[leeperry]

BTW, Gearslutz.com - View Single Post - ART MPA Gold Mods

Quote:

Any opamp change must be viewed on a scope to determine if it's operating in a linear region.[..] Audio band parts like OPA2134, AD 8599 are usually safe, the LM4562/LME49720 is a 55 mhz bandwidth part, watch out. The LM6172 is a 100 mhz part. This is not like swapping the tubes on your old color TV, one can quickly make things worse without knowing it.

Home Recording - View Single Post - LME49720NA for ART Digital MPA?
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The motorboating is oscilations, if you socket chips you really need to use machined sockets the flat pin ones are bad for oscilations and moaterboating and usually need decoupling caps across power an ground

the stock 2114D on my soundcard have a 15Mhz slew rate, I think 50Mhz and above is over the top as it's too far from the original design...plus the damn thing has very crappy sockets

the first time I put 49720NA in there, they gave a wooshy sound...constantly oscillating.

so the lower the gain bandwidth, the better I'll be doing I think...the LT1358 has a 25Mhz gbw, and it sounded FAR more stable than any LM/LME part I tried..

PS: damn, some of my LT samples were "shipped" 3 weeks ago.....they use pigeons to ship them?

 

[leeperry]

humm, I can get a pretty huge oscilloscope for 90 EUR at a pawnshop...its last calibration has expired a few months ago.

I still dunno how to measure if an opamp would be oscillating

 

[Pars]

Quote:

Originally Posted by leeperry /img/forum/go_quote.gif humm, I can get a pretty huge oscilloscope for 90 EUR at a pawnshop...its last calibration has expired a few months ago. I still dunno how to measure if an opamp would be oscillating

Look at the output and recall what the definition of oscillating is... you may see a waveform of some sort at up to several MHz (or possibly more). Any sort of ringing on the output would indicate a problem (no signal on the input).

 

[leeperry]

alright, but I can't just plug it on the audio output? I have to measure two pins of the opamp I guess?

 

[ROBSCIX]

Do you have any experience with a O-scope?

 

[leeperry]

yep, from school like 20 years ago

 

[Cynips]

Just wrote about my impressions of the OPA2111KP as well as a comparison of the LT1358CN8#PBF with the LT1358IN8 I reviewed before.

 

[murrays]

Quote:

Originally Posted by leeperry /img/forum/go_quote.gif yep, from school like 20 years ago

Looks like time to start re-learning it all over again. Surely there must be a helpful "howto" somewhere on the intaweb, or a techie friend?

You can just check the output of the amp, OR you can check the pins on the op-amp. Your results will probably differ. What I did to check the amp output was to build a test plug - 1/4 inch TRS plug with 2 load resistors (similar value to your 'phones - I used 33 ohm 5 watt) and that gives you a convenient place to hook the probe onto.

Oscillation - the most severe sort will just look like a broad blur and you will probably have to switch up to a very fast timebase to see the individual cycles of the signal. With nothing playing you should get a clean straight line - not blips or spikes or blurry fuzzy crap. try switching through all timebase ranges - some artifacts only show well at certain scan speeds. A sine wave test tone should look like a clean drawn curvey line, but if the scan is too slow a large number of cycles will get blurred together, too fast and you will only see a small portion (nearly horizontal) of one cycle. You will need to translate time to frequency and vice-versa (use the 1/n button on your calculator).

Also, you are getting very hung up on the op-amps themselves, but if you do get a scope, then I suggest you take a good look at the power rails. You must always consider the power pins as a signal input also.

 

[leeperry]

oh ok! well I've seen some USB oscilloscopes on ebay for pretty cheap..

anyway, anyone knows the difference between CN8/ACN8/IN8 on LT chips? it's not documented anywhere

 

[murrays]

Quote:

Originally Posted by leeperry /img/forum/go_quote.gif oh ok! well I've seen some USB oscilloscopes on ebay for pretty cheap.. anyway, anyone knows the difference between CN8/ACN8/IN8 on LT chips? it's not documented anywhere

Read the supplier's datasheets. It's all in there. e.g. N8 is packaging, A/C/I are spec levels.

 

[leeperry]

ahhh, good point thanks! so I is the extreme temp version?

but Cynips said he prefered the 1358C over 1358I....so a higher grade IC doesn't necessarily mean "better" SQ?

I've also ordered extreme temp version samples of TI chips(THS4032 and so)

 

[murrays]

Quote:

Originally Posted by leeperry /img/forum/go_quote.gif ahhh, good point thanks! so I is the extreme temp version? but Cynips said he prefered the 1358C over 1358I....so a higher grade IC doesn't necessarily mean "better" SQ?

Chances are that given the same assortment of chips you will follow a different journey and come to a different conclusion. Every case is unique, and the number of variables are numerous. Comparing opamps tells just as much about the accompanying circuit as the chip itself. Don't just limit yourself to comparing op amps, you will also have to try (e.g.) all possible combinations of power supply bypass capacitors.

 

[leeperry]

well Cynips has pretty much the same soundcard as mine, and so far the LT1358 is one of my fav

I'll check the 1355/1364/1469 and especially 1057 before making up my mind, but I only ordered the more expensive extreme temp versions

but anyway, it's appear that between two batches of the same exact opamp you could also have slight SQ differences...and the I/C versions seem to be identical, it's just that the I are speced as extreme temp...where the C could work, but are not guaranteed to do so

 

[Bonthouse]

Quick question guys, has anyone noticed a difference between the AD797ARZ and the AD797BRZ?

I requested BRZ's, but got ARZ's..

 

[majkel]

Should be. At least there is a difference between BRZ and ANZ, the latter beign spec-wise the same as ARZ.