Try it. You might find the results verrry interesting!

Anyhow, to me, EQ is EQ, no matter where you do it. Every single change you make to the sound is nothing more than an EQ change. So, when you change a cord, a pickup, a pedal, an amp, or a speaker, or anything else (even strings) to get a different sound, all you're really doing is altering the EQ. If we remove the "sustain" and attack variables, and you give me enough EQ, I can make any guitar sound like any other guitar (that's of similar design). No, no amount of EQ will make a Gretsch Country Gentlemen sound like a Stratocaster, (the overtone structure is too different), but it will make a Tele sound just like a Strat or an SG. Or, it will make an Emmons sound just like a Sho~Bud, or vice-versa.

If, on similar instruments, you take sustain and attack out of the picture, EQ is all that's left to differentiate the sound.

Indeed, EQ is not only everything, it's the only thing! And if you don't believe it, then you've never fooled around with a good active graphic equalizer.

Re the meter...I assume that you mean an Ohm Meter because you say resistance. The answer to your question is maybe. Resistance as measured with an Ohm Meter is a DC (direct current) measurement. Impedance is an AC (alternating current) measurement. Resistance and Impedance are equal when the frequency in the AC is 0 Hz.

If there is a reactive component(capacitor/inductor or??) in the chain your Ohm Guesser will just read the ohms, not impedance. Dc does not pass thru a capacitor (except for leakage) so a capacitor in series with the leads will not let your meter see what may be on the other side. If the capacitor is in parallel with the leads, its impedance to ground (which is frequency dependent) will not be seen. Same kind of thing for inductors in the circuit.

If the chain is purely resistive, then Resistance = Impedance (at 0 Hz).

Donny H: The most popular circuit design/analysis program that I know of is named SPICE (or one of it's offsprings). It handles transients (think attack).

A bit more detail is given here:
http://ist-socrates.berkeley.edu/~phylabs/bsc/PDFFiles/bsc1&2.pdf

The upshot is that the input impedance may be a function of frequency. In addition, if the input signal is large, it may also be a function of the input signal level. One generally makes these measurements with sufficiently low input voltage levels that the input circuit is not overloaded, i.e., runs in its linear region.

Brad, the load may change the overall frequency response of the combined pickup-impedance, Zp(jw), and load input-impedance, Zi(jw), system. One can view the pickup as a Thevenin equivalent circuit, with the voltage induced in the pickup coils, Vp(jw), as the voltage source and Zp(jw) as the pickup Thevenin equivalent impedance. The load is directly connected to these, and we're concerned with the voltage dropped across the load input, Vi(jw). This is a simple voltage divider, and Vi(jw) may be computed for any angular frequency w as:

Vi(jw) = {Zi(jw)/[Zp(jw)+Zi(jw)]}*Vp(jw)

or = {1/{1+[Zp(jw)/Zi(jw)]}}*Vp(jw)

This is the voltage transfer function form. You can see that the pickup drops significant voltage signal at frequencies where |Zp(jw)| is not very small compared to |Zi(jw)|. If the load impedance varies with frequency, it distorts the effect of the pickup frequency response.

Ed, of course pickup makers need to understand how the various design parameters affect the pickup voltage generated and the frequency response of the coil. I think that guys like Bill Lawrence have this well in hand. I agree with you that serious measurements across lines of pickups would be useful to establish a baseline for players and designers of equipment.

I know that it is often difficult to do this, but it would be useful to translate such technical ideas into descriptions that are meaningful for guitar or steel players. I don't think most players are going to ever think in terms of frequency responses or transfer functions. They need something simple and intuitive to help them decide if a pickup, pedal, effects unit, or amp will sound good with what they have.

As far as input impedance goes, I believe it is well understood that everything in the signal chain should be low-output-impedance into high-input-impedance as much as possible, unless one wants to muddy things up. Some people do - e.g., jazz and blues guitarists often do that intentionally.

Donny, I've used plenty of EQs. As you say, EQ doesn't add attack or overtones that aren't there, nor do they equalize the many nonlinear things involved in the sound. They can also mess with the linear phase response and add a lot of noise of their own. Used judiciously, they can be very useful, but I don't like using them to make large changes in guitar sound. It may make a Les Paul or SG with HB credible in a single-coil context, but I've never heard anybody really make one sound exactly like a trad Tele to my ears.

Preamp, high-gain input (no pad): 220K Ohms
Preamp, low-gain input (-10dB pad): 44K Ohms
Patch Input: 220K Ohms
Power Amp Input: 22K Ohms

I think other recent vintage Peaveys are similar. BTW, Brad - on my Session/LTD 400 manual, it says input impedance is 330 K Ohms, not 1 M. The circuit diagram indicates both inputs are the same on those.

Input impedance specs on classic Fenders like the Twin Reverb are:

Input 1 (Higher gain): 1 M Ohms
Input 2 (Lower gain): 136 K Ohms

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The "individuality" comment is cute...I take it as a euphemism for "can't make two alike".

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The Peavey inputs are cap blocked so it's not so simple to just read the load with a meter. You may just get the value of the volume pedal instead.

Also consider how these load values change with the volume pedal position. At full volume pedal, you actually get the lowest load value because the wiper at full lets the secondary load reflect entirely in parallel with the pedal load. With the wiper in a lower position, you have to incorporate the pot resistance in any given position other than full, thus the load value rises as the volume pedal goes down. It's more dramatic with the amps that have lower input Z's, like the Nashvilles. So that theory would say that the tonal response would actually get a big brighter as you back down the volume pedal.

I think I need one of those equalizers that'll make me sound like Buddy.

This thread has been fun. Thanks Brad for starting it. Gave me something to do while sitting on my back porch here in the mountains of AZ and watching the leaves turn while sopping up sunshine. Typical rockin'chair, shotgun, hound dog, and jug place!

We have done everything except whip out the integral signs for a duel re the mag fields of the pickup...probably because we are partially differentiated...pun intended.

Dave M: Looks like you have collected the I/O info re a bunch of gear...care to compile and publish it on the Forum for general consumption and reference?

Jay: One further comment on the Ohm Meter thing...if there is a semiconductor junction in the loop (diode/transistor) your Ohm Meter may also give a false reading. You can tell this if you get different values by reversing the leads.

Ed, I guess I may have collected a bunch of manuals. Let me root around and see what I can come up with. But that list above covers a lot of the amps steel players actually use - Session/LTD 400, 500, NV 400 and offshoots. Just looked at specs for a NV 112:

High gain input: 220K
Low gain input (-10dB pad): 68K
Pre-EQ Patch return: 220K
Post-EQ Patch return: 1 M

I haven't looked, but I assume most of the modern Peavey steel amps are in the same ballpark. The white, brown, blackface, and silverface Fenders are generally 1M input 1, 136K input 2. Earlier tweed amps vary quite a bit. One needs to look at the circuit. The Fender Field Guide at http://www.ampwares.com/ffg/ has those for a wide variety of old Fender amps.

I think the point here is that, if someone isn't getting enough high-end, it may be worth finding the input impedance and consider using a buffer like the Black Box or some other kind of High-Zin / Low-Zout preamp or effects unit.

[This message was edited by Dave Mudgett on 08 October 2005 at 09:57 AM.]

In this context, I've got a setup that results in something I don't understand. Here's what it is:

I run a 99 Carter D10 w/GeoL TPPP p/u's straight into a SGBB, then to a Hilton VP, then to a Webb; all Geo L cables.

If I remove the SGBB, I get way, way fewer highs. With the SGBB in the chain I get worlds more.

If I understand the main points raised here, that shouldn't happen unless the output impedance of the SGBB is not what the Hilton VP is expecting. Also, the tone trim pot in the VP is unable to compensate even at its extreme ccw position.

Any comments anybody?

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I think the point here is that, if someone isn't getting enough high-end, it may be worth finding the input impedance and consider using a buffer like the Black Box or some other kind of High-Zin / Low-Zout preamp or effects unit.

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I was attempting to offer a solution to this exact point with my earlier post, suggesting the use of impedance-matching resistor pads on both sides of an op-amp.

So the input chain would be: Pickup to "pi" pad to op-amp to "pi" pad to pre-amp.

A "Tee" configuration could be used instead of the "Pi".

The first pad would match the pickup to the op-amp. But all you might need here is just a coupling capacitor, since an op-amp can be made to show very high input impedance of 1M.

The second pad would match the op-amp output to the pre-amp. A relatively accurate calculation is important here to interface the low output impedance of an op-amp with an amp input impedance of 220K, for example, as Brad referenced originally.

The op-amp could provide gain to restore the pad loss.

Actually, the effects pedals mentioned perform some impedance matching close to this idea since most I think have op-amps doing the work with outboard parts, but a calculated pad could be made for an exact match. No?

I am not an engineer, just a tech. Just wondering if anyone else thinks like this.

Or am I wrong with this whole thing?

Impedance matching is generally to achieve maximum power transfer and highest signal to noise as I recall. Our problem is more getting the most voltage out from a varying impedance source in the audio band, so lowZ out into HiZ in is the rule of the day...preserves signal level across the band. Re input Z, one meg is nice...ten meg is better. Re output Z, industry standards have been 600 ohms, 50 ohms, and now it looks like the 32 ohm (headphone) value is in.

Not too sure about the "pad(s)"issue but if you like the results, publish it. Most of us do not want what we get direct from the pickup (just want all we can get to start with)...then we turn around and tweak it to taste. What you don't have, you can't tweak.

Restoring lost signal level generally costs signal to noise ratio.

Upon retrospect, I probably should have concluded this after reading posts by Dave & Brad also.

Thanks to Brad for starting this great, educational thread.

Not sure what the circuit is inside. They may try to restore some highs via the pots on the bottom. The output Z appears to be about 100 Ohms as I recall, so line driving S/B good.

My old tek 453 died a couple of years ago...high voltage diode problem in the display...have not found a replacement. The input stages still work as an amplifier so probes and chan 1 out can be used as a buffer for measurements. The computer pgm I have is both an FSA and an o'scope with swept freq in sine, ramp, and square. Much more convenient. Worst problem with the computer is the line in Z. Solution is to buffer with the voltage follower circuit.

Brad I just emailed you twice and it got returned.

Jim writes:
"Although I haven't had the chance to examine a lot of new steels, my guess is you wouldn't find it there, so steels are probably OK as far as the thing I refer to."

So we know it doesn't have to do with steel tone, past vs. present.

Other clues?...

"There is another very BIG reason that todays instruments don't have the sparkle that the instruments in the "old days" had, that I discovered about 15 years ago."

Are we talking electric guitars now?

"Another reason is I don't want to encourage people to make any kind of modification that they may botch up,..."

"That's because what I'm talking about is so simple anyone should be able to see it. The manufacturers surely know but don't care."

"It's such a simple thing I think it's just a case of overlooking the obvious."

"Everyone with a little electronic knowledge would know the electronic theory concerning this, but maybe no one is paying attention to some basic areas of application."

"Don't let all the knowledge of impedance, reactance, frequency, etc. cause you to overlook the simple things."

I dunno?... I remember a friend had an old Les Paul "Studio" with low impedance pickups that sounded pretty sweet... Were all guitars back then Low Impedance?

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http://www.steelguitar.ca

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Does the cords used make any difference?

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Oh yes, especially with modern, high-impedance and humbucking pickups!

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Now somebody "s'plain dat!!!

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Really simple. The majority of modern guitar cords are loaded with capacitance. It's like turning your tone control about 1/3 down, more with more cords. The cord from your guitar to your effects, a big tone-sucking capacitor; the cord connecting your effects, eq, etc., another cap and the cord going from the last effect into your amp, another one. Attempting to make the nice flexible cables we all like and making them cheap as possible is likely the cause of the really low-quality of cables. Higher quality coax usually isn't as flexible but has less capacitance and a clearer sound.

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I'm surprised that no one has commented as to how the natural resonance of the guitar body itself affects the tone and overall frequency response of the whole setup.

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Of course, we have, but not in Electronics:
http://steelguitarforum.com/Forum10/HTML/200939.html

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Before this thread dies, can anyone out there give me a good reason why every instrument amp made doesn't have an input impedance of at least 1 megohm? (It seems like such a small thing to ask for.)

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Tubes are naturally high-impedance, transistors are not. Op-amp feedback resistors complicate this some - there are design tradeoffs. Check one more advantage to tubes, IMO.

But let me say that for some things, a lower impedance may be just the ticket. For example, I like the way a jazz guitar sounds into a lower-impedance solid-state amp.

I just noticed that today looking at the Nashville 400 mod kit instructions and schematic.

I have a 1983 LTD400 with the 1502-4 speaker. The amp sounds great. I am changing the Opamps to Burr Brown chips. I am reluctant to to change R3 and R10, as I think it may alter the frquency response of the amp too much. If the amp had a 1501-4SB I would do the complete mod, as more bass is needed.

No, I'm not going to post this in the Humor section. I think I'm about to get banned from that section.

[This message was edited by Rick Collins on 18 April 2006 at 04:57 PM.]