AFD100 Attenuation

[joec63]

Pic of the manual regarding the built in attenuation...coolest feature to me.

[surfnorthwest]

Yes this is a great feature to start making its way into production amps. You will hear it be called many things such as "power scaling". While it is attenuation it works differently and sounds much better then traditional attenuators which I hate.

I recently purchased a little 40 watt Fender HotRod modified for me by Granger amplification and as part of the mods they installed the power scaling into it. Amazing. While it does not work on the clean channel it is wonderful on the crunch channel.

[Wildone]

That is very cool, if it works as they say. I would love to have this option in my 1959HW but I will not sacrifice its great sound.

[Slashwannabe1]

That is very cool, if it works as they say. I would love to have this option in my 1959HW but I will not sacrifice its great sound.

The only thing you'll sacrifice is what happens to the speaker at high volume...mainly the air it pushes and the speaker distortion from the output won't be like at high volume because when the wattage is down its not being pushed like at high volume. Other than that the tone stays intact from the amp from 0.1 to 100 watts! It is the best attenuation there is.

You can get these power scaling systems for almost any tube amp I believe now. I'm thinking about it for my VM even though the VM has great volume managment the way it is, it would still be great in the future.

[KevinOConnor]

Hi Guys

The myth about speaker breakup is a hard one to overcome because almost no one ever experiences it.

Loud sounds cause your hearing to protect itself and aurally compress the incoming sound (to your inner ear). What you _think_ you are hearing is an illusionary sound - not the real thing at all. You "hear" a round and compressed sound that is smoother than the true pressure wave because you are subjecting yourself to a sound level that human hearing was not designed to sustain for much time.

In nature, the loudest sound we might here is a thunder clap, or a waterfall. The first is transient; the second does not usually surprise us. Amplified sounds go way beyond the human range of tolerance, and speaker breakup as most people refer to it happens in that beyond-human-scale loudness range. You simply do not hear it as you think you do.

What most players misinterpret to be speaker breakup is their amp creating a squarewave output. The woofers we use to play through cannot reproduce the higher harmonics and the sound is pretty harsh and fizzy if you stand far enough away to hear the full tone.

There are cone breakup modes that happen on a frequency-basis rather than an SPL-basis. These occur because the entire cone simply cannot vibrate at treble frequencies, so the out portion "decouples from" or "breaks away from" he inner part of the cone. The inner portion is stiffer and can move faster being next to the voice coil. Interferometer movies of this look like the cone is a fluttering wavy leaf in the wind. These breakup modes people do hear.

Pushing a driver to its limits or next to its limits is not a good way to attain a consistent sound. You will certainly be keeping the driver manufacturers in business if you try.

So, speaker breakup is not an issue to be concerned with when considering tone maintenance from loud to quiet. Power Scaling maintains the transfer curve of the output stage, which is the only relevant parameter when trying to maintain tonal integrity. This maintains speaker damping among other things of interest to tech-minded players. The 2/3 Power Scaling approach used in the Slash model offers a bit of tube life extension, but not the full life extension possible using the full Power Scaling method. A demonstration of this is found in SSH and TUT4. Tonally, Power Scaling is achieved both ways.

Have fun
Kevin O'Connor

[surfnorthwest]

Great take Kevin, you explained it very well.

[thunderkyss]

Reducing voltages?

This is more like Van Halens Variac idea, nothing like traditional attenuation at all.

[HF1600ie]

Isnt this something that Van hallen did to the output transformer where a resistor is applied, and If that resistor is too small or too high it can burn ?

This what this guy calls it : the Cerrem Mod :

http://www.twistyneck.net/cm.html

Imagine that that resistor is variable. Maybe this is what power scaling is ?

[kissfanps]

Reducing voltages?

This is more like Van Halens Variac idea, nothing like traditional attenuation at all.

Doesn't a variac adjust the mains voltage?

[KevinOConnor]

Hi Guys

"Eddy used a variac to reduce voltage."

"Eddy used a variac to increase voltage."

"Eddy had a heavily-modified amp."

"Eddy used a stock amp."

"Eddy pulled one power tube (of four)."

"Eddy Plays a tube."

All the Eddy runours were perpetuated by a typical low-self-esteem guitar player who wanted to throw others off his trail. he played with his back to the audience before everyone realised how he did eight-finger tapping, then there was no point.

Eddy told a reporter who inquired about his sound, "I thought it was a little brown." He thought it was crap. Now everyone wants 'brown' sound.

Apart from the pointlessness of following rumours, the fact is that a variac has limited application in live use of a guitar amp. It reduces output power at the expense of tube life - nonintuitive but true. Heater voltages reduce along with everything else, causing the cathodes not to be heated to the correct operating temperature, which causes cathode "poisioning" reducing the life of the cathode.

You can learn about this, about Power Scaling, about variacs, about the use of light-bulbs as attenuators, and many other things, from TUT4 (The Ultimate Tone vol.4). The attenuation method used in the AFD is presented there as well.

Have fun
Kevin O'Connor

[Slashwannabe1]

Hi Guys

The myth about speaker breakup is a hard one to overcome because almost no one ever experiences it.

Loud sounds cause your hearing to protect itself and aurally compress the incoming sound (to your inner ear). What you _think_ you are hearing is an illusionary sound - not the real thing at all. You "hear" a round and compressed sound that is smoother than the true pressure wave because you are subjecting yourself to a sound level that human hearing was not designed to sustain for much time.

Now you are probably right on most of what you said, BUT!...

In recording, what do we record & hear the amp with in the studio? a microphone & monitor system! That takes out the middle man (our ears in the speaker distortion argument) and thus in the comfort of the control room we can experience Speaker Distortion & Break up without our ears playing tricks on us.

With a live human doing the listening Live to an amp we may never hear all those nuances of "speaker distortion" that we can in a recorded or monitored realm, now if you use a low wattage speaker you'll definitely hear it distort and it doesn't have to be bone crushing loud.

Yours was a very technical post and right about a lot of things but there is the other factor that was not mentioned....our way of hearing it electronically, like EVPs (Electronic voice phenomenon) in Ghost Hunting can be heard on recorder playback as can speaker distortion.

[Mats A]

Hi Guys

"Eddy used a variac to reduce voltage."

"Eddy used a variac to increase voltage."

"Eddy had a heavily-modified amp."

"Eddy used a stock amp."

"Eddy pulled one power tube (of four)."

"Eddy Plays a tube."

All the Eddy runours were perpetuated by a typical low-self-esteem guitar player who wanted to throw others off his trail. he played with his back to the audience before everyone realised how he did eight-finger tapping, then there was no point.

Eddy told a reporter who inquired about his sound, "I thought it was a little brown." He thought it was crap. Now everyone wants 'brown' sound.

Apart from the pointlessness of following rumours, the fact is that a variac has limited application in live use of a guitar amp. It reduces output power at the expense of tube life - nonintuitive but true. Heater voltages reduce along with everything else, causing the cathodes not to be heated to the correct operating temperature, which causes cathode "poisioning" reducing the life of the cathode.

You can learn about this, about Power Scaling, about variacs, about the use of light-bulbs as attenuators, and many other things, from TUT4 (The Ultimate Tone vol.4). The attenuation method used in the AFD is presented there as well.

Have fun
Kevin O'Connor

Where can i obtain this TUT4?

-- Sat Jan 15, 2011 5:24 pm --

Hi Guys

"Eddy used a variac to reduce voltage."

"Eddy used a variac to increase voltage."

"Eddy had a heavily-modified amp."

"Eddy used a stock amp."

"Eddy pulled one power tube (of four)."

"Eddy Plays a tube."

All the Eddy runours were perpetuated by a typical low-self-esteem guitar player who wanted to throw others off his trail. he played with his back to the audience before everyone realised how he did eight-finger tapping, then there was no point.

Eddy told a reporter who inquired about his sound, "I thought it was a little brown." He thought it was crap. Now everyone wants 'brown' sound.

Apart from the pointlessness of following rumours, the fact is that a variac has limited application in live use of a guitar amp. It reduces output power at the expense of tube life - nonintuitive but true. Heater voltages reduce along with everything else, causing the cathodes not to be heated to the correct operating temperature, which causes cathode "poisioning" reducing the life of the cathode.

You can learn about this, about Power Scaling, about variacs, about the use of light-bulbs as attenuators, and many other things, from TUT4 (The Ultimate Tone vol.4). The attenuation method used in the AFD is presented there as well.

Have fun
Kevin O'Connor

Where can i obtain this TUT4?

[fortress]

maybe try google

[toxx]

Just search for Kevin O' Connor on google, he basically invented Power Scaling (or didn't you?).

Kevin, I own TUT and TUT3 and I'm really happy with it, but as Slashwannabe1 wrote - you write with a very technical approach (also in the TUT's), and sometimes I'm not really shure wether you maybe forget to take the guitar player as a human beeing who perceives things not only on a (deficient) physical but on a psychological level...

Well, and one thing (maybe even not only psychological) seems to be speaker distortion. So my question is, too: Why then can we hear it on a recording? It can't be the microphone compressing, can it?

[KevinOConnor]

Hi Guys

The player _is_ considered in everything I've written. Ultimately, it is a player who uses the amp, whether he buys the amp, commissions it, or builds it himself. Our books are necessarily written for hobbyists and builders with enough skill to be safe around tube voltages, so some minimum of electronics knowledge is assumed - especially for TUTs 1,2,4&6.

Speaker break-up is something that is very tenuous to have as a factor of your sound. The speaker is after-all _breaking up_. That means it is in the process of destroying itself. If this sonic characteristic is critical to your sound then you will be going through a lot of speakers.

When the microphone is placed near a speaker, it is capturing the sound at that position with respect to the speaker. If the amp is clipped, then the speaker is trying to reproduce a square-wave as described above. It cannot do this and so distorts the signal modifying the resulting sound. The bulk of the sonic signature is still just that of a clipped amplifier but without full treble reproduction - the fact of using a woofer for guitar. If you wanted to hear the clipped signal more accurately, you would connect a full-range speaker to the amp.

Microphones cannot capture the sound of a square-wave either, even if you have the best condenser mic. High-SPL sound fields will cause the mic to distort, especially if it is the typical dynamic types, such as SM-57 or SM-58. These have no real treble response to speak of, and are chosen because they colour the sound. But... assuming you have the best condenser mic around, and it is away from the speaker where the SPL is lower, the bulk of the sound is still that of the clipped amp.

If someone wants to truly hear "speaker break-up", they should get a powerful clean amplifier and connect a low-wattage speaker. Bring the volume up slowly. Monitor the sound from far away so that aural compression does not alter what you hear. A microphone can be placed away from the speaker, to make a recording for later assessment. You will hear a garbled sound until the speaker dies, then it will be quiet.

Only because you asked, you can find our books at our online store www.londonpower.com

Have fun
Kevin O'Connor