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The Opamp thread - Page 258

post #3856 of 4753

zilch0md: from diagram you posted above: for 10V and 20kHz you need at least ~2.5V/us to keep rough shape (good looking on scope) of sine-wave. But you need much more (e.g. ten times more) to keep THD low.

1KV/us is useless if you ask me, but there are many other things that matters more than SR.

 

In amp that I designed I am using LT1122 (60V/us) which are better than LT1363 in my opinion. Even LT1115 (only 10V/us) sounds great (still better than LT1363 for me). The other amp - electrostatic one - I designed (not using OA) is quite slow (only 25V/us) and still sounds lovely.

 

So I don't think there is correlation between very high SR and "good sound".

post #3857 of 4753

Thanks for the explanation!

post #3858 of 4753

The slew rate is far in excess of what is needed.

It was more of a case of "it didn't cause any problems".

Quote:
Originally Posted by zilch0md View Post

 

Nice.  I envy your having the satisfaction of building your own amp.  

 

Would you say the ultra-sonic (1000 V/ms) slew rate of the LT1363 played a factor in how nice the amp sounded, or just that the high slew rate didn't cause any audible problems?

 

Thanks,

 

Mike

post #3859 of 4753

The 1363 never really did it for me even though Leeperry thought it was the best thing since sliced bread at one point. This of course be down to lots of factors like circuit, musical genres, source etc..... The only LT OpAmp to really get me was/is the 1122, I like it a lot.

 

At the moment I have various OpAmps on the go.

 

AD797BRZ in my EF-5

LME49990 in my PB-2

OPA1662 in my Fi-Q

THS4032 in my P4

 

They all sound great for different reasons...

post #3860 of 4753

Yes, I agree...no one op amp is a do all, end all for every situation.

I have LME49990 in my DAC.

post #3861 of 4753

I think the major issue is that most ppl roll opamps blindly and expect miracles.....I think what we need badly is a tutorial including a cheap USB oscilloscope explaining how to ensure that those chips aren't oscillating like hell.

 

Rolling AD797 or LT1208 blindly is bound to fail, and it will...even TI say so(thanks MadMax for the link!), I guess they'd know biggrin.gif : http://e2e.ti.com/support/amplifiers/precision_amplifiers/w/design_notes/upgrading-op-amps-in-audio-equipment.aspx  

 

LME49990 and LT1363 are the exact same story. I will never roll blindly ever again, either I will gain the knowledge to ensure stability or I'll give it up altogether.

 

Anyway, I've heard stunning DAC's using OPA2132 and OPA627 in their output stage....it's all about their surrounding design as usual. A dual opamp used a LPF out of a voltage output DAC will always sound poor, c'est la vie.

post #3862 of 4753

does anyone have any thoughts or opinions on the LME49990 with the ibasso p4? what are the signatures of this opamp? is it pretty good?.

post #3863 of 4753

Spudharris thinks it's an amazing combination.

post #3864 of 4753

LOL

 

And here!

post #3865 of 4753
Quote:
Originally Posted by leeperry View Post

I think the major issue is that most ppl roll opamps blindly and expect miracles.....I think what we need badly is a tutorial including a cheap USB oscilloscope explaining how to ensure that those chips aren't oscillating like hell.

 

Rolling AD797 or LT1208 blindly is bound to fail, and it will...even TI say so(thanks MadMax for the link!), I guess they'd know biggrin.gif : http://e2e.ti.com/support/amplifiers/precision_amplifiers/w/design_notes/upgrading-op-amps-in-audio-equipment.aspx  

 

LME49990 and LT1363 are the exact same story. I will never roll blindly ever again, either I will gain the knowledge to ensure stability or I'll give it up altogether.

 

Anyway, I've heard stunning DAC's using OPA2132 and OPA627 in their output stage....it's all about their surrounding design as usual. A dual opamp used a LPF out of a voltage output DAC will always sound poor, c'est la vie.

 

Gulp.... thats more or less what I have been doing blink.gif

 

well, i read a lot of your early posts in this thread and made a list of opamps to try above my current selection (mainly for the I/V section in my STX.)

 

I have tried:

  • JRC2114D (stock)
  • AD797BR
  • LT1057ANC8
  • THS4032
  • OPA827
  • 2xLME49710HA (it was the twin leaning towers of Piza, but i got it right, wasn't worth the dodgeyness)

 

And now I want to try:

  • OPA132UA
  • 2xLT1363CN8
  • LT1678IS8
  • LT1208ACN8
  • 2xLT1122
  • LME49990
  • OPA2132P
  • AD8599
  • OPA627
  • OPA1611

 

Should I avoid any of those for any reason? Ignoring sound Characteristics.


Edited by WiR3D - 5/21/12 at 1:16am
post #3866 of 4753
Quote:
Originally Posted by WiR3D View Post

Gulp.... thats more or less what I have been doing blink.gif

 

"You can only get smarter by playing a smarter opponent".

 

We'd need to find someone kind enough on diyaudio(Moonly?) or so to explain us how to check for oscillation, and especially how to cure it. Cluelessness has a cure, it's called shared knowledge cool.gif

post #3867 of 4753
Quote:
Originally Posted by leeperry View Post

 

"You can only get smarter by playing a smarter opponent".

 

We'd need to find someone kind enough on diyaudio(Moonly?) or so to explain us how to check for oscillation, and especially how to cure it. Cluelessness has a cure, it's called shared knowledge cool.gif

is oscillation even audible? if not then whats the problem? or does it generate a kak load of extra heat?

post #3868 of 4753

Oscillation itself is very often (almost alvays) inaudible, but it can cause increased hum, THD,... which are audible. It can also cause excessive heating of OA.

Oscillation can be detected by HF voltmeter.

post #3869 of 4753
Quote:
Originally Posted by AmarokCZ View Post

Oscillation itself is very often (almost alvays) inaudible, but it can cause increased hum, THD,... which are audible. It can also cause excessive heating of OA.

Oscillation can be detected by HF voltmeter.

So then how would I detect it? I have a multimeter, but I really don't think that will cut it.

post #3870 of 4753

Multimeter is useless, but you can try a HF probe like this and connect it to multimeter, but HF voltmeter (or good scope) has higher sensitivity.

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