Optimizing TDA7294 Output - Page 27 - diyAudio
Go Back   Home > Forums > Amplifiers > Chip Amps

Chip Amps Amplifiers based on integrated circuits

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
Reply
 
Thread Tools Search this Thread
Old 21st January 2013, 12:03 PM   #261
diyAudio Member
 
Join Date: Jan 2011
It is good to read what is written in French translated into English,,It looks like it was written when TDA7294 was just BORN ,,lol.... good stuff...
  Reply With Quote
Old 22nd January 2013, 12:38 AM   #262
diyAudio Member
 
danielwritesbac's Avatar
 
Join Date: Nov 2007
Quote:
Originally Posted by simply14prem View Post
At 1K,22k,what value will be for cap?
Since large capacitor discharge blowing out the small signal section is unsafe, the resulting capacitor value is: DC Tracker
__________________
Tools, Models & Software for DIYClipNipper boostLM1875 TurboPowerful TDA7293 kitTDA7294 pt2pt ♦ My post has opinion.
  Reply With Quote
Old 23rd January 2013, 02:08 AM   #263
diyAudio Member
 
Join Date: Jan 2011
Quote:
Originally Posted by danielwritesbac View Post
000u with 680R and this isn't a good
idea because it is hard to find small
signal worthy 1000u caps and that
much cap discharge can break the
input transistors.
  Reply With Quote
Old 23rd January 2013, 02:09 AM   #264
diyAudio Member
 
Join Date: Jan 2011
Quote:
Originally Posted by danielwritesbac View Post
1000u with 680R and this isn't a good
idea because it is hard to find small
signal worthy 1000u caps and that
much cap discharge can break the
input transistors.
What do you mean,,can u plz xplain a bit,Why not 220,470u with 680R ?
  Reply With Quote
Old 23rd January 2013, 07:54 AM   #265
diyAudio Member
 
danielwritesbac's Avatar
 
Join Date: Nov 2007
Quote:
Originally Posted by simply14prem View Post
What do you mean,,can u plz xplain a bit,Why not 220u or 470u with 680R ?
That will work with LM3886. The undersize NFB cap will cause some 2nd order harmonic distortion at the bass and warm up the sound.
However. . .
TDA7294 doesn't have an inbuilt hard clipper. Nope. So, we don't have any sort of spike system mids&treble noise to combat. Instead of sudden onset, TDA7294's softie limiter doesn't make mids&treble distortion. No free lunch--Unfortunately, the only means to do softer limiting is earlier engagement. Basically, instead of upper midrange distortion like NatSemi's LM3886. . . ST's TDA7294 omits the low bass. Big difference! Omitting the low bass during loud playback is a highly effective means of current management for safety but it also causes "warm sound" artifacts, such as muddy sound.
Unfortunately, this also affects dynamics.
Actually, both NatSemi's hard clipper and ST's softie limiter do affect dynamics. Both are providing a necessary safety function, but neither is fun.

Well, that's a mess. Let's just say the dynamic tone is different. Thus the audiometric tuning needs are different.

TDA7294 is already warm enough, that is distortion, especially on dynamics and louder playback, and we don't want to make it worse.

SO, to get good low bass out of ST's TDA7294, we have to prepare with a larger NFB cap, a larger bootstrap cap, larger power supply reservoir and a larger transformer. And we don't dare try for much "warm up" with TDA7294 because that would do nothing but mid-fi mud, and as you can tell by that, undersize NFB cap is a mistake we'd like to avoid.

Also, to avoid excess "warming" (mud) with TDA7294, we don't put super-large caps on the amplifier board (much different than with LM3886). However, if you did happen to want larger capacitance on a TDA7294 amplifier board, you could use several 220u (or smaller) in parallel per each rail as the small cap still sounds clean even if you gang up several of them. I don't know why.

Most of ST TDA7294's softie limiter system is thermally reactive, so in order to keep the "mud slinging" to a minimum we must make tweaky tuning choices based on heatsink temperature--Consider anything that causes more heat a "veto." Before starting any tweaky tuning, an excellent head start would be clean power so the chip can run cooler. That's why I've been rather persistent with the power circuit on this thread. When the chip runs cooler, the resolution is a LOT higher.

P.S.
A much shorter answer to your question is: Bass blocker/distorter, and we don't need that extra distortion.
Undersize NFB cap error can make the cap selection extremely difficult to do, because it is the wrong size and thus finding a suitable brand of audiophile capacitor (of the wrong size) could be quite frustrating and time consuming.

P.P.S.
Easiest fix for undersize NFB cap is to decrease the +input cap size (input filter roll-off at least an octave higher frequencies than the feedback-shunt RC). This is quite the useful consideration for rear channel amp and mids&treble amplifiers for bi-amp system. Small, small value +input caps for clean sound.
__________________
Tools, Models & Software for DIYClipNipper boostLM1875 TurboPowerful TDA7293 kitTDA7294 pt2pt ♦ My post has opinion.

Last edited by danielwritesbac; 23rd January 2013 at 08:19 AM.
  Reply With Quote
Old 31st January 2013, 01:06 PM   #266
bcmbob is offline bcmbob  United States
diyAudio Member
 
Join Date: Dec 2009
Location: Bay City, Michigan
Default He's Back :)

Sorry, been playing in the discrete amp sandbox for my three design challenge project. (if interested check here)

I needed a method to start the component swap testing so I built a open bottom brace. I'll use that in combination with sockets when I start the comparison process. Will be adding some alternative parts in the next online orders.

Also got a start on a PS by mixing some new and some on-hand components. Between emails and posts, Daniel has me thoroughly confused so I'll just post what I have and ya'll can set me straight.
Attached Images
File Type: jpg 20130131_082928.jpg (61.5 KB, 264 views)
File Type: jpg 20130130_163926.jpg (67.9 KB, 265 views)
File Type: jpg 20130130_163516.jpg (115.4 KB, 232 views)
__________________
Bob M.
"Arrange Whatever Pieces Come Your Way."
  Reply With Quote
Old 31st January 2013, 10:18 PM   #267
diyAudio Member
 
danielwritesbac's Avatar
 
Join Date: Nov 2007
Bob, most of those parts look good.
However, I see a 3 divergences that don't match the schematic. . .
1). No need to cause ringing with the unexpected extra 100u caps (omit for now).
2). If your transformer is dual-secondaries, the bass could be better if you use dual-secondaries specific support. See photos (attached).
3). Capacitor polarity needs checked. See photos (attached).
Attached Images
File Type: gif polarity-DS.gif (19.7 KB, 207 views)
File Type: gif polarity-diode.gif (35.2 KB, 196 views)
File Type: gif polarity-CT.gif (19.2 KB, 40 views)
__________________
Tools, Models & Software for DIYClipNipper boostLM1875 TurboPowerful TDA7293 kitTDA7294 pt2pt ♦ My post has opinion.
  Reply With Quote
Old 3rd February 2013, 01:48 PM   #268
diyAudio Member
 
danielwritesbac's Avatar
 
Join Date: Nov 2007
We need to talk about "Derating."
Bob, in regards to that one mystery 35v cap on the rails in your picture:
The 35v rated cap on 35v rails is like setting the cruise control on a Chevy Corsica stuck at maximum speed, 143 miles per hour, which would shorten longevity dramatically. Likewise, the 35v rated cap running on 35v rails won't last long.

Derating for longer lasting:
50v rated caps, 35v rails, TDA7294, 24+24vac transformer
63v rated caps, 48v rails, HoneyBadger, 35+35vac transformer

The deal is that getting any practical long-term use out of anything either electronic or automotive requires it be used at somewhat less than floorboarded. Unfortunately, the sensational headlines of marketing figures (like the voltage printed on the side of caps) don't usually include longevity, and datasheets are advertisements, especially the first page with the headline/destructive test, peak rated figures that aren't for practical use.

Some approximate examples:
An active device may run up to 40% of its rating at conservative voltage or up to 20% of its rating at higher voltage.
A passive part may run up to 60% of its rating at room temperatures or up to 35% of its rating at warmer temperatures.

Those generalizations are somewhat imprecise, but none of them run at 100% of their advertisements. Therefore, the voltage figure printed on the side of the capacitor is not really trustworthy--it is a "headline figure" aka marketing BS. The fix for this problem is Derating.
__________________
Tools, Models & Software for DIYClipNipper boostLM1875 TurboPowerful TDA7293 kitTDA7294 pt2pt ♦ My post has opinion.

Last edited by danielwritesbac; 3rd February 2013 at 01:50 PM.
  Reply With Quote
Old 3rd February 2013, 02:33 PM   #269
bcmbob is offline bcmbob  United States
diyAudio Member
 
Join Date: Dec 2009
Location: Bay City, Michigan
Hey Daniel,

There may just be a computer graphics problem here. I used the drawing attached to post # 78 as my key. I saw uF and on closer examination that may nF - not sure.

But I'm glad you caught it. That's why I posted what I have before heating up the soldering iron. Also the red PS in the same post has a cap in a similar spot, so some more clarification may be needed. Are you suggesting that specific cap be completely eliminated, replaced with a different value or it's something for center tapped transformers only?
Attached Images
File Type: jpg Ladderback Schematic.jpg (84.8 KB, 71 views)
__________________
Bob M.
"Arrange Whatever Pieces Come Your Way."
  Reply With Quote
Old 3rd February 2013, 09:07 PM   #270
diyAudio Member
 
danielwritesbac's Avatar
 
Join Date: Nov 2007
Quote:
Originally Posted by bcmbob View Post
But I'm glad you caught it. That's why I posted what I have before heating up the soldering iron. Also the red PS in the same post has a cap in a similar spot, so some more clarification may be needed. Are you suggesting that specific cap be completely eliminated. . .
Yes, that 100n can be eliminated. Let's call it "TBD" (to be determined) status. You may want something as small as 22n polyester dip (not box) cap, or as large as 2u electrolytic. . . or no extras at all. There's no telling until after an audio amplifier is connected.
The wrong cap can really put a dreadful kink in the treble, but omission does not have that risk. For sure you'll want to try the power supply, first, without that extra cap.
__________________
Tools, Models & Software for DIYClipNipper boostLM1875 TurboPowerful TDA7293 kitTDA7294 pt2pt ♦ My post has opinion.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
OPtimizing the VBE MUltiplier fglabach Solid State 41 17th January 2013 01:27 PM
Optimizing active crossover atledreier Multi-Way 27 19th August 2011 02:53 PM
optimizing the VBE multiplier hienrich Solid State 80 29th November 2010 10:25 PM
Interesting linestage optimizing ideas PixelPlay Tubes / Valves 5 23rd June 2008 10:18 PM
optimizing for efficiency Dwiel Solid State 13 10th May 2005 09:31 PM


New To Site? Need Help?

All times are GMT. The time now is 09:10 PM.


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