Adding noise gate to distortion pedal

[Dpk136]

I'm building a distortion. Pedal based off the boss HM-2. The person that I'm doing this for loves a lot of gain and dark distortion. The problem is that the amp just squeals and there is a ton of noise. He doesn't play anything but a distortion pedal and doesn't want to have to make sure to click on 2 pedals to use distortion.

How can I get the guitar sound from before the distortion, but apply the noise gate after all the clipping? I want to do this with 1 knob, like the %^&* blocker, and I don't want to have to add more jacks to the pedal.

Any ideas?

[Mark Hammer]

1) Make sure that the bandwidth of whatever is entering the pedal is something he can use.
2) Make sure the bandwidth of whatever is leaving the pedal is something he can use.

Many people who use noise gates are applying them to remove something that should never have entered a high-gain pedal in the first place, and ended up being amplified.  The result is that the gate has to be used in a heavy-handed way, which is a big part of what creates the bad reputation of noise gates.

And do you mean it is based on the HM-2 or MD-2, because there appears to be no such thing as an HD-2.

[amptramp]

There are a couple fo ways to add a noise gate to a distortion pedal:

1. put back-to-back diodes in the signal path with both ends returned to ground via resistors and capacitive coupling in and out.  Once the signal goes below the diode drop, it is gated off.  This gives crossover distortion which sounds bad for general program material but good as a guitar effect.

2. Add this circuit or its solid state equivalent to avoid the abrupt shutoff of a typical noise gate:



This is a circuit used by RCA in their radio-phonographs in the 1940's.  The triode amplifies the incoming signal and the diode rectifies it so a negative voltage comes out at the signal level (with a time constant set by an R-C network) that biases the control grid of the pentode reactance tube.  When the signal level is high, the pentode is cut off and the signal goes from in to out with capacitors going to a high-impedance point.  When the signal drops, the pentode effectively multiplies the 27 pF capacitor to where it cuts the highs from the signal.  This circuit was called the Magic Monitor and it was used to reduce the hiss between different cuts on a record album.

Whereas a noise gate is an abrupt on-off function, the Magic Monitor sets a lowpass rolloff that is reduced in frequency as the signal level gets lower.  There is no noticeable step function in throughput.  It would be easy to replace the triode with an op amp or transistor and the pentode with a JFET but you would have to calculate bias voltage to sweep the FET between low and high gain.

[FiveseveN]

1. put back-to-back diodes in the signal path

The HM-2 already has that.
And I know the "proper" way to use it is with EVERYTHING DIMED but there is a point where the signal gets buried in the noise floor. Is he using it with additional distortion from the amp?
That being said, having a gate with the clean signal as the key could indeed help. Look at the NS-2 for how this is implemented, the Decimator, Censored Word Blocker etc. are similar. Just keep in mind that this kind of circuit might be more complex than the distortion itself.
So going back to the series diodes option, I'd say try the Amptweaker variation first and see if it helps.

[Vivek]

1. put back-to-back diodes in the signal path

So going back to the series diodes option, I'd say try the Amptweaker variation first and see if it helps.

I learnt from this forum that they are called CORING DIODES.

https://patents.google.com/patent/US4571511A/en

[garcho]

The problem is that the amp just squeals and there is a ton of noise.

You should fix that first, then worry about whether or not you need a gate later.

[iainpunk]

i know that it has been said before but i want to echo the antiparallel diodes in the signal path.
if you use multiple gain stages, i recommend putting the crossover "dirty gate" in between gain stages, this makes sure that there is less noise being amplified to begin with.

Fancy Lime, one of our users made a unique design that is centered this ''dirty gate'' and it sound really good if you like death metal, D-Beat, grindcore, crust punk etc.



cheers, Iain

[anotherjim]

Coring diodes can have a resistor across them so the crossover cut isn't so apparent - some signal can still bleed through.

[iainpunk]

Coring diodes can have a resistor across them so the crossover cut isn't so apparent - some signal can still bleed through.

or you use leaky germaniums like the boss HM-2 does

[Mark Hammer]

And, dang it all, I did it again, failing to look at the number of posts of an OP.  Welcome to the forum! 

And since it often - though not always - goes unexplained, diodes going to ground or in the feedback loop of an op-amp, clip the top and bottom of the waveform.  Diodes in series with the signal prevent anything below a given amplitude from passing, but one of the effects of that is to clip the "sides" of the waveform, since it prevents signal passing until it has risen to some minimum threshold, or dropped to a given negative level.  Since it prevents a smooth transition from the negative to positive portion of the waveform, it is referred to as "crossover" distortion.

I suppose others' experience may vary, but my own experience is that crossover/Xover distortion likes bridge pickups more than it likes neck pickups.

[iainpunk]

I suppose others' experience may vary, but my own experience is that crossover/Xover distortion likes bridge pickups more than it likes neck pickups.

i personally love crossover distortion on a bass guitar's neck PU, it really gives the bass a fat, rumbly tone.

cheers, Iain

[Dpk136]

Thanks for the advice. Yes, I meant the HM-2. I was watching videos on 4K TVs and must have had HD in my mind.

So with the circuit that fancy lime posted, would the "chug pot" serve as the single knob to control the noise gate?

The pedal I'm building already has the clipping diodes in the same spot (mostly), but the only thing that it looks like I'm missing is the chug pot. I'll slap that in there and see if I can get it to work. I was also thinking about putting a momentary switch on there to raise the noise gate to give a quicker cut-off, cleaner chug.

[FiveseveN]

So with the circuit that fancy lime posted, would the "chug pot" serve as the single knob to control the noise gate?

Not really, that's a gain control. What you're looking for is

Coring diodes can have a resistor across them so the crossover cut isn't so apparent - some signal can still bleed through.

the Amptweaker variation

[roseblood11]

The Boss ME-5 had a very simple, but effective noise gate circuit. The schematic is in the service manual.

[iainpunk]

Thanks for the advice. Yes, I meant the HM-2. I was watching videos on 4K TVs and must have had HD in my mind.

So with the circuit that fancy lime posted, would the "chug pot" serve as the single knob to control the noise gate?

yeah, it is basically to match the gating action to the particular pickups/guitar you use. this particular design was more meant to add crossover distortion than to add a gate, but gating is a nice side effect to have with really high gain. he uses the 1N400x series diodes for the distortion, not for the gating, i recommend 'red LED' or '1N4148 w/ germanium diodes in series' for a bit less harshness.

The pedal I'm building already has the clipping diodes in the same spot (mostly), but the only thing that it looks like I'm missing is the chug pot. I'll slap that in there and see if I can get it to work. I was also thinking about putting a momentary switch on there to raise the noise gate to give a quicker cut-off, cleaner chug.

the chug pot is just a gain control, in the minisagverket (mini sawmill in swedish/danish) its meant to determine the amount of gating/crossover distortion, but it also gives you a ton of gain. if you want the cutoff to be harsher with a switch, this might be the simplest option:


choosing the diodes is really important for the tone, changing crossover diodes has way more impact than changing clipping diodes!!!!!!!

if you like the HM-2, you might be interested in a pedal i designed around the same time Lime designed the minisagverket, we also posted the designs on the same day without knowing what the other was up to... mine is called 'pink' because the enclosure is painted soft grey-ish pink (i used wall paint)


cheers, Iain