Another worthwhile thread in tube amp design (if you're not spending lots) is GC Will's Lamington series which use much cheaper iron than "proper" clones of standard designs.
But, again, it comes down to what you're wanting.
There's a range of high plate voltage pedals around (e.g. I have a Seymour Duncan Twin Tube Classic but you'd rather the Blue) which get a long way towards the sound.
If you're just after something cheap and quick, the Ruby with a half decent speaker is surprisingly useful.
But a valve circuit with a decent speaker is another thing. (Then I'm hearing good things about the Katana)
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Thanks for that information!
You may have noticed that there are electric guitar amplifiers, and there are acoustic guitar amplifiers. There are almost no guitar amplifiers that can do both, with one glorious exception, the Boss Katana 50. (Which is definitely not a DIY project, but is a remarkably good amplifier at a remarkably affordable price. If you're not adamant on DIY, check one out!)
If you are set on DIY, you're looking at two independent projects (twice the time, labour, money, effort, etc), so my suggestion is to focus on one, and finish it first.
For the electro-acoustic guitar, building a DIY solid state guitar amp is fairly straight-forward, and depending on what you want, you may not have to do much actual building.
For electric guitar, I agree with the other posters who said that if you DIY, you'll almost certainly have to go with tubes, high voltages, risk of death by electrocution, weight, cost, bulk, et cetera. (Yes, many people have built DIY tube amps. Yes, it is dangerous, and expensive. Yes, you can buy a Boss Katana 50 for less money, and it sounds better than some tube amps that cost a lot more.)
Okay. If you're set on DIY, a solid-state amp for the acoustic guitar is a fairly easy nut to crack. In my opinion, an acoustic guitar preamp really should have reverb at a minimum, and it's really nice to have reasonably detailed EQ options too. Onboard piezo pickups often sound too bright, and too bassy.
You can fix a good bit of this if you have a graphic EQ with several independent frequency controls. The guitar itself often includes three (bass, mid, treble), but if you're picky about your plugged-in sound, it really helps to have finer frequency control, i.e., more separate bands of EQ.
The thing is, building your own solid-state reverb is tricky, typically involving tiny surface-mount chips and a custom PCB. And much the same is also true of graphic EQ.
On the plus side, the magic of mass produced electronics from China allows you to buy inexpensive reverb and graphic EQ pedals. For instance, I bought a Donner 'Verb Square ( https://www.amazon.com/Donner-Digital-Reverb-Guitar-Effect/dp/B0719CBYXJ/ref=sr_1_1 ) for a similar project of my own, and I like it a lot.
For EQ, I've relied on a couple of Danelectro Fish-n-Chips 7 band graphic EQ pedals for years. They aren't in production now, but this looks like a reasonable equivalent: https://www.amazon.com/ammoon-Guitar-Equalizer-Effect-Aluminum/dp/B01MXYIK42/ref=sr_1_fkmr1_2
So one way to go with your build would be to use an inexpensive class-D amp board, suitable switching power supply, and an off-the-shelf guitar graphic EQ pedal and reverb pedal for the electronics, leaving you to sort out the loudspeaker, cab, and cosmetics.
You can certainly build (or buy!) a straight-forward preamp using an op-amp or something like that. It will cost you at least as much, and won't sound as good, because it won't have reverb or graphic EQ.
How much power do you want? That will narrow the search down a lot.
Keep in mind that there are lots of "100 watt" amp boards advertised, and some will only put out 10 watts. In reality, maximum clean power output is decided by the power supply voltage, and the loudspeaker impedance. As long as the class D chip can handle that voltage and that speaker impedance, you can calculate the actual output power you can expect (within maybe 20% or so, which makes very little difference to actual loudness.)
Here is an example board: https://www.amazon.com/TDA7498-Ampl...keywords=class+D+board&qid=1575553829&sr=8-23
This will actually deliver about 30 watts to each of the two suggested 8 ohm speakers, if powered by a 24V supply that's capable of supplying enough power. (Such as this: https://www.amazon.com/Signcomplex-...s=24V+100W+power+supply&qid=1575554081&sr=8-3 )
More input from you about what you want will help steer the rest of the thread in a direction that's useful to you.
-Gnobuddy
I would almost certainly electrocute myself if I built a tube amp. I have repeatedly been bitten while working on my house electrical system (120V US), and I understand that tube amps can be even more deadly. It's not a question of "if" but "when." ... unless there is a surefire way to discharge all stored energy, wherever it may lurk, after unplugging everything.
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Then by all means avoid building a tube amp! Stay safe, you can't enjoy your guitars (or anything else) unless you're alive and healthy!
We all have our limits, and it's wise to know them, and to respect them. I had a friend who handled hydrofluoric acid in her lab. I was terrified of the stuff and wouldn't even touch the container. If you are unfortunate enough to drip the stuff onto your body, it not only burns through skin and flesh, but will then burn into your bones, until it's eaten enough calcium out of your skeleton to neutralize itself and stop. It makes battery-acid (sulphuric acid) look like Koolaid.
-Gnobuddy
A slew of op-amps (and I do mean a lot of them!)
I didn't trace the circuit, but I'm told it was, shall we say, very heavily inspired by the circa-2008 Sansamp Blonde pedal from Tech21's Character series ( Tech 21 Character Pedals - Blonde | MusicRadar )
I've seen an unofficial schematic for the original Sansamp, but I did not manage to understand how it works. It's nothing like any of the hundreds of other distortion pedals out there.
-Gnobuddy
How does one discharge energy stored in a cap? I assume touching both leads will do it. I've read one can do it with an LED; any idea how to wire one without exceeding its rating and making it explode?
This is a very bad idea. The huge current spike from being shorted damages normal electrolytic caps, and may destroy them. It also risks arc-welding the shorting tool to the cap wires - there is a lot of energy in a good big filter cap charged up to high voltage.
Used to discharge a tube amp power supply cap, an LED by itself will die instantly.
You can put a big resistor in series with the LED and connect that combination across the cap. The resistor value should be chosen to flow enough current to light the LED when the cap is fully charged. This is not "one size fits all", because modern LEDs come in a wide variety of efficiency ratings. The LED will go out when the cap is discharged.
I usually wire LED-resistor combos like this right into every high voltage power supply I build. When the LED is fully dark, I have some assurance that there are no dangerous voltages present - but I always double-check with a DMM (what if the resistor goes bad, or the LED?)
You don't actually need the LED - a resistor by itself will do the job of discharging a cap. But you don't get the visual indication when it's finished.
There is much more to high-voltage safety than just discharging caps, though. For one thing, you can't always work with the caps discharged - some types of troubleshooting and even routine tasks like setting output valve bias current require that you work on a "live" amp. For another, safety always starts with a mindset, and always requires many separate elements, all in place at the same time to protect you. Miss one of them, and you are no longer safe.
If you have a history of being shocked by 120V electricity, I really do urge you to "Just say no" to tube amp building. Its not worth the risk to your life and health. The next shock could be your last.
Solid-state amps running on relatively low voltages, using commercially manufactured, sealed, fully insulated, power supplies, are much safer. You could build yourself a SS acoustic guitar amp with much less risk to yourself (though there is always some risk.)
-Gnobuddy
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Do you have any idea how much current the Joyo draws from the 9 volt supply? The manual says 4mA, but that's kinda hard to believe.
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The unofficial schematic I saw years ago included several TLC272 op-amps; these are early CMOS op-amps that were specifically designed to have rail-to-rail output swing and no latch-up problems. Good choices for a circuit that is all about carefully engineered clipping behaviour.
It appears that someone has reverse-engineered the product and is offering a kit to build your own DIY version: tonepad -- FX projects
The attached image shows a schematic from Tonepad, allegedly a sound-alike for one of the many Sans Amp family of products. Interestingly, there are no TLC272s in the Tonepad version.
The TI datasheet for the TL07x series shows 2.5 mA maximum supply current per op-amp (and only 1.4 mA typical draw per op-amp.) There are eight op-amps in the Tonepad schematic, suggesting a worst-case current draw of 20 mA, and a typical draw of only 11.2 mA.
Not so long ago, a single indicator LED needed 10 mA to light up brightly. So 11.2 mA of current consumption for 8 op-amps just goes to show how good these little devices are when it comes to power consumption.
-Gnobuddy
It appears that someone has reverse-engineered the product and is offering a kit to build your own DIY version: tonepad -- FX projects
The attached image shows a schematic from Tonepad, allegedly a sound-alike for one of the many Sans Amp family of products. Interestingly, there are no TLC272s in the Tonepad version.
The TI datasheet for the TL07x series shows 2.5 mA maximum supply current per op-amp (and only 1.4 mA typical draw per op-amp.) There are eight op-amps in the Tonepad schematic, suggesting a worst-case current draw of 20 mA, and a typical draw of only 11.2 mA.
Not so long ago, a single indicator LED needed 10 mA to light up brightly. So 11.2 mA of current consumption for 8 op-amps just goes to show how good these little devices are when it comes to power consumption.
-Gnobuddy
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