Hello - this is more of a loose curiosity question for future experimenting.
Is anyone able to site a hi fi tube amp design/model that was known for having unusually high output power but also somewhat unacceptable distortion?
Thanks. I realize this is a very indefinitive question but, would like to see if there are any models of amps or topologies that come to mind. This is for experimenting with a variety of instruments that are shown to benefit from a more hi fi presentation but, have proved to not sound too great through guitar amp type topologies.
Thank you,
Phil D.
Is anyone able to site a hi fi tube amp design/model that was known for having unusually high output power but also somewhat unacceptable distortion?
Thanks. I realize this is a very indefinitive question but, would like to see if there are any models of amps or topologies that come to mind. This is for experimenting with a variety of instruments that are shown to benefit from a more hi fi presentation but, have proved to not sound too great through guitar amp type topologies.
Thank you,
Phil D.
Many or most amplifiers, regardless of their maximum output power rating, can be extremely overdriven.
At that point, they are either soft clipping or hard clipping.
Personally, I find that to be un-acceptable distortion.
Your acceptable amount of distortion may vary.
At that point, they are either soft clipping or hard clipping.
Personally, I find that to be un-acceptable distortion.
Your acceptable amount of distortion may vary.
Many circuits used as AM modulators do exactly that. Both in the power stage,
And its driver which is often compressed & clipped to increase what is referred to as voice power. 🙂
Public address amplifiers normally ran in class B. more distortion than acceptable for HiFi use, the focus was/is on loudness.
Thanks all, and yes, I may be looking for something (or probably build something) that is somewhere between a hi fi reproducing amp and a PA, or, at least a nice sounding but fairly loud stereo stage monitoring system, something that fills a decent size stage pretty well and can be miced Left/Right and panned out through the "real" PA system.
Its tempting to start with a known hi fi amp and experiment with different levels of NFB but, I may need to know more than I do now to accomplish that prudently. I've built amps with adjustable NFB and sure, there is a notable trade off between output volume and NFB, but, those were more guitar type amps which seem to have too much distortion even when they have alot of NFB.
At this point, there isn't really a great way of knowing how much distortion is acceptable for the application but, perhaps I will start with something like a higher power Mullard or Williamson and experiment a bit to hear what happens.
Thank you,
PJD3
Its tempting to start with a known hi fi amp and experiment with different levels of NFB but, I may need to know more than I do now to accomplish that prudently. I've built amps with adjustable NFB and sure, there is a notable trade off between output volume and NFB, but, those were more guitar type amps which seem to have too much distortion even when they have alot of NFB.
At this point, there isn't really a great way of knowing how much distortion is acceptable for the application but, perhaps I will start with something like a higher power Mullard or Williamson and experiment a bit to hear what happens.
Thank you,
PJD3
A higher power Williamson is a hard to tame beast due to the marginal stability of the design. IMHO it is best to stay away from it, the success depends for a large extend on the output transformer.
Negative feedback versus power?
For this discussion, let us consider maximum output power to be just before the amplifier clips.
Given a certain combination of:
output tubes, plate and screen voltages, plate and screen currents, and output transformer . . . then the maximum output power is mainly dependent on which output circuit mode you choose: Pentode/Beam Power; Ultra Linear; or Triode wired.
The maximum unclipped output power, from largest to smallest usually goes in this order: Pentode/Beam Power; Ultra Linear; or Triode wired.
The amount of global negative feedback that you apply to that amplifier changes:
the gain of the amplifier (how much voltage at the input of the amplifier is required to get maximum power output),
if you turn up an external preamp's gain, you can get the maximum output power, even if the amplifier input sensitivity is low because of lots of global negative feedback,
and
the amount of global negative feedback changes how much distortion the amplifier has before clipping.
The amount of global negative feedback generally does not significantly change the unclipped output power level.
All generalizations have exceptions.
For this discussion, let us consider maximum output power to be just before the amplifier clips.
Given a certain combination of:
output tubes, plate and screen voltages, plate and screen currents, and output transformer . . . then the maximum output power is mainly dependent on which output circuit mode you choose: Pentode/Beam Power; Ultra Linear; or Triode wired.
The maximum unclipped output power, from largest to smallest usually goes in this order: Pentode/Beam Power; Ultra Linear; or Triode wired.
The amount of global negative feedback that you apply to that amplifier changes:
the gain of the amplifier (how much voltage at the input of the amplifier is required to get maximum power output),
if you turn up an external preamp's gain, you can get the maximum output power, even if the amplifier input sensitivity is low because of lots of global negative feedback,
and
the amount of global negative feedback changes how much distortion the amplifier has before clipping.
The amount of global negative feedback generally does not significantly change the unclipped output power level.
All generalizations have exceptions.
With the volume levels at concerts how could you even tell 0.01% THD to 10%?
Maybe not concerts but things like movie theaters and drive ins probably used high power class B amps with distortion considered unacceptable for hifi.
Has anyone made some recent fft measurements on class B amps? I’m curious what the plot looks like.
Maybe not concerts but things like movie theaters and drive ins probably used high power class B amps with distortion considered unacceptable for hifi.
Has anyone made some recent fft measurements on class B amps? I’m curious what the plot looks like.
Thank for your replies. I'm not trying to challenge any extremes of power vs NFB specifications outcomes or results, its more that I've found that one "can" trade off" volume and NFB for textural purposes, when operating the amp/instrument in a moderate range of its potential volume or output power. What I'm getting ready to do is furnish a tone generating amp for one or two odd instruments, things I built that are neither guitar, nor flute, nor electric violin, but live somewhere in the middle of all of them. So this isn't quite a science I'm ready to delve into on this, its as much as an art as anything. I don't think anyone knows what will work best for this yet. I've just found that too much distortion does not compliment the instruments but, perhaps there may be instances where a decrease in NFB to a certain degree may infact be desirable in certain instances. If may very well turn out that amps of the most hi fi and clean nature are just what it needs all the time. But, this is a project that will be finding itself. I"m just looking for a few good starting points. I'm not on an engineering level but have been able to design little mods and adjustments to amps to offer a little more adjustability to the texture of the sound. So, for this project, I am the epitome of generalization! I have to live with that until I get more versed in what it is I need out of an amp for this odd application. I just know that if I had a choice between a guitar amp or hi fi amp, I would definitely go full hi fi. But, there will need to be a little experimenting to find out.
Thanks for your patience, I realize my concerns are odd at best.
PJD3
Thanks for your patience, I realize my concerns are odd at best.
PJD3
My standard approach is to get the best results on test with a open loop circuit after the test of the single stage of the entire amp
I mean a wide frequency answer; then the THD vs frequency and fixed level and in the function of the level ( fixing a value of THD, in my case 2-3%, max 5% just to see )that says a lot mainly on low and high frequency.
Check the phase, of course.
And this means that the OT trafo must be done at the best (=not cheap).
After that I play with the NFB finding a low-mid value to get a better results.
Walter
I mean a wide frequency answer; then the THD vs frequency and fixed level and in the function of the level ( fixing a value of THD, in my case 2-3%, max 5% just to see )that says a lot mainly on low and high frequency.
Check the phase, of course.
And this means that the OT trafo must be done at the best (=not cheap).
After that I play with the NFB finding a low-mid value to get a better results.
Walter