OPA549 listening impressions........ - diyAudio
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Old 20th September 2012, 06:03 PM   #1
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Default OPA549 listening impressions........

I have built opa549 on forum members suggestions and infact these were my impressions from the time its turned on..

Day 1: initially the the circuit didnt work figured out that the mute pin is not grounded and once did they started singing...

Hr 1: The sound was very very low and eventually if i try to increase the input signal there was strange crackling happening... thought something went wrong and was bit worried as everything was point to point checked... so i listened to very low volume as it was crackling... lil bit disappointed thought to check later what happened...

Hr 2: The crackling was reduced significantly by the end of second hour and the mids was very good was happy to see that it had nice not pronounced vocals.. the highs were not yet opened...

Hr 3: The fog was getting cleared and i could see the instrument saperation happening decently..

Hr 4-6: Can see the treble opening up and found I can bear the sound without crackling and the mids were still good even at this burning period...

left all the night in music at very low volume..

Day 2: The mids were awesome they had all the sweetness... I can feel the distinction of the vocals pretty good...

End of day 2 i called couple of friends said its just awesome and the highs were not harsh but very smooth but not brighter...

I fell in love with the mids very warm sounding like somebody said they have that tube sound I agree if its not complete substitute but this chip has that...

infact I have to try to add a preamp now and tweak it.... havent tried polystyrenes as decoupling....

I get speaker popping when some switch turn on in the room... how to take this out?

But overall i was very doubtful about this chip but it certainly surpassed my expectatoins and...

Pinkmouse, AndrewT and everybody who helped me in giving tips to get this one executed properly...

Ill post the impressions again after 50hr... but since its already 15hr i dont think they will open more... but its pretty mellow sound...

I havent tried LM3886 but when it comes to mids they were better than what Ive expected..

If anybody might have used both do let me know about your impressions... soon or later Ill build LM3886..
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Old 20th September 2012, 06:20 PM   #2
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Now try it in the inverted configuration.
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Old 20th September 2012, 06:29 PM   #3
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does it really makes difference?
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Old 20th September 2012, 06:41 PM   #4
osscar is offline osscar  Latvia
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check with scope (if possible) , in output of opa 549 glitches can be observed above 5kHz...., P.Macura was alos mentionet this problem.
Glitches on OPA549 output when loaded - Precision Amplifiers Forum - Precision Amplifiers - TI E2E Community
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Old 20th September 2012, 07:44 PM   #5
rsavas is offline rsavas  Canada
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Hello,

You have not stated anything with regard to the layout? Proper supply bypassing is very important, from the datasheet,
"Power-supply terminals should be bypassed with low series impedance capacitors. The technique shown in Figure 1, using a ceramic and tantalum type in parallel, is recommended.Power-supply wiring should have low series impedance.
Not sure what you mean "infact I have to try to add a preamp now and tweak it.... havent tried polystyrenes as decoupling...."
As power supply bypass caps? Not sure if this will make any difference? Layout/grounding, may play a much more important roll!!
Popping noises = strange behaviour = investigate. Have you looked at any waveforms on the scope?
I get speaker popping when some switch turn on in the room... how to take this out?
Generated by the Power Supply or through the signal source? Need to determine which it is? = Welcome to Design Engineering
Now try it in the inverted configuration.does it really makes difference?
Sure it can, the data sheet is, what I assume, based on non-inverting configuration. The inverting configuration can, depends on the device design, have a larger GainBandWidth Product and increased positive & negative slew rate. How this would affect the sound, is for the instruments, your ears & brain to tell!!

Cheer
Rick
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Old 21st September 2012, 02:04 AM   #6
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all class AB has some sort of crossover distortions so its expected...
im not using any preamp for this amp just playing thru my pc so there could be some improvement in sound with preamp
polystyrenes made big difference with tweeters but as decoupling caps near the psu pins i havent tried...

Im pretty sure it should be coming from the psu...
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Old 21st September 2012, 05:45 AM   #7
osscar is offline osscar  Latvia
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imho such high visible distortions are not normal at such a high output level (a few volts). LM3875 / 3886 of the same configuration (non-invert) amplifier does not have a visible distortion. This affects the sound imho.
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Old 21st September 2012, 06:51 AM   #8
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I've built lots of OPAs and never noticed a glitch like that on the scope.

Sandy, running inverted reduces distortion, but usually needs an input buffer if you use a passive volume control.
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Old 21st September 2012, 06:55 PM   #9
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pinkmouse thank you for the input. Ill try using but man somehow I feel that this amp is not giving the highs which I feel need little brighter... not much... how do I do that or this is the nature of this amp?

Btw Iam thinking of biasing this chip in class A. IMHO it will become hot but im ready to put a massive heatsink.... Even if im getting 8w in class A i want to experience it once...
I think we need to use a resistor from output pin to -ve signal... i dont know exactly how its done but want to try once whats your call on this?
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Old 21st September 2012, 08:16 PM   #10
AndrewT is offline AndrewT  Scotland
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What filters have you fitted to the input?
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