# Boogie Monster squealing



## Billyhank (Mar 30, 2021)

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?


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## Billyhank (Mar 30, 2021)




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## Betty Wont (Mar 30, 2021)

Did you bias the fets? To what voltage? You might want to lower the bias until the squeal goes away. It might only take lowering the first one a bit.


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## Billyhank (Mar 30, 2021)

I did. I biased to 4.5v. I tried the pedal before biasing to make sure it worked, but then I biased. The squeal wasn’t as bad after biasing but it was still there. 
Before biasing it was squealing if I turned the gain up past 9 o’clock. After I had to turn it up to about noon before it squealed.
I can try lowering them though. Appreciate it!!


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## temol (Mar 31, 2021)

You can also try to replace wiring - use shielded wire.


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## Mir9 (Mar 31, 2021)

I had the same problem on my build.
I read about raising the 3.9k  (R11) to 39k from a few places.  I put a 50k trim and adjusted till the noise went away and thankfully it didn't change the tone.  It's just as heavy now, but without the squeal.

I have a real Dual Recto and it sounds pretty close when connected to the power amp.


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## Billyhank (Mar 31, 2021)

Which trimmer did you change? All or just the one over the 3k9?


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## Mir9 (Mar 31, 2021)

Billyhank said:


> Which trimmer did you change? All or just the one over the 3k9?


I replaced the 3k9 with a 50k trimmer as I read of others modding it to 39k.   I didn't replace any of the existing trimmers.


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## temol (Mar 31, 2021)

I'm afraid that with Q3 source resistor changed from 3k9 to 39k you won't be able to bias Q3 @ 4.5V. It's going to be closer to 7V, even with a trimmer set to 100k. So.. this lowers Q3 gain, less noise, no squeal.. but that's not a proper solution in my opinion. Similar effect would be just to set Q3 drain voltage to 7V without changing R11 value (not exactly the same but close).


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## Elijah-Baley (Apr 1, 2021)

I built the Dr. Boogie on stripboard, so it's another story, but during the test of the circuit out of the box it squeals awfully. I changed the 3.9k resistor with a 39k with the a 39k (with a 500k trimpot I had instead the stock 100k to get the 4.5v). This solved just at low gain setting the issue.
I used shielded wires in the input, the output and even between the treble pot and the Volume pot (of course with the stripboard the pots have wires). Nothing. The only solution was to use a buffer in front.
Until I tried to make cut track on the board in the input and output stripe to make it shorter, because for a certain length those were close. This definitely solved the problem, with gain and all the eq pots at max I got no squeal, though I still have shielded wires, that probably I'll try even to replace with normal wires, if I can. Else I'll use them again while I'll box it up.
So I guess to shield the input and output wires and take away from each other is very important in circuit like this.


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## music6000 (Apr 1, 2021)

Billyhank said:


> I did. I biased to 4.5v. I tried the pedal before biasing to make sure it worked, but then I biased. The squeal wasn’t as bad after biasing but it was still there.
> Before biasing it was squealing if I turned the gain up past 9 o’clock. After I had to turn it up to about noon before it squealed.
> I can try lowering them though. Appreciate it!!


Did you check to see if they are 4.5v after you got to the last adjusted transistor?
Did you max the Gain pot & check the Bias @ 4.5v on each transistor?


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## music6000 (Apr 1, 2021)

After you have the Bias correct as above:
You can also get a 50K Potentiometer and attach 2 wires to Legs 1 & 2, remove R11 (3K9) & temporary solder the wires to the 2 pads & slowly adjust to where your not getting oscillation with Gain pot at Max.
Dont knock the Pot, Remove wires & measure Resistance between the 2 wires & replace with a resistor to the  same value!


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## Chuck D. Bones (Apr 1, 2021)

I suspect that there is stray coupling thru the power supply rail.  This circuit is supposed to emulate a tube preamp.  Like the tube preamp it's emulating, this circuit has poor power supply rejection.  Noise on the power supply rail couples into each stage and each stage couples signal and noise onto the power supply rail.  C100-C102 are supposed to keep Vcc & Vdd clean, but no capacitor is perfect.  I'd try increasing R102 to 1K in order to get more isolation between Vcc & Vdd.  Usually, the input stage is at the end of the power supply filter chain. This circuit has the input stages at the beginning of the filter chain.  C11 makes things worse by providing a high-freq path between Q3's drain and Vdd.  I don't know why the designer did that, connecting C11 to ground instead of Vdd would eliminate that coupling path without changing the overall freq response.


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## temol (Apr 2, 2021)

There's many possible causes here. It's a hi-gain circuit, packed tightly into 125B enclosure. Bare IN/OUT wires (blue wire from the input jack goes very close to gain and bass potentiometers). IN/OUT wires too long. 
I've build 4 or 5 Boogies. All of them in 1590bb enclsoures, with shielded wires. Zero problems, no oscillations.


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## Elijah-Baley (Apr 2, 2021)

Chuck D. Bones said:


> I suspect that there is stray coupling thru the power supply rail. [...]


If it was that, it's enough to try it with a battery, I think. If with the battery it's ok it's a power supply issue, and to solve it the circuit need a better power supply filter, or a different PSU.
When I had this problem with my Dr. Boogie stripboard battery or PSU was the same.


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## Chuck D. Bones (Apr 2, 2021)

A battery will be a cleaner source, but it won't fix a coupling problem on the power rail, at least not in this circuit.  I'm not saying power supply coupling IS the problem, I'm just turning over rocks. Until we know what's causing the problem, we have to consider all possible causes.


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## fig (Apr 2, 2021)

Not likely related, but just FYI @Billyhank 
That output tab is awfully close!


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## fig (Apr 3, 2021)

Gotta bump this.

When I read this, I built the one I had [using my last @PedalPCB 3PDT board..heh].

@Billyhank, hoping you've made some headway?



Billyhank said:


> I’ve got a squeal when I turn the gain up. It starts before halfway and just gets worse if I go up.



The only time I hear squealing is with the out jack disconnected, or if I dime a trimmer (specifically t1). There is a good deal of noise however using the hookup wire (high-gain circuit), so I concur with the others regarding some shielding to reduce it.

@temol - will you offer a source for the shielded wire you used? I have some pushback that would work fine, but I built this one with hookup wire to see if I had the same issue(s).

I didn't read @Chuck D. Bones suggestion until after populating, but I'm willing to switch that resistor. As for C11, there is a nearby ground pad.  You want I should re-route a leg to it? 

I do have a question regarding the trimmers. It appears Q4 & Q5 share T4. Q4 is connected via the drain, and Q5 connected via the source. That means adjusting the trimmer increases resistance to one and reduces it to the other, correct? This is the behavior I saw when adjusting. This does limit the bias to a single voltage. On my build, I set these first, and matched the others to that. I also tried several variations using the ear, voltmeter, and a magic 8-ball.

I'll swap the wire as well, and offer any groovy findings.


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## music6000 (Apr 3, 2021)

fig said:


> Gotta bump this.
> 
> When I read this, I built the one I had [using my last @PedalPCB 3PDT board..heh].
> 
> ...


Chuck is going to test on his breadboard to confirm his mods will solve this issue!
if you are willing to try it, 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.


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## temol (Apr 3, 2021)

fig said:


> will you offer a source for the shielded wire you used? I have some pushback that would work fine, but I built this one with hookup wire to see if I had the same issue(s).


I can't recommend any particular brand. I just use whatever wire I have. Sometimes I buy it in local store, sometimes I just take old RCA cables and split them.  Thin microphone cable is also ok.
You can take anything between 2-3mm in diameter, with good, dense braid, not too stiff.

ps. RG174. It's a 50 ohm coaxial cable. Good quality wire  but bit stiff though.. RG178 is also ok.


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## Billyhank (Mar 30, 2021)

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?


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## fig (Apr 3, 2021)

music6000 said:


> 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.


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## fig (Apr 3, 2021)

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.


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## Chuck D. Bones (Apr 3, 2021)

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.


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## fig (Apr 3, 2021)

Chuck D. Bones said:


> 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!


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## Chuck D. Bones (Apr 3, 2021)

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.


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## fig (Apr 3, 2021)

@ 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.


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## Chuck D. Bones (Apr 3, 2021)

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.


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## fig (Apr 3, 2021)

Chuck D. Bones said:


> 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.


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## music6000 (Apr 3, 2021)

fig said:


> 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.


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## fig (Apr 4, 2021)

music6000 said:


> 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?


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## Chuck D. Bones (Apr 4, 2021)

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.

All JFETs are PF5102s.
R4, R6 & R14 are 3.3K to get the drain current back to about where it would be with J201s.
Trimmer are all 47K resistors, that gets the bias where is should be with 24VDC power.
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.
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.


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## fig (Apr 4, 2021)

Chuck D. Bones said:


> 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 .


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## Chuck D. Bones (Apr 4, 2021)

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


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## Chuck D. Bones (Apr 4, 2021)

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.


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## Betty Wont (Apr 4, 2021)

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.


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## music6000 (Apr 4, 2021)

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!!


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## fig (Apr 4, 2021)

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

@music6000 ...right?!?


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## music6000 (Apr 4, 2021)

fig said:


> 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!


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## Chuck D. Bones (Apr 4, 2021)

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.


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## music6000 (Apr 4, 2021)

music6000 said:


> 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 !


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## Billyhank (Mar 30, 2021)

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?


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## Chuck D. Bones (Apr 4, 2021)

When it comes to terminating shielded wire, there are as many exceptions as there are rules.  One end is probably good enough and the jack end is the easiest.


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## fig (Apr 4, 2021)

Yep, soldered to jack. Mark it Donnie.


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## Elijah-Baley (Apr 5, 2021)

I like the tone of my Dr. Boogie, I'm using a 9v PSU because I have just it. The only thing I don't like too much is the dynamic lacking, even if could be the nature of the effect. I have really little difference in distortion hitting the string soft or hard, and just setting very low the guitar volume pot I can decrease a bit the distortion.

I'm not sure I got what happen if we increase the voltage. If I use a 18v (or more) charge pump (re-setting the trimmer, of course), I understand I'll have more volume. But what about the amout of distortion? I think I'll get a bit less gain, but even more dynamic?


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## Chuck D. Bones (Apr 5, 2021)

I initially thought increasing the power supply voltage would increase the headroom and dynamic range.  My experiments and analysis indicated that raising the voltage increases the gain more than it increases the headroom.  As a consequence, there is the same or less dynamic range because the higher gain keeps the last 2 stages saturated most of the time.  If you want more gain, increase the voltage.  I thought there was more than enough gain at 9V and it sounded better.  YMMV.


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## music6000 (Apr 5, 2021)

fig said:


> Yep, soldered to jack. Mark it Donnie.


So, what is your final assesment of the pedal with the shielded wire now in place.


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## Elijah-Baley (Apr 6, 2021)

Chuck D. Bones said:


> I initially thought increasing the power supply voltage would increase the headroom and dynamic range.  My experiments and analysis indicated that raising the voltage increases the gain more than it increases the headroom.  As a consequence, there is the same or less dynamic range because the higher gain keeps the last 2 stages saturated most of the time.  If you want more gain, increase the voltage.  I thought there was more than enough gain at 9V and it sounded better.  YMMV.



I thought the same thing you thought. But, honestly, if you think that the first thing you can notice when the voltage is higher (at least it was for me) is that it became louder, it's easy imagine that all the stage push more.
Another consideration is, if at higher voltage the stage push more, maybe we can to use the original 39k (in the dual rectifier schematic) instead the 3.9k. I know, but I could wrong, it was changed because a voltage question. That third stage maybe is used to push not so much before the last two.
If you still have the circuit on the breadboard you could try to supply it at 18v (or more) and change the 3.9k with a 39k or so to see what happens.

Yes, I think it has enough gain, even if it's weird to me say this, I was agree to sacrifice a bit of gain in favor of a major dynamic. But, after that thing you said... I'm not sure I want to add a charge pump, now. Actually I made one test at 18v, but the PSU I have is too noise (waste of money). Noise aside, I thought I had less gain but maybe I was wrong.

If the last two stages at higher voltage saturate more, do you think we could add a resistor to keep those less gainy?

I hears someone tell that this kind of jfet circuits to sounds good have to work at higher voltage. This guy in some forum I don't remember said that its Dr. Boogie works at 40v.


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## Chuck D. Bones (Apr 6, 2021)

I have removed the Boogie Monster from my breadboard.  I had tried increasing R11 to 6.8K, 10K and 39K.  Not much sonic difference when the other three stages are driven to saturation.  

If you want the same gain you had at 9V, just put the trimmers back to the same resistance you had at 9V.  Once you've done that, try different power supply voltages and see if you like the tone.

I don't know if "this guy in some forum" explained how the circuit works, so I will.  JFETs act like current sources.  In this circuit the gate bias voltage is 0V for every JFET except Q5*.  The DC drain current of Q1-Q4 does not depend on power supply voltage.  It only depends on Vp, Idss and the source resistor.  Those three quantites are constant, therefore the DC drain current is constant.  Transconductance is a function of drain current.  Since drain current doesn't change with power supply voltage, transconductance doesn't change either.  The voltage gain of each stage is equal to the transconductance times the load impedance.  The trimmers have the strongest influence on load impedance.  If we change the power supply voltage but don't change the trimmers, then the gain doesn't change.  If we increase the trimmers when we raise the power supply voltage, then the gain goes up.

*Q5 is a source follower.  Its voltage gain is always unity.  Since Q5's gate voltage is the same as Q4's drain voltage, changing the power supply voltage or Q4's trimmer will change Q5's drain current.  Still, Q5's gain will always be unity.

FYI, J201s are rated for 40V max, therefore I would not recommend running them higher than 40V.  I do not know how the filter caps are rated, so that's a concern.


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## temol (Apr 6, 2021)

Chuck D. Bones said:


> If you want the same gain you had at 9V, just put the trimmers back to the same resistance you had at 9V.  Once you've done that, try different power supply voltages and see if you like the tone.



The gain would not be exactly the same. 
See Boogie frequency response graphs below. 
Red - 9V, transistors biased around 4.5V
Green - 24v, no bias adjustment
Blue - 24V,  transistors biased around 12V.






See the output signal envelopes also


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## fig (Apr 6, 2021)

music6000 said:


> So, what is your final assesment of the pedal with the shielded wire now in place.


It's a high-gain pedal with a LOT of 201s. Unwanted noise is a byproduct of this design.

Of all the changes or adjustments made, these two seemed to yield the most "bang for the buck";

1.* Shielded cable* - it mitigates EM amplification, which is needed with a circuit of this nature. I use 9v power supply cable. The insulator is delicate so you have to pay attention when soldering or it will melt well back into the length and you'll be dealing with a ground-short.

2.* Biasing* - Two schools here. a) in accordance with the design criteria and given formulae, or b) turn those cute little thingys until it sounds good. I set mine to taste by setting all pots fully CW, trimmers at max, and backing them down one at a time. I started with T4 and worked back. There is a third biasing option; but it's difficult to source the correct chicken bones, and improper use could be disastrous!

The TMB is pretty weak in my opinion with little more nuance than a tone knob. For me, this was a bigger factor than the noise. If you can't effectively shape the "preamped" signal, what's the point?

I initially jumped in to offer another build to experiment, in light of @Billyhank 's squeal. I am confident that it can be trimmed out.

As is typically the case; there are hidden gems of knowledge in this thread that I appreciate greatly. Thanks again to all!

EDIT: Almost forgot...someone on another thread suggested that naming pedals is a good idea. I named this one "Booger".


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