The Opamp thread

[Mad Max]

Quote:

Thanks for your help! I'm purchasing a new Essence ST that comes with 2 LME479720NA's, so if there's no difference to the LME49720 then I'll just pop in the NA's.

'NA denotes the plastic DIP8 version.  If you end up liking it, then you may like the metal can version even more (LME49720HA).

 

[leeperry]

 

Try LT1028ACN8  

This one is hard to roll blindly...whatever in my Spitfire DAC or on the Prodigy HD2, it would make a loud crackling noise when my fridge motor turns on/off or someone turns off my bathroom neon...I also had it checked w/ an oscilloscope by a pro, and it was oscillating in the Mhz range. Clearly not for blind rolling IME.
 
LT1363 is a far better candidate

 

[dlaloum]

Quote:

 

This one is hard to roll blindly...whatever in my Spitfire DAC or on the Prodigy HD2, it would make a loud crackling noise when my fridge motor turns on/off or someone turns off my bathroom neon...I also had it checked w/ an oscilloscope by a pro, and it was oscillating in the Mhz range. Clearly not for blind rolling IME.
 
LT1363 is a far better candidate

Well it sounds like the fridge motor is throwing out both a spike and additional RF noise.... and the Power Supply is not up to controlling it.
 
So my take on that type of issue would be... regardless of the opamp this will have an impact (some more audible than others) - so first fix the PSU - and if the LT1028 is particularly sensitive to it - us it as your sensor, your "canary".
 
1) Put something on the power line to absorb the spike (surge protector, power regulator, isolating transformer, regenerator or UPS) - pick your flavour and budget... but a common computer sine wave UPS can help (make sure it is a full sine wave version! otherwise it is nasty).
2) Put some chokes on either end of your power cables (all power cables going into and out of ANY interconnected piece of equipment in your rig. (Once the noise is in there, it can pollute your ground and spread to other components via interconnects - even if the components are off)
 
There are articles on the web about eliminating RF noise - also lots of articles from Ham Radio people (they suffer worse than Audio people do from RF issues... for obvious reasons - they are working within the RF bands!)
 
Once the noise is eliminated from the LT1028 - then you can listen to see if you like to OPAMP, and you can try your other favourites - you may find they have improved....
 
 I just recently went through extensive choking of all in and out lines of my rig - and it has definitely helped! - I was previously getting some hash at low levels in my RMAA measurements (which helped me to identify the problem) - the chokes on all the lines have eliminated that - and grounding everything to a common ground has eliminated a low level hum problem as well - and on the RMAA graphs the harmonics of the 50Hz power have dropped to less than half what they were before. 
 
Some say that the biggest gains in Audio quality all come down to power supply - both adequacy (enough in a timely manner when required) - and cleanliness.... they may be right.

 

[murrays]

 
Quote:

Well it sounds like the fridge motor is throwing out both a spike and additional RF noise.... and the Power Supply is not up to controlling it.  
So my take on that type of issue would be... regardless of the opamp this will have an impact (some more audible than others) - so first fix the PSU - and if the LT1028 is particularly sensitive to it - us it as your sensor, your "canary".
 
1) Put something on the power line to absorb the spike (surge protector, power regulator, isolating transformer, regenerator or UPS) - pick your flavour and budget... but a common computer sine wave UPS can help (make sure it is a full sine wave version! otherwise it is nasty).
2) Put some chokes on either end of your power cables (all power cables going into and out of ANY interconnected piece of equipment in your rig. (Once the noise is in there, it can pollute your ground and spread to other components via interconnects - even if the components are off)
 
There are articles on the web about eliminating RF noise - also lots of articles from Ham Radio people (they suffer worse than Audio people do from RF issues... for obvious reasons - they are working within the RF bands!)
 
Once the noise is eliminated from the LT1028 - then you can listen to see if you like to OPAMP, and you can try your other favourites - you may find they have improved....
 
 I just recently went through extensive choking of all in and out lines of my rig - and it has definitely helped! - I was previously getting some hash at low levels in my RMAA measurements (which helped me to identify the problem) - the chokes on all the lines have eliminated that - and grounding everything to a common ground has eliminated a low level hum problem as well - and on the RMAA graphs the harmonics of the 50Hz power have dropped to less than half what they were before. 
 
Some say that the biggest gains in Audio quality all come down to power supply - both adequacy (enough in a timely manner when required) - and cleanliness.... they may be right.

Leeperry said his amp was oscillating in the RF range.  The stability problem must be addressed first before you even start to consider filtering external inputs. My amplifiers are stable and I do not even have shielding on my interconnects, let alone any chokes, filters, ferrites, etc.  The HF oscillation will colour the sound (IMD) and cause sensitivity to environmental phenomena. By the way, if it not done right, adding filters to trap/block noise can actually create more problems than they solve, even positioning can play a part. 
HF noise spikes do not always enter by the power supply as you would expect; sometimes the coupling is via electrical ground, or air (EMI), or inductive coupling with wires in the walls or other nearby equipment.
You are correct about grounding  - a good ground is very important, and needs careful attention.

 

[qusp]

yep, thats why due to everything in my system being DIY, I have floated all shield grounds tied to my plumbing. agreed on PSU quality though, until its sorted out everything else is coloured by it and nothing you will do with signal can stop that till its done. the opamp is oscillating because its a very wide bandwidth chip being used for lowly audio signals and as with all of its kind, it needs compensation in the feedback loop to address this,I think you'll find its in the datasheet, plus I mentioned it earlier

 

[leeperry]

 

 
Well it sounds like the fridge motor is throwing out both a spike and additional RF noise.... and the Power Supply is not up to controlling it.

Good point. But both the computer ATX PSU for the HD2 soundcard or the "Firestone Supplier" linear regulated PSU couldn't control it. Using a "Unity Gain Stable" opamp fixes the problem completely.

 

[yiancar]

Hey guys am new to the opamp trip.

I am building a phono preamp where a Chopper stabilized DC-servo is used. Its based on a MAX420 but this chip stopped manufacturing right? As a replacement I found OP07. Any other suggestions?

 

[Satellite_6]

I don't suppose it's a good idea to pry the original op amp out at an angle. . . I can't take the EF2A completely apart without an allen key and I can only get at the adapter at an angle.

 
EDIT: I got it out without destroying it, does it matter which way the new one goes in?
 
EDIT: nvm, I got it.

 
EDIT: Clarity has increased a bit with the LT1364 and the sound sig of my EF2A has become more analytical. . . now I have to get used to the sound sig all over again! I suppose if I end up not liking it I can try something else.

 

[Pluto2]

Speaking of oscillation, I recently installed some ADA4627-1s and opa827s in my circuit (+_15V), and noticed that the ADA chips got much hotter than the opa ones, though I understand the ADAs draw 2 mA more each, but, would it feel much hotter for a 210mW dissipation than a 150mW? actually it was a bit unbearable with a finger touch......
 
I used to have LM4562s and opa2211s at the same locations but they were just warm....Can I assume there is no oscillation at the ADAs, given that LM4562 has higher GBW product than the ADA? Ah,....would the adaptors have something to do with it? I do have 0.01 uFs on the main board though but not very close to the adaptors. Thanks!

 

[ROBSCIX]

Who here is using any bypass caps on their opamps?
If so what type of caps do you use?
I have read varying opinion on this subject so figured I would ask you guys what you think...
opinions?

 

[jageur272]

Quote:

Who here is using any bypass caps on their opamps?
If so what type of caps do you use?
I have read varying opinion on this subject so figured I would ask you guys what you think...
opinions?

 
A decent quality polyprop or tantalum coupled with a ceramic should have all of your bases covered.  Using electrolytics as bypasses doesn't help at all.  I find that a 2.2uF polyprop with a .01uF good quality ceramic has been my modus operandi for the past few amps I've made.  Great results thus far.  I may add a 1uF tantalum on my next one.
 
Adding bypass caps is vitally important if you want to preserve the high speed of the opamps which translates into better fidelity.  I am of the opinion that opamps sound different, but each circuit has a bigger change on the sound of an opamp than anything else.  The capacitance that it's driving, the topology of the circuit, etc. are more important than which adapter sounds better.  In fact, adapters are ALWAYS detrimental to the sound of an opamp, stray capacitance will always make the circuit less stable.
 
But I digress.  Bypasses are important.  The smaller values should be placed as close to the pins as possible or right on them even if possible.  Bass seems tighter compared to unbypassed in a simple (cmoy-esque) circuit.

 

[Mad Max]

Noted.
 

 

[Satellite_6]

I think I'm going to have to go back to the original op amp in my EF2A. There is the possibility that what I'm hearing is just placebo or something but here it is. . .
 
The bass sucks now! It has no omph and overall the sound isn't as dark. I loved the dark-ish, musical sound that the 5654 tubes gave me and now that's gone. It's even more noticeable when using the EF2A as just an amp and using my Cowon as the source. The i7 has never sounded so dry! The sound is marginally clearer I think but the sound sig doesn't go well with the HD 650s. To be fair, I don't think this is a bad thingmajob, it just doesn't go with the 650s. I'm not going to switch back right away but I think I will eventually. The difference is pretty small anyway I think, not the kind of improvement I got from rolling tubes.
 
Any advice for a more "musical" sounding op amp? I might try another or decide to settle with the original.
 

 

[leeperry]

your EF2 runs off a wall wart, LT1363/4 has a low PSRR...it will not sound good.
 
Try AD797B/LT1028AC/ADA4627-1B/OPA827/etc?

 

[Satellite_6]

Quote:

your EF2 runs off a wall wart, LT1363/4 has a low PSRR...it will not sound good.
 
Try AD797B/LT1028AC/ADA4627-1B/OPA827/etc?

Bummer, I guess that was a bad recommendation then?
 
I will keep listening though.