This one has always had some issues because the original schematic was wrong and there was a typo on the Zener.
I checked the schematic against PCB pics on this site:
http://www.effectsdatabase.com/model/mxr/m106#
and found some more differences!.
I encourage you to count the number of 1uF and 10uF tantalums, and to count the number of 10nF and 50nF ceramics.
Note there is *no* 1uF NP cap on the PCB. This cap is actually 10nF, it is located on the right hand side where there is a 10nF under a 50nF.
Updated Schematic: [Obsoleted see below]
(https://i.postimg.cc/hfC4tWdw/mxr-ng-fix-robs-V1-1-2019-07-07.gif) (https://postimg.cc/hfC4tWdw)
Summary of Errors and Fixes for MXR noisegate schematic:
(Robin Tomtlund's schematic circa pre 2003)
1) I believe the zener should be a 1N5231 (Vz = 5.1V, Pz = 0.5W) not
1N5331. The zener is running ar very low currents 180uA so it's
probably only going to produce 4.7V or less.
From the MXR phase 90 the 1N5231 produces 4.82V at 360uA.
500mW Zener will be about 4.5V.
1W Zener will be about 4V
2) Error FET T3 gate and drain reversed.
3) The sensitivity pot should be 500k not 600k.
Probably log (A) taper.
4) [2019] output cap 10uF tant
5) [2019] Cap on base of T2 in parallel with 100k is 10nF; not 1uF
6) [2019] 1N914 diode across supply rails.
I found another error. Another clearer pic I have shows quite clearly the
10uF tant to the JFET drain has the cap's + terminal going to the drain.
EDIT: FWIW, the + to drain actually makes sense because the the drain is at Vref whereas the emitter is at Vref-Vbe ie. lower than Vref.
Here's the 10uf "cap-flip" fix,
7) Flipped 10uF to JFET drain.
[Obsoleted see below]
(https://i.postimg.cc/RqBLrTY3/mxr-ng-fix-robs-V1-2-2019-07-07.gif) (https://postimg.cc/RqBLrTY3)
Well, well well, poking around at more pics I found yet another bug.
8 ) The resistor on the counter-clockwise side of the pot is 10k not 1k.
What I'm not sure about is if 1k was ever used.
I have two pics clearly showing 10k and one not so clear one where I can't tell if it's 1k or 10k.
Here's the update with the XLR connector added: [Has error]
(https://i.postimg.cc/1nbkP9tQ/mxr-ng-fix-robs-V1-3-2019-07-08.gif) (https://postimg.cc/1nbkP9tQ)
Connections and colors
Numbering from left to right component side with chamfers at top.
1 Red +9V
2 Brown Pot 1 (ccw)
3 Yellow Input
4 Blue Pot 3 (cw)
5 Black 0V
6 Orange Switch
7 Grey Pot 2 (wiper)
8 Violet Output
Just for the non-believers, I found this post from back in 2010 on diystompboxes!
Quote
JUANSNEIDER
Re: MXR Noise Gate 150K (Ra) ???
Reply #7 on: September 15, 2010, 12:35:15 AM
All schematics on the web concerning the MXR Noisegate are wrong including the one from tonepad.
Referring to version 2 from 2003 (which I have on my HD):
- Input cap is in reality 10n (0.03) input resistor 10k.
- The 10µ electrolytic between the 22k and the FET is drawn in the wrong direction -
positive should be on the Fet-side.
- Output cap is 10µ instead of 1µ.
- the capacitor before Q2 in parallel to the 100k is a 10n (0.03) instead of a 1µ.
The only thing I disagree with is the Threshold pot has the 10k instead of 1k, not the input resistor.I checked this against and I realized the 10k resistor is in fact the input resistor!
Will update schem.
8 ) Input resistor 10k not 1k.
Hopefully this is now correct:
(https://i.postimg.cc/D4hm66yG/mxr-ng-fix-robs-V1-4-2019-07-08.gif) (https://postimg.cc/D4hm66yG)
Connections and colors
Numbering from left to right component side with chamfers at top.
1 Red +9V
2 Brown Pot 1 (ccw)
3 Yellow Input
4 Blue Pot 3 (cw)
5 Black 0V
6 Orange Switch
7 Grey Pot 2 (wiper)
8 Violet Output
A small point. DIY units vs original
The original units had a Threshold control which was wired with pins 1 and 3 reversed to what is shown. That makes the *threshold* higher as you rotate the pot clockwise. The Theshold pot was a 500kC reverse audio taper pot.
DIY units are wired as shown and the pot is Sensitivity. That makes the unit more sensitive as you rotate the pot clockwise. In this case the pot is a 500kA audio taper pot.
In this day and age the DIY version makes more sense and as a bonus that the audio taper pots are easier to get.
Thanks for that, Rob...any suggestion for a common BJT to replace the SC's they used?
> a common BJT to replace the SC's they used?
Look like jellybeans.
You could probably pull them out of a 1990s VCR from the thrift-shop. "Blindly", except you want NPN on that plan. So it may be easier to use 2N3904.
QuoteThanks for that, Rob...any suggestion for a common BJT to replace the SC's they used?
Your could probably put anything in there and it will work. A higher gain transistor for the buffer would be better. If you look at the callat thread you will see the circuit might be affected in a small way by the gain of the other "peak detector" transistor.
On paper the originals had gains around 210 to 340. Small Bear sells copies with hFE=250 and other have reported measuring gains of around 300 to 360.
I owned on of these little grey boxes back in the day, and I distinctly remember the footswitch having the definite click of a latching, rather then momentary, switch. Should it be momentary?
May I ask for a reupload of the up-to-date schematics please, Rob? I can't seem to display it :icon_rolleyes:
does this work?
mxr-ng-fix-robs-V1-4-2019-07-08.gif
Quote from: duck_arse on December 07, 2023, 08:27:02 AMdoes this work?
mxr-ng-fix-robs-V1-4-2019-07-08.gif
Thanks a bunch, it does!
Quick question; the 2SC1489 seems unavailable in Turkey, This (https://obsoletetellyemuseum.blogspot.com/2010/09/table-of-2sc-series-transistor.html) website suggests an alternative for this one as BC168, BC183, and BC238, of those -183 and -238 are available locally. Can I use one of them?
The same goes for 2N5952 as well, it seems rare and available but rather expensive, 2n5457 is unavailable, maybe other suggestions?
And regarding the 741, I know its the original design but what would be the difference if a single 4558 or similar used?
I've redrawn the schematic on EasyEDA, I'm trying to improve my layout skills, so I'm preparing a PCB for this.
I've excluded the XLR output and Momentary switch section (as I would not use it), am I doing good ? :icon_redface:
(https://i.postimg.cc/5jMxv0jB/mxr.jpg) (https://postimg.cc/5jMxv0jB)
Make C1 100μF, place a 10 - 100 nF in parallel, place a 100R reistor between D1 Cathode and C1 and take +9V T to C1 positive leg.. :icon_wink:
Quote from: antonis on December 08, 2023, 04:50:29 PMMake C1 100μF, place a 10 - 100 nF in parallel, place a 100R reistor between D1 Cathode and C1 and take +9V T to C1 positive leg.. :icon_wink:
But its not the same as duckarse shared?
It's just a R/C filter for the supply rail and is good practice. The only difference would be a lower noise floor .
Quote from: Baran Ismen on December 09, 2023, 04:47:39 AMBut its not the same as duckarse shared?
We DO love duck_arse a lot but reason other than his sharings..!! :icon_wink:
Quote from: antonis on December 09, 2023, 10:52:36 AMQuote from: Baran Ismen on December 09, 2023, 04:47:39 AMBut its not the same as duckarse shared?
We DO love duck_arse a lot but FOR reasonS other than his sharings..!! :icon_wink:
looking at this picture it looks like the input resistor is 1K
(https://i.postimg.cc/sBpSn1r9/MXRNoise-Gate.png) (https://postimg.cc/sBpSn1r9)
(https://i.postimg.cc/TLtKSDHm/MXR-Noise-Gate-56x65.png) (https://postimg.cc/TLtKSDHm)
Quote from: zbt on December 10, 2023, 07:38:19 PMlooking at this picture it looks like the input resistor is 1K
it's not the input resistor. It's the 1k on the threshold pot. The pin is marked P1.
The input wire is yellow and goes to a 10k.
Quote from: antonis on December 08, 2023, 04:50:29 PMMake C1 100μF, place a 10 - 100 nF in parallel, place a 100R reistor between D1 Cathode and C1 and take +9V T to C1 positive leg.. :icon_wink:
Is this better? :icon_lol: We're decreasing the voltage fed to the IC's and transistors this way, though, right?
(https://i.postimg.cc/jL2PMs9d/mxr-1-1.jpg) (https://postimg.cc/jL2PMs9d)
source schematic
(https://i0.wp.com/farm5.static.flickr.com/4095/4748454412_a9328bd439_o.jpg)
corrected schematic
(https://www.diystompboxes.com/smfforum/index.php?action=dlattach;attach=157)
1) the zener should be a 1N5231
(https://rvb-img.reverb.com/image/upload/s--GqAxr_Yc--/a_90/f_auto,t_supersize/v1602319242/aqnvkb5jste9ybxhnv2c.jpg)
(https://reverb.com/item/36194881-mxr-noise-gate-line-driver-1980s)
(https://i.ebayimg.com/images/g/NlUAAOSwk7NhqOlF/s-l1600.jpg)
2) Error FET T3 gate and drain reversed.
according datasheet 1 G 2 S 3 D
(https://i.postimg.cc/KkFsGPnK/Screenshot-from-2023-12-11-12-50-37.png) (https://postimg.cc/KkFsGPnK)
3) The sensitivity pot should be 500k not 600k.
MXR9479 1377940, compare with dynacomp is sensitivity which is 500K
(https://i.ebayimg.com/images/g/518AAOSwIs9hqOk~/s-l1600.jpg)
as picture
4) 10uF
5) 10nF
6) IN914 ? not IN4007
7) Flipped 10uF to JFET drain.
8 ) Input resistor 10k not 1k. correct ZO = ZI 10K
block
(https://i.ebayimg.com/images/g/NlUAAOSwk7NhqOlF/s-l1600.jpg)
script
(https://i.ebayimg.com/images/g/yzIAAOSwzolkiyD6/s-l1600.jpg)
:) sneak peak
(https://i.postimg.cc/YGZt02xL/MXRNoise-Gate.png) (https://postimg.cc/YGZt02xL)
Well done, Sir :D
Quote from: Baran Ismen on December 08, 2023, 03:15:53 AMQuick question; the 2SC1489 seems unavailable in Turkey, website suggests an alternative for this one as BC168, BC183, and BC238, of those -183 and -238 are available locally. Can I use one of them?
answer
Quote from: PRR on August 28, 2019, 12:57:42 AM> a common BJT to replace the SC's they used?
Look like jellybeans.
You could probably pull them out of a 1990s VCR from the thrift-shop. "Blindly", except you want NPN on that plan. So it may be easier to use 2N3904.
check datasheet for pin
Quote from: Baran Ismen on December 08, 2023, 03:15:53 AMThe same goes for 2N5952 as well, it seems rare and available but rather expensive, 2n5457 is unavailable, maybe other suggestions?
R.G. sensei second law?
Quote from: Baran Ismen on December 08, 2023, 03:15:53 AMAnd regarding the 741, I know its the original design but what would be the difference if a single 4558 or similar used?
TI Tender Loin 071?
Quote from: zbt on December 11, 2023, 03:01:13 AMWell done, Sir
Thanks a lot for checking. You can't check this stuff enough, it's so easy for errors to creep in. I know I put a lot of time into that one.
I hope I wouldn't be sworn at if I ask what's the purpose of Tantal's instead of regular polar caps :icon_wink:
Quote from: Baran Ismen on December 11, 2023, 05:09:14 AMI hope I wouldn't be sworn at if I ask what's the purpose of Tantal's instead of regular polar caps :icon_wink:
Your choice is going with NASA or Green Peace ;D
Quote from: zbt on December 11, 2023, 05:14:42 AMQuote from: Baran Ismen on December 11, 2023, 05:09:14 AMI hope I wouldn't be sworn at if I ask what's the purpose of Tantal's instead of regular polar caps :icon_wink:
Your choice is going with NASA or Green Peace ;D
I can't tell I understood what you mean by that but seems you know it better than me indeed, so I'll shut up :icon_smile:
Here are my recent work. RC filter added as suggested before.
(https://i.postimg.cc/7fFCChcd/1-23.jpg) (https://postimg.cc/7fFCChcd)
(https://i.postimg.cc/7bQJkmNx/1-2pcb.jpg) (https://postimg.cc/7bQJkmNx)
(https://i.postimg.cc/F7dds3P0/mxr-1-2.jpg) (https://postimg.cc/F7dds3P0)
Can anyone confirm if its good to do theoretically at least? :icon_rolleyes: :icon_rolleyes:
Quote from: Baran Ismen on December 11, 2023, 06:41:32 AMI can't tell I understood what you mean by that but seems you know it better than me indeed, so I'll shut up :icon_smile:
no, some how the answer is down here, I just follow the masters
https://www.diystompboxes.com/smfforum/index.php?topic=94856.40 (https://www.diystompboxes.com/smfforum/index.php?topic=94856.40)
From Coda Effect (https://www.coda-effects.com/2015/04/capacitors-which-one-to-choose.html)
correction the input 10K resistor series with 10nF, would not be for frequency about 1500 Hz?
so if use 1K then the cap is 100nF
question
1. Why using zener? would not use 22k resistor should be enough as VB?
2. Two 1M resistor connect to pin 3 output opamp, would be just simple enough connect 1M to VB?
3. The protection diode (IN914) how long would be last, would not be add one diode is much safer,
and use IN400X series?
Quote from: Baran Ismen on December 11, 2023, 05:09:14 AMI hope I wouldn't be sworn at if I ask what's the purpose of Tantal's instead of regular polar caps
A lot of stuff from the old days used tantalum for longer life. They don't dry-up like electrolytics.
For pedals that tends to work. For test equipment you will see a lot of tantalums used for power-supply bypassing and they fail all the time. Where the difference lies is when you turn on a piece of test equipment the tantalums see a large current spike - eventually that kills them. For pedals even the battery has limited turn on current although external power supplies could promote failure. The other positions in the circuit tend to be safe. In some circuit tantalums were use for low leakage, for example on LFO's with high impedance resistors.
Quote from: zbt on December 14, 2023, 12:11:31 PM1. Why using zener? would not use 22k resistor should be enough as VB?
2. Two 1M resistor connect to pin 3 output opamp, would be just simple enough connect 1M to VB?
3. The protection diode (IN914) how long would be last, would not be add one diode is much safer,
and use IN400X series?
1. The Vref circuit bias the JFET so you want the VREF to be constant when the battery voltage varies. That's why you have a zener. Same idea for the Phase 45 and Phaser 90.
2. Pretty sure they wanted to maximize the headroom. The zener voltage, which is determined by the JFET, is a little higher
than desirable.
3. Agreed. Many pedals and inboard preamps use 1N914s for protection they eventually die in action. 1N400x is a far better choice.
My firmly held belief is that MXR used tantalums instead of electros for many of their early pedals, not out of any electronic design reason, but simply because one could bend a tantalum over to lie flat. Remember that, between the big pots and Carling stompswitches, there wasn't a lot of room between those components and the back plate of the 1590B-sized enclosures. That's why they also bent ceramic caps over as well, in order to make the whole board as low profile as possible. And because there wasn't much space for the board, that's also why they included the foam rubber (that would invariably decompose over time) to make sure the board didn't short out against the enclosure, as well as holding the battery in place.
Thank You, Sir Mark Sir Rob
Quote from: Baran Ismen on December 14, 2023, 12:03:58 AMCan anyone confirm if its good to do theoretically at least? :icon_rolleyes: :icon_rolleyes:
I always collide with this thing, but feel at ease in diy wonder realm :)
(https://i.postimg.cc/hzzWMDPt/SAE.png) (https://postimg.cc/hzzWMDPt)
Quote from: zbt on December 14, 2023, 11:52:33 PMThank You, Sir Mark Sir Rob
Quote from: Baran Ismen on December 14, 2023, 12:03:58 AMCan anyone confirm if its good to do theoretically at least? :icon_rolleyes: :icon_rolleyes:
I always collide with this thing, but feel at ease in diy wonder realm :)
(https://i.postimg.cc/hzzWMDPt/SAE.png) (https://postimg.cc/hzzWMDPt)
I'm still a bit lost but seems the one I've drawn is suitable with the yours.
Quote from: Baran Ismen on December 15, 2023, 06:17:54 AMI'm still a bit lost ...
join the crowd
(https://alchetron.com/cdn/monolith-space-odyssey-3a6cbd9b-c327-4368-b1b1-d224c710e24-resize-750.jpeg)
Quote from: zbt on December 11, 2023, 03:01:13 AMR.G. sensei second law?
What is that 2nd law of R.G? Board is ready except this transistor to give it a try.
And for the in/out momentary switch side. What's that about? I've removed it from my schematic but did I do something wrong? What's that part for? Does the switch works different than normal pedals?
Today I've finished this. Seems working, but as I've never used a noise gate before (only on my good old GT-10's integrated one), I'm unsure if it's working properly or not.
It's blocking the hi-gain noise indeed when strings are muted, but the sensitivity pot seems to act a bit unusual. Consider that my volume level is 10 on my preamp;
In the first quarter of the pot range, the volume level is around 7, gating works,
On the 2nd, it is 10 but the attack ripples/distorts a bit and gating doesn't seem to work,
From the 3rd quarter until the end of the range, the volume level is around 3, and gating works.
I've tried some suggestions on Tonepad's build reports, but they seem not to work, it's a bit different schematic anyway so I didn't have much hope for that.
Used 2x 3904's (no idea about their matches or Hfe's, my DMM can't measure that), and 2n5485 in reverse for 5952. Cap's are not tantalum.
Quote from: Rob Strand on December 14, 2023, 02:48:00 PMQuote from: Baran Ismen on December 11, 2023, 05:09:14 AMI hope I wouldn't be sworn at if I ask what's the purpose of Tantal's instead of regular polar caps
A lot of stuff from the old days used tantalum for longer life. They don't dry-up like electrolytics.
For pedals that tends to work. For test equipment you will see a lot of tantalums used for power-supply bypassing and they fail all the time. Where the difference lies is when you turn on a piece of test equipment the tantalums see a large current spike - eventually that kills them. For pedals even the battery has limited turn on current although external power supplies could promote failure. The other positions in the circuit tend to be safe. In some circuit tantalums were use for low leakage, for example on LFO's with high impedance resistors.
Dry-slug tantalum capacitors are more compact because the tantalum pentoxide dielectric has a relative permittivity of 27 versus 10 for aluminum. Tantalum pentoxide is also pinhole-free, so leakage is less than aluminum oxide. But there is a problem: any defect in the tantalum pentoxide may turn it at high temperature to tantalum dioxide, which is conductive. If a failure occurs, you tend to get a firestorm that propagates through the capacitor that burns it up due to pentoxide being converted to dioxide, so the defect spreads. Tantalum capacitors of this type are good where there is resistance in series and therefore not much current available to transform the pentoxide to dioxide. Dry slug tantalum capacitors have capacitance characteristics that go into the megahertz range because there is no foil to act like an internal inductor. Aluminum foil caps behave more like tuned circuits, requiring ceramic capacitors in parallel to maintain high frequency power filtering.
There are wet-slug tantalum capacitors that do not have this failure mode but any reverse voltage of more than 0.3 volts will cause bridging of the dielectric and an instant short circuit, but they can be used on power rails.
The safest of the tantalum capacitors for power supply lines are the tantalum foil capacitors, formerly using the CL69 or CL71 numbers or CLR69 and CLR71 numbers for devices with established reliability. They do not fireball like dry slug or short due to reverse bias like wet slug capacitors. I have successfully used them on a shuttle-to-satellite adapter to filter 28 volt power in the Space Shuttle and prevent power converter noise from feeding back into the supply. The power line is about 90 feet long, so you don't want it to become an antenna. This was back before SPICE became popular and I had to use SYSCAP for design simulation. It worked - the finished filter was within 0.5 db of the simulated value in most places and within 1 db everywhere.
One final note: tantalum is a conflict metal, the blood diamonds of the metal world. Most people don't know about it but it may become an issue at some point.
If you have a stent installed near your heart, you're generally walking around with tantalum in your body.
Quote from: Mark Hammer on December 28, 2023, 11:30:57 AMIf you have a stent installed near your heart, you're generally walking around with tantalum in your body.
That is one other property of tantalum: it is inert inside the human body due to the tough pentoxide coating. It is also used in items like stomach staples.
Thanks for all the information you have provided guys :)
What about the below issue?
Quote from: Baran Ismen on December 27, 2023, 02:10:47 PMToday I've finished this. Seems working, but as I've never used a noise gate before (only on my good old GT-10's integrated one), I'm unsure if it's working properly or not.
It's blocking the hi-gain noise indeed when strings are muted, but the sensitivity pot seems to act a bit unusual. Consider that my volume level is 10 on my preamp;
In the first quarter of the pot range, the volume level is around 7, gating works,
On the 2nd, it is 10 but the attack ripples/distorts a bit and gating doesn't seem to work,
From the 3rd quarter until the end of the range, the volume level is around 3, and gating works.
I've tried some suggestions on Tonepad's build reports, but they seem not to work, it's a bit different schematic anyway so I didn't have much hope for that.
Used 2x 3904's (no idea about their matches or Hfe's, my DMM can't measure that), and 2n5485 in reverse for 5952. Cap's are not tantalum.
first, you'll need to measure the DC voltage across the Zener
second, confirm side-chain activity with DMM while strumming instrument
by measuring voltage across 1uF capacitor (the one that goes across T2)
see that Vc drops to near 0v (GND) during dynamic activity with sensitivity control turned up sufficiently ...
and then re-charges back to Vz upon release
---
Vgs on jFET is set by voltage divider 1Meg+1Meg+100k between Vz and Vc
ie., Vgs = (Vc - Vz ) *1.1/2.1
when cap is fully discharged this becomes -Vz*(1.1/2.1)
let's say roughly -Vz/2
during normal operation jFET goes from full-on (gating during idle) ie., Vgs = 0v
to fully off ... ie., hovering somewhere below Vgs(off)
preferably well below that and not just on the edge
for the jFET to be fully off and therefore not experience volume drop and distortion when gate is open
we thus need to satisfy the following condition:
that |Vgs(off)| be less than Vz/2 and, preferably by some margin
the actual device family is somewhat secondary here
J201, 2n5457, etc should all work, provided above condition is met
---
the easiest and most accurate way we have for estimating this Vgs(off) parameter for n-chan jFET's
is to apply (+) and (-) from a fresh 9v battery (or power source) to Drain and Gate, respectively
then set DMM to volt reading and apply meter probes between Source and Gate nodes on the device
this way the internal resistance of DMM plays the role of (high valued) Rs in biasing jFET
this method assumes that |Vgs(off)| is less than 9v by at least a few volts
and note, using a meter with 1Meg internal resistance will provide an estimate shy by roughly 20mV
---
btw, the sometimes perceivable distortion on the exits can't be fixed
something the original manual mentions ...
good luck
Quote from: Eb7+9 on December 29, 2023, 05:57:47 PMfirst, you'll need to measure the DC voltage across the Zener
second, confirm side-chain activity with DMM while strumming instrument
by measuring voltage across 1uF capacitor (the one that goes across T2)
see that Vc drops to near 0v (GND) during dynamic activity with sensitivity control turned up sufficiently ...
and then re-charges back to Vz upon release
---
Vgs on jFET is set by voltage divider 1Meg+1Meg+100k between Vz and Vc
ie., Vgs = (Vc - Vz ) *1.1/2.1
when cap is fully discharged this becomes -Vz*(1.1/2.1)
let's say roughly -Vz/2
during normal operation jFET goes from full-on (gating during idle) ie., Vgs = 0v
to fully off ... ie., hovering somewhere below Vgs(off)
preferably well below that and not just on the edge
for the jFET to be fully off and therefore not experience volume drop and distortion when gate is open
we thus need to satisfy the following condition:
that |Vgs(off)| be less than Vz/2 and, preferably by some margin
the actual device family is somewhat secondary here
J201, 2n5457, etc should all work, provided above condition is met
---
the easiest and most accurate way we have for estimating this Vgs(off) parameter for n-chan jFET's
is to apply (+) and (-) from a fresh 9v battery (or power source) to Drain and Gate, respectively
then set DMM to volt reading and apply meter probes between Source and Gate nodes on the device
this way the internal resistance of DMM plays the role of (high valued) Rs in biasing jFET
this method assumes that |Vgs(off)| is less than 9v by at least a few volts
and note, using a meter with 1Meg internal resistance will provide an estimate shy by roughly 20mV
---
btw, the sometimes perceivable distortion on the exits can't be fixed
something the original manual mentions ...
good luck
Zener reads of 4.6v precisely. I'll try the sidechain thing this evening.
I made another trial for this and went with the Tonepad version this time, with the mods of 680ohm/1uf to 4.7k/3.3uf (resistor solved the oscillation problem, cap is for gating response), keeping the 1m as it is instead of 1.8k (actually went with 1.5m, as increasing seemed to be better responding, changed the IC with LM358 (rc4558 I had had a feint background distortion),
I wonder if it's possible to increase the attack time more (applied no attack/decay mods), right now gate's activation is around 25-30ms give or take. Release is faster.
Quote from: Rob Strand on July 07, 2019, 05:33:15 AMHere's the 10uf "cap-flip" fix,
7) Flipped 10uF to JFET drain.
[Obsoleted see below]
(https://i.postimg.cc/RqBLrTY3/mxr-ng-fix-robs-V1-2-2019-07-07.gif) (https://postimg.cc/RqBLrTY3)
Which is the correct one, Rob? Most of the projects I've found seem to keep this cap as negative side facing to FET, positive to 22k.
Quote from: Baran Ismen on January 11, 2024, 09:27:01 AMWhich is the correct one, Rob? Most of the projects I've found seem to keep this cap as negative side facing to FET, positive to 22k.
From a technical perspective, as shown is correct. The + side of the cap sits at the zener voltage. The zener voltage feeds the 470k to the base of the transistor Q1. The base current will cause the base to sit at a lower voltage than the zener voltage. Then on top of that the emitter will sit at 0.6V below the base. So, as shown, the negative side of the cap must sit lower than the positive side of the cap which is correct.
Putting that aside I'm pretty sure I would have checked the polarity of the cap on the original board when I re-traced the circuit.
I'm not sure what problem you are chasing at the moment. It would be wise to put a 22pF to 100pF cap across the 1M resistor at IC1, as mentioned in the notes. That's especially the case if you aren't using a LM741. As far as holes in the original design go, you could also add 470ohm in series with the 47nF cap which appears after IC1. The reason for that is the 470 ohm would help fend-off oscillations due to capacitive loading on IC1.
Quote from: Rob Strand on January 11, 2024, 09:04:49 PMQuote from: Baran Ismen on January 11, 2024, 09:27:01 AMWhich is the correct one, Rob? Most of the projects I've found seem to keep this cap as negative side facing to FET, positive to 22k.
From a technical perspective, as shown is correct. The + side of the cap sits at the zener voltage. The zener voltage feeds the 470k to the base of the transistor Q1. The base current will cause the base to sit at a lower voltage than the zener voltage. Then on top of that the emitter will sit at 0.6V below the base. So, as shown, the negative side of the cap must sit lower than the positive side of the cap which is correct.
Putting that aside I'm pretty sure I would have checked the polarity of the cap on the original board when I re-traced the circuit.
I'm not sure what problem you are chasing at the moment. It would be wise to put a 22pF to 100pF cap across the 1M resistor at IC1, as mentioned in the notes. That's especially the case if you aren't using a LM741. As far as holes in the original design go, you could also add 470ohm in series with the 47nF cap which appears after IC1. The reason for that is the 470 ohm would help fend-off oscillations due to capacitive loading on IC1.
Tonepad version is actually working now and I've did this mentioned change as well last night, flipped the cap, haven't noticed any difference on gating action but it somehow working now.
I've noticed a weird thing that, with some DC adapters I have, this circuit seems to pulsate on current, its like when activated, it turns on, but you hear a pulsating wave sound around every half of a second, its like a synth sub bass sound, and the indicator LED (which is connected via 3DPT) pulsates accordingly. You can also hear the guitar sound in the background.
It's not like reverse polarity, that's for sure, that case pedal doesn't open at all, but this is something I've never seen before. Polarity is correct.
Quote from: Baran Ismen on January 11, 2024, 11:58:44 PMTonepad version is actually working now and I've did this mentioned change as well last night, flipped the cap, haven't noticed any difference on gating action but it somehow working now.
FYI, I checked the polarity of the cap by tracing the PCB pics posted earlier in the thread. I'm pretty sure I checked everything on this one to make the "corrected" schematic. Anyway the negative side goes toward the emitter.
https://www.diystompboxes.com/smfforum/index.php?topic=122689.msg1278238#msg1278238
It's possible put the cap in the wrong way cause some sort of leakage which then hides some other problem.
While I'm confident the a schematic is correct there does seem to the some general issues with that circuit. I don't know how MXR got the units out in production. Possibly a fluke characteristic of the opamps from back in the day.
QuoteI've noticed a weird thing that, with some DC adapters I have, this circuit seems to pulsate on current, its like when activated, it turns on, but you hear a pulsating wave sound around every half of a second, its like a synth sub bass sound, and the indicator LED (which is connected via 3DPT) pulsates accordingly. You can also hear the guitar sound in the background.
It's not like reverse polarity, that's for sure, that case pedal doesn't open at all, but this is something I've never seen before. Polarity is correct
That's totally whacked. The pulsing LED is showing the power is going on and off. That's not normal. In fact I can't even see how the pedal circuit could do that. I'd be thinking something is wrong with the PSU, PSU connectors, 6.5mm sockets. Maybe even a wiring error on the board - but even then how does it release the fault, seem unlikely.
Quote from: Rob Strand on January 12, 2024, 03:03:09 AMQuote from: Baran Ismen on January 11, 2024, 11:58:44 PMTonepad version is actually working now and I've did this mentioned change as well last night, flipped the cap, haven't noticed any difference on gating action but it somehow working now.
FYI, I checked the polarity of the cap by tracing the PCB pics posted earlier in the thread. I'm pretty sure I checked everything on this one to make the "corrected" schematic. Anyway the negative side goes toward the emitter.
https://www.diystompboxes.com/smfforum/index.php?topic=122689.msg1278238#msg1278238
It's possible put the cap in the wrong way cause some sort of leakage which then hides some other problem.
While I'm confident the a schematic is correct there does seem to the some general issues with that circuit. I don't know how MXR got the units out in production. Possibly a fluke characteristic of the opamps from back in the day.
QuoteI've noticed a weird thing that, with some DC adapters I have, this circuit seems to pulsate on current, its like when activated, it turns on, but you hear a pulsating wave sound around every half of a second, its like a synth sub bass sound, and the indicator LED (which is connected via 3DPT) pulsates accordingly. You can also hear the guitar sound in the background.
It's not like reverse polarity, that's for sure, that case pedal doesn't open at all, but this is something I've never seen before. Polarity is correct
That's totally whacked. The pulsing LED is showing the power is going on and off. That's not normal. In fact I can't even see how the pedal circuit could do that. I'd be thinking something is wrong with the PSU, PSU connectors, 6.5mm sockets. Maybe even a wiring error on the board - but even then how does it release the fault, seem unlikely.
That's ok, I mean it's working if the mentioned cap is flipped or not. But this pulsation seems quite weird, leads me thinking of a possible PSU problem because its not happening with ANY psu I use, it happens with some of them (I got 4, 2 are voltage & polarity changeable, 2 are regular smps')
It's a weird circuit indeed, literally no one could manage to make it good to go upon building it, everyone tries something different and fails/succeeds, some use 6.2v zener, and some change the cap/res. combo, some decrease the 1m to 1.8k (in my case didn't work i.e), etc etc. It's not something like a TS or something else. Also, the pot works CCW, I know I can use a C type and connect in reverse, but why would MXR prefer something like this anyway..
I wish NF-1 had a layout, it seems to be a better working noise gate. I can read its schematic indeed and draw anew and there I can prepare a layout, but I don't know how to remove the flip-flop section off of it.
Quote from: Baran Ismen on January 12, 2024, 04:07:38 AMI wish NF-1 had a layout, it seems to be a better working noise gate. I can read its schematic indeed and draw anew and there I can prepare a layout, but I don't know how to remove the flip-flop section off of it.
IMHO, the Boss NF-1 is a better version of the MXR. You could graft the differences onto the MXR circuit, however, the overall structure of the Boss is better.
Here's how to chop out the flip-flop:
(https://i.postimg.cc/8JDkVPYc/Boss-NF-1-Noise-Gate-Flip-Flop-Removed-V10.png) (https://postimg.cc/8JDkVPYc)