Recently witnessed a 1970s pioneer spec 1 preamp at my friend's home. The sound appeared to have more dynamics and live.
On looking at the schematics, noticed they used +/- 48 volts supply with transistor based circuits.
And all the earlier discrete preamps were complete class A operation from input to output.
Most of the modern era instrument preamps with IC use only +/- 15 or 18 volts max.
(The opamps cannot be really set to class A operation)
Not sure to say, if high voltage supply like +/- 48 volts play important role in the dynamics.
The later models from that era use lesser and lesser voltages, like +/- 40, 30 24 volts etc, still transistor preamps.
I am aware of discussions why just 9 volts is enough in the pedals for 150 mv outputs, or +/- 15 is enough for the preamps to output up to 10 volts rms.
Anyone made any discrete preamp at such high voltages with any success?
Regards.
On looking at the schematics, noticed they used +/- 48 volts supply with transistor based circuits.
And all the earlier discrete preamps were complete class A operation from input to output.
Most of the modern era instrument preamps with IC use only +/- 15 or 18 volts max.
(The opamps cannot be really set to class A operation)
Not sure to say, if high voltage supply like +/- 48 volts play important role in the dynamics.
The later models from that era use lesser and lesser voltages, like +/- 40, 30 24 volts etc, still transistor preamps.
I am aware of discussions why just 9 volts is enough in the pedals for 150 mv outputs, or +/- 15 is enough for the preamps to output up to 10 volts rms.
Anyone made any discrete preamp at such high voltages with any success?
Regards.
A guy that goes by KMG has done a few high voltage designs (intended to emulate vacuum tubes) using the 2SK216 and LND150 MOSFETs. See this SSGuitar post as well as his personal page.
You might just clone that Pioneer preamp.
Guess schematic can be found and transistors must certainly be replaceable by modern versions.
You´d still need to design your own PCB but if lucky you might have an image of the original one to guide you as to preferred layout.
Guess schematic can be found and transistors must certainly be replaceable by modern versions.
You´d still need to design your own PCB but if lucky you might have an image of the original one to guide you as to preferred layout.
High voltage transistor preamps certainly have more headroom for really hot signals or when excessive low frequency EQ is being used. You can run out of headroom with only +/-13V swing if the gain structure is poor. And you can bias as heavily as you care to with a discrete design of course.
There are tricks to make standard op amps run in class A if you are so inclined. Still limited to the voltage swing, and the current/dissipation capability of the op amp.
There are tricks to make standard op amps run in class A if you are so inclined. Still limited to the voltage swing, and the current/dissipation capability of the op amp.
Thanks for all the replies. I started to feel that there is some magic in the higher supply voltage regarding the transients or the dynamics. May be */- 15 volts used for the opamps be just nice but not enough. In the Hi-Fi systems, Even for the 2.5 milli volt input MC preamps, I see they used +/- 48 volts supplies, with a overload margin as high as 500 mv without distortion. All high end preamps of the early days have these level supply voltages.
For guitar signals, the attack in the waveform is more important for the preamp first stage to preserve the dynamics. In a tube preamp, the grid have this behavior.
I had been working with tubes (valves as we called it) since I was 8 years old. We had lots of variants of tubes at home (around 1200) which my father got as war surplus. So I had the joy of experimenting with very large range of tubes available those days. (2A3, 6F6, 6V6, 6L6, 6SJ7, 6C5, 6SN7, 807--you name it. How many of you know about Loctal tubes, used in portable receivers of that time. Operates on 2 x 45 volts batteries for plate supply and 2 volts lead acid cell for the filaments. Tube pin side had the center guide similar to that of a guitar phono plug to lock on to the Loctal base)
Once you hear the sound from a tube, something locks up in the brain which can't be explained, making you to look for that sound again. Somehow it connects the guitar and the player more psychologically closer than average solid state.
Still studying some materials. Regards.
For guitar signals, the attack in the waveform is more important for the preamp first stage to preserve the dynamics. In a tube preamp, the grid have this behavior.
I had been working with tubes (valves as we called it) since I was 8 years old. We had lots of variants of tubes at home (around 1200) which my father got as war surplus. So I had the joy of experimenting with very large range of tubes available those days. (2A3, 6F6, 6V6, 6L6, 6SJ7, 6C5, 6SN7, 807--you name it. How many of you know about Loctal tubes, used in portable receivers of that time. Operates on 2 x 45 volts batteries for plate supply and 2 volts lead acid cell for the filaments. Tube pin side had the center guide similar to that of a guitar phono plug to lock on to the Loctal base)
Once you hear the sound from a tube, something locks up in the brain which can't be explained, making you to look for that sound again. Somehow it connects the guitar and the player more psychologically closer than average solid state.
Still studying some materials. Regards.
One of the (many) Front Ends for the VFET amplifiers that diyAudio sold last summer, is "Dreadnought". It operates from a 60 volt, single ended power supply. Easily reconfigured to +/- 30 volt rails. Maybe you might think about starting with circuits similar to it. Pull the datasheets for the semiconductors, I think you'll discover they all are >100 volt rated, so if you upped the voltage (and turned down the bias current to keep device power dissipation reasonable!), you probably don't need to hunt around for higher voltage replacements.
(for the purposes of this thread you can ignore the blocks labeled POLARITY INVERT and JBOOST1D. What you are interested in -- the preamp circuit itself -- is here on this page.)
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(for the purposes of this thread you can ignore the blocks labeled POLARITY INVERT and JBOOST1D. What you are interested in -- the preamp circuit itself -- is here on this page.)
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Another VFET front end with a different topology. BEWARE the D45H11 output transistor is "only" rated for 80 volts. Maybe you'll feel better with the KSB546 which is rated for 120V. (All the others are >100V though). Designed for 60 volts single ended supply (+/- 30V dual rail), extensible to +/- 45 volts straightforwardly.
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Thank you very much. I have ordered a 30-30 volts 15 VA transformer yesterday. Have most of the other components in my junk.
Must start as soon as I can. Regards.
Must start as soon as I can. Regards.
As a guitarist, musician, and electronics hobbyist, I have formed exactly the opposite opinion. IMO, accurately preserving electric guitar starting transients leads to a very harsh sound that quickly fatigues the ear. Solid-state preamps with lots of negative feedback are very precise, accurately replicating the harsh transients. This sounds bad, particularly as SPL levels go up.
Good tube guitar preamps, on the other hand, tend to "squash" those big transients a little, usually starting right at the input grid, with more gentle "squashing" occurring in subsequent stages. The end result sounds less harsh to the ear, and depending on the amount of peak-squashing, may also seem to have more sustain.
Tubes also add small but perceptible amounts of harmonic distortion, which enrich the thin, cold, bland sound of a naked solid-body electric guitar.
I think that the reason simple tube guitar amp circuits sound much better than op-amp based solid state guitar preamps is precisely because of these failings of tube guitar amps. The tube amp squashes peaks and adds audible distortion - and that makes the guitar sound better. The solid-state amp reproduces the ugly sound of the instrument precisely. Result: thin, cold, "steely" treble, no warmth, and harsh transients.
KMG (the Russian engineer referred to earlier in this thread) made imperfect solid-state guitar preamps that squash the signal and add audible THD - and his "bad" solid state preamps sound much better than "good" op-amp based guitar preamps.
I've found that using a single JFET at the input of a solid-state preamp is enough to subtly reduce harshness in the sound. I speculate that this occurs because the JFET is sufficiently nonlinear to do some squashing of any big guitar transients. It's just "bad" enough to do some good to the sound. 🙂
In a nutshell, IMO, an electric guitar sounds best through a "bad" amplifier, and a "good" amplifier makes an electric guitar sound bad. By "good" I mean what any audio engineer outside the musical instrument field considers good: extremely linear, low THD, high headroom, flat frequency response. Great for Hi-Fi, but absolutely horrible for electric guitar.
I have been looking for explanations for years now. I made more than my share of terrible-sounding solid state guitar amps in the process, and was shocked when I first plugged into a tube guitar amplifier - it sounded so much better!
But solid state guitar amps have really made progress lately. The little Flamma Preamp (well under $100 USD) has many spectacularly good "tubey" sounds in it. Brett Kingman is a fantastic guitarist; look at what he can get out of one of these inexpensive little pedals:
-Gnobuddy
Thanks.
I notice most of the transistor preamps are under biased. The emitter voltage is usually about 1 volt or less.
Earlier 60s SS amps did not have any emitter resistors and sounded harsh when strummed..
When you strum the guitar strings heavily, you get a peak to peak voltage exceeding the bias setting.
Those preamps are good for clean solo with guitar set at full volume or light strumming with controlled volume from guitar.
When I raise the emitter voltage 2.5 or 3 volts, it is very clean with heavy strumming.
But to get a reasonable gain I have to increase the supply voltage to more than 40 volts.
To me FET sounds harsh. If you play distortion, you may like that grit.
FETs are suitable for the first input section only. They are not good in amplifying larger clean signals.
The signal level at the gate must be reduced in some way to amplify again.
There are lots of RC networks in a preamp that eliminates the attack (rate of rise).
The real harshness could be the biasing of input stages.
Another one is the wide frequency response of SS amps.
JC 120 is clean because of low input impedance (47K in the transistor and thick film IC TA 7122)
Coupling capacitors are smaller and has less of bass response. What you hear as bass may be more of the harmonics.
Peavey uses 220 K on input resistors and also is clean but more bass than a JC series.
Through out the valve circuit, the minimum frequency required is above 60 Hz.
The output transformer itself is designed for lack of low frequency response.
SS amps produce the beat notes of strings more prominently and sounds a bit muddy compared to valve amps.
This can be overcome by introducing lower value of coupling capacitors (I use 3 values selected with a switch).
Another thing is valve amps have very generous head room in the preamp section.
That is why I am interested to see if higher voltage solid state discrete preamps will sound better.
Most commercial guitar preamps use +/- 15 volts for opamps or from 20 to 30 volts for the discrete..
I am trying to build a 50 or 60 volts version when I get more time.
Still learning, may be right or wrong.
Best regards.
I notice most of the transistor preamps are under biased. The emitter voltage is usually about 1 volt or less.
Earlier 60s SS amps did not have any emitter resistors and sounded harsh when strummed..
When you strum the guitar strings heavily, you get a peak to peak voltage exceeding the bias setting.
Those preamps are good for clean solo with guitar set at full volume or light strumming with controlled volume from guitar.
When I raise the emitter voltage 2.5 or 3 volts, it is very clean with heavy strumming.
But to get a reasonable gain I have to increase the supply voltage to more than 40 volts.
To me FET sounds harsh. If you play distortion, you may like that grit.
FETs are suitable for the first input section only. They are not good in amplifying larger clean signals.
The signal level at the gate must be reduced in some way to amplify again.
There are lots of RC networks in a preamp that eliminates the attack (rate of rise).
The real harshness could be the biasing of input stages.
Another one is the wide frequency response of SS amps.
JC 120 is clean because of low input impedance (47K in the transistor and thick film IC TA 7122)
Coupling capacitors are smaller and has less of bass response. What you hear as bass may be more of the harmonics.
Peavey uses 220 K on input resistors and also is clean but more bass than a JC series.
Through out the valve circuit, the minimum frequency required is above 60 Hz.
The output transformer itself is designed for lack of low frequency response.
SS amps produce the beat notes of strings more prominently and sounds a bit muddy compared to valve amps.
This can be overcome by introducing lower value of coupling capacitors (I use 3 values selected with a switch).
Another thing is valve amps have very generous head room in the preamp section.
That is why I am interested to see if higher voltage solid state discrete preamps will sound better.
Most commercial guitar preamps use +/- 15 volts for opamps or from 20 to 30 volts for the discrete..
I am trying to build a 50 or 60 volts version when I get more time.
Still learning, may be right or wrong.
Best regards.
I've seen 'scope captures here on diyAudio, showing 10 volts peak-to-peak, straight from a hot humbucker pickup!
10 volts is definitely unusually high. But 1-2 Vpp is not unusual.
So I agree, the input stage has to be designed to cope with signals in that vicinity.
Now, what did Leo Fender do in his most famous tube guitar amps? The input stage was half of a 12AX7, with the grid tied to ground, and the cathode floating up to around 1.4 volts.
Grid current begins to flow when the grid voltage gets within roughly 0.5 volts of the cathode. So any positive signal peaks bigger than about 0.9 volts will cause some grid current to flow. That grid current flowing through the guitar electronics (volume pot, etc) will round off the voltage peak a little bit. Transients from the guitar are already softened a little by the very first preamp tube grid!
Sure, those numbers make perfect sense. Are you strumming an electro-acoustic guitar (acoustic with some sort of pickup), or a solid-body electric guitar?
The former (electro-acoustic) sounds fine through a solid state preamp, as long as you keep it from clipping. As you say, this means you either use high DC supply voltage, or keep the voltage gain low.
To my ears strumming a solid-body electric guitar, through the sort of amp you described, produces a cold, thin, unpleasant sound, with painful transients that feel like being stabbed in the ear with needles, particularly if you turn up the SPL.
On the supply voltage requirement: I have a little Fender Mustang Micro headphone amplifier. It runs on a single internal lithium cell (4.2V fully charged). Most likely the DSP chip inside runs on 3.3 Vdc.
You can set it to a clean tone, and strum hard, and there is no audible clipping. I was surprised by that.
I suspect this little amplifier has a resistive attenuator right at the input, cutting down the guitar signal, so that you can put it through a preamp and A/D converter that can only handle signals of less than 3.3 volts peak-to-peak.
I don't think we're talking about the same kind of FET circuit.
I typically make sure Vgs is at least 1.5 volts (by choosing a suitable JFET), don't bypass the source resistor, and feed the circuit from +18 volts DC. Voltage gain is kept low enough (by choice of Rd) to keep the JFET from audible clipping, even under hard strumming.
I never hear any harshness from this sort of circuit. In fact, I find the reverse to be true: there is less harshness than the perfectly-linear op amp or transistor stage fed from high supply voltage.
To reduce the rate of rise, you'd have to use a low-pass filter (not something I see in most guitar amps). And even if you had a low-pass filter, it wouldn't work on the big initial transients at the start of every guitar note, which tend to have lots of both low and high frequency content.
I agree that you can certainly get harshness by overdriving a stage.
But I'm talking about something else. Imagine this: plug a solid-body guitar into a 500-watt solid-state Hi-Fi amplifier. Set levels loud, but no clipping. This is "clean tone" in the most extreme form. But I find the sound harsh, and the starting transients unbearable.
These are not entirely accidental. If you reproduce the huge starting transient from the thicker guitar strings accurately, it will destroy the speaker quickly.
This is why even solid-state guitar amps do something to filter out low frequencies. There's no useful content below 82 Hz from a guitar in standard tuning anyway.
Beat notes come from nonlinearity. If your amplifer is basically a high-voltage op-amp, it will be very linear. This shouldn't cause beats, and I don't hear them myself. 😕
With most crude SS amps, if you turn up the treble, they sound harsh. Turn it down, they sound muddy.
Tube amps, with their softened transients and small amounts of level-dependent harmonic distortion, don't seem to suffer these problems to the same extent (unless you set them for extreme levels of overdrive, in which case all guitar amps sound like power tools grinding on a tin roof. I've never understood the attraction of those sorts of guitar sounds.)
Lots of headroom on the anode side...but what about the input grid? Not much headroom there at all.
I can hear subtle (but clearly audible) "tubey" distortion from a single-coil Fender 'Strat plugged into a single half-12AX7 gain stage. This is still very much "clean guitar tone", but there is already a few percent of low-order distortion there.
I have one guitar - an Ibanez AS73 with fairly hot humbucker pickups - which, plugged straight into the input of my Fender '65 Princeton Reverb (reissue), puts out a strong enough signal to quite audibly overdrive the input stage!
Even though the input-stage triode in the PRRI is run at something like +350 volts B+, it has very little input headroom.
In Leo's time, his guitar pickups were far weaker than the ones in my Ibanez, so he probably never encountered this problem.
I agree with you 100% that we don't want unintentional clipping of the preamp.
Where we don't (yet!) agree, is whether we also want the preamp to be perfectly linear, like a good op-amp, or deliberately faulty and slightly nonlinear, like a half-12AX7 triode. 🙂
KMG's FET preamps used high supply voltages (just as high as a 12AX7 stage). Output headroom is huge. But he went to a great deal of trouble to introduce deliberate nonlinearities into this preamp stages, mimicking the heavy nonlinearities in a half-12AX7.
To my ears, KMG's designs sound excellent. Until quite recently, they were probably the best-sounding solid-state electric guitar amplifiers I'd heard. And this wasn't because they were linear and accurate: it was because they were nonlinear, and inaccurate!
You can get there easily with LND150 MOSFETs, if you want. Don't use KMG's nonlinear diode strings in the source bias network; just use an unbypassed, or only partially bypassed, source resistor. And make sure Vgk is at least 1.5 volts. And keep voltage gain low enough to avoid output clipping when a guitar is plugged in and strummed hard.
Same here. But have had too many bad experiences with terrible guitar sound resulting from "perfect" Hi-Fi preamps (op-amps, whether discrete or integrated). I am quite sure the lovely little discrete op-amp that Mark Johnson posted above, for instance, will sound horrible if you plug a solid-body electric guitar into it. It's perfect for Hi-Fi, but horrible for electric guitar.
We need imperfect amplifiers if we want good sound from solid-body electric guitars. Mark Johnson's amp is too perfect, just like other similar discrete or integrated op-amp based circuits. Perfect preamp + solid-body electric guitar equals harsh and unpleasant sound.
(Acoustic-electrics are different. Big hollow-body jazz archtops are different. Hi-Fi amps work for those.)
Maybe we'll agree. Maybe we won't. Hopefully, you'll have fun with your project either way. 🙂
-Gnobuddy
I agree with you, that Hi-Fi can "work" on acoustic electrics up to point, but they can still sound rather flat and clinical. I recently did a live jam with
my acoustic with a deArmond coil pickup, and plugging in my homebuilt FET preamp before my Traynor solid state amp (through the effects return, bypassing the amp's preamp section) and it made a noticeable difference in a very good way. More presence, livelier and some of that warmth that tube amps have. Low order harmonics and what we've discussed about dynamic bias shifting with discrete , "self-biased" stages..I believe that even just a couple of these stages is enough to make a major difference to the "clean" sound. Nothing over the top, it's really interacting in a subtle way. Slightly imperfect, non-linear response is a very natural organic sound. Think of the way the overtones change on the note attack and decay and playing volume of an acoustic instrument such as a piano, saxophone, violin for examples.
There is (or was) an America boutique tube guitar amp manufacturer, whose lineup included a tube-based amplifier for acoustic-electric guitars. I've never heard one, but it was well reviewed in guitar magazines, for whatever that's worth.
Now this is interesting! To my ears, low-inductance magnetic pickups on acoustic guitars still sound very "electric", even though they have a wider frequency response than other types of magnetic pickups used on purely electric guitars. They have more treble, but still have some of that electric-guitar harshness to their tone, sounding very different from the same guitar unplugged.
I wasn't sure why, until I ran across a university student research project involving mathematical modelling of a typical magnetic guitar pickup. Here's the interesting part: the magnetic pickup itself creates a lot of harmonic distortion!
This happens because of the way the pickup works. There is very little variation in magnetic field strength across the width of a pickup pole, so transverse vibrations of the string (in the same plane as the guitar top) produce little output from a magnetic pickup.
On the other hand, the magnetic field around the pickup poles dies away rapidly in the direction perpendicular to the guitar top. So string vibrations perpendicular to the guitar top generate lots of output from the pickup.
However, the magnetic field dies away with distance in an extremely nonlinear fashion. As the string moves through this varying spatial field, the magnetic field in the pickup coils varies - but in a distorted way, not matching the actual physical movement of the strings. The pickup coil then responds to this distorted magnetic waveform, by generating a distorted electric field.
As the Maxwell equations of electromagnetism tell us, the actual electrical output of the pickup coil depends on the rate of change of magnetism with time (i.e., the time derivative of the magnetic flux through the coil).
Because of the time derivative, this electrical signal looks even less like the actual physical movement of the strings. But it too is heavily distorted, just like the magnetic field waveform through the pole-pieces was.
And that, I think, is why magnetic pickups on acoustic guitar still sound very "electric". They produce the same sort of distorted waveforms as every other e-guitar magnetic pickup, the only difference being a wider frequency response due to the reduced self-inductance.
I know that quite reputable acoustic guitar manufacturers - Taylor, for instance - have gone back and forth between piezo pickups, and magnetic pickups, in the search for a more natural sounding plugged-in sound. To my ears, the piezo pickups get much closer to this, especially if you apply a little judicious equalization to tame any excessive high frequencies.
Anyway, I speculate that the fact that you were using a magnetic pickup (rather than a piezo) on your acoustic guitar might have something to do with the fact that the sound was noticeably improved by going through a slightly-distorting amplifier. The pickup already sounds a bit harsh and "electric" by itself, and benefits from slight amplifier nonlinearity in the same way as every other magnetic guitar pickup.
That said, my best acoustic guitar is a Takamine, with a piezo pickup and onboard Takamine "Cool Tube" preamp, using an actual 12AU7. Plugged in, it sounds more natural than my other piezo-equipped acoustic guitars. Whether that is due to the tube gain stage, or something else, I can't be sure.
Agree 100% with you.
It's an interesting thing, that the difference between mediocre art, and great art, always comes down to very subtle things. I first noticed this while walking through a museum full of priceless paintings with my wife (who is a trained artist, and was kind enough to educate me about some of what I was seeing). But the same thing applies to music just as much as to visual art - subtle changes make all the difference.
I listened to several Gary Moore tracks in my car on the way to work this week. What a great guitarist he was! And so much of his amazing guitar playing was about small subtleties: his playing usually includes a wide dynamic range from soft to loud, a wide distortion range from almost-clean to heavily overdriven, a wide array of picking speeds from long sustained notes lasting an entire bar or more, to blizzards of lightning fast 32nd notes. Moore packed in a whole lot of subtleties, which lesser guitarists never notice they're missing.
Again, I agree with you 100%.
On my commute back home after work last night, I was drumming with my hands on the plastic dashboard of my car while waiting for the traffic light to change from red to green.
I had just been listening to Gary Moore, and thinking about the subtleties in his playing. And maybe because that was on my mind, I noticed that I was getting quite a range of different percussive sounds out of the plastic dashboard, simply by varying the force of the impact, and the position and angle of my hands.
It made me think about how expressive "organic" sounds tend to be - there is subtlety built into even the sounds a plastic dashboard (!) makes when hit with a human hand! Overtone changes, note attack changes, playing volume changes.
For the same sort of reason, when playing guitar solos through my Flamma preamp, my favourite model is the Two Rock Coral one. It's very organic, very responsive to picking intensity, and can vary from very clean to quite distorted just by varying your picking dynamics.
My favourite when strumming chords is the Fender Blues Deluxe model, set to the clean channel. It's a really nice simulation, and to my ears, it actually sounds more organic and "tubey" than my actual tube Fender Princeton Reverb does!
-Gnobuddy
IIRC, I found a small stock of a 50-volt rated audio op-amp at Digikey Canada not long ago, in an 8-pin DIP package.
It was marked as an obsolete part, but it's perfect for hobbyists - the shinier new replacements are all surface-mount parts. Much more of a pain to solder at home, and you'd need a breakout board or custom PCB.
I can't remember the op-amp part number, but if there's interest, I'll try to look it up.
As already mentioned, I don't think a high-voltage op-amp is the way to good electric guitar sound, particularly for solid-body guitars.
-Gnobuddy
back to the days that 5532 at the first time it hits the market, some of the professional audio equipment manufacture found it can be running at +-22v, although the rated voltage is only +-18v. that was factory overclocking(overvoltage?) behavior.
Even now, the ti website(or pdf?) of the ne5532 has a special warning of "not to overvoltage this chip".This is very different from a common notification of "absolute maximum ratings".
Even now, the ti website(or pdf?) of the ne5532 has a special warning of "not to overvoltage this chip".This is very different from a common notification of "absolute maximum ratings".
Just for fun, I drew up a high-voltage guitar preamp input stage using two LND150 MOSFETs. I've built similar circuits for other purposes.
The +170V DC supply rail is easily obtained by rectifying the output of a 120:120 line isolation transformer. The -24V rail is easily obtained from a 12-0-12 transformer, or a voltage doubler connected to a 12V AC transformer.
The use of a 24V negative supply rail simplifies biasing, and makes the operating point rock stable against parameter variations in the MOSFETs, and/or temperature variations.
The two pairs of red LEDs are used to protect the MOSFETs from excessive gate-source voltages in either direction. You can use green LEDs here if you want to allow wider Vgs swings before protection kicks in, but it isn't necessary.
The 10k series input resistor reduces the chance of picking up local radio stations via the guitar cable and internal wiring.
Voltage gain is set to 10x (+20 dB) by R1/R2/C1/R5. C1 also sets the lower -3dB frequency, chosen well below the 82 Hz lower limit of a guitar in standard tuning.
R5 can be reduced if you want more voltage gain. I wouldn't go for more than 50x gain (+34 dB), which will be achieved if R5 is reduced to 1k. C1 should be increased to 4.7uF if this is done, to maintain bass response.
C3 rolls off high frequency response above roughly 20 kHz. There is nothing good from an electric guitar above 5 - 10 kHz, and by limiting excessive high frequency response, we get a stabler amplifier that's less prone to be bothered by RFI or electrical noise.
R8 is a build-out resistor to keep the second LND150 (M2) stable, and stop it from oscillating at radio frequencies if the output of the circuit is connected to the wrong sort of load (a long coax cable, for instance).
C2 can be changed, depending on the impedance of the load the circuit is feeding.
The circuit will easily handle 3Vpp input signals from the guitar (hard strumming with hot pickups) with no clipping anywhere. There will be tiny amounts of good-sounding harmonic distortion in the output, particularly if you raise the gain by using R5 = 1k.
-Gnobuddy
The +170V DC supply rail is easily obtained by rectifying the output of a 120:120 line isolation transformer. The -24V rail is easily obtained from a 12-0-12 transformer, or a voltage doubler connected to a 12V AC transformer.
The use of a 24V negative supply rail simplifies biasing, and makes the operating point rock stable against parameter variations in the MOSFETs, and/or temperature variations.
The two pairs of red LEDs are used to protect the MOSFETs from excessive gate-source voltages in either direction. You can use green LEDs here if you want to allow wider Vgs swings before protection kicks in, but it isn't necessary.
The 10k series input resistor reduces the chance of picking up local radio stations via the guitar cable and internal wiring.
Voltage gain is set to 10x (+20 dB) by R1/R2/C1/R5. C1 also sets the lower -3dB frequency, chosen well below the 82 Hz lower limit of a guitar in standard tuning.
R5 can be reduced if you want more voltage gain. I wouldn't go for more than 50x gain (+34 dB), which will be achieved if R5 is reduced to 1k. C1 should be increased to 4.7uF if this is done, to maintain bass response.
C3 rolls off high frequency response above roughly 20 kHz. There is nothing good from an electric guitar above 5 - 10 kHz, and by limiting excessive high frequency response, we get a stabler amplifier that's less prone to be bothered by RFI or electrical noise.
R8 is a build-out resistor to keep the second LND150 (M2) stable, and stop it from oscillating at radio frequencies if the output of the circuit is connected to the wrong sort of load (a long coax cable, for instance).
C2 can be changed, depending on the impedance of the load the circuit is feeding.
The circuit will easily handle 3Vpp input signals from the guitar (hard strumming with hot pickups) with no clipping anywhere. There will be tiny amounts of good-sounding harmonic distortion in the output, particularly if you raise the gain by using R5 = 1k.
-Gnobuddy
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Thank you very much.
I studied KMG's designs, heard the mp3 demos but found too complicated for me.
I do not play distortion at all. My amp is 2 x 40 watt capacitor coupled, driving 2 nos 12" speakers in open back cabinet.
I find most speakers do not sound good if driven more than 30 watts.
Speakers with thinner cones sound beautiful.
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Wanted to do the same as your design with bjt, but there are not many choices for a low noise hv transistor.
Will look in to this. Thank you again.
Best regards.
I studied KMG's designs, heard the mp3 demos but found too complicated for me.
I do not play distortion at all. My amp is 2 x 40 watt capacitor coupled, driving 2 nos 12" speakers in open back cabinet.
I find most speakers do not sound good if driven more than 30 watts.
Speakers with thinner cones sound beautiful.
====
Wanted to do the same as your design with bjt, but there are not many choices for a low noise hv transistor.
Will look in to this. Thank you again.
Best regards.