Boogie Monster squealing

[Billyhank]

Hi everyone!

I just finished the Boogie Monster but I’ve got a squeal when I turn the gain up. It starts before halfway and just gets worse if I go up.
I checked everything and can’t find anything wrong.
Has anyone else had this issue and figured out how to make it stop or does anyone know why it would be doing this?

 

[fig]

C11 can be still connected to top pad & bottom unsoldered & connected to Volume 1 pad which is going to Ground.
Try that First before doing the R102 - 1K resistor.

10-4 . I'll pull that trebles pot to get to the cap. I could bend the legs but that hakko 301 makes it too easy. I'll leave the wiring as is for now.

 

[fig]

The cap mod DID in fact lower the overall noise by a third or so by my estimation (even with the back off). I never doubted Mr Bones.

I decided to re-adjust the trimmers and set all but Q4 to 6.0v. This was done with a strat plugged in and dimed volume, and the box volume and gain also maxed. It seems a very nice balance, and lets the guitar volume and amp do their jobs. It's still a high-gain pedal, so it aint noiseless.but I am impressed. I have some shielded around or pushback wire around so I'll do that as well since I have yet to clean the board and have the lid off.

Are there any other mods you'd like to give a whirl whilst the patient is still sedated? Happy to oblige.

 

[Chuck D. Bones]

Try running it at higher voltage. You can go as high as 24V. You'll need to reset the bias, of course. I have a couple of other ideas, but they need to be fleshed out on the breadboard. Hint: take a look at the Mesa Boogie Dual Rectifier preamp schematic (the actual amp, not a pedal) and you'll see some other mod options.

 

[fig]

Try running it at higher voltage. You can go as high as 24V. You'll need to reset the bias, of course. I have a couple of other ideas, but they need to be fleshed out on the breadboard. Hint: take a look at the Mesa Boogie Dual Rectifier preamp schematic (the actual amp, not a pedal) and you'll see some other mod options.

It seems to carve better at around 18v. I biased to 16v to smooth it out.Circling back to the OP, I found a definite angry pig hiding in Q4 when biasing below 15.5v.

I'll check that schematic. Thanks!

 

[Chuck D. Bones]

Increasing the trimmer resistance increases the gain proportionately. If it wants to "squeal like a piggie" at 15.5V, it's too damned close to the edge at 16V. Q5 has the biggest AC drain current and therefore imparts the largest disturbance onto the power supply rail. It might be helpful to increase R15 which will lower the drain current if you're running at higher power supply voltages.

 

[fig]

@ 9V, I can create the squeal below biasing below 6v, so increasing R15 would help @ any voltage I take it? What value would you suggest?

The squealing can be biased out as is, but at the cost of gain.

 

[Chuck D. Bones]

If the root cause is power supply coupling, then increasing R15 will help at any voltage. If the root cause is something else, then increasing R15 won't help. You can try 22K to see if that does any good. Some pedals (King of the Britains) use 100K there.

 

[fig]

If the root cause is power supply coupling, then increasing R15 will help at any voltage. If the root cause is something else, then increasing R15 won't help. You can try 22K to see if that does any good. Some pedals (King of the Britains) use 100K there.

I'll give it a try later this evening. It's a rockin' pedal, even biased back a bit, but no reason to miss a chance to improve upon a circuit.
Sweet! Just got a shipment of boards. I see a Roboto and a Thumbsucker in the shrinkwrap.

 

[music6000]

I'll give it a try later this evening. It's a rockin' pedal, even biased back a bit, but no reason to miss a chance to improve upon a circuit.
Sweet! Just got a shipment of boards. I see a Roboto and a Thumbsucker in the shrinkwrap.

Cool!, this circuit design has had an issue with Oscillation since it was designed & shielded Input & Output wire seems to solve most of the issue.
Chuck is breadboarding the circuit as we speak for his own take on what mods are needed so Hang Five & play with your latest PCB's that arrived.

 

[fig]

Chuck is breadboarding the circuit as we speak for his own take on what mods are needed so Hang Five & play with your latest PCB's that arrived.

yep. I'd rather hear his analysis than my own *gasp*. Here's why; Mr. Bones has experience, knowledge, and definitely not least...exposure. He knows how it "should" sound. Granted there is consideration for taste, but this example is not about nuance. I thought the circuit was very usable "out of the box", but yeah..it was quieter with each tweak, so woot!

I have more than enough to keep me doused in d-wipes awhile. <---like my pedal lingo?

 

[Chuck D. Bones]

I agree with temol, shielded cable is needed here. My breadboard squeals at around 1KHz when the input is left open-circuit. Mind you, it's a breadboard and is more likely to have stray coupling problems than a PC board. This circuit is very high gain, around 120dB when running at 24V. Even the tiniest bit of stray coupling will set it off. My first breadboard layout was on the edge oscillation. I had to rearrange things to get more separation between the input and the tone controls.

I built my breadboard in accordance with the build docs, except I subbed a few parts because I'm out of J201s at the moment.

1. All JFETs are PF5102s.
2. R4, R6 & R14 are 3.3K to get the drain current back to about where it would be with J201s.
3. Trimmer are all 47K resistors, that gets the bias where is should be with 24VDC power.
4. R11 is 10K. This one is a judgement call. In the Dual Rectifier, the 3rd stage cathode resistor is 39K and the plate resistor is 100K. This stage is deliberately biased cold in the DR. Clipping is very asymmetric which makes both even and odd harmonics. Increasing R11 reduces the gain, but believe me, there is still plenty of gain.
5. C11 returns to ground, not Vdd.

I tried the power supply mod I suggested above. It does not cure the squealing.

The only mods I would suggest at the moment are C11 and R11. Purely optional. Once the shielded cable is installed and all outboard wiring is shortened up, this pedal should work fine.

I use RG174 when I need shielded cable in a pedal. The stuff I bought on Amazon is pretty flexible.

 

[fig]

I agree with temo...

Thanks! I think I'll use this build to apply all of the above, and dedicate it to 24v.

Let us know how you fare @Billyhank .

 

[Chuck D. Bones]

Before you do that...
My build is extremely bright. Sounds much brighter than the demos. I'll investigate and get back to you.

 

[Chuck D. Bones]

Here's what I've found out.
Higher voltage means higher gain because we end up adjusting the trimmers to higher resistance. The difference between 9V and 24V is over 40dB.
I set the power supply to 9V, lowered R4, R8 & R14 to 2.2K (just slightly above the stock 1.8K) and ended up with 10K resistors For TRIM1, TRIM2 & TRIM4. TRIM3 is 22K and R11 is 3.9K. This is what worked for the JFETs I used. Every JFET will be different, that's why there are trimmers.

It's not as bright as before, but still brighter than I like. I increased C11 to 2.2nF to take a little of the edge off. I may end up going higher. I removed C10 to drop the 2nd stage gain by 16dB. I find the GAIN range more useful that way. I increased C14 to 10uF to fatten up the bottom end after most of the distortion stages. The DR amp has switches that take C4, C10 and C14 in and out of the circuit.

I'm still not satisfied with the Tone controls. I end up setting TREBLE and PRESENCE to zero. Next, I'll try moving the TMB stack before Q4 and retuning the PRESENCE control.

Fiddling component values are easy mods for an existing board, but rearranging the tone stack requires major surgery. For most people, the Boogie Monster is just fine as-is. I started this experiment to see what could be done about the squealing. Once I got a handle on that, I started tweaking based on personal preferences. As far as amplifier emulators go, the Boogie Monster is not my cup o' tea without extensive mods.

 

[Betty Wont]

It's finicky for sure. I've built a few different ones over the years and was always underwhelmed. Always used through-hole fets and had to mess with biasing to get a compromise between gain and noise. I've since built a couple of the Pedalpcb version with smd fets and am quite pleased. They biased up easily and are very high gain with low noise. I did not use shielded wire. They chug great even though the Mesa isn't my metal tone. I like it most for how easily and controllably it makes feedback.

 

[music6000]

Now Gibson has taken over, the Mesa's will get all the issues sorted out just like they have with the weight relief in their Guitars that nobody wants!!

 

[fig]

I've still got it gutted so I may fiddle with it some more. I have your notes.

@music6000 ...right?!?

 

[music6000]

I've still got it gutted so I may fiddle with it some more. I have your notes.

@music6000 ...right?!?

As Chuck has listed, Up R11- 3K9 to 10K & use shielded cable on Input & Output leads & call it Quits!
It's up to you where you run the Voltage at, Higher Voltage will yield more Headroom though I doubt this needs it!

 

[Chuck D. Bones]

I think I've had enough fun with The Boogie Monster. I believe there is value in playing with R11, C4, C10 & C14. They won't cure the squeal, but are useful for tailoring the tone. Bumping those caps up to 10uF restores the bass. I'd start with C14 and work backwards.

 

[music6000]

As Chuck has listed, Up R11- 3K9 to 10K & use shielded cable on Input & Output leads & call it Quits!
It's up to you where you run the Voltage at, Higher Voltage will yield more Headroom though I doubt this needs it!

With the shielded wire, normal practice is to attach the shield to Ground on one end only, ie Jack Ground !