I'm relatively new to electronics so would like to use this as a learning project. I've restored a number of early transistor & tube audio amps and one SS guitar amp. Have dmm, oscilloscope, sg, soldering station, etc.
Are there any amps out there I can clone or are there any tried and true schematics available that I can use?
My goals are:
all discrete circuit (no op-amps, IC's, etc.)
10-20 watts (+-)
treble & bass controls
capacitor coupled output
thanks in advance
From your words I deduce that you want to build a musical instrument amplifier, not a HiFi unit.
10 Watts is nothing for a MI amplifier. Although the power itself is not the restriction, it is the lack of headroom.
SS amps clipped sound awful. A 10W tube amp can create the appearance of being of much higher wattage due to the compression and benign clipping, which most of the time goes unnoticed.
Your description fits SS amplifiers from the past, such as early John Linsley-Hood class-A designs. He was designing for HiFi, and even he, at a later time, went to higher wattage push-pull designs.
You create the impression of believing that discrete design is less demanding - it is not. In fact the contrary is the case, worsened by the fact that op-amp design is better understood today than discrete.
Schematics are around, but be aware that this is only half the story. PCB and other layout is ultra critical with power amps. The components reach up into the MHz range, and they can and will oscillate vigorously if you are not experienced, most time leading to immediate self-destruction. This can hinge on simple things like two tracks running in parallel for a length. This reaches deeply into HF design, where other rules apply, and they are not forgiving.
For a newcomer into that field, this is a very ambitious endeavor.
If you are determined, be at least prepared for harsh set-backs.
Thanks for the response.
Yes, I would like to build a guitar amp. What inspired me was an old Univox SS amp I found recently, it has all of the attributes I mentioned except it has a "tone" control and I would like separate bass and treble. I suppose I could build a clone of it (I have the schematic) but would like some options.
Quote from: aquataur on June 04, 2026, 03:20:35 AMYou create the impression of believing that discrete design is less demanding - it is not. In fact the contrary is the case, worsened by the fact that op-amp design is better understood today than discrete.
I don't have the impression that discrete design is less demanding. I'm interested in learning how amplifiers work and how the components interact with each other.
The only assumption I have is that opamps or IC's do the work of numerous discrete components. I would like to have a better understanding of basic electronic circuits.
I have seen it expressed by some fellow (somewhere in the jungle of boards and threads...) that they stay away from discrete circuits, because they grew up with OPAs... That's that excluded anyway.
QuoteI'm interested in learning how amplifiers work and how the components interact with each other.
Well that's a noble approach and a good propellant.
Just saying, that
power amplifiers have a side to them, which a normal pedal tinkerer hardly ever crosses into - HF. And also, since comparably huge current flows are involved, low frequency issues - speak: hum.
Many of the layouts of stompbox PCBs I see on forae are showcase. You can tell that immediately by cosmetically beautiful component placement and by ground planes that flood everything with the totally wrong assumption, that this helps.
With a stomp box, you get away with murder, but a PCB for a power amp is unforgiving. Been there, done that.
This is certainly several levels above stomp boxes.
Except for a few "utilitarian" stomp boxes that I bought kits for, I have always made my PCBs by myself. The were never as posh, but they are quieter, to name one thing. There is lots and lots you can learn from that.
You certainly will choose the right path, and I wish you the best for it.
So you don't have any suggestions, just a lecture?
The title of this particular forum is: "The Newcomer's Forum"...am I in the wrong place?
Right. So you seem determined.
For designing amps, there is several books that I can recommend.
My starter book was from London Power (Kevin O´Connor), TUT2. You have to buy it.
There is also a book by Merlin, Designing Valve Preamps For Guitar And Bass. An early version is available for download (https://vdoc.pub/download/designing-valve-preamps-for-guitar-and-bass-1ivm2upmosf0). Chapter 12 talks about grounding, since I mentioned that to be of prime importance. I presume it is OK by Merlin, otherwise he would have taken it down.
Although these books are about tubes, the underlying principles are universally valid.
There is also a ton of information available from Rod Elliott (https://www.sound-au.com/).
Those are cook-book guidelines for a tough matter. It does not get simple.
Thank you
Thanks for coming here - I'm always glad to have a new face and I love the idea of building a fully discrete practice amp. I've had thoughts to do the same myself and haven't had a chance to do so yet.
Honestly, this isn't nearly as large a task as it seems. For the preamp side of things, you can use any discrete pedal amp circuit that you like the sound of. You can either keep it as-is, or find one you want to modify. Something like Jack Orman's Mosfet Booster (https://tonepad.com/getFile.asp?id=87), RunOffGroove's Peppermill (https://runoffgroove.com/peppermill.html), or even my 5th Gear Overdrive (https://www.ssguitar.com/index.php?topic=4795.msg37909#msg37909) would make a good gain stage.
You could make the booster for the initial input, go into a tonestack of your choosing (see Duncan TSC in the web (https://www.guitarscience.net/tsc/vox.htm#RIN=717&R1=100k&R2=10k&RT=1M&RB=1M&RL=600k&C1=47p&C2=22n&C3=22n&RB_pot=LogA&RT_pot=LogA) for ideas), then go into another gain stage for recovery and drive (like the 5th gear OD).
After the preamp is complete, you could send it into an amp from Rod Eliot, like his project 10 (https://sound-au.com/project10.htm) - a 20w Class A discrete amplifier.
Whatever options you choose, definitely come back and let us know how it goes or if you need help!
That's awesome, thank you. I've considered building a class A for audio, didn't know it could work for guitar as well.
So, is it safe to say that the main difference between guitar and audio amps is in the "preamp" section?
Quote from: branko_76 on June 10, 2026, 12:01:27 AMThat's awesome, thank you. I've considered building a class A for audio, didn't know it could work for guitar as well.
So, is it safe to say that the main difference between guitar and audio amps is in the "preamp" section?
It certainly can be the main difference, and nowadays I would say "yes". In older, and current tube design, amplifiers - no. Older guitar amps would have "sag" in the power amplifier section, particularly in tube amps. This creates a significant amount of compression and a certain sound of distortion. Current amps all basically use a super clean power amp (like you would for hifi use) and get all the distortion, compression, etc from the preamp section.
Check the schematic in post #7 of this thread:
https://www.ssguitar.com/index.php?topic=3747.msg29227#msg29227
It uses just enough feedback to set the DC operating point. Softly clips when the output gets near the rails. Gain is about 100 so it can be driven by a stomp box.
I forgot to add the Randall RG100 power amp. At first look it's pretty normal, but it's really a current output (very high output impedance) amplifier. You can find the schematic on this site, search for RG100.
Quote from: Loudthud on June 14, 2026, 10:50:57 PMCheck the schematic in post #7 of this thread:
https://www.ssguitar.com/index.php?topic=3747.msg29227#msg29227
It uses just enough feedback to set the DC operating point. Softly clips when the output gets near the rails. Gain is about 100 so it can be driven by a stomp box.
What kind of output would you expect into a 4, 8, or 16 ohm load from this?
Quote from: joecool85 on June 18, 2026, 01:44:30 PMWhat kind of output would you expect into a 4, 8, or 16 ohm load from this?
Because there is no global AC feedback, output depends on the beta of the output transistors and the resistors in the split bootstrap current source. both are 2.2K in the schematic. That value was chosen to give an output impedance of 5 Ohms with the pair of output transistors I had on hand IIRC. With a 50V rail that gives about 50 Watts (+/- 20V) into 4 Ohm load or about half that into 8 Ohms. The high output impedance makes the amp act more like a tube amp with no feedback like the famous 5E3.
This isn't a very good amp for a novice builder because you really need an oscilloscope to tweek it up and get it running correctly. Without a scope, you need to try different resistors for the 2.2Ks, somewhere between 1K and 4.7K until you get it sounding the way you want.
Also, this schematic has no short circuit protection so shorting the output could damage the output transistors. I have newer versions but they are a little more complicated.
Quote from: Loudthud on June 19, 2026, 02:31:20 AMAlso, this schematic has no short circuit protection so shorting the output could damage the output transistors. I have newer versions but they are a little more complicated.
Have you thought about a dual supply version, DC coupled to speaker?
Quote from: Kaz Kylheku on June 19, 2026, 02:19:06 PMHave you thought about a dual supply version, DC coupled to speaker?
It's the simplicity of a single Voltage gain stage without global feedback that makes the amp sound more like a tube amp. Cap coupled outputs just sound better. DC coupled outputs are why transistor amps sound bad.
MEF is back. Check this thread:
https://music-electronics-forum.com/forum/amplification/guitar-amps/theory-design/49294-
I forgot to mention: There are 48V power supplies that can be used to power a 59W @ 4 Ohm guitar amp.
Example: https://www.jameco.com/z/PSA120U-480L6-R-Phihong-120W-48VDC-Output-Desktop-With-C14-Inlet-and-4-Pin-Din-Connector_2670879.html
Some have a barrel connector like used on effects pedals. I'd stay away from those because you don't want to plug 48V into a 9V stompbox by mistake :( Choose one with the 4 pin DIN connector. Most have a Universal Mains input so it can be plugged in anywhere on earth. All you need is the right Mains cord for wherever you are. The minus side of the 48V is usually connected to the Mains safety ground inside the brick. For a 50W amp you need something like 125W power supply.
Quote from: branko_76 on June 03, 2026, 11:28:06 AMI'm relatively new to electronics so would like to use this as a learning project. I've restored a number of early transistor & tube audio amps and one SS guitar amp. Have dmm, oscilloscope, sg, soldering station, etc.
Are there any amps out there I can clone or are there any tried and true schematics available that I can use?
My goals are:
all discrete circuit (no op-amps, IC's, etc.)
10-20 watts (+-)
treble & bass controls
capacitor coupled output
thanks in advance
You will find lots of discrete 15-50W power amps , specially before the 2000s.
Peavey, Marshall, Crate, Laney, Vox, Ampeg , Fender, search , lots of possible amps to copy.
Now Preamps started using Op Amps very early, late 60s Kustom amps already used them.
I remember ONE 70´s Marshall discrete preamp, I´ll post it here if I find it.
Here, I found it, discrete end to end.
Unobtainium MJE3001/2501 must be replaced by TIP142/147
That said, not much "learning" from them, beyond hand dexterity and build practice which is not bad at all.
if you don´t study theory first, and run some textbook experiments yourself, you´ll be "painting by the numbers", just blindly following printed instructions.
A few modern-ish (70s 80s) Roland , Yamaha ibanez preamps are discrete, but use FETs which are in a quite different league. Same with original Randall preamps.
Want to experiment and learn?
Then follow and copy Forum member "saturated" posts, he´s doing a very good job at that. :dbtu:
Quote from: J M Fahey on July 27, 2026, 07:47:30 PMI remember ONE 70´s Marshall discrete preamp, I´ll post it here if I find it.
Here, I found it, discrete end to end.
Unobtainium MJE3001/2501 must be replaced by TIP142/147
If you attached something it did not stick. Here is a nicely re-drawn version of the one I think you mean, the 2195 from the late 70s. It does have one Fet in the preamp, TR4.
Any higher power solid state power amp section can easily be downscaled to low power so that is not a problem for the requested power output. However, it is not cap-coupled output so it does not meet that requirement. I guess you could just add a cap, but I'm not sure what the intent was that the OP wanted a cap for the output.