Reducing noise with with low effect volume and clean boost?

[iamjackslackof]

Hi all,

I'm trying to reduce the noise floor of some of my effects, especially my main OD, a Skreddy Screwdriver. The noise is quite noticeable when I dime the volume pot to get the output level I want, so my idea was to keep it low, and use a transparent clean boost at the end of my signal chain to bring up the total volume to where I want it.

So far I don't have any true clean boosts, but I've used a rangemaster and an EP-3, and I'm still getting a comparable amount of noise. Power-wise, I have a conditioning powerstrip, feeding my Harley Benton PSUs (which I think are isolated?), and each effect getting it's own power (no daisychaining).

I know there's a lot of factors that go into noise, so I'm trying to cover all my bases, and it seemed to me that a clean boost might be an easy way to get some volume without increasing it.

So any recommendations on a quiet clean boost? I'm looking at the Transcendence Boost, but I'm open to suggestions.

Also, is it worth considering shielded inputs/outputs on my pedal jacks?

Thanks!

 

[Alan W]

I’m a big fan of the Transcendence boost. I’m not sure how well it will do what you want at the end of the chain—it will amplify whatever noise is in the chain along with your signal. How much overhead does the Screwdriver have? If it can handle it, you might want to try a clean boost going into it; this ups you signal strength, adds little noise while doing it, and then whatever noise the Screwdriver adds will be lessened, relative to the signal strength.

When you turn up the volume pot on the Skreddy, does the sound change much besides getting noisier? If you like the sound at the lower level, but want it louder, it’s worth a shot I think. If nothing else, I think everyone should own a nice clean boost.

Possibly someone can chip in with knowledge about running the Skreddy at more than 9 v; if it can take it, you’d get increased headroom, and possibly lower noise. I’m also not aware of how quiet the Benton PS are; even if the outputs are isolated, it doesn’t mean they are quiet.

I’m not going to comment on the shielding idea; I just do this habitually, and know that it has helped with LFO interference, but on boost type pedals, it’s of questionable effectiveness.

 

[iamjackslackof]

Thanks @Alan W ! I will try the Screwdriver at 18V, as well as a clean boost in front. I have the Transcendence in my cart as we speak lol.

I love the basic tone I get with the Screwdriver, and the volume knob only seems to adjust output volume and not the tone, so I may be able to get away with a boost in front. I may already have it 18V as well, I forget. I've built lots of pedals, but I'm still a noob when it comes to signal chains and battling noise and all that stuff, so I appreciate the advice.

 

[HamishR]

I wonder if a different AC127 will help reduce noise in your Screwdriver? I've built a few and noise has never really been an issue with the Screwdriver. But Ge transistors can vary considerably in how much noise they generate.

 

[giovanni]

What kind of noise are we talking about? Is it main hum? Or just hiss caused by high gain?

 

[Feral Feline]

Sticking a boost in front will push the Screwdriver into more distortion sooner — not necessarily giving it more output vol with better SNR.

 

[swyse]

I have a couple suggestions, but they might be more than you're looking to do. This circuit is kinda like a hybrid fuzz face with a SHO in front of it, and the problem with this is the fuzz face isn't known for it's low noise and mosfets are inherently kinda noisy themselves.
My first suggestion is trying to add more filtering, or perhaps the capacitance multiplier boss uses, although this will cost you some voltage so it might not be ideal, you can see an example of this here
My second suggestion is a circuit redesign where you ditch the SHO section for an op amp boost, which also might not be ideal because you may not get the exact same character as the mosfet boost.

 

[iamjackslackof]

I wonder if a different AC127 will help reduce noise in your Screwdriver?

I hadn't thought about that, but I will swap it out and see.

What kind of noise are we talking about? Is it main hum? Or just hiss caused by high gain?

I'm not sure how to tell. I'm assuming it's high gain hiss, as it gets louder when I up the volume knob.

 

[giovanni]

I hadn't thought about that, but I will swap it out and see.

I'm not sure how to tell. I'm assuming it's high gain hiss, as it gets louder when I up the volume knob.

Humbuckers or single coils?

 

[iamjackslackof]

Humbuckers. I will say it's not terrible, but in general I would like to reduce the noise floor of my rig, and I'm assuming this is a major source. I do have quite a few pedals in my chain, though only a few are on at any given time. I did build a noise gate, which works great, but it clamps down to hard when I roll back my volume to clean up, so I can't really use it much. I'm using custom soldered cables I made as well, Mogami + SP400s.

 

[giovanni]

What model power supply do you have? With humbuckers you should have a pretty quiet rig unless you are running some crazy amount of gain. Do you get noise with just the Skreddy powered from a battery?

 

[eh là bas ma]

I have a cheap noisy industrial overdrive that I like, it can get so noisy with the treble above 12' that I had to do something...

This worked with it and with every other noisy circuits :

The Noisegate - Noisegate kit, 20,00

This is a simple noise gate that cuts off the signal once the level falls below the threshold set This kit contains all parts you need to build a fully f

www.musikding.de

 

[JTEX]

I've done quite a bit of research in low noise design for guitar stuff (and not only). The only way that I managed to reduce overall noise when dimming the guitar volume pot is to install a quiet, onboard active buffer with a low value volume pot after it. I'd suggest a 10k pot or even lower. I use a 1k volume pot, which is fine as long as your buffer can deal with a 1k load.

A typical passive guitar pickup has a DC resistance of about 5k for singles and 10k for humbuckers (more or less - this is a simplification). This resistance dictates the absolute lowest noise level (hiss) theoretically achievable, since any resistor (or resistive component of a coil) will have a noise voltage across it (Johnson noise, or thermal noise). If you follow a 10k pickup with a 500k volume pot, you will significantly degrade the noise floor as soon as you dim the pot, since you're introducing tens, if not hundreds, of noise-making kiloohms in series with the 10k pickup. If you've ever wondered why hiss actually goes UP when you dim the volume pot, reaching a maximum somewhere around the middle of the pot rotation, this is why.

Basically, you need an onboard buffer with lower self noise than a 5k or 10k resistor, followed by a low value pot. You can't make this into a pedal, because by the time the signal gets to it from the guitar, the hiss from the 250k-500k volume pot is already baked in.

Trust me, if you go this way, you'll never again accept the amount of hiss that comes from the conventional guitar setups.

Of all ICs I've tried for such buffer, OPA207 is my favorite. Low noise and low power. Surface mount, though -- like all good ICs these days.

 

[iamjackslackof]

@JTEX Thank you for this, very interesting stuff that I've never seen discussed before.

 

[JTEX]

@JTEX Thank you for this, very interesting stuff that I've never seen discussed before.

You're welcome. It later occurred to me that you can work around the need to have the buffer onboard by incorporating it into a buffered volume pedal (as the first thing in your pedal chain), and using the guitar volume pot as an on/off switch, either 100% or 0%, where it does not contribute any excess hiss. But this is not the most elegant solution IMO, unless you already like using a volume pedal.

 

[Passinwind]

I've done quite a bit of research in low noise design for guitar stuff (and not only). The only way that I managed to reduce overall noise when dimming the guitar volume pot is to install a quiet, onboard active buffer with a low value volume pot after it. I'd suggest a 10k pot or even lower. I use a 1k volume pot, which is fine as long as your buffer can deal with a 1k load.

A typical passive guitar pickup has a DC resistance of about 5k for singles and 10k for humbuckers (more or less - this is a simplification). This resistance dictates the absolute lowest noise level (hiss) theoretically achievable, since any resistor (or resistive component of a coil) will have a noise voltage across it (Johnson noise, or thermal noise). If you follow a 10k pickup with a 500k volume pot, you will significantly degrade the noise floor as soon as you dim the pot, since you're introducing tens, if not hundreds, of noise-making kiloohms in series with the 10k pickup. If you've ever wondered why hiss actually goes UP when you dim the volume pot, reaching a maximum somewhere around the middle of the pot rotation, this is why.

Basically, you need an onboard buffer with lower self noise than a 5k or 10k resistor, followed by a low value pot. You can't make this into a pedal, because by the time the signal gets to it from the guitar, the hiss from the 250k-500k volume pot is already baked in.

Trust me, if you go this way, you'll never again accept the amount of hiss that comes from the conventional guitar setups.

Of all ICs I've tried for such buffer, OPA207 is my favorite. Low noise and low power. Surface mount, though -- like all good ICs these days.

I have a bunch of OPA207 sitting unused, and I figured all along that the specs implied they would be best used for my purposes as buffers. Into the work queue this goes!

 

[JTEX]

I have a bunch of OPA207 sitting unused...

I have OPA2205/2206 on my radar for future projects. They were not yet available a couple of years back when I could have used them, but they are now. They seem even better than OPA207 (same noise but at lower idle current, and dual!). Pricey though.

Keep in mind that I am heavily biased towards low power parts, since I do mostly onboard, battery-powered stuff. If you can spare a few mA, there are many more options.

You can have low power, low noise and low cost -- but you have to pick two!

BTW, how low is low enough noise in a buffer? A 5k resistor (single coil pickup) has a self noise of about 9nV/sqrt(Hz) over a 20k bandwidth. A 10k humbucker is at ~13nV/sqrt(Hz). So, I'd say that 7 or 8 nV/sqrt(Hz) is good enough for an op amp used in a guitar buffer. Going much lower will cost more (in $ and power), while provining diminishing returns.

 

[Passinwind]

I have OPA2205/2206 on my radar for future projects. They were not yet available a couple of years back when I could have used them, but they are now. They seem even better than OPA207 (same noise but at lower idle current, and dual!). Pricey though.

Keep in mind that I am heavily biased towards low power parts, since I do mostly onboard, battery-powered stuff. If you can spare a few mA, there are many more options.

You can have low power, low noise and low cost -- but you have to pick two!

BTW, how low is low enough noise in a buffer? A 5k resistor (single coil pickup) has a self noise of about 9nV/sqrt(Hz) over a 20k bandwidth. A 10k humbucker is at ~13nV/sqrt(Hz). So, I'd say that 7 or 8 nV/sqrt(Hz) is good enough for an op amp used in a guitar buffer. Going much lower will cost more (in $ and power), while providing diminishing returns.

I like and need low power parts in many instances, but the pedals I've been using recently have afforded the chance to branch out and try some of the newer moderately priced moderate current ones like OPA1641/1642 and OPA1655/1656. And as you say, dimishing returns kick in sooner than later. A bass with a -70dB noise floor doesn't necessarily benefit fully from a preamp sitting at -105, but somehow that doesn't keep me from continuing to make them!

 

[JTEX]

I like and need low power parts in many instances, but [...]

Guitars benefit more than basses from low noise circuitry, since they're often used with effects chains with lots of gain.

 

[Passinwind]

Guitars benefit more than basses from low noise circuitry, since they're often used with effects chains with lots of gain.

Great food for thought, and I‘ve only been focusing on acoustic-electric guitar when I could be working on stuff for electric too.