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abraxalito abraxalito is offline

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    abraxalito posted a comment on page TDA1387 X8 NOS DAC 13th July 2015

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  • Last Activity: Today 05:58 AM
  • Join Date: 19th September 2007

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Posted 20th September 2016 at 12:24 PM by abraxalito Comments 0
Some years ago I reverse engineered the coefficients of the Philips SAA7220 filter, just for fun. At that time the microcontroller I implemented the filter on (LPC1114) didn't have a fully implemented I2S interface so I needed additional logic to get the data in (an array of 74HC595s) and I used the SSP to output a serial stream, albeit not reliably as I didn't implement a foolproof method of generating WS. Hence the filter wasn't ready for primetime.

Now though STM has introduced a Cortex M0 MCU which does have the dedicated I2S ports to realize a pukka emulation of the SAA7220. At least that's what I'm hoping - I know the code worked on the LPC1114 but I seem to recall I needed a slight overclock - there is a report that the STM32F072 can be overclocked but I shall need to check this out for myself. One major advantage this replacement will have is going to be lower power consumption - something of the order of 100mW or under.

In order to kick this project off,...

Posted 18th September 2016 at 02:45 AM by abraxalito Comments 6
Posted in Power chip amps
A number of interesting amps have caught my eye on Taobao of late, they (except for the last) are true digital amps in the sense that they're 'power DACs'. The first is using ST's STA333W which is a phenomenally cheap fully-integrated digital amp chip, hence the very low price of this board - ns=1&abbucket=13#detail ns=1&abbucket=13#detail USB input, speaker out but needs an external power brick of some sort, up to 20V.

The second one's a boxed product, albeit with an external power supply. Its using Intersil's D2-audio chipset (D2-41051), the first implementation I've noticed on Taobao. It uses discrete MOSFETs in the output stage. The enclosure and controls look to be in the PS Audio territory, a cut above the usual Taobao cheap stuff -

Posted 7th July 2016 at 11:58 PM by abraxalito Comments 0
Posted in Power chip amps
I've not posted for a few months here as I've been involved in moving apartment which was quite a major project given the quantities of parts and assemblies I've accumulated. Even though I've been in my new place for over two weeks now, very little has been unpacked so far, but I have just yesterday rebooted my desktop active XO/amp system which had been quite literally assembled on my desktop with no casework whatsoever Its still without casework and survived the move with only a few wires falling off but now 'installed' in a drawer (pic attached). Its being fed from my 'Domino' balanced TDA1387 DAC and Taobao TFcard player and delivering bags of emotional satisfaction through stand mounted '3Nod' two-ways.

The amps are all LM4766 bridged running from 60V total but with heroic measures to keep supply noise under control, the central PSU has a CLC configuration and ferrite input transformers are used for coupling between AXO and amps. Output transformers (ferrite for...

Posted 15th April 2016 at 04:09 AM by abraxalito Comments 0
Listening to headphones creates, on many recordings, an unnaturally wide soundstage. I decided to play with the idea of 'crossfeed' whereby some deliberate crosstalk is introduced between the two channels. With transformers its jolly easy to do - just create an extra winding with the right number of turns then put this winding in series with the main output of the opposite channel.

In the picture I've done this with some EP17 ferrite cores and added a DPDT changeover switch to A/B between the original and crossfed version. The crossfeed factor I've gone for is 25%. It works in practice in that there's a more natural presentation without any 'extreme' stereo effects (almost a kind of phasiness on some recordings). But sometimes I enjoy the 'all around' effect so switchable is the name of the game

Trafo winding details as follows - primary 500T of 0.1mm, two secondaries first 120T 0.21mm, second 40T 0.21mm.

Made a second one as a colleague liked...

Posted 5th April 2016 at 09:39 AM by abraxalito Comments 2
I was going to call this amp 'fleapowered' but after doing some searching online I found fleapowered amps in general were much higher output power than this - single digit Watts typically. Whereas this one is more than a couple of orders of magnitude lower than that (under 10mW) so deserved a different moniker. Seeing as a mite is smaller than a flea, 'mighty mite' seemed to me as good as any descriptor for it.

The mighty mite started life in my imagination after I walked into a local headphones shop and tried out some cans that the shop assistant recommended to me - AT MSR7s. I'd brought my 'Buffalito' headphone buffer with me and some step down transformers for its output - fed from my mobile phone its way too loud for my AKGs and Superluxes. However the MSR7s were too loud even with the 2:1 step down trafo so I told the assistant I'd come back and listen again once I had a more suitable trafo. I figured it needed to be 4:1 step down, so I built a pair of those (PQ32/20)...
Recent Comments
Thanks Matt, I hadn't...
Posted 10th October 2016 at 11:01 PM by abraxalito abraxalito is offline
Did you see this thread,...
Posted 10th October 2016 at 01:14 PM by matt_garman matt_garman is offline
Yes it looks OK, I have...
Posted 9th October 2016 at 05:52 AM by abraxalito abraxalito is offline
Hi Richard,
Posted 8th October 2016 at 08:51 AM by robert1325 robert1325 is offline
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