Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Instruments and Amps Everything that makes music, Especially including instrument amps.

Reducing Fuzz Box Noise - Boss MT-2
Reducing Fuzz Box Noise - Boss MT-2
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 16th September 2019, 10:39 PM   #11
Gnobuddy is offline Gnobuddy  Canada
diyAudio Member
 
Join Date: Mar 2016
Quote:
Originally Posted by ITPhoenix View Post
...TL071 op-amp with a gain of 3-5V/V. This is too much boost to place as the first stage of the MT-2; it will have to be attenuated to unity gain. Is it necessary to have this gain to keep the noise low?
To address your last question first: Yes, if you don't have gain in the first stage, you add noise without increasing the signal voltage...so the second stage is as noisy as ever, and the first stage has made things even worse by adding additional noise!

This is exactly why having the (slightly less than) unity-gain JFET source follower is not a great idea from the noise point of view.

Back to your problem: why not simply lower the gain of the first op-amp stage (3A) in the MT-2? All you'd have to do is increase the value of the 1k feedback resistor (RD41) from the non-inverting input to ground. Increase that to 4.7k, and you drop the gain by a factor of about five. Now you can insert the TL071 with a gain of 5 in front, and end up with about the same signal level out of op-amp 3A.


-Gnobuddy
  Reply With Quote
Old 16th September 2019, 11:26 PM   #12
ITPhoenix is offline ITPhoenix  United States
diyAudio Member
 
Join Date: Mar 2012
Location: New York
Default First opamp stage identification

@Gnobuddy: Thank you for the clarification. Looks like the first opamp is 3b. In which case I would lower the 220k, 044., or increase the 10k, 054. Are you using the schematic in the post?
__________________
Venturing where the wise refuse to go, may or may not yield great revelations theretofore unknown; either with considerable expense.
  Reply With Quote
Old 16th September 2019, 11:33 PM   #13
voltwide is offline voltwide  Ireland
diyAudio Member
 
Join Date: Jan 2010
To give an idea this is the PreAmp you heard in the sound sample:
Attached Images
File Type: png GuitarPreAmp3D.png (179.8 KB, 95 views)
Attached Files
File Type: pdf GuitarPreAmp_sch.pdf (66.6 KB, 10 views)
File Type: pdf GuitarPreAmp.pdf (33.9 KB, 7 views)
__________________
tuby or not tuby, that is here the question!
  Reply With Quote
Old 17th September 2019, 01:56 AM   #14
PRR is offline PRR  United States
diyAudio Member
 
PRR's Avatar
 
Join Date: Jun 2003
Location: Maine USA
Quote:
Originally Posted by ITPhoenix View Post
...I see a 1M elevating resistor before the JFET gate. Would this add significant noise to the circuit...
That is in *shunt* with the signal source. Approximating guitar as 20k, and another 10k RF protection, the hiss voltage of the 1Meg is attenuated 30:1. Hiss would be lower if you made it 10Meg, but the difference would be inaudible.

Mostly, it's just got a LOT of gain. The devices and circuits are not lowest-hiss, but not far off. Taking gain out one place and putting-back another is unlikely to change things much.

Guitar should be full-up most of the time; ample source signal is the first rule of "low noise".

There is a remote chance that JFET or opamp have been zapped by excess level or static shock. This is an occasional problem on much older gear, and this one is not young anymore.
  Reply With Quote
Old 17th September 2019, 04:29 AM   #15
Gnobuddy is offline Gnobuddy  Canada
diyAudio Member
 
Join Date: Mar 2016
Quote:
Originally Posted by ITPhoenix View Post
Are you using the schematic in the post?
Yes, but you are right, and I got it all wrong.

Between the tiny schematic and the ancient thrift-store computer monitor I use at work (because it's better than the official one!), I managed to completely miss the first op-amp, surrounded as it is by clouds of JFETs and resistors and caps.

I agree with PRR that you won't get a huge noise improvement by shuffling gain around. But it's easy enough to get whatever small improvement can be had by using an external clean-boost pedal between guitar and MT-2.

You could tack-solder a resistor in parallel with that 220k NFB resistor to lower the gain, so you can easily remove it if you want to return the pedal to stock.

Who knows, that MT-2 might be worth enough for you to retire on some day, if you leave it stock. Stranger things have happened!

-Gnobuddy
  Reply With Quote
Old 17th September 2019, 04:55 AM   #16
mandu is offline mandu  Singapore
diyAudio Member
 
Join Date: May 2010
A noise gate will keep the silent passages quiet for the worst case
  Reply With Quote
Old 17th September 2019, 10:57 AM   #17
ITPhoenix is offline ITPhoenix  United States
diyAudio Member
 
Join Date: Mar 2012
Location: New York
@PRR:
"That is in *shunt* with the signal source. Approximating guitar as 20k, and another 10k RF protection, the hiss voltage of the 1Meg is attenuated 30:1. Hiss would be lower if you made it 10Meg, but the difference would be inaudible."

With the guitar plugged in and not outputting anything, the filter cap is isolating the the instrument, so I'm having trouble seeing the parallel resistance in this case.

"Mostly, it's just got a LOT of gain. The devices and circuits are not lowest-hiss, but not far off. Taking gain out one place and putting-back another is unlikely to change things much."

The pedal has a reputation for being noisy, due to its very high gain nature and lower than Hi-Fi component quality. Deleting the first JFET and jiggling the gains around is inexpensive and not that time consuming. The effort would be worth it to me if a 5% hiss reduction is achieved.

Guitar should be full-up most of the time; ample source signal is the first rule of 'low noise'.

This is impossible for those who wish some amplitude dynamics. Technique is enough for "mind-blowing shredders".

"There is a remote chance that JFET or opamp have been zapped by excess level or static shock. This is an occasional problem on much older gear, and this one is not young anymore."

The seller admitted the pedal came in with almost zero voltage on the 4.5v leg. and the unit had zero output. He replaced all the opamps which solved the problem. He also surmised the unit had the wrong power supply connected which blew the blocking diode. The box in question is one of the older models with a through-hole PCB. Since 2017 they use SMT.

@Gnobuddy:
"Yes, but you are right, and I got it all wrong." Don't sweat it, we all do it.

"I agree with PRR that you won't get a huge noise improvement by shuffling gain around. But it's easy enough to get whatever small improvement can be had by using an external clean-boost pedal between guitar and MT-2." I would rather incorporate the "clean boost" technique into the MT-2.

"You could tack-solder a resistor in parallel with that 220k NFB resistor to lower the gain, so you can easily remove it if you want to return the pedal to stock." This is a truism.

@mandu: "A noise gate will keep the silent passages quiet for the worst case." I'm actually looking for a level of distortion not far from the MXR Distortion Plus, which did not require a noise gate, but had no EQ. The MT-2 is unwieldy in stock form but more versatile. The Fromm kit corrects this and improves quality. Speaking of the Fromm kit, I received this response to my question as the whether their kit reduces hiss:

"Yes the kit will help to lower some of the noise in the circuit. We upgrade a number of blocking caps with the kit and that can help a low with hiss and noise."

This does not sound too comforting. I think he meant to say, "..can help a little with hiss and noise."
__________________
Venturing where the wise refuse to go, may or may not yield great revelations theretofore unknown; either with considerable expense.
  Reply With Quote
Old 17th September 2019, 11:45 AM   #18
voltwide is offline voltwide  Ireland
diyAudio Member
 
Join Date: Jan 2010
"We upgrade a number of blocking caps with the kit and that can help a low with hiss and noise."

Caps rolling is what people do who have no clue
__________________
tuby or not tuby, that is here the question!
  Reply With Quote
Old 17th September 2019, 12:05 PM   #19
ITPhoenix is offline ITPhoenix  United States
diyAudio Member
 
Join Date: Mar 2012
Location: New York
@voltwide: I like your approach with your design, especially the noise reduction. I had an idea myself that is similar in its effect. I called it a "soft-gate", meaning it did not completely shut off the signal, but slowly attenuated it to near zero as the notes/chords decayed. The reason being that it would not be that noticeable.

There are pedals that sport some kind of "smart" circuitry at significant expense. But I'm not going to buy one only to find out I don't like it.

For me, the best and first assault would be in the inherent reduction of hiss, and then go with the gate only if necessary.

The only reason I am messing with this pedal is due the nature of the Fender Vibrolux Reverb. I had used the MXR Distortion Plus with a Super Reverb and it worked flawlessly, except with much limited distortion when compared with the MT-2.

"Caps rolling is what people do who have no clue." Fromm does not state the kit reduces any kind of noise. It's advertized as a performance enhancing mod.
__________________
Venturing where the wise refuse to go, may or may not yield great revelations theretofore unknown; either with considerable expense.

Last edited by ITPhoenix; 17th September 2019 at 12:07 PM. Reason: Added a comment
  Reply With Quote
Old 17th September 2019, 02:23 PM   #20
Gnobuddy is offline Gnobuddy  Canada
diyAudio Member
 
Join Date: Mar 2016
Quote:
Originally Posted by voltwide View Post
To give an idea this is the PreAmp you heard in the sound sample:
I remember that you posted some details of your Tramp about a year ago.

The sound-clip you posted has a distortion level appropriate to blues or early ("classic") rock. But metal demands much, much, higher gain, and much harsher distortion.

For metal, you keep adding gain until the guitar stops sounding like a guitar, and begins to sound like a circular saw cutting through a tin roof, and then you add another 20 dB of gain for good measure.

I have a hypothesis that the music we love as adults echoes the ambient sounds we heard around us as children. For instance, classical Western music echoes the sounds of nature, with horns that sound like the bellowing of cows or antelope, the viol family that sounds like the human voice, etc. Some music of the time is quite explicit about this - Vivaldi's "Four Seasons", say, or Vaughan William's "The Lark Ascending". A few hundred years ago, that's what people heard around them as they grew up - the sounds of nature.

Classic rock echoes nature too, but a more aggressive side of nature. Thunder, growling predatory animals, things like that.

But IMO metal echoes the sounds of a big city in the mid to late 20th century: jackhammers tearing up the streets, big trucks accelerating with deafeningly loud growling engines, shrieking metallic train brakes, metal dumpsters being banged about and dragged along the concrete by the trash truck, et cetera. The sounds of tortured metal, in other words. The fact that the music is called "metal" isn't a coincidence!

So the purpose of a metal distortion pedal is to take a musical instrument, and make it sound like the worst part of inner-city Chicago in the 1980s. You need a lot of gain to do that!


-Gnobuddy

Quote:
Originally Posted by ITPhoenix View Post
I had an idea myself that is similar in its effect. I called it a "soft-gate", meaning it did not completely shut off the signal, but slowly attenuated it to near zero as the notes/chords decayed. The reason being that it would not be that noticeable.
It's a very old idea. Nearly fifty years ago, in the early 1970s, Phillips designed and sold their "Dynamic Noise Limiter", a circuit that rolled off treble frequencies, but only when the input signal was below a certain strength. It was intended to reduce playback hiss from the company's audio Compact Cassettes, and it worked quite well. (Then Dolby B came along, and took over much of the market.)

Google should turn up the DNL's schematic; I built one in my teens, and it did quite a good job of reducing cassette hiss as best I can recall. The circuit wasn't complex, being from the dawn of solid-state audio circuitry. But it used silicon epitaxial transistors and small-signal silicon diodes, so it didn't suffer from the problems of previous circuitry using germanium transistors.
Quote:
Originally Posted by ITPhoenix View Post
"Caps rolling is what people do who have no clue." Fromm does not state the kit reduces any kind of noise. It's advertized as a performance enhancing mod.
Changing the value (capacitance) of a cap can change the frequency response, which can be audible. But substituting one type of cap for a different (invariably more expensive) cap of the same value makes no audible change at all, despite legions of technically ignorant audiophiles making such claims.

Lots of people still do it, and usually convince themselves that they hear a change - which is very easy to do. We humans very routinely fool ourselves into hearing and seeing things that don't actually exist (Google "optical illusions" or "auditory illusions" for plenty of examples), so this sort of subjective impression is rarely meaningful, unless it's the result of a proper series of double-blind listening tests, followed by a proper statistical analysis to confirm that the test results are unlikely to have occurred by sheer chance.

I know nothing about Fromm or the kit in question - if the kit supplies different cap values from the original pedal, it might change the sound in a way that some musicians might prefer. If it only substitutes more expensive caps of the same value, though, then all it does is siphon money out of your wallet.


-Gnobuddy

Quote:
Originally Posted by ITPhoenix View Post
With the guitar plugged in and not outputting anything, the filter cap is isolating the the instrument, so I'm having trouble seeing the parallel resistance in this case.
The coupling cap isolates the instrument at DC - but the whole point of a coupling cap is that at the frequencies of interest, it couples the input signal through (because its reactance is infinite at DC, but falls as ~1/frequency .)

I said the same thing as PRR in post #2 - i.e., that the 1M resistor is shunted by the source impedance of the input signal.
Quote:
Originally Posted by ITPhoenix View Post
"You could tack-solder a resistor in parallel with that 220k NFB resistor to lower the gain, so you can easily remove it if you want to return the pedal to stock." This is a truism.
Remember, people sign up at diyAudio with varying levels of expertise in electronics. Some have essentially zero knowledge, others come in with Master's degrees in engineering and years of experience in the field. Most are nearer to the former than the latter end of the spectrum.

So, until I know better, I assume very little previous knowledge when responding to posts from a user I haven't encountered before. Not everyone realizes that it's easier to tack-solder an additional resistor in parallel, than to desolder and remove an existing resistor on a PCB and replace it with a different value. Not everyone even realizes that either thing accomplishes the same end-result in a negative feedback network.

So, it's a truism for you (good!) But not necessarily for everyone who posts here.


-Gnobuddy
  Reply With Quote

Reply


Reducing Fuzz Box Noise - Boss MT-2Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Reducing Hum and Noise Bonsai Construction Tips 12 19th March 2019 01:31 AM
Need Help with reducing noise of my boombox suyashpaliwal Power Supplies 2 7th June 2017 06:10 AM
Need help reducing noise of Amp! tommy1 Solid State 16 9th February 2010 05:52 PM
Reducing regulator noise. electron-ic Power Supplies 3 23rd March 2008 07:26 PM
boss hyper fuzz honsten Instruments and Amps 0 19th May 2004 09:36 PM


New To Site? Need Help?

All times are GMT. The time now is 07:59 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki