Very nice LND150 Preamp, Gnobuddy. 20dB is a good range of amplification to work with, going into solid state amps. On the coiled pickup versus piezo on an acoustic, that could be an entire topic for discussion! Just to say that my acoustic had a built in preamp for the bridge mounted piezo, and it was noisy, peaky distortion (not nice) even with EQ. I yanked the preamp out and stuck the deArmond in there and it worked much better. One day I may get around to building a "proper" preamp for the piezo and have the ability to mix the two sounds (coil and piezo). Cheers!
I picked up a cheap John Linsley-Hood 1969 amplifier to mess around with. No need for +60V headroom, the amp will be in clipping well before then. Working in Class A there will not be any concern with crossover distortion. Yes it will burn up watts but a single 6V6 will do the same. Just need to come up with a reasonable preamp to feed it. No need for a higher supply voltage for the preamp than the power amp. I do not have high output pickups to concern with. I do have one set sitting around, may need to use the guitar volume with that one at some point.
I know what you mean. Not long ago I went to a nearby pub to hear live music (one of my friends plays in the band). My friend's mandolin sounded great, and their female vocalist is just incredible. But the band leader's plugged-in acoustic guitar tone - absolutely horrible! The harshest piezo sound you've ever heard, made even harsher by feeding it through the house PA with typically brassy compression horn tweeters.
Thanks for the kind words!
-Gnobuddy
FWIW, the pickups in my Ibanez AS73 are factory-stock. The guitar is a thin semi-hollow type, "inspired" by the Gibson ES-335. When I bought it, it was pretty much the only alternative guitar of that type available in North America. IIRC I paid around $350 USD for it, at a time when the overpriced Gibson equivalent probably cost five to ten times as much.
I think it's interesting that Ibanez chose to put a very different type of pickup in their AS73, compared to the ones Gibson puts in their 335s. The AS73 will make nice sparkly-clean or muted jazzy sounds if you want, but it's also quite happy pumping out rock music with plenty of growl.
The "hot" aftermarket pickups of the 1980s and early 1990s were, in my opinion, a very poor evolutionary dead-end. Very high Z, very muffled tone, and a poor engineering solution to the desire for heavier distortion. A little FX pedal with some gain in it is/was a far better solution, without the heavy compromises that come with extremely overwound pickups.
-Gnobuddy
Most guitar players preamp is the first pedal there plugged into. Probably a TL071 OA running off a 9V battery. Then the tubes. I don't hear any say the pedal destroys there sound.
IME the first pedal in the chain for most guitarists is most often a distortion or overdrive pedal, not a clean preamp.
A clean preamp set for a gain of more than about 2x (+6 dB) and powered by a 9V supply will clip frequently with a guitar plugged into it, depending on playing style and pickups.
As you said yourself, a tube amp is part of the picture. It does a good job of removing the harsh clipping transients from whatever solid-state pedals preceded it.
Have you ever heard the sound of a solid-state FX pedal into a solid-state analogue guitar amplifier? Without a tube amp to soften the solid-state harshness, usually this produces a thin, cold, and unpleasant sound when set for clean tone. They overdriven sound is worse, harsh and buzzy.
The other thing to keep in mind is that most solid state "preamps" designed for guitar use nonlinear elements in the signal chain, so that the gain falls as input signal increases. They are not Hi-Fi preamps - they are preamps that have a nonlinear gain-vs-input level transfer function, usually in the hope that this will produce tube-like distortion.
The nonlinear transfer function might be created with diodes in the feedback loop of that TL071. They prevent the op-amp itself from clipping. The diodes introduce their own form of harsh clipping, though.
-Gnobuddy
What I meant: all guitar pedals (distortion compressed etc.) first stage is a high impedance buffer (linear) often with gain ( this is the "preamp") and theres usually an input pot to set level, so no clipping unless you want it. Almost always 9 volt and usually a TL072 OA.
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Indeed, high input impedance is really important for a guitar's electromagnetic pickups. About one megohm should be good enough. The circuits in posts #7 and #8 have two 100k bias resistors in parallel, giving a 50k input impedance which will reduce the higher frequencies due to the large series inductance of the pickup. Guitars use 250k and 500k volume pots to keep from putting too much load on the pickups. The high impedance design works really well for the time it was designed, straight into the grid circuit of a vacuum tube.
I used to think so once, a long time ago. But I kept hearing this harshness in solid-state (analogue) guitar amps built with op-amps or audio power ICs (which are basically high-power op-amps).
Take a look at the two attached images, 'scope captures of the signal straight from the pickup of an electric guitar. (Both images are the work of Rod Elliott, here: https://sound-au.com/articles/guitar-voltage.htm )
See how huge the signal is when it starts? In one of the traces, the enormous negative transient is about twenty times as big as the end of the waveform (four screen divisions vs 0.2 divisions).
With only 9 volts power (which means maybe 6 Vpp maximum output from a TL072), that is a challenging waveform to deal with.
You could avoid damaging the waveform if you keep the gain (signal levels) really low (i.e. it's not a useful preamp!) If you do this, you now have an accurately reproduced huge transient 26dB bigger than the rest of the signal. That huge transient will sound painful and harsh, even though it's brief, even though the guitar/amp is set for clean tone.
Very low gain from a preamp is useless, so in practice, gain will be turned up. With the gain turned up, now that huge initial spike will be harshly clipped by the op-amp. Once again, the guitar will sound harsh even for clean tones.
So you're damned if you do (high gain), and damned if you don't (low gain). Either way, you get harshness.
With a 9V power supply, a requirement for line-level output (i.e. a signal not far below 300 mV peak to peak even at the end of the guitar note), and the very spiky nature of a guitar signal, an accurate and precise preamp (like an op-amp) is caught between Scylla and Charybdis.
By contrast, an imprecise, "squashy" preamp that fairly gently squashes the dynamics - a sort of crude compressor - avoids these difficulties. I think that's what you naturally get from a good tube guitar amp.
The low voltage (9V) is a huge part of the problem.
By comparison, a tube amp stage would probably be running on over 300 volts DC, so there's enormous headroom. In addition, grid current flow will squash positive signal peaks gently, and curvature of the tube characteristics will squash negative signal peaks gently.
Op-amps, on the other hand, by their very nature, clip very harshly. It's the side effect of having lots and lots of negative feedback. All that negative feedback makes op-amps have vanishingly low distortion - perfect for Hi-Fi or signal processing. But to get that low distortion, you have to guarantee that the op-amp will never run out of output headroom - you have to guarantee the output will never clip.
This is easy to do in most cases (preamp for a sound card output, say). But it just doesn't work with the spiky, rapidly decaying waveform from an e-guitar.
But there's good news. After literally decades of harsh solid-state e-guitar amps, we've finally turned a corner: affordable digital (DSP) guitar amps that sound really good are here.
I'm not sure how they address the clipping problem in these digital amps - probably by keeping input guitar signal level very low until it is digitized, so there is no actual analogue clipping, only whatever deliberate "squashing" is built into the DSP code. But that's just a guess.
However it's done, it works. I'm very happy with the sounds I can get from my little Flamma FS06 Preamp. I don't hear the sort of harshness I hear from old-school op-amp guitar input stages.
I'm also getting good results running the output of the Flamma Preamp into the input of my Boss Katana 50, set to its Acoustic channel.
-Gnobuddy
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Your wrong. There no clipping if you turn down the input pot. Simple as that. Nobody else is hearing your harshness, you don't need a high voltage preamp for guitar this is proven on thousands of recordings. Not one of the scope captures from Rod Elliot's page show levels over 1 volt, most are below 200mv. A 9volt amp will not clip at these levels even without the input pot. And you better tell all the active guitar makers there guitars are harsh.
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Yes, there is no clipping if you turn down the input level to the point where there preamp is useless, because the output signal isn't big enough.
There is also no clipping if you leave the guitar in its case, and don't actually plug it in or play it.
Enjoy your day.
-Gnobuddy
There's no input pot on 'decent' guitar amps or most pedals.
That kinda went out in 1965 because it hisses all the time.
There's no magic in having more voltage than the next stage can swallow. Good level management means setting appropriate gain throughout.
That transient is what, 1/100th of a second. Yes, it's going to make a click or something extra at the start of the sound, but I have a hard time believing that's the cause of the harshness you hear.
That transient looks like a glitch. Would have to zoom in to be sure.
https://dsp.stackexchange.com/questions/41032/weird-note-structure-on-guitar-audio-waveform
Not one glitch in all of these.
https://www.google.com/search?q=ele...ih=543&biw=977&rlz=1C1KDEC_enCA926CA926&hl=en
And even if it isn't a glitch how's a high voltage amp make any difference, the level is 400mv.
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0.4V x 50 (gain for bypassed 12AX7) = 20V, so a swing of 40V is needed. A supply of 100V can do it. A 12AX7 just scrapes by at this voltage to my ears.