چند روزی پهنای باند سایتم تموم شده بود و منم به فکر افتادم پهنای باندش رو زیاد کنم.

این چند روزه هم خبری نداشتم فقط تنها اتفاق خیلی مهم اینه که هوا فوق العاده باحال شده ، این هوا خیلی عشقولانه شده و بقول شاعر خوش فرح بخش هواییست خدایا بفرست نازنینی که به رویش می گلگون نوشیم.

یک گزارش از محصولات جدید آقای رحمانی هم بزودی مینویسم و منتظرم تا یکی دو هفته دیگه مارتن برسه.

یک مقاله جالب از استو بخونید :

http://www.decware.com/newsite/paper110.htm

Higher power amplifiers, say anything over 100 watts solid state or 50 watts tube, will force the magic point on the volume control higher before there is a nice bloom.

When the sound quality isn’t there at higher volumes with a big amp the extra power is worthless.

So how does one get dynamics out of a small 5 watt amplifier?  Start by loosing the assumption that it is somehow handicapped in that area.  Pair it with an efficient pair of speakers so you can play it loud if you want.  Dynamics are greater on low power tube amps matched with high efficiency speakers than you’ll be able to get from a high power amp on low efficiency speakers – aka the hi-fi industry.  In a quiet room with a low power amp and speakers of 94dB or higher efficiency you can expect around 30 dB of dynamic range in the first watt. (NOTE: It takes a doubling of power to increase the volume by 3dB). When you add a second watt of power you increase the dynamic range by only 3 more dB.  If you double the power again to 4 watts you’ll gain another 3dB and 8 watts gets you 3 more.  By the time you keep doubling your power to get that additional 30db you require 1024 watts.  So obviously power has a steep ramp of diminishing returns. a 100 watt amp is only 3dB more power than a 50 watt amp, almost un-noticeable.

This has been my tag line in the forums for many years.  But consider the fact that many big audiophile loudspeakers with multiple drivers and complex crossovers have not the ability to resolve the first watt at a usable volume level.  This is because a portion of the first watt is lost in the crossover network before it ever reaches the drivers and because the drivers have too much moving mass to be heard with what’s left. So for the mainstream hi-fi industry it all starts with the second watt – meaning that first 30 dB of dynamic range (music) is largely missing.  It’s not surprising many audiophiles build large high power systems up to 1000 watts trying to reach a dynamic range of 30 dB while at the same time some guy is sitting in his listening room getting more than 30dB out of a 2 watt amplifier with the appropriate speakers.

If you have music playing at 60dB above the noise floor in your room you’re probably at an SPL of around 100dB. (40dB noise floor + 60dB music)  In that 60 dB of dynamic range, the first 30 dB or so is all the ambience, detail, and micro detail in the music.

Since the tendency in this hobby is to put things in categories let me take this opportunity to mention that not all low power amps have a high percentage of usable power.  Some have nearly 100% usable power, while others may have less than 50%. The determining factor is the design of the amplifier itself.  This is very obvious when you start to evaluate different offerings from different designers.  The good designs will always have higher ratios of usable power to total power than the bad ones.  There are less good designs than bad ones in this hobby right now, more than ever in fact as everyone including China has been jumping on the “hey let’s make a tube amp” bandwagon.  Neverthess when you look at several different amplifiers and their rated power you will never see a spec or any disscussion about USABLE POWER so assuming you only tollerate the best sound and never rotate the knob past the usable power limit, you really have no idea how much power each amplifier really has.

Since usable power is largely enhanced with class A operation you want to watch out for amps boasting high power figures because they go into class AB operation quickly to get the efficiency up.  Take the following example:  A Zen amp uses a 150ma transformer that makes around 400Volts DC after rectification.  It has two small output tubes each biased at 47ma and makes about 2 watts per channel or about 6 watts in mono.  By employing techniques to increase efficiency, such as fixed bias, push pull, ultralinear transformers and bigger tubes I can get the same power transformer to work in a 50 watt KT88 based amplifier. In fact I can push it to 60 watts if I want to.

I have seen designs that take a pair of output tubes to nearly 80 watts that had less than 1 watt of usable power.  Nevertheless they would have 80 watts RMS with low distortion – look pretty good on paper, sound like crap.

There is just no reason to build amps beyond 50 watts if your intent is to serve the music.  If your intension is to make money by building amps that will play today’s low efficiency hi-fi speakers then consider 50 watts about the lower limit of the power range you should be targeting for a successful business.