Need to build a buffer like Boss, not like a Boss.

[alphadog808]

hey guys,
  so I'm finding out that the pinnacle build I'm working on will only be silent(no squeal) every/all the  time IF I have a Boss pedal in front of it. Strangely, it works even when the boss pedal is unpowered.  Anyways, I'm at the point that I think the only solution for me is to build a small buffer that would do the same thing as the Boss pedal would do and try to fit it into the pedal.  Would this layout do the trick?



If you think there's a better one that is small, please let me know, I'd rather just have to order and build one buffer than to just keep building buffers till I find one that works.   

Thanks so much!

[chptunes]

http://www.muzique.com/lab/buffers.htm

On a tiny piece of perfboard, you could build the basic 5 component Buffer that Jack Orman outlines here.  You could even omit the 0.1µf Cap that he drew on the input.

[GibsonGM]

http://www.muzique.com/lab/buffers.htm

(CHP beat me to it!)

[Gus]

What is a pinnacle?  You might not need a buffer.
Can you provide a link to a schematic?

Search for buffer at this forum there are a number of threads

Define better
What is the input resistance you want?
What is the buffer driving?  This is where the schematic is helpful. You might not need a buffer if the pinnacle does not have one .

I found this, is this it?
http://revolutiondeux.blogspot.com/2012/02/wampler-pinnacle-distortion-limited.html

It does not look like it needs an input buffer it has a jfet input. 
I would guess you have a layout issue or wiring issue
Is it in an metal enclosure?

[musiclikscreams]

If size is an issue it looks like that layout could be sized down. After a cursory glance I think I saw 3 traces that could be omitted

[Ice-9]

Correct me if I'm wrong , but any Boss pedal would need power to pass a signal through it no matter what is before or after it. The bypass is done using a flip flop (discrete bi-stable) and fets, so if no power no sound.

[kingswayguitar]

that gearmanndude/youtube audio sample sounds nice
I prefer the one in the narrower box
2:41 vibrato

[alphadog808]

Sorry if I wasn't clear...I mean the boss pedal in front of the pinnacle stops squealing whether there is power to the boss.  Of course, when the boss has no power, no sound.    When there is power, there is no squealing as well.  I can play through it, no problem.

Gus, the pinnacle is a BSIAB made by Wampler.  Normally, there is no buffer for this pedal.  But due to my wiring, layout, etc, I just cannot stop the whining.  This is in boost mode and with the knobs up very high, full essentially.  I've tried numerous things, but only the Boss in the chain is the only consistent solution I've found.  It is enclosed in a metal casing.

Here is the vero I'm using.

I believe it's based off of this

[R.G.]

You have a problem with a very high input impedance and possibly wiring issues.

Many pedals with a very high input impedance will oscillate when their input is open. The input is so high an input that the very small stray capacitances from everywhere to everywhere else can funnel enough of the output back to the input to make it oscillate.

The reason that putting a Boss pedal in front of it makes this stop is the the output impedance of the Boss Pedal is low enough that it "shorts out" the feedback - actually, the low output impedance attenuates the feedback until it's too small to cause oscillation.

Think of it this way: your pedal oscillates with nothing in front of it. If you put a shorting wire from your pedal's input to ground, it will stop oscillating. Somewhere between a shorting wire and several inches of air there is a resistance that just barely stops the oscillation. Your Boss Pedal output just happens to be lower than that.

[alphadog808]

RG,  you are right.  If I put a very low resistance(4x510k resistors in parallel) from input to ground, it stops the whine in boost mode.  BUT, it really eats the treble frequencies, which I expected.  But I wanted to see how low I could go.

As for wiring, I've done so many things and nothing has truly cured it.  I'll try to take some pics so you can see.  It's not as nice as it was before as I've tweaked this SO much, but it will give you an idea.  I'm at the point where the buffer is the ONLY thing I can do to "fix" this.  Yes, it doesn't fix the true issue, but I can't seem to find it.  I've spent..hmm...maybe 20 hours on this?  It's a learning experience for sure, it's just getting discouraging at this point.

I'll have some pics up in a few.

[alphadog808]

Here it is...

In a nutshell, and in most cases
  Red is 9v
  Black is ground
  Purple is ground as well, just for offboard grounds.  One purple goes to ground rail to feed the other grounds
    The stray purple was for another ground but it works without it due to the enclosure; I haven't taken it off yet.  I've tried testing with it connected as well
  White coming off the shields is bunched together going to a ground on the input sleeve lug
  Yellow to vintage/mod switch
  Orange to vol3
  Blue to contour1
  onboard whites to Tone1,2,and 3
  Green is to gain 2 and 3 and one green to boost
  Brown wire to boost...note I've tried shielded for that long run, no dice.
  I've tried taking out the trimmers and putting in the appropriate resistors, no dice.

I just noticed that I must have taken off a ground wire to explictly feed one of the pots ground.  I had it before.
There back of the board looks like an area between the 3rd and 4th rail that looks shorted.  It's not.  I just double checked it now.
I cleaned the drilled hole on rail 9..the pic makes it look like there could have been a short.

I resolderd all points on the board and shot contact cleaner on the board last night.
 
Let me know if you have questions.

[Thecomedian]

http://www.muzique.com/lab/buffers.htm

On a tiny piece of perfboard, you could build the basic 5 component Buffer that Jack Orman outlines here.  You could even omit the 0.1µf Cap that he drew on the input.

unless you use the Reference voltage from the first diagram to augment the circuit.

[alphadog808]

Holy crap, I think I figured it out!  I've been focusing so much on correct voltages on the J201s, wirin,  etc that I neglected to let my ears do the work.  I figured out that I could tune Q5 and Q6 to stop squealing.  And as I turned the trimmer the tone changed for the better/worse.  It seems that Q6 is tied to volume.  Once I brought it down to a non squealing level, I could then tweak Q5 to taste.  It is TOTALLY quiet on all settings!    When I checked the voltages of Q5 and Q6, here's what I got..

Mine:
Q5 - 1.36
Q6 - 8.86

Wampler:
Q5 - 3.59
Q6 - 3.86

So, I guess the fact that the jfets didn't match as well as Wampler's means I had to tweak by ear rather than by their spec.  I think everything is good!!  

Thanks so much for the help guys, I hope this can help someone else in the future.

[tommycataus]

Hey dude, so glad you managed to get it sorted, truly, because it is also a pain in my ass and I feel your anguish! Can I just get some clarity - did you tweak the two trimpots by ear, those that are biasing your transistors?

Only reason being that I'm a total n00b too and this same problem has caused me weeks of pain. I totally abandoned my MXR distortion II build which has been sitting on my desk for a couple of months due to squealing issues (http://www.diystompboxes.com/smfforum/index.php?topic=101377.msg933935#msg933935).

I've recently embarked on the Xotic BB preamp which behaves pretty much like your Pinnacle, I tried putting an input resistor in series which works but it saps tone big time. The guitar I was testing this out on actually has an optional buffer circuit I fitted off-the-shelf a few years ago and activating it eliminates the problem totally, so I came to the same conclusion that you have hence finding your post here.

I'm wondering whether I need to replace the resistors that are biasing my trannys with trimpots so I can set them manually like you. I tried building my own buffer for the circuit and chose this one (http://i52.tinypic.com/20t4g11.jpg) as it has a small footprint but it seems to make no difference...

[alphadog808]

TommyC,
   So what I ended up doing was making that buffer and adding it to the inside of my case.  The buffer gave me alot more leeway on the trimpots.

After that, I tweaked by ear.  It seems that there are certain sweet spots, but it can be subtle at times and it seems to gradually change as I turned the pot.  From what I remember, Q6 felt like it was controlling volume and Q5 felt like it made the bottom looser or tighter.  I basically just trimmed by ear; if I went by the actual voltages, I think I'd still get squealing with the buffer...and IIRC, it was too much gain anyways.

[tommycataus]

Thanks alphadog, you're a gent

[alphadog808]

Guys, I have an update, and was hoping I could get more insight from you gurus!  I just can't stop tweaking this pedal until I get it working exactly right..grrr.

I have the buffer connected in the enclosure and the pedal still squeals.  If I put a boss pedal in line(buffer is still connected) the pedal gets quiet again.  Is there anything in the buffer above that might help increase the buffer so I don't need to lug my boss pedal along?  For kicks, I had some caps around, so I tried increasing both cap values, didn't make a difference. Maybe it wasn't enough?  Or maybe I need to build an actual boss buffer?  I haven't seen a layout for that tho.  Any suggestions on a more powerful buffer?  

Also...I ended up putting trim pots for the 10K on Q1 and Q3 and noticed that the pedal sounds better and the transistor voltage is in SPEC when the trim pot is basically 0!  When it's 0, it seems to negate the boost(which I think makes sense as the boost grounds the boost wires).  Not quite sure why that's happening, I kinda wonder if maybe I have a wrong component upstream in the chain that is making me have to have 0 resistance to bias the transistor correctly.  

Oh, one more thing, not sure if it will help...but I notice that if I turn the guitar's volume knob down a little, the squeal goes away.  Not sure why that is...

I now understand why people despise this pedal because of the transistors...but it sounds really good otherwise...

[chptunes]

I heard you say 'more powerful buffer'..

Link:  http://www.muzique.com/lab/superbuff.htm

-Corey

[alphadog808]

I heard you say 'more powerful buffer'..

Link:  http://www.muzique.com/lab/superbuff.htm

Thanks Corey.  I think I may have been too rash in my other post.  I guess before I start just trying different buffers, I should focus my approach. 

I'm no electrical guy, but here is my current thinking. 
1) whine goes away when turning down the guitar pot a little.  More impedance added to the circuit line, I believe.
2) The buffer's impedance is set by R1, which is 10M. 
3) If I increase the resistance of R1, this might fix the problem?

Another thing I read was that some pedals have buffers in the beginning, end, or both sides of their circuits.  Maybe I'll have a different result if I put the buffer at the end?

Or maybe just give up and buy a pinnacle!  haha!