The Latest and Greatest Amp...

organ

Awesome looking int. I love the beefy looking stuff out there.

Maurice

dorokusai

There are multiple answers for the question due to many different amplifier designs being present in the world of audio. The specifications of gear vary due to design values and build.

You should know all this...you're a Guru

In regards to the amplifier mentioned in the thread its still a generic answer beings noone here knows exactly HOW they built it, just the general method of design and build.

I'm sure your fingers can do the walking into Amazon.com.

The answer is also on the internet for you to peruse, put forth some effort, I'm not your dog.

Read and ye shall be enlightened. - Book of Polk 20.12

F1nut

Originally posted by dorokusai
There are multiple answers for the question due to many different amplifier designs being present in the world of audio. The specifications of gear vary due to design values and build.

No kidding.

dorokusai

This is simply one answer in regards to damping factor, one of the issues between PM's and here....which is what started the inability to use fingers.

Damping Factors, Slew Rates and other Voodoo

Slew rate is another specification that exists for historic reasons, and is less significant as technology improves. To understand the significance of slew rate, consider the early transistor amplifiers when they appeared in the 1970’s. At that time transistor amplifiers could achieve frequency response beyond 20kHz at the top end, at reasonable power levels (100 watts or more) and with total distortion below 1%, but unfortunately not necessarily all at the same time. For example if you measured the frequency response of a 100 watt transistor amplifier in those days at 10 watts, you would easily see a full 20Hz to 20kHz range at low distortion levels. However, as you approached the 100 watt level you would see a huge loss of dynamic range and very high levels of distortion in the upper frequencies.

The Slew Rate of these designs caused distortion if there was too much high frequency content at high power. The voltage at the output could not change fast enough to go from full positive and back to full negative ( the top and the bottom of a sine wave) within the time required to produce 100 watts at 20kHz in early transistor design. For a 1200 watt amplifier at 4 ohms, the required slew rate to generate 20kHz full power without distortion would be 13 volts per microsecond. Current amplifier designs similar to our AP4040 easily boast a slew rate of over 25 volts per microsecond, much more than required to produce a full 20Hz to 20kHz frequency response with minimal distortion. This makes the slew rate specification less important a number in 2002 than it may have been in the decades past.

There is also a great deal of confusion surrounding another of those holdovers from early specification charts, the Damping Factor. What really counts is the damping factor of the entire loudspeaker system, the cabinets, the cabling AND the amplifier as a system. The loudspeaker designer will adjust many factors including damping factor to achieve the desired frequency response at the best possible efficiency. As a user, it is important to allow the loudspeaker to operate the way the designer intended.

There are three parameters that work as one: amplifier damping factor, cable resistance and voice coil resistance. To understand the effect of amplifier damping factor you consider the actual amplifier as a perfect amplifier with a resistance in series with the output. This resistance equals rated load impedance divided by the damping factor. This number is typically very small for a modern amplifier, typically 0.01 to 0.004 ohms. The speaker cable resistance is typically 0.16 to 0.8 ohms. The voice coil resistance is typically 3 ohms for a 4 ohm rated loudspeaker or 6 ohms for an 8 ohm loudspeaker.

To the loudspeaker, what counts is all of these added together. It is obvious that the voice coil resistance is by far the dominant effect, with the cable resistance having effect only if the wire is too thin and too long. The effect of the amplifier resistance is insignificant, an extra 0.006 ohms is nothing compared to the 4 ohms or so of a typical system. In short, as long as the damping factor is greater than about 20 on any amplifier, it is safe to consider it unimportant. In the case of most modern amplifiers, Damping Factors in the order of 400 to 600 are common.

dorokusai

And another damping factor discussion....while not amplifier specific, I think you get the idea.

Total search time: 1 second....they were bookmarked

Damping Factor... What is this?
The Damping Factor of an amplifier in general refers to the ratio of the amplifier's output load impedance (the speaker, nominally 8 ohms) to the output impedance of the amplifier. Ideally, the damping factor would be infinity (in other words, the ideal output impedance for an audio amplifier is zero ohms). Damping factor, like many amplifier specifications, is a function of many factors and is thus difficult to quantify with a single number. As such, "low end" manufacturers can have a "field day" with this spec, publishing fantastic numbers (however with no information as to how the measurement was made).

The damping factor if an amplifier depends greatly upon the speaker to which it is connected, the wire connecting the speaker to the amplifier, the signal frequency that the amplifier is sending to the speaker, and the power level at which the amplifier is operating, among other things. Damping factor is most critical at low frequencies, generally 100 Hz and below (i.e. frequencies that a woofer reproduces). At such frequencies, a high damping factor is desirable in order to maintain a "tight" sound. If an amplifier/speaker pair has a low damping factor, the bass response is likely to be "boomy", "uncontrolled", and "loose" sounding.

Specifying damping factor as a simple single number does not really tell the whole story. Damping factor is a ratio of two numbers, one of which (the speaker impedance) varies by a large amount depending upon frequency. This being the case, the damping factor will also vary considerably as a function of frequency. Most of the variation in damping factor is due to the characteristics of the speaker connected to the amplifier. The wire which connects the speaker to the amplifier has finite resistance which must be accounted for; basically it is lumped in with the impedance of the speaker. So, it is wise to use heavy speaker wire in order to minimize degradation of the damping factor.

As mentioned, the output impedance of an amplifier is ideally zero. In the real world, this is never the case. The next best thing would be a very low constant (non changing) impedance. Again, the real world does not allow this either. The output impedance of most amplifiers is relatively constant except for when they approach the last 10% or so of their voltage output. This is due to the nature of the waveform from which most power supplies obtain their energy (especially analog supplies) . What this means is that the output impedance of an amplifier tends to rise considerably as it approached its output limit. As the amplifier's output impedance increases, the damping factor must decrease proportionally. In my opinion, if manufacturers specified the output impedance of their amplifiers, there would be a lot less ambiguity among the numbers.

High damping factor numbers go hand-in-hand with amplifiers that can drive very low impedance loads (these are amplifiers with power supplies capable of delivering tremendous current). If you want to "artificially" degrade the damping factor of your system (to hear the effects), a simple test can be done. Listen to your system at a "healthy" volume (use a CD with lots of low, tight percussion type sounds); be sure to use a heavy gauge short length speaker wire. If you have a sound level meter, note the sound level you listened at. Then, connect your speaker up through a 100 foot (give or take) wire with much smaller gauge (use #20 or higher). Play the same music as before, but make sure the volume (to your ears, not the volume control!) is the same (this is where the sound level meter comes in handy). The volume control on the amp will have to be turned up a bit to overcome the power loss in the smaller wire. You should be able to tell that the sound has changed (for the worst, in most people's opinion).

Do not be terribly concerned with damping factor when choosing quality equipment. Most of the good amplifiers and speakers available today will yield excellent sound when used together. To avoid degrading the damping factor of your system, simply follow these (easy) steps:

Don't load up an amp with multiple pairs of low impedance speakers
Use heavy gauge speaker wire, ESPECIALLY in long runs
Never wire resistors in series with your speakers (you can't change a 4 ohm speaker to 8ohms by doing this!)
Use a heavy duty (i.e.12 gauge or heavier) extension cord when plugging your amp into the wall outlet.

RuSsMaN

Hey Henry, know what the DF is that gorgeous Marantz 8?

You can count it on both hands.

How's it sound? DF is so over-rated, it's almost become the new 'thd'.

Cheers,
Russ

dorokusai

A couple nuggets in regards to Maximum Current - Peak Amps....all these and more have control over that number. The number is simply not indicitive of the quality and performance of any gear as it depends again, on design.

You can also refer yourself to Ohm's law R = V / I .

Common Limiting Ratings
All active devices have certain parameters in common (although they will have different naming conventions depending on the device). Essentially these are ...

Maximum Voltage - The maximum voltage that may be applied between the main terminals of the device. This varies from perhaps as low as 25V (sometimes even less) for small signal transistors and FETS, and up to 1,200V or more for some valves and high voltage transistors. MOSFET voltages are typically up to about 600 to 800V for switching devices for use in power supplies.

Maximum Current - The maximum current that the device may pass safely. Ranges from a few mA up to many amps. This will never be while the device also has the maximum voltage across it, as this would result in power dissipation far in excess of ...

Maximum Power Dissipation - The maximum power that the device may dissipate (in mW or W), under any condition of voltage and current. (Called plate dissipation for valves).

Heater Voltage/Current - (Valves). The operating voltage and / or current for the filament (directly heated cathodes) or heater (for indirectly heated cathodes). This should always be within 10% of the quoted value, or cathode life will be severely shortened.

Maximum Junction Temperature - (Semiconductors) The maximum temperature that the semiconductor die will tolerate without failing. At this temperature, most semiconductors will be unable to perform any work, as this would raise the temperature above the maximum permissible.

Temperature Derating - (Semiconductors). Above a specified temperature, the allowable power rating of semiconductor devices must be reduced to remain below the maximum allowable junction temperature. The power is normally derated above 25 degrees C.

Thermal Resistance - (Semiconductors). The thermal resistance between junction and case (high power) or junction and air (low power). Measured in Degrees C/W, This allows a suitable heatsink to be determined.
This is by no means all of the ratings, there are many more, and vary from device to device. Some MOSFETs for example will have Peak Current ratings, which will be many times the continuous rating, but only for very limited time. Bipolar transistors have a Safe Operating Area (SOA) graph, which indicates that in some circumstances you must not operate the device anywhere near it's maximum power dissipation, or it will fail due to a phenomenon called second breakdown (described later).
With most semiconductors, in many cases it will not be possible to operate them at anywhere near the maximum power dissipation, because thermal resistance is such that the heat simply cannot be removed from the junction and into the heatsink fast enough. In these cases, it might be necessary to use multiple devices to achieve the performance that can (theoretically) be obtained from a single component. This is very common in audio amplifiers.

dorokusai

You should add this link to your folder....it's an nice quick reference. There are some others as well that have been posted in the forum at one time or another.

http://sound.westhost.com

Alot of what you find on the internet also has models and/or schematics to show you how things work at known values using design guidelines.....or formulae. In others words, a bunch of math that just confuses me personally, but I eventually get thru it using the "fly open" method.

The book explanation is better, but if you think I'm going to sit here and type all that, you're crazy. You should always invest in some desk reference materials if you want to be fully aware if not exactly educated. Meaning, I'm no engineer....I need books.

Specifications are far more important to the designer and builder than the end user, who in most cases is an average person. The only way that specifications can hold water or be proven is if you know far more information than the manufacturer has released....or more simply, by your ear...if it sounds good, it is good right?

pjdami

Wasn't the original question about the DK Design Class A operation and what appears to be a "small" peak current design on the amp?

I was just reading this article:

http://sound.westhost.com/class-a.htm

I do see some effin huge power supplies on that DK Design amp though. The reviews on the DK Design amp say that it doesn't too hot either..heat sinks and all.

As far as specs, the Plinius 9200 I briefly owned last year had it all in spades. After listening to it for 3 weeks I got bored of it. Just didn't do it for me and was too polite.

The DK Design amp is an amp to keep on the radar for a demo if I decide to consolidate a couple of smaller rigs for a single better one down the road.

I think I'll have a couple of beers after that one and relax / listen to some tunes.

F1nut

Originally posted by dorokusai
....or more simply, by your ear...if it sounds good, it is good right?

Right!

Good reads, thanks.

dorokusai

PJ - Yea, about peak current(amps) in this design as oppossed to another similar or different design. 18 vs say....60.

I posted the information in the wrong order. I added the damping factor information as a sidenote, just to show how the numbers are sometimes only part of the equation needed to know what the number actually means.

It's a great link for quick information.

michael_w

thanks for the info and link... very interesting and maybe I'll ask for some reading material for my upcoming birthday.

Tour2ma

Thanks, doro, but please, fewer italics next time. My head is listing badly to starboard...

Also read pj's link. All is now clear as mud. Must have missed the part explaining how Class A's get away with violating Ohm's law.

Originally posted by pjdami
The reviews on the DK Design amp say that it doesn't too hot either..heat sinks and all.

Surprised me how cool it ran. After an hour at moderately loud levels it was barely warm to the touch. Only over the tube line-up could any appreciable heat be felt rising from it... of course it was on arrays (~94 or 95 dB sensitivity). Not that the DK couldn't drive less efficient speakers.

Fred grabbed a pair of watt-meters and put them on his homebrew arrays and peaks were only racking up 20 to 30 wpc.

audiobliss

@_@




AWESOME looking amp.

I'll hafta read those articles y'all posted, sounds interesting. Thanks!