diyAudio - Uncategorized
Go Back   Home > Forums > Blogs > abraxalito

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Uncategorized Entries with no category
Old

Cost optimized active crossover

Posted 7th April 2015 at 07:03 AM by abraxalito

I've driven the BOM cost of this board down quite hard by choosing some 'disrespected' opamps to build it around - TL084s. They go for 0.5RMB on Taobao (about $0.08, same as a recycled TDA1387). Listening so far is positive but I've got no audiophile opamp reference to check it against. In terms of bang for the buck though, its going to be very hard to beat. All filter caps are NP0 ceramics, resistors are bog-standard thick film 0805s.

What's different about this build for me is its fully balanced and classA operation in order to cancel power supply noise. To get classA operation from TL084s means the feedback/filter networks must be very high impedance so as to draw under 100uA peak currents. Opamps aren't used as output buffers, rather I've gone for emitter followers loaded by two-transistor CCSs.

The picture is my second prototype, using the best (aka lowest ESR) caps I could get hold of - Nichicon HZ and Nippon Chemi KZE. All the copper wires sticking up around...
Attached Images
File Type: jpg MkIIAXO.jpg (103.6 KB, 86 views)
abraxalito's Avatar
diyAudio Member
Posted in Uncategorized
Views 411 Comments 0 abraxalito is offline
Old

Supercapacitor b*ll*cks

Posted 15th February 2015 at 11:50 PM by abraxalito
Updated 16th March 2015 at 03:25 AM by abraxalito (Red Wine it isn't, just the same designer)

Here's something very misleading in the 6moons preview of Vinni Rossi's (of Red Wine Audio fame) latest supercapacitor powered kit. They have 18 * 350F supercaps in the box and they say '...the total rating becomes a whopping 6300F'. However each capacitor is only 2.7V so presumably to get any audio signal at all out, they need to operate these caps in series. Caps in series don't multiply, they divide so the total capacitance drops by a factor of 18. Hence only 19.4F. Not a small difference from 6300F or did I miss something?

http://www.6moons.com/audioreviews2/vinnierossi/3.html (the text at this link has since been updated to remove the 'total rating...whopping' remark).

I think I may have missed something - they aren't using all the supercaps all the time, rather there are 9 discharging and 9 charging. So the total capacitance in the audio circuit at any time is 350/9 = 39F. Still an impressive amount of capacitance but the problem is that the ESRs add too....
abraxalito's Avatar
diyAudio Member
Posted in Uncategorized
Views 690 Comments 9 abraxalito is offline
Old

At last, NXP has a low-end, low-power Cortex M4

Posted 8th November 2014 at 01:46 AM by abraxalito
Updated 8th November 2014 at 02:00 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
abraxalito's Avatar
diyAudio Member
Posted in Uncategorized
Views 414 Comments 0 abraxalito is offline
Old

Taobao has a TDA1387 DAC (apparently)

Posted 23rd October 2014 at 02:33 AM by abraxalito
Updated 15th January 2015 at 01:19 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

Update - seems one particular vendor has quite a range of TDA1387 DACs now, all very affordable. The cheapest is this one (48rmb kit, 88rmb built in my limited understanding) - http://item.taobao.com/item.htm?spm=2013.1.20141002.7.yoDoCx&scm=1007.100 09.2083.i41769520252&id=41937738376&pvid=402c7a10-8221-4bca-82c0-99c1c511877f.
This one has 8 chips, I guess its a tribute DAC to the DAC-AH - http://item.taobao.com/item.htm?spm=...cket=17#detail...
abraxalito's Avatar
diyAudio Member
Posted in Uncategorized
Views 779 Comments 2 abraxalito is offline
Old

Amplifier-centric two-way XO (and system) design

Posted 3rd July 2014 at 04:30 AM by abraxalito
Updated 5th July 2014 at 02:55 PM by abraxalito

The traditional view is that the speakers are the weakest link of the audio system and hence they're not really designed with amplifiers in mind. Why make amp design easier when speakers are plenty hard enough to get right?

In my experience speakers don't contribute very much to the listening satisfaction. They're more a matter of taste, but a much better speaker can't undo the faults of an amplifier (or DAC for that matter). That's not to say some speakers don't sound better than others - I mostly prefer my Paiyons to the much cheaper Denons but their 'betterness' is orthogonal to the way to the manner DACs and amps sound better. Electronics has had the biggest impact on my listening satisfaction so far so here is an XO designed to make the electronics' job as easy as possible.

Given that the critical parameters of an amp designed for listener satisfaction aren't THD+N and FR, rather multitone IMD (aka MTPR) and PSRR it makes sense that an amp is given the narrowest...
Attached Thumbnails
Click image for larger version

Name:	twowaysch.jpg
Views:	150
Size:	56.4 KB
ID:	1319   Click image for larger version

Name:	twowayXO.jpg
Views:	75
Size:	83.3 KB
ID:	1320  
abraxalito's Avatar
diyAudio Member
Posted in Uncategorized
Views 593 Comments 5 abraxalito is offline
Old

Just for fun - an ultra-low impedance AIF

Posted 18th June 2014 at 11:40 PM by abraxalito

DIYing high enough Q inductors for anti-imaging filters is a bit of a challenge so here's another way to approach this. I found its possible to build very high Q inductors by simply slipping ferrite beads over a fairly thick copper wire. The limitation though is that the beads I have offer about 1.2uH per bead. So making a ferrite bead version of a 660uH inductor will call for over 500 beads - rather impractical.

To make such a ferrite bead inductor filter a practical possibility its necessary to work at a much lower impedance. I've taken a 1ohm working impedance inititally to develop this filter. Now the largest inductor just needs 10 beads. Given this very low impedance the post-amplifier's noise performance becomes rather a challenge - but a transformer will probably do the trick nicely. I plan to try this with a 1:7 step up trafo and see how it goes.

This kind of filter is probably very suitable for DACs with higher output current - the communications type...
Attached Thumbnails
Click image for larger version

Name:	ultra-low-Z-AIF.jpg
Views:	117
Size:	32.9 KB
ID:	1308  
abraxalito's Avatar
diyAudio Member
Posted in Uncategorized
Views 380 Comments 0 abraxalito is offline
Old

Tweeter line level passive XO

Posted 13th June 2014 at 04:47 AM by abraxalito
Updated 16th June 2014 at 04:51 AM by abraxalito

I'm really impressed with the bang for the buck with my 228rmb speakers, but have a theory they're rather being limited by their crossover. Especially the first order tweeter crossover which hasn't enough LF rejection.

In search of a steeper XO for the tweeter I've decided to go the whole hog and design a kick-*** filter that'll allow me to fully activate these puppies and see just how much they're limited by their electronics. kinku just pointed me to a filter design program called AADE which I've just finished using to design my first LC bandpass filter.

Its bandpass because I want to stick it straight after the DAC and it needs the anti-imaging function, meaning a steep low pass around 18kHz. The tweeter doesn't need this as they're fairly low on IMD, but the tweeter amp sure benefits from having no ultrasonics. Hence here is my first attempt at a tweeter bandpass filter, to go between the DAC and a dedicated tweeter amp.

For now I'll use the TDA1521...
Attached Thumbnails
Click image for larger version

Name:	PLLtweeterXO.jpg
Views:	199
Size:	37.5 KB
ID:	1303   Click image for larger version

Name:	TWeeter bandpass FR.jpg
Views:	148
Size:	95.3 KB
ID:	1304   Click image for larger version

Name:	TweeterXO.JPG
Views:	232
Size:	716.7 KB
ID:	1305   Click image for larger version

Name:	5thordertweet.jpg
Views:	167
Size:	38.7 KB
ID:	1307  
abraxalito's Avatar
diyAudio Member
Posted in Uncategorized
Views 977 Comments 17 abraxalito is offline
Old

Linsley Hood amp on Taobao

Posted 4th June 2014 at 05:27 AM by abraxalito

Looks like a bargain, around $120. Sorely tempted to get one to play with - what do you think ?
Attached Thumbnails
Click image for larger version

Name:	JLH.jpg
Views:	646
Size:	58.8 KB
ID:	1301  
abraxalito's Avatar
diyAudio Member
Posted in Uncategorized
Views 1472 Comments 8 abraxalito is offline
Old

Cheapo passive speakers breaking in

Posted 1st June 2014 at 06:02 AM by abraxalito
Updated 2nd June 2014 at 03:54 AM by abraxalito

A pair of these were delivered yesterday. At first I thought their bass sucked and the top end was too 'phasy' - it was only after a while I realized I'd connected them out of phase

Now they're wired up correctly on my TDA1521 amps, they're starting to come on-stream. I rate them as a bargain at the asking price of 228rmb (around $35).

After they've fully broken in I plan to explore what the lowest hanging fruit is by way of tweaks to the crossover....

Update1 - here's the XO, very simple 1st order. 250uH inductor on the bass (0.1ohm DCR, 6ohm bass/mid) and 1.5uF cap for the tweeter (8ohm). The NP cap for the tweeter has a rather high ESR (3ohms at 1kHz) so there might be some mileage in substituting this for a foil cap.

Plotting this arrangement on LTSpice gives a crossover frequency (if -6dB) around 7kHz which seems a little high. If we were to assume a -3dB crossover (because they're in quadrature for a 1st order) then it would...
Attached Thumbnails
Click image for larger version

Name:	Denon228s.jpg
Views:	133
Size:	12.4 KB
ID:	1295   Click image for larger version

Name:	DenonXO.JPG
Views:	180
Size:	678.4 KB
ID:	1299  
abraxalito's Avatar
diyAudio Member
Posted in Uncategorized
Views 525 Comments 6 abraxalito is offline
Old

TDA1521 chip amps rock!

Posted 23rd May 2014 at 03:13 AM by abraxalito

Here's my prototype TDA1521 dual mono arrangement - two chips per channel in bridged/parallel, sat atop 400,000uF hexacaps. The neutrality has taken a while to get used to but I'm lovin' em....
Attached Thumbnails
Click image for larger version

Name:	P1010105.JPG
Views:	786
Size:	711.2 KB
ID:	1292  
abraxalito's Avatar
diyAudio Member
Posted in Uncategorized
Views 889 Comments 4 abraxalito is offline
Hide this!Advertise here!

New To Site? Need Help?

All times are GMT. The time now is 07:04 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2015 DragonByte Technologies Ltd.
Copyright 1999-2015 diyAudio

Content Relevant URLs by vBSEO 3.3.2