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My System
 Passive preamplifier |
Today, many signal sources such as CD players have sufficient output level to drive
most power amplifiers directly. It means that no additional amplification is required,
so for level purposes there is no need for a preamplifier. With a passive volume
control in between, the signal from the source may be fed directly to the power
amplifier. In many cases, a passive preamplifier sounds as good or better than the best active preamplifiers. In other cases, it is our experience that a good line stage following the volume control may sound more dynamic than a passive volume control. It seems to depend on many different circumstances, which solution is the better. For instance, the type and length of cable connected to the output of a passive volume control is critical.  stepped attenuator (24 steps with Vishay/Dale military grade resistors) An active preamplifier usually has high input impedance and low output impedance. This fact makes the choice of interconnect cables relatively uncritical. When the preamplifier is replaced by a passive volume control, the situation is different. The input impedance of a passive volume control is usually not as high as that of a power amplifier and the output impedance is usually high compared to a preamplifier's output impedance. If care is taken in dealing with this issue it is not a problem in most Hi-Fi systems. The most important matter is to take care of the impedance of the interconnect cables. The output impedance of the source (for instance a CD player) is usually relatively low. Therefore, the interconnect cables between the source and the passive volume control are not as critical as the interconnect cables between the passive volume control and the power amplifier. The key factor to look out for is the loading capacitance on the volume control's output. In order to maintain a large bandwidth, the loading capacitance should be as small as possible. Otherwise, the load capacitance combined with the volume control output resistance makes a low pass filter that cuts away treble in the audible frequency range. Calculate Stepped Attenuator 
 final stepped attenuator [ 10kOhms ] Source: Danish Audio ConnecT Click here to download PDF version (129KB) of this Passive Preamp Technical Paper from DACT Here you can buy a stepped attenuator for a goed price |
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 ELMA Rotary Switch Type 04 |
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Some important point:
Your sound system is only as good as the weakest link. Volume control is one of them. Passive PreAmplifier schematic |
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Calculate Stepped Attenuator
My Passive PreAmplifier The front panel is designed with the Front Panel Designer from Schaeffer AG You design your front panel and if you are finished, it is possible to check the price and to order this panel! You should try this application, it is free! |
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Transformer Attenuator |
 Benefit of Transformer Attenuator: The benefit of replacing plastic type volume control to stepped attenuator is obviously the accuracy of tracking and the quality of selector switch plus low noise resistors can reduce the signal loss to some degrees. However the regular stepped attenuator featuring resistor type fails to offer better impedance matching over plastic volume control. That's why at high attenuation level (low signal out, low listening level) the bandwidth of such volume control is very poor and the bandwidth is not constant over any switch position. Transformer offers much lower signal loss and much lower output impedance (10 times lower than regular stepped attenuator) thus it will process very wide frequency response at any attenuation setting.
Comming weeks i will change the Stepped (resistor) Attuneator in my Passive Pre-Amplifier with this new Transformer Attenuator...  This transformer can be used in replacement of any existing volume control device in pre-amp or integrated amp, but it can also be great used as stand alone Passive Pre-amplifier. Since it has very low output impedance, it can drive long cable better than regular Passive Pre-amplifier; moreover, its ability to make +6dB signal makes it very versatile in environment where source level is low or load input sensitivity is low.  You can get such a transformer at: The transformer i use is from SACThailand |
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| 240V Passive Mains Filter |
240V Passive Mains Filter Considering the quality of the mains voltage with dishwashers, vacuum cleanders, dimmers, computers and halogen lumination, it is a miracle that most HiFi equipment seems to be immune to most of the mains polution anyway. After investing so much money in your HiFi set you probably want to minimize your chances on humm, clicks, HF noise etc. that could spoil the fun after all.  move cursor over picture for larger version 
What is the purpose of filtering? A filter is a device that lets mains frequencies pass and blocks other before they enter the audio equipment. In case of a mains filter, it's task is to let the 50Hz 'signal' pass the filter and use it to power our equipment and at the same time block all other frequencies since these frequencies are not designed to be used by power supplies of hifi equipment. Don't forget to use a shielded mains cable and use high quality mains cable to connecting your equipment as well. Don't let mobile phones or other HF pollute your mains connections on the last meters. Schematic 240V mains filter Used Main Cable: ÖLFLEX CLASSIC 100 CY |
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