Resource to calculate, building and measuring Hi Fi Loudspeakers and more...

Wednesday, 14 November 2018
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  My System

"The sole objective of the audio industry as a whole is to sell products..."

Projects which are planned, in progressor finished   Free distortion and performance analysis software that i'm using for my measurements

 Active Components

 Passive Components

Tube Line Pre-Amplifier I Tube Line Pre-Amplifier II Tube Buffer-Amplifier Tube Phono Pre-Amp   MM-Phono Pre-Amp Accuphase Dynavox VR 70-E Passive Pre-Amplifier Transformer Attenuator Passive Mains Filter



Rega P2 RB300 Tonearm Denon DL 160 Metz DE81 Cartridge Specs. Tonearm/Cartridge Capability StepUp Transformers TML Basspipe   in-akustik Reference LS-602 Loudspeaker Cable   Bowers & Wilkins CDM 1   Syntar 200 T Jordan Horn Speaker Interconnect M550i 4PR Loudspeaker Cable

 Passive Components

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 parts
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 (10k)
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

Source switch
ELMA Rotary Switch Type 04

Some important point:
  • Use as short interconnect cables as possible
  • Use cables with low capacitance
  • Use low attenuator resistance values (recommended total resistance: 10kOhms)

Your sound system is only as good as the weakest link.
Volume control is one of them.

Passive PreAmplifier schematic

Passive Pre Amplifier    Circuit

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!

Contact cleaning
In rare cases a DACT switch (attenuator or input selector) may start making noises in the speakers when operated. The necessity of cleaning will depend on the environment in which the switch is used (air pollution, humidity, temperature, dust).
The phenomenon has to do with particles being attracted and attached to areas on the gold plated contacts on the PCB, rivets or sliding contact.
It shows up as noises in the speakers when the switch is operated. It often only occurs at a single or a few of the switch positions.
Unless any unusual noises are heard there is absolutely no reason for carrying out the contact cleaning procedure - we recommend never to make any cleaning unless clearly necessary!
DACT only warrants one cleaning agent for this purpose: Tuner 600 manufactured by Kontakt Chemie (CRC Industries Europe NV), Belgium. Tuner 600 is a quick-drying solvent cleaner, leaves no residue and is neutral on materials. It does not contain aromatic and chlorinated hydrocarbons.

The product is commonly available from main electronics distributors.

Examples of such are:
RS Components (
VFarnell (
Conrad (

In case of any sourcing problems we recommend visiting the manufacturers web site at

Source: Danish Audio ConnecT

Transformer Attenuator

Price for this Supermalloy Transformer Attenuator STA-522: about $340 USD / pair

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.

Step dB attenuation Step dB attenuation
1 -48 12 -22
2 -44 13 -20
3 -40 14 -18
4 -38 15 -16
5 -36 16 -14
6 -34 17 -12
7 -32 18 -10
8 -30 19 -8
9 -28 20 -6
10 -26 21 -3
11 -24 22 0

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

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.

    Power Filter
move cursor over picture for larger version

Main Power Filter

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