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有源 Ultimate Attenuator 介绍
首先我未用过,也不是卖这个的.
因为见识有限,以前见过的管箱衰减器都是无源的.所以对这种新东西会有兴趣.
http://www.ultimateattenuator.com/index.html
内有足够信息.我贴点其中有趣的在下面.
用一个不精确但通俗的归纳就是--输出给喇叭的信号 变少后经一个晶体管放大电路再送到喇叭. 而这晶体管放大电路得音量当然会很好调. 具体效果,各人自己看英文. 看来有优胜之处.
http://www.vintageamps.com/plexiboard/viewtopic.php?f=1&t=81179&sid=3f262b4a7596ef206bff914ae39546e3&start=45
Re: hot plate/powersoaks  by plexi on Wed Feb 11, 2009 6:56 am
I'verun many different, if not all the major brands of attenuators in mymany years of working with Vintage Amps. Of all those I've used, theygenerally have the same result. There is a flattening of brightness andan overall degradation of the sound quality. As transparent as thosebrands claim they are, I must be honest, there is no such thing as aperfectly transparent attenuator. There are a number of built inmethods as well to help tame amp volume levels. The first that come tomind are the brands using the Kevin O'Conner system, Power Scaling. My own amp line, Mojave has a system we developed called Power Dampening.This is a good way to go with a new amp but it does not help with avaluable investment grade vintage amp and I would never prescribe orendorse modifying a vintage quality amp with an internal modificationlike Power Scaling or Power Dampening or anything else for that matter.Its destructive and devalues the product. The best solution is to finda safe and palatable way of getting the volume and tone to a point youlike without ruining your amp. I do know that Mercury Magnetics doesnot want their OUTPUT TRANSFORMERS used with any attenuators. They havedone their own investigating and feel that running attenuation isdamaging to the transformers. I tend to agree with them since the truthis, the load is static and the transformer will not behave the samewith loads such as an 8 or 16 ohm resistor or even inductive loads. Thetruth is, they don't sound that good either. If your amp is set to 16ohms and your pumping 100 watts into a 16 ohm load attenuator, yourtheoretically matching your load to your amps Output Transformer. Thatis supposed to get you the correct frequency response and provide anatural effect. the truth is, that by the time you reduce the powerlevel to the point where your satisfied with the volume, your morelikely to be disappointed with the tone quality.
With respectto the Ultimate Attenuator there is a difference. The first palce thisdifference exists is the load resitor. The Ultimate Attnuator, alsoknown as the "UA" uses a 30ohm load resistor. I do not know exactly why that value was chosen, butI do know this. It's safer. A lot safer. Your amps power output is amathematical equation. If you match the load to the ohmage tap on thetransformer, say 8 ohms to the 8 ohm tap on the amp, your amp willprovide maximum power efficiency. That means it works hard and willpass the maximum current. That also means heat. Heat in the Powertransformer and the output transformer. That is because its passingloads of current. Dangerous for an old amplifier. This is not an idealscenario for a vintage Marshall. The older original transformers weresimply not designed for this kind of use or better yet "Abuse". Withthe Ultimate Attenuator, your amps current is reduced leaps and bounds.
For instance, if your amps set for a 8 ohm load, the UA is onlygoing to see a maximum of around 25 watts made by your 100 watt amp.That is because the load is approximately 4 times larger. The result isthe power amp is full throttle but the power output is low. That isgood. It saves not only your output transformer but your powertransformer. This is probably a good answer to the Mercury Magneticsconcern now that the amp is not actually making any where near its fullpower even though the power amp is full tilt. The power transfered fromthe amp to the laod simply cant be any higher then the equation allowsfor.
Now what about the tone. The load is so far mismatched, how can the sound be correct? The UA has a built in low impedancepower amplifier. The term low impedance means strong high frequencyresponse and with their well crafted internal audio coupling, they havemanaged to retain and preserve the sound quality while keeping the ampat a low volume. The reduction of actual power is safer and the audioquality is preserved and enhanced via the audio coupling circuitry aswell as the built in low impedance power amplifier, which does exactly what you need for low volume high frequency preservation.
Becauseof these two basic facts, the Ultimate Attenuator is definitely thesafest product you can use and it delivers that low volume sound withthe least impact which results in a very accurate quality of soundreproduction. For what its worth, this is just my opinion and myexplanation was provided here to try and help some of you understandthe way these things work.
Over the years, I have always toldmy customers that it was safer to use both a Hot Plate and a Variactogether. The reason was simple, you can knock down the volume with theattenuator but you need to lower the power that is fed to the amp whichresults in how much power is made by the amp to protect it fromcatastrophe. I also recommended that the customer not use his besttubes since a variac will lower the heater voltage and thus reduce thetemperature of the cathodes and that causes the preverbal Cathode Stripping, which simply put, ruins your tubes very quickly.
Ifyour using an attenuator at present, I strongly advice you incorporatea Varaic to dial back the power level the amp can make. Reducing thepower by 30 volts is enough to prevent catastrophe. The coretemperature of the transformers can get very high internally and thatwill melt insolation between wire and cause shorts. The attenuator thatis set way down for good volume control and even if it sounds good toyou will be absorbing full power. Full power means full throttle on thecurrent flowing through the transformers and full throttle on theinternal core temperatures, several hundred degrees F. That can damageyour amplifiers original transformers. Newer transformers like Mercuryhave developed improved insulation and with a quality improvement inover all design materials, they can withstand the increased coretemperature much better but it's still a risk not really worth takingif you can simply avoid it.
The UA offers a higher load to startwith and that makes it safer. You can mismatch a passive attenuator buyusing a 16 ohm Hot Plate or similar attenuator on your amplifiers 8 ohmoutput tap, thus reducing the power in half, but the mismatch and thefact that your using a passive system will further erode tone qualityif not dealt with some how. Again, the UA has adapted audio couplingand incorporates the low impedance power amp which resolves the toneissue.
I'm in no way claiming the UA is perfect but it does thebest job to my ears and technically speaking there is a safety factorwhich is worth considering especially if you want to keep those oldtransformers from blowing or over heating.
I was informed thatthere is a protection circuit to prevent a major issue if you plug upyour amp to the UA in reverse. That is to say you plug the output ofthe amplifier into the speaker output of the UA. That would result in aproblem if there were no protection for that. Thanks to Tone-Freak, Ihave made the correction to my previous comments that you could have aproblem with the UA because of its built in power amp. It's not anissue and that is very cool to know.
Sorry to admit it but I amguilty of this mistake. Thank God it was a passive Hot Plate. I didplug the amp into the speaker connection and the speaker into theamplifier input of the Hot Plate. There is no damage and no ill effect.The unit simply does not work as an attenuator. If you reverse thewires your back in business and all is well. one of the safer factorsof a passive system.
For the money and trouble of buying both apassive Attenuator and a Variac and the fact that you will have to lugaround an additional 13 pounds of iron using the variac and think aboutyour tubes dying off, It makes a lot of sense to stick with the UA. Theunit provides safety, good tone and you can use your best Mullard powertubes. The UA does have a 100 volt power outlet on the rear of the unitto allow you to run your amp 20 volts down for a good measure of safetyespecially if your using an old JMI that runs on 100VAC or 105 VAC.That goes for old Marshalls as well. We did many old Coffin logo, Blocklogo and Script logo Marshalls. They run exactly right at 240VAC but ifyou set them for US voltage, typically 105-115VAC on the back of theamps selector, they are over voltage at 120VAC. 100VAC is ideal for theolder amps and will keep those internal voltage low enough not to blowup your original capacitors. Just another good reason to have the UA.When you guys use your older Marshalls or Vox amps or any British ampthat was originally built for UK use, be sure to check this out or havesomeone check it out for you. You can see if your amps running hot buymeasuring the heater voltage on pins 4 and 9 of the pre amp tubes. Theideal voltage for the heaters is 6.3VAC. If your looking at 8 VAC,you've got a problem and your running the amp with a very high internalvoltage most likely. This is where a Varaic can help. It will lower thepower down until the amps running at 6.3 Volts AC on the heaters. Nowyou can see where your amps AC input needs to be. If it sits at 100VAC,then that is the input you can safely use. If the running voltage worksout to say 115 VAC input, your probably ok to just go ahead and run120VAC since the difference is not outrageous and your not jeopardizingthe amp. This is off topic but I mention it because the heaters reflectthe internal voltages. That is to say if the heaters are way high, thenyour going to most likely have very high internal voltages inside youramp and then your in danger of over voltage on the old capacitors andputting tremendous stress on older tubes and power output will increaseas well. Al these things are tied together. |
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发表于 2010-8-13 05:44:57
是不是等于串了一个晶体管功放,然后再改变音量?就像van halen在机头后面接一个HH晶体管功放再到箱体一样?利用晶体管功放不受音量影响来做到不损失声音?
您也起得挺早啊.按这个价格,其实就是一台功放了
