MXR Noise Gate (M-106) Corrected Schematic

[zbt]

looking at this picture it looks like the input resistor is 1K

[Rob Strand]

looking 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.

[Baran Ismen]

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..

Is this better?    We're decreasing the voltage fed to the IC's and transistors this way, though, right?

[zbt]

source schematic


corrected schematic


1) the zener should be a 1N5231 




2) Error FET T3 gate and drain reversed.
according datasheet 1 G 2 S 3 D


3) The sensitivity pot should be 500k not 600k.
MXR9479 1377940, compare with dynacomp is sensitivity which is 500K


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

script

sneak peak




Well done, Sir

Quick 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

> 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

The 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?

And 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?

[Rob Strand]

Well 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.

[Baran Ismen]

I hope I wouldn't be sworn at if I ask what's the purpose of Tantal's instead of regular polar caps 

[zbt]

I hope I wouldn't be sworn at if I ask what's the purpose of Tantal's instead of regular polar caps 

Your choice is going with NASA or Green Peace 

[Baran Ismen]

I hope I wouldn't be sworn at if I ask what's the purpose of Tantal's instead of regular polar caps 

Your choice is going with NASA or Green Peace 

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

Here are my recent work. RC filter added as suggested before.

[Baran Ismen]

Can anyone confirm if its good to do theoretically at least?   

[zbt]

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

no, some how the answer is down here, I just follow the masters

https://www.diystompboxes.com/smfforum/index.php?topic=94856.40

From Coda Effect

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?

[Rob Strand]

I 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.

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?

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.

[Mark Hammer]

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.

[zbt]

Thank You, Sir Mark Sir Rob

Can anyone confirm if its good to do theoretically at least?   

I always collide with this thing, but feel at ease in diy wonder realm

[Baran Ismen]

Thank You, Sir Mark Sir Rob

Can anyone confirm if its good to do theoretically at least?   

I always collide with this thing, but feel at ease in diy wonder realm

I'm still a bit lost but seems the one I've drawn is suitable with the yours.

[Eb7+9]

I'm still a bit lost ...

join the crowd

[Baran Ismen]

R.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?

[Baran Ismen]

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.

[amptramp]

I 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.

[Mark Hammer]

If you have a stent installed near your heart, you're generally walking around with tantalum in your body.

[amptramp]

If 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.