Noise gate crackling noise

Hi there,
I'm a new and proud owner of a GM 36, I bought it used a week ago and it does just fine. I'm already planning an improvement, swapping the stock power tubes with a matched quartet of JJs.

I noticed a slight defect in the noise gate section: if I keep long soustained chords or notes, when the noise gate kicks-in, canceling the remaining sound, it produces a brief crackling noise. This is most audible if NG is set to Hard, shortening he decay time.

I keep NG engaged mostly on lead and ultra channels, since the amp will produce a clear hum. If not engaged, especially at 18watts and full power

Any suggestions ?

Welcome!

I have the NG on for almost all my patches (I have the NG knob set to soft or full CW) and have never noticed this. But I also use a noise gate on my board (I hate noise), so maybe it kicks in before the GM NG.... Are you using any overdrive on the input to the GM?

Hi, thanks for replying.
No, I'm using just the amp, with the midi pedalboard connect, stompbox mode.

I also set the NG fully clockwise to soft; in this way the NG kick-in after 10-12 seconds or so, which are enough to pass this issue almost unnoticed.
I was simply wondering what could be the most likely cause, it's a pity for this beautiful piece of gear.

Hi Wazo, welcome to the forum from me too.  I'm glad Namklak has come in on this one as someone with real experience using it.  My thoughts would also have been that this is not what you would want in a noise gate.  In trying to prevent noise it introduces a crackle?  Doesn't seem sensible to me.  But I have to admit that I'm not a user of the noise gate, I normally play on the Clean/Crunch channels and have an occasional foray into Lead territory, Ultra just isn't my thing, and I'm anal about some things but not a bit of noise against a band background.

I'll have to check on this on my own amp tomorrow morning, it's late at night here and my neighbours don't like my playing that much.      I'll try it out and get back to you in about 12hrs.  In the meantime let's see if Namklak can advise.

Hi Botdonbert,
Thank you for your welcome, too.

Reading your reply I understand I have to explain myself better, since my words could be a little misleading.
The Noise Gate is working just fine, when it is engaged the amp is perfectly silent even at hi gain settings.
If disengaged, I can hear a soft hum coming from the amp, it's almost inaudible at low wattages, but it increases when the power soak is set to 18wats, or the amp is running full power, and crunch/lead channels are selected with robust gain settings.

Therefore I normally keep NG engaged in these cases. The crackling noise can be only heard for a second or two, when the sound signal "goes away", following its normal decay time (long sustained chords or notes, or very low, sweet picking on the strings. that causes reduced output)

This malfunction occurs in 5% of my normal playing activity, but nonetheless it's a little annoying and I would like to understand the possible
Causes.

Cheers.
É.

As I just posted in another thread, I saw Namklak's post above and tried it out.  I'm now a convert to the NG.  I certainly would have no need to use it in any aggressive way, it works on my GM at the most sensitive setting to just remove the slight background sheen, but it would be really no consequence in a live situation, I just don't have that much of a problem with noise.  Very light fingering rather than plucking with a plectrum doesn't seem to be affected and the dying away crackle doesn't happen for me.

The NG works by taking the signal after the Input Buffer stage and amplifying a selected amount according to the Intensity control setting in both +ve and -ve directions across two stages. One of these is a high gain 1000x stage and the other just an inverter.  The +ve and -ve signals are both compared with a 7.5V reference voltage and when the amplified signal goes above or below this they pull a line down via a couple of diodes.  That in turn switches on a couple of JFETs which were cutting out the signal and it kicks in.  This is very fast in general, depending on teh size of the signal you feed to it, and it has safety mechanisms in there to prevent switching noise but these will be pretty well tuned.  It sounds like yours could be chattering a little when it gets to the critical level, though a little hysteresis is usually built into systems like this.  I wonder if it is variation in the JFETs' characteristics, they are one of the most unreliable components we have in terms of the range of their quoted figures and these figures are quite important in use.

I'm still looking at this one but I can't see anything which could be a real definite cause.

Thank you for replying. I bought this amp used, when I tried it before buying it, it was at at loud volume, therefore it was almost impossible to notice this defect.
I'm not into amp electronics enough to understand 100% your explanation, but I understand that it could be a small defect of some kind in the NG circuitry that clips the signal abruptly from the input buffer, when it goes below a given input level.

The softer the setting, longer the signal will last, therefore, less probability of NG crackling.

Anyway, this amp has got great tone, therefore , should the the hum turn to be so annoying at hi-gain levels or high volumes, I think I still can buy an external NG, to manage the situation.

Anyway, who knows, maybe I will discover what this issue is all about, sooner or later.

Thanks for helping

E.

The same issue over here.
I boought the amp new.
Got it out of the box, played a bit and then i engaged the noise gate....
Tone sustains for 5-10 seconds then i get the crackling noise you mentioned and the tone is killed instantly, almost as if the amp shuts down.
If i press the noise gate button again, the string tone contibues as if nothing happened.
Definitively a defect in the noise gate.