Under Construction - last updated April 24 2001

This summarises 2 articles in LLDIY Newsletters 39 and 40

Introduction

A lot of the effort spent on the interface has centered around improving what was there already. When we've been poking around, it has been a concern that the PSU is of modest design which means it only does what it has to.

When we looked at the output of the bias supply, we found all sorts of hash, much as we expected due to the use of cascaded 1/2 wave voltage doublers. In all our research, we have yet to find anyone getting the bias for an ESL any other way. This probably explains why some of the things such as the ferrite beads and the neon have the effect they do.

Andy finally decided to take this on and built himself a mains regerator for his QUAD ESL63s. Upon hearing this on my Acoustats, I knew I had to have one.

What got Built

Block diagram of Regenerator

As mine are in experimental form, the following lists how they have been implemented

1. Fuction Generator set to 50Hz
2. BK Electrical MF100 amplifier module
3. a heater transformer left over from the preamp 240V/12V @ 2A winding connected backwards
4. existing ESL (Acoustat or QUAD in our case) interface

This lot is all sitting on various bits of wood lying about the floor - nice! So what effect do they have? In a word, amazing! It is hard to describe fully. It is like cleaning a dirty window is the best analogy I can think of. Not only what you see improves in detail but the 3 dimensions of the object are easier to make out also. Subtle shadings in shape, texture and body are easier to see. Now relate that effect to hearing into the sound-space with your ears. Its got less crud in the way is another way of expressing the same thing. The frequency extremes, sense of headroom and loudness were also extended and purer. I believe the improvement to be proportional to the quality of the equipment upstream i.e. it is an unblocking effect. It is as though the mains crud has been masking a wealth of subtle detail especially spatial information. This is not subtle! On my Acoustats, it had the greatest effect, followed by Andy's QUADs. We tried Andy's early regens on some Innersound Eros and although the effect was apparent, it was not as great as in our systems. We will revisit that later.

Unfortunately this all came at a price. The increase in resolution ruthlessly exposes faults in the electronics upstream and the quality of the speaker itself. It made me review the setup of every component upstream and I found fault in each. Also the speaker became troublesome to listen to but I couldn't figure out why for a long time. It was then I realised it was the frame and so built the new one. This combination now has huge resolving power and impact (for an ESL) but is very musical at the same time.

What Next?

Build them properly! For the oscillator Andy designed a simple circuit using the 8038 function generator follower by an op-amp follower. I have yet to do this.

The next plan is to do the HT part properly. We have always wanted to be rid of the cascaded voltage doublers as they are high impedance, introduce a huge amount of hash and do little in the way of smoothing the rectified input. We intend to drive a dedicated transformer with 10V primary and 3600V secondary. This will feed a regular bridge and power supply - full details are sketchy at present. The transformers can be had for about £30 each for 10 off.

This solution should give us the smoothest 5kV DC for the panels that we can think off.

In the new design, the block diagram components will be represented by

1. This will be Andy's oscillator
2. The BKElec amplifier module will remain for now
3. New 10/3600V Tx
4. New EHT PSU in own case

More here soon