Optimizing TDA7294 Output - Page 17 - 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 6th January 2013, 02:21 PM   #161
diyAudio Member
 
danielwritesbac's Avatar
 
Join Date: Nov 2007
Quote:
Originally Posted by KSTR View Post
TDAs did well in some standard "current pumps" and mixed output impedance amplifiers I designed. Howland type is critical because common mode voltage is high (67% of the output voltage in the MyRefs) and could exceed chip limits, which are unknown for the TDAs other than that the input stage cuts off when pulled to V-. True usable input CM range is something I want to find out in detail sometime, in comparison to the LMs. Both have not specified this parameter in their datasheets so we can only assume a guaranteed range of no more than about 1/10th of the ouput voltage plus some unknown headroom, depending on supply voltages and their balance.
I'm curious about the TDA7293, with the inputs shorted (per the datasheet's "modular" schematic), and used merely as output devices for current pump amplifier. It looks almost silly except much easier to heatsink than discrete SMD powerfets, costs less than rare latfets, and the chip amp also has stable production so that the design doesn't have to be changed every few months to accommodate parts availability.
But, that might be a topic for a different thread.
__________________
Tools, Models & Software for DIYClipNipper boostLM1875 TurboPowerful TDA7293 kitTDA7294 pt2pt ♦ My post has opinion.

Last edited by danielwritesbac; 6th January 2013 at 02:25 PM.
  Reply With Quote
Old 6th January 2013, 02:48 PM   #162
diyAudio Member
 
danielwritesbac's Avatar
 
Join Date: Nov 2007
Quote:
Originally Posted by redjr View Post
I think that might have been what happened, unless it was possibly heat related. But with no signal, I would suspect that the amp would not continue to heat up.
First of all, heat indicates an unhappy chip amp doing too much non-audio work, such as oscillation and/or simply affronted by power supply issues causing a lot of extra work when it tries to amplify that in addition to the audio.

Well, just consider that if it amplifies "only audio" then it should be running very cool.

Fortunately, while you're exploring options, this chip usually responds "the cooler the clearer" which is convenient and straightforward in getting both higher resolution audio and a cooler running amplifier, simultaneously.


P.S.
One way, and perhaps the easiest way, to compensate a chip amp is to increase the power amp gain a bit, and I wouldn't have suggested that except that the Zune MP3 player can perform better and more suitable to amplify when not straining to push a power amp. If you didn't want to change the gain, it is also possible to run a bit less feedback current by raising both the feedback resistor and feedback-shunt resistor to higher values proportionately. So, there's two different adjustments which can be explored. One is for voltage and the other is for current. This can be done separately or together, depending on need and results.
__________________
Tools, Models & Software for DIYClipNipper boostLM1875 TurboPowerful TDA7293 kitTDA7294 pt2pt ♦ My post has opinion.

Last edited by danielwritesbac; 6th January 2013 at 02:55 PM.
  Reply With Quote
Old 7th January 2013, 04:29 AM   #163
redjr is offline redjr  United States
diyAudio Member
 
Join Date: May 2011
Location: Danbury, CT
Quote:
Originally Posted by danielwritesbac View Post
First of all, heat indicates an unhappy chip amp doing too much non-audio work, such as oscillation and/or simply affronted by power supply issues causing a lot of extra work when it tries to amplify that in addition to the audio.

Well, just consider that if it amplifies "only audio" then it should be running very cool.

Fortunately, while you're exploring options, this chip usually responds "the cooler the clearer" which is convenient and straightforward in getting both higher resolution audio and a cooler running amplifier, simultaneously.


P.S.
One way, and perhaps the easiest way, to compensate a chip amp is to increase the power amp gain a bit, and I wouldn't have suggested that except that the Zune MP3 player can perform better and more suitable to amplify when not straining to push a power amp. If you didn't want to change the gain, it is also possible to run a bit less feedback current by raising both the feedback resistor and feedback-shunt resistor to higher values proportionately. So, there's two different adjustments which can be explored. One is for voltage and the other is for current. This can be done separately or together, depending on need and results.
Daniel - Where and how do you add a manual gain control to these little chipamps. Most of the ones I've built have not included any kind of gain control. I don't think it's as simple as adding a pot to the input either, but I have done that with one amp. Am I wrong? I would love to know the correct way to add a proper gain control and when they need to be used. I was using my Zune directly so that I could 'force' some level control on the amp.

My spanky new Doug Self preamp has plenty of gain. So much so, that I barely have to turn it up past 8:00 on the dial before it's blowing the walls down. There's literally no way to listen at lower volume levels without having some 'gain' control on my amps to compensate for the massive gain of my pre. Hence my dilemma with using the pre with (at least) the 7294.

I know we're going off topic a bit here... but if I intend to use the new pre with a certain power amp I build, then I need some way to limit the input voltage (gain/sensitivity) of the power amp. I would prefer for it to be variable, but a set, constant resistance would work to. Best approach?

Rick
__________________
redjr
  Reply With Quote
Old 7th January 2013, 06:13 AM   #164
diyAudio Member
 
ashok's Avatar
 
Join Date: Jun 2002
Location: 3RS
Default Optmizing the TDA7294

There are two mods that could be done to the TDA7294 to 'improve' it's performance and increase it's load handling capacity. Both have been covered long ago and only a good pcb needs to be made. Sure lots of members may have already done this as the topic is quite old !

Note that Ilimzn's wonderful explanation of the operation of the 7294 isn't new. He posted the information first in 2006 ! Not many seem to have read it/used it since then !

The concept of adding power driver transistors to the output has been bandied around for a very long time , to increase power handling of several chip amps.

So we just need to supply clean power to the input stage and add a pair of power transistors at the output to bump up the load capability to handle 4 ohms easily at high supply voltages.

I did work on a design but never got round to trying it and the attempt faded away with lots of distractions that arose in the meantime.
Maybe 2013 will bring back the urge to try it again ,especially as I bought several 7294 chips in 2006 !
__________________
AM
  Reply With Quote
Old 7th January 2013, 05:28 PM   #165
diyAudio Member
 
danielwritesbac's Avatar
 
Join Date: Nov 2007
Quote:
Originally Posted by redjr View Post
Daniel - Where and how do you add a manual gain control to these little chipamps. Most of the ones I've built have not included any kind of gain control. I don't think it's as simple as adding a pot to the input either, but I have done that with one amp. Am I wrong? I would love to know the correct way to add a proper gain control and when they need to be used. I was using my Zune directly so that I could 'force' some level control on the amp.

My spanky new Doug Self preamp has plenty of gain. So much so, that I barely have to turn it up past 8:00 on the dial before it's blowing the walls down. There's literally no way to listen at lower volume levels without having some 'gain' control on my amps to compensate for the massive gain of my pre. Hence my dilemma with using the pre with (at least) the 7294.

I know we're going off topic a bit here... but if I intend to use the new pre with a certain power amp I build, then I need some way to limit the input voltage (gain/sensitivity) of the power amp. I would prefer for it to be variable, but a set, constant resistance would work to. Best approach?

Rick
You need a non-dulling volume-range control?
Let's fake that feature from Lightspeed Attenuator, but at lower cost. . . Just get a 50K dual-gang (stereo) pot and experiment with adding resistors to both of the outboard pins so that it cannot either go up all the way nor down all the way. You can further experiment by adding a resistor load to the input side. Also get a sack of short length alligator clip leads and clips by themselves to help speed exploration. And then solder the results of your exploration using a miniscule bit of gel flux for assured connection quality. After some play, the volume-range control prospect makes a novel non-dulling potentiometer for about $4, which cost less than the lightspeed attenuator, with the same benefit of not dulling the audio and with the same caveat of limited range. This goes almost all the way up, almost all the way down.
Location: Potentiometers are bad at driving cables, so this sort of device must go in close proximity to the input of a power amp. You can make it as an accessory in a cute little box with input RCA jacks and up to 1 foot "pigtail" RCA cable for output. Or you can actually use it as a power amplifier's volume-range control to get the cable length shorter for somewhat better results.

Loud is loud; but, loud and good is a different matter.
It may be useful to straighten out the source device before amplifying. Discrete buffer is a fun and simple alternative to multi-op-amp projects. These measure at extremely low distortion for measuring equipment; but, to the ear, a good discrete buffer can be amazing. Location of a buffer is as close as possible to the source for which it is useful. A beneficial buffer may be hard to find since descriptions are probably not given in audiophile terms. Since we know that impedance adjustments can make buffers unnecessary, when you find an engineer who consistently uses his buffer design, he's caught red-handed with an excellent block-rocker device that you will very much enjoy. In my opinion, these buffers are a great way to improve the quality of the source that you already own, and more practical or at least considerably faster than a long search for the elusive perfect source, which will, of course have this sort of buffer built in. You can DIY that piece.

Since potentiometers are particularly bad at driving cables, I suggest to put the new volume-range control directly onto the Input of a nice buffer project. I also suggest individual "cancel" switches for both features, because those can be fun and informative to use; and, because any good hi-fi effect always has a cancel switch, no matter if you intend to use the switch or not. Personally, I would mark one switch "boost" and the other switch "turbo" just for fun.

Or like this:
Click the image to open in full size.
And do consider the buffer, because we need the signal good before the power amp makes it loud.
__________________
Tools, Models & Software for DIYClipNipper boostLM1875 TurboPowerful TDA7293 kitTDA7294 pt2pt ♦ My post has opinion.

Last edited by danielwritesbac; 7th January 2013 at 05:44 PM.
  Reply With Quote
Old 7th January 2013, 07:59 PM   #166
KSTR is offline KSTR  Germany
diyAudio Member
 
KSTR's Avatar
 
Join Date: Jul 2007
Location: Central Berlin, Germany
Quote:
Originally Posted by ashok View Post
So we just need to supply clean power to the input stage and add a pair of power transistors at the output to bump up the load capability to handle 4 ohms easily at high supply voltages.
This would be nice of course, but would surely file under "scope creep". My idea was more like trying to make an excellent but still simple standalone TDA7294 amp.

To get to a better (at least in terms of any measurments) and more powerful amp which is still quite simple and safe, I'm more inclinded to use 2..3 pcs. 7293s in master/slave config based on the simple amp's powering appoach, then adding a small-signal opamp to form a composite/nested amplifier. Even with the best conditions any standalone 7293/7294 amp will have a quality limit which is best overcome with a composite type of amplifer with high open-loop gain and careful compensation.
  Reply With Quote
Old 7th January 2013, 08:11 PM   #167
redjr is offline redjr  United States
diyAudio Member
 
Join Date: May 2011
Location: Danbury, CT
Quote:
Originally Posted by danielwritesbac View Post
You need a non-dulling volume-range control?
Let's fake that feature from Lightspeed Attenuator, but at lower cost. . . Just get a 50K dual-gang (stereo) pot and experiment with adding resistors to both of the outboard pins so that it cannot either go up all the way nor down all the way. You can further experiment by adding a resistor load to the input side. Also get a sack of short length alligator clip leads and clips by themselves to help speed exploration. And then solder the results of your exploration using a miniscule bit of gel flux for assured connection quality. After some play, the volume-range control prospect makes a novel non-dulling potentiometer for about $4, which cost less than the lightspeed attenuator, with the same benefit of not dulling the audio and with the same caveat of limited range. This goes almost all the way up, almost all the way down.
Location: Potentiometers are bad at driving cables, so this sort of device must go in close proximity to the input of a power amp. You can make it as an accessory in a cute little box with input RCA jacks and up to 1 foot "pigtail" RCA cable for output. Or you can actually use it as a power amplifier's volume-range control to get the cable length shorter for somewhat better results.

Loud is loud; but, loud and good is a different matter.
It may be useful to straighten out the source device before amplifying. Discrete buffer is a fun and simple alternative to multi-op-amp projects. These measure at extremely low distortion for measuring equipment; but, to the ear, a good discrete buffer can be amazing. Location of a buffer is as close as possible to the source for which it is useful. A beneficial buffer may be hard to find since descriptions are probably not given in audiophile terms. Since we know that impedance adjustments can make buffers unnecessary, when you find an engineer who consistently uses his buffer design, he's caught red-handed with an excellent block-rocker device that you will very much enjoy. In my opinion, these buffers are a great way to improve the quality of the source that you already own, and more practical or at least considerably faster than a long search for the elusive perfect source, which will, of course have this sort of buffer built in. You can DIY that piece.

Since potentiometers are particularly bad at driving cables, I suggest to put the new volume-range control directly onto the Input of a nice buffer project. I also suggest individual "cancel" switches for both features, because those can be fun and informative to use; and, because any good hi-fi effect always has a cancel switch, no matter if you intend to use the switch or not. Personally, I would mark one switch "boost" and the other switch "turbo" just for fun.

Or like this:
Click the image to open in full size.
And do consider the buffer, because we need the signal good before the power amp makes it loud.
Thanks Daniel for your detailed reply. I have used the 50k pot solution on the input of one my recent builds (LJM class D amp). I kept the cables very short (< 2") from the amp inputs. This worked very nicely and it sounds very good. It addresses the issue with my 'over-bearing' pre. I may explore mods that I could easily make to my new Doug Self pre without necessarily affecting its fine specs. It sounds great and is essentially noise free. At some point it will find a permanent home in my preferred stereo rig, but that hasn't happened yet.

I do like the idea of the Lightspeed Attenuator and in the future may build a portable one with RCA in and out. But it sounds like it 'okay' (maybe not ideal) to use a 50k pot in a power amp as long as it's close to the input.

I'm somewhat of a newbie with building amps and have therefore limited my selection to full kits, or assembled modules so far. I haven't ventured into buffers and some of the other external circuitry that may be required between amps and pre's. Could you point to any threads, or links that provide details on building and using a buffer circuitry? I need to study up on buffers!

Rick
__________________
redjr
  Reply With Quote
Old 7th January 2013, 09:25 PM   #168
diyAudio Member
 
danielwritesbac's Avatar
 
Join Date: Nov 2007
Quote:
Originally Posted by redjr
Could you point to any threads, or links that provide details on building and using a buffer circuitry? I need to study up on buffers!
Me too. Analog Line Level looks like an obvious place to find them, but that is not the case. Locations of the most promising buffers are generally in the Solid State and Tube amplifier forums. Probably, that's because a "safe bet" for performance is to put a buffer at the input of the power amp rather than make assumptions about what all sources should do? So, the actual place to research buffers is here: diyAudio - Search Forums
Quote:
Originally Posted by KSTR View Post
This would be nice of course, but would surely file under "scope creep". My idea was more like trying to make an excellent but still simple standalone TDA7294 amp.

To get to a better (at least in terms of any measurments) and more powerful amp which is still quite simple and safe, I'm more inclinded to use 2..3 pcs. 7293s in master/slave config based on the simple amp's powering appoach, then adding a small-signal opamp to form a composite/nested amplifier. Even with the best conditions any standalone 7293/7294 amp will have a quality limit which is best overcome with a composite type of amplifier with high open-loop gain and careful compensation.
Either way, it looks like the purpose is for keeping the large signal impact off the gain stage.

If I understand correctly, your plan with the schematic reading inverting mode plus lead lag comp, involves cutting the gain down until compensation is required thereby giving the creative freedom to add much nicer quality compensation--much better than is inside the chip. And a lot less power amp gain is likewise a lot less power supply influence on audio. Then, the majority of the gain task can be relocated to a preamp run on clean power which is a more suitable spot to have the gain. Right?
That plan looks builder friendly.
Generally speaking, I like this prospect of taking one big task and turning it into a few simpler, smaller and more doable tasks (divide and conquer), for the purpose of assuring high quality results.
__________________
Tools, Models & Software for DIYClipNipper boostLM1875 TurboPowerful TDA7293 kitTDA7294 pt2pt ♦ My post has opinion.
  Reply With Quote
Old 7th January 2013, 09:48 PM   #169
bcmbob is offline bcmbob  United States
diyAudio Member
 
Join Date: Dec 2009
Location: Bay City, Michigan
Though I don't want to sound like a sales agent for Stanton, I have had excellent results with this pre. In short, to me it has almost all of the clarity of my Lighter Note (Uriah Dailey - buildanamp.com) but with a healthy amount of gain. I even combined the LN to drive that pre in one build with happy results. I mention both here simply as a couple options to keep in the back of our minds. There are of course many other solutions I haven't built or heard.
Attached Images
File Type: jpg Pin0.jpg (183.4 KB, 301 views)
__________________
Bob M.
"Arrange Whatever Pieces Come Your Way."
  Reply With Quote
Old 8th January 2013, 09:11 AM   #170
KSTR is offline KSTR  Germany
diyAudio Member
 
KSTR's Avatar
 
Join Date: Jul 2007
Location: Central Berlin, Germany
Daniel,

your guess on my rationale to try inverting is right; drop down the gain to the lowest level, could be as low as only 3x with a powerful pre than can deliver 8Vrms or so.
Inverting has the advantage of an easier scaling of the gain to just the needed level. This can be had with non-inverting, too, but one needs more parts and the source impedance becomes critical.

I plan to try, in the breadboarding stage of things, both inverting and non-inverting with the exact same amp chip, setup and power config etc and compare/check perfomance difference pretty much in realtime, something that didn't happen before and could be worthwhile. Just in case the net benefit of low gain inverting + pre won't be significant, I might go back to standard gain non-inverting, we'll see...
Same thing for seperate power for chip frontend positive rail...

One thing seems clear, though, I'l be using a lot of local supply capacitance, more than ususal, fed from a softer than usual main supply.
  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 08:36 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