and lose highs.

So, maybe the key to making this work for most gear set-ups is having an optional buffer in front.

My test rig for this project was an 88 Strat and my trusty VOX AC4. I picked the pot values listed in the project doc because those are what gave me the gain without oscillation. But, obviously it's not a one size fits all solution.

[CK1]

Appreciate the explanation of why this is working, MB.  I'm enough of a n00b that even if I think I know what's wrong with something, I often don't know how to fix it.  

No justification necessary about the test rig, though.  You can't possibly try all the theoretical combinations ahead of time.  Plus, we've all got different setups, so I'm just glad that I can ask a question and get some decent answers from the more experienced members here.

Now the question is, what would be a good option for a stand-alone buffer for the beginning of my signal chain?  I know there were some options floating around here on the forum (Klon buffer comes to mind), but does anyone have a recommendation/link?  Thanks in advance.

[shawnee]

I am using a Klon clone in front of my boneyard with great results (still openned up with nothing shielded and wires going everywhere). Maybe this would work for you:
http://www.madbeanpedals.com/forum/index.php?topic=2304.0

[CK1]

I am using a Klon clone in front of my boneyard with great results (still openned up with nothing shielded and wires going everywhere). Maybe this would work for you:
http://www.madbeanpedals.com/forum/index.php?topic=2304.0

That's the one I remembered seeing but couldn't find earlier today.  Thanks for the link!

I've been playing this thing on and off throughout the day, and I just can't get over how open and big it is.  Great, great pedal, and surprisingly amp-like (that term is overused, but I think it fits here).

[shawnee]

I agree, this pedal is THE best Marshall in a box to date. I have been working on mods like adding treble mid and bass for a while now. It sounds even better and more open at 24v. If you have a TC1044 for your charge pump and not the MAX1044, you can just put 12v in and it will work fine. The MAX chip can't take it. I am also trying to be able to put in the normal 9v and get 24v internally. It can be done with two TC1044's easily but I trying some other layouts that I have seen. This pedal is worth the effort.

[Myramyd]

I've been having the same issue however, it just started happening out of the blue. I may have changed pedal order without realizing it but, it is after a Boss PS-5 in the chain. I'll have to try different buffers to see if it goes away. Mine also has a slight "slapback" delay after higher gain notes, especially at higher pitches. That may just be short oscillation.

My question is: Does the original CM version have an input buffer? I'm wondering if that's what the difference is. I know most DIY versions of pedals take those out (usually a good thing).

Other question: With a good buffer in front, would it be theoretically possible to use bigger pots to get more gain? I like the openness of the pedal but need just a hair more gain on each channel (using with a clean Fender DRRI).

I am going to try switching out the MAXX for a TC1044 and slipping in the 150pF cap as well, just to see. I will probably redo most or all of my offboard wiring too, since it's not the greatest.

I had already ordered the pots and was ready to take it apart but, it started doing this last week.

J