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Some basics about inductors, diodes, output, etc.

4/10/1999 7:38 PM
Mark Hammer	Some basics about inductors, diodes, output, etc. There are a bunch of misconceptions floating around in this thread, many of which stem from widespread misuse of terms, and some of which are the product of simply being new at this. So, I'll stick on my teacher's hat, and try and clear things up. Hope I don't don't sound too caustic or condescending. 1) Pickups don't have "gain", they have "output". Gain implies that some initial signal has been amplified, which is not the case with regular passive, magnetic pickups, until AFTER the pickup signal has gone somewhere that amplifies. The amplitude of the pickup output varies as a function of many things, but for practical purposes, lets say it varies as a function of: - the degree to which the string influences the magnetic field that the pickup coil is wound around (which also implies pick attack, string size, composition of the string, how close the poles are to the string itself, etc.) - the nature of the magnetic field to be influenced (which also implies the strength of the magnet, the physical dimensions and layout of polepieces/rails, whether the opposite poles are at the top and bottom of the pickup or in a side-by-side humbucker configuration, Lace-like magnetic variations, influence of metal plates and Tele bridges, etc.) - the nature of the coil which will translate that into a voltage (which implies # turns, physical relationship of coil to polepieces and shape of coil, wire gauge, etc.) 2) Because pickups themselves don't have gain, that means that (unless you stick in active electronics) anything tacked between the pickups and the output jack can only TAKE AWAY from the signal. So volume and tone controls, no matter what their design, can only alter the degree to which components of the pickup signal are removed. I know people talk about the apparent increase in high end when pot values are increased, but this is not an increase, merely a reduction in how much is normally removed by lower-value pots. 3) Because any additional circuitry REMOVES signal, anything after the guitar that needs a larger amplitude signal to work the magic it is famous for (i.e., overdrive, fuzz, compressor, etc.) may not work as optimally when the signal coming out of the guitar has been altered by an assortment of controls (tone, volume, midrange cut, etc.). This is but one of the reasons why some guitarists disable some or all of the controls on their guitars, and why some makes of guitar have a switch function that can cut out adjunct circuitry. This arrangement allows the maximum signal from the existing pickups to exit the guitar. This also means that what can be advertised or talked about as a terrific mod may be very useful when a clean, unclipped sound is desired, but simply get in the way when the used seeks to push the pre-amp of another device, but with a different guitar voicing. What you do to get that other voicing (e.g., use of mid-cut) may push your guitar output below the desired amplitude range for driving the next stage. 4) Although pickups don't have gain, and normal passive controls eat signal in order to shape it, most of the attendant problems can be surmounted by use of a simple onboard preamp, something with just enough gain to compensate for the effects of passive tone controls. If you use a discrete transistor pre-amp, these can run off of minimal current, and voltages lower than 9v, so you don't need to route anything or have a large control-cavity to take advantage of them. A transistor, couple of caps and resistors, couple of 3v lithium calculator batteries, and away you go. 5) Pickups have resonances that are the product of all those parameters that influence output signal (including whether pickups are in series or parallel), and such resonances are reinforced or offset by the guitar the pickup is installed in. Whereas normal "tone" controls simply cut out anything higher than a certain frequency range (i.e., they are very broad is effect, and not tuned), inductor-based tone circuits are reasonably frequency-selective. This means that they may be tuned to a frequency-band which is not optimal for that guitar, even though that band may be quite good-sounding for a different pickup and guitar. The ideal is to have a tapped inductor/choke, and several capacitors, to select from, perhaps with dipswitches inside the control cavity, so that the ideal midrange can be identified for that particular guitar. Just as important, too, whereas a treble-cut signal can still be quite substantial in amplitude (high end being the teeniest part of the signal), and drive the bejeezus out of a distortion unit, a mid-cut signal may have a considerably large drop in amplitude because the range where the cut is may be the strongest part of the original signal, and cutting that mid-band guts the sound. DO NOT confuse a stompbox with high and low end boosted to achieve a mid-scoop, with a passive guitar that has had the midrange excised with an inductor circuit. The dip in frequency-response may well be in the same place, but how it got there can make all the difference in the world.

4/10/1999 7:38 PM

Mark Hammer

Some basics about inductors, diodes, output, etc.

There are a bunch of misconceptions floating around in this thread, many of which stem from widespread misuse of terms, and some of which are the product of simply being new at this. So, I'll stick on my teacher's hat, and try and clear things up. Hope I don't don't sound too caustic or condescending.

1) Pickups don't have "gain", they have "output". Gain implies that some initial signal has been amplified, which is not the case with regular passive, magnetic pickups, until AFTER the pickup signal has gone somewhere that amplifies. The amplitude of the pickup output varies as a function of many things, but for practical purposes, lets say it varies as a function of:
- the degree to which the string influences the magnetic field that the pickup coil is wound around (which also implies pick attack, string size, composition of the string, how close the poles are to the string itself, etc.)
- the nature of the magnetic field to be influenced (which also implies the strength of the magnet, the physical dimensions and layout of polepieces/rails, whether the opposite poles are at the top and bottom of the pickup or in a side-by-side humbucker configuration, Lace-like magnetic variations, influence of metal plates and Tele bridges, etc.)
- the nature of the coil which will translate that into a voltage (which implies # turns, physical relationship of coil to polepieces and shape of coil, wire gauge, etc.)

2) Because pickups themselves don't have gain, that means that (unless you stick in active electronics) anything tacked between the pickups and the output jack can only TAKE AWAY from the signal. So volume and tone controls, no matter what their design, can only alter the degree to which components of the pickup signal are removed. I know people talk about the apparent increase in high end when pot values are increased, but this is not an increase, merely a reduction in how much is normally removed by lower-value pots.

3) Because any additional circuitry REMOVES signal, anything after the guitar that needs a larger amplitude signal to work the magic it is famous for (i.e., overdrive, fuzz, compressor, etc.) may not work as optimally when the signal coming out of the guitar has been altered by an assortment of controls (tone, volume, midrange cut, etc.). This is but one of the reasons why some guitarists disable some or all of the controls on their guitars, and why some makes of guitar have a switch function that can cut out adjunct circuitry. This arrangement allows the maximum signal from the existing pickups to exit the guitar. This also means that what can be advertised or talked about as a terrific mod may be very useful when a clean, unclipped sound is desired, but simply get in the way when the used seeks to push the pre-amp of another device, but with a different guitar voicing. What you do to get that other voicing (e.g., use of mid-cut) may push your guitar output below the desired amplitude range for driving the next stage.

4) Although pickups don't have gain, and normal passive controls eat signal in order to shape it, most of the attendant problems can be surmounted by use of a simple onboard preamp, something with just enough gain to compensate for the effects of passive tone controls. If you use a discrete transistor pre-amp, these can run off of minimal current, and voltages lower than 9v, so you don't need to route anything or have a large control-cavity to take advantage of them. A transistor, couple of caps and resistors, couple of 3v lithium calculator batteries, and away you go.

5) Pickups have resonances that are the product of all those parameters that influence output signal (including whether pickups are in series or parallel), and such resonances are reinforced or offset by the guitar the pickup is installed in. Whereas normal "tone" controls simply cut out anything higher than a certain frequency range (i.e., they are very broad is effect, and not tuned), inductor-based tone circuits are reasonably frequency-selective. This means that they may be tuned to a frequency-band which is not optimal for that guitar, even though that band may be quite good-sounding for a different pickup and guitar. The ideal is to have a tapped inductor/choke, and several capacitors, to select from, perhaps with dipswitches inside the control cavity, so that the ideal midrange can be identified for that particular guitar.
Just as important, too, whereas a treble-cut signal can still be quite substantial in amplitude (high end being the teeniest part of the signal), and drive the bejeezus out of a distortion unit, a mid-cut signal may have a considerably large drop in amplitude because the range where the cut is may be the strongest part of the original signal, and cutting that mid-band guts the sound. DO NOT confuse a stompbox with high and low end boosted to achieve a mid-scoop, with a passive guitar that has had the midrange excised with an inductor circuit. The dip in frequency-response may well be in the same place, but how it got there can make all the difference in the world.

4/10/1999 8:27 PM
Blues Lyne	DO NOT confuse a stompbox with high and low end boosted to achieve a mid-scoop, with a passive guitar that has had the midrange excised with an inductor circuit. The dip in frequency-response may well be in the same place, but how it got there can make all the difference in the world. This is definately true. A mid-cut on a guitar, ala Torres, can be used to clean up your tone when going into a slightly overdriven tube amp or to get a somewhat acoustic sound out of electrics. I had one in a Yamaha Weddington, basically a Les Paul type guitar with fairly hot humbuckers. I liked it alot since I was playing into a slightly distorted amp and could dial out some mids for clean strummed type rhythm. It doesn't seem like it would be as effective on single coils. I've got some Tom Holmes PAF style humbuckers in that guitar now and I find the mid control less useful since there are less mids in the pickups to begin with. It definatly is not going to help if you are going for a scooped mid distortion type thing. Blues

4/10/1999 8:27 PM

Blues Lyne

DO NOT confuse a stompbox with high and low end boosted to achieve a mid-scoop, with a passive guitar that has had the midrange excised with an inductor circuit. The dip in frequency-response may well be in the same place, but how it got there can make all the difference in the world.

This is definately true. A mid-cut on a guitar, ala Torres, can be used to clean up your tone when going into a slightly overdriven tube amp or to get a somewhat acoustic sound out of electrics. I had one in a Yamaha Weddington, basically a Les Paul type guitar with fairly hot humbuckers. I liked it alot since I was playing into a slightly distorted amp and could dial out some mids for clean strummed type rhythm. It doesn't seem like it would be as effective on single coils. I've got some Tom Holmes PAF style humbuckers in that guitar now and I find the mid control less useful since there are less mids in the pickups to begin with. It definatly is not going to help if you are going for a scooped mid distortion type thing.

Blues

4/14/1999 2:24 AM
Steve A.	Blues: As you say, the passive mid-cut control will decrease distortion and clean up a dirty signal (or sweeten up an already clean signal). You can also set it way low to get an "acoustic-like" sound from single coil pickups (never fooled me, but it does get a different tone). For strats, I like to use the passive mid-boost control to tame the bridge pickup a bit (yes, it actually cuts the highs and lows to "boost" the mids; in any case it is a lot easier on the ears!) Or use the mid-cut on the notched positions to get a sound like Buddy Guy from the early 60's (when the Chess Bros told him to turn down that sh*t!) I never liked having 2 seperate treble-cut tone controls on a strat so I usually stick a push-pull pot wired up as a master mid-cut/mid-boost-cut control in the middle and a master TBX on the bottom. While I may not use either control that much, I like having them there when I do need them. You can find the wiring for the pp mid pot on the FrankenStrat harness on my site: http://www.techaccessinc.com/blueguitar/franken1.gif" TARGET="_top">http://www.techaccessinc.com/blueguitar/franken1.gif Steve Ahola P.S. The 1.5H inductor uses the primary windings (not CT) of a TL021 audio transformer from Mouser. Or buy them from Torres for twice as much...

4/14/1999 2:24 AM

Steve A.

Blues:

As you say, the passive mid-cut control will decrease distortion and clean up a dirty signal (or sweeten up an already clean signal). You can also set it way low to get an "acoustic-like" sound from single coil pickups (never fooled me, but it does get a different tone). For strats, I like to use the passive mid-boost control to tame the bridge pickup a bit (yes, it actually cuts the highs and lows to "boost" the mids; in any case it is a lot easier on the ears!) Or use the mid-cut on the notched positions to get a sound like Buddy Guy from the early 60's (when the Chess Bros told him to turn down that sh*t!)

I never liked having 2 seperate treble-cut tone controls on a strat so I usually stick a push-pull pot wired up as a master mid-cut/mid-boost-cut control in the middle and a master TBX on the bottom. While I may not use either control that much, I like having them there when I do need them. You can find the wiring for the pp mid pot on the FrankenStrat harness on my site:

http://www.techaccessinc.com/blueguitar/franken1.gif" TARGET="_top">http://www.techaccessinc.com/blueguitar/franken1.gif

Steve Ahola

P.S. The 1.5H inductor uses the primary windings (not CT) of a TL021 audio transformer from Mouser. Or buy them from Torres for twice as much...

4/11/1999 3:32 AM
David Manson	Thanks.. that helps out alot.. I'm still wondering about the last guy's suggestion with the diode in the guitar... normally it would be in a pedal or in the amp.. but that is interesting.. My marshall also gets most of its distortion from diodes..(from what i hear) and i'm wondering if i can put in different diodes.. (i know they are LED's -- i've seen them) or put more diodes inside... do they work this way? some more basics please... thanks..

4/11/1999 3:32 AM

David Manson

Thanks.. that helps out alot.. I'm still wondering about the last guy's suggestion with the diode in the guitar... normally it would be in a pedal or in the amp.. but that is interesting.. My marshall also gets most of its distortion from diodes..(from what i hear)
and i'm wondering if i can put in different diodes.. (i know they are LED's -- i've seen them) or put more diodes inside... do they work this way? some more basics please...

thanks..

4/12/1999 3:15 PM
Mark Hammer	If you check out the various distortion-related threads in the effects forums here, you'll find out more than you ever wanted to know about them. If you look in various ancient 101 Easy-to-Build Electronic projects books and mags, you will see lots of mention of using diodes for clipping, or maintaining a steady Ham radio mic volume, among other things. What you should realize, however, is that the diodes will do little clipping if the signal going into them isn't already above their clipping threshold. Any fuzz player knows that if you turn down the fuzz and guitar volume and strum gently, the sound produced isn't much different than the straight sound. The question you need to ask is whether the signal produced by pickups alone will be enough to result in clipping, using diodes alone (i.e., no pre-boosting). The answer is no. I've built all kinds of pickups with very high output, and even with a Pete Townsend "birdman" swipe at the strings, you won't get much above 200-300mv much of the time. Consider that many pickups are lower output than that, that most playing consists of more than power chords, and that volume and tone controls figure into it, and you quickly realize that a diode with a half-volt clipping threshold isn't going to be doing much clipping. If you check out the various schematics for fuzz devices found at many of the websites, you will see that they all involves an initial amplification stage, that boosts the overall signal high enough that it will almost always be above the clipping threshold of any diodes that follow it. That being said, there are all kinds of places where you can shove a diode pair in to get a little more distortion. E.g., most phase shifters have an initial op-amp stage to buffer the input. You can easily stick a diode pair in there to get a little more grit from your phase shifter. Wanna get wacky? Stick a diode pair after the regeneration control in your delay line and crank that sucker up high enough to produce lots of repetitions. Every repeat will get fuzzier. In each of these applications there will be a signal level that is high enough to produce clipping when the diodes are inserted.

4/12/1999 3:15 PM

Mark Hammer

If you check out the various distortion-related threads in the effects forums here, you'll find out more than you ever wanted to know about them.

If you look in various ancient 101 Easy-to-Build Electronic projects books and mags, you will see lots of mention of using diodes for clipping, or maintaining a steady Ham radio mic volume, among other things. What you should realize, however, is that the diodes will do little clipping if the signal going into them isn't already above their clipping threshold. Any fuzz player knows that if you turn down the fuzz and guitar volume and strum gently, the sound produced isn't much different than the straight sound.

The question you need to ask is whether the signal produced by pickups alone will be enough to result in clipping, using diodes alone (i.e., no pre-boosting). The answer is no. I've built all kinds of pickups with very high output, and even with a Pete Townsend "birdman" swipe at the strings, you won't get much above 200-300mv much of the time. Consider that many pickups are lower output than that, that most playing consists of more than power chords, and that volume and tone controls figure into it, and you quickly realize that a diode with a half-volt clipping threshold isn't going to be doing much clipping. If you check out the various schematics for fuzz devices found at many of the websites, you will see that they all involves an initial amplification stage, that boosts the overall signal high enough that it will almost always be above the clipping threshold of any diodes that follow it.

That being said, there are all kinds of places where you can shove a diode pair in to get a little more distortion. E.g., most phase shifters have an initial op-amp stage to buffer the input. You can easily stick a diode pair in there to get a little more grit from your phase shifter. Wanna get wacky? Stick a diode pair after the regeneration control in your delay line and crank that sucker up high enough to produce lots of repetitions. Every repeat will get fuzzier.

In each of these applications there will be a signal level that is high enough to produce clipping when the diodes are inserted.

4/12/1999 6:51 PM
David Manson	Ok.. so a diode actually wouldnt work inside a guitar because there isnt enough voltage to make it clip but a regular circuit in a pedal or an amp would be fine.. Do diodes put out more distortion as you put more in a series? or parallel maybe.. I like the sound of my amp already... it just needs a little shove... I was thinking of adding another diode in series with the others (2 LED's) -- i wonder if that will work... thanx for all the info -- really appreciate it..

4/12/1999 6:51 PM

David Manson

Ok.. so a diode actually wouldnt work inside a guitar because there isnt enough voltage to make it clip but a regular circuit in a pedal or an amp would be fine.. Do diodes put out more distortion as you put more in a series? or parallel maybe.. I like the sound of my amp already... it just needs a little shove... I was thinking of adding another diode in series with the others (2 LED's) -- i wonder if that will work...

thanx for all the info -- really appreciate it..

4/12/1999 9:13 PM
Mark Hammer	You should move this to the FX DIY forum, where there are more folks interested in this sort of thing. More diodes = less clipping. If you want more clipping, you either need to switch to germanium diodes (typically 1N34a's, bought at Radio Shack), since these have a lower clipping threshold, or goose your input more. A simple pre-amp, in between guitar and pre-amp can provide the "little shove" you desire. For that matter, if you have a compressor, you can simply reduce the compression completely, turn the gain up full, and use your compressor like a booster. That can often put a little hair on your tone by overworking the input stage of the amplifier pre-amp.

4/12/1999 9:13 PM

Mark Hammer

You should move this to the FX DIY forum, where there are more folks interested in this sort of thing.

More diodes = less clipping.
If you want more clipping, you either need to switch to germanium diodes (typically 1N34a's, bought at Radio Shack), since these have a lower clipping threshold, or goose your input more. A simple pre-amp, in between guitar and pre-amp can provide the "little shove" you desire. For that matter, if you have a compressor, you can simply reduce the compression completely, turn the gain up full, and use your compressor like a booster. That can often put a little hair on your tone by overworking the input stage of the amplifier pre-amp.

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