The Opamp thread

[Spacehead]

My PPA V2 gave out some hiss because of the high gain the OPA637 needed.
I lowered the gain to unity and installed LME49860.

LME49860 required that input impedances are balanced pretty closely or there would be about 100 mV (or more) DC Offset.

LME49860 sounds pretty good in my PPAV2. The soundstage is closer than OPA637. Highs are snapping but they aren't disturbing bright. Bass is balanced, not too heavy or too light. Pretty neutral presentation. Maybe less colored op amp. I have ADA4898-1 in my X-FI so sound is all bipolar. I have used to somewhat dark sound coming from bipolars but this feels neutral in that regard too. I have to check if offset shifts when the amplifier warms up. LME49860 could sound a little grey, dull, and lifeless. Maybe it is coloration or just accurate.

I wish that I hadn't ever even tried how another op amp sounds. How I can cure this disease. I see that Andrea is into op amps too, is the overly enthusiastic approach reason for a ban?
I can cure myself by building a discrete amplifier next.

I have a 3 transistor amplifier and it sounds super. Then I need to get a dac that has passive IV and discrete buffer.

The gurus here, can you tell how to gain some kind of introspect into op amp listening? Another set of headphones? Or is this op amp rolling sane thing to do at all?

 

[Spacehead]

OPA2613:

presentation is close
accurate
not annoying
pleasant
not warm
not dark
bit messy
a little HARD (in a good way)

in X-FI differential to single ended converter + filter, heard through PPAv2 ADA4627-1ARZ + LME49860 on ground

I have no means to measure if high speed op amps oscillate or misbehave on X-FI, I guess it is fairly well compensated if op amp just can drive capacitive loads. and this one should be able to do that.

It passes RMAA test, so it should behave well in audio band?
http://i41.tinypic.com/1zmfnmb.jpg

X-FI: http://i43.tinypic.com/sces1z.jpg

This op amp is pretty cold for BB op amp, but not bad... not great either, but that might indicate good transparency

I chose to try to this over OPA2674 or OPA690, I guess those op amps don't work in that circuit.
The dip to soic adapter is so well epoxied to the card that I might burn an op amp in it someday

 

[murrays]

Quote:

Originally Posted by Spacehead /img/forum/go_quote.gif OPA2613: I have no means to measure if high speed op amps oscillate or misbehave on X-FI, I guess it is fairly well compensated if op amp just can drive capacitive loads. and this one should be able to do that.

If you don't have access to an oscilloscope (the best way to check) there is always the rule of thumb. Test how hot it gets with the end of your finger. A chip fully oscillating above the audio band (typcally ~ 1MHz) will get very hot - most of its power will be driving frequencies that you can't hear. Normally most chips only get lukewarm. If music is playing, an oscillating opamp will "broadcast" (modulate) RF - I have heard that you can tune in to it with an adjacent AM radio. I have yet to try this for myself as I have carefully stabilised my amps, but will try it out when I have one that oscillates. Has anyone else here tried that one?

 

[Spacehead]

Quote:

Originally Posted by murrays /img/forum/go_quote.gif If you don't have access to an oscilloscope (the best way to check) there is always the rule of thumb. Test how hot it gets with the end of your finger. A chip fully oscillating above the audio band (typcally ~ 1MHz) will get very hot - most of its power will be driving frequencies that you can't hear. Normally most chips only get lukewarm.

Nice, this one (OPA2613) is about as warm as my finger. Sometimes oscillating chip sounds very hard and harsh.
But anyway OPA2613 has "GAIN BANDWIDTH PRODUCT: 125MHz". That isn't overly much.
About it's distortion. In differential configuration, 100 kHz and -105 dB THD and it get's lower. That is pretty low, right?
When I ordered these I thought only about the high output current, limited to 500 mA. But other specs are on par too, 1.8nV/sqrtHz input noise voltage is very low too.

 

[leeperry]

Quote:

Originally Posted by Spacehead /img/forum/go_quote.gif (OPA2613) is about as warm as my finger.

well, how warm's your finger then?

yes, Andrea was banned on diyaudio.com for no reason, except being obsessed about opamp rolling...these ppl listen to their oscilloscope and datasheets, they can't quite grasp the idea that all the opamps sound different

and you were right about tubes sounding "tubey" hummmmkay, but I've found a nice "in-between" solution: http://www.head-fi.org/forums/6565903-post442.html

 

[ROBSCIX]

Quote:

Originally Posted by Spacehead /img/forum/go_quote.gif Nice, this one (OPA2613) is about as warm as my finger. Sometimes oscillating chip sounds very hard and harsh. But anyway OPA2613 has "GAIN BANDWIDTH PRODUCT: 125MHz". That isn't overly much. About it's distortion. In differential configuration, 100 kHz and -105 dB THD and it get's lower. That is pretty low, right? When I ordered these I thought only about the high output current, limited to 500 mA. But other specs are on par too, 1.8nV/sqrtHz input noise voltage is very low too.

Sometimes they osciallate outside of the audible bandwidth so trying to listen for anomolies is no good in this case. You can use the heat test as describe by others or you can pull out the pencil and paper and compare how much current it should be drawing to how much it actually is drawing. If the opamps is osciallting it is drawing way too much current as this is the cause of the extra heat.

 

[theSeekerr]

Quote:

Originally Posted by leeperry /img/forum/go_quote.gif yes, Andrea was banned on diyaudio.com for no reason, except being obsessed about opamp rolling...these ppl listen to their oscilloscope and datasheets, they can't quite grasp the idea that all the opamps sound different

Andrea was banned for making contradictory claims, including claims about opamps he'd never heard.

As for whether opamps sound different....well, certainly they can, but assuming an opamp is matched to its application, the differences are far less profound than is often claimed here.

 

[leeperry]

Quote:

Originally Posted by theSeekerr /img/forum/go_quote.gif As for whether opamps sound different....well, certainly they can, but assuming an opamp is matched to its application, the differences are far less profound than is often claimed here.

well, most ppl in this thread would strongly disagree w/ this statement, as it couldn't be farther from the truth IME.

and noone even mentioned to Andrea why he had been banned all of a sudden, tough luck...we can all change, he could have improved his behavior if asked so...anyway he's living well now and doesn't care much I think

 

[12Bass]

Quote:

Originally Posted by theSeekerr /img/forum/go_quote.gif As for whether opamps sound different....well, certainly they can, but assuming an opamp is matched to its application, the differences are far less profound than is often claimed here.

Hmmmm.... I'd say that op amps make less of a difference than transducers, though if a system is sufficiently revealing, such differences can often be easily detected. Moreover, I'd often appreciate it if I didn't hear any differences, as it would keep me from trying to find something which sounds better.

 

[theSeekerr]

Quote:

Originally Posted by 12Bass /img/forum/go_quote.gif Moreover, I'd often appreciate it if I didn't hear any differences, as it would keep me from trying to find something which sounds better.

Might I politely suggest ABX testing? Yes, it'll require you to build up 2 identical amps to AB, and that's a pain, but still.

"But ABX testing is flawed - because it *insert your own excuse here*, I can't hear things which I know to be true!"

Just because you hear a difference doesn't mean it exists.

Don't worry, I won't post in here again, this thread doesn't need to hear this debate play out again. Anyone is welcome to PM me if they want to argue on their own time.

 

[Mad Max]

Quote:

Originally Posted by Spacehead /img/forum/go_quote.gif The gurus here, can you tell how to gain some kind of introspect into op amp listening? Another set of headphones? Or is this op amp rolling sane thing to do at all?

You could try the RE0 as far as 'phones. *Very* transparent earphone.
My AD700 is very sensitive to treble extension, and soundstage changes as well though seemingly to a somewhat lesser extent.

 

[qusp]

yes leeperry, I know you are brothers in arms and everything, but thats some serious rose coloured glasses you got on there, i'm surprised you can see at all.

just soldered in some OPA827 again in place of the stock opamps for the DC servos on my dual mono QRV08, destined for the output stage of my ackodac sabre32 dac. the servo only has an audible effect down low in the bass regions and I found OPA827 to have the most amazing clean yet slightly musical (natural is probably the word) bass

using AD825 in the 8 onboard jung super regulators. the build should be finished in the next couple of weeks and will make sure to post impressions of them in this placement. the amp section itself is discrete SMD

 

[leeperry]

Quote:

Originally Posted by theSeekerr /img/forum/go_quote.gif Might I politely suggest ABX testing?

hehe well, all the opamps sound different..they just do, believe me we really wish they didn't

this guy says that 4562/1028 sound identical to him: The best sounding audio integrated opamps - diyAudio

I'd suggest retiring from the audio hobby completely, and do something more rewarding w/ his time.

 

[buz]

I'm starting to think the LT1028C has too much bass. I even started eq'ing down the bass on my D2000 - sure as hell the first time in my life I ever did that

. Heck it even brings out bass in the RE0...

Maybe try a somewhat colder, analytic, very transparent opamp. Any suggestions?

 

[12Bass]

Quote:

Originally Posted by theSeekerr /img/forum/go_quote.gif Might I politely suggest ABX testing?

I have done some single-blind testing and been able to reliably tell the difference between devices. Generally, I am a proponent of the scientific method.