Class D amp at full volume?

[Rip Van Dan]

Couldn't you just mic a smaller amp into the venues PA? That + a DI or something might do the trick. I get what you're saying though and you're probably right. At least for fairly large venues.

More and more people are adopting more modern rigs though, I saw Brit Floyd recently and they were using Fractal audio gear for a lot of their sounds. It sounded really good though I almost want to say the last time I saw them they sounded better with whatever they were using before. But it was awhile ago so it's hard to really say. Both shows were great though.

Back in the day (early 70's) when I was touring nightclubs in the Western and Mid-Western US it was VERY unusual to find an FOH system at a club. Almost none of them had one. Some would have the Shure Vocalmaster PA columns or the Kustom columns, but you only ran vocals through those, not guitars, drums, or bass. So yeah, we had to provide what ever level the room needed.

Even with modern full FOH support though, you still need to have enough stage volume to hear yourself. I still would not feel comfortable using my old 50-watt Fender Bassman tube amp for that in a lot of places. A good FOH with everything running through it and a decent stage monitor pointed at your face will be much easier to hear.

Now having said that, I use a 210 cab almost everywhere we play now whether or not there is good FOH support. It's a DNS-210 which is an unusual 210 cab in that it can handle 700-watts rms (mechanically as well as thermally) and produces a maximum SPL of 134db. So it's a loud cab.

Although I feed it with an 800-watt amp. I can easily feed it with a 400-watt amp and get gig level volumes out of it. I feed it with a ~115-watts at rehearsal but we're in a small room. I feed it with an 800-watt amp for gigs because I have it, The cab can handle more power than I actually send it, and I love the sound I get.

If you want to use a smaller wattage amp such as a 50-watt all-valve (tube) amp, it will certainly run fine into an FOH but don't count on it holding it's own on stage without a good monitor right smack dab in front of you.

 

[TomB]

Back in the day (early 70's) when I was touring nightclubs in the Western and Mid-Western US it was VERY unusual to find an FOH system at a club. Almost none of them had one. Some would have the Shure Vocalmaster PA columns or the Kustom columns, but you only ran vocals through those, not guitars, drums, or bass. So yeah, we had to provide what ever level the room needed.

Even with modern full FOH support though, you still need to have enough stage volume to hear yourself. I still would not feel comfortable using my old 50-watt Fender Bassman tube amp for that in a lot of places. A good FOH with everything running through it and a decent stage monitor pointed at your face will be much easier to hear.

Now having said that, I use a 210 cab almost everywhere we play now whether or not there is good FOH support. It's a DNS-210 which is an unusual 210 cab in that it can handle 700-watts rms (mechanically as well as thermally) and produces a maximum SPL of 134db. So it's a loud cab.

Although I feed it with an 800-watt amp. I can easily feed it with a 400-watt amp and get gig level volumes out of it. I feed it with a ~115-watts at rehearsal but we're in a small room. I feed it with an 800-watt amp for gigs because I have it, The cab can handle more power than I actually send it, and I love the sound I get.

If you want to use a smaller wattage amp such as a 50-watt all-valve (tube) amp, it will certainly run fine into an FOH but don't count on it holding it's own on stage without a good monitor right smack dab in front of you.

Just to support your point, most bands I worked with in those days never put ANYTHING but vocals into the PA, and Shure Vocal Masters ruled the small clubs. Sure there were big bass bins and 300 watt Crown amps around the big dance clubs and concert halls, but even there the practice of instrument micing grew commonplace only slowly, as I recall it - I'm not talking Woodstock here . Class D has been a game changer for FOH.

 

[StatesideRambler]

Good Point but as I said, this IS my 1st Class D power amp and all I hear is that the AUDIO INPUT determines the VOLUME/OUTPUT/WATTAGE & Current Draw which does seem just SO unlike the Tube circuitry we're all used to

Are trying to compare a power amplifier with an integrated [i.e. a head with a preamp and power amp] amplifier? Your posts here sure read that way. Volume and tone functions are done by the preamp stages which, in turn, feed the power amp input.

 

[merseymale]

Are trying to compare a power amplifier with an integrated [i.e. a head with a preamp and power amp] amplifier? Your posts here sure read that way. Volume and tone functions are done by the preamp stages which, in turn, feed the power amp input.

I agree with the last part of your post but what I'm trying to ascertain is this:

is it true that a Class D power Amp just stays FULL ON ALL THE TIME or
does it have a separate Master Volume OR does it increase its power consumption and its output based on how loud the preamp section Is feeding the Class D's input?

so far I'm beginning to believe it's the latter of these three

 

[agedhorse]

I agree with the last part of your post but what I'm trying to ascertain is this:

is it true that a Class D power Amp just stays FULL ON ALL THE TIME or
does it have a separate Master Volume OR does it increase its power consumption and its output based on how loud the preamp section Is feeding the Class D's input?

so far I'm beginning to believe it's the latter of these three

All power amps deliver power proportional to the signal level fed to them.

 

[merseymale]

All power amps deliver power proportional to the signal level fed to them.

Yes but that's not what I was asking!

if you're saying the power & output of ALL power amps automatically increase & decrease depending on their input then I'd have to -with respect- disagree IMO

IF, however, this IS the behaviour of Class D amps then I'd like to know/have it confirmed

 

[agedhorse]

Yes but that's not what I was asking!

if you're saying the power & output of ALL power amps automatically increase & decrease depending on their input then I'd have to -with respect- disagree IMO

IF, however, this IS the behaviour of Class D amps then I'd like to know/have it confirmed

You might disagree, but you would be factually incorrect.

The very definition of a linear amp is that the output power is directly proportional to the square of the input voltage. This is the same for ALL amplifiers that operate as a linear amp.

(The definition of linear in this discussion is the input-output transfer function, not the amplifier mechanism itself)

Pout = (Av x Vin)**2/R

 

[Sid Fang]

Yes but that's not what I was asking!

if you're saying the power & output of ALL power amps automatically increase & decrease depending on their input then I'd have to -with respect- disagree IMO

IF, however, this IS the behaviour of Class D amps then I'd like to know/have it confirmed

Please adjust your attitude here. Agedhorse is a serious, pro, electrical engineer who designs amps, including some very well reviewed bass amps, for a living. I'm also an engineer, though my day job is in the digital domain, so while I'm capable of troubleshooting and repairing my old SVT, I am light-years away from Agedhorse's level of expertise. But we're both telling you the same thing. Please listen and stop worrying about being right.

You asked a question that was sort-of in three parts but not really clear. Rather than picking an unclear option, Agedhorse gave you the core truth.

It is the job of an amplifier to amplify a signal. That's why they are called amplifiers. BY DEFINITION the output increases with the input. If the input is zero, the output is zero. As the input increases, the output increases. Whether "-with respect-" or not, your disagreeing with this basic point is nonsensical.

Given that basic truth, there's no actual need to have a gain control (volume, if you like) for every stage of a multi-stage amp design, and for cost/complexity/reliability you're not going to add one that isn't needed. For a couple of reasons, it makes more sense to make the pre-amp stage the one with the variable gain "master" for the whole chain. Whether it's tube, class AB solid state, or class D, the power stage of an instrument amp is wired to run flat-out, with the level from the pre-amp determining the output level (and the power consumed to drive it to that level). It's POSSIBLE to make a variable gain power amp, it's just not generally useful, especially for instrument amps, so not generally done.

 

[StatesideRambler]

I agree with the last part of your post but what I'm trying to ascertain is this:

is it true that a Class D power Amp just stays FULL ON ALL THE TIME or
does it have a separate Master Volume OR does it increase its power consumption and its output based on how loud the preamp section Is feeding the Class D's input?

so far I'm beginning to believe it's the latter of these three

It's probably too late in the thread to bring this up but I will anyway. Among the most important things in any inquiry is to ask the right questions in order to get the needed answers.

... But can't see where the volume potentiometer should be connected. Surely a Class D amplifier is not expected to run flat out continuously and rely only on a preamp to adjust the output volume?!

The simplest answer to this question is that a power amp does not have a volume control. As you surmise, but don't understand, it is strictly the input level from the preamp stage(s) that determines the power amp's output. The power amp is flat out only when its input is flat out, i.e. at the max value in the spec. You need much more than a volume pot to bring that product into usefulness for your wants.

A power amplifier's output is determined by its design and the level (voltage) of the signal applied to its input. A small input signal yields low power output and a large signal yields high power output. As agedhorse stated above, this is true of every kind of linear amplifier including class A, class AB and class D circuits. The signal into the power amplifier comes from a preamplifier. It's in the preamplifier where you can adjust the volume by increasing and decreasing the signal voltage that you then apply to the power amp input.

The preamp in that evaluation board is not a full audio preamplifier with volume and tone shaping (EQ). The evaluation board you've bought is exactly that: it's a product for use by engineers and designers to evaluate its suitability for their proposed uses. It's therefore sold in a form that presumes that the buyer has the knowledge and skill to adapt it to his purpose, in this case, the ability to make or select a preamp with volume and tone shaping circuits that will provide a signal to the input of that board that will drive it to full output while not overloading it beyond its tolerance.

FWIW quite a few members here are engineers, some working in the musical instrument amplification industry and some of those have replied. As a retired engineer myself I try hard to give clear and complete answers to questions but often answers are just not possible to reduce enough to fit into a forum reply. "Everything should be made as simple as possible, but no simpler." Until you get considerably more understanding of electronics than you have so far you won't realize that you're asking an awful lot from us.

 

[agedhorse]

Well said StatesideRambler

 

[TomB]

Well said StatesideRambler

FWIW, this discussion has been very informative for some of us non-engineers, so I thank all you engineers (once again) for your clearly-stated replies.

Question - So, in the simplest terms then: for amps with gain/master set-up, such as most commercial bass amps, "gain" controls the input to the preamp, "master" controls the preamp output to the power amp? And for a typical PA power amp (not the powered-speaker type) the single volume control serves both functions; it controls the amount of input going to the power section?

 

[merseymale]

It's probably too late in the thread to bring this up but I will anyway. Among the most important things in any inquiry is to ask the right questions in order to get the needed answers.

The simplest answer to this question is that a power amp does not have a volume control. As you surmise, but don't understand, it is strictly the input level from the preamp stage(s) that determines the power amp's output. The power amp is flat out only when its input is flat out, i.e. at the max value in the spec. You need much more than a volume pot to bring that product into usefulness for your wants.

A power amplifier's output is determined by its design and the level (voltage) of the signal applied to its input. A small input signal yields low power output and a large signal yields high power output. As agedhorse stated above, this is true of every kind of linear amplifier including class A, class AB and class D circuits. The signal into the power amplifier comes from a preamplifier. It's in the preamplifier where you can adjust the volume by increasing and decreasing the signal voltage that you then apply to the power amp input.

The preamp in that evaluation board is not a full audio preamplifier with volume and tone shaping (EQ). The evaluation board you've bought is exactly that: it's a product for use by engineers and designers to evaluate its suitability for their proposed uses. It's therefore sold in a form that presumes that the buyer has the knowledge and skill to adapt it to his purpose, in this case, the ability to make or select a preamp with volume and tone shaping circuits that will provide a signal to the input of that board that will drive it to full output while not overloading it beyond its tolerance.

FWIW quite a few members here are engineers, some working in the musical instrument amplification industry and some of those have replied. As a retired engineer myself I try hard to give clear and complete answers to questions but often answers are just not possible to reduce enough to fit into a forum reply. "Everything should be made as simple as possible, but no simpler." Until you get considerably more understanding of electronics than you have so far you won't realize that you're asking an awful lot from us.

well, TBH, I realise this forum's expertise otherwise I wouldn't ask and I also realise how much I am asking and thought I was sufficiently thankful in my posts

However if I'm not may I just make it clear, now, that I am thankful to everyone who has posted any answers to any of my questions, on TalkBass, EVER.

I also believe my questions were sincere and clear...& I'm afraid that I still do.

I have since spoken at length on the phone (corona lockdown has its uses!!) to the designer of the circuit I mentioned and he echoes what I'm being told: namely that the input determines the audio output and also the power consumption too. Fine. You & I are both in agreement on this point, now.


It is always been my understanding that the master volume 'bridging', as it were, between a preamp and the power amp of a bass guitar amplifier or similar only 'regulated' what was sent to that power amp by the preamp and also that a master volume on the power amp stage was just that.
No more. No less.

This is why it seems obvious to ignorant me that in other classes of amps this is not Always the case...

anyway, despite my newfound knowledge -not least from this forum- may I ask how is it, when one turns up the power amp volume on an amplifier, there is audible hiss?
Why is it amplifying at all if the gain &/or volume on the preamp is turned down, say in a combo?

Why would most (i.e. non-class d) amps Emit Hiss even when there is no instrument connected and that this circuit noise goes up in volume as the volume is turned up if, as you imply, the power amp needs some sort of input 1st?

Why is it that in hybrid amps with a tube power stage, like the Roland Bolt60, frinstance, do the tubes glow without any input?

Witnessing these phenomena; information I have since received and schematics I have encountered; all points, for the sake of my limited knowledge at least (!), that not EVERY power amp lies dormant until it receives an input and then it suddenly jumps into life

but, as ever, YMMV

 

[merseymale]

You might disagree, but you would be factually incorrect.

The very definition of a linear amp is that the output power is directly proportional to the square of the input voltage. This is the same for ALL amplifiers that operate as a linear amp.

(The definition of linear in this discussion is the input-output transfer function, not the amplifier mechanism itself)

Pout = (Av x Vin)**2/R

Goodness Me!

I am in No Way disagreeing with you about the point you raise but I AM saying that it is NOT the point that I raised!

"The definition of linear in this discussion is the input-output transfer function, not the amplifier mechanism itself" oh really? I don't remember the OP asking that..?

but if you want to point-out the obvious now then feel free to -it's not hijacking a thread if the OP has his answer by now... (Which I do)

the Original Question WAS, largely,of a "mechanical" nature in that it queried how the separate circuits of a complete amplifier would interface with one another to achieve a physical sound wave from a Speaker

the Speaker in question may well be linear enough but the question concerned the comparison of other classes of Amplifier with it.

just sayin'

 

[agedhorse]

FWIW, this discussion has been very informative for some of us non-engineers, so I thank all you engineers (once again) for your clearly-stated replies.

Question - So, in the simplest terms then: for amps with gain/master set-up, such as most commercial bass amps, "gain" controls the input to the preamp, "master" controls the preamp output to the power amp? And for a typical PA power amp (not the powered-speaker type) the single volume control serves both functions; it controls the amount of input going to the power section?

Yes, this is generally correct.

 

[agedhorse]

well, TBH, I realise this forum's expertise otherwise I wouldn't ask and I also realise how much I am asking and thought I was sufficiently thankful in my posts

However if I'm not may I just make it clear, now, that I am thankful to everyone who has posted any answers to any of my questions, on TalkBass, EVER.

I also believe my questions were sincere and clear...& I'm afraid that I still do.

I have since spoken at length on the phone (corona lockdown has its uses!!) to the designer of the circuit I mentioned and he echoes what I'm being told: namely that the input determines the audio output and also the power consumption too. Fine. You & I are both in agreement on this point, now.


It is always been my understanding that the master volume 'bridging', as it were, between a preamp and the power amp of a bass guitar amplifier or similar only 'regulated' what was sent to that power amp by the preamp and also that a master volume on the power amp stage was just that.
No more. No less.

This is why it seems obvious to ignorant me that in other classes of amps this is not Always the case...

anyway, despite my newfound knowledge -not least from this forum- may I ask how is it, when one turns up the power amp volume on an amplifier, there is audible hiss?
Why is it amplifying at all if the gain &/or volume on the preamp is turned down, say in a combo?

Why would most (i.e. non-class d) amps Emit Hiss even when there is no instrument connected and that this circuit noise goes up in volume as the volume is turned up if, as you imply, the power amp needs some sort of input 1st?

Why is it that in hybrid amps with a tube power stage, like the Roland Bolt60, frinstance, do the tubes glow without any input?

Witnessing these phenomena; information I have since received and schematics I have encountered; all points, for the sake of my limited knowledge at least (!), that not EVERY power amp lies dormant until it receives an input and then it suddenly jumps into life

but, as ever, YMMV

Power amplifiers amplify whatever signal is present plus whatever noise is present, plus generate their own "self-noise. All 3 of the above terms are what make up the signal to noise tatio of a complete amplifier.

ALL power amplifiers generate some noise. It does. It matter what the class is.

Depending on where the noise is generated, and how much noise is present in each source can have an effect on perception.

A sudden change in noise floor when signal becomes present (whike playing) might indicate the use of a noise gate which acts as a "signal controlled switch" being used to decrease noise under no signal conditions. This is not part of the power amplifier.

Tubes have to glow in order to
work. It's the heat from the heater on the cathode that boils off the electrons thatvare then controlled by the grid on the way to the plate. I don't know what you mean by the tubes glowing with input.

 

[Sid Fang]

Question - So, in the simplest terms then: for amps with gain/master set-up, such as most commercial bass amps, "gain" controls the input to the preamp, "master" controls the preamp output to the power amp?

Correct. The input gain control, the one labeled "Gain", serves to normalize the input, mostly to deal with the fact that the input signal level varies quite a bit between passive and active basses. Some amps simply have an active/passive switch for this.

 

[merseymale]

Power amplifiers amplify whatever signal is present plus whatever noise is present, plus generate their own "self-noise. All 3 of the above terms are what make up the signal to noise tatio of a complete amplifier.

ALL power amplifiers generate some noise. It does. It matter what the class is.

Depending on where the noise is generated, and how much noise is present in each source can have an effect on perception.

A sudden change in noise floor when signal becomes present (whike playing) might indicate the use of a noise gate which acts as a "signal controlled switch" being used to decrease noise under no signal conditions. This is not part of the power amplifier.

Tubes have to glow in order to
work. It's the heat from the heater on the cathode that boils off the electrons thatvare then controlled by the grid on the way to the plate. I don't know what you mean by the tubes glowing with input.

so, basically you're in agreement with me, then.

 

[mcnach]

 

[agedhorse]

so, basically you're in agreement with me, then.

Frankly, I'm not sure.

 

[merseymale]

Frankly, I'm not sure.

Ok ok ok

Let's agree that @LEAST one Class of amp relies on its input to determine both its output & its power consumption & therefore requires no potentiometer of its own & forget about other amps as far as this thread is concerned and leave it at that

once again let me add how grateful I am to all the wisdom so freely given here by all