Had a similar experience with one of my handsoldered pcbs.
What I learned:
On power-up the TPAxxxx check all outputs for shorts against VPP and GND and if found immediately shut down into an error state.
So I measured all outputs with a circuit-tester against the powerrails and finally discovered some solder bridge at the output pins, removed that and now that board worked.
It really is not easy to destroy these chips packed with protection logic.
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I like the way you are thinking.
I do not understand, and I admit I know nothing about what happens in class D amplifiers, but why when eliminating two stages with a gain of 1 you are losing "power".
Those little 5532s powered with one 12 volts rail are doing some kind of current driving? Seems like they would not be capable of doing much of anything at all.
I assume you have used the amplifier. Are you really experiencing a loss of power?
Please explain what I do not know. PS just realized that would overwhelm the forum - just what i am missing here!
Rick -- with one of the bridged inputs is grounded, that amplifier module's output is sitting at 0.5*Vcc, sourcing or sinking current from the other terminal that is swinging from 0 (ground) to Vcc. This is opposed to a case where both outputs are swinging from 0 to Vcc, but in opposite directions (centered at 1/2 VCC)
Daniel,
Thanks for your answer but you gave me too much credit!
I get some of it but I wonder if you are saying this would be a problem with an amp configured for stereo but might not be a factor with both channels in parallel?
Greinedo, I looked back and saw where you went into some detail. I had forgot about that and had to go reread it.
What is interesting: in the 3255 specifications none of these op amps are in the "suggestions" on how to use. It certainly looks like one does not need the op amps. Plus the gain is specified as being in the 3255.
So, back to Daniel, is what you are speaking of always the case no matter how the amp is configured?
One part of me thinks that TI does not have THAT many 5532s in surplus so I figure there is some very good reason for them to be there. The question: are they there for anything to do with sonics or some kind of "one size fits all" solution that will work everywhere in any kind of condition. Certainly a laudable goal for an engineer but not much fun for the obsessive who is willing to work around problems.
So if I may ask or a simpler explanation of why these are needed? I am going to use the amp (if I like it i will get another) in the parallel bridged mode with differential input for a low bass speaker. I do not have to use the differential input, it could be SE. Would any of these factors have anything to do with not bypassing the op amps? Yes, I love bypassing op amps.
Thanks, in advance, for your patience.
Thanks for your answer but you gave me too much credit!
I get some of it but I wonder if you are saying this would be a problem with an amp configured for stereo but might not be a factor with both channels in parallel?
Greinedo, I looked back and saw where you went into some detail. I had forgot about that and had to go reread it.
What is interesting: in the 3255 specifications none of these op amps are in the "suggestions" on how to use. It certainly looks like one does not need the op amps. Plus the gain is specified as being in the 3255.
So, back to Daniel, is what you are speaking of always the case no matter how the amp is configured?
One part of me thinks that TI does not have THAT many 5532s in surplus so I figure there is some very good reason for them to be there. The question: are they there for anything to do with sonics or some kind of "one size fits all" solution that will work everywhere in any kind of condition. Certainly a laudable goal for an engineer but not much fun for the obsessive who is willing to work around problems.
So if I may ask or a simpler explanation of why these are needed? I am going to use the amp (if I like it i will get another) in the parallel bridged mode with differential input for a low bass speaker. I do not have to use the differential input, it could be SE. Would any of these factors have anything to do with not bypassing the op amps? Yes, I love bypassing op amps.
Thanks, in advance, for your patience.
hi rick
i know how you feel. if i get crazy in my head i read this. belive me i do not understand everything
http://www.irf.com/product-info/audio/classdtutorial.pdfchris
@chermann Thank you ! Very interesting link.
@rickmcinnis,
I assume you have used the amplifier.
Yes, I'm using it continuously. It has now a nice musicality to me. And I have no criticism to the evaluation board. I was motivated since beginning for tweaking a bit
Are you really experiencing a loss of power?
With tpa3251evm, connected the normal way, just be removing jumpers on J35 and J27 you will experience drop of power (possible only on J27 for tpa3255evm). But turning more the volume level compensates the drop and music quality is maintained to my ears. This was my entry into this investigation.
So if I may ask or a simpler explanation of why these are needed? (op amps)
Main reason seems to me the need for a Single Ended to Differential Converter. Please read this doc : http://www.ti.com/lit/an/slaa719/slaa719.pdf I spend many effort on my DAC output stage with op amps, IC, discrete, independent power supply considerations, decoupling caps etc... that I think the input stage here on the board would mess a bit that audio signal (the 5532 less than the general "cost effective" design).
Moreover my hobby is not that much bypassing op amps. I was motivated here to play with film coupling caps on inputs like on my other amps. But on that board this is only possible if you avoid also the input stage with it's own electrolytic coupling caps.
Spent some time reading about coupling caps and found Cyril Bateman's work in discussions and documents (may be old). I had not courage to read a lot but others who did concluded ceramic X type are not the best for coupling audio. Currently there is only 1 DC blocking between DAC and tpa3251 (big Jantzen film cap and his small bypass cap). Without bypass cap, something is missing. I tried different bypass caps and the allowed freedom to choose the sound type is interesting. fkp1 100nf ultra detailed very bright, but some fatigue listening, at the opposite Styroflex 10nf much darker, still nice sound stage but a bit shy, fkp3 100nF somewhere in-between, best balance to my taste until now.
Dominique
@rickmcinnis,
I assume you have used the amplifier.
Yes, I'm using it continuously. It has now a nice musicality to me. And I have no criticism to the evaluation board. I was motivated since beginning for tweaking a bit
Are you really experiencing a loss of power?
With tpa3251evm, connected the normal way, just be removing jumpers on J35 and J27 you will experience drop of power (possible only on J27 for tpa3255evm). But turning more the volume level compensates the drop and music quality is maintained to my ears. This was my entry into this investigation.
So if I may ask or a simpler explanation of why these are needed? (op amps)
Main reason seems to me the need for a Single Ended to Differential Converter. Please read this doc : http://www.ti.com/lit/an/slaa719/slaa719.pdf I spend many effort on my DAC output stage with op amps, IC, discrete, independent power supply considerations, decoupling caps etc... that I think the input stage here on the board would mess a bit that audio signal (the 5532 less than the general "cost effective" design).
Moreover my hobby is not that much bypassing op amps. I was motivated here to play with film coupling caps on inputs like on my other amps. But on that board this is only possible if you avoid also the input stage with it's own electrolytic coupling caps.
Spent some time reading about coupling caps and found Cyril Bateman's work in discussions and documents (may be old). I had not courage to read a lot but others who did concluded ceramic X type are not the best for coupling audio. Currently there is only 1 DC blocking between DAC and tpa3251 (big Jantzen film cap and his small bypass cap). Without bypass cap, something is missing. I tried different bypass caps and the allowed freedom to choose the sound type is interesting. fkp1 100nf ultra detailed very bright, but some fatigue listening, at the opposite Styroflex 10nf much darker, still nice sound stage but a bit shy, fkp3 100nF somewhere in-between, best balance to my taste until now.
Dominique
Rick -- I'll try to give you a much more earnest answer tonight with some pictures of waveforms to convey what's going on and to save me the several thousand words.
It's not a problem.D
Thanks, DPH.
I guess the easy answer is - I am surmising - is that if supplied with differential inputs, which is what I was intending to do - these op amps are not really needed unless they so something for the "sound" of the amplifier, which, of course they would.
Do you think the TI fellows thought it sounded better with the op amps than without? Or simply as greinedo explained just there to give the amp chip the differential input it requires? That is all I can surmise form the schematic, too.
One wonders if there are aspects of the 3255's sound alone that are tempered by the added op amps? I figure in my limited frequency requirements for the amp/s that I can do without the op amps, maybe. If it is easy to bypass them I will try that after I get the things working. Easy enough to adjust the level of the preceding component to compensate
Got my PS from CONNEX today. Thanks to wushullu for his recommendation.
They look good together.
Take care,
I guess the easy answer is - I am surmising - is that if supplied with differential inputs, which is what I was intending to do - these op amps are not really needed unless they so something for the "sound" of the amplifier, which, of course they would.
Do you think the TI fellows thought it sounded better with the op amps than without? Or simply as greinedo explained just there to give the amp chip the differential input it requires? That is all I can surmise form the schematic, too.
One wonders if there are aspects of the 3255's sound alone that are tempered by the added op amps? I figure in my limited frequency requirements for the amp/s that I can do without the op amps, maybe. If it is easy to bypass them I will try that after I get the things working. Easy enough to adjust the level of the preceding component to compensate
Got my PS from CONNEX today. Thanks to wushullu for his recommendation.
They look good together.
Take care,
The configuration of the 5532's and the respective jumpers, as several have stated, is in there to make the different inputs (single ended or balanced) work out fine. It affords a good deal of flexibility. This said, I'd be more suspicious of needing two coupling caps than I am of the 5532 imparting any flavor onto the music. The TPA chip itself, followed by the output filter are the most likely weak points in the whole thing, and thereby dominate the "sound".
Coming from a balanced input as you have, especially one that you're confident will drive the TPA3255 input (which *should* be higher impedance than the 9.1k of the inverted 5532), then try feeding your input through the respective pins on the audio interface board header (http://www.ti.com/lit/ug/slou441/slou441.pdf pg 17 dead center). The header has connections that bypass the 5532 entirely (although I'd short the 5532 inputs all to ground to be safe). This requires no soldering iron on the board.
Second, I'd be reluctant to bypass C17, C28, C55, C63 the way Dominique did (no slight!), because I'd be worried about those big caps acting as a nice antenna for radiated energy in the output filter. A more compact capacitor aligned orthogonal to the output inductors would make me feel better. It may measure just fine however, making my concern moot!
Dear Daniel and Rick,
Before extreme testing with big film caps I was tempted to try much smaller electrolytic Elna Silmic II 22µF bypassed by film cap 0.1, I had on hands. I prepared the components and solder iron was already heated up when I realized I had no idea if tpa pin side is the positive or the negative side of the coupling cap ! I was not ready to take a risk and the attempt stopped stupidly here.
Yesterday I read by error the schematics of tpa3251d2evm, and there are C17... electrolytic cap clearly shown with negative pin on tpa chip side. So one test could be replacing all 4 ceramic coupling cap by small electrolytic Elna Simic II 10 µF, bypassed by small film cap 0.1 (best for me fkp3). This could have already great result, better effort/benefit ratio especially if Rick intends driving a low bass speaker. Or even only one bigger electrolytic (100-220µF) if bass is the unique goal. But royal choice is still big film cap Coupling capacitor and bypass choices
Nevertheless the current crazy test here is to my ears is very successful and I don't want to change something, just listening good music. But something must change at short term. The capacitor artwork in from of TV has over-passed the WAF
Dominique
Before extreme testing with big film caps I was tempted to try much smaller electrolytic Elna Silmic II 22µF bypassed by film cap 0.1, I had on hands. I prepared the components and solder iron was already heated up when I realized I had no idea if tpa pin side is the positive or the negative side of the coupling cap ! I was not ready to take a risk and the attempt stopped stupidly here.
Yesterday I read by error the schematics of tpa3251d2evm, and there are C17... electrolytic cap clearly shown with negative pin on tpa chip side. So one test could be replacing all 4 ceramic coupling cap by small electrolytic Elna Simic II 10 µF, bypassed by small film cap 0.1 (best for me fkp3). This could have already great result, better effort/benefit ratio especially if Rick intends driving a low bass speaker. Or even only one bigger electrolytic (100-220µF) if bass is the unique goal. But royal choice is still big film cap Coupling capacitor and bypass choices
Nevertheless the current crazy test here is to my ears is very successful and I don't want to change something, just listening good music. But something must change at short term. The capacitor artwork in from of TV has over-passed the WAF
Dominique
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This weekend I will try it with and without the input stage in the circuit and HEAR if I hear a difference. I will pick one or the other and live with it for awhile.
One thing about replacing those signal ceramics with SILMICS is if you put them in the wrong way they won't blow up! But I bet it would be a pain to have to reverse the polarity.
There is always the choice of biasing at the center point two electrolytics in series (with the proper polarity of voltage).
This could have the advantage of being much better sounding than the ceramics without being too ungainly in size. DPH is right to be concerned about the size of big films creating unwanted effects. COMPROMISE, damned COMPROMISE is the humbling lesson we learn from this hobby.
So even though a pair of small electrolytics would be smaller than a film cap they will still be huge in comparison to that dainty smd ceramic.
I have learned to temper my ceramic cap phobia (a little bit) but from what I can see there are no good dielectrics available that one could fit on those pads. How my old eyes and old limbs hate smd components. Of course I can see their advantages but most of them in my experience are just not good enough for high quality audio.
When I went to the CONNEX site to order my power supply I read what they wrote about their own class D boards and the fellow cautioned, just as DPH has, about trying to substitute good capacitors. As we know sometimes one can move one step forward while not realizing you have actually been moved two steps back. It takes a week of listening to a variety of material to really be sure about these changes. I know all too well the desire to consider a modification a success only to find, due to some surprising circumstance that makes you return to the original configuration that it was not as good as we wanted it to be.
I know my application should be simplicity in comparison to those who are trying to get the most of this board for the almost impossible task of being a full range amplifier. I do not think anyone makes a truly full range amplifier in any class or configuration but I hope people continue trying!
There is lots to be said for using several amplifiers tuned for the range they are being asked to play. Of course, this is usually because of the limited power of most really good topologies. The seemingly endless supply of power
available with class D makes it tempting to let one amplifier do it all. For most applications this is fine, of course, I am speaking of those trying get the last little bit out of their systems.
Of course, we are kooks but we are trying very hard to find something good.
Let us continue ...
One thing about replacing those signal ceramics with SILMICS is if you put them in the wrong way they won't blow up! But I bet it would be a pain to have to reverse the polarity.
There is always the choice of biasing at the center point two electrolytics in series (with the proper polarity of voltage).
This could have the advantage of being much better sounding than the ceramics without being too ungainly in size. DPH is right to be concerned about the size of big films creating unwanted effects. COMPROMISE, damned COMPROMISE is the humbling lesson we learn from this hobby.
So even though a pair of small electrolytics would be smaller than a film cap they will still be huge in comparison to that dainty smd ceramic.
I have learned to temper my ceramic cap phobia (a little bit) but from what I can see there are no good dielectrics available that one could fit on those pads. How my old eyes and old limbs hate smd components. Of course I can see their advantages but most of them in my experience are just not good enough for high quality audio.
When I went to the CONNEX site to order my power supply I read what they wrote about their own class D boards and the fellow cautioned, just as DPH has, about trying to substitute good capacitors. As we know sometimes one can move one step forward while not realizing you have actually been moved two steps back. It takes a week of listening to a variety of material to really be sure about these changes. I know all too well the desire to consider a modification a success only to find, due to some surprising circumstance that makes you return to the original configuration that it was not as good as we wanted it to be.
I know my application should be simplicity in comparison to those who are trying to get the most of this board for the almost impossible task of being a full range amplifier. I do not think anyone makes a truly full range amplifier in any class or configuration but I hope people continue trying!
There is lots to be said for using several amplifiers tuned for the range they are being asked to play. Of course, this is usually because of the limited power of most really good topologies. The seemingly endless supply of power
available with class D makes it tempting to let one amplifier do it all. For most applications this is fine, of course, I am speaking of those trying get the last little bit out of their systems.
Of course, we are kooks but we are trying very hard to find something good.
Let us continue ...
Dear Daniel and Rick,
Before extreme testing with big film caps I was tempted to try much smaller electrolytic Elna Silmic II 22µF bypassed by film cap 0.1, I had on hands. I prepared the components and solder iron was already heated up when I realized I had no idea if tpa pin side is the positive or the negative side of the coupling cap ! I was not ready to take a risk and the attempt stopped stupidly here.
Yesterday I read by error the schematics of tpa3251d2evm, and there are C17... electrolytic cap clearly shown with negative pin on tpa chip side. So one test could be replacing all 4 ceramic coupling cap by small electrolytic Elna Simic II 10 µF, bypassed by small film cap 0.1 (best for me fkp3). This could have already great result, better effort/benefit ratio especially if Rick intends driving a low bass speaker. Or even only one bigger electrolytic (100-220µF) if bass is the unique goal. But royal choice is still big film cap Coupling capacitor and bypass choices
Nevertheless the current crazy test here is to my ears is very successful and I don't want to change something, just listening good music. But something must change at short term. The capacitor artwork in from of TV has over-passed the WAF
Dominique
Pity on the capacitor artwork! Not seeing polarity on the C17 (et al) caps on either EVM schematic, which makes me think it was a BOM oops as opposed to anything else. Quick search through Digikey for potential parts would have me suspect it's a 35 V x7r (we can dream it's a 50v part).
Might be worth seeing if there's a 50'ish volt SMD radial bipolar electrolytic that fits nicely on the 1206 pad (4-5 mm end to end, 2mm gap, 1.6mm pad width). That said, the TPA3255/51 side of the capacitor better be the higher side at 1/2 VCC, unless there's a HUGE DC offset between equipment (which says there's some big problems with your setup).
A few volts Ti says. See here -> [Resolved] TPA3251: Input DC-block capacitors really needed? - Audio Amplifiers Forum - Audio Amplifiers - TI E2E Community 3.9V here.
All nonpolar electrolytics are reported to sound even worse than polarized. Not a solution.
I think the best solution is to remove the ceramic and replace with a jumper when bypassing the op amps and just place a cap, you would prefer, in the input circuit from the component preceding the amp. At the headers.
I think the best solution is to remove the ceramic and replace with a jumper when bypassing the op amps and just place a cap, you would prefer, in the input circuit from the component preceding the amp. At the headers.
Rick, bipolar vs polarized electrolytic caps for ac coupling is an extremely specious statement which I don't think you'll find any evidence to back up. And anecdotes run the gamut. Use as you like, however.
Agreed if you want to remove these caps that the best operation is to solder bridge the 1206 pad and bring the replacement cap in before the headers.
Agreed if you want to remove these caps that the best operation is to solder bridge the 1206 pad and bring the replacement cap in before the headers.
I would welcome a recommendation! Anecdotes can run the gamut but I have never heard anyone report a good sounding nonpolar electrolytic so it does not seem to be controversial. Of course, the BLACK GATE Ns sound good. I would be surprised if the new AUDIO NOTE nonpolars sound bad.
Just because something it is anecdotal doesn't make it false.
AS Mr. Recklinhausen said so many years ago if something measures well and sounds bad you measured the wrong thing.
Not to mention the question of whether we can even measure the right thing with the devices we have at the moment.
Call it anecdotal but if someone whose opinion I trust uses a component and says it sounds bad I will take their word for it! Now I if I had been cursed with a life without death i would try them all out for myself!
Just because something it is anecdotal doesn't make it false.
AS Mr. Recklinhausen said so many years ago if something measures well and sounds bad you measured the wrong thing.
Not to mention the question of whether we can even measure the right thing with the devices we have at the moment.
Call it anecdotal but if someone whose opinion I trust uses a component and says it sounds bad I will take their word for it! Now I if I had been cursed with a life without death i would try them all out for myself!
The Nichicon Muse ES (I think that's their bipolar line) haven't let me down, and, well, they sure seem to behave well when used right: Nichicon Muse ES bipolar caps measured: <-120dB THD, <-140dB IMD
I'm of the opinion any of the major manufacturers bipolar electrolytic lines are going to play nice. I've read both good and bad about bipolars, along with "inaudible". Take your pick.
I'm of the opinion any of the major manufacturers bipolar electrolytic lines are going to play nice. I've read both good and bad about bipolars, along with "inaudible". Take your pick.