SOLVED Muzzle (Classic) and low threshold settings

[m1nl]

Hi everyone, hi first, as this is my first post here!

A few months ago, I built a Muzzle (Classic) pedal from a Musikding kit. I believe the circuit works as intended. I really like it and agree it's one of the best noise gates I've ever used!

What bothers me is whether the pedal behaves correctly when the threshold is set low (below approximately 1/3; high sensitivity setting for range switch). When the input signal is zero (input jack tip connected to the ground), the LED indicator suggests that the pedal is never gating. Given the way the threshold pot works (its setting also affects the dynamics of the noise gate), I cannot say if the gate really works, as the output level difference is subtle. I took a few measurements, and indeed, the red LED indicator starts working when there is at least 0.6V at pin 18 of the IC - this is expected as lower values won't turn on the Q3 transistor. When the threshold knob is set to lower than 1/3, there is less than 0.6V even when the input is grounded, so the LED won't turn at all. The voltage sets at around -100mV when the threshold is further lowered to its minimum.

I don't know whether this works as intended and the LED indicator won't turn on when the threshold is set low by design, or there is something wrong with my circuit. Can somebody please tell me how your build behaves?

I took some other measurements, and the only thing I found strange is output voltage from LT1054 - instead of -8.4V on pin 5 (9V minus voltage drop on D1), I only get around -8V. Because of the voltage drop over Q2, I have around -7.4V as the negative power supply for the circuit. I am unsure if it matters and can affect threshold control.

My build uses THAT4301 retrofit module. A few photos attached:
- red LED indicator on when threshold is set just to the point when voltage equals 0.6V
- red LED indicator off even there is no input signal
- general gut shot of my build

 

[m1nl]

Hi, I spent some time reviewing the circuit today and taking additional measurements.

What I found strange is that I get around -150mV at the output of RMS detection (THAT4301 pin 4) when the input is connected to the ground. The output level varies depending on the signal level and turns slightly positive whenever I touch the input jack tip instead of grounding it. After reviewing the datasheet, I don't understand whether I should expect 0V at the RMS output, when there is no input signal present. Nevertheless, I'd expect the detector to behave this way; negative value could potentially shift down the level which triggers the noise gate and it has to be compensated by the threshold pot being set to certain level to make the circuit work.

I'd appreciate if somebody could share the RMS detector output voltage when the input is grounded as I tend to suspect that's THAT4305 / retrofit module issue...

EDIT: OK, it looks it's normal, I reviewed some other datasheets for THAT RMS detectors and of course output can be negative if input current is below 7.5uA (0db). Still looking for some ideas to help with my troubleshooting...

 

[guitarbruno76]

Hi mate,
I've read you with attention, and it could be interesting to deeply study the Muzzle , that I own, calling it "damned Muzzle" because of the lack of clarity of the schematics, especially how to wire the stereo switches of the side chain, which lastly I definitively fix the issue (I could only use the noise gate with the in/out but no way with the side chain! Because of the necessity to join the sleeves of both stereo switches to the negative pole of the 9 volts, because the enclosure of the stereo swithes is made of plastic, it seems you own the same switches, with the brand Amphenor maybe , looking at your pic).
Lastly another issue is the potentiometer, I replaced it with a B50K , in spite of B25K cause it sucks after a while.
Knowing that the potentiometer works as a dividing bridge, it occurs that when I stack overdrives and distortions with some big gain, it involves the threshold triggers too much soon and stop the sustain.... when I am soft with saturation pedals, it works pretty fine...
I'm looking for a B25K, the 50K was the one I have in my drawers...
Greetings from France.
Bruno

 

[m1nl]

Thank you for your answer!

It actually depends on the power supply you're using - in my case, I have three sections in my power supply, and there are separate ground buses for different pedal chains - one goes directly into amp input, and the others are in the effects loop. In this case, connecting the key input ground to the input signal ground would create a ground loop. Given that the key should be a non-amplified signal from the guitar, it would increase the overall hum level as the loop would be introduced very early in the signal chain. In the end, the way you connect the ground depends on your setup and it'd be nice if there is a note about this fact in the build docs. Another thing is that Muzzle / Zuul should key signal should be taken from a buffered splitter. Otherwise, it may negatively affect the tone - in my case, I'm just using bypass output from my Boss TU-3.

According to the schematic, IMHO replacing the potentiometer with B50K would extend the range of the threshold knob - similarly to what the mini-switch does.

Do you experience issues similar to those outlined in my first post? If you turn the threshold knob all way down or below ~20%, does the LED indicator shows that the signal is gated if you mute your guitar using the volume knob?

Greetings,
Mateusz

 

[m1nl]

OK, I should have searched the board better...

After reading https://forum.pedalpcb.com/threads/muzzle-gate-threshold.16566/, I followed Dr. Don's suggestion to replace R11. I ended up with 420kOhm, which works just fine. To calculate the value, I set the threshold to the point when the gate closes with no signal at the input. Then, I measured the voltage on the divider (middle connector of the threshold pot) to calculate the current going through R11. Then, I turned the threshold low, and given the current and measured voltage, I calculated the resistor needed.

The way the circuit works is the currents from the RMS output and threshold pot have to compensate each other to close the gate. The higher the threshold, the higher the RMS output needed to open it, but when the threshold is too low (it provides too much current), idle RMS output won't close the gate. In my case, the last value is around -150mV, which is too high (it should be more negative). Increasing R11 decreases the current from the threshold pot, so the gate finally closes. The datasheet for THAT4305 says there is a 60dB dynamic range (-30db to 30db), and RMS output rises by 6.2mV for every db, so -150 equals around -24dB, which is off by 6db :/

I'm marking the topic solved; however, I'm not really happy with the solution - something is wrong here, and either these chips are not calibrated properly, or there is something in the circuit I'm not getting... I'd really appreciate feedback and some experiences from other makers.

 

[guitarbruno76]

If you turn the threshold knob all way down or below ~20%, does the LED indicator shows that the signal is gated if you mute your guitar using the volume knob?

Hi m1 nl,
The led stays in green, when I turn the knob all the way down or near 20% ( so not gated) .
Actually, my range switch is mounted as an external switch, I can precise the "high range" starts to gate at 11 o'clock, the "low range" at 9 o'clock. You know, I'm wondering the exact interest of this switch... I usually use the "high range".
My own reflexion is about the unic and alone knob of threshold to adjust the gate, some other possibilities of actions miss, like the Fortin Zuul+ noise gate , the "hold" and the "release" knobs could be a great update!

 

[guitarbruno76]

I ended up with 420kOhm, which works just fine

Unfortunatly, I've tried same replacement, from 220 K to 470 K, the behaviour is as following: the led is red when the threshold is at zero, but anyway the sound crosses the gate, noticing the led becomes green when I play , and when I increase the threshold, I can reach a good gate to stop the buzzes when a dist or OD is on , but whatever I adjust the gate with the knob, there's not enough sustain, however I precise I use the side chain ( not very easy to explain, hoping you understand the issue).
So I mounted back the 220 K.
You are both persons to try this replacement with success, what's the trouble with me?...

 

[m1nl]

Hi Bruno,

It's hard to tell what's happening without taking a few measurements. However, I'd start by replacing the pot with the standard value (25k). Higher pot resistance increases the maximum threshold setting available and makes the usable range smaller, so you may struggle to set the threshold correctly.

Zuul / Muzzle will start cutting the notes eventually when the threshold is set too high - it looks like most people stay with a "default" setting, having the threshold knob somewhere between 10 and 11 o'clock. Increasing the threshold above 12 causes the sustain to decrease considerably.

I think it's just because most guitars provide similar output levels, so when dry guitar output is used as the key for the noise gate, there is not really much to tune with the threshold knob (unless you want to sound really tight and do a lot of "chugging").

EDIT: one more thing, if you're using guitar signal as key input, you should stay with switch being set to "low range"; "high range" is going to make threshold knob very sensitive and IMHO it only makes sense when gate is triggered by some very highly compressed signal or key input is not used at all.

 

[Paradox916]

ever considered that there is nothing wrong with the pedal, it’s that maybe you just do like it? I have built a few pedals that work as designed I just hate what they sound like. It happens.

 

[m1nl]

ever considered that there is nothing wrong with the pedal, it’s that maybe you just do like it? I have built a few pedals that work as designed I just hate what they sound like. It happens.

In my case, the pedal didn't work as designed, as I had an additional 1/3 non-usable threshold range CCW After I've tuned R11, it works exactly as in the video above, and now I like it. I am not sure why it was needed; I studied many data sheets and design notes from THAT, and the default value should be acceptable if the chip parameters are correct. I would consider replacing THAT4305 in the retrofit module, but now its availability is limited, and the shipping cost from Mouser is 3x the price for the chip, so I gave up this idea.

I believe Bruno's problems may be caused by invalid pot resistance.

 

[Paradox916]

This project definitely isn’t for everyone I have seen more troubleshooting threads than I have successful build reports, it can be a tricky troubleshoot especially for those punching above their weight class.

 

[guitarbruno76]

However, I'd start by replacing the pot with the standard value (25k).

I believe Bruno's problems may be caused by invalid pot resistance.

Hi all, thx for replying,
The 25 K pot is back in the pedal.
For the moment, I keep the default R11.
I notice , when using the side chain, is the amount of sustain of clean sound, which is better.

But by the way, I wanted to explain another problem, when using Muzzle and stacking some OD pedals.
A YT video, with me playing with the Muzzle, could be more evident to explain.

My pedal with blue knobs is not a Brown Eye "ID", but a Brown Eye "OD" ( just a detail...) !

 

[m1nl]

Sounds really good; nice tone!

Check for ground loops; I remember reading a topic on this forum where somebody could narrow down high-pitch squeal issues to ground loops between key and pedal input. Key input ground should not be connected to the PCB, nor should it be connected to the pedal metal enclosure; however, it has to be connected to the sidechain output ground connector (if used). The same rules apply to sidechain output - ground should not be connected to PCB, nor should it be connected to the pedal metal enclosure.

 

[guitarbruno76]

Uh, uh....
My wiring of the side chain ground is as follow:
Actually, you see black lines as the ground wiring, because my stereo switches has the screw pitch made of plastic, so they are insulated with the metallic enclosure, that is linked to the negative pole of the PS 9 volts.

 

[m1nl]

It's should be like that IMHO to avoid ground loops - effects loop and preamp ground buses should not be connected to each other as they're already connected together in the preamp circuit. Ensure your main input jack is not isolated so it connects the enclosure with GND. Otherwise you need to make a dedicated connection to ensure enclosure acts as a shield.

You can also isolate signal chains with audio transformers (https://www.thomann.pl/behringer_microhd_hd400.htm). I'm using this box to connect two channels of my Boss EQ-200 to both preamp pedal and effect loop chains.

Also read this topic as it looks Mattallica75 experienced very similar issue to yours:

SOLVED - Muzzle (Classic) Side Chain

Alrighty, I am closing in on finishing up a Muzzle build (with an enclosure I am particularly proud of) and I am having some issue with the side chain (Decimator G String style build). When I use the side chain I get a high pitched whine when I get into high gain territory (my tone for my bands...

forum.pedalpcb.com

You can also provide some photos of jacks and connnections to ensure we're on the same page.

 

[guitarbruno76]

There is kind of solution, the whistle/squeal is still there, I think there's no real solution, but the sustain is greatly increased!

Edit : We have posted at the same time!

That you suggest, cutting the link to the ground (central point between the Key 1 and 2) made that I could'nt use the side chain!!!

 

[guitarbruno76]

See the ground links I've cut ... (red crosses)

 

[guitarbruno76]

Ensure your main input jack is not isolated so it connects the enclosure with GND. Otherwise you need to make a dedicated connection to ensure enclosure acts as a shield.

That's the case, if you speak about the jacks from the guitar, or jacks to the amp, I always wire them ( TS ones) as follow : hot point to hot point ( = tips) , cold point to cold point ( = sleeves) and the ground strap (= the shield in fact) of the cable only linked to only one cold point ( becoming kind of capacitor )
We speak about same thing?

 

[guitarbruno76]

You can also isolate signal chains with audio transformers (https://www.thomann.pl/behringer_microhd_hd400.htm). I'm using this box to connect two channels of my Boss EQ-200 to both preamp pedal and effect loop chains.

Nice idea, thank you, and it doesn't ruin our wallet!

 

[guitarbruno76]

You can also provide some photos of jacks and connnections to ensure we're on the same page.

You see the type of stereo switch, Amphenor brand, with all plastic enclosure, including the screw pitch.

Stereo swich "I" = input of the side chain
Stereo switch "O" = outpout of the side chain

Also you see the pieces of wire, from the ground of "In/Out" of the noise gate, which are cut.