Optimizing TDA7294 Output - Page 46 - 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 9th May 2013, 01:12 AM   #451
boroson is offline boroson  United States
diyAudio Member
 
Join Date: Feb 2008
I have two final questions before ordering the last of the parts.
1) Is the 2.2uf cap on the input a non-polarized electrolytic such as I use for speaker crossover work
2) Is the resistor in parallel with the speaker output 6.8ohm or 6.8kohm. I feel it is the latter but want to be sure. Or should this value be varied depending upon the impedance of the speaker
  Reply With Quote
Old 9th May 2013, 01:13 AM   #452
boroson is offline boroson  United States
diyAudio Member
 
Join Date: Feb 2008
Excuse me, the resistor should be the former or 6.8ohm.
  Reply With Quote
Old 9th May 2013, 02:54 AM   #453
diyAudio Member
 
danielwritesbac's Avatar
 
Join Date: Nov 2007
You can use the output RC that comes with the kit. No need to buy more. The value can be varied somewhat, depending on need. Most reasonable values outperform omission by far.

The input cap can be 1uF, 1.47uF or 2.2uF, so I suggest to collect some of the little green Bipolar Nichicon ES series, in sizes, 0.47u, 1u, and 2.2uF to test drive and find out which you like. They're very high resolution performers at low cost.
For input cap there exists other charming options, such as an Elna Cerafine in parallel with a tiny value polyester.

I've used the 0.47uF little green Nichicon ES bipolar electrolytic in parallel with my NFB-shunt cap for enhanced clarity. It is generally trouble-free for use as a bypass cap. A really ordinary 1uF electrolytic cap *may* do a similar job for bypass tasks.

Ah, but don't forget to get multi-turn cerment trimmers (little blue box) in either 100R or 200R value. In three days of soldering effort with resistors, the best performance was from the schematic that shows the trimmer.
__________________
Tools, Models & Software for DIYClipNipper boostLM1875 TurboPowerful TDA7293 kitTDA7294 pt2pt ♦ My post has opinion.

Last edited by danielwritesbac; 9th May 2013 at 02:59 AM.
  Reply With Quote
Old 9th May 2013, 03:40 PM   #454
boroson is offline boroson  United States
diyAudio Member
 
Join Date: Feb 2008
I'll do it. Thanks.
  Reply With Quote
Old 9th May 2013, 10:19 PM   #455
diyAudio Member
 
danielwritesbac's Avatar
 
Join Date: Nov 2007
A collection of boards by the same artist:
TDA7294 solo: TDA7294 65W Mono Amplifier Board Kit 28 | eBay
TDA7293 solo: 1 PC x Assembled Finished 85W TDA7293 Mono Power Amplifier Board Support BTL | eBay
TDA7293 Parallel: TDA7293 x2pcs 170W Mono Amplifier Board Kit 29 | eBay
TDA7293 Triple: TDA7293 x3 BTL 250W Mono Amplifier Kit 26 | eBay

These seem to share one flaw: The feedback-shunt resistor is arranged decoratively/mistakenly, causing a weird metallic tone. The fix: When you move the feedback-shunt resistor and the feedback resistor to under-board, extremely close to the (master) chip, the "sound of the board" influence is subtracted. That indicates the rest of the layout, especially power layout, is working well.

-----------AND-----------

So far, progress on the TDA7293 Parallel amp. . .
It works without supplementary compensation added; however, I'll be trying out some new compensation from Keantoken to see about the resolution and imaging possibilities.

Consider the attached schematic a work in progress as it is not quite finalized. Without using supplementary compensation, it is stabilized by gain and it sounds best stable. It does play rather nicely. A 100R or 200R cerment trimmer (little blue box) is good and with no "wrong" setting, just dial it in for pretty audio (and definitely not an arbitrary gain setting). Suggested trimmer startup value is exactly 50 ohms (if your power board is driven from a 25+25vac transformer like mine and if your speaker is 8 ohms like mine).
Input load is marked "TBD" and plausible range of input load is from 12K to 27K whereby the 12K is more forwards or the 27K is more laid back, so adjust within that range as you like. The plan of adding compensation should broaden the range of the "sweet spot" and make the amplifier easier to adjust and use, and I'm working on that.
This is the one I'm using to refit my receiver, and since the receiver's power circuit is slightly different, including voltage, I'll definitely be needing the trimmer to dial in for audio quality.
Attached Images
File Type: gif TDA7293-proto.gif (18.3 KB, 278 views)
__________________
Tools, Models & Software for DIYClipNipper boostLM1875 TurboPowerful TDA7293 kitTDA7294 pt2pt ♦ My post has opinion.
  Reply With Quote
Old 14th May 2013, 12:06 AM   #456
bcmbob is offline bcmbob  United States
diyAudio Member
 
Join Date: Dec 2009
Location: Bay City, Michigan
Hey Guys, for those of us interested in a new PCB for this project, I did get a reply from Klaus. As with all of us, he has activities and commitments beyond the fun audio DIY projects we all enjoy so much. No doubt when things balance out he will become active again - but that won't be anytime soon. Not a problem.

Daniel has given us much to explore and I for one, need and will take the time to develop that path for now. Anyone wishing to present ideas beyond that, or extensions of Klaus's comments are certainly encouraged to do so.

Thanks All !
__________________
Bob M.
"Arrange Whatever Pieces Come Your Way."
  Reply With Quote
Old 15th May 2013, 02:44 AM   #457
diyAudio Member
 
danielwritesbac's Avatar
 
Join Date: Nov 2007
The TDA7293 parallel turned out to be a bit better performer, I think.
Starting here: TDA7293 Parallel board thread
I'm doing up some build photos like these:

How to relocate the feedback resistor and the feedback shunt resistors
Click the image to open in full size.


How to fit a large size nfb-shunt cap and antiparallel 1N4007's.
If a 680u is unavailable, a pair of 330u or trio of 220u will fit for 660u.
Not shown: treble bypass, 1u or 0.47u electrolytic, fits under-board
Click the image to open in full size.



P.S.
Coming up soon, next photo up (there-->: TDA7293 Parallel board thread <--link), should be the task of fitting MOAR 220u power caps and a couple of big diodes on such a small board. I believe it works about like this: MBR (0.25v) schottky with 220u or less per rail; OR, MR/MUR (0.47v) fast silicon with 440u or less per rail; OR 6A05 (0.65v) standard silicon with 660u or less per rail. In this case, simple 6A05's from the Radio Shack, seem most useful because they work for All of the examples. However, from the farm, the Radio Shack and 6A05's are 108 mile round trip drive. Sometime this week, I'll probably make that drive.
__________________
Tools, Models & Software for DIYClipNipper boostLM1875 TurboPowerful TDA7293 kitTDA7294 pt2pt ♦ My post has opinion.

Last edited by danielwritesbac; 15th May 2013 at 02:47 AM.
  Reply With Quote
Old 15th May 2013, 06:29 AM   #458
tyger23 is offline tyger23  United States
diyAudio Member
 
Join Date: Nov 2010
Guys - just FYI. I built in Daniel's circuit on top of my AudioSource AMP-100. Essentially, this is a mono TDA7294 for each side. I want to thank you guys for all the hard work that's being done.

I did want to report back, though, that the "lead lag compensation" circuit is a really bad idea. I took a frequency response curve of the amp and there's a ~+10dB boost at around 20KHz with this circuit in place. No, that's not a typo. Basically this circuit seems to be creating an over-damped filter, and the ringing occurs smack dab in the treble region.

FWIW - I had used a 15 ohm + 68nF.

When I removed this circuit, the FR curve went back flat. I'll post pictures tomorrow when I get back to work and have access to my AP again.

I did verify that the issue is in the amp circuit only. None of the other preamp circuits on the AUDIOSOURCE are presenting the same boost. So, the issue is wholly with the amp.

I would recommend that someone else try this test - it's pretty easy.

With the desired circuit in place, play a 997Hz sine wave. Measure the output from your source and also measure the output from the amp. Then play a 19000Hz sine wave. Again, measure the output from the source and measure the output from the amp.

Essentially, you should see no differences whatsoever in the RMS voltage level for either measurement. If the level is changing coming out of your source, then your source (like a computer) likely has some processing applied. Find a different source, or remove the processing. If the level is changing out of the amp, then something is wrong with the circuit of the amp. This latter case is what I discovered.

Again, I'll post back tomorrow...

Last edited by tyger23; 15th May 2013 at 06:32 AM.
  Reply With Quote
Old 15th May 2013, 07:51 AM   #459
diyAudio Member
 
danielwritesbac's Avatar
 
Join Date: Nov 2007
Thank you! Question: If you change the cap, progressively smaller, what's the biggest size cap you can use and still get a flat response?
It'll be smaller than 68n for sure.

P.S.
We're planning to use a different type of compensation for the TDA7293 Parallel amp, not lead lag.
__________________
Tools, Models & Software for DIYClipNipper boostLM1875 TurboPowerful TDA7293 kitTDA7294 pt2pt ♦ My post has opinion.
  Reply With Quote
Old 15th May 2013, 05:03 PM   #460
tyger23 is offline tyger23  United States
diyAudio Member
 
Join Date: Nov 2010
OK - So here's the data requested. Again, I'm doing this on an AudioSource AMP-100, which is essentially the same as a mono TDA7294 per channel. I've verified that none of the preamp circuits in the amplifier are affecting the signal, so these frequency response graphs are wholly the responsibility of the TDA7294 circuitry chosen.

My circuit matches Daniel's last one posted (on page 43 or 44 I think) with the exception of the fact that I used a 1000uF NFB capacitor instead of a 680uF, and I used a single 732-ohm feedback shunt resistor instead of a 510+220 solution.

Personally, I would remove the lead-lag compensation all together. It is creating an over-damped low-pass filter with significant ringing. I cannot fathom why this circuit would aid the chip in any way. The only reason I can contemplate is if your power supply is extremely noisy and tanking the out-of-band noise is providing some benefit.

However, the power supply on my Audiosource AMP-100 is pretty decent, and the ones being designed by Bob and others are far superior to that. So - again, I say remove it, but you guys can make your own decision. If you want to leave it, I would recommend NO MORE than 4.7nF.

Here is the picture of the 15R + 68nF.
Click the image to open in full size.

Here is one channel with 47nF and the other with 27nF.
Click the image to open in full size.

Here is 10nF and 5.6nF. It shows roughly +12dB at 20KHz:
Click the image to open in full size.

Here is 2.7nF and 1nF:
Click the image to open in full size.

Finally - here is NO lead lag compensation:
Click the image to open in full size.
Attached Images
File Type: jpg 1.jpg (133.5 KB, 254 views)
File Type: jpg 2.jpg (163.7 KB, 252 views)
File Type: jpg 3.jpg (151.4 KB, 251 views)
File Type: jpg 4.jpg (150.9 KB, 252 views)
File Type: jpg 5.jpg (125.8 KB, 251 views)
  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 45 17th September 2014 07:22 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 01:15 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