I Think This is The Right Forum For a General Amp Question.

[Zut8083]

Hi, Alembicians,

I have a question that I cannot answer to my satisfaction, and I hope this is the right part of the forum to solicit general technical insight, so here goes...  I had an accidental discussion with a friend of my wife who plays/played bass in a band, and when I was talking about using low impedance pickups or a buffer circuit to enhance the clarity of the base signal, driving the signal through cables and circuits PRIOR to arriving at the pre-amp stage mostly intact, I received a stony mandate that low impedance electronics can be bad for a bass amplifier.  I thought that this was as peculiar an answer when I first heard the statement as I have thought it to be over the last month of mentally gnawing on it daily. 

I don't understand how can this break the amplifier?  Where will it break it?  The pre-amp?  Will it blow a tube, will it blow a fuse, will it throw a rod; why not just tune the gain for clarity and be careful while adjusting the sound?  My imprecise reasoning in this matter is that I have never heard of low impedance electronics or buffer circuits which can increase the amperage directly to the point that you have phased plasma in the 40 watt range, and presumably, increase the voltage to obscene levels in a circuit with a set impedance via V=IR.

This is similarly seen with active electronics/pre-amps, which I may incorrectly understand to increase signal voltage as the instrument's output directly for incorporation into a signal path and then for introduction into an amplifier.  From tiptoeing through the internet, it seems to me that common guitar pickup voltages have been approximately cited as 0.1-1+V, rms, depending on how hot the pickup is (https://en.wikipedia.org/wiki/Pickup_(music_technology)).  As guitar pickups, and presumably bass pickups, were supposedly developed around the 12AXY tube, which begins to clip at 1.5V rms max (stolen from here: http://www.diystompboxes.com/smfforum/index.php?topic=81285.0), that was the limit set for the amplitude of most passive pickups to avoid overloading/clipping the preamp.  For bass pickups, from this TalkBass thread, I surmised that passive pickups can maintain 0.1-1+V rms for varying passive pickups, and ~4.5+ rms for active pickups, which may be too hot for a single 12AXY tube.  None of these data address signal or potential loss due to the capacitance of the cable to the amp or any intervening circuits prior to the preamp; however, that would only seem to offset this supposedly detrimental magnitude of amperage or voltage from the instrument on an amplifier.

Now, this data and the indication that guitars and basses are constructed with existing technology in mind leads to the real question: who would build a set of pickups or electronics that would destroy pre-amps or power amps via negligence?  There is little to no talk of intervening circuits being necessary to abate the low impedance signal coming from your instrument as if it were an asteroid rocketing through your cable.  Instead, I have only seen that more current or voltage into the pre-amp would induce clipping and potentially generate square-wave distortion at that place in the signal path.  Thus, it seems to me, any instrument that was too "hot" could just be dialed down in the initial preamp stage, should it be necessary. 

Again, these are the two questions which fail the litmus test- who would break from common sense and engineering tradition by building an unreliable, destructive circuit into your instrument that decimates pre-amps WITH EXTREME PREJUDICE due to a few inherent engineering flaws, AND why you could not design newer amplifiers to accept this supposedly science-fiction-like signal, regardless?  At this point, I don't see where Alembics and other pickups were designed to SLAY all amplifiers, like Genghis Khan scything through the Steppes.  Are there no fuses/breakers in the amp?  Was this not worried about when incorporating stomp boxes or daisy chaining amps like Hendrix and his legion of Plexi SuperLeads behind him?  I am sure that this caveat must have been address, likely by Alembic while modding gear or producing the initial Series instruments, as I don't recall ever being told to NOT plug an Alembic or a set of EMGs/Bartolinis/etc. into a cheap practice amp, nor be told to NOT floor it.  I mean, I already have done just that, and nothing started to smell like burning plastic or brimstone, so unless preamp inputs have bigger and heftier impedances to stave off potential/signal, I am really confused (obviously). 

For the record, I have read that the output from bass can work fine with the electronics of a guitar amp (re: Lemmy, a Rickenbacker, and a mountain of Marshalls), but that setups can destroy speakers in the cabinets, and the reflexive jump in resistance after frying cones can potentially then cook fuses or transformers if the wrong enclosures were used and can't provide the right peak to peak range.  So, since I am lost on the other person's point which did not have a concrete reason at the time, and since, this now feels like a "If one train leaves Cleveland heading towards Chicago at 100 miles per hour, and one train leaves Sacramento heading to Pluto at the speed of light....." on the SAT, I would love it if someone who comes across this frustrating quandry/thread can help me either call shenanigans or take my medicine.  I can't prove it one way or another to myself due to my lack of experience with electronics, shy of "plug and play", and trying to figure this out and understand the circuity/electrodynamics is driving me bananas.  I also really stink at physics, so, the best I could muster then and now is the gain argument, different inputs for active and passive basses in some amps, and amplifiers being chock full of resistors and at least one fuse, that this cannot be unfathomable.  But it feels like a really weak point, and I would like to understand this point from an educational point of view, and not bragging rights.  Yeesh.

Thanks again, folks.

-Zut8083

[growlypants]

Well, alrighty then!!!  (Welcome back, by the way...). As most of the folks on this board already know, I haven't got a clue about any of this electronic stuff.  But I'll certainly read any further posts, in case any happen to make sense!  Welcome, once again.

[Zut8083]

Dear. growlypants,

Thanks for the welcome.  I too am not very knowledgeable about the exact workings of my instrument or my amps, certainly not enough to discuss it beyond saying "Nuh-unh!".  I just have never seen a circuit with different impedance to skew the voltage or the current associated with Alembics or with active basses to make the input "palatable".  Maybe with vintage amps it could be that way, and because I haven't seen it, doesn't mean it's not actually there.  And I still really don't appreciate the physics of circuits.  So all I have is a gut feeling about something I know diddly about, which is not very persuasive. 

Anyhow, it's nice to comb through the different threads, here, and it's nice that people are still welcoming and congenial here.  And the basses and guitars are pretty, too.  Thanks again for the welcome.  Cheers.

[lbpesq]

I have played for many years with many different Alembic bass players playing through many different bass amps.  Nothing has ever blown up, blown out, or spontaneously combusted.  I would take your wife's friend's opinion with a very large grain of salt.  And I'll bet he plays a Fender.

Bill, tgo

[adriaan]

The short of it is that Alembic pickups are low impedance (much smaller number of windings around the magnet) meaning they produce a very clear but relatively weak signal. You don't need an onboard preamp to go with low impedance pickups, but it certainly helps to get the signal across a guitar cable.

You may have noticed that modern amps have either "passive" and "active" inputs, or an input pad switch (like -15 dB). The active option (which would be through the labeled input, or with the pad engaged) is appropriate for instruments with an onboard preamp.

So this friend may be confusing the one and or the other - like the true fact that one can fry an amp by attaching speakers that present an impedance lower than what the amp is designed to work with.

[edwin]

Your acquaintance is dead wrong. With the voltages and current at play here, there's nothing you could do to break your amp, unless your amp is due to break anyway. There could be an issue with noise or gain in rare exceptions, but here's the thing. You want the impedance of the output device to be lower than the input device. This is why acoustic instruments with piezo pickups need a very high input impedance buffer, on the order of 3-10Mohms because they have a high output impedance. Otherwise, the sound is thin, scratchy, and weird. Similarly, a passive bass guitar output impedance is about 10kohms. As a general rule of thumb, you want the input impedance to be at least 10x the output. So a lot of amps, especially Fender style ones, which include the F2B, have an input impedance of about 1Mohm. Alembic pickups back in the day were quite low (I have a pair of caramel SI pickups that measure around 800 ohms resistance) and have since settled to a medium impedance. Why not just leave it as is and run to the amp or effects without an onboard preamp? Low impedance in a pickup is achieved by putting fewer turns of wire on the magnet, which decreases the output (high output pickups also have a higher impedance), and with a low output traveling down a long cable (i.e., lots of resistance), you lose even more and then have to make it up with gain at the amp and all that resistance in the wire can create noise (aka Johnson-Nyquist noise), so it makes sense to amplify the signal as early along the chain as you can. Phil's first active bass had discrete preamps wired together right on the bottom of the pickup. It also buffers the signal from interacting with other stages down the line (another part of the discussion is the fact that resistance is part of the calculation in an LCR circuit (inductance, from the coil of the pickup, capacitance from the cable, and resistance, from the length of wires in the cable to the amp) which is otherwise known as a tone control, in this situation, one that robs you of highs. The longer the cable, the more highs get rolled off, but if you separate the inductance from the resistance, i.e., pickup from the cable, then you maintain all the high frequencies that the pickup is capable of reproducing.


So, in many ways, a low impedance pickup with a preamp right next to it is the ideal setup. If you want clean, and clear. Les Paul thought so.

The only thing I can think of is if he was confused about instrument impedance with speaker impedance. You can blow up amps if impedance is mismatched, depending on the type of amp and the amount of mismatch. However, in this day age, that only applies to tube amps, generally if you have no speaker plugged in or a huge amount of speakers with a load of 1/2 ohm on a 16 ohm output tap. Also, don't plug the speaker output of an amp into another amp input.

Long story short, have fun, you aren't going to hurt anything!
 

[Zut8083]

Dear edwin,

That is a beautiful, educational, and clear response; thank you very much.  I think that I might have seen the point you made about the input resistance on the preamp being 10x+ the output from the instrument earlier today on a different thread elsewhere, so I am glad to hear that for the rather manageable signal intensity or voltage in these instruments, nothing poses a threat to the amplifier unless the amp has an existing liability.  Thanks again for your instructive and very intuitive response; this discussion is very helpful for my own understanding.  Cheers.

[edwin]

Aw shucks, you are entirely welcome! I'm glad I learned something from my years of plugging the wrong things into other things the wrong way!

[Zut8083]

You guys are alright!  Not only did you give great overlapping and complimentary answers to my thesis, you made me think of a brand new one.  I'll post it tomorrow, I promise...I guess this is a headstart, or something.

Thank you, again.  It's better to know stuff than to just pontificate or be downriver from pontifications.

[bigredbass]

Zut, your 'friend' is exactly the sort of guy that led me to buying all kinds of wrong stuff in the beginning, which led me to learn the basics of why this does that, etc., so I wouldn't wind up with some fool telling me low impedance would blow my amp.  Gee, the Wickershams, the Turners at EMG, Bill Bartolini, and a lot more must have huge insurance riders to cover the liability of all those burnt-up amps !

Leave this guy to being President of the Flat Earth Society, put him on the train back to Hooterville, and leave music and the related technologies to people who know what they're doing.  Guys like that make me crazy . . . . . as if I needed any help . . . . . .

[Zut8083]

As if the knowledge base could not improve, including the recounting ofnfirsthand experience of this exact conundrum, now giving a nearly statistical cohort to defang the fallacious evils of low impedance systems..."Hooterville" was then put on the table!  Fantastic!  I am rapidly recalling why I liked this forum.  I am also very glad that this question could be resolved quickly, and then shored up with a consensus.

Thank you folks once again.  But why do I hear the Monkees in my head, now?

[elwoodblue]

Love this thread, glad to have you onboard Zut8083 


I just came across this recollection that adds a rare caveat to the discussion
(Like if you happen to be using old HiWatts).
 As someone who is about to Jam with friends with a Stratoblaster equipped baritone and maybe an additional
tube booster through an '81 Marshall, maybe I should make sure the Marshall design prevents too much current downstream
if the preamp tubes are pushed to the max. So far I haven't smoked any amps.


 anyway...here's the quote (RT talking about Lindsey's gear)


"For Lindsey, my main contribution during Rumours was installing an Alembic “Stratoblaster” in his Strat exactly like the one I’d put in Lowell George’s guitar, the one you hear on Little Feat’s live album, “Waiting for Columbus.” For Lindsey, the sound of the electric on Rumours is his guitar with the ‘Blaster gain all the way up, basically destroying a succession of HiWatt amps. Evidently, the HiWatts did not have adequate current protection; they were fine with normal electric guitar output levels, but when we boosted that by nearly 12 dB, the amplifier just tried to pull more and more current through the power transformer, and after about 20 or 30 minutes of high gain sustaining guitar solo, the transformers would literally go up in smoke. Luckily, they had three of them, and every day one would go off to Prune Music to be repaired."
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[Zut8083]

Please accept my apologies for having picked the wrong location in this forum to start my initial threads.  I will make myself more aware of the governing, selective criteria that underlie each of the forum's subdivisions for any of my subsequent posts.  Thank you, adriaan, for correcting my errors in this regard.  I am sorry for the inconvenience.  Cheers.

[dfung60]

@Zut - This discussion is a bit confusing because some of the terms are used in different senses.

Electric guitars and basses all work by the electromagentic properties when you put wire, magnets, and ferrous strings in proximity.  A simple pickup is a magnet with a coil of wire wrapped around it.  The magnet projects a magnetic field from the pickup that your strings are sitting in.  When the strings vibrate, they perturb the magnetic field, which causes an electrical flow in the coil of wire.  The electrical output is proportional to the movement of the strings, so if you amplify that electrical signal, you'll hear something which is similar to the string motion.

Every part of your guitar, the hardware, strings, and electronics have an effect on how that final signal sounds.  If you use a bigger magnet, you get a stronger signal, but the magnetic force may drag on the strings, giving you less sustain.  You can wind more wire on the coil and you'll also get a stronger signal, but because of the physics of wire wound around the coil, it may pass less treble to the final signal.  You can change the size of the wire, type of magnet, ad infinitum and there will be all these subtle changes.  By you physics textbook, you can make a pickup that's more "correct" in terms of the fidelity of the output signal to the original vibration, but a big part of electric musical instruments is that "what you like" is "best.  You can make a pickup that's more accurate than a Gibson PAF, but for many people the PAF is what you want it to sound like.

Wire resists the flow of electricity.  When you're putting direct current through a wire (like a power supply), that resistance is called "resistance" (see, science is easy!).  When you put alternating current through a wire, like the signal induced by a moving guitar string, that way the wire behaves is very complicated because it's affected by magnetic fields that are generated as the signal changes.  AC "resistance" is called "impedance". 

When the first electric guitar pickups were made, the goal was to get enough signal out so that the sound was loud enough to be heard over background noise when you amplified it.  Given the amps of the time, a desirable signal level was in the 0.1V range.  This required a bunch of decisions about how much wire to use, what magnets, etc.  And this created tradeoffs where some treble was getting lost, or the pickup coil affected the tone (these are the "resonant peaks" that you see in pickup specs). 

One way to address these problems is to use a less powerful magnet and less coil on the wire, which your physics teacher will tell you will give more accurate response.  The problem is that combination will also give you very low output, so you'll need to have a different kind of amplifier to use it.  This is a simple "low impedance" pickup.  Less wire has less impedance.

By the time you're in the Alembic era, you've got a lot more technology to work with, and renaissance guys like Ron Wickersham on the job.  He realized that he could make a optimal low-impedance (and low-output) pickup but actually put a tiny amplifier in an integrated circuit IN the bass which would kick the signal up to a more traditional level.  This was something that Leo Fender couldn't do in the 50's since integrated circuits and op-amps weren't invented yet.  And it took an Alembic kind of effort to do this - this meant the electronics in the instrument were much more complicated and would require a power supply, so there was going to be some cost associated with perfection.  But that experiment worked, and opened the door for active electronics on all sorts of instruments now.

You get some extra benefits when you have an onboard preamp.  One of the big ones is that the output of the op-amp is SUPER low impedance, so there's less treble loss from your guitar cable.  And you can set the output level of the onboard preamp.  To us simple humans, if you have two things that sound the same, you'll probably think the louder one sounds better, so I think it's normal that the output level is a little hotter.  On most Alembics, there's a trimpot that lets you adjust that level, and it has a VERY wide range of amplification.   An active EMG pickup has a tiny circuit board with the op-amp sealed inside the pickup cover and there's no output level adjustment, but they're set quite hot -probably 2x a passive pickup. 

So, this shaggy dog story actually gets around now to one of your original questions.  The warning about low-impedance instruments is really about active instruments where the output level has been set really high.  A modern amp won't care - there is usually an active input that just has less sensitivity so it's throwing away the extra signal.  A vintage amp probably doesn't have that padded input.  If you plug your Alembic in there, you may not be able to get a clean sound on the amp.  You won't hurt the amp, but it won't sound great.  Actually, it's not even really a problem.  You can turn the volume knob down on your bass until you get an appropriately weak output to work with the amp.  Another good thing about having the onboard amp is that it eliminates the interaction between the volume and tone controls, so as you turn down the volume, the tone won't change.  Your P-bass won't act that way.

At the end of the day, you want you instrument to sound good to you and your listeners.  An Alembic Series pickup is very different sounding than a traditional J bass pickup.  Some will prefer one and some will prefer the other.

[Zut8083]

Dear dfung60,

Thanks for your insight and input (signal jokes, gotta love them), and I agree with you in your points on how taste is perceived and esteemed, namely its being very subjective.  I also think, as I suspect you and many other musicians may as well, that the expansion or improved definition of one's personal perception and one's appreciation of what is pleasing or in some way virtuous is a very vital component of the development and refinement of one's acumen, one's knowledge base, and to better see what is subtle, elegant, serendipitous, or striking/surprising where we might not have before.

That cathexis to progress, I think, is the challenge of any application of "Strong Inference" to improve ourselves.  It is most challenging for people to make progress, to expand their understanding expeditiously, and not get hung up on lots of dead ends or trivium.  At least that is my experience, and I really don't mean to project.  Otherwise, I would guess that I, personally, would still be trying to play faster, harder, and louder, while failing to be "heavier", as that was not necessarily playing "better" nor serving the song.  Worse, this inefficiency would probably be compounded by still subsisting off of Totino's Pizza Rolls, french fries, and soda and living in my mother's house, and trying to sponge $20 on a Friday night while waiting for my friends to pick me up to do very little.  NOW I borrow money from my wife to do very little.  Thank you very much.    Cheers.