SOLVED Another Squealing/Oscillating Boogie Monster

[debrad]

Completed my Boogie Monster build and it is sounding pretty good except I seem to be one of the unfortunate ones with some squeal/oscillation at the top ends of the VOLUME and GAIN controls.

I followed the advice from @Chuck D. Bones, socketing R102 so I could swap the stock 100r with 1k and connecting C11 to ground rather than Vdd but, with my smd J201s biased around 4.8v, the oscillation began with the GAIN fully CW and the VOLUME around Noon.

After replacing the input and output wires with shielded wire, replacing R102 with the 1k, upping R11 to ~13k, I was able to up the VOLUME to about 3:00 before the oscillation kicked in. With this arrangement (i.e. R11 @ 13k), I noticed that I couldn't bias Q3 any lower than ~5.5v...

At this point, I have all the J201s biased to 6v and the circuit is JUST on the verge of oscillation with the VOLUME and GAIN fully CW. I think I can live with this as the pedal sounds pretty good and I can't imagine ever REALLY using this thing with the VOLUME and GAIN fully dimed; however, the OCD part of me can't stop obsessing over what might be preventing me from getting this thing as quiet as others have...especially closer to the 4.5v bias settings. Part of me wonders if I should mount everything inside a 1590BB enclosure so that I can get the jacks away from the potentiometers...

Anyway, here's a shot of the component side of the board...in case any of you can see something obvious:

 

[Fama]

I'm a total beginner, so this might sound stupid, and won't help at all with changing the circuit to not oscillate at lower voltages... but if you want to avoid any oscillation with the pots at full, you could just add a small resistor in series with those? Effectively changing the pots from 0-500k (or whatever) to 10-510k, for example?

More of a cosmetic thing since it would decrease the usable range, just removing the oscillating range completely from the controls. But I figured I'd pitch that idea anyway.

 

[debrad]

I have a sneaking suspicion I am just going to have to be content to run the controls at lower levels...which is probably fine for the amount of volume and gain this circuit has...but I'd sure love to know what causes my build to oscillate and another to be oscillation free. Makes sense when comparing different layouts but, with the exact same board, I'd like to think it should all be pretty consistent (part tolerances considered, of course).

 

[Robert]

...but I'd sure love to know what causes my build to oscillate and another to be oscillation free.

Could be variations in transistor gain.

I've put this one on my list to revise the layout and rearrange some components / space some of the traces out a bit. It might make no difference at all but it's worth a shot.

Two questions:

1) When it's oscillating does the oscillation stop if you turn your guitar volume all the way down?
2) Have you tried a buffer in front of it?

 

[debrad]

The oscillation changes pitch and eventually goes away when I adjust the guitar volume but using a buffer doesn't help (I tried my Boss Blues Driver and my DIY "buffer battle" which is the Klon buffer on one side of the 3PDT and the Cornish buffer on the other side).

 

[Robert]

Got it, that's helpful, thanks!

 

[micmac]

Hi debrad,

Could you upload a short sound sample with all knobs at 100%? I got a Boogie Monster, too, and find it strangely quiet. When I have all knobs at 100% I get what I would call a bit of feedback. But not sure if you're having just the same or if it's completely something else.

 

[angelrulax]

I´ve built one in a Fuzzdog´s PCB and is recommended to use 2n5457 transistors for Q1 and Q2. Mine works fine.

 

[Robert]

I've done some much needed rearranging and trace optimization.

Although I've never experienced oscillation with the older layout, we'll see how it goes.

 

[debrad]

Could you upload a short sound sample with all knobs at 100%?

I tried to shoot this short video but found that I couldn't hold the guitar, dampen the strings, adjust the knobs AND focus the camera so I put down the camera, set the guitar on the floor AWAY from the amp (to avoid regular feedback), and dampened the strings while I adjusted the pedal.

The oscillations come in the dark but I can tell you that the Presence, Bass, Middle and Treble were set to Noon and the Gain was set to full CW. Oscillations began when the Volume got to about 1:00 or 2:00 and changed in pitch as I rolled it past 3:00.

@Robert, I really appreciate you taking another look at the layout. The fact that others have built the previous layout without oscillations leads me to believe that the issue isn't with the PCB; however, if you think this new layout will be even better then that is great. As I said, I can't help but wonder if my build might benefit from being remounted inside a 1590BB enclosure with side jacks instead of top jacks; however, I haven't tried someone else's suggestion which is pulling the input jack and placing it outside the enclosure just to see if that helps.

The other things I haven't tried...but hope to do later...is 1) shielding the short wire wire from the 3PDT to the PCB input and 2) test driving some other JFETs. Is there any chance that my SMD J201s and adapter boards might be contributing to the problem?

The only other thing that is really different on my build is that I didn't have 90 degree potentiometers for all of my controls so I used solder pots with cut-offs from my resistor and capacitor leads. They are short and straight just like the board mounted pots but I'm curious about your thoughts on those as well...

 

[micmac]

Thanks for the video debrad!

I have some spare SMD J201s lying around so I tested with the through-hole J201s that came with the Musikding Boogie Monster kit and the SMD ones.

I think I may have been able to recreate the noise from your video, you be the judge. The attached recordings are all done with hand over strings while turning guitar volume pot between fully counter clockwise and fully clockwise. All Boogie Monster pots are fully clockwise.

rec1: through-hole J201s, Q1-Q4 at 4.5V drain voltage (Q1 Vp 876 mV, Q2 Vp 854 mV, Q3 Vp 814 mV, Q4 Vp 713 mV, Q5 Vp 708mV) (NOISY)

rec2: SMD J201s, Q1-Q4 at 4.5V drain voltage (Vp values: Q1 665, Q2 553, Q3 588, Q4 585, Q5 559) (NOISY)

rec3: SMD J201s (same ones as above, just in different order), Q1-Q4 at 4.5V drain voltage (Vp values: Q1 665, Q2 588, Q3 585, Q4 559, Q5 553) (NOISY)

rec4: SMD J201s (same ones as above, same order as in rec3), drain voltages set as per ROG Fetzer Valve calculator (Q1 5.87V, Q2 5.79V, Q3 5.81 V, Q4 5.79 V) (NOISY)

rec5: SMD J201s (same ones as above, same order as in rec3), drain voltages same as I normally use with my through-hole J201s (Q1 6.37V, Q2 6.37V, Q3 6.34V, Q4 6.27V) (LESS NOISY)

rec6: same through-hole J201s as in rec1, with their respective ROG Fetzer Valve settings (Q1 6.37V, Q2 6.37V, Q3 6.34V, Q4 6.27V) (QUIET)

The Vp values are probably not 100% accurate, I used a cheap 25€ tester. But at least the numbers should give an indication about the differences between the used JFETs.

I didn't deviate from the BOM at all, all parts from Musikding kit. Some pics are here in another thread.

 

[debrad]

Thanks for doing all that testing and sharing your results @micmac ! It's super interesting that you do not some differences between the SMD and through hole J201s and the fact that your "preferred" bias settings are over 6v make me feel a little better about having mine in that range before they start to quiet down a little. I've read a few comments on biasing by ear but I'd love to hear more opinions on what the "Dual Rectifier tone" might gain or lose with the higher bias.

In the meantime, your references to the "ROG Fetzer Valve Calculator" and "Vp" will have me doing a little further research and I'm also going to test out some of the alternative JFETs recommended by other PedalPCB builders and folks who put the circuit together using PCBs from other sources (Bucksears from DIYStompboxes mentions the MPF102, and both FuzzDog and GuitarPCB mention using the 2N5457).

 

[micmac]

No problem debrad, I have the JFETs in sockets so it's not a big deal.

By the way, I just tried the SMD JFETs again with ROG settings. When I put a buffer in front of it the squealing stops immediately. I tried it with my tuner, a TC Polytune 3, which has a buffer built in. Putting a buffer up front sounds like an easy solution

 

[debrad]

As some of you may have seen, I just ran into a similar issue with oscillations with my new Mofeta build so I was back here in the forums looking for advice on troubleshooting again.

While test driving a suggestion from @Robert to move my input jack further from the Master potentiometer, something dawned on me:

My current basement rig has the guitar running to a 2 loop switcher then out to my amp and I have been testing the Mofeta and the Boogie Monster in the first loop. With that arrangement, the input and output jacks of the loop are close together AND the cables that run from those jacks to the pedal jacks are just as close, if not closer.

Soooo...I pulled the Mofeta from the loop, ran my guitar straight to the pedal, and then ran a cable from the output straight to the amp. Guess what?

You guessed it, NO OSCILLATION!

I put the Mofeta input jack back inside the pedal...NO OSCILLATION!

I replaced the Mofeta with the Boogie Monster...NO OSCILLATION!

So, like many previous oscillation problems, it looks like the issue was the proximity of the input and output wires; however, in this case it was the cables OUTSIDE the pedal instead of the wires INSIDE.

I went back to the trim pots for these two pre-amp pedals and found that I could dial them back closer to the recommended values without inducing any squeals or oscillations. For the Mofeta, that was about 4.5v for Q1 and 4.25 for the rest and for the Doctor Boogie, it was about 5v for all trimmers. Not perfect but MUCH better!

Thanks everyone!!!