Strain on an amp or no ?

[joessportster]

It is my understanding that an amp is always putting out its max power and the Pre-amp acts to Cut that max down to your desired level. If that is correct and an amp is always putting out its max then will it put undue strain  on an amp to have it connected to a Passive pre with the volume always at max ? Speaking about tube amps  

 

What say you ?

[Guest wdecho]

Depends on whether the tube amplifier is class A or A/B. In class A it will be working as hard as it is biased for all the time but it will not do the amp any harm with the volume control wide open. Whether wide open or not it will not matter with a class A amplifier. The pot only controls how much signal the amplifier will see. 

[joessportster]

, Class A all the way SET You worded that so much better than I   Pot controls how much source signal the amp sees thereby affecting how loud  things sound. I now have a new / better understanding of how things work Perfect  Thanks much

 

I was trying to make sure I am not straining the tubes un necessarily ,Amp is designed to put out its max at all times and the source is actually what affects volume not amps output .

[Dave1290]

Well then by all means crank it up!   😂 🤣 😂

[JohnA]

On 8/23/2018 at 6:31 PM, joessportster said:

It is my understanding that an amp is always putting out its max power and the Pre-amp acts to Cut that max down to your desired level. If that is correct and an amp is always putting out its max then will it put undue strain  on an amp to have it connected to a Passive pre with the volume always at max ? Speaking about tube amps  

 

What say you ?

 

Not true at all.  A power amp does operate at max "gain", amplifying every signal it gets by, say 30 dB.  But that 30 dB could generate anything from .00001 to 300  watts.  The limit is the design output of the power amp.  Heat is usually proportional to power output and "stress" would be approximately proportional to heat. 

[joessportster]

11 minutes ago, JohnA said:

 

Not true at all.  A power amp does operate at max "gain", amplifying every signal it gets by, say 30 dB.  But that 30 dB could generate anything from .00001 to 300  watts.  The limit is the design output of the power amp.  Heat is usually proportional to power output and "stress" would be approximately proportional to heat. 

Ok I think I was saying pretty much the same thing Power amp always putting out max power I.O.W.... gain (terminology is not my strong point, But it does not need to be, I am not designing nor building electronics).  An amp rated at 2.5 WPC will put out that 2.5 WPC at all times (Tube difference, Electrical fluctuations, or anything else that may affect the amps performance not withstanding of course) That was my initial point Though not necessarily in the terminology that some expect / like. 

 

It stands to reason that an amp rated at X will generate Heat said heat may rise over time from constant use but not because of extra power / gain, and of course that heat due to time will stress anything

 

My question was more will using an amp at full output / Gain cause undue stress. Answer is no with caveat that constant / extended use at max gain in a situation where heat may rise could cause undue stress and shorten tube / component life 

[Guest wdecho]

18 minutes ago, joessportster said:

My question was more will using an amp at full output / Gain cause undue stress. Answer is no with caveat that constant / extended use at max gain in a situation where heat may rise could cause undue stress and shorten tube / component life 

Not in class A, working full blast all the time. This is the reason SS class A amps have to have big heavy heatsinks and class A/B does not have to have near the heatsinking. A good analogy is a relay race. In SE class A amps one runner is given the baton and runs as fast as he can. In a class A push pull amplifier the runners run as fast as they can and pass the baton. In class A/B the runners slow down to a trot and pass the baton. Class B the runners stop and then pass the baton.  

[JohnA]

On 8/25/2018 at 11:49 AM, joessportster said:

Ok I think I was saying pretty much the same thing Power amp always putting out max power I.O.W.... gain (terminology is not my strong point, But it does not need to be, I am not designing nor building electronics).  An amp rated at 2.5 WPC will put out that 2.5 WPC at all times .............

 

No, not really.  An amp, regardless of class, is READY to put out max power, via its designed gain, but will only output the power demanded by its input voltage.  The power drawn from the wall and that sent to the speakers could be nearly 0, for some designs, if there is no input connected, and yet it is still running at full gain, maybe think of that as potential or capability.

 

[pzannucci]

10 hours ago, JohnA said:

 

No, not really.  An amp, regardless of class, is READY to put out max power, via its designed gain, but will only output the power demanded by its input voltage.  The power drawn from the wall and that sent to the speakers could be nearly 0, for some designs, if there is no input connected, and yet it is still running at full gain, maybe think of that as potential or capability.

 

Power sent to speakers may be nearly zero but in Class A the current use due to biasing is high causing it to be hot and eat a lot of power all the time.  High heat typically equals stress.

[Guest wdecho]

Stress that can be controlled if one stays within boundaries. For an example a typical mosfet that is used in many FW amplifiers is the IRFP240 which has a max temp rating of 150C that is operated in production amps around 55C. They will last 20 or 30 years or longer being operated this way. I sometime push some of my builds 65C or higher with the understanding that the transistors will not last quiet as long as being run more conservatively. The advantage of working a transistor really hard is better sound. "A working boy is a happy boy." Transistors as a rule sound better the more they are worked, until they self destruct due to excessive heat. There are those that have pushed a transistor to it's limit claiming the amp was the best sounding one has ever heard, for 5 minutes. Firstwatt and Passlabs amplifiers are recommended to be turned on for an hour before doing serious listening for this reason. To achieve optimal operating temperature. Many owners of these amplifiers have noticed a difference in the sound from cold start to correct temp. 

 

In other words class A is working hard all the time up to the design limits whereas in A/B amplifiers the input signal controls how hard the transistors are working. Most have noticed this with their A/B amplifiers at a low volume being cool to the touch but heating up when the volume is increased.   

[pzannucci]

4 minutes ago, wdecho said:

Stress that can be controlled if one stays within boundaries. For an example a typical mosfet that is used in many FW amplifiers is the IRFP240 which has a max temp rating of 150C that is operated in production amps around 55C. They will last 20 or 30 years or longer being operated this way. I sometime push some of my builds 65C or higher with the understanding that the transistors will not last quiet as long as being run more conservatively. The advantage of working a transistor really hard is better sound. "A working boy is a happy boy." Transistors as a rule sound better the more they are worked, until they self destruct due to excessive heat. There are those that have pushed a transistor to it's limit claiming the amp was the best sounding one has ever heard, for 5 minutes.

 

 

Just like some speakers I've heard.  Seriously opened up the sound when over-driven then pop.  

[ClaudeJ1]

On 8/25/2018 at 11:49 AM, joessportster said:

Ok I think I was saying pretty much the same thing Power amp always putting out max power I.O.W.... gain (terminology is not my strong point, But it does not need to be, I am not designing nor building electronics).  An amp rated at 2.5 WPC will put out that 2.5 WPC at all times (Tube difference, Electrical fluctuations, or anything else that may affect the amps performance not withstanding of course) That was my initial point Though not necessarily in the terminology that some expect / like. 

 

It stands to reason that an amp rated at X will generate Heat said heat may rise over time from constant use but not because of extra power / gain, and of course that heat due to time will stress anything

 

My question was more will using an amp at full output / Gain cause undue stress. Answer is no with caveat that constant / extended use at max gain in a situation where heat may rise could cause undue stress and shorten tube / component life 

The term "put out" need a better definition. The Voltage Gain of a power amplifier an be switched on some designs. Assuming we are dealing with a fixed voltage GAIN, say 20 DB, , how much power is in the OUTPUT depends on the current draw of the speaker relative to output voltage amplitude. It also varies with impedance, which varies with frequency as controlled with the voltage seen at the INPUT. How many WATTS get "pulled out" (are more appropriate laymen's term) of the amplifier is controlled by the input. That is the basic definition of an amplifier regardless of class.

[JohnA]

Obviously a mildly complex situation with the different possible amp designs.  Perhaps an analogy; your kitchen cabinets are under constant stress from the, sometimes considerable, load of lots of dishes.  Yet they hold up for decades because the stress is  well within their design capacity.  If an amp is allowed the cooling air it was designed to get, it will also last for decades, without damage, regardless of class or average power output.  IOW, they are designed to withstand whatever stress they may see in normal use for many long years. 

 

I have 3 receivers from 1979 that are all happily running as they did almost 40 years ago.