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Department of Dispelling Stupid Ass Amplifier Myths

TitaniumTroy said:
SH, what about tube amps vs transistor amps for planer magnetic speakers? Over at the Planer Asylum, somebody is always making the claim that their 80watt @8ohm tube amp can blow away some 200watt @8ohm transistor amp. This would be powering a speaker that has a sensitivity of say 85db and runs around 4ohms or lower and powering a large planer speaker like my Magnepan 3.6's.

One side says the transistor wins, via it's higher power and higher damping factor. The other says the softer clipping of a tubes and the "higher quality" (whatever that means) of their watts make them the better choice.

While tube amps generally clip more gracefully than transistor amps do, this behavior is very dependent on the type of tube amp. An ultralinear or other similar type of tube amp will eventually clip almost as hard as a transistor amp, whereas a class A single ended triode tube amp will never really go into hard clipping no matter how hard its driven (part of this is because of the fact that ultralinear amps using tetrodes or pentodes use global negative feedback - usually about 20dB - whereas a triode amp generally will have zero negative feedback).

The "80 tube watts verses 200 transistor watts" analogy is not far fetched; we're only talking roughly 4 dB difference in loudness, which is a relatively small difference to the ear. Its not unreasonable for the tube amp to take that extra 4 dB of output until its clipping is as hard as the 200 watt transistor amp.

All that being said, if I had a 4 ohm speaker with a sensitivity of 85 dB (planar or regular dynamic), I would probably buy a good transistor amp to drive it. Tube amps start to be at a disadvantage as the impedance starts to dip to 4 ohms, and are at more of a disadvantage if the load is complex. This is because the output transformer, because it is composed of coils of wire, will have a resistance which imposes a hard limit on the ultimate damping factor. A good ultralinear tube amp can achieve a damping factor of around 20, where a transistor amp can have a damping factor in excess of 100 (damping factor is the ratio of amplifier source impedance to the speaker's impedance). It has been demonstrated however that the ear cannot detect any difference once an amplifier's damping factor reaches approximately 20.

In the end, we're talking about a system of components which must be matched to each other in order for each component to perform at its best. Tubes are at their best with higher efficiency speakers with moderate impedances, and are at their absolute best with good horn speakers utilizing active crossovers (which eliminates the complex load of a passive crossover network).

I would still urge you to see if you can demo a good tube amp with your planar speakers, if for no other reason to satisfy your curiosity. While I can type away all day about the theoretical strengths and weakness of each type of amplifier with different loads, the ear is the ultimate judge, and you might find either that you like tube amplification better with your speakers, or are happier with transistors. That's part of what makes the audio hobby fun (or frustrating .....) :angry-banghead:
 
Hey Troy...

I’ve also followed those interesting discussions over there – the 80 watt tube amp claim doesn’t sound too farfetched to me simply because he listens at normal levels – my personal experiences with Maggie’s 1.6’s mated to a lowly Jolida 40 watt tube integrated amp have always been positive – the dissimilarity between the Jolida and my two Crown K1 amps is in the bass where the Crowns reproduce tighter bass - the Jolida seems to slow down the overall presentation (not a bad thing) making musical passages easier to comprehend – this is something I never see discussed over there – perhaps it’s me - another tube observation is in the reproduction of strings/brass they’re so much easier on the ear with certain recordings – my listening habits rarely exceed 85db peaks - for reasons stated I like both – pending on mood or music.

Troy ... we also have another member at the Asylum I’m sure you know - who seems quite knowledgeable on panel speaker and swears by the KR Audio brand – his two main recommendations are KR VA 350I @30 watts and Kronzilla SXI @ 50 watts – when pushing Accustats or other panel speaker.
SH ... can you talk a little about the KR Audio brand and how they might differ in their approach in tube amps - perhaps they're justified in been hailed as 'best tube amps ever made' – they are certainly pricey.
 

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Vinyl said:
SH ... can you talk a little about the KR Audio brand and how they might differ in their approach in tube amps - perhaps they're justified in been hailed as 'best tube amps ever made' – they are certainly pricey.

I could talk about them, but I wouldn't know what I was talking about as I'm not familiar with that brand.
 
Those are transmitter tubes, which is one popular way to build a SET amplifier, but it offers no particular sonic benefit other than more power.

The first picture looks like a screaming phallic symbol........... :scared-eek:
 
Agreed!
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:text-bump:
soundhound said:
3) Apparent gain in volume: BULLSHIT, BULLSHIT, B U L L S H I T ! ! ! ! ! Basically all home theater amplifiers have a standardized gain of 28dB, which is the same gain specified in THX specs. The differential (XLR) and single ended (RCA) inputs have buffering which reduces the voltage of the differential input by 6dB, which makes the net gain of the amplifier the same, whether the differential or single ended inputs are used.
I've read this (quote below) online more than once so I'm wondering, are these people misinformed?
"about the unbalanced *** is that it doesn't have enough output voltage to drive a professional amp to full output"
 
soundhound said:
5) Lower Distortion: Yep, that's true...but be careful what you wish for. When talking about distortion, the percentage of distortion is not nearly as important as the spectra of the distortion. Even order harmonic distortion is both easily accepted by the ear (it's simple octaves of the original frequency), and its presence tends to mask the presence of the odd order harmonic distortion components. Odd order harmonic distortion is of a much more complex relationship to the fundamental frequency, and as a consequence is more grating to the ear. Differential amplifiers get their "lower" distortion spec by eliminating the even order harmonic distortion components and leaving the odd order ones laid bare.
Another question. Amount of distortion can be controlled by the amount of NFB (negative feed back) used? If so, does this mean some amp touting its low distortion may have drawn out harmonics up to 9th even though they are low? I would think that would not be helpful in the sound characteristics. :confusion-scratchheadblue:
 
Negative feed back lowers the loop gain of the amplifier, lowers output impedance, and reduces nonlinearities (distortion). The even order harmonic distortion components are cancelled by the summing action of the differential output signal into the load.
 
soundhound said:
Balanced amplifiers. Beamed down from the heavens as the answer to everyone's amplification nirvana. The touted features of these wonderful machines are, according to ATI:

1) Lower Noise
2) Double the slew rate
3) Apparent gain in volume
4) Immunity to stray fields
5) Lower Distortion
6) Reduction in all types of amplitude distortion
7) Immunity to hum
8) Better transparent performance

Here, I intend to rip these "features" a new asshole.

First, some important background. Whatever you might hear from manufacturers, and whatever your mommy told you, "balanced" amplifiers (really, the correct term is differential, and I will use that from now on) were created mainly to reduce the heat generated by multichannel amplifiers which have as many as 7 channels stuffed into a single chassis. Without differential design, the multichannel amplifiers we have today would not be possible because they would generate far too much heat. As a consequence, they would need so much expensive heatsinking and/or fans as to render them either far too expensive for consumers, or too noisy from the fans.

Differential amplifiers pull off this heat reducing trick by reducing the + and - rail voltages by as much as a half. Where a traditional 200 watt class A/B amplifier might have rail voltages of +/- 80VDC, a differential class A/B amplifier would typically have rail voltages of +/- 40-50 VDC. By having lower rail voltages, there is less voltage potential across the output transistors, and as a consequence, less power dissipated by the output transistors in the form of heat (remember - class A/B amplifiers are at best 60% efficient).

A 200 watt differential amplifier is really nothing more than two 50 watt amplifiers in bridge mode. Yes, that's right...nothing more than that. If you have any old stereo 50 watt amplifier which could be put into bridge mode, then you would have exactly the same thing as a "balanced" amplifier.

Let's do some math. A 50 watt amplifier puts out 20 volts into an 8 ohm load. If you take two of those 50 watt amplifiers, invert the polarity of one of them and connect the 8 ohm load across the "hot" terminals of the two amplifiers, then you would see a total of 40 volts across the 8 ohm load. Using Ohm's law, E (voltage) squared divided by 8 (ohms), equals....viola....200 watts!

That is how a differential amplifier works. The only other requirement is that each channel, and the power supply, must be robust enough to support that 200 watts output. So in practice each channel of a differential amplifier has more output transistors than would be required for a "normal" 50 watt amplifier, and the power supply is capable of more amperage.

Differential amplifiers usually have "balanced" (that's really differential) XLR inputs. When you are inputting a signal which is already differential (one phase normal, and one inverted), those two polarities are sent directly to the two halves of the amplifier. When you input a single ended signal into a differential amplifier, the signal goes directly to the "+" side of the amplifier, and also, via an inversion stage, to the "-" half.

Now for the alleged "benefits" (which are really bullshit marketing to make something which doesn't sound all that sexy (heat control) into whiz-bang "features"):

1) Lower Noise: A differential amplifier behaves basically in the same way as any differential circuit - it has common mode rejection. If the cables going to your power amplifier are picking up hum and noise, then that will be largely canceled. Unless the cables to the power amplifier are really long, are routed near large motors, or are in an area where EMI/RFI are prevalent, then there is no reason to buy a differential amplifier for this feature.

2) Double the slew rate: This one is true. However it should be noted that every competent "regular" power amplifier has more than enough slew rate to reproduce the highest audio frequencies. If an amplifier has a specification that it can output 200 watts all the way out to 20kHz, then it has enough slew rate to do the job. Having "more" slew rate is not buying you anything.

3) Apparent gain in volume: BULLSHIT, BULLSHIT, B U L L S H I T ! ! ! ! ! Basically all home theater amplifiers have a standardized gain of 28dB, which is the same gain specified in THX specs. The differential (XLR) and single ended (RCA) inputs have buffering which reduces the voltage of the differential input by 6dB, which makes the net gain of the amplifier the same, whether the differential or single ended inputs are used.

4) Immunity to stray fields: Nope, bullshit. This is because differential circuits rely on the fact that the "+" and "-" polarities of the signal are intimately placed next to each other - i.e. in a cable, the two wires are twisted tightly together. This assures that any interference which impinges on the cable equally effects both wires (both polarities). The input of a differential circuit sums the signal on the two wires together. That which is different between the two wires is passed (i.e. the audio), and anything which is common and equal on both wires is canceled (i.e. the noise). The relatively widely spaced physical layout of the circuitry inside a power amplifier makes it impossible for any real cancellation at any frequencies which would be useful.

5) Lower Distortion: Yep, that's true...but be careful what you wish for. When talking about distortion, the percentage of distortion is not nearly as important as the spectra of the distortion. Even order harmonic distortion is both easily accepted by the ear (it's simple octaves of the original frequency), and its presence tends to mask the presence of the odd order harmonic distortion components. Odd order harmonic distortion is of a much more complex relationship to the fundamental frequency, and as a consequence is more grating to the ear. Differential amplifiers get their "lower" distortion spec by eliminating the even order harmonic distortion components and leaving the odd order ones laid bare.

6) Reduction in all types of amplitude distortion: To be honest, I don't know what the fuck they're talking about here. Amplitude "distortion" is non-flat frequency response, and differential amplifiers are no better than regular ones in this respect. This is an example of what happens when marketing people take too many drugs...

7) Immunity to hum: Bullshit for the same reason as #4 above.

8) Better transparent performance: Bullshit. Transient response is directly dependent on bandwidth, and differential amplifiers don't have bandwidths any better than conventional ones. A "transient" wavefront is nothing more than a fundamental frequency with many harmonics riding on top of it - just like a square wave, the most "transient" signal of them all is nothing more than a fundamental with every harmonic component present at equal amplitude, theoretically up to infinity. If the bandwidth of an amplifier is sufficient to reproduce all the frequencies up to and slightly beyond the audio spectrum, then it has good enough "transient performance" to reproduce the steepest waveform the human ear can hear.

Wow...I feel much better now.... :p



I have read most everything on this link and discovered that I am way over my head in this discussion. Please KISS just for me. From what I was able to glean from everything that has been written; if you have a good amp that provides you with the power to comfortably drive your speakers without interference than you will not necessarily improve your sound by switching amps. Right?

I have AT1505 that does a very good job. However, I have been tinkering with the idea of getting a new inexpensive amp but if I am reading what you are writing correctly unless I was willing to put out several $$$$ then I should stay with what I have.

In other words a good amp doesn't get out dated??
 
Snake Doctor,

I don't think Soundhound has been around much lately, but I think I can give you a near adequate response.

You will have to spend several times as much $$$ to get an amp that you would possibly notice an improvement over your ATI 1505, and I don't just say that because I have one.

You said you have been tinkering with the idea of getting an inexpensive amp, why? What is your 1505 not doing?
 
Snake Doctor said:
From what I was able to glean from everything that has been written; if you have a good amp that provides you with the power to comfortably drive your speakers without interference than you will not necessarily improve your sound by switching amps. Right?
Right.



Snake Doctor said:
I have AT1505 that does a very good job. However, I have been tinkering with the idea of getting a new inexpensive amp but if I am reading what you are writing correctly unless I was willing to put out several $$$$ then I should stay with what I have.
That's correct.



Snake Doctor said:
In other words a good amp doesn't get out dated??
Nope.
 
Nothing is wrong with my amp - I had been reading a lot of reviews and got it into my head that at some point I should get a new amp and would have to get more of an entry level which worried me. However, I could never understand how that would help my system. Then I read soundhounds great explainations along with the questions and comments of the group here and decided I was crazy and could save my pennies for something that would actually improve my system. But, being the kind of guy that likes to make doubly sure I decided to ask the question in plain english so that even I could understand the answer.

The other thing was I wanted to be able to turn the amp on and off with the pre/pro. I knew a newer amp would provide the connection and make the system more wife friendly.

Thanks to everyone for the clear response - I am keeping my AT1505 and continue to enjoy it. That is one sweet amp!!!
 
Snake Doctor said:
The other thing was I wanted to be able to turn the amp on and off with the pre/pro. I knew a newer amp would provide the connection and make the system more wife friendly.
Check out the woodworking tool websites, somebody makes a small box that senses current going thru it, and then turns on an onboard outlet. Its designed to turn on a shop vacuum when you, say, turn on your tablesaw, but it might work in your case too. Just make sure you can return it, as it may not have a required "pop" filter built-in.
 
Snake Doctor said:
Nothing is wrong with my amp - I had been reading a lot of reviews and got it into my head that at some point I should get a new amp and would have to get more of an entry level which worried me. However, I could never understand how that would help my system. Then I read soundhounds great explainations along with the questions and comments of the group here and decided I was crazy and could save my pennies for something that would actually improve my system. But, being the kind of guy that likes to make doubly sure I decided to ask the question in plain english so that even I could understand the answer.

The other thing was I wanted to be able to turn the amp on and off with the pre/pro. I knew a newer amp would provide the connection and make the system more wife friendly.

Thanks to everyone for the clear response - I am keeping my AT1505 and continue to enjoy it. That is one sweet amp!!!

There is no such thing as "stupid questions" around here. Just stupid people who don't ask questions!

I remember asking why the Volume readout on my Pioneer Elite gets smaller as it is turned up? In other words, the numbers go down as the volume goes up. :confusion-scratchheadyellow:

Also, I just leave my amp on. It's been on for about 6 or 7 years now. Not a problem!


Dennie
 
My amps are within couple feet from my pre and disc player. Reaching over to turn them on and off is not an issue for me so I don't need those extra devices. ;)
 
My Outlaw setup has a "trigger" switch on the pre-pro that turns on the amp when the pre-pro is turned on.
 
My Onkyo AVR only has a trigger for Zone 2, not Zone 1, so I get to turn the Amps on and off manually, however it really is not an inconvience.
 
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