[Tilpo]

You can do that but it still doesn't sound the same as a zero feedback tube amp that has a true matching output impedance. I know because I've had both & made my own impedance matching networks for transistor amps in order to drive horns & while it did improve the sound over the original transistor sound the zero feedback tubes still had the sound to die for even though the output impedance was matched on both with the output network on the transistor amp. Even the output power was matched with the tube amp with the impedance matching network on the tranny amp, 25 Watts /channel to the speaker. By the way the tranny amp still neded to have a resistor network across the terminals at the back of the amp as well as the resistors in series with the speaker to sound it's best with the Altec Lansing Voice Of The Theatre A7-500 that I had at the time. This in part hid the reactance of the speaker from the amp Which was an Adcom GFA 545 which was modified. I had used it to drive many other speakers before, even some as low 2ohms & is sounded great on them but really needed the impedance matching network to sound it's best on the horns even though the load was an easy load for the amp. The easiest load that amp has ever seen with me. 
 
Of coarse this does not apply to headphones, They should be driven with the output impedance that they were designed with originally & not make assumptions that we know best how to drive them without consulting the manufacturer.

Out of interest, would you be able to elaborate in technical terms why the tube amp behaved better? Or is it simply an observation?

 

[germanium]

Quote:

Out of interest, would you be able to elaborate in technical terms why the tube amp behaved better? Or is it simply an observation?

Zero feed back tube amps if properly built should have flat power response as opposed flat voltage response of tranny amps. Into a resistor they cam measure remarkably flat with modern output transformers to beyond audability.when diving a speaker the amp isn't trying to correct after the fact for what the speaker is doing because there is no feedback. With feedback , even corective negative feedback there is always a delay to the correction & this introduces it's own form of distortion that is not always easily quantifiable. If you have a tube amp with defeatable negative feedback this distortion becomes quite pronounced in a loss of dynamics & the sound becomes somewhat lifeless compared to when the feedback is removed. without the feedback the sound is more lively & dynamic, not squashed like it was with the feedback. Also the amp isn't trying to control the driver by damping it excessively. It's just driving the speaker with flat power response. I belive that it is in part this attempt to control the driver that squashes the sound.
 
By flat power response I mean that they will deliver about the same power into the normal speaker impedance flutuations it would likely experience. Example is an 8 ohm speaker would likely vary in impedance anywhere from  between 4-5ohms to 16 ohms or a little beyond, somtimes even double that but between 4 & 16 ohms it will deliver close to the same power as it does into the 8 ohm resistor.Distortion will go up some when driving out of spec impedances but not to an audible degree in most cases.
 

 

[Tilpo]

Zero feed back tube amps if properly built should have flat power response as opposed flat voltage response of tranny amps. Into a resistor they cam measure remarkably flat with modern output transformers to beyond audability.when diving a speaker the amp isn't trying to correct after the fact for what the speaker is doing because there is no feedback. With feedback , even corective negative feedback there is always a delay to the correction & this introduces it's own form of distortion that is not always easily quantifiable. If you have a tube amp with defeatable negative feedback this distortion becomes quite pronounced in a loss of dynamics & the sound becomes somewhat lifeless compared to when the feedback is removed. without the feedback the sound is more lively & dynamic, not squashed like it was with the feedback. Also the amp isn't trying to control the driver by damping it excessively. It's just driving the speaker with flat power response. I belive that it is in part this attempt to control the driver that squashes the sound.
 
By flat power response I mean that they will deliver about the same power into the normal speaker impedance flutuations it would likely experience. Example is an 8 ohm speaker would likely vary in impedance anywhere from  between 4-5ohms to 16 ohms or a little beyond, somtimes even double that but between 4 & 16 ohms it will deliver close to the same power as it does into the 8 ohm resistor.Distortion will go up some when driving out of spec impedances but not to an audible degree in most cases.
 

Don't speakers rely on the amplifier to be damped? In that case, wouldn't a non-feedback tube amp only be better for specific speakers?

 

[xnor]

Quote:

Zero feed back tube amps if properly built should have flat power response as opposed flat voltage response of tranny amps.

If that's the case then there is not a single properly built tube amp out there because of the wildly non-flat speaker impedances as load. Btw, what's a "tranny amp"?
 
Quote:

Into a resistor they cam measure remarkably flat with modern output transformers to beyond audability.

I do not understand this sentence.
 
Quote:

when diving a speaker the amp isn't trying to correct after the fact for what the speaker is doing because there is no feedback. With feedback , even corective negative feedback there is always a delay to the correction & this introduces it's own form of distortion that is not always easily quantifiable. If you have a tube amp with defeatable negative feedback this distortion becomes quite pronounced in a loss of dynamics & the sound becomes somewhat lifeless compared to when the feedback is removed. without the feedback the sound is more lively & dynamic, not squashed like it was with the feedback. Also the amp isn't trying to control the driver by damping it excessively. It's just driving the speaker with flat power response. I belive that it is in part this attempt to control the driver that squashes the sound.

I don't think thats what's going on. What you call lively & dynamic is in fact large amounts of (harmonic) distortion. Also, the high output impedance mostly adds bass like an equalizer - granted, some speakers need that.
You're talking about "control of the driver that squashes the sound" but what is going on with a low output impedance (~0) amp is that if there is 1 V at the input and the gain is 1x then the output also will be 1 V regardless of frequency or impedance of the speaker. It doesn't matter if the load is a resistor or some fancy speaker - 1 V in means 1 V out. With a higher impedance tube amp the output will change depending on the frequency/impedance of the speaker, so for example 1 V in could result in 2 V out at 100 Hz but 0.8 V at 1000 Hz and so on..
 
Quote:

By flat power response I mean that they will deliver about the same power into the normal speaker impedance flutuations it would likely experience. Example is an 8 ohm speaker would likely vary in impedance anywhere from  between 4-5ohms to 16 ohms or a little beyond, somtimes even double that but between 4 & 16 ohms it will deliver close to the same power as it does into the 8 ohm resistor.Distortion will go up some when driving out of spec impedances but not to an audible degree in most cases.

Just add resistors as described before and you'll get the same with any low output impedance amp. These resistors will affectively defeat the feedback.
 

 

[germanium]

Quote:

Don't speakers rely on the amplifier to be damped? In that case, wouldn't a non-feedback tube amp only be better for specific speakers?

Yes that is true & if you read my earlier comments you would find acoustic suspension speakers do better with tranny gear, they need the extra damping in most cases as they are not designed in general to be flat as possable to begin with. Most have a 3 to 5db boost at the resonance of the woofer system even with a tranny amp & this would be essentuated by the zero feedback tube amp. They were also invented after the advent of tranny amps & were designed with them specifically in mind. Most other types generally do as well if not better with zero feedback tube amps unless of coarse they were specificall designed for tranny amps. 
 
All internally biamped speakers are designed with tranny amps inside & the drive systems are designed to work with them.
 

 

[germanium]

Quote:

Quote:

Zero feed back tube amps if properly built should have flat power response as opposed flat voltage response of tranny amps.

If that's the case then there is not a single properly built tube amp out there because of the wildly non-flat speaker impedances as load. Btw, what's a "tranny amp"?
 
Quote:

Into a resistor they cam measure remarkably flat with modern output transformers to beyond audability.

I do not understand this sentence.
 
Quote:

when diving a speaker the amp isn't trying to correct after the fact for what the speaker is doing because there is no feedback. With feedback , even corective negative feedback there is always a delay to the correction & this introduces it's own form of distortion that is not always easily quantifiable. If you have a tube amp with defeatable negative feedback this distortion becomes quite pronounced in a loss of dynamics & the sound becomes somewhat lifeless compared to when the feedback is removed. without the feedback the sound is more lively & dynamic, not squashed like it was with the feedback. Also the amp isn't trying to control the driver by damping it excessively. It's just driving the speaker with flat power response. I belive that it is in part this attempt to control the driver that squashes the sound.

I don't think thats what's going on. What you call lively & dynamic is in fact large amounts of (harmonic) distortion. Also, the high output impedance mostly adds bass like an equalizer - granted, some speakers need that.
You're talking about "control of the driver that squashes the sound" but what is going on with a low output impedance (~0) amp is that if there is 1 V at the input and the gain is 1x then the output also will be 1 V regardless of frequency or impedance of the speaker. It doesn't matter if the load is a resistor or some fancy speaker - 1 V in means 1 V out. With a higher impedance tube amp the output will change depending on the frequency/impedance of the speaker, so for example 1 V in could result in 2 V out at 100 Hz but 0.8 V at 1000 Hz and so on..
 
Quote:

By flat power response I mean that they will deliver about the same power into the normal speaker impedance flutuations it would likely experience. Example is an 8 ohm speaker would likely vary in impedance anywhere from  between 4-5ohms to 16 ohms or a little beyond, somtimes even double that but between 4 & 16 ohms it will deliver close to the same power as it does into the 8 ohm resistor.Distortion will go up some when driving out of spec impedances but not to an audible degree in most cases.

Just add resistors as described before and you'll get the same with any low output impedance amp. These resistors will affectively defeat the feedback.
 

This should be good reading on this subject
 
http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php
 

 

[xnor]

Quote:

This should be good reading on this subject
 
http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php

 
An article on the site of an expensive audiophile tube amp manufacturer? Good reading, I doubt it.
 
Btw: some points confirm what I posted above.

 

[germanium]

Quote:

 
An article on the site of an expensive audiophile tube amp manufacturer? Good reading, I doubt it.
 
Btw: some points confirm what I posted above.

Actually not all his products are hugely expensive, some are but not all. This company has a reputation for some of the best sounding amps available at any price, even from his less expensive amps.They have lower distortion than most zero feedback amps in real objectiver terms as well as in actual performance under real loads. They just opereate on a different priciple than tranny amps do. One that suits many speaker types better than tranny amps do.
 

 

[Tilpo]

Hmmm, yes. But you still should take every article posted on the website of a manufacturer with a big grain of salt.

 

[xnor]

Yeah, check this out:
 
 
Quote (wolcott audio, sells tube amps):

[size=small]conventional vacuum tube amplifiers, as well as sounding warm and endearing, also do a whole lot of things wrong. Output tube drift, soft top octave, mushy bass, high noise levels, slow overload recovery, plenty of euphonic distortion for that rich fat sound, and erratic frequency response into difficult speaker loads.[/size]

 
Quote:

[size=small]What if we told you that our very different tube amplifier had highly accurate autobiasing, a nearly infinite damping factor, acted as a pure voltage source into almost any real world speaker load, had a full power bandwidth of nearly 60kHz (3db down point), had distortion below 0.01%, and a signal to noise ratio of better than 100db? What if we told you that you still get shockingly accurate timbres, breath taking dynamics, and amazing sound staging, but that you also get the tautest, most controlled bass you'll ever hear?[/size]

 
Quote:

[size=small]"Great bass for a tube amp" is the typical sort of faint praise you see in mealy mouthed reviews of vacuum tube products. In fact practically all tube amps have lousy bass simply because their output impedances are so high and their damping factors are so poor.[/size]

 
bla bla and so on and on...

 

[firev1]

Funny that you would trust a audio manufacturer without any sort of proof and data rather ones who took measurements using proper equipment and methods.

 

[germanium]

Quote:

Funny that you would trust a audio manufacturer without any sort of proof and data rather ones who took measurements using proper equipment and methods.

I would trust the designer to tell me what type of amp they designed to so I would at least know how best to drive them, Whether Either zero impedance, matched Impeance or anything in between. The designer would know. However most large manufacturers you are not going to get a hold of the designers. Often times it would go through some commitee & end up sounding like all thier other products in the end anyway at large corperate manufacturers.
 

 

[Chris J]

OP

Maybe stick this stuff in the articles section?

 

[germanium]

Quote:

Yeah, check this out:
 
 
 
 
 
bla bla and so on and on...

Funny, While some of what you are saying is true tubes are still used in much of the pro gear & the pro gear does not have most of the sonic issues you talk of. No soft rolled off top, not soft rolled off bottom. Distortion can be well below audibilty. Distortion at max power on tube power amps may look ugly but we don't listen at max power, do we? Pro tube power amp can have as low as .02% distortion at typical listening levels. What they do have is the typical midrange transpeancy that tubes in general are known for & that is where most of the music is & that is where up untill recently solid state has failed. Solid state now has approached tube sound pretty well in the mids but still can be improved apon at least in power amps.
 
Exception may be Halcros power amps which I have read are extremely good sounding as well as having specs that are out of this world as in distortion on thier top amp that at least at the time they were designed were unmeasurable , they were so low. However Halcro amps are not cheap amps, you have to be pretty rich to afford one
 
.http://www.halcro.com/productsDM88.php
 

 

[Willakan]

Quote:

Funny, While some of what you are saying is true tubes are still used in much of the pro gear & the pro gear does not have most of the sonic issues you talk of. No soft rolled off top, not soft rolled off bottom. Distortion can be well below audibilty. Distortion at max power on tube power amps may look ugly but we don't listen at max power, do we? Pro tube power amp can have as low as .02% distortion at typical listening levels. What they do have is the typical midrange transpeancy that tubes in general are known for & that is where most of the music is & that is where up untill recently solid state has failed. Solid state now has approached tube sound pretty well in the mids but still can be improved apon at least in power amps.
 
Exception may be Halcros power amps which I have read are extremely good sounding as well as having specs that are out of this world as in distortion on thier top amp that at least at the time they were designed were unmeasurable , they were so low. However Halcro amps are not cheap amps, you have to be pretty rich to afford one
 
.http://www.halcro.com/productsDM88.php
 

Please explain in what way tubes have a more transparent midrange than solid state amps. This reads like unsubstantiated myth propogation.