[SpudHarris]

I still have the 827's in my P3+ and I love em'

. I've tried them biased to class A and as with the 49710HA's I didn't like them with this trick, they seemed too airy and lacking body or depth. I'm a little confused now about the class A trick as I noticed an earlier post with 2 x 10k resistors (I only use a 2.2k between pins 6 & 7).

Anyhow with the 49710HA's in G/VG and Hi-C Buf634's the OPA827's will take some beating.....

 

[ROBSCIX]

Quote:

Originally Posted by SpudHarris /img/forum/go_quote.gif I still have the 827's in my P3+ and I love em' . I've tried them biased to class A and as with the 49710HA's I didn't like them with this trick, they seemed too airy and lacking body or depth. I'm a little confused now about the class A trick as I noticed an earlier post with 2 x 10k resistors (I only use a 2.2k between pins 6 & 7). Anyhow with the 49710HA's in G/VG and Hi-C Buf634's the OPA827's will take some beating.....

The circuit would be a factor also as would your phones/speakers. I want to try it just for the sake of testing and searching for better sound. A buddy sent me a couple Buf634's.. when you say HI-C Is that a mod your talking about?- I don't know too much about those units or any mods that involve them. I have yet to research about them...card to enlighten me?

 

[crapback]

Do any of you guys have an IR thermometer to check the temps of your gear? My 827's were running at around 45C which is as hot as my opa earths are supposed to run. I know that's well within specs for those chips but I would expect them to run much cooler than discrete opamps. It has me wondering if there is some oscillation occurring that I can't hear. If that's the case I'd really like to find out how to stop that and retest them again.

 

[ROBSCIX]

All IC generate some heat. Opamps can generate quite a bit and still be operating within proper specs Also depends greatly on what they are doing in the circuit.
Usually when they are oscillating they draw way too much current and they get very hot. Can you leave your finger on them for awhile? You can figure out the current draw and then compare the paper value with the actual measured value. Aside from that you can use a scope... There are a couple good pages about working with opamps that are touchy. Usually fixing the oscillation requires adding caps...This page may help, Working with Cranky Opamps
Let me know how it goes..

 

[12Bass]

Don't recall the OPA827s being overly hot, and nothing approaching an AD8397 running at 24V. Could be unstable. Any capacitor bypassing on or across the power pins?

 

[crapback]

No bypassing of the opamp. I just don't know what temp the 827 should be operating at. According to the specs it can operate between -40C and +125C so a reading of 45C is about right in the middle. I'd think that's right where it should be but Kingwa told me that his hdams draw about 5 times the power of chip opamps and they run at 45C also. I have no problem holding my finger on them as that's only about 115F.

I've been a bit OCD about electronics temps since I sent an athlon1700 to an early grave. I just wanted to know if anyone else had taken any temp readings. The 827's won't be replacing my hdams so it's not important anyway.

Speaking of hdams, rolling some 827's got me comparing stuff again so I spent a little more time with the opa moon and I think I'll be keeping that in the dac of my zero for a while.

 

[leeperry]

ok I see Kingwa didn't ship my Earth yet, I've asked if I can get some Moon on top...you only live once

tomorrow I might try to swap my OPA2132 for an OPA827, but well an HDAM will be doing the final buffer anyway...the only real questions are :
-Moon or Earth(300H of burn-in yiiiiikes)
-will 1028 sound better than 1364 on vocals? I kinda doubt it.

 

[murrays]

Quote:

Originally Posted by SpudHarris /img/forum/go_quote.gif I'm a little confused now about the class A trick as I noticed an earlier post with 2 x 10k resistors (I only use a 2.2k between pins 6 & 7).

Dual op amps need 2 resistors - one on each output. The resistor value differs according to voltage rail and desired bias current. A constant current source is supposed to give better results (see Tangent's article). I found out recently that all the op amps in my old Adcom DAC have a CCS on each output. So I've been unknowingly listening to biased op amps all along!

 

[SpudHarris]

Quote:

Originally Posted by ROBSCIX /img/forum/go_quote.gif The circuit would be a factor also as would your phones/speakers. I want to try it just for the sake of testing and searching for better sound. A buddy sent me a couple Buf634's.. when you say HI-C Is that a mod your talking about?- I don't know too much about those units or any mods that involve them. I have yet to research about them...card to enlighten me?

Hi-C is just another trick with a 220ohm resistor between pins 1 & 4. It is one of those tweaks that costs next to nothing but has quite a large effect on SQ. Only problem with portable amps though is running Buf's in Hi-C runs the batteries down quicker.

I posted some pics earlier, give it a go you'll be amazed what a difference it makes.

 

[diditmyself]

OPA827 draws 5 mA quiescent. At higher voltage supplies it should be a little warm but not steaming hot. At what voltage supply is your OPA827 held?

Regarding "working with cranky opamps", it's not recommended for JFET input opamps, and I don't like the concept of those high resistor values for bipolar opamps either and this is why: http://www.head-fi.org/forums/f6/ad-...ml#post6099224

Regarding class A biasing of opamps, it's more elegant to use a JFET since the dynamic impedance is negligible and the current is kept constant, but... think of it, what load does the opamp in front of a buffer "see", almost nothing, several 100's of kOhm and most often low capacitance. It's different when it's driving MOSFETs, like in M3. I used to class A bias opamps, but then I listened blind and biased it live/while playing, and I couldn't hear any difference. When you notice any difference, is that difference to the better or just different, and are you sure the difference is really there?

 

[SpudHarris]

Well I have noticed positive differences in Opamps such as AD744, AD797 and the DIP version of LME49710's when biased to Class A. That said, there have been negative effects IMO on the OPA132's and OPA827's.

At the moment I only have my buffers in Hi-C and have no other Opamps in my P3+ biased. My current chip set ticks all the boxes at the moment, I have even gone back to the AD797's in L/R but prefer the OPA827's

The P3+ runs on 6AA 1.5v Batteries or a 9v mains adapter so that's whats powering OPA827's in L/R - Buf634's (Hi-C) - LME49710HA's in G/VG.

 

[12Bass]

Quote:

Originally Posted by SpudHarris /img/forum/go_quote.gif I have spent the weekend with the OPA827's in L/R of my P3+. I had to mess about with buffers and ground/V.ground to begin with but settled with Buf634's (Hi-C) and LME49710's (not the HA's). All I can say at this stage is that they are really, really beautiful Opamps. It's weird because warmer sounding opamps to my ears seem to miss certain details which is why I personally would describe an opamp as warm or tube like, these however seem warm but still have clarity and resolution in spades. In my set up they are not a nuetral sounding opamp but they are the best I've heard for a long while.

This sounds similar to my impressions. Initially, I found the OPA827 a bit on the warm and bland side.... then I listened a little more and found it was smooth throughout the midrange, had fullness in the lows, yet retained clarity and detail, not veiled like other "warm" op amps. Definitely better than the OPA2132, IMO.

 

[SpudHarris]

The only thing that has changed in my set up since posting that is that I use the 49710HA's now in G/VG. I didn't like them when I wrote that because they were biased to class A, I've since taken the resistors off the HA's and much prefer them that way. In G/VG they really bring detail and depth to the party.

 

[12Bass]

Hmmm.... I'm not convinced about "class A" biasing op amps, largely because modern op amps are already highly optimized, making biasing a questionable practice. Then again, I haven't tried it yet... so perhaps one of these days I'll mess around with it and see if there's any difference/improvement. I'm a bit concerned about the practice, however, as a number of my circuits are DC coupled, and I suspect that adding bias may produce DC offset at the output.

Any thoughts on the LME49710HAs compared with the AD827s?

Planning on getting some OPA132UAs in the near future to see if they are really as good as some here claim, as well as OPA1612s. Still have AD797, ADA4898-1, and some others I can't remember at the moment to test....

 

[ROBSCIX]

Quote:

Originally Posted by 12Bass /img/forum/go_quote.gif Hmmm.... I'm not convinced about "class A" biasing op amps, largely because modern op amps are already highly optimized, making biasing a questionable practice. Then again, I haven't tried it yet... so perhaps one of these days I'll mess around with it and see if there's any difference/improvement. I'm a bit concerned about the practice, however, as a number of my circuits are DC coupled, and I suspect that adding bias may produce DC offset at the output. Any thoughts on the LME49710HAs compared with the AD827s? Planning on getting some OPA132UAs in the near future to see if they are really as good as some here claim, as well as OPA1612s. Still have AD797, ADA4898-1, and some others I can't remember at the moment to test....

If I had to choose I would still take the 710HA module. However, maybe I will do some direct comparisons here today. I also have some OPA132's to try out, as I want to try the single channel version over the 2132. You reminded me I also have some 1611's to build. I have a pile of dual SOIC8 to dip 8 so I guess today is the day... I am also interested in the Class A mod just to check on the differences.