My Passive Controllers

LAST UPDATE 15th September 2007 New T Passive added

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TOM HEMSLEY HOLCO/RODERSTEIN L PAD

VISHAY DALE LADDER

New T Passive (Magnetic Passive Preamp)

Matched to my current power amplifiers this new passive is easily the finest of the four I own.

It uses two multi tapped transformers wound by Earle Weston.

Its has 23 steps although I am using 22 this frees up step 1 ( most attenuated) to link simply to ground.

I obtained the SEIDEN switch from the site listed below (text copied from this site)

http://www.diyhifisupply.com/diyhs_dact_switches.htm

Seiden Switches : 21 position stereo switch or Seiden 6 position selector with switchable ground. These are beautifully made switches from Japan with a silky smooth action. Contacts are silver on gold and are enclosed by a transparent cover.2-2-21-15 degrees shorting Seiden switch from Japan 200VDC, 0.2AAC, 0.1ADC, shorting (make-before-break) , 21 position, body is (lxwxh): 40mm (inside chassis) x 38mm x 38mm, easily solder-able tabs, gold contacts. High quality switch that is perfect for implementing the TX102 in passive/active applications or for making your own stepped attenuators.

A true BLACK BOX

both transformers visible here

single input

48 links attached to switch (very tricky)

Earles labels left on (aid servicing later?)

22 enamelled wires bundle through plastic tube helps organise layout)

AUDIO SYNTHESIS PASSION

Gold sockets from Dick Smiths (Fremantle). The silver plated copper is coated with Teflon and is supplied by RS in Perth. The wire is excellent but very difficult to use and wrap. Please notice the heavy sterling silver U shaped earth bar. The wire was supplied by Sievers in Perth and is 3mm thick. A wire that found its way into all my power amp designs. This passion has a varying impedance, a common Vishay  15K is switched in with each step. The night I soldered this together was one of the hottest I remember in Perth. The joints are most likely contaminated with NaCl and other electrolytes (sweat, dear!)

The excellent selector switch was obtained from Clifford H da Souza (Audio Synergy, Perth) It is an ELMA and made in Switzerland (as far as I know, cost $50)

http://www.thlaudio.com/ELMAmne.html

The Shallco switch on the right was obtained for $400 at CD Audio, Hobart Tasmania. Speak to CHRIS on

(03) 62 238775 please note this number is very old and may have changed

 SONICALLY THIS IS VERY HARD TO BEAT. VERY CLEAN, HIGHLY DETAILED

 The basic model (drawings by Chris)

The Late Tom Hemsley Passive Controller 

TOP

This is a brilliant device built by my good friend Tom Hemsley in Perth. We had visited Audio Synergy and heard the Ben Duncan passive volume control in a modified N.V.A. preamp, and of course had to try to copy it.

Tom is a sort of audio silver smith, who has had a huge experience with audio gear, (has first rate soldering skills) and is basically the person who got me back on track with my audio interest back in the early nineties.

After lots of experiments with all sorts of resistors, we finally opted for a combination of Holco (whole copper) and Roderstein resistors.

From listening to an all Roderstein design we decided that it sounded a bit bright emphasizing the high frequencies.

The wafer switch was obtained from RS,the extremely expensive gold plated toggle switch has been set up as a 13dB mute switch. This means that you effectively get 2 ranges of volume, background levels and main listening. The resistors used in the switch are Vishay (obtained from Sonic Frontiers in America) They are probably the best resistors available anywhere, and rather expensive. The gold sockets at the rear are cheap, chunky gold plated items obtained at Dick Smith's. The box has been lined with lead plate, this stops it moving around when in use. No other Spooky reason!!!! Audioquest midnight LC-OFC wire was used internally, the copper helps to provide a little more warmth (along with the Holco resistors) when matched with the Roderstein resistors.

Click on any of the following to see a better picture

larger view

larger view

SADLY TOM HEMSLEY DIED PEACEFULLY IN HIS SLEEP 4th JAN 2004. A GREAT FRIEND WHO WILL BE GREATLY MISSED

VISHAY DALE LADDER TYPE ATTENUATOR

TOP

Added Sept 2005

There are two versions of stepped attenuators used: the series connected and the ladder-type. In a series connected attenuator, there are as many resistors in series as the number of steps, essentially replacing a potentiometer. At very low volume you have practically all the resistors in the signal path, and as you increase the volume, the number of resistors are reduced. Using a good quality switch and good resistors, this type of attenuator is still significantly better than most potentiometers.

In a ladder-type attenuator there are only two resistors and a couple of switch contacts in the signal path at any volume setting. This is the best solution to a volume control.

My Dale stepped attenuator.

I bought this example from Wanfai (eBay HK) He describes this controller as follows;

I highly recommend this seller please check out his other diy products

http://search.ebay.com.au/_W0QQsassZwanfai
 

This auction is for One 100K Stereo 23 steps attenuator ( Ladder type ) using High quality Dale RN60D resistors (The one Gold Point using )and a high quality OCC copper wire for ground with 2% silver solder.

As used in high-end audio use this kind of stepped attenuator, it will manufacture on top of the purely sonic; increased reliability, lower distortion and better tracking accuracy between channels. By using this will avoid the problem is that in most applications a potentiometer (variable resistor) will be used directly in the delicate signal path. This can have potentially disastrous effect on sound quality.

Simple plastic box $4.00

Metal knob from an old Sony amp

Chunky gold sockets from DSE Australia ($2.50 each)

Teflon coated silver plated copper wire (I have had these reels sitting around for over ten years)

The sockets were soldered before locking into place with a chunky adjustable spanner (they will not be working lose!)

A bit rough but very effective. The copper earth actually came out of a short piece of Audioquest midnight speaker cable (LC-OFC)

THIS IS A GREAT SOUNDING POT, TOTAL COST APPROX $80

 ALSO VISIT Audio Synthesis UK

MF Audio and Rothwell also manufacture high quality passive devices.

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