World Audio Designs PHONO II and PSU II
After the success of the Fostex horns I worked up the courage to have a go at the now defunct World Audio Design (WAD) PHONO II and PSU II kits. I hadn’t really used a soldering iron before but was encouraged by the supposedly easily construction thanks to the pcbs and reassured by the thriving community on the old WAD BB.
The kits consisted of an RIAA stage using 3no. ECC83 double triodes remotely powered from a solid state power supply. A matching PRE II preamp was also available using a 6922 double triode.
Everything required was included in the kits, from chassis, brushed aluminium front plates and cables to pcbs, components and valves. Being somewhat cautious with my first build I followed the instructions closely and took my time. Construction was pretty straightforward: populate the pcbs and solder the components on both sides of the pcbs. Even a novice like me managed. No problems.
Having read the warning in the instructions that electrolytic caps wired up with incorrect polarity can explode I was rather nervous the first time I switched on. Fortunately my trepidation was unfounded and it worked first time! This was a bit of a surprise, though, in reality, following the instructions and taking plenty of time is all that was needed to complete a successful build.
These kits make a very nice sound, no doubt about it, and are an improvement over the inbuilt stage in my Exposure IIV pre amp. Having heard other valve phono stages since, to make a significant improvement requires significant expenditure.
There are a number of improvements that could be made, from valve rolling to a complete rebuild with fancy bits. The only changes I have made so far (apart from adding Lundahl LL9206 MC step-ups) are to the valves, which I guess is a measure of how good the phono stage is in its basic form.
Perhaps fortuitously, one of the originally supplied Ei ECC83s died after about a year, so I replaced it and another of the remaining good Eis with Svetlana 12AX7s. This improved the sound – more detailed and perhaps a little tauter and refined. The improvement left me thinking the Eis were rather uninspiring.
A much bigger improvement was changing all three valves for some old 5751s. These are similar to ECC83s but with less gain. They are also reputed to have a nicer sound and they certainly improved my PHONO II. I have some Mullard ECC83s, I should compare them to the 5751s sometime...
In its standard form the PHONO II does not correct for the 3.18us RIAA equalisation time constant. This is sometimes used to protect the cutting head during recording, and there is an FAQ on the World Designs forum for correcting this. Reported results are mixed; some hear a small improvement others hear none. I have the resistors, just waiting for a period of stability in my system (ha!) so I can see if it makes any improvement.
The caps in the PHONO II are prime candidates for upgrade and I really must get around to trying some fancy ones.
Lundahl LL9206 MC Step-ups
As I experimented with my Garrard 401 the time came where I had to try the infamous Denon 103. As my existing cartridge, a Dynavector 10X4, is a high output MC I didn't have any step-ups. Initial experimentation with the 103 without step-ups was promising: a good sound but the system ran out of gain on quieter pressings. Looking on the WD forum the LL9206 MC step-ups had some good feedback and didn't cost the earth. There is no Lundahl supplier in the UK so I got mine direct from Sweden. There are suppliers in Europe, but it seemed easier to go direct to Lundahl.
The LL9206 have an amorphous core and mu metal can. The datasheet says that the primary side must have a ground reference. From experience I can confirm this, unless you like listening to lots and lots of hum! They can be configured 1:5, 1:10 and 1:20 for gain. 1:10 seemed to fit my system best, so I used schematic C (no center tap).
The small pins protruding from the cans are frustratingly fiddly to solder to, a right royal pain in the posterior. I had seen on a couple of websites that small pcbs are available to facilitate installation. Not appreciating how difficult it would be to solder them I didn't bother, but if I was soldering them for the first time again I would be sorely tempted to get a couple of the pcbs. Once soldered I attached each one to the chassis with a zip tie.
For cartridge loading, the 103 has an output impedance of 40R but wants to see, say, 6 to 10 times this, or 240R to 400R. Some 103 users report good result up to 1000R. The 1:10 ratio transforms the impedance by 100 (the gain squared i.e. 10 x 10), so the stock 47k resistor at R13/R14 should be replaced by one between 24k and 40k. As this is pretty close I have left the 47k resistors alone, but will eventually try 20k and 100k, and tune from there if there is an improvement.
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