Help with Guitar ampf

Heelloo! Greetings of the day!

My friend gave me some schematics of guitar amp and he wants me to review it and suggest some improvisation, but I'm really confused about the circuit since it uses valve circuits. I have attached the schematics I received. I told him that valve circuits are past technology and he replied yes, but they offer much more good sound quality. Also one of the schematics uses PIC MCU (I'm not at all familiar with PIC family) and he has asked me to migrate the entire design from PIC to AVR.

Speaking about the amp schematics, if any one could tell me what is the scope of improvisation in existing circuit and what changes should be made in it I would be really obliged. Or even if you share just your views about the schematics like what you feel is it a good design is it a bad design with lil of explanation would help me to dig in the matter further.

Thanks in advance. Stay blessed and have a great day ahead :slight_smile:

[Mod edit: Copyrighted documents removed]

Your post was MOVED to its current location as it is more suitable.

In order to improve the circuit you have to first know what it is about it you want to improve. In what way could it perform better? What are the shortcomings in its performance? Once you know that you can consider what you can to to get the enhanced performance.

As for the PIC in the circuit what does it do? If you want to replace it with a different processor work out what it is doing and replicate that on your preferred processor. You don't need to know anything much about the PIC family, you just(!) need to know what it is doing in this case.

Did you read and understand this copyright notice before posting those documents?
Copyright Notice

Well spotted.

I have removed the schematics due to the copyright notice prohibiting them being shared publicly. You may put them back if you can show that you have permission of the copyright holder to do so.

Are you sure you have? :face_with_raised_eyebrow:

I don't know. I removed the links to them but they might still be in the forum software. I don't know how to find them or remove them if they are. Do you know?

Paul, I have asked for advice as the links are slightly hidden but clearly still there. Thanks for pointing it out.

@Paul_B Is that better? Are they now invisible to you? The problem for me is as a mod I can still see them if I am logged in. Hopefully they are invisible to you.

No they don’t this is one of many just myths banded about by Audiophiles.

Like the gold plated connectors, and oxygen free copper, and the demonisation of ceramic capacitors. If it can’t be measured it isn’t real.

In the case of valve amplifiers they have a modicum of second harmonic distortion which some people think is present., that is all.

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This is about a guitar amplifier. This is not for Audiophiles. A guitar amplifier is not a hi-fi amplifier, but a part of the instrument. It is not supposed to reproduce a sound neutrally, but is part of the sound production. Therefore, non-linarities and certain distortions are desired here, which are more likely to occur with tube amplifiers than with high-quality transistor amplifiers.
There are also guitar amplifiers that emulate these 'non-ideal' amplifier characteristics with digital signal processing.

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No not withstanding that this is for a Guitar the claim was made that the sound quality was better. Which clearly it is not, unless you are saying better quality does not mean an output that follows the input.

Yes I know all about effects peddles and how distortion can be desirable, but you can not say the sound quality is better if it introduces distortion. It is a common misconception that a valve amplifier or preamplifier provide better sound. Look at the number of preamplifiers are on the high end audio market, as if they were a desirable thing.

A guitar amp is an effects box that happens to also amplify. they're not generic sound reproduction systems!!!, they've got overdrive without clipping, and implement various forms of EQ (including the speaker acoustics!), limiting, distortion and tremolo.

You can get digital guitar pedals that emulate a massive selection of "classic" guitar amps so you don't have to deal with the real thing (and its unreliability, fragiility and expensive replacement valve purchases!)

Do you actually think I do not know that?

Well I do.

I was questioning the original rubbish statement that the sound quality was better.

You know that and have chosen, in your typical way, to deliberately misunderstand what I wrote. This is a tiresome habit of yours. And not one of your endearing qualities.

You obviously have a wrong understanding of what 'sound quality' means in the context of a guitar amplifier. It's the quality of the guitar sound. That's certainly very subjective but it is a 'sound quality'. Like the 'sound quality' of any other instrument.
It's not about the quality of a reproduced sound.
And when you say you know that, your answer is all the more incomprehensible.

Sound quality is very open for interpretation in this context - a flat guitar amp has very dissappointing sound quality for a guitar setup as particular kinds of distortion are wanted and others are not (in particular very soft clipping is essential and frankly only valves or emulating them digitally does a good job at this).

Similarly a distorting general purpose amp has very dissapointing sound quality, and are expected not to be driven into clipping constantly.

It depends which qualities matter in the context, and the context is a guitar amplifier. Well that's how I read it - and you conflated this with another issue of audiophoolery, leading to my misunderstanding.

It would be virtually impossible to reverse engineer the software. And the AVR isn't powerful enough for DSP.

Do you know what the processor is for? It could be used for effects and in that case it would make more sense to build a separate effects box/pedal. Or it could be used to simulate the sound of different amplifiers. That's more difficult because you'd have to know the characteristics of those amps, plus the characteristics of this particular amp.

[quote]I told him that valve circuits are past technology and he replied yes, but they offer much more good sound quality.[/quote]Most guitar players do prefer tubes and they usually have a preference for a particular amp/cabinet. (just like they have a preference for a particular guitar & pickup).

I'm pretty sure you can make a solid state amp that distorts "exactly" like a tube amp and there are "modeling amps" that simulate a variety of existing amps but "good luck" convincing a guitar player that it sounds the same...

Overdriving is clipping, but tubes & guitar amps tend to "soft clip" (something like a limiter or analog tape saturation).

You have removed the ability to see the edits. :+1:

Now we have moved onto the "tube" train. :rofl:

However, similar myths and misunderstandings exist in connection with that non-linearity, as with the linearity that is sought after in hifi. For example, the concept of "distortion without clipping". Clipping happens in the time domain, so it is the instantaneous amplitudes that are affected. Consequently, even with "soft clipping", which necessarily must be anti-logarithmic, the actual input range of soft clipping is very narrow, most of the time the signal is almost linear since it's below the threshold, or clipped rather hard because it's way above the threshold. Since a guitar signal has a strong initial attack and log decay, the main audible effect of clipping, is compression. As the input signal amplitude is increased, more and more of the decay signal exceeds the clipping limits and is audible as distortion.

So while soft clipping is a real thing, and pleasant to listen to, it plays a very minor role unless the instrument is played with minimal amplitude into the amp, or unless the signal is pre-compressed so the amplitude is more confined to the soft limiting zone.
But, by the time it reaches marketing and instrumentalist discussions, none of that is understood or mentioned, and it's reduced to things like "sustain" or "punch" or even more incomprehensible things like "articulation", "note separation" and so on, are used.

An actual valve (tube) amp has some subtle things going on that a generic electronics engineer wouldn't consider at first, mainly because they're used to seeing circuits work at less than overload levels. Nothing like, for example, the effect of plate voltage on a push pull circuit dropping due to a a strong input signal and an unregulated supply. Somewhere, a musician expresses that as "munch" or some strange thing that nobody can really grasp.

A lot of innovation in amps now, post DSP where you can punch in practically any sound, is focused on making solid state amps sound half decent. An actual tube amp really doesn't have much need of improvement, from an electric guitarist standpoint.

But people will always try to nurture some tenous need in order to send a product to market and profit, to do that they need to differentiate their product and that is where the exaggerated claims usually come in.