diyAudio - Power chip amps
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
Power chip amps More watts for less money in power amps.
Old

The real story about closed vs open loop class D amps

Posted 11th July 2014 at 12:11 AM by abraxalito
Updated 23rd July 2014 at 09:51 AM by abraxalito

Very interesting paper which I'd not come across before which poses about as many questions as it answers. Thanks to Bob Cordell mentioning it in his book, here's the link :

http://www.eetasia.com/STATIC/PDF/20...URCES=DOWNLOAD

Compare the FFT in fig3 (closed loop) with fig4 (open loop) in the text - which do you think will sound better?

Here's my take on what the paper is claiming, FWIW. That PSRR measurements when the amp has a BTL (balanced) output aren't appropriate because there is output stage cancelling of them. My first head-scratch moment came because this is true of other amp topologies too, not just classD as BTL outputs are very much alive and well in NXP's range of chipamps for automotive use. So why restrict this to just classD?

Secondly what's the argument that PSRR in BTL amps isn't appropriate? They seem to be saying (though they don't express this very clearly) that whilst output stage...
abraxalito's Avatar
diyAudio Member
Posted in Power chip amps
Views 372 Comments 17 abraxalito is online now
Old

TDA8932 class D amp

Posted 27th May 2014 at 12:39 AM by abraxalito
Updated 16th June 2014 at 01:09 AM by abraxalito

One channel is completed - barring the off-board hexacap shunt - second channel under construction. Then for a comparison with the TDA1521s

Update1 - both channels running now, 160,000uF on each. Bass is tuneful but LF colourations noticeable on piano (Ashkenazy Diabelli Variations). Solution to this is simple - more caps

Update2 - an extra ring of caps around the original hexacaps now, so we're around 250,000uF. Bass is so much better than from the TPA3116 but the HF is more ragged, less transparency overall than the TPA3116. So I'll next try an outrageously decoupled implementation just to check I'm not limiting the chip with poor PSU hygiene....

Update3 - I have over 30 1206 10uF caps per side now as local decoupling - HF problems are slight. Makes me wonder if I use it only on the bass/mid and a TDA1521 for the tweeter duty we might reach audio nirvana.... Looking at the DS its easy to see why the HF's a bit of a mess - the PSRR is about...
Attached Thumbnails
Click image for larger version

Name:	P1010109.JPG
Views:	121
Size:	697.5 KB
ID:	1293   Click image for larger version

Name:	P1010110.JPG
Views:	115
Size:	719.9 KB
ID:	1294   Click image for larger version

Name:	extreme.jpg
Views:	84
Size:	67.8 KB
ID:	1300   Click image for larger version

Name:	P1010114.JPG
Views:	70
Size:	678.7 KB
ID:	1302   Click image for larger version

Name:	TDA8932taobao.jpg
Views:	64
Size:	63.8 KB
ID:	1306  

abraxalito's Avatar
diyAudio Member
Posted in Power chip amps
Views 389 Comments 5 abraxalito is online now
Old

Line input RF reject filter

Posted 19th February 2013 at 07:24 AM by abraxalito
Updated 26th February 2013 at 03:09 AM by abraxalito (Added zoomed passband plot)

I've only simmed this so far, no listening tests. The aim here is to have a passive filter which works into a line level impedance (i.e. 10k or greater) and which gives a decent amount of RF rejection without compromising SQ. I plan to incorporate it behind the RCA input jacks of my chipamp.

Design-wise, it started life as a simple 2nd order filter with single series L and shunt C. But when it came to wind the inductor I didn't have a wire diameter small enough to make the required value (44mH). So I split up the inductor into 2 * 22mH and then couldn't resist hanging a cap off the centre tap. The result has turned more into an over-damped elliptic with a higher corner frequency than the original, but with an impeccable phase response to 20kHz. The elliptic-type plot comes about because of the SRF of the two inductors (around 350kHz).

Since fas42 remarked on the phase performance, I've added the group delay plot for the passband. Almost pure time delay of...
Attached Thumbnails
Click image for larger version

Name:	passive-line-input-filter.png
Views:	326
Size:	7.2 KB
ID:	878   Click image for larger version

Name:	passive-line-FR.png
Views:	196
Size:	5.3 KB
ID:	879   Click image for larger version

Name:	passive-line-input-zoomed.png
Views:	163
Size:	5.9 KB
ID:	880   Click image for larger version

Name:	28mH-chokes.png
Views:	257
Size:	338.7 KB
ID:	881  
abraxalito's Avatar
diyAudio Member
Posted in Power chip amps
Views 1117 Comments 8 abraxalito is online now
Old

High-end chipamp build project

Posted 24th January 2013 at 07:21 AM by abraxalito
Updated 15th February 2013 at 05:12 AM by abraxalito

Go here : Possibly the most frugal high-end sounding amp?

If you have comments, feedback, critique or improvements and don't want to put it on that thread, feel free to leave it in the comments here.

Here are the first measurements - the Nitro amp being fed by the Ozone DAC with a six-tone multiple, peak digital level -20dB. Peak output power around 100mW in an 8R speaker (connected for this test). It looks from this that the datasheet is a little pessimistic on THD, though here I'm measuring the TDA8566, not the 8561. No measurement graphs are presented in the 8566 DS and the 8561 only has plots for 2R and 4R loads, not 8R.

Schematic now added. BOM here : https://docs.google.com/spreadsheet/...Hc&usp=sharing

Additional schematic showing how to use TDA8566Q in place of TDA8561Q as the latter isn't available from Mouser. Mouser only has fewer than 300 TDA8566Q in stock so best...
Attached Thumbnails
Click image for larger version

Name:	hexatone-scale.png
Views:	134
Size:	2.4 KB
ID:	861   Click image for larger version

Name:	hexatone-ozone-nitro.png
Views:	285
Size:	9.5 KB
ID:	862   Click image for larger version

Name:	Nitro-sch-attach.png
Views:	988
Size:	720.2 KB
ID:	873   Click image for larger version

Name:	TDA8566Q-mods.png
Views:	849
Size:	402.1 KB
ID:	874  
abraxalito's Avatar
diyAudio Member
Posted in Power chip amps
Views 4407 Comments 51 abraxalito is online now
Hide this!Advertise here!

New To Site? Need Help?

All times are GMT. The time now is 01:02 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2