Making my own guitar amp - Page 1
Forum section: electronics / beginners

author: ArchieAltz
author_rank: Contributor
timestamp: March 26, 2025, 01:07:42 am
content: Hello !I am a first year electrical engineering student (Still in high school) and I've been wanting to combine my interest in music and my electronics tinkering into one by making a guitar amp.I believe it would be easier if I made a solid state(transistor based) amp instead of a electronic tube one.It should be ~10W and have some basic EQ and Gain control.I do know that it would probably be easier to buy a cheapo amp , however I do want to learn more extra knowledge extracurricularly.Any help is appreciated :-)

author: Analog Kid
author_rank: Super Contributor
timestamp: March 26, 2025, 01:31:59 am
content: I admire your ambition, and hope you get lots of good help on that project.

author: TimFox
author_rank: Super Contributor
timestamp: March 26, 2025, 03:02:08 am
content: Here is a source for relevant books, most of which are vacuum-tube oriented:https://www.tubesandmore.com/products/books_dvds_software

author: MathWizard
author_rank: Super Contributor
timestamp: March 26, 2025, 03:04:15 am
content: Ok let's keep it simple for now, and say you just have a single winding, step-down transformer, like 120VAC to 24VAC. Then you would rectify that AC, and make some voltage rails, like maybe +12V, +5V, and some higher power supply rail, for the speaker drive.So you can make some basic ones w/ BJT's and probably diodes or zener's. Or make or use op-amp's, or regulator IC's like the 7812, 12V regulator.So for the input audio, some AC or even DC audio signal can be coming in, I guess AC for a basic electric guitar. So then you can add some type of RLC filtering, to do things like bass/treble, tone, volume, etc. That can be passive with just RLC parts, and/or active, meaning with powered devices like BJT's and op-amps. That stuff can run from the 12V control rail.And then you have to start amplifying your signal, and/or do it while filtering. And eventually get up, to a clean enough signal, for the levels needed to drive the input to some output power amp stage. Now the whole thing could be a bunch of small, equal steps up too. Or you might get some special 10W audio output IC, you can find all sorts of this stuff in old TV's and stereo's.So in this case for a single winding step-down transformer, and the 12V control rail, you could make a 6V rail, that all the AC audio signals are centred on.And your power amp could also be centered, at 1/2 it's supply rail. Now to get all that to working nicely and linearly for 10W speaker power, yeah IDK. It would be a project for me for sure.Having the power amp centered at 1/2 the DC supply rail, wastes a lot of power, so you could maybe use a class-D amp, with a pulse-width-modulated MOSFET, not centered at some voltage and on all the time. But I've never tried them.Or people use center-tapped transformers, with a common point in the middle, so +/-Vout. And then use upper and lower output drivers, which can be biased to near 0V, and nearly off, when there's no audio signal.I own a 10W guitar amp, I made a schematics of it somewhere, but it just does about what I've said. It uses some 25V or whatever transformer, and 1 or 2 op-amps, for making "distortion". And it's driven by some cheap, and very small, 5-pin audio amp IC.

author: RJSV
author_rank: Super Contributor
timestamp: March 26, 2025, 03:13:56 am
content: In your circumstances, maybe consider buying the amp brand, 'ORANGE' which sounds dumb, (I know). But consider that you would gain a bunch of components:Speaker box and speaker, ready to use with your own circuits.2.). Besides the audio jacks and binder posts for external speaker, you also get the power input jack, and stereo ext. input.3.). The small existing speaker, in an ORANGE AMP, is quite good, compared to what I might build, especially at that size !4.). In a school, that entire AMP will tuck into your backpack, when on a bike, etc.Of course the SAD part is that it might be necessary to trash or remove the existing PC board (and control pots).Instructors might balk, but you could argue, that it's an 'UPGRADE', to 10 watts, from the original 3 watts.

author: planet12
author_rank: Regular Contributor
timestamp: March 26, 2025, 03:22:45 am
content: A good way to start would be by building the pieces individually.You'll normally want in a guitar amplifier:An input buffer - you generally want 500kohm or higher input impedance for a guitar signalAn overdrive section, eg. an opamp stage with adjustable gain and clipping diodesA clean/overdrive switch that routes the buffered signal around the overdrive section for when you want a clean tone. If adding one of these you'll likely also want a separate volume control on the overdrive section output to allow volume matching between clean and distorted settingsA tone control sectionA master volume controlA power amplifierPower supplies for the above - a bipolar supply is ideal, but a single-ended supply is achievable with virtual grounds for the signal sections and a single-supply power amplifierThere are large "DIY pedal" communities online where you can find inspiration for many of these items. Reading and understanding the schematics for various pedals and existing guitar amplifiers will help you. There's many options for overdrives, tone stacks, etc.How deep you go depends on how long you want this to take and how much you want to learn - for example you could use a chipamp such as the old-but-still-decent LM1875, or you could learn your way around Lin-topology power amplifiers and design your own.

author: Analog Kid
author_rank: Super Contributor
timestamp: March 26, 2025, 03:35:55 am
content: For a possible starting point, here's a schematic of a Pignose amp, a small self-contained guitar amp:For those describing complex power supplies: look how simple this one is! Transformer, bridge rectifier, filter caps. That's it.I doubt if this will supply 10 watts of power (which actually will provide alotof sound), but as I say, a starting point.

author: MathWizard
author_rank: Super Contributor
timestamp: March 26, 2025, 03:53:20 am
content: If money is an issue, and to save stuff from the dump, you could salvage a bunch of parts, and try making it that way. TV's can easily have 2, 10W speakers, and drivers, regulators, etc. But these days they probably won't have linear transformers. But stereo's and small radios still usually do. And have op-amps, etc. And a lot of lower end stuff like DVD players or even stereo's can have single chip audio power amp IC's.You could also buy a broken amp, and try fixing it.

author: pqass
author_rank: Super Contributor
timestamp: March 26, 2025, 04:56:05 am
content: Seethis guitar projectand othermusical instrument projectsfrom sound-au.com.In fact, you should eventually readall the articles and projects. You will learn a lot.

author: TimFox
author_rank: Super Contributor
timestamp: March 26, 2025, 02:18:46 pm
content: Quote from: Analog Kid on March 26, 2025, 03:35:55 amIs that diagram missing a center-tap connection on the power transformer secondary winding?

author: cte
author_rank: Regular Contributor
timestamp: March 26, 2025, 02:45:54 pm
content: Quote from: TimFox on March 26, 2025, 02:18:46 pmI guess this is kind of a floating ground. Look at the ground connections between Q1/Q2 and Q3/Q4 and how the speaker is connected...

author: TimFox
author_rank: Super Contributor
timestamp: March 26, 2025, 03:37:19 pm
content: Quote from: cte on March 26, 2025, 02:45:54 pmYes, I saw the speaker and transistor connections, but every solid-state power amplifier I have seen without output capacitor has used a center tap before the rectifier bridge, along with the two large filter capacitors shown on the drawing: it looks like an inadvertent drawing error.

author: Terry Bites
author_rank: Super Contributor
timestamp: March 26, 2025, 04:33:44 pm
content: Here's a little starter project:https://www.redcircuits.com/Page120.htmhttps://www.freestompboxes.org/viewtopic.php?t=32957

author: RJSV
author_rank: Super Contributor
timestamp: March 26, 2025, 08:47:20 pm
content: One feature I've always liked is being able to put a larger 12 inch speaker into a parallel connection. It's even possible to mess with any phone jack; insert until contact is made.That way you've got the two (speakers) in parallel. Of course better to wire that, perhaps also with a switch.That way you get a good low end with clear highs.Suggested, listening: Try Jimi Hendrix 'Rainy Day' for some good sax and guitar interaction.(Plus the song has a 'groovy' beat with bongo drum 'chunky' beat !!).The Orange mini-amp is 3 watts, with a 4 inch speaker. Runs on 9 volt battery.Check out that 'Rainy Day' and also 'Hot Summer Nights' is another good one.

author: RJSV
author_rank: Super Contributor
timestamp: March 26, 2025, 10:57:34 pm
content: Oops, my mistake:Better to use, 'Hendrix, Long Hot Summer Night'.Otherwise you might get the movie,'Hot Summer Night'.Sorry - - Rick-Jack

author: Analog Kid
author_rank: Super Contributor
timestamp: March 27, 2025, 12:40:45 am
content: Quote from: RJSV on March 26, 2025, 08:47:20 pm3 watts? Really? On a 9-volt battery?If that's true, it'll run for maybe 20 or 30 minutes at continuous maximum output, assuming something north of 50% efficiency (a 9V battery is generally rated at about 1 ampere-hour).

author: ArchieAltz
author_rank: Contributor
timestamp: March 27, 2025, 01:15:44 am
content: Quote from: Analog Kid on March 27, 2025, 12:40:45 amI think I'll keep mine connected to Mains AC however it does sound fun running one on batteries.P.S. Quick updateI've been looking at some of these schematics and jotting them down , seems like there is plenty of work here about figuring some specs out haha .

author: Simmed
author_rank: Frequent Contributor
timestamp: March 27, 2025, 01:59:36 am
content: Quote from: ArchieAltz on March 26, 2025, 01:07:42 amyou are making only the amp?or a box with a speaker ?like a "crate" ?

author: ArchieAltz
author_rank: Contributor
timestamp: March 27, 2025, 02:03:45 am
content: Quote from: Simmed on March 27, 2025, 01:59:36 amNice one :-)Just making the electronics

author: RJSV
author_rank: Super Contributor
timestamp: March 27, 2025, 02:11:50 am
content: On the 9 volt battery, it DOES drop out, in brief times, in sync with the BASS peaks.But that's only when the ext. 12 inch (DUAL brand) is connected, as the volume knob approaches maximum.For a nice, rich low end, having the extra 12 inch, (along with internal 5 inch), works OK and without drop-outs, with volume knob up to about 3/4 the way up.With just ORANGE AMP 5 inch speaker, the perception is that it's LOUD, plenty, and kept turned down, at maybe half-way.Yeah, it's going to drain, eventually.Many half-hour sessions, on the one 9 VOLT battery. I did have to use the best batt on the shelf, especially with the woofer.Very happy, and has that stereo input useful for YouTube music.P

author: RJSV
author_rank: Super Contributor
timestamp: March 27, 2025, 02:24:16 am
content: LOVING IT !....rick

author: Teledog
author_rank: Regular Contributor
timestamp: March 27, 2025, 02:41:17 am
content: A beginners cheap amp might be a LM386 based unit.I've rebuilt a couple of dead "pocket amps" with 386sNot super loud or great sound, but certainly easy to make.Can add a switched 10uF cap & between pins 1-8 for a gain boost.Can build from scratch & add tone control/WHY to suit, or they have the basic "modules" at Ali for cheap9V battery powered.An efficient speaker also helps.G' Luck!

author: tooki
author_rank: Super Contributor
timestamp: March 27, 2025, 08:31:50 am
content: Quote from: Analog Kid on March 27, 2025, 12:40:45 amActually far less, even! I looked at a few datasheets, and it’s about 600mAh best-case (very low current). At higher current draws it plummets.

author: RJSV
author_rank: Super Contributor
timestamp: March 27, 2025, 04:24:58 pm
content: Yeah but, to repeat myself, the whole system is used in a context of REASONABLE VOLUME LEVELS, along with normal 20 minutes at a time. That means I've done at least 3 for an informal total.Sheeez, feels like I have to APOLIGIZE ! IF I can spell it, lol.Not even interested in locating my little DC wall wart. Heck, a person could ROCK OUT there, in front of the high school, on a battery driven Pig Nose Amp, or an Orange brand mini amp.In fact, later I'd like to find out about any other Mini-Amp products .

author: TimFox
author_rank: Super Contributor
timestamp: March 27, 2025, 04:31:07 pm
content: For hobby purposes, a single-ended tube power amplifier with a 6V6 or similar beam-power tube output is easily built,ifyou can find reasonably-priced power and output transformers.For preamplifier and tone controls, the various solid-state or IC circuits cited above are more practical.

author: Terry Bites
author_rank: Super Contributor
timestamp: March 27, 2025, 04:41:30 pm
content: OTL with cheap triodes?

author: RJSV
author_rank: Super Contributor
timestamp: March 27, 2025, 04:52:16 pm
content: Bottom hatch has the Alkaline Eveready battery, although not so dirt resistant located there !As in many projects, the uh, 'unexpected' little problem involves the ext. (external) input jack (a mini), that regularly CROWBARs my Alcatel cellphone. The stereo input seems to favor one side of the usual left and right audio channels.Roommates expressed pleasurable listening, to my Hendrix-inspired technical limitations, which, actually is an accomplishment in itself.But, I'm no artist, as the Microprocessor is my real, detailed occupation.Anything and everything electrical is the most interesting, for myself.o

author: RJSV
author_rank: Super Contributor
timestamp: March 27, 2025, 04:53:53 pm
content: Picture, of battery hatch, on bottom.

author: themadhippy
author_rank: Super Contributor
timestamp: March 27, 2025, 05:52:20 pm
content: As a starting point you could go old skool and adapt an old radio,normally you can tap into the amp stage at the volume pot.

author: TimFox
author_rank: Super Contributor
timestamp: March 27, 2025, 05:57:11 pm
content: Quote from: Terry Bites on March 27, 2025, 04:41:30 pmOTL with cheap triodes (no output transformer) normally requires a higher load impedance than typical guitar speakers.Cheap triodes are typically two halves of a 6AS7 dual pass tube, or triode-connected beam power tubes, working into > 100\$\Omega\$ load impedance.An example of a series push-pull 6AS7 working into 72\$\Omega\$, along with how to construct a 72\$\Omega\$ speaker:https://www.tubecad.com/2010/12/blog0195.htmThe classic Futterman OTL amplifiers used multiple 6AS7s in parallel to drive a 16\$\Omega\$ load.

author: TimFox
author_rank: Super Contributor
timestamp: March 27, 2025, 06:01:56 pm
content: Quote from: themadhippy on March 27, 2025, 05:52:20 pmThat can work, but be careful about the "hot chassis" problem encountered with many old radios.The output transformer from an old radio could be salvaged, but most old radios did not have a power transformer.There are signal-level transformers that can safely couple into the volume pot of an ungrounded radio.I have used these transformers successfully in test circuits, but they are pricey:https://www.tubesandmore.com/products/transformers_chokes?filters=2341a3027c740a91c65a740The same vendor has power and output transformers useful for guitar amplifiers, ranging from roughly $20 to $60 ea.https://www.tubesandmore.com/products/transformers_chokes

author: Analog Kid
author_rank: Super Contributor
timestamp: March 27, 2025, 09:08:57 pm
content: Quote from: TimFox on March 27, 2025, 05:57:11 pmOy, the TubeCAD guy.Don't get me wrong: the guy is definitely a tube-amplifier guru, knows his stuff. But my god, the gyrations and permutations he pretzels us through in his endless dissertations on almost exclusively triode-based amps. Especially his obsession with "SRPP" ...One question: why doesn't he just use a symmetrical push-pull cathode-follower output stage? Wouldn't that have a low enough impedance to drive a speaker (8-ish ohms) directly, rather than that weird, what is it, cascode? stage he has there, with its 72 ohm output impedance? (Analogous to an emitter-follower PP output stage.)Anyhow, OP: my suggestion, take it or leave it: forget about tubes, at least for now.Yeah, yeah, I know: they're fascinating, fun to work with (so long as you observe reasonable safety precautions). But a solid-state first project would be a hell of a lot simpler for you. Especially when it comes just to obtaining parts, like power and output transformers, tube sockets, etc.Once you've got that down you might attempt a 2 or 3-tube amp. (But please, please, donotattempt to use "an old radio", as you'll be dealing with a "hot chassis", which is dangerous; don't ask me how I know that!)

author: themadhippy
author_rank: Super Contributor
timestamp: March 27, 2025, 09:21:14 pm
content: QuoteIndeed,however i was thinking more along the lines of something battery power, like the ole boom boxes

author: Analog Kid
author_rank: Super Contributor
timestamp: March 27, 2025, 09:35:30 pm
content: Quote from: themadhippy on March 27, 2025, 09:21:14 pmOr the original Pignose amps, which were totally portable battery-powered ones. Plenty loud, too.

author: TimFox
author_rank: Super Contributor
timestamp: March 27, 2025, 09:38:38 pm
content: Quote from: Analog Kid on March 27, 2025, 09:08:57 pmIf you analyze a tube amp (or a solid state amp with very different supply voltage and current) you will find that, for a given set of devices and power supply, the appropriate load impedance is the same for common-cathode (normal) and common plate (cathode follower) operation. You are confusing output (or source) impedance with load impedance (a common misunderstanding of the infamous Maximum Power Transfer Theorem). A cathode follower will have a lower output impedance (due to negative feedback) and require more voltage drive, but can only supply the same out voltage and current as the equivalent plate output. I cited that article as an example of why an OTL was not appropriate.The author you criticize is straightforward and quantitative, not one who waves his hands in despair of mathematics or calculation.My suggestion above was to try a simple single-ended beam power tube, followed by a reason not to use an OTL triode.

author: Analog Kid
author_rank: Super Contributor
timestamp: March 27, 2025, 09:51:58 pm
content: Quote from: TimFox on March 27, 2025, 09:38:38 pmWell again, don't get me wrong: I'm certainly not qualified to criticize the guy. Just pointing out his output volume, which is overwhelmingly prodigious.QuoteWhich would require an output transformer, right?To me, that's a major stumbling block to playing with tube audio, since transformers are often unobtainium.

author: Smokey
author_rank: Super Contributor
timestamp: March 27, 2025, 09:59:06 pm
content: If you actually want to learn stuff, get this book and read through until you understand everything. You will learn a bunch of stuff about general analog electronics in addition to power stuff. It's well written and has both great explanations and great fully functional example circuits. Everything from fully discreet BJT and FET amps to integrated stuff.https://www.amazon.com/Designing-Audio-Power-Amplifiers-Cordell/dp/1138555444/If that book is too expensive for a highschool kid wherever you may happen to live, maybe google "Designing Audio Power Amplifiers pdf"

author: TimFox
author_rank: Super Contributor
timestamp: March 27, 2025, 10:09:12 pm
content: Quote from: Analog Kid on March 27, 2025, 09:51:58 pmThat goes without saying. However, appropriate transformers are easily available to one who seeks, although more expensive than not using a transformer.Two manufacturers of appropriate units:Hammond (replacement units)https://www.hammfg.com/electronics/transformers/classic/1750(app note)https://www.hammfg.com/electronics/transformers/audio/overview?referer=968Edcorhttps://edcorusa.com/products/copy-of-cxse5-7k-5w-7k-ohms-single-ended-tube-output-transformerand see their catalog for power transformers and push-pull transformersA retail vendor of this kind of thing:https://www.tubesandmore.com/products/transformers_chokesI also posted a suggestion to salvage an output transformer from an old tube radio.The actual wiring diagram for a simple tube amp is quite simple, and tube sockets are readily available.For examplehttps://audioxpress.com/article/you-can-diy-build-a-single-ended-guitar-tube-amplifierNo PCB is required: point-to-point wiring is still a valid technique at these frequencies.

author: Analog Kid
author_rank: Super Contributor
timestamp: March 27, 2025, 10:59:17 pm
content: Quote from: TimFox on March 27, 2025, 10:09:12 pmYikes; $44.24 for that puppy.Obtanium, but budgetbustium.Thanks anyhow, though: didn't know that so many transformers were still available.

author: TimFox
author_rank: Super Contributor
timestamp: March 27, 2025, 11:18:07 pm
content: Quote from: Analog Kid on March 27, 2025, 10:59:17 pmFrom the retailer I cited:https://www.tubesandmore.com/products/transformer-output-5w-5k-8k-primary-options-upgrade-fender-champfor $20.

author: themadhippy
author_rank: Super Contributor
timestamp: March 27, 2025, 11:33:17 pm
content: Quotebest you dont look at sowterhttps://www.sowter.co.uk/acatalog/E_A_Sowter_Ltd_SINGLE_ENDED_OUTPUT_15.html#a65

author: TimFox
author_rank: Super Contributor
timestamp: March 28, 2025, 12:34:11 am
content: Quote from: themadhippy on March 27, 2025, 11:33:17 pmYes, Sowter sells to the hi-fi crowd. Getting good bass response with a single-ended tube (DC in the primary) is expensive.