Optimizing TDA7294 Output - Page 33 - 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 16th February 2013, 03:45 PM   #321
bcmbob is offline bcmbob  United States
diyAudio Member
 
Join Date: Dec 2009
Location: Bay City, Michigan
Made some progress on the TDA kit project. Added more metal to the heat management system and tidied up the power and signal wires. The build sounds great on the big speakers (shown here with mini 2496 DAC driving Sunflowers)

The new power supply made bigger improvements than I had anticipated. My biggest gripe with the stock build was a low ceiling before the sound got mushy on the top end, as well as what I interpret as IM distortion. For the most part, that lack of headroom is gone. The natural clarity and warmth of the chip can be heard well above 90% of the volume slider as opposed to trouble near 65 - 70% with the old power supply. The amp is still limited in sparkle and shimmer compared to some of my LM3886 builds, but the dynamics are full and immediate. The low end sounds more stable and accurate but no sensation of extension is perceived. There is nothing missing but I'm used to a heavier bottom output from the MyRefs/FEs.

I'm adding a link to a "torture test" track I use for complexity and wide response. It has top end cymbal/cymbal bell, pure tone sounds in all ranges, active - sometimes heavy bass activity and wide dynamic changes. Everything you hear in the middle is super with the new PS. If my wishes were granted there would be a bit more grunt on the kick drum and bass, Dario's FEs really shake the floor with engulfing resonance on those low runs. Better definition of the segment containing the shaker along with some improvement in depth of stage might well be a mater of component choice. I don't know how much PCB design effects those two elements. The piano runs on the track are clean, musical, warm and accurate. I think that's the audio segment this chip can handle best - almost perfect to my ears.

So the next step is Daniel's bottleneck. I'm wondering if I can use one of the 220 uF caps I have instead of two 100s. The pic shows what I found in the stash.

I put some resistors in my Mouser cart as part of the power supply upgrade and snubbers but am wondering if that provides anything more that a voltage match. After the break-in I'm reading +32.2 VDC and -32.19 (sometimes flashing to -32.2) There is no problem adding the snubbers if it is still recommended.

Great work on the power supply Daniel - a very significant improvement.

Torture Track download
Attached Images
File Type: jpg 20130216_081304.jpg (146.4 KB, 205 views)
File Type: jpg 20130216_081722.jpg (84.6 KB, 195 views)
File Type: jpg 20130216_083753.jpg (246.6 KB, 192 views)
File Type: jpg 20130216_083726.jpg (608.6 KB, 186 views)
File Type: jpg Caps Choice.jpg (43.0 KB, 172 views)
File Type: jpg Bk_fx.jpg (172.3 KB, 73 views)
__________________
Bob M.
"Arrange Whatever Pieces Come Your Way."
  Reply With Quote
Old 17th February 2013, 05:17 AM   #322
diyAudio Member
 
danielwritesbac's Avatar
 
Join Date: Nov 2007
Quote:
Originally Posted by bcmbob View Post
The amp is still limited in sparkle and shimmer compared to some of my LM3886 builds, but the dynamics are full and immediate. The low end sounds more stable and accurate but no sensation of extension is perceived. There is nothing missing but I'm used to a heavier bottom output from the MyRefs/FEs.
We're not quite done with the power circuit. Louder mids at the amplifier board power circuit sounds exactly like poor treble combined with poor bass.

With your report of both insufficient bass and treble, I recommend increasing the 22u amplifier board power caps up to 220u caps before proceeding with other small signal fine tuning. On your board, this is the pair of caps located at the DC screw terminals of the amplifier board. The only reason I can think of for the kit to have come with such a bizarre value is that the smaller caps aren't as easily flattened in the mail.

For example 100u would be slightly too small (albeit quite clear at the cost of the mids being somewhat louder than both treble and bass), so I've no idea why that kit board has 22u, which is not really valid.

For TDA7294, amp board power caps of 470u would be too large and maybe dull, so at that point you'd need to step back, try the rail to rail cap and possibly try multiple parallel 100u caps or parallel 220u caps. But, I think that simply swapping the 22u for 220u and then using a rail to rail cap, could be a home run.

For example, if you want to use small power caps on the amp board (not smaller than 100u), then a great trick to turn down the mids while increasing resolution is one ~2u polyester cap from V+ to V- (rail to rail) at the DC power terminals of the amplifier board.

EDIT: On your caps photo, I see some 50v compact 220u caps that could be ideal for amplifier board power caps (to replace that pair of 22u located at the amp board DC terminals). We must undo the shout at the power circuit before removing the extra warm bottleneck at small signal.


After turning down the midrange loudness at the power circuit so that we have a chance at hearing the bass and treble, then we can try a couple of other things.
Fix the bootstrap cap bass blocker (install 47u).
Fix the NFB-shunt cap bass blocker (see post#27).
Fix the treble:
You can head over to the Radio Shack for some of the 10n (0.01u) and 22n (0.022u) little green polyester caps and try them in parallel with Input cap and NFB-shunt cap to get that treble sparkle.
Quote:
Originally Posted by bcmbob View Post
There is no problem adding the snubbers if it is still recommended.
Snubbing the transformer's secondaries is for audio quality and that is recommended. This is closing the barn door Before the horse gets out. It can probably help the DAC too, because it is highly effective on both unregulated and regulated power supplies.
__________________
Tools, Models & Software for DIYClipNipper boostLM1875 TurboPowerful TDA7293 kitTDA7294 pt2pt ♦ My post has opinion.

Last edited by danielwritesbac; 17th February 2013 at 05:41 AM.
  Reply With Quote
Old 17th February 2013, 05:16 PM   #323
bcmbob is offline bcmbob  United States
diyAudio Member
 
Join Date: Dec 2009
Location: Bay City, Michigan
Hey Daniel - et al.,

I'm up against a conflict I thought might develop. I'm not the best Mouser searcher, but the smallest 220uF 50V cap I see is 10mm in diameter - as are those in my posted photo. Mounting those near the DC terminals is possible but somewhat kludgey. Those alone are acceptable but I'm anticipating additional component swaps might result in quite a conglomeration.

My original thought about upgrading the existing kit/board had the intention of staying close to the format/footprint as shipped from the vendors. I have no doubt that Daniel's suggestions will produce the improvements, as evidenced by the great PS results, but I fear trying to pack too much in a small area might be a questionable path. This is based on the assumption that a new larger board is still in the offing and might better accommodate a wider selection of components.

With all the other amp builds around my castle , considering this kit as a bench/experimental project is certainly valid and will provide needed learning opportunities for me. I am however somewhat concerned that we are singing a duet and other potential builders may not desire to join in at this point.

So let me pose a couple questions.

Are there some DIYers watching the thread with the intention of buying/upgrading the existing kit. If so please let us know.

Haven't heard from KSTR and others about any new PCB developments in a while. So is there any new information/progress available on that front?

Is there interest in moving toward a P2P project for experimenting while the new design is being developed. That is an approach that I intend to do at some point just because it sounds like fun.

So please consider this post an opportunity to calibrate our direction and collect any thoughts that might be floating around. What say ye all?


P.S. I still firmly believe the TDA7294 is a real gem. It reminds me of what I used to say about my daughter-in-law when I was mad at her: "A little Sherman tank on roller skates"
__________________
Bob M.
"Arrange Whatever Pieces Come Your Way."
  Reply With Quote
Old 17th February 2013, 07:35 PM   #324
SoIL4x4 is offline SoIL4x4  United States
diyAudio Member
 
Join Date: Nov 2011
Location: Carterville, IL
Bob, I have been following this thread and the p2p thread closely (though the p2p thread seems to have gotten a little off track). I am wraping up a couple of other projects right now, but when they are singing it wont be long until I will have to start another (DIY is compairable to chain smoking, hopefully better for you though ).

I would be interested at some point in an optimized board, but like you the p2p project sounds like fun, and I think that is what I will go forward with. This week I recieved a mouser order that among other things included a pair of TDA7294 chips and a few of the items for the amplifier circuit. I also have a few of the caps etc. on hand allready so I will order the rest when I go through my inventory and see what I do and dont have. Aside from assorted wire, I have none of the elements of the power supply and I am still going back and forth on what value cap I will use. A dual mono power supply will be costly with above average components, but I think definately worth it. With that in mind it may be a few weeks before I am ready to really get started, but this project in some form will be the next.

hopefully I will have more to contribute, but in the meantime I will be following along.
__________________
Will.
  Reply With Quote
Old 17th February 2013, 07:59 PM   #325
bcmbob is offline bcmbob  United States
diyAudio Member
 
Join Date: Dec 2009
Location: Bay City, Michigan
Thanks Will,

Looking forward to hearing how you progress. I lucked out on the PS as I already had half the 3300 uF caps and more LEDs than needed. If/when the new PCB shows I think it will be well worth investing in discrete power supplies if in fact that is recommended. I'm hooked and am anticipating the next level of sophistication beyond what I built.

Thanks for keeping in touch.
__________________
Bob M.
"Arrange Whatever Pieces Come Your Way."
  Reply With Quote
Old 17th February 2013, 10:04 PM   #326
bcmbob is offline bcmbob  United States
diyAudio Member
 
Join Date: Dec 2009
Location: Bay City, Michigan
Thumbs up No Green Smoke

As luck would have it the only 220/50 caps on hand were used, with little stubs for leads. But the handy-dandy Dremell tool (cut off some green plastic), pointy needle nose pliers and a tiny drill got everything to fit.

The board with the new caps runs ~ 3-4 degrees warmer topping out at 84 on the chip flange. HS is ~ 91 with the bulb tester.

I'll let it marinate for a time tonight on the tester and the bench speakers while I create some good mono tracks for comparative tests in the morning.

Upwards and onward.
Attached Images
File Type: jpg 20130217_164717.jpg (128.4 KB, 63 views)
File Type: jpg 20130217_174356.jpg (201.2 KB, 246 views)
File Type: jpg 20130217_171205.jpg (166.8 KB, 50 views)
File Type: jpg 20130217_171221.jpg (197.0 KB, 59 views)
File Type: jpg 20130217_173130.jpg (338.7 KB, 54 views)
__________________
Bob M.
"Arrange Whatever Pieces Come Your Way."
  Reply With Quote
Old 17th February 2013, 10:13 PM   #327
diyAudio Member
 
danielwritesbac's Avatar
 
Join Date: Nov 2007
Quote:
Originally Posted by bcmbob View Post
. . . The new power supply made bigger improvements than I had anticipated. My biggest gripe with the stock build was a low ceiling before the sound got mushy on the top end, as well as what I interpret as IM distortion.
For the most part, that lack of headroom is gone.
The natural clarity and warmth of the chip can be heard well above 90% of the volume slider as opposed to trouble near 65 - 70% with the old power supply. . . .
Great work on the power supply Daniel - a very significant improvement.
You did very nicely with the build quality too!!
With the 200va transformer, I estimate that it is probably safe to hook up those 4 ohm speakers.
Quote:
Originally Posted by bcmbob
I'm up against a conflict I thought might develop. I'm not the best Mouser searcher, but the smallest 220uF 50V cap I see is 10mm in diameter - as are those in my posted photo. Mounting those near the DC terminals is possible but somewhat kludgey. Those alone are acceptable but I'm anticipating additional component swaps might result in quite a conglomeration.
Well, sir, the kit is tuned to create enough 2nd order harmonic distortion, warm midbass bloom to be loud enough to level out with the loud mids problem of the 22u power caps. This comes at the cost of bass extension. So, to unscrew that problem, grab the 220u caps, take aim, and push! After you get that done, we can lower the pitch of the feedback-shunt RC to enable higher resolution bass.

With any change to larger caps, the temps will go slightly warmer until the rail-to-rail cap is installed, which, if the right size/cap is found, will decrease midrange loudness (more room to tune up for bigger bass), clarify midrange, and decrease temps.
__________________
Tools, Models & Software for DIYClipNipper boostLM1875 TurboPowerful TDA7293 kitTDA7294 pt2pt ♦ My post has opinion.

Last edited by danielwritesbac; 17th February 2013 at 10:15 PM.
  Reply With Quote
Old 17th February 2013, 10:19 PM   #328
diyAudio Member
 
danielwritesbac's Avatar
 
Join Date: Nov 2007
Need to finish soldering the pin7 jumper?
If the predrive goes missing the V+, it might become annoyed or have a fit.
Click the image to open in full size.
While you're at it, you can relocate the feedback resistor off the board, and then, onto the chip from pin2 to pin14 (trackside, under board, right at the chip).
__________________
Tools, Models & Software for DIYClipNipper boostLM1875 TurboPowerful TDA7293 kitTDA7294 pt2pt ♦ My post has opinion.

Last edited by danielwritesbac; 17th February 2013 at 10:22 PM.
  Reply With Quote
Old 17th February 2013, 10:28 PM   #329
bcmbob is offline bcmbob  United States
diyAudio Member
 
Join Date: Dec 2009
Location: Bay City, Michigan
Thanks Daniel,

That pin has solder, just not enough Just fixed it. I'll hook up and listen tomorrow. Carpets couldn't handle another walk-through so everything is all tore up and drying.

O.K. I'll do the resistor in the morning.
__________________
Bob M.
"Arrange Whatever Pieces Come Your Way."

Last edited by bcmbob; 17th February 2013 at 10:30 PM.
  Reply With Quote
Old 17th February 2013, 10:57 PM   #330
diyAudio Member
 
danielwritesbac's Avatar
 
Join Date: Nov 2007
The NFB-shunt cap size has improved and will allow more bass to pass intact, however fully utilizing that also takes the right size feedback-shunt resistor. Although the 50v caps might (or might not) be better, you can actually use 25v caps at small signal if you need something physically smaller. This is "inverting input cap" and takes the same amount of care and experimentation as any input cap. And, it is big.
Therefore. . .
Treble quality:
You'll really want to experiment with some little treble bypass caps in parallel with your NFB-shunt cap.
Although any single large value cap can have its treble patched up to excellence by much experimentation for finding a just right bypass cap for it. . . you might prefer the speed and ease of identical models of parallel 100u caps to get a 200u value without the bother of lengthy experimentation.
__________________
Tools, Models & Software for DIYClipNipper boostLM1875 TurboPowerful TDA7293 kitTDA7294 pt2pt ♦ My post has opinion.

Last edited by danielwritesbac; 17th February 2013 at 11:09 PM.
  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 12:45 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