Editor's News & Views

Every external power supply puts out fairly clean DC power... it is your pedal that is noisy! Many boutique pedals do not have even the most basic power supply filtering so even the smallest noise or hum that is riding on the DC power input will be magnified by the gain of the circuit. Examples of this are the Fuzzface or LPB2 booster. Neither have any type of filtering on the voltage input, which was okay with the originals because they were battery powered and had no provisions for an external power source. However, boutique builders have cloned these circuits and added a power jack but without considering the necessary filtering that should be added to decouple the circuit from the power adapter. The result often is noise or hum in the audio signal.

A simple R-C filter is enough to eliminate the noise in most pedals and there is more information about them in the Lab Notebook. With high gain circuits and a switching power supply, an L-C circuit will be more effective and may be necessary to clean up the DC power completely.

There may be a tiny amount of noise or hum on the DC power adapter's voltage, but a well-designed pedal circuit can easily filter it out and eliminate the noise. A poorly designed clone pedal will just amplify any noise that makes its way in via the power jack. Put the blame where it belongs...

I recently had to cost out every item that went into a boutique clone box that I had made and was a little astonished to find that there was $57 worth of materials involved in making it, from pc board to electronic components to paint and decals. This doesn't include the labor involved in putting it together - at least 3 hours of construction time - and if you use $10 per hour for labor, that adds another $30 on to the cost. The cost of goods with direct labor is now up to $87 and there hasn't been a cent of profit yet.

While the boutique builder can save some money by buying parts in bulk, the critic who wants to knock off his design cannot purchase large quantities just for a copy or two.

I recently purchased some germanium transistors for about $1 each, but when sorted for leakage, two out of every three had to be thrown out, making the final cost $3.00 each! Germanium diodes are becoming more scarce and costlier, and exotic opamps are often demanded by the ever sophisticated players.

All of this means there is no such thing as a $10 guitar effect unless you are making the most basic design with no footswitch in an electrical junction box and no paint or decals. But the critcal audience is ever demanding more and boutique effects are expensive for a reason.

February 5, 2003 - Replacing Caps: Super Sound or Snake Oil? [CAUTION: RANT AHEAD]
There has been a lot of interest recently in upgrading commercial effects boxes by replacing the electrolytics with metal film capacitors and other audiophile quality parts for more transparent or hi-fi sounds. Also, some boutique builders hype the quality of the capacitors used in their designs.

There is no reason to replace electrolytic capacitors in effects boxes. Repeat after me... capacitor upgrades do not make any audible difference in stompboxes.

Cyril Bateman has published a very extensive evaluation of capacitors in recent issues of Electronics World. Some basic information can be extracted from this series for our purposes.

• Tantalum capacitors produce at least 10 times more distortion than even a cheap electrolytic
• Low ESR is always best
• Electrolytics are inductive at audio frequencies
• Electrolytics should be biased to reduce distortion
• Electrolytic distortion is mostly third harmonic

Buy low ESR capacitors, but consider that the distortion that is produced by the capacitor is on the order of 0.001% and the distortion from clipping runs in the double digits (>10%). Even if you replace 4 or 5 capacitors in a circuit with perfect devices you can only eliminate the 0.005% that they could possibly contribute (and I'm being very generous here).

Typically a stompbox is designed to be powered by a single supply voltage which means that most of the circuit points that are connected to an electrolytic capacitor will have a DC voltage bias present. The typical 4.5v value is a good bias level for most capacitors which further serves to reduce the distortion. This means that the distortion produced by the capacitor is probably reduced to 0.0005% or less.

While electrolytic distortion is mostly third harmonic, so is the distortion produced by diode clippers or saturated transistors and at a level 10,000 times stronger or more. You cannot hear the capacitor's contribution under these conditions, nor can you hear it in chorus or phaser devices where all kinds of phase and delay transitions are filling the audio spectrum. The average listener struggles to hear 1% distortion in a pure audio signal and 0.001% is far below the threshold of perception. A very clean (audiophile) vacuum tube amplifier produces 0.1% THD (total harmonic distortion) and some models will go as high as 2.0% at full power (DHT monoblocks).

Douglas Self, a well-known expert in audio electronic design has the following to say about the limits of perception and the abilities of the human ear:

"The smallest step-change in amplitude that can be detected is about 0.3dB for a pure tone. In more realistic situations it is 0.5 to 1.0dB. This is about a 10% change. The smallest detectable change in frequency of a tone is about 0.2% in the band 500Hz-2kHz. In percentage terms, this is the parameter for which the ear is most sensitive. With mostly low-order harmonics present the just-detectable amount is about 1%, though crossover-distortion can be perceived at 0.3%, and probably lower. There is certainly no evidence that an amplifier producing 0.001% THD sounds any cleaner than one producing .005%"

When should you change the capacitors in an effect box? You should only switch out electrolytics in order to accomplish a specific electronic purpose, i.e. more filtering on a power supply or for altering the frequency response of a gain stage. Old effects may have capacitors in which the electrolyte has dried up or leaked out and these are defective parts that need replacing. Switching electrolytics for metal film caps of the same value (uF) is a waste of time and money. Brand new Boss pedals do not need to have capacitors "upgraded"! (Note: Many of the people modifying Boss pedals make other changes to the circuitry that are certainly audible and do change the tone and response.)

Boss and Ibanez pedals have jfet switching systems that introduce much more distortion into the circuit than any capacitor ever could - even when bypassed. The signal passes through two jfets that do not have the proper bias network for minimum distortion. If you want to improve the sound of those pedals, eliminate the jfets from the signal path and you'll get much more "hi-fi" response than any other mod you could do to them.

Repeat after me... capacitor upgrades do not make any audible difference in stompboxes. Read the Capacitor FAQ for more info...

Update: From the emails I have received, this commentary has struck a few nerves... get over it. Make two identical pedals except for the capacitors (electrolytic vs. metalfilm) and then listen to them on identical settings with your back turned to the pedals and someone else switching them in and out... prepare to be enlightened.
Still more: Just to clarify for those who miss the point, this is about selecting new capacitors when building a circuit or replacing electrolytics in brand new commercial pedals. Old pedals or new pedals that are made with old "surplus" capacitors may have electrolytics that need replacing because they have become defective or were sub-standard low quality to begin with.
Just for fun: Read about the Rockstar's New Stompbox.
Mica capacitors have also been recommended for stompbox use. Walter Jung, one of the most knowledgeable audio circuit experts, said about mica, "They are nowhere nearly as bad as ceramics or the Al and Ta oxides, but neither are they as good as the films."
Fall 2003 Update: So you think changing capacitors makes a difference? Well, are you breaking them in? New capacitors require break-in time to get the best sound... so build you own device to break-in capacitors before installing them in your stompbox! (removes tongue from cheek)

May 14, 2000 - 20 Commandments of FX Design

1. Analog rules.
2. Exotic opamps usually aren't any better than regular opamps for FX.
3. True bypass will not fix a crappy sounding effect.
4. Ge transistors do not guarantee a good sounding unit by themselves.
5. Oxygen-free hookup wire doesn't make a bypass switch sound any more transparent.
6. A Mil-Spec doesn't mean the part is any better than commercially available parts.
7. You cannot truly imitate tubes with transistors; not even jfets.
8. All 4558 opamps sound the same in Tube Screamers.
9. Starved-plate tube circuits don't really sound that great.
10. Double sided pc boards with plated-through holes aren't any better than single-sided boards.
11. High gain usually means high noise.
12. An effect that sounds great today, may not sound so hot tomorrow.
13. Gold and silver plated jacks are attractive but that's all.
14. Using plastic enclosures does not mean the device will pick up hum.
15. Clean boost does not come from an overdrive unit.
16. True Class A doesn't mean anything in FX circuits.
17. Jfets are just as static-resistant as bipolar transistors.
18. If there is a chance to put the transistors in wrong, you probably did.
19. Fresh 9v batteries all sound the same.
20. Just using a vintage pedal never made anyone a guitar legend.

    ©2000 by Jack Orman

May 4, 2000 - Cookbook Circuits? [CAUTION: RANT AHEAD]
I'm fired up for a major rant this month since this is a subject that really irritates me. I have seen the comment more than once from someone on a message board that "XYZ Project is just a cookbook circuit". On occasion it has been addressed at me and/or one of my projects. It seems to be the intent of the person making the comment to denigrate the circuit design, the ability of the designer and/or the utility of the project. Without fail, the person making the remark has no web page of designs and has never contributed anything to the fx community in the way of creating a new circuit.

Electronic circuit application notes are an excellent source of reference for beginning a new design. Almost every circuit from a TS-808 to your television set is made by combining the building blocks from circuit cookbooks to make an end-use product for a specific application. Craig Anderton made a reputation by adapting cookbook circuits for use by musicians and there is absolutely nothing wrong with that.

There are very few applications that will work properly for music use straight from the reference - in fact, many will not work at all! It takes a lot of time and effort to make the necessary changes, select the right components, draw the schematic, design the pcb, build and test a prototype, write the article and then share it freely with others on a web page. Whew! Sounds like a lot of effort to put into a project, and it is.

A good example is the mini-booster circuit and while the most basic form comes from an out-of-print application book by National Semiconductor, there is only one simple drawing and exactly 47 words of text about the circuit in the book; the last sentence of which is misleading and unnecessary. Every other aspect of the mini-booster SRPP circuit is derived from my article and projects that use the circuit. Everything. Make the circuit as shown in the cookbook and you'll be disappointed - make some other version and you'll be delighted... but that version would not be available if not for the work that I did with the "cookbook circuit".

I spent many hours testing other jfets to determine which work best, revising the components for lower noise, adding features for frequency and gain control and tweaking the components to make a mature funtional block for fx and audio use. Yet some bozo had nerve enough to comment that "it's basically a cookbook ciruit". Screw you bozo.

Many times making a new design is about voicing... optimising the circuit for the best sounds with the instrument that it is intended to work with. Other times it involves adapting an op-amp circuit block to work from a single supply voltage. Sometimes a simple new feature makes a big difference in how a circuit sounds.

Let's look at how you would proceed with creating a fuzz design. Basically, they are all preamps followed by clippers with a tone control on the output.

• Preamp
  • Op-amps?
  • Inverting or non-inverting?
  • How much gain?
  • Low frequency rolloff?
• Clippers
  • Diodes?
  • Overdriven gain stage?
  • Ge diodes? Si? both? Something else?
  • Current limit resistor? Cap to reduce harshness?
• Tone control
  • Active or passive?
  • Use another op-amp? Transistors?
  • Midrange?
  • What frequencies to effect?
• Output buffer?
• Fine-tune the Voicing?

In a quick scan through the Musician's Friend catalog, the Real Tubes 901 is called an overdrive and the Budda Phatman is called a distortion... both of which contain tubes. The Big Muff is also called a distortion but then so is the Boss Metal Zone. I guarantee you neither of them sound like the Phatman. The Bixonic Expandora claims to go from crunch to overdrive to distortion as the Gain control is turned up. Crunch?

The real deal is that there is no real distinction between the descriptive labels applied to signal distorting effects boxes. All of them are boosting the signal; some are overdriving gain stages and others are using clipping diodes. All create distortion and add harmonics. However, in general terms I usually use them in the following order from mildest to the most heavy: crunch - overdrive - distortion - fuzz.

Once again (as always), let you ears be the guide and don't use labels as a guideline for making decisions on what crunch/overdrive/distortion/fuzz unit to buy.

Let's skip over the obvious copyright issues because just as important is another reason, which may be explained by the following example. Someone copied a project of mine to their own web site not long after it was posted. I had made a small typo on the pc board layout when I originally drew it up but the error prevented the circuit from working. I found the error and corrected it very soon after posting but the person who copied my files still had the original layout on their web site. A visitor to their site many months down the road used the original flawed pc layout to make the device and could not get it to work. So they e-mailed the person who ran the web site, who knew next to nothing about circuits design, and of course, that person referred the irritated effects builder to me. After many e-mails back-and-forth and several hours of my time invested, I discovered what was the problem and got the device working for the person. Of course, the builder remained agitated at me because the flawed pc layout was what he had used.

Bottom line? Do everybody a favor and do not copy files to your web site. Use links instead. I almost never change the link names and that way your links will always be pointed to the most current and correct files. Thanks.

February 12, 2000 - Clean Boost... NOT! [CAUTION: RANT AHEAD]
A good clean boost can bring out new and different sounds from an amplifier, or overdrive it for just the right touch of distortion. I keep the AMZ Dual Booster in my studio for just this purpose and it works great. The Mini-Booster is another of my projects that can readily fill this need.

All too often, I see postings on newsgroups or message boards asking for recommendations on a device to use for clean boost. Without fail, the clueless will chime in and suggest one of the many boutique TS clones claiming it will give clean boost and a 'transparent sound'. Get real! They are distortion boxes; there is nothing clean about them, no matter how low you turn down the drive control. Furthermore, the frequency response of the circuit is shaped to provide a pleasing sound when the guitar signal is distorted. Both the bottom and top ends of the signal response are restricted giving the device a mid-range heavy sound. This works out good for the distortion but clearly is not transparent. Other boutique distortions that are sometimes suggested for clean boost have much the same problems and do not serve the purpose any better. They are distortions; use them for that and get something better suited for clean boost.

If you are not into DiY projects or cannot find anyone to make one of the above mentioned projects for you, the MXR Micro-Amp is a good choice for clean boost. Also, one of the 7 band EQs in a stompbox can also be used and if the sound does need a little tuning to get the most from your amp then a touch of the slider will bring it out.

The amount of bad advice on the newsgroups is staggering. A newbie can post just like an expert will and there are not many ways to discern the skill or expertise of the writer from a short message. Always remember what NET stands for: Not Entirely True. Don't believe everything that you read on the Internet... except for what I write, of course  

June 12, 2003 - Is it Okay to Clone?
Read my article about the legalities of copying a commercial pedal design.