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Old 28th May 2013, 01:25 PM   #481
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Well, amplifiers can sound different from one another; however, the adjustable schematic at the bottom of post#474 can be set for system symmetry or you could dial it in to imitate a different amplifier if you wanted to.

The parallel amp can use a larger input cap and should use a larger bootstrap cap; but otherwise, the solo and parallel (master chip) can use that same schematic.

I'm actually removing LM3886's from my integrated receiver and installing Parallel TDA7293 boards. Indeed the LM3886's are clearer at the cost of more forwards (great for analytics, voicecomm and movie soundtracks) and have the name brand hard clipper, SPIKE system noise as well. Personally, I don't need those television amplifier features in my integrated receiver. And, I believe that the Parallel TDA7293 boards are more significant for rocking the house with music, because that amp can run to the rails and maintain a palatable tone in all conditions. I think that since the usage is so much different, the LM3886 and TDA7293 are not really 1:1 comparable. The ST part, on usage, is most likely to direct-replace STK chips and inexpensive tube amplifiers, for music replay, but definitely not for the clearest voice track on your television. Natsemi markets the LM3886 for television movie soundtracks and they were wise to do so because it excels at replaying extra intelligible voicecomm (at some cost to tone).

If we want both of the above features simultaneously from 1 chip amplifier, the makers of LM3886 (National Semiconductor division of Texas Instruments) suggests that we upgrade to LME49830 if music replay is desired. However, ST suggests that we take the Parallel TDA7293 board, set BOTH chips to slave mode for zero gain (input is then pin#11, and the feedback loop is relocated) and drive these rather inexpensive lateral fet packs ($1.90 ea @10 units each of which contain 2 latfets) with a replacement voltage amplifier stage, which can be made of tubes like Akido, or BJT, like the SSA, or small signal chips.
Natsemi/TI makes highly favorable made-for-music (awesome "made for using" devices that are far better quality than "made for selling" devices) LME chip amplifiers, and ST makes inexpensive latfet packs that are unlikely to have an availability shortage. So, of course I'm curious if a "shotgun wedding" can be arranged?

Instead of a have your cake and eat it too scenario, what I currently have is some LM1875's for analytical purposes and relaxed SPL listening at superb quality. Although they may be frail, the LM1875's are getting the job done for my analytic purposes.

After the LM3886's are evicted from the receiver, I may attempt a fine tuning on those because they are indeed capable of superior imaging. They can beat the LM1875's on imaging but not on tone (and the basic "resolution" appears to be nearly break even). In that comparison, the LM1875's are more suited to mixer desk and near field needs, but the LM3886's are certainly better at distance. However, that receiver has been unplugged for some years on account of unfriendly tone when cranked up loud with the LM3886's. This has made the volume control some odd 75% useless, since it is fantastic at low volume but almost broken bone painful when turned up loud. Well, of course, I'm absolutely certain that the TDA7293 Parallel boards can beat the LM3886's in that one performance aspect (when small venue and high SPL meet, aka "rockin the house").

SO, to try for an answer to your question:
The ideal usage for the TDA7293 versus the LM3886 varies so greatly that it is like apples and oranges. It would be possible to say which is better if given a specific application, but otherwise they're impossible to compare.
On the second part of your post, most chip amplifiers show exactly the same 22k vs 1k or 22k vs 680R with some odd random caps for generic datasheet schematic. . . despite the fact that the chips differ in internal design. Be careful! That sort of generic schematic is for showing where the parts should go. But the component values are nonspecific/generic, and that may cause overheat, sound like a caffeinated Basset Hound, install a severe bass blocker, cause audible distortion or even cause breakage. I would not be able to explain this thoroughly, since I'm not an engineer, so here's Eddie on the topic of changing the generic schematic to something more specific that supports the chips:
Quote:
Originally Posted by Fast Eddie D View Post
Well I got it out because I intend to add a preamp (tone controls etc) to it so it is a truly integrated amp. . . and found out that I have TDA7296 chips running off a 62 volt split supply.[a 31+31vdc split rail supply]. . .I used the same board that was in the "no-fi" tabletop stereo. I removed the ripple caps (2200uF per rail is all it had) and installed 330 uF caps on the board. I used a capacitor bank like Daniel's with 4x2200 uF per rail and it made a noticeable improvement. Then I swapped the bootstrap and feedback caps (it used the data sheet 22 uF caps with smaller feedback resistors - really terrible!) with 100 uF caps and it made a huge difference.. . .It works really great. . .I am truly inspired that such performance is available from such a generic chip by optimizing design and layout. . . .
Unabridged version is at post#354
Solo amp bootstrap cap range is 33u~47u.
Parallel amp bootstrap cap range is 68u~100u.
See also AndrewT's posts on the topic of NFB-Shunt cap sizing for clear quality bass.
Future plans for the TDA7293 Parallel involve begging Kean for some help on improving the imaging (indeed he can do that) because I'm a bit greedy when it comes to imaging; but, otherwise, and except for the need of clean power which was not difficult, the amp is excellent.

P.S.
That's about all the typing I'm good for today. My fingers are sore from the "house brand" of HTML and trying to outdo Google, which was, apparently, possible, albeit some effort to do it.
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Last edited by danielwritesbac; 28th May 2013 at 01:30 PM.
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Old 28th May 2013, 02:36 PM   #482
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That adjustable schematic at the bottom of post#474 has turned out to be really quite pleasant. Just now, I tried it with that rather bad single layer board, and it worked appreciably (at somewhat near 40x before the darned thing was practical). Of course, I'd much prefer to use the TDA7293 Parallel dual layer compact board; however, the single layer solo TDA7294 board was more educational in the form of a challenge.
P.S.
I'm pretty much in "on break" status, except for refitting that one receiver for the purpose of rocking the house.
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Old 29th May 2013, 11:59 PM   #483
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Quote:
Originally Posted by redjr View Post
Let us know when you get it hooked up. I'm getting too many TDA* based amps around here myself - with too little time to work on them. Plus a move to CT coming up this Summer. Might grab a couple of these for fun!
I put together a ps with a 28-0-28 transformer I salvaged from and old SS amp and connected up the 7294. Absolutely dead silent.
I cannot detect any sonic advantage over the 7297 I was using except for it's annoying blue led.
I tried several speakers I have laying around.
RS Minimus 8, RS minimus 7, PSB 30 MKII (which I recently refoamed)
Dual CL172 (placed among the top in huge 1976 speaker soundoff in Japan) and my regular Tannoys.
All the speakers are getting on in years, if that makes a difference? but, to me, the bigger the speaker the better the sound.
I've switched back to the 7297, it runs cooler with just an excuse for a heatsink and ps.
Not being compentent enough to be modder, I wonder if changing a few periferal components on these little amps makes the kind of difference that speakers can make?
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Old 30th May 2013, 04:34 AM   #484
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Talking What you say about this design?

Quote:
Originally Posted by tiefbassuebertr View Post
What you say about this design?

APEXAUDIO
Attached Images
File Type: jpg BRIDGE TDA7294 SD 400%.JPG (254.2 KB, 494 views)
File Type: jpg TDA7294 BRIDGE 400%.JPG (331.0 KB, 483 views)
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Old 31st May 2013, 11:23 AM   #485
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Quote:
Originally Posted by SERGIODS View Post
What you say about this design?

APEXAUDIO
nice !!! I like the elco arrangement, very neat !

This is mine, a 3 channel amp using 3886 for high/mid and a 7293 for the unabridged lows as the 3886 spike doesn't like my woofer It's based on a 100x80 mm doubleside board, is still under construction because next to a 3ch substractive filter, limiter and dc protection I also like to add some automatic on/off logic.

Click the image to open in full size.

But the get back on topic : I've seen 7293 designs where the driver and final stage rails were separated using diodes, anybody anything to say on that ???
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Last edited by chriscam; 31st May 2013 at 11:30 AM. Reason: logic
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Old 31st May 2013, 12:14 PM   #486
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Quote:
Originally Posted by chriscam View Post

But the get back on topic : I've seen 7293 designs where the driver and final stage rails were separated using diodes, anybody anything to say on that ???
This has been brought up so many times. There are also several replies on older threads. You should search for TDA7294/7293 and look for threads a few years old ! It was explained beautifully by ilimzn !
Search for a thread called 'TDA7293v' June 2002 ! Ilimzn posted sometime in April 2006 !
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Old 31st May 2013, 08:13 PM   #487
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Quote:
Originally Posted by ashok View Post
This has been brought up so many times. There are also several replies on older threads. You should search for TDA7294/7293 and look for threads a few years old ! It was explained beautifully by ilimzn !
Search for a thread called 'TDA7293v' June 2002 ! Ilimzn posted sometime in April 2006 !
this one?
Tda7293v
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Old 31st May 2013, 08:22 PM   #488
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Quote:
Originally Posted by danielwritesbac View Post
Well, amplifiers can sound different from one another; however, the adjustable schematic at the bottom of post#474 can be set for system symmetry or you could dial it in to imitate a different amplifier if you wanted to.

The parallel amp can use a larger input cap and should use a larger bootstrap cap; but otherwise, the solo and parallel (master chip) can use that same schematic.

I'm actually removing LM3886's from my integrated receiver and installing Parallel TDA7293 boards. Indeed the LM3886's are clearer at the cost of more forwards (great for analytics, voicecomm and movie soundtracks) and have the name brand hard clipper, SPIKE system noise as well. Personally, I don't need those television amplifier features in my integrated receiver. And, I believe that the Parallel TDA7293 boards are more significant for rocking the house with music, because that amp can run to the rails and maintain a palatable tone in all conditions. I think that since the usage is so much different, the LM3886 and TDA7293 are not really 1:1 comparable. The ST part, on usage, is most likely to direct-replace STK chips and inexpensive tube amplifiers, for music replay, but definitely not for the clearest voice track on your television. Natsemi markets the LM3886 for television movie soundtracks and they were wise to do so because it excels at replaying extra intelligible voicecomm (at some cost to tone).

If we want both of the above features simultaneously from 1 chip amplifier, the makers of LM3886 (National Semiconductor division of Texas Instruments) suggests that we upgrade to LME49830 if music replay is desired. However, ST suggests that we take the Parallel TDA7293 board, set BOTH chips to slave mode for zero gain (input is then pin#11, and the feedback loop is relocated) and drive these rather inexpensive lateral fet packs ($1.90 ea @10 units each of which contain 2 latfets) with a replacement voltage amplifier stage, which can be made of tubes like Akido, or BJT, like the SSA, or small signal chips.
Natsemi/TI makes highly favorable made-for-music (awesome "made for using" devices that are far better quality than "made for selling" devices) LME chip amplifiers, and ST makes inexpensive latfet packs that are unlikely to have an availability shortage. So, of course I'm curious if a "shotgun wedding" can be arranged?

Instead of a have your cake and eat it too scenario, what I currently have is some LM1875's for analytical purposes and relaxed SPL listening at superb quality. Although they may be frail, the LM1875's are getting the job done for my analytic purposes.

After the LM3886's are evicted from the receiver, I may attempt a fine tuning on those because they are indeed capable of superior imaging. They can beat the LM1875's on imaging but not on tone (and the basic "resolution" appears to be nearly break even). In that comparison, the LM1875's are more suited to mixer desk and near field needs, but the LM3886's are certainly better at distance. However, that receiver has been unplugged for some years on account of unfriendly tone when cranked up loud with the LM3886's. This has made the volume control some odd 75% useless, since it is fantastic at low volume but almost broken bone painful when turned up loud. Well, of course, I'm absolutely certain that the TDA7293 Parallel boards can beat the LM3886's in that one performance aspect (when small venue and high SPL meet, aka "rockin the house").

SO, to try for an answer to your question:
The ideal usage for the TDA7293 versus the LM3886 varies so greatly that it is like apples and oranges. It would be possible to say which is better if given a specific application, but otherwise they're impossible to compare.
On the second part of your post, most chip amplifiers show exactly the same 22k vs 1k or 22k vs 680R with some odd random caps for generic datasheet schematic. . . despite the fact that the chips differ in internal design. Be careful! That sort of generic schematic is for showing where the parts should go. But the component values are nonspecific/generic, and that may cause overheat, sound like a caffeinated Basset Hound, install a severe bass blocker, cause audible distortion or even cause breakage. I would not be able to explain this thoroughly, since I'm not an engineer, so here's Eddie on the topic of changing the generic schematic to something more specific that supports the chips:

Unabridged version is at post#354
Solo amp bootstrap cap range is 33u~47u.
Parallel amp bootstrap cap range is 68u~100u.
See also AndrewT's posts on the topic of NFB-Shunt cap sizing for clear quality bass.
Future plans for the TDA7293 Parallel involve begging Kean for some help on improving the imaging (indeed he can do that) because I'm a bit greedy when it comes to imaging; but, otherwise, and except for the need of clean power which was not difficult, the amp is excellent.

P.S.
That's about all the typing I'm good for today. My fingers are sore from the "house brand" of HTML and trying to outdo Google, which was, apparently, possible, albeit some effort to do it.
My question to this good eplanation are to read here (post #22):
lm3886 tda7293 tda1514
thank you therefore.
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Old 1st June 2013, 02:57 AM   #489
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Quote:
Originally Posted by tiefbassuebertr View Post
this one?
Tda7293v
Yes.
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Old 2nd June 2013, 02:04 AM   #490
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Originally Posted by bcmbob View Post
Well see, we already have a problem. My life's goal is to wipe out all amlpified guitars (except Wes Montgomery & Barney Kessell of course) and convert all those musicians to brass and woodwind instruments. (read - Chicago, Blood Sweat & Tears)


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