Results 1 to 24 of 24

Thread: Integrating noise-gate circuit

  1. #1
    Member BeŽlzeM's Avatar
    Join Date
    Dec 2008
    Posts
    61

    Integrating noise-gate circuit

    Hey guys,

    I've got this schematic:
    http://img407.imageshack.us/img407/4...ereduction.jpg

    The first part of the circuit is a boost circuit, something like a Tubescreamer or an SD-1 or whatever. But then those two lines from the boost circuit go into the second part of the schematic which is a noise-gate. It's that THAT4301 chip. The gate is supposed to kick in when not playing but it lifts off when you're playing. It grounds the signal the moment you touch the strings but it can feedback for a while, the kind of feedback you want to have.

    In the upper right corner of the schematic are two LEDs, a red and a green one. The green one lights up when you're playing (noise-gate off), and the red one lights up when you stop playing (gate kicks in).

    The pot VR7a just controls the gate. VR8a controls the amount of boost by the overdrive circuit.

    I can't really figure out the noise-reduction circuit. I want to take the clipping overdrive circuit out of it all and just have the noise-gate left. I want to have one input and one output obviously for a guitar signal to go through.

    Any help on this would be great
    Last edited by BeŽlzeM; 04-09-2009 at 06:56 PM.

  2. #2
    Noodle of Reality Steve Conner's Avatar
    Join Date
    May 2006
    Location
    Glasgow, Scotland
    Posts
    7,251
    Hi,

    The circuit is a little confusing because there are two inputs to the noise gate. The plain guitar signal, before the distortion stage, is fed to the gate chip's level detector. This is the path to pin 1 via R30, C20.

    The distorted signal is then fed to the actual gate part of the chip via C1, R5 into pin 17.

    So, my first line of attack would be to unhook C1 from IC2b's output, and hook it up to IC3a's output instead, so that both the level detector and the gate get the same signal. Then you can get rid of IC2 and all the parts that go with it.

    This circuit also seems to include some EQ. TR1 and TR4 are gyrators of the kind used in graphic EQs.
    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

  3. #3
    Member BeŽlzeM's Avatar
    Join Date
    Dec 2008
    Posts
    61
    Hey, thanks for the reply. So this would be pretty much it?:
    http://img266.imageshack.us/img266/9...eduction2x.jpg

    I wasnt sure if I could feed the signal into both the level detector and the gate at once in this circuit.

    Yeah there was some EQ'ing in the OD circuit but I wanted to take that out anyway.

    If this should work than I think I'm trying this one...

    Cheers

  4. #4
    Member BeŽlzeM's Avatar
    Join Date
    Dec 2008
    Posts
    61
    In addition to my post above (I'm still not sure if my second schematic is correct):

    Are there ways to reduce noise with a simple circuit? I've seen circuits like these to reduce noise in some signals. Circuits like these for example:



    Or this:




    These should reduce noise for about 35 dB between 100 Hz and 20 kHz. Would anything like this work?

    Jerry from FJA has something like this and I was wondering how he's doing that:
    http://www.youtube.com/watch?v=UxCeN4zKq48

  5. #5
    Noodle of Reality Steve Conner's Avatar
    Join Date
    May 2006
    Location
    Glasgow, Scotland
    Posts
    7,251
    Your above circuit seems correct to me, though I was hoping for a second opinion from someone else.

    The two circuits you just posted don't seem to have anything to do with audio noise reduction. The second one is a capacitance multiplier to remove noise from DC voltages, and I've no idea what the first one is.

    Peavey used to use a pair of back-to-back diodes in the signal path of some high-gain amps as a kind of ghetto "noise gate". I bet the FJA mod is something like this. The 5150 achieved a similar effect by just biasing the power tubes very cold.
    "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

  6. #6
    Member BeŽlzeM's Avatar
    Join Date
    Dec 2008
    Posts
    61
    Quote Originally Posted by Steve Conner View Post
    Your above circuit seems correct to me, though I was hoping for a second opinion from someone else.

    The two circuits you just posted don't seem to have anything to do with audio noise reduction. The second one is a regulator to remove noise from DC voltages, and I've no idea what the first one is.
    Alright, just forget about the noise reduction circuits in my last post. Was just a shot in the dark actually. Weren't those Peavey noise filters just 2 diodes in series with a resistor in parallel? I'm curious how that FJA circuit works.

    Thanks for helping me out on the first circuit though, if it looks fine I think I'm trying that. Any more opinions?

  7. #7
    Senior Member
    Join Date
    May 2006
    Posts
    538
    You didn't mention where do you want the NG integrated but I'll assume you meant in a tube amp. If this is your case it's not difficult to do and after you're done there will be only one additional LDR in the sound path.
    I don't know how effective is Peavey's reverse didodes NG but many people say it sucks.

  8. #8
    Member BeŽlzeM's Avatar
    Join Date
    Dec 2008
    Posts
    61
    Quote Originally Posted by Gregg View Post
    You didn't mention where do you want the NG integrated but I'll assume you meant in a tube amp. If this is your case it's not difficult to do and after you're done there will be only one additional LDR in the sound path.
    I don't know how effective is Peavey's reverse didodes NG but many people say it sucks.
    Yeah, in a tube amp. Just between the input jack and the preamp I think. What do you mean with an additional LDR? The schematic isn't using any LDR's right? Or am I misunderstanding you?

    I haven't really heard good things about the Peavey noise filtering, either. There are ways to filter out the noise by a good amount, have no idea where to look for basically.

    Oh, by the way. Would this circuit alter tone significantly?

  9. #9
    Senior Member
    Join Date
    May 2006
    Posts
    538
    Yeah, in a tube amp. Just between the input jack and the preamp I think. What do you mean with an additional LDR? The schematic isn't using any LDR's right? Or am I misunderstanding you?
    I don't think placing a NG between the input jack and preamp is a good idea. It should be after the preamp especially if it's higher gain preamp.
    The gating element in the schematic I meant is an LDR which forms a voltage divider with a resistor thus cutting the signal out. I've used this many times and even a high gain amp becomes dead quiet.

  10. #10
    Member BeŽlzeM's Avatar
    Join Date
    Dec 2008
    Posts
    61
    What if there are no +/- 15v regulators inside the amp? I assume I have to build a regulator circuit in the amp as well. Should I take that from the PT? Is the reverb driver transformer any good for this? It's a modded JCM 800 Marshall btw. But I'm also looking at building this inside of a 5150 in the future, just experimenting first though. I'm not doing it just yet, my 800 has some other problems that I need to take care of first, but I just want to get this clear for myself.

  11. #11
    Senior Member
    Join Date
    May 2006
    Posts
    538
    What if there are no +/- 15v regulators inside the amp? I assume I have to build a regulator circuit in the amp as well. Should I take that from the PT? Is the reverb driver transformer any good for this? It's a modded JCM 800 Marshall btw. But I'm also looking at building this inside of a 5150 in the future, just experimenting first though. I'm not doing it just yet, my 800 has some other problems that I need to take care of first, but I just want to get this clear for myself.
    I don't know what kind of power supply you have in your JCM800 but you don't need +/-15V to run the NG. I guess you can rectify the filament supply and add a charge pump to create negative voltage. This NG will run on +/-6V without any problems. In 5150 you already have the voltages you need.

  12. #12
    Member BeŽlzeM's Avatar
    Join Date
    Dec 2008
    Posts
    61
    http://img6.imageshack.us/img6/1781/...mpowerpsdc.jpg

    That's my powersupply. I just need to take one 6.3v lead from the filaments supply and invert the other with something like this? Any help on how to wire that up would be cool. Will that have any consequences for my filaments supply?


  13. #13
    Senior Member
    Join Date
    May 2006
    Posts
    538
    Actually you may not need the charge pump but you can use voltage doubler instead. Check out how it's done in Mesa Mark IV.
    You won't need so big value capacitors because it will draw much less current.
    Attached Thumbnails Attached Thumbnails markiv-filsupply.jpg  

  14. #14
    Member BeŽlzeM's Avatar
    Join Date
    Dec 2008
    Posts
    61
    Quote Originally Posted by Gregg View Post
    Actually you may not need the charge pump but you can use voltage doubler instead. Check out how it's done in Mesa Mark IV.
    You won't need so big value capacitors because it will draw much less current.
    I'm not sure how I would do that. How do I get that from the filaments supply, and where is the negative voltage?

    I know this is a way to do it. But I can't get this from the filaments supply, can I?
    http://img13.imageshack.us/img13/922...regulatorl.jpg

    The voltage doubler will get me 12.6 volts on each lead from the filaments supply, right? From which 6.3 is for the powertube heaters and then I have another 6.3 left for the noise gate circuit. How would I wire what to the filaments supply? Any directions? I will still need to create the negative voltage, right?
    Last edited by BeŽlzeM; 04-12-2009 at 04:42 PM.

  15. #15
    Member BeŽlzeM's Avatar
    Join Date
    Dec 2008
    Posts
    61
    So I have these two 6.3 volt filament supply leads from my power tranny going to the heaters of the powertubes.

    How do I wire these, and what additional circuit do I need to power that noisegate circuit that runs on +6.3v and -6.3v.

    I think I need to double the voltage on one filament supply lead for the positive voltage. And double the second filament supply lead and invert the doubled signal with a voltage inverter.

    Am I right? How would I do that?

  16. #16
    Senior Member
    Join Date
    Mar 2008
    Posts
    365
    Filaments should be wired as usual. Use the curcuit you linked to - it's in parallel with the filament supply.

  17. #17
    Member BeŽlzeM's Avatar
    Join Date
    Dec 2008
    Posts
    61
    Quote Originally Posted by GainFreak View Post
    Filaments should be wired as usual. Use the curcuit you linked to - it's in parallel with the filament supply.
    Which circuit? The voltage inverter? I still need to double my voltage right? I need another 6.3 volts positive and negative for the noie-gate.

  18. #18
    Senior Member
    Join Date
    Mar 2008
    Posts
    365
    The circuit you linked to doubles the voltage on both sides and you get positive and negative voltage. As mentioned before maybe you won't need doubling the voltage:

    http://img13.imageshack.us/img13/922...regulatorl.jpg

    You can always use a small PCB power trasformer and build a separate supply around it and then stick it somewhere into the chassis with silicone or similar.

  19. #19
    Member BeŽlzeM's Avatar
    Join Date
    Dec 2008
    Posts
    61
    Quote Originally Posted by GainFreak View Post
    The circuit you linked to doubles the voltage on both sides and you get positive and negative voltage. As mentioned before maybe you won't need doubling the voltage:

    http://img13.imageshack.us/img13/922...regulatorl.jpg

    You can always use a small PCB power trasformer and build a separate supply around it and then stick it somewhere into the chassis with silicone or similar.
    Alright. So I have to place this circuit in parallel with the 6.3v filaments supply? I can as well take the WP117 lead in that circuit and solder that to the heater of one powertube socket, and take WP119 and solder that to the heater of the other socket. And WP118 to the center tap of the filaments supply?

    That will get me 6.3 volts for the tube heaters so that's okay, no change there? But also give me + and - 15 volts for the gate?

  20. #20
    Old Timer tedmich's Avatar
    Join Date
    Apr 2008
    Location
    Sonoma CA
    Posts
    3,092
    of course the anti parallel diodes used in the Peavey Rockmaster/Bravo preamp is designed as a "coring" circuit which trims the waveform and removes some noise. In later versions a parallel 1M resistor is added, then the XX got a slightly different version:


    the JSX gets a fancier version with an adjustable noise gate

    which can easily be added once you convince yourself its not an evil "diode clipping" circuit

  21. #21
    Senior Member Guitarist's Avatar
    Join Date
    Jul 2006
    Posts
    497
    Ha! I remember seeing those diodes in the Rockmaster. I thought is was a clipping circuit. So now I understand. What is the switch for?

  22. #22
    Old Timer tedmich's Avatar
    Join Date
    Apr 2008
    Location
    Sonoma CA
    Posts
    3,092
    I think it switches between lead/ultra but I could well be wrong; the JSX is a little too complex as I'm a Bravo kinda guy.

  23. #23
    Senior Member
    Join Date
    May 2007
    Location
    Silicon Valley ; USA
    Posts
    1,095
    Quote Originally Posted by Guitarist View Post
    Ha! I remember seeing those diodes in the Rockmaster. I thought is was a clipping circuit. So now I understand. What is the switch for?


    I can tell you what it does. When the switch is off, it puts the 1 nF cap in the noise gate to shunt only the high frequency noise to ground. When the relay contacts are engaged, it shorts around the cap to shunt all noise frequencies to ground.







    -g

  24. #24
    Junior Member
    Join Date
    Jul 2015
    Posts
    1

    Integrated Noise Gate

    Quote Originally Posted by Steve Conner View Post
    Hi,

    The circuit is a little confusing because there are two inputs to the noise gate. The plain guitar signal, before the distortion stage, is fed to the gate chip's level detector. (...) The distorted signal is then fed to the actual gate part of the chip (...)
    This seems so simple and yet so brilliant!

    Are you guys aware of any distortion pedals with integrated noise gate that work like this? I think that this integrated solution might work much better than a traditional in-line combination of Distortion+Noise Gate pedals, even better if we use with high gain distortion.

    Does anyone here have a copy of the image that BeŽlzeM posted on the very first post showing the circuit?

    Thank you!

    Thales.
    GAMMOTH Death Metal

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. will this circuit work?
    By yunger in forum Theory & Design
    Replies: 20
    Last Post: 02-20-2009, 09:01 PM
  2. Big Briar etherwave CV, gate and pitch out mod.
    By sean k in forum Music Electronics
    Replies: 5
    Last Post: 09-07-2008, 08:45 AM
  3. Noise/
    By NightWinder in forum Pickup Makers
    Replies: 10
    Last Post: 09-03-2007, 02:55 AM
  4. overdrive circuit
    By drlowlow in forum Theory & Design
    Replies: 3
    Last Post: 01-16-2007, 01:36 PM
  5. Solen, Black Gate, etc for Power Supply
    By greg in forum Mods & Tweaks
    Replies: 21
    Last Post: 10-12-2006, 06:56 PM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •