Posted 26th February 2012 at 04:28 AM byabraxalito
Of late I've been enjoying snacking on this book EDAgraffiti which is a romp through various aspects of the economics of semiconductors. Recommended for those who are interested not just in the technical side of the digital revolution but also the commercial perspective too.
One comment from the book jumped out at me, which was a prediction made by Clayton Christensen a few years ago about the end of Moore's Law. He's reported as saying the following at an engineering conference organised by Cadence. Moore's Law will come to an end when the semiconductor industry tries to deliver more capability than the mainstream requires at a price which is higher than the mainstream wants to pay. 450mm wafer processing technology and EUV lithography pretty much do seem to fit the bill here.
This article on The Inquirer is saying pretty much the same thing - gaming and video transcoding have kept the push for faster PCs alive but even in those applications demand is now...
Cute little board. Diamond buffer with BD-135/136 transistors and a built in Z-reg. Designed to buffer the output of op amp circuits to help drive cables and otherwise isolate the op amp feedback loop from the big bad outside world. It can also be used as a unity gain preamplifier, or, with by changing a couple of resistors and adding small heatsinks, to drive headphones.
Posted 17th February 2012 at 09:55 PM byrjm Updated 6th March 2012 at 04:21 PM byrjm
A real, honest-to-goodness voltage regulator has three parts: a fixed voltage reference, an error amplifier, and a pass element.
Most people only put eyeballs on the final, all-wrapped-up-in-a-tidy-IC-package version, typified by the LM7812, or with a couple of extra gain-set resistors, the LM317. These chips have a working bandwidth about about 2 kHz, as they are designed to 1) reduce 120 Hz ripple and 2) be rock stable no matter what abuse they are subjected to. As a result at audio frequencies and above they are pretty much noise generators...
Knowing this, many people have set out to build better regulators for audio work.
The most obvious route is to build a high performance LM7812 from discrete components. (Most excellent review here.) AD797 for the error amplifier, high stability, low noise voltage reference, etc. The trick though, is stability. The LM7812 is low bandwidth not because it's too cheap to manage anything better, but because...
Had this running for a few weeks now, and the sound coming from the Sonys altogether better, now just a bit bass heavy rather than treble shy. The speakers are mounted right next to the ceiling in the room corners, so not really a surprise.
I have simulated the crossover and equalisation circuit of the preamp section, and realised that I can add a variable resistor to adjust the amount of bass boost the circuit gives, not a horrible mod, just one pot, and a new cap, just need some time to do it.
The not passive pre has no muting circuit in at present, so power sequencing is required. I intend to make it direct coupled at the output. To do this I am planing to do a micro controller servo loop. When I made the Class A digital amplifier, mentioned earlier I used an opamp servo, and I can state that this circuit does definitely have an effect on the sound.
In the interests of minimalism the Not Passive Pre II is already being...
The designer, Henry Nurdin, has kindly posted a full schematic.
Ignore the fact for a moment that it's designed as a tiny battery-operated module to retrofit into electric guitars, the basic circuit block with 5-6 dB non-inverting gain could be used as a front end for a headphone buffer stage like, I'm thinking especially, the Szekeres MOSFET buffer.
That's if the bandwidth is sufficient for high-end audio (should be!?) and, slightly more worrisome, acceptable gain matching between channels can be achieved without resorting to trim pots.
This circuit reminds me of something. ... Sziklai pair? Time to do some more dredging...
Posted 10th February 2012 at 11:20 PM byrjm Updated 10th February 2012 at 11:26 PM byrjm
File this under "things-I-should-have-learnt-to-do-many-years-ago-but-was-too-lazy-to-bother".
Many pcb fab outfits that do business with hobbyists and DIYers choose to accept Eagle .brd files, which means they do the conversion to Gerber output so you don't have to. I've relied on that for far too long, but when an error showed up in one the .pdf proofs on the last batch of boards I sent out for fabrication, they asked me to send the Gerber files instead. So I bit the bullet and after a couple of false starts managed to give them what they wanted. Looking back at it, it was easy and something I should have learnt, as I wrote up above, years ago, but, for posterity, here's how it's done:
(In Eagle 6.1, on Windows Vista)
Make a working folder for the Gerber files.
Copy the Eagle board (.brd) file to this directory.
Posted 10th February 2012 at 10:49 PM byrjm Updated 11th February 2012 at 02:48 AM byrjm
Finally got around to some more comparison listening with the Sapphire headphone amplifier. To recap: the circuit has an open loop diamond buffer output, so the op amp is just providing voltage gain. It configured for a non-inverting gain of 21 dB to match my 300 ohm HD600 headphones. Pretty much textbook operating conditions.
The op amp inputs are impedance balanced at about 1 kohm. This is about the crossover point where you start thinking about using FET input stages, but BJTs should still be fine.
I'm interested to see if there is a definite signature to a FET-input opamp. The original build called for an OPA134, which is a JFET input circuit. I tried the OPA27, which is a low-noise, high-input-current BJT design, and last night I tried the NE5534A, a classic general purpose audio opamp with bipolar inputs.
I've long been in agreement with Douglas Self on the NE5532/NE5534 : anyone who reports these op amps sound bad is either not using...
