Craig Sawyers

Yeah - cutting coolant sure smells "characteristic" when it gets an infection.

Just looked at this again - there are 8 DAC's (hence Octave), ie 4 per channel. I think it uses the concept I first saw on Cambrige Audio CD players shortly after CD's were introduced - you time delay the digital signal to each DAC, so they do linear interpolation between the data points. Which gives you an extra two bits. Colloms measured a resolution of 18 bits, which would be the 16 bits of the individual DAC's, plus 2. It may be that they use something more sophisiticated than linear interpolation, but I have absolutely no evidence either way. Notice the lack of anything resembling a PLL or crystal. I have no idea how they recover the clock - it is something in the row of four IC's near to the pulse transformer, but other than that I just don't know.

Yeah - that's the way to do it!

Video skype with text messaging - from 1928

Coming; it is not a pretty sight though! I forgot the headphone systems. Mostly KG stuff. Triode E/S feeding original Lambdas. Dynalo with outboard PSU feeding either AKG K701 or Beyer DT990. SRM-T2 clone feeding 007's from a Tent CD in the bedroom. And a Blue Hawaii in the other bedroom waiting to be wired up and looking for a pair of phones to be fed by it.

A hot-rodded and rather ancient CD player, converted to a transport. Multiple mains tansformers, a regulator glued to the top of every chip, clock board (my design) with OPA623 S/PDIF driver (1ns rise time), and focus and tracking servos run from a dedicated supply. Metrum Octave, Audio Research LS3 pre, Audio Research D125 power, Quad ESL57's

Yes - the board is hand soldered. Nicely hand soldered. I'll bite for the SC transformer (I've just been downloading and speed reading his AES papers; he knows what he's talking about for sure!) - I'll PM you.

Comparing the Newava and Lundahl pulse transformers, the interwinding capacitance is 0.5uH and 1.3uH respectivly, and the interwinding capacitance is the same at 15pF. A figure of merit is root(leakage inductance x interwinding capacitance), and this is proportional to the rise time. So the Newava should have a rise time 62% of the Lundahl - ie it is faster. But the primary inductance of the Newava is only 0.225mH, whereas the Lundahl is 40mH (180 times greater). The winding inductance is related to the droop in the top of the pulse, and smaller inductance gives more droop. Calculation for the Newava shows that the top of the pulse will droop to around 80% for a typical pulse length. The Lundahl has an unmeasurably small droop. Droop gives rise to jitter (because of the variable pulse length encoding of serial digital data) - so it is good to keep it as low as possible. The low winding inductance of the Newava is all to do with use of a ferrite core, which has a relatively low permeability. The more expensive constructions use either spin melt amorphous ribbon, or mumetal, both of which have 200 to 500 times the permeability of most ferrites. And yes - the 50 ohm BNC connectors is just plain stoopid on a 75 ohm system. If that was a RF power amplifier feed to a transmitting antenna, there would be so much backward wave that the amp would blow. And RCA! There are supposed 75 ohm RCA's (WBT do a cable RCA plug and maching chassis socket), but I remain skeptical until I measure the darned things. Might be able to actually do that during the next two weeks. Now 75 ohm N-type! that would be the way to go with a clean sheet of paper! Craig

I bought one of these around 10 days ago, based on Martin Colloms' recommendation in HiFi Critic, in which he billed it as a real giant-killer. Initial thoughts were exceptionally good, and as it warmed up progressively better. But I can't resist getting things right that are wrong. The first problem is common to most DAC's and CD transports - RCA connectors. I did a whole host of measurements using Time Domain Reflectometry, and basically putting a fast pulse into a 75 ohm coax terminated with an RCA, into an RCA socket, with a surface mount 75 ohm resistor tacked onto it - and it is a disaster. Massive reflections - and reflections add jitter. The only way to do things *properly* is to maintain a clinical 75 ohm environment for the whole digital signal chain, and that means 75 ohm BNC connectors throughout. And most digital cables, if not terminated in RCA's are terminated in 50-ohm BNC's! In fact the only audio high-end 75 ohm BNC's are Oyaid. I just use regular clamp-on greenpar and RG302 teflon cored coax. After doing that (and measuring the TDR response into the Octave) the DAC really started to sing. Then I spotted the hokey little pulse transformer (visible in the picture above). This is a $2 part, a standard Murata ferrite cored pulse transformer. I replaced it with a far better (electrically) Lundahl LL1572, which uses an amorphous ribbon core. In the UK this is £35 - so not cheap. After swapping transformers (invalidating the warranty of course) I can honestly say I have never heard a DAC sound that good regardless of cost. I've just ordered an Audio Note toroidal pulse transformer wound on a mumetal ribbon core, so it will be interesting if that improves it further, or otherwise. I can't stop listening to it! Craig PS The DAC's are intersting. They are 16-pin devices (with the type number taken off, of course), so they are definitely not Burr Brown or any of the other audio DAC's, which have far more pins. So I think they must be DAC's intended for instrumentation or data acqisition applications. And they are supposedly R2R ladder DAC's too. I've done an initial trawl of manufacturer's data, but have not been able to find anything that looks like those.

Check.

Could have sworn that I posted to this thread - or am I losing my marbles and imagined it?

Well, the Triad toroids spec sheets say that the temperature rise at full rated power is 50C - which means 70C if the ambient temperature is 20C. The only way to escape the inevitible temperature issue is to use a transformer with much higher VA rating than is needed. So if the nominal spec is 150VA, and you use a 300VA transformer, the temperature rise will be closer to 35C (resulting in a transformer temperature of 55C). Note that is all with the transformer sitting in air at 20C - as soon as you put it in a case, the air temperature is a lot higher, and the transformer will run hotter still. In this forum we obey the laws of thermodynamics (to misquote The Simpsons)

The disadvantage of having the transformer inside the case is thermal. A transformer running at its rated VA will heat up to typically 50C+. Inside a case with little ventilation, it will get hotter, all of which will compromise the life of the smoothing caps and other components. I'd stick it outside (it looks like a Hammond) and run the lead outs through grommets in the top of the case. Craig

Formally that is called the transformer regulation - the percent difference between fully loaded and no load. For your numbers (490 cf 450) that is 9%, and is typical of a 120VA transformer. That percentage also takes into account that when loaded the transformer will heat up - typically to 50 - 60C, and the copper windings will increase in resistance.

Well, his worst work is Eine Kleine Nacht Musik. It is musical popcorn. But the guy wrote 600-odd pieces of music, so he is allowed the odd bad one. The most wierd one he composed was for glass harmonium. This was a mechanically driven set of rotating glasses tuned to different notes, and sounded by a keyboard linked to felt pads which pressed on the rim. Kind of like the thing we've all done of rubbing a finger around a part full wine glass. The guy who funded that piece clearly had bought this instrument from hell, and Mozart was commissioned to write something for it. But I have no idea how you would write a list of his best pieces. The operas? The clarinet concerto and clarinet quintet? The requiem? I love everthing I've heard of his, with the exception of EKNM, which drives my nuts.

This guy http://www.hobbithou...s/snakewood.htm seems to have a large load of snakewood. I've never come across the wood before, but I can see why it is highly thought of looking at the photos. Scratch that - he just hosts pics of other peoples wood!!!!

Yup - done.

Nice! How about Cocobolo http://www.exotichardwoods.co.uk/Woods_List/Cocobolo.asp

An 8-bit birthday Seriously I love Mozart's works - if I were stranded on a desert island, and all I had was a collection of his works (and a solar powered CD or MP3 player...) I would not go mad.

Cool! We're just expecting a kitchen designer to arrive, and here in the UK Corian is twice the price of real marble. Allegedly this is because DuPont are focused on the large installation market, like top quality hotels, and the prices for the sort of quantity you need for domestic kitchen worksurfaces are through the roof. Kitchen through the roof???!!?? And I haven't had anything to drink. Yet

Sticky Killer Davis. I think I'll keep to the day job