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Design ideas for Aune M1 DAC card

Posted 15th November 2014 at 03:51 AM by abraxalito
Updated 19th November 2014 at 06:43 AM by abraxalito

I'll outline here some thinking in choosing the major building blocks (aka ICs) for this card - any comments welcome as this progresses.

First up the DAC chip will be the TDA1387 initially. I don't know for sure that the output from the ARM/Xilinx card is I2S but I'm going to verify that fairly soon. There's nowhere near enough room for the passive shunt I've adopted previously so the bass performance probably is going to have to suffer. I shall pay considerable attention to the power supply arrangements though in an attempt to make up for the LF lack.

After the DAC, passive I/V will follow and then a filter using the TDK 7mm inductors I've used previously. I've slotted them into the gap between the PCB and the case and there's just enough height available. Since space is at a premium I'll experiment with a 3 inductor design - the stop band attenuation will suffer but probably I'll add a secondary LC filter at the output to make up for that somewhat. The secondary...
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New .wav player from Aune looks very interesting

Posted 11th November 2014 at 02:26 AM by abraxalito
Updated 15th November 2014 at 10:27 AM by abraxalito

Thanks to jambul for alerting me to this one - 赵宇为作品 - Aune M1 便携式播放器测评报告 [Soomal·数码多] (link is in Chinese but its mainly for the pics).

Notice that although its using the PCM1793 chip the D/A and analog circuits are all on a daughter board. This gives rise to the possibility of engineering a daughter board with a much better DAC chip (think TDA1387) and improved head-amp...

Street price here is around 800rmb (80, $130) so I shall be ordering one to have a play.

Update - looks like I'm rather slow to catch on, Taobao already has somebody's alternative DAC-AMP card, which appears to be selling fairly well, here : http://item.taobao.com/item.htm?spm=...cket=13#detail

I've now placed the order for the M1, hopefully it'll arrive tomorrow and then I'll follow Dave (EEVBlog)'s advice : 'don't turn it on, take it apart'. The main question I want an answer to is how...
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Why I DIY

Posted 10th November 2014 at 11:46 AM by cspirou

This entry probably would have made more sense as my first post.

From my observations it seems like most people persue this from a cost/benefit standpoint. Companies will cut corners a lot of the time in order to control costs. The more expensive products don't cut corners but the result is a higher price. The DIY enthusiast is willing to put the time in that many companies won't in order to get superior sound. No matter what though it seems like the end goal is to have the best sounding system given the resources you have.

Personally though I don't do this hobby as pursuit for the perfect system, even though that is my end goal. I am more interested in building my own system from an educational stand point. My first love has always been science. Figuring out puzzles is what I really enjoy. So while I love music, what I enjoy most are the calculations and the planning involved to make this a reality.

The reason I chose audio is because a lot of the...
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At last, NXP has a low-end, low-power Cortex M4

Posted 8th November 2014 at 02:46 AM by abraxalito
Updated 8th November 2014 at 03:00 AM by abraxalito

NXP's ARM offerings I find to be the most power efficient and I've searched for a long time for a current-sipping M4 which is available in a lowish pin count package. Up until now the best offering in that realm has been STM's F411 with 13mA @ 100MHz. NXP's latest offering the LPC54100 beats that by a healthy margin, turning in a sub-10mA draw at the same clock rate. There's also a dual-core variant with a 100MHz M0+ with around half the current requirement. Respect - the fly in the ointment though is only 2 SPI peripherals which don't support TI mode. Pricing looks great at $2/10k.

http://www.nxp.com/news/press-releas...ng-market.html
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Old

CD is better than vinyl, which is why vinyl sounds better than CD

Posted 2nd November 2014 at 01:40 PM by cspirou

For my first blog post I wanted to write about digital vs analog sources, or more specifically CD vs vinyl. The title seems contradictory but hopefully my thesis will be clear by the end of this article. I will mainly be emphasizing dynamic range.

First I want to say that from a technical stand point, the CD is superior to vinyl. The average dynamic range of vinyl is 80dB while CD is capable of 150dB. There are also many issues with recording on LP vs CD which I won't elaborate on because I believe the following article does a pretty good job.

http://www.vox.com/2014/4/19/5626058...etter-than-cds

Yet there are many audiophiles that continue to claim that records sound better than CDs. Are these people brainwashed? Is it because an LP system is introducing a pleasing form of distortion?

Well I am here to claim that these audiophiles are not wrong. I don't just mean in a way to argue about subjective experience but...
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Integration and test of CS4398 / PIC based Direct Digital Synthesiser

Posted 2nd November 2014 at 05:03 AM by googlyone
Updated 2nd November 2014 at 10:48 AM by googlyone

About 6 months ago I finished off a CS4398 (DAC) and PIC32MX450 (microcontroller) based direct Digital Synthesiser.

I recently packaged this into an instrument case, and added a power supply cum interface card that allows this to all neatly plug together. As a final chapter to the development of this synth, I have tried to measure the harmonics it generates and to use it to test an example amplifier.

What does it look like? Not super fancy, but neat enough and laid out pretty reasonably I think:

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The larger home made board at the back is a power supply - well five of them in fact - to allow clear isolation between a number of digital and analogue rails.

The square board on the base of the case is the PIC board. This runs the human machine interface and more importantly does all the calculation of the waveforms. You can generate any waveform you want, provided it is repetitive and can be...
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Aiming for maximum isolation

Posted 2nd November 2014 at 03:42 AM by abraxalito

Getting isolation from the mains supply is an on-going challenge for me. Here's my latest stab at getting as close to a battery as I can currently manage - a ferrite line-output trafo soon to be pressed into service as a low-capacitance isolation transformer.

The back story is that I'd heard that split bobbin trafos were the way to go for the best isolation from the mains. Having just acquired some for chipamp-drive unit interfacing I was curious to check out their credentials. I measured around 20pF interwinding capacitance which is about the lowest of any mains trafo I've checked. Of that it seems that the majority of the capacitance is directly between the windings, a smaller amount is due to coupling via the steel core (which of course is conductive). So then I figured that even if the windings could be moved infinitely far apart the steel core would be the limiting factor in reducing the capacitance.

Air core trafos are a possibility but then they're hopeless...
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Old

My latest infatuation - transformers

Posted 25th October 2014 at 09:11 AM by abraxalito
Updated 6th November 2014 at 11:51 PM by abraxalito

I've found that some of the el-cheapo trafos (18rmb each) at a shop at the local electronics market are of split bobbin construction. This makes bodging up an audio OPT from two mains trafos a fairly straightforward matter.

I bought some with 9-0-9V and others with 0-12V secondaries. Then I disassembled them (fortunately they're not varnish dipped) and swapped out the 220V primary bobbin for the secondary of the other one. This gives me a trafo with 18V on the primary and 12V on the secondary, a step down of 1.5:1, impedance ratio of 2.25:1. So it makes a 4R drive unit appear as 9ohms to the chipamp.

And when I applied this to the output of the bass/mid of my chipamp (residing in the Phenix active speakers, its a TDA7265), apart from it sounding quieter I suddenly realized how much power supply noise I was still listening to. Incredible

So if you want to know if your chipamp PSU decoupling is really up to snuff, see how much difference a 1.5:1...
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Old

Taobao has a TDA1387 DAC (apparently)

Posted 23rd October 2014 at 03:33 AM by abraxalito

Its rather difficult to work out whether there's a line-level output here or if the phono sockets are inputs to the LM1875 amps. The TDA1387 is a plug-in module for the USB-input DAC section which might feed only the amps. Anyone who's good at reading Chinese, please contribute in the comments

http://item.taobao.com/item.htm?spm=...8-3f2abc0f8bd9
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Old

Denon DL-103

Posted 14th October 2014 at 01:55 PM by rjm
Updated 14th October 2014 at 01:57 PM by rjm

Eye candy.

My fourth. Each one comes packaged the same, with a serial number and individual calibration sheet.

This little guy is no. 2096, .39/.40 mV. Signed off by Mr. Nemoto (根本さん、ご苦労様!)
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