Tonal differences between different solid state POWER amps?

[TheCheapGuitarist]

All else being equal (cab, speaker, etc), would plugging into the effect return of one SS amp be any different than any other? If I already have a cab and preamp, should I just get the cheapest, high wattage amp (with an effects loop) that I can find?

TIA

I've actually been thinking of doing this, under the assumption that all S.S. power amps provide the same uncolored output.

 

[printer2]

The amps themselves should not vary in sound. What will vary is speakers if you're talking combo or frfr type plastic box amps. And many amp makers now include DSP processing post-eq and power protection modes which will colour sound by reducing rather than cutting sound like older systems. You'd have to understand the two particular amps and any circuitry implemented.

By and large speakers is the single biggest determinant of sound with solid state. Modern amps won't clip at all - it's instant destruction. The obnoxious tones you hear if you drive one to clip is the protection system cutting in and out. If you get one howling with feedback you'll cook a speaker.

I've had two modern class D PA amps bust drivers - a new speaker returned them to function. They don't even get hot run continuously in a club at 110°f heat. If they do go it's usually the power supply.

Modern amps? Which amps are modern, Class D or Class AB? Or is there another consideration?

Drive solid state into distortion, even driver chips for a phase inverter will cook if you put enough square wave through them. To a chip square wave looks like a dead short. That's what eventually killed many. Analogue solid state does not like square wave.

Modern solid state amps are kept as far from distortion as possible. All the tone generation/distortion is done in software. It's like playing metal through your car audio.

Why can a Class D amp run cool? Because the SS devices (Mosfet) passing current has two conditions, off and on. They pass square waves. Much easier to find the graph I want for tubes, will have to settle for two.

Here is the power dissipation curve for a transistor. The violet line is the power dissipation limit for the transistor. In a Class A amp the bias point would be right in the middle of the load line (diagonal line from 3A - 24V). It is dissipating the most power at idle, no power out to the speaker and all the heat dissipated by the transistor. As we make some power, the more the outputs are driven the farther away from the middle section the (lets use a sine wave) the cooler the transistor runs.

Here we have the load line with the sine wave imposed on it.

This curve shows the power dissipation of a transistor (red), if idling at 10V the most power is dissipated. If it is passing no current (0 mA, 20V across the transistor using a 20V power supply) there is no power dissipated by the transistor. If it is at the other end there is 40 mA flowing through the transistor but all the voltage (minus 0.7V) is across the load. Power = voltage x current, we have maximum current but little voltage to multiply it with resulting in little dissipation across the transistor.

A clipped signal in the form of a square wave has the amp operating mainly at two points, the extreme left or the extreme right on the load line. Both places where the power dissipation is lowest. This is a single transistor amp in Class A. A Class AB would have the bias at, say 4 mA and the two transistors (in clipping) cycle from the bias point 4 ma to full current 40 mA almost instantaneously (the more closer to a perfect square wave the less time it takes, the less time the transistor has to heat up).

On chips not liking square waves, lot of distortion pedals will disagree. On analog SS amps not sounding good (relatively speaking) the Pathfinder amp is not too shabby. But it uses a chip amp that was originally designed for car stereo use where the amp is sure to be used in clipping some of the time.

 

[11 Gauge]

There are also power amps designed by Quilter and Peavey (and probably others) that intentionally have low damping/high impedance at their outputs, which makes the power amp behave much more like what happens with a tube power amp.

I would think that the vast majority of non-guitar amp-specific SS power amps would all have as high of damping as possible, since they are intended to amplify source signals that consist of anything and everything, where a nonlinear response at the speaker would be awful.

IMO, unless you've got some kind of speaker/cab sim that you're using in conjunction with a power amp with high damping, then it tends to sound kind of flat or dull, even with a preamp that's creating 'significant enough' harmonic distortion on its own.

 

[11 Gauge]

On chips not liking square waves, lot of distortion pedals will disagree. On analog SS amps not sounding good (relatively speaking) the Pathfinder amp is not too shabby. But it uses a chip amp that was originally designed for car stereo use where the amp is sure to be used in clipping some of the time.

I think Eric Pritchard primarily used op amps in his preamps, and found ways to shift the bias with them similar to what happens with a tube triode stage.

Along with the Pathfinder, I know that at least the older AD-series of Valvetronix amps all had chip power amps, TTBOMK. I have an old AD15VT that sounds good even when maxed out (at least on the models I prefer). IDK if the 12AX7 is really responsible for causing that (I know it's only used in conjunction with the power amp vs the preamp), but always thought that it was being used more in conjunction with SS phase inverter-type circuitry.

 

[Nogoodnamesleft]

I haven't worked with power amps on a chip designs, but using discrete components for SS amps. Most circuits were based on the same idea (A or AB). Specific components might present different results but the designs were so similar (and the goal - as clean as possible reproduction).

Tube amps - I can usually hear the difference between say a 6V6 based amp and an EL84. But, having said that, two different amps means two different circuit designs, layouts, speakers, transformers, and everything else at play.

Given what I was taught 30 years ago in engineering school, class D looks more like a pulse than a sine wave. Perhaps the least accurate representation of an input signal possible. I would have never thought back then they would make it into music reproduction in any form.

My point? This shows what little I know when it comes to how something will end up sounding, even if engineering school says I should think differently.

 

[printer2]

I think Eric Pritchard primarily used op amps in his preamps, and found ways to shift the bias with them similar to what happens with a tube triode stage.

Along with the Pathfinder, I know that at least the older AD-series of Valvetronix amps all had chip power amps, TTBOMK. I have an old AD15VT that sounds good even when maxed out (at least on the models I prefer). IDK if the 12AX7 is really responsible for causing that (I know it's only used in conjunction with the power amp vs the preamp), but always thought that it was being used more in conjunction with SS phase inverter-type circuitry.

The 12AX7 is used to clip the signal, one triode for each half of the waveform. They used a transistor Long Tail Pair to create out of phase signals to feed the 12AX7. They then combine the outputs of the two triodes and feed it to the power amp. I had the same idea but implemented differently.

 

[Swirling Snow]

There are also power amps designed by Quilter and Peavey (and probably others) that intentionally have low damping/high impedance at their outputs, which makes the power amp behave much more like what happens with a tube power amp.

I would think that the vast majority of non-guitar amp-specific SS power amps would all have as high of damping as possible, since they are intended to amplify source signals that consist of anything and everything, where a nonlinear response at the speaker would be awful.

IMO, unless you've got some kind of speaker/cab sim that you're using in conjunction with a power amp with high damping, then it tends to sound kind of flat or dull, even with a preamp that's creating 'significant enough' harmonic distortion on its own.

This is the real quibble. As far as the sound of the SS amps themselves is concerned, all but the cheapest will sound the same while you're busy playing.

Guitar speakers are wickedly over-damped. They have to be, because some of us slap and pop the strings and the speaker has to stay attached to the frame, even when given a stupid signal. So... the amp has to be a bit loose and bouncy to compensate.

 

[ficelles]

Given what I was taught 30 years ago in engineering school, class D looks more like a pulse than a sine wave. Perhaps the least accurate representation of an input signal possible. I would have never thought back then they would make it into music reproduction in any form.

Class D uses Pulse Wave Modulation... they are popular now for being compact as well as better than 90% efficient. I have a 60 watt Class D amp in a tiny plastic box (1" x 1.5" x 2") driving a sub, external power of course.

 

[JustABluesGuy]

Thanks. It shows how long ago it was that I plugged into a solid state amp. I was curious about the overdrive in solid state va modeled distortion (I should have been more clear). I have no idea what the overdrive cct looks like (I'm gonna look it up out of curiosity). from what you said, it sounds like that's not done in the op amp.

With solid state amplification the preamp circuitry creates the distortion and the power amp just amplifies it. Solid state power amps aren’t designed to clip. They are designed to just amplify the input signal with as little harmonic distortion possible. As mentioned most SS power amps sound bad when they distort, because they aren’t designed to clip.

Tube amps weren’t originally designed to distort either, but musicians pushed them into it, and found it pleasing even if, in a raunchy way, and many still seek power tube distortion.

Personally I think power tube distortion sounds better because it soft clips (solid state hard clips) the signal and produces harmonic overtones that are pleasing to the ear.

People sometime argue that running a bunch of SS pedal into a tube amp is useless and you aren’t hearing the tubes, but this isn’t the case IME. I can use many hard clipping pedals (that sound like a chain saw into a clean SS amp) through my tube amp and the tubes don’t reproduce the hard edges. The smooth things out. The round the corners of the wave form.

I watched a video years ago that used an oscilloscope and a DS-1 to demonstrate the principle. On it’s own, the DS-1 produces a rip saw like sine wave with jagged points. It sounds terrible into a clean amp. It sounds great into a tube amp on the edge of breakup. I wouldn’t even try it into a SS amp as I am pretty sure if wasn’t designed for that use. It was designed to push a tube amp into distortion.

Sorry I can’t find the video or I would post it. It was about tube amp gain stages, and was part of a series. I found it very helpful understanding gain staging and clipping better.

 

[redhouse_ca]

With solid state amplification the preamp circuitry creates the distortion and the power amp just amplifies it. Solid state power amps aren’t designed to clip. They are designed to just amplify the input signal with as little harmonic distortion possible. As mentioned most SS power amps sound bad when they distort, because they aren’t designed to clip.

Tube amps weren’t originally designed to distort either, but musicians pushed them into it, and found it pleasing even if, in a raunchy way, and many still seek power tube distortion.

Personally I think power tube distortion sounds better because it soft clips (solid state hard clips) the signal and produces harmonic overtones that are pleasing to the ear.

People sometime argue that running a bunch of SS pedal into a tube amp is useless and you aren’t hearing the tubes, but this isn’t the case IME. I can use many hard clipping pedals (that sound like a chain saw into a clean SS amp) through my tube amp and the tubes don’t reproduce the hard edges. The smooth things out. The round the corners of the wave form.

I watched a video years ago that used an oscilloscope and a DS-1 to demonstrate the principle. On it’s own, the DS-1 produces a rip saw like sine wave with jagged points. It sounds terrible into a clean amp. It sounds great into a tube amp on the edge of breakup. I wouldn’t even try it into a SS amp as I am pretty sure if wasn’t designed for that use. It was designed to push a tube amp into distortion.

Sorry I can’t find the video or I would post it. It was about tube amp gain stages, and was part of a series. I found it very helpful understanding gain staging and clipping better.

Super insightful, thanks a ton!

 

[Dacious]

Modern amps? Which amps are modern, Class D or Class AB? Or is there another consideration?


Why can a Class D amp run cool? Because the SS devices (Mosfet) passing current has two conditions, off and on. They pass square waves. Much easier to find the graph I want for tubes, will have to settle for two.

Here is the power dissipation curve for a transistor. The violet line is the power dissipation limit for the transistor. In a Class A amp the bias point would be right in the middle of the load line (diagonal line from 3A - 24V). It is dissipating the most power at idle, no power out to the speaker and all the heat dissipated by the transistor. As we make some power, the more the outputs are driven the farther away from the middle section the (lets use a sine wave) the cooler the transistor runs.

Here we have the load line with the sine wave imposed on it.

This curve shows the power dissipation of a transistor (red), if idling at 10V the most power is dissipated. If it is passing no current (0 mA, 20V across the transistor using a 20V power supply) there is no power dissipated by the transistor. If it is at the other end there is 40 mA flowing through the transistor but all the voltage (minus 0.7V) is across the load. Power = voltage x current, we have maximum current but little voltage to multiply it with resulting in little dissipation across the transistor.

A clipped signal in the form of a square wave has the amp operating mainly at two points, the extreme left or the extreme right on the load line. Both places where the power dissipation is lowest. This is a single transistor amp in Class A. A Class AB would have the bias at, say 4 mA and the two transistors (in clipping) cycle from the bias point 4 ma to full current 40 mA almost instantaneously (the more closer to a perfect square wave the less time it takes, the less time the transistor has to heat up).

On chips not liking square waves, lot of distortion pedals will disagree. On analog SS amps not sounding good (relatively speaking) the Pathfinder amp is not too shabby. But it uses a chip amp that was originally designed for car stereo use where the amp is sure to be used in clipping some of the time.

Modern - class D. Old - class A mono or A/B multi chip. Class D where a lot of chips amplify in a phased array. It's simple to pick the difference - no large finned heatsink, no fan and these days not even any cooling slots. Old power amps and speakers with heatsinks could get hot enough to burn your hand. That's in normal mode - not abusing them.

As someone noted - the whole Class D amp can run at high efficiency and power but the individual chips run in a low duty cycle of maybe 15-20% per phase. It's why the rated power consumption is often only 110% of rated peak power, whereas a 15 watt tube amp might be 200-300 watts consumption.

By chips not liking square wave, I mean power amps passing significant power while amplifying an overdriven signal from their attached driver chip. Working on an old pv 70s power anp now that is deadshorted on one side despite having thermistors in the protection circuit - online, the repair gurus say clipper signal source, leading cause (advent of disco - too much low end).

Even in modern amps with good protection circuits you can see the clip lights illuminating if you over amplify a clipping source and the manufacturer still advises not to allow the device to clip. Playing a distorted music source through a PA at moderate volume or something like a distortion pedal into a clean amp at low input gain is not the same thing as driving the chips in a solid state power section to clip which will reduce their life significantly.

But it does have an impact, unquestionably. Turn your pa gain up to max playing a Metal sound source and check the PFL. . It'll be flashing 'clip' at you. Sooner or later something will cook if you run it like that consistently. .

 

[redhouse_ca]

Yes it is good to distinguish Analog Solid State (ASS?) from digital solid state (DSP digital signal processing). No, I do NOT find digitally-modeled distortion to sound better than 'analog' SS distortion. But everybody likes what they like and that's OK with me. I do like some digital effects like delay and reverb, but I prefer the sound of analog SS distortions. OK... I admit... my rig's distortion sounds like ASS(!) ☺And I love class-d amps with a warm JFET preamp in front, much more than tube amps these days.

I like a lot of the modeled sounds. It's so specific to the software and tone, but I've found some great sounds. You sure can't beat it for convenient access to a lot of different tones.

 

[printer2]

Modern - class D. Old - class A mono or A/B multi chip. Class D where a lot of chips amplify in a phased array. It's simple to pick the difference - no large finned heatsink, no fan and these days not even any cooling slots. Old power amps and speakers with heatsinks could get hot enough to burn your hand. That's in normal mode - not abusing them.

As someone noted - the whole Class D amp can run at high efficiency and power but the individual chips run in a low duty cycle of maybe 15-20% per phase. It's why the rated power consumption is often only 110% of rated peak power, whereas a 15 watt tube amp might be 200-300 watts consumption.

By chips not liking square wave, I mean power amps passing significant power while amplifying an overdriven signal from their attached driver chip. Working on an old pv 70s power anp now that is deadshorted on one side despite having thermistors in the protection circuit - online, the repair gurus say clipper signal source, leading cause (advent of disco - too much low end).

Even in modern amps with good protection circuits you can see the clip lights illuminating if you over amplify a clipping source and the manufacturer still advises not to allow the device to clip. Playing a distorted music source through a PA at moderate volume or something like a distortion pedal into a clean amp at low input gain is not the same thing as driving the chips in a solid state power section to clip which will reduce their life significantly.

But it does have an impact, unquestionably. Turn your pa gain up to max playing a Metal sound source and check the PFL. . It'll be flashing 'clip' at you. Sooner or later something will cook if you run it like that consistently. .

"Chips amplify in a phase array"?

The more answers the more it seems I need to learn. I never heard of this one.

"As someone noted - the whole Class D amp can run at high efficiency and power but the individual chips run in a low duty cycle of maybe 15-20%"

Maybe my post?

"By chips not liking square wave, I mean power amps passing significant power while amplifying an overdriven signal from their attached driver chip. Working on an old pv 70s power anp now that is deadshorted on one side despite having thermistors in the protection circuit - online, the repair gurus say clipper signal source, leading cause (advent of disco - too much low end)."

The thermistor is used to control the fan, is it not? It will take much longer for the heat sink to heat up as compared to the transistor(s) frying due to overcurrent. "gurus say clipper signal source, leading cause"? I do not understand clipper signal source, is that a section of the circuit?

"Even in modern amps with good protection circuits you can see the clip lights illuminating if you over amplify a clipping source"

Darn rights. We would see the leds flash in time with the thumping of the bass drum. It was a given clipping the bass amp, why would you need to biamp or triamp and have the midrange and high end amps run clean in order to mask the distortion of the bass? We were pushing 300W into each bass bin, nobody ran clean.

"Playing a distorted music source through a PA at moderate volume or something like a distortion pedal into a clean amp at low input gain is not the same thing as driving the chips in a solid state power section to clip which will reduce their life significantly."

What reduces their life? The heat or the back emf of the speaker?

 

[John_doe_blc]

While all solid-state power amps aim to amplify a signal, there can be tonal differences between different models due to variations in the circuitry and components used. These differences can affect the overall sound character, including the frequency response, harmonic content, and distortion.

Plugging into the effect return of one solid-state amp versus another may result in some tonal differences, but these would likely be subtle and dependent on the specific models being compared. The main purpose of the effects loop is to allow external effects processors to be inserted into the signal chain without affecting the amp's preamp section.

If you already have a cab and preamp, then getting a cheap, high-wattage solid-state power amp with an effects loop may be a good option. However, it's important to note that factors such as build quality, reliability, and ease of use should also be considered when making a purchasing decision. It's also worth trying out different amps if possible, to see if you prefer the tonal character of one over another.

 

[Jakedog]

Understatement, trust me. Particularly with bass amps, Class D clipping is horrible.

Absolutely true. But… you’re not supposed to push them into clipping. If a person is doing that, they need a more powerful amp so it won’t do that, or they need an amp designed for power amp distortion. In other words, not class D.

Class D works brilliantly when used as designed. Which is to faithfully reproduce a preamp signal with no additional distortion or coloration. And when you want wicked fast recovery and zero sag.

If one employs a class D amp for purposes of power amp distortion, one bought the wrong tool.

 

[ficelles]

Absolutely true. But… you’re not supposed to push them into clipping. If a person is doing that, they need a more powerful amp so it won’t do that, or they need an amp designed for power amp distortion. In other words, not class D.

Class D works brilliantly when used as designed. Which is to faithfully reproduce a preamp signal with no additional distortion or coloration. And when you want wicked fast recovery and zero sag.

If one employs a class D amp for purposes of power amp distortion, one bought the wrong tool.

The problem is there is a trend for overstating output power in Class D amps making expectations too high. I used to gig bass with a sub-200 watt Laney SS A/B amp through a couple of cheap 115s and never lacked power. I've had 500 watt and even 800 watt modern Class D heads hit the horrible clipping scenario at similar volumes, through much more efficient cabs.

 

[codamedia]

The problem is there is a trend for overstating output power in Class D amps making expectations too high.

Absolutely true, but once you learn this or become aware of this you buy appropriately. It's not a fault of CLASS D technology that company's are allowed to market these absurd ratings. I just laugh at them, and buy appropriately.

This is where Fender is getting the usage of Class D right with their Tonemaster series (IMO). The Deluxe is rated at 22 watts, the amount of Class D power that is actually being used to create that is irrelevant and it's capped before it's allowed to clip. The user never has to worry about it... and the amp is rated at a level guitar players can relate to.

 

[11 Gauge]

Class D works brilliantly when used as designed. Which is to faithfully reproduce a preamp signal with no additional distortion or coloration. And when you want wicked fast recovery and zero sag.

If one employs a class D amp for purposes of power amp distortion, one bought the wrong tool.

Quilter has a bunch of products available with low damping out, which is what probably lots of folks tend to confuse with being 'the sound of power amp distortion'. And yes, they achieve this with class D.

The low damping is a feature that you'll find with the Peavey Transtube stuff, albeit not with class D, TTBOMK. The folks at Peavey were smart enough to know this, and that it's actually not 'tube power amp distortion' as technically defined, that many guitarists seem to like.

Or, put another way - even to this day, lots of guitarists seem to be unaware that a tube power amp (in a guitar amp, anyway) basically has a very nonlinear response with the speaker. This nonlinear response is basically another form of distortion, just not with the definition of harmonic-generating clipping, per se. And this is why (IMO) many guitarists will say that a tube amp 'sounds 3-D' (or whatever), even when played clean, because this specific effect isn't clipping-related distortion.

I'd argue that the effect from low damping is a very much preferred 'coloration' with guitar power amps, that '100% completes the picture'. If you have a SS power amp that only faithfully reproduces the preamp signal only louder, and then it outputs that with high damping to the speaker, then something will be missing.

 

[Jakedog]

The problem is there is a trend for overstating output power in Class D amps making expectations too high. I used to gig bass with a sub-200 watt Laney SS A/B amp through a couple of cheap 115s and never lacked power. I've had 500 watt and even 800 watt modern Class D heads hit the horrible clipping scenario at similar volumes, through much more efficient cabs.

I find this interesting. I haven’t had any issues like this using class D bass amps. Or the class D power amps in my powered PA cabs. I have heard people push class D way too hard and get them to clip, but they were also WAY too loud for the room they were in when it happened.

I wonder if perception plays a roll? I know when I used analog SS AB bass amps they sounded very loud when I was standing in front of them, but not as much out in the room. My Markbass rig is the opposite. Standing in front of it I never feel like it’s loud enough or has enough power. When I have someone else play through it so I can hear it out in the room, I inevitably end up turning it down by quite a bit.

My class D Carvin rig I had previously did the same thing. FOH engineers hated that rig. Many complaints that it was stupid overpowered and they couldn’t get a clean mix because it was so loud in the room, yet the band was always saying on stage that they couldn’t hear me at all and begging me to turn up.