Don't worry, you are not the only one with "tin ears". In the early 80ies, when the H2-hype came up, I did my own investigations. At that time I built my distortion units around the OTA CA3080, which works quite symmetrical producing H1, H3, H5 etc. To make it asymmetrical I feed a portion of the output signal into it Iabc-input. This kind of signal quadrature produced the H2, H4 overtones as expected. I did some listening tests and decided it not being worth the effort. Obviously I do have tin ears, but I do not care. The hole debate about ultimate guitar sound is a side-show for me, a waste of time better investigated in improving the own guitar playing abilities.
...and you would hear it even more clearly if the signal had gone through several triode stages as well as at least one pentode stage, no? That's what would happen with any actual tube guitar amp.
Pentodes are considerably more nonlinear than triodes, and there is a definitely audible amount of distortion from a single-ended 6V6, for instance. A lot of blues players like single-ended output stages.
With a push-pull output stage odd harmonics cancel (to a degree decided by the actual balance of circuit components), and output stage THD is considerably lower, at least until you start driving it into the beginnings of clipping.
Back in 2010 or so, my first tube amp was actually a hybrid, a Fender Superchamp XD, with an analogue/digital preamp, and an all-tube power amp section (two triode stages, two 6V6 beam power tubes in push-pull). The preamp had several digitally simulated "voices", but one of them was "clean", i.e., the preamp didn't appear to add any digitally generated distortion; all you heard was the squeaky-clean op-amps, followed by the tube power amp.
Quite a few people who posted on guitar forums I belonged to, ended up with that "clean" voice being their favourite. Many guitarists who also owned larger and more expensive tube guitar amps commented that the little SCXD produced really nice Fender "Blackface" clean tones.
AFAIK nobody did THD measurements on the preamp-only to prove with 100% certainty that there was no DSP-generated "tubey" THD on the clean channel, but the fact remained that lots of people preferred the clean tones from this hybrid amp to the clean tones from any of Fender's other solid-state amps. I think there is good reason to believe that this was because of the small, but audible, amount of "tubey" distortion from the four tubes in the power amp section.
Going back to your simulation, there's no doubt that it's easier to hear small amounts of THD with a pure sine wave, than with a guitar signal, which already contains many harmonics.
When more than one frequency is present at the input, slight nonlinearities in the tubes also create intermodulation distortion (IMD), which is usually much more audible than small amounts of THD.
Small amounts of IMD add subtle colour to the guitar tone. Larger amounts add audible "roughness". Depending on the style of music and the guitarist's preferences, that may or may not be desirable.
One test simple test I use with DIY tube preamps, is to play a perfect fifth interval (play the notes C & G simultaneously, for instance), and listen for any audible change in timbre.
While I've done some LTSpice tube simulations, I'm not sure I fully trust the results of running audio through them.
-Gnobuddy
So why are you participating on this thread at all? Shouldn't you be out wood-shedding (American for practicing your instrument) instead?
Seriously, can you imagine a classical pianist saying "I have zero interest in playing a Steinway Grand piano, it is a waste of time. I prefer to continue to do all my practicing on my 1975 Sammick upright piano" ?
It's not as though you have to pick one extreme or the other, you know. There's a whole spectrum in between (crap equipment + diligent study) and (great equipment + no study). Just because a person has an interest in good-sounding equipment, does not mean that they have to stop working on their guitar playing abilities. It just means they'll get better-sounding results from all of their hard work.
Yes, there are people who are constantly buying new equipment in a never-ending search for better sound. And I agree that is a futile pursuit, and an unsatisfying one; blind consumerism disguised as a substitute for diligent personal development. This attitude is very common on guitar forums, and that's the reason why I no longer participate on any of them. Most threads are about purchasing gear, not about learning to be a better musician.
But that's only one end of the spectrum. At the other end, is gear that is so limited in sound or playability, that it hinders the development of the musician. And that end of the spectrum is equally futile, equally unsatisfying. It's like trying to become a fine painter, but limiting yourself to using nothing but a set of children's wax crayons.
I've spent time at that latter end of the spectrum. I know personally how limiting and frustrating it can be, trying to get good sound out of bad equipment. As the old saying goes, "You can't make a silk purse out of a sow's ear"! But, at the time, I was a poor student living on a tiny scholarship, and I had no money to buy anything better.
One of the remarkable developments of recent times, is that good-sounding equipment that works well, doesn't have to be expensive now, at least for those of us fortunate enough to live in a first-world country. So there's no reason to limit oneself to poor-sounding equipment any longer.
For example, this reviewer really liked this $100 USD guitar (and it's obviously perfectly playable):
The same reviewer really liked this $200 USD tube guitar amp, and gets lots of excellent sounds out of it:
I don't know of a solid-state guitar amp that sounds equally good, plays equally loud, and costs as little. Maybe in a few more years?
-Gnobuddy
I definitely don't completely disagree with this. Good tone makes practice more enjoyable and may be a source of inspiration, so I don't think the pursuit of better tone is a complete waste of time. That said, however, I'd rather listen to an exceptional player with mediocre gear than a mediocre player with exceptional gear...
My current circuit design already emulates the output tube nonlinearities reasonably accurately (required to reproduce the crossover distortion and related compression correctly) as well as the preamp tube nonlinearities at clipping (including the bias excursion), so I've been trying to figure out whether also emulating the preamp tube nonlinearities below clipping levels is worth the effort.
I made some new samples with an entire JTM45-style preamp in LTspice. One has tubes (Immler's 12AX7 model again), and the other has ideal (zero distortion) gain stages with the basic parasitics included (Miller capacitance and output impedance). I set the input level so that the tube version would very slightly clip the loudest transients. Stimulus was some chords played on my guitar.
I loaded the level-matched outputs into ABX comparison software and ran 20 trials. I got 18 correct (statistically significant result), so it looks like I can indeed hear the difference. But it's pretty darn subtle, at least to my ears. Basically, I heard a very slight difference timbre.
A MOSFET based Sziklai pair sims very nicely. (BSS123N, BSS84, 4.7k, 4.7k). Cascoded JFETs might better, but I haven't checked yet, and you can't trust the simulator because they are likely to be perfectly matched, which is unrealistic.
I think it makes sense, with a simulation like you did THD would stay quite low. Maybe 0.5 % or so, and it is mostly H2. That is not so easy to discern.
The way I had it set up, the loudest instantaneous peak was clipped by about 5dB (perhaps "very slightly clip" wasn't the best choice of words in my last post). With a 1kHz sine of equal amplitude to the loudest peak, the THD is 17% (H3 dominant). At -6dB, the THD is 6.5% (H2 and H3 about equal level). At -10dB, the THD is 2.7% (H2 and H3 about equal level again). At -18.3dB (the RMS level of the input sample relative to the loudest peak), the THD is 0.6% (H2 dominant).
The H2 level relative to H3 is a bit lower than one might expect. This is because there are two inverting gain stages driven at similar input levels, so their even-order components partially cancel.
And I definitely do not disagree with you - just at a certain point of my life I decided my amps are good enough for me 🙂
And I think that level is most of what you hear, the peaks are over before you know it.
18 out of 20 is certainly a solid statistical result. Nice work. 🙂
You may hear more differences at higher volume settings, more typical of live e-guitar.
That said, the difference between ho-hum art, and great art, is invariably quite subtle. Remember the story about Michaelangelo?
Once a musician gets beyond a basic command of the instrument, everything that follows is diminishing returns; we practice, and study, and work, more and more hours, to get smaller and smaller gains. We only gain subtleties from that point on.Michaelangelo said:
But it is those increasingly small gains that take us from beginner to intermediate, and from intermediate to expert, if we ever get there.
Another thing: the single most crucial tool any musician can have is their ears. Ear-training is part of the routine curriculum at famous guitar-teaching institutions - but those of us who are self-taught amateurs rarely realize that this is an important part of our musical development. If we work at it, we can train our ears to be better at recognizing pitch, to be better at recognizing intervals - and to be better at recognizing subtleties in timing and timbre. But we need a guitar and amplifier capable of producing subtleties in timbre, or we cannot develop our ears in this way.
IMO, the goal is to have equipment that's good enough not to hinder that progress. Nobody needs a $15,000 Gibson acoustic to learn their first chord on. But if we stay with a solid-state Fender Frontman 20 for five years of music study, we stifle our development as musicians.
When I first got interested in electric guitars, I was still a student with no money. I built my own electric guitar (pic attached) using whatever scrap materials I could scrounge or buy. I leveled the frets with a whetstone, but had no crowning tool, so the guitar was hard to play. I made the pickups from scraps of ceramic magnet from a broken loudspeaker, and wire I got by taking apart a broken relay. They worked, but were very low output. The lightweight body was mostly pine (from an orange crate!), the lightweight bridge I sawed and filed from a scrap of aluminum u-channel. The guitar had very little sustain, probably because of the light parts.
I played that guitar for several poverty-stricken student years. It got me through those initial stages as a beginner guitarist. I learned to find chords and play scales over the entire neck of the guitar, and I could play simple solo parts that didn't require lots of sustain. But eventually the guitar's limitations were holding me back.
And that was the point at which I finally bought a budget Squier Strat, which got me through another couple of years of musical development.
But my solid-state guitar amplifiers continued to hold me back. I built many, all of which sounded bad. Once I got my first job, I bought several over the next few years. All sounded bad. I bought another guitar or two. They sounded bad.
I could sound good on an acoustic guitar, but I always sounded horrible on any electric guitar I owned. Having apparently tried everything, I was coming to the conclusion that it was just my own limitations - apparently I could not sound good with an electric guitar to save my life. I gave up playing entirely for several years.
Then a wonderful thing happened. I'd had access to the Internet for years in college, but it had been limited to a few university websites and exchange of scientific research publications and data. But the public Internet had started to take off, and by the time I got interested in guitar again, guitar forums existed. And that's when I found out that some people thought that tube guitar amps sounded better than solid-state guitar amps.
I was very skeptical. Tubes were old and obsolete before I was born. I had been working with solid-state electronics literally since I was a child, and they did everything I wanted (except with guitar). How could old obsolete electronic devices possibly sound better than the vastly improved newer solid-state devices I'd been using most of my life?
But I was sick of sounding bad every time I picked up an electric guitar, and I had nothing to lose. So I drove to Guitar Center and bought my first tube (actually hybrid) guitar amplifier, a Fender Super Champ XD. This wasn't a token "throw one 12AX7 in the box and run it on 12 volts DC" hybrid; in the SCXD, the entire power amplifier section was all tubes, run on 350+ volts DC, in a circuit almost identical to a $1000 Princeton Reverb power section.
So I got home with my new amplifier, set it on the floor, grabbed one of my guitars, plugged it in, turned on the amplifier and waited for it to warm up, then strummed a simple beginner chord, with the amplifier set to the clean channel. And my jaw almost hit the floor: there, for the first time in my life, was a lovely sound from an electric guitar in my hands.
I couldn't believe it, but there was no denying what I was hearing: this amplifier, with the century-old obsolete electronic devices in it, sounded better than any guitar amplifier I had ever plugged into until then.
That was the beginning of my interest in tubes. I don't think tubes are magic, and I think they are a terrible choice for Hi-Fi audio. But I know for a fact that if you simply throw a few tubes together, and build a circuit cobbled together by Leo Fender sixty years ago, it will sound great with an electric guitar. And it is very difficult to make a solid-state guitar amplifier that sounds equally good.
However, tubes continue to get more and more expensive, and so do ancillary parts like output transformers. They have relatively poor reliability, tube amps are heavy, and they are bulky. They tend to be too loud for me, and they do not turn down well; to get good sound, they have to be operated loudly.
And because of all these failings of tubes, I eventually developed an interest in trying to get "not-horrible" sounds from a solid-state guitar amplifier. That doesn't seem like a high bar, but it took me a lot of tinkering, and a lot more complexity than I anticipated, before I got there. A few years ago I managed to design and build a "not horrible" solid-state guitar amplifier for a senior-citizen friend with a physical disability. He walks with two canes, and cannot carry a large heavy amplifier - it had to be small and light, meaning it had to be solid-state.
That amplifier produces okay clean tones. Not horrible, but not as good as my old Super Champ XD with its tube power amplifier section. With DIY solid-state guitar amplifier designs, I never got much beyond "not-horrible". I never got to great, or even to excellent.
Some time after that, I found out about KMG's work. He got well beyond "not-horrible".
I probably have enough bits and pieces in the junk-box to build one of his MOSFET gain stages and tinker with it. But by then I was back to building tube guitar amps; it was so much easier to get a good sound if you used tubes!
-Gnobuddy
Attachments
And, as I wrote here many, many posts ago, that makes you a lucky man. 🙂
-Gnobuddy
Two fairly affordable solid-state guitar amps that sound pretty good:
(Neither one is DIY, though.)
-Gnobuddy
(Neither one is DIY, though.)
-Gnobuddy
I've tried out the Katana, and agree it does have some really good sounds in it. I didn't notice any significant latency, which is important for the playing "feel" of an amp.
I think that's been a big leap in DSP recently, getting the processing speed fast enough that it doesn't feel sluggish and unresponsive.
I actually own a Katana 50. I bought it because, IMO, it can produce clean tones that sound more "tubey" than my actual tube Fender Princeton Reverb!
To my ears, the Katana series was the first DSP/modelling tube guitar amp that sounded good and didn't cost well over $1000. Here in Canada I ended up paying almost $500 for my Katana 50, but that is still a lot less expensive than a Kemper or Axe-FX or Atomic Amps AmpliFIRE.
The '65 Princeton Reverb reissue suffers from Fender's decision to use a 440 volt B+ rail. 6V6 output tubes are only rated for 350 volts, and many current-production tubes will not tolerate being abused at 440 volts for long.
The insanely high B+ apparently results from the decision to use a original 1965-spec reproduction power transformer. Back in 1965 Leo Fender ran his 6V6 amps at far too high a B+ in the attempt to squeeze more power from cheap tubes, and since that time our AC mains voltage has increased from maybe 115 V to maybe over 120 V. Put those things together, and now you have 440 volts on the plates of tubes that are only rated for 350 volts.
So my PRRI ended up with JJ 6V6S output tubes in it. These are considered the toughest current-production 6V6 tubes available - but they sound nothing like a proper 6V6, and the tube internals look nothing like a 6V6, either. These 6V6S tubes sound much too clean.
I never measured the B+ to the 12AX7's in the preamp, but they might also be very high.
What I can say for sure, is that my PRRI borders on solid-state sterile clean. And my hybrid Super Champ XD, which has an all-tube power amplifier section very similar to the one in the PRRI, when set to the clean channel, sounds more "tubey" than the all-tube PRRI!
I have had some dealings with DSP in the past, and to my surprise, the ubiquitous 44.1kHz clock rate - which is frequently used outside the actual DSP core - can produce significant latency.
At 44.1 kHz, samples come along every 22.67 microseconds. That's a very short time indeed, but because microprocessors, USB chips, and DSP chips all have varying latencies (they can't respond while they're busy doing something else), there might be an occasional slowdown in the regular arrival or departure of digital samples.
That is intolerable, so we have to use input and output buffers, which store enough samples to ensure that they can smooth out any irregularities in the arrival of data. Once the buffer is full, samples can be clocked out with perfect regularity, and there will always be a small reservoir of samples still in the buffer so there are no data drop-outs.
And that's where audio delays can become significant. If a 44.1 kHz input buffer stores 256 samples, the corresponding delay is 5.8 milliseconds. If the output buffer stores another 256 samples, that's another 5.8 mS of latency, for a total of 11.6 mS.
I'm not the fastest musician in the world, and for me, I found 10 milliseconds of delay was acceptable. 15 mS of latency started to feel weird (I perceived it as the guitar being unresponsive, as though the strings had grease on them and were slipping off my guitar pick/fingers.) 30 mS was distinctly unpleasant, and it went rapidly downhill from there.
Considering that 10 mS of latency is roughly equivalent to the time it takes for sound to travel ten feet, I was surprised that such small latencies could even be perceived.
Back when I was involved with all this, the DSP processor itself ran at tens or hundreds of MHz, and latencies within the actual DSP processor tended to be very low. It was the unavoidable data buffers, combined with the CD-standard 44.1 kHz clock rate, that caused most of the latency.
I assume newer DSP appliances use higher internal clock rates to reduce this problem.
-Gnobuddy
I think under 10 mS latency, the ears/brain/fingers can adjust and compensate for the lag time while playing live. Below 5 mS and things start to have the right feel and response. More than about 15 mS and it's just distracting to play along with a beat with any time precision, you are basically trying to play notes in anticipation of the upcoming beat. As you mentioned 15 mS starts to feel weird. A lot of classic rock guitar songs play at about 100 Beats/minute which is 1.66 beats a second. That's 600 mS per beat. A run of eighth notes would be time intervals of 75 mS , each note. A run of 16th notes 37.5 mS per note. I don't think an individual event (note) with 10 mS latency is too discernable, but trying to keep in sync playing consistently in time with the song, our brains notice right away the time differences between "real time" of the song playing, and the notes we're trying to get out of the amp in time with the music. Really distracting on a relatively fast run when the latency time is a significant portion of the note intervals.
Earlier in this thread, I suggested that some solid-state guitar amplifiers produce brief harsh clipping at the start of each guitar note.
I didn't sleep well last night, and while lying in bed awake at 4 AM, I remembered a long-ago You Tube video where I heard this phenomenon quite clearly. Today I found the video in question, fortunately still up on You Tube after nine years.
The video below features a Joyo guitar pedal that emulates a Fender Deluxe. As solid-state guitar pedals go, this one was popular, because it does a pretty credible job of sounding like the tube amp, while costing about 5% as much.
In the video, a good guitarist alternately plays the same lick through the real Fender tube amp, and also through the Joyo pedal. Amp and pedal were set to sound as much alike as possible. The alternating sound clips are labelled either "A", or "B", and the listener asked to guess which one is the real tube amp, and which one the budget-priced solid-state pedal.
When I first listened to these clips nine years ago, using tiny computer speakers plugged into a PC, I couldn't immediately tell which was which. But when I plugged in a pair of headphones and listened through those, I had no trouble telling the solid-state device from the tube device. There are multiple places in the video where I heard brief harsh distortion from one device, but not from the other. That harsh distortion is the signature failure of most solid-state guitar amplifiers, so it was an immediate giveaway.
Try it yourself, and see what your ears tell you!
One example: in the first sample sound clip, starting around 1:12 minutes, the guitarist uses his strumming hand to give a gentle percussive "thwack" to the strings at intervals, to add to the rhythm. Listen to the way the amplifying device responds to that "thwack".
Listening through headphones, one device produces an audible burst of harshness, the other one produces a clean "thump" with no audible harshness.
Here we go:
If you didn't already hear it, I recommend going back and re-listening to the segment right around 1:18 minutes as a particularly glaring example.
Though the Joyo suffers from intermittent harshness, I bought one anyway, because at the time (9 years ago), it did a better job of sounding like a decent tube guitar amplifier, than any other affordable solid-state guitar "amp".
In actual use, I found the failings of the pedal are much more audible than they are in the You Tube clip. But, nine years ago, it was still very good bang for the buck. I've even used it on one of my home recordings, when time ran out on me, and I needed to quickly track a guitar solo.
With duty cycle modulation, I think SS circuits can do a decent job of sounding like a tube guitar amp during very heavy overdrive. IMO the big challenge is to produce good "tubey" (nearly) clean sounds, and to avoid harsh-sounding distortion when the amp is just barely overdriven.
In other words, IMO, it's a lot easier to make a solid-state guitar amp sound like Pantera, than to make one that sounds like Mark Knopfler in "Sultans of Swing".
-Gnobuddy
I didn't sleep well last night, and while lying in bed awake at 4 AM, I remembered a long-ago You Tube video where I heard this phenomenon quite clearly. Today I found the video in question, fortunately still up on You Tube after nine years.
The video below features a Joyo guitar pedal that emulates a Fender Deluxe. As solid-state guitar pedals go, this one was popular, because it does a pretty credible job of sounding like the tube amp, while costing about 5% as much.
In the video, a good guitarist alternately plays the same lick through the real Fender tube amp, and also through the Joyo pedal. Amp and pedal were set to sound as much alike as possible. The alternating sound clips are labelled either "A", or "B", and the listener asked to guess which one is the real tube amp, and which one the budget-priced solid-state pedal.
When I first listened to these clips nine years ago, using tiny computer speakers plugged into a PC, I couldn't immediately tell which was which. But when I plugged in a pair of headphones and listened through those, I had no trouble telling the solid-state device from the tube device. There are multiple places in the video where I heard brief harsh distortion from one device, but not from the other. That harsh distortion is the signature failure of most solid-state guitar amplifiers, so it was an immediate giveaway.
Try it yourself, and see what your ears tell you!
One example: in the first sample sound clip, starting around 1:12 minutes, the guitarist uses his strumming hand to give a gentle percussive "thwack" to the strings at intervals, to add to the rhythm. Listen to the way the amplifying device responds to that "thwack".
Listening through headphones, one device produces an audible burst of harshness, the other one produces a clean "thump" with no audible harshness.
Here we go:
If you didn't already hear it, I recommend going back and re-listening to the segment right around 1:18 minutes as a particularly glaring example.
Though the Joyo suffers from intermittent harshness, I bought one anyway, because at the time (9 years ago), it did a better job of sounding like a decent tube guitar amplifier, than any other affordable solid-state guitar "amp".
In actual use, I found the failings of the pedal are much more audible than they are in the You Tube clip. But, nine years ago, it was still very good bang for the buck. I've even used it on one of my home recordings, when time ran out on me, and I needed to quickly track a guitar solo.
With duty cycle modulation, I think SS circuits can do a decent job of sounding like a tube guitar amp during very heavy overdrive. IMO the big challenge is to produce good "tubey" (nearly) clean sounds, and to avoid harsh-sounding distortion when the amp is just barely overdriven.
In other words, IMO, it's a lot easier to make a solid-state guitar amp sound like Pantera, than to make one that sounds like Mark Knopfler in "Sultans of Swing".
-Gnobuddy
I found that to be where the Fender Frontman (Solid state, op amp based) series fell short. The clean channel was totally void of any distortion, and the drive channel had hardly any room to be "barely" overdriven without getting that "harshness". With the Peavey transtube series, I heard a bit of harshness in the crunch (initial attack of the notes) but it was workable. I don't find that JFETs clip as harshly, and when overdriven with a big signal at the input stage they can sound great..maybe a bit too compressed and squishy, but running them at higher supply voltage, and being careful how much signal gets fed to the proceeding stage, can help.
Agree 100%. About a decade ago (2011?), Guitar Center offered the littlest Frontman (15R) in bright red Tolex at Christmas time. It must not have sold well, so GC dropped the price. I forget how much, but I think it was way under $100 - might have been $65 or something like that.
I quite liked the bright red, and the low price was tempting. I thought it might make a good leave-it-at-work amp for playing during my lunch break. But I quickly found I couldn't stomach the cold, sterile cleans, or the harsh-sounding overdrive.
The Frontman did turn out to be usable as a (very quiet) bass guitar amplifier, though! Turn it up and the speaker would bottom out and rattle, but it could get just barely loud enough to fatten the sound of an unamplified steel-string acoustic guitar a little. Perfect for me and a buddy sitting at two ends of the same couch!
Agree on JFETs being less harsh.
I've become curious about the idea of trying the other edge of the datasheet, i.e. trying JFETs on very low supply voltage, just for a "dirt" channel. There won't be any clean headroom, but if there's barely enough voltage for the JFET channel to conduct, will it produce softer saturation on negative half-cycles? Maybe if the JFET is operated at 4.5V or 3V or even 1.5V it will saturate more like a triode?
Older JFETs like the old 2N3819 produce very little voltage gain at 9V, and may produce less than unity voltage gain if run at such low voltages. But I found that a J112 had much higher transconductance, and it stayed high down to low drain currents, meaning you could use a much larger drain resistor. I got a voltage gain of about 30 dB (roughly 35 times) from one, running on 18 volts. Maybe it would still produce usable gain when run on 5V or 3.3V.
That may be worth a quick breadboard experiment to find out. 🙂
-Gnobuddy
Definitely keep us posted if you do. I've been trying to find some time to continue on this stuff..but been too busy lately, Frustrating because it's really
my favorite part of electronics, just to try out new ideas or improve on some older ones. Always something to learn.
Same problem here. 🙁
Having both music and electronics as hobbies is a great mix. A musical need can inspire some DIY electronics, and DIY audio electronics can inspire new music. Each one can inspire progress on the other. 😀
-Gnobuddy