MXR NOISE GATE

[percyhornickel]

Hi, I´ve been reading many posts about the MXR noise gate and how the tonepad´s version needs to change some values to make it work with original values or simply make it work better.

Some of the changes I have read are:

1K input resistence is 10K
47n input cap is 10n
1u N/P cap is 10n
10u positive goes to Q3d
1u output cap is 10u
680R is 4.7k
1u cap (pin 2 of IC1a) is 2.2u
1M resistence (Q3b - 1M  - 150K/+1u/Q2/1M) is 1.8K (with 5.1V 0.5W zener)

For the jfet I just have 2N5458 instead 2N5952.

My 2N5458 readings are:

Vgs Off: -3.3V
Idss: 5.25mA

The 2N5952 datasheet values are:

Vgs Off: -1.3V / -3.5V
Idss: 4mA / 8mA

I need a second opinion about the Jfet working window which seems to be fine for me but since I have no other jfets I don´t want to start collecting parts or build the circuit later knowing that the jfet will not work.

Thank you.

[POTL]

I remember a lot of negative reviews about this scheme, the main problem is repeatability, it did not work for everyone and not always correctly. To be honest, I am very skeptical about all discrete circuitry except distortion circuitry (I feel like a conservative snob). I think you should think about something modern and more practical. 1) Schemes with VCA chip from THAT company, modern and excellent solution. 2) OTA LM13700, on this forum there were several topics about a successful scheme.

[PRR]

> about the MXR noise gate

Is there a schematic link?

[percyhornickel]

POTL, yes I know there are other ones but I live in Venezuela and I am very limited to get the right parts so I build with what I have in hands!!. Not easy to find ICs like the LM13700 here believe me.

PRR, the schematic link:

http://www.tonepad.com/getFile.asp?id=77

This is the version with some of the mods done:

https://1.bp.blogspot.com/-aCJPkgMkgyw/VsuE5q2R4YI/AAAAAAAACcY/2chWm2EpGsA/s1600/MXR%2BNoise%2BGate.png

As I remember the schematic shows some errors like an backwards electrolitic and different values from the original MXR, thats why I have collected the  tips I wrote before.


Thanks for the answers.

[PRR]

The JFET difference is not very important.

The TonePad link you gave has two variants; this one maybe?

[Mark Hammer]

It's been 40 years since I owned one, but my recollection is that it used a latching stompswitch with a very obvious click, not a momentary.

[Rob Strand]

That circuit is a can of worms.    Very fickle.


Here's a corrected schematic,

https://www.diystompboxes.com/smfforum/index.php?topic=122689.0


Here's the thread full of headaches.

See the mods on reply #91 (page 5) from aspangev.  Also following posts.

https://www.diystompboxes.com/smfforum/index.php?topic=122682

[percyhornickel]

Yes is the same.

PRR, ok if you say the jfet is not that important I think I could start collecting parts to give it a try.

What do you think about the values that I wrote? Most of them are from the original circuit according some threads I had read in here.

I saw a video with a latching stompswitch instead momentary, seems to be more usefull...      ...Mr. Mark Hammer / an honor to read you in this  post.


Saludos desde Venezuela.

[percyhornickel]

That circuit is can of worms.    Very fickle.


Here's a corrected schematic,

https://www.diystompboxes.com/smfforum/index.php?topic=122689.0


Here's the thread full of headaches.

See the mods on reply #91 (page 5) from aspangev.  Also following posts.

https://www.diystompboxes.com/smfforum/index.php?topic=122682

Thanks for the answer Rob, I was reading this thread a few hours ago, even the reply 91 which is kind of crazy..   ...more for me because I speak spanish first lenguage. I would never imagine impedance issues...   ...I am petroleum engineer..  ...so, never..

One thing, the 10u -  jfet drain. The positive side is pointing to 22R and I have read it goes to jfet drain. The tonepad´s layout (not the sch) aparently
shows the correct way.


At least I am taking notes about the problems in this circuit too.

Well..    ..I don´t know if my little hum noises in my rat worths a possible headache building this one..   ..let´s see.

[Rob Strand]

Thanks for the answer Rob, I was reading this thread a few hours ago, even the reply 91 which is kind of crazy..   ...more for me because I speak spanish first lenguage. I would never imagine impedance issues...   ...I am petroleum engineer..  ...so, never..

One thing, the 10u -  jfet drain. The positive side is pointing to 22R and I have read it goes to jfet drain. The tonepad´s layout (not the sch) aparently
shows the correct way.


At least I am taking notes about the problems in this circuit too.

Well..    ..I don´t know if my little hum noises in my rat worths a possible headache building this one..   ..let´s see.

Tonepad might have some fixes already.

The problems in that circuit aren't obvious.    On paper it sort of looks ok.   However when you start digging into the fine details cracks appear.   I spent a lot of time looking for problems in that thread.   The more I looked at it the more problems showed up.  What it really needed was for someone to 'redeveloped' the circuit - that's where aspangev's work saved the day.

[sharp01]

Personally I gave up on this circuit. Tried all mods from several sources and after 2 years just desoldered all components and threw pcb away. No regrets. There are a lot of good pedals and life is too short

[Eb7+9]

My 2N5458 readings are:

Vgs Off: -3.3V
Idss: 5.25mA

There are no worms in this circuit ... basic analysis shows that if the 5.1v Zener is biased at 4.5v as suggested there is no way for the jFET to ever stop shunting signal if |Vgs(off)| is greater than 2.25v ... notice the similarity between the side-chain discharge circuit and that of the Dynacomp

[percyhornickel]

I just wanted to write here a little update with this project since I just finished this an hour ago and is working perfect now. I spent many time collecting parts to, I am happy with the result. The circuit is right after my diy distortion plus mod with max gain and works so nice cutting the backend nicelly.

What I use:

- Pot A250K (better control than A500K)
- Jfet 2N5457 / 2N5458 (both worked / I used sockets)
- Zener 5.1V 1/2 watt - smooth cut  (4.7V the cut is too drastic but the noise is cero) I am thinking to put a selector switch in here.
- 2N3904 (hfe 328 both)

Thank you all for the answer


Layout:
https://effectslayouts.blogspot.com/2016/03/mxr-noise-gate.html?showComment=1635119683651#c4221159827617513679

Schematic / Building doc:
https://pcbguitarmania.com/wp-content/uploads/2018/07/No-Noise-Gate-Building-Docs.pdf

I have to say the circuit has just cables right to the protoboard and here I have the last couple of jacks and dc power jack I use for all the circuits I try..   ....even connecting the circuit this way this one works great.

I live in Venezuela so my projects/circuits are time defined by "when I find something in here".

Thanks everyone...