The Opamp thread

[SpudHarris]

I really must have another listen to the OPA1641, I've heard good things about it........

 

[Charminbaer]

After long time reading datasheets and trying to understand opamp circuits, i came to the conclusion that the AD797 can´t be put in the m-stage without modification of the circuit.
 
So i paralleled the source input resistors with 100ohms and also put 100ohms and 22pf in the feedback loop. 
 
Sound-stage opened up dramatically! It sounded like the instruments are right in front and around you. I compared it against LM4562 and it has no chance against Ad797BR. In every aspect.
 
Now i only have know where the resistor for the inverting input (-IN) is. Does someone have any clue?
 
Nevermind, i found it.
 
Also did Class A Bias. Brought another improvement in instrument separation and sound-stage.
I will add some RMAA measurements later on.
 

 

[Charminbaer]

I just measured the dc offset at the headphone output, it´s 9.9mv and -4.8mv. Can i measure the offset directly at the opamp output pins to ground? 
I´ve read somewhere it can be reduced by using a pot between pin 1 and 5. Is that correct or do i have to pay attention to something else?
 
 

 

[qusp]

sure you can use a pot to inject some of the output signal back into the inverting input to get rid of offset, but seriously, I wouldnt worry too much about that level of offset

 

[qusp]

Quote:

After long time reading datasheets and trying to understand opamp circuits, i came to the conclusion that the AD797 can´t be put in the m-stage without modification of the circuit.
 
 
 

 
hehe theres a saying i'm searching for here somewhere, can you help me out here? 'I told you so' is that it? hehe

 

[Charminbaer]

 
Quote:

sure you can use a pot to inject some of the output signal back into the inverting input to get rid of offset, but seriously, I wouldnt worry too much about that level of offset

 
Ok. I just wondered what would happen if i removed the coupling cap. Therefore i wanted to know how high the offset is before going through the cap. Do you think it is a good idea to remove it if i can trim down dc offset?

 
Quote:

Quote:

After long time reading datasheets and trying to understand opamp circuits, i came to the conclusion that the AD797 can´t be put in the m-stage without modification of the circuit.
 
 
 

 
hehe theres a saying i'm searching for here somewhere, can you help me out here? 'I told you so' is that it? hehe

Yep, you were right.
 
But i´m glad i tried it. I learned many new things.
 
And i´m very happy with the sonics of the AD797, never heard something similar. The sound-stage is HUGE

 

[qusp]

sure no cap is a good cap, if you can avoid them absolutely. actually now rereading your post I had forgotten about the null pins and was just describing how you might do it with a regular differential input opamp ie inject DC into the inverting input, but the 797 has its purpose built pins for this, so yeah go for it. youve done the distortion cancellation trick too yeah? its a tricky little opamp and the datasheet is full of good info and now you can see why you cant just drop it in and expect the best results. 
 
indeed bass slam and soundstage are superb with this chip.

 

[Charminbaer]

 
Quote:

sure no cap is a good cap, if you can avoid them absolutely. actually now rereading your post I had forgotten about the null pins and was just describing how you might do it with a regular differential input opamp ie inject DC into the inverting input, but the 797 has its purpose built pins for this, so yeah go for it. youve done the distortion cancellation trick too yeah? its a tricky little opamp and the datasheet is full of good info and now you can see why you cant just drop it in and expect the best results. 
 
indeed bass slam and soundstage are superb with this chip.

okay

I measured dc offset directly from the opamp output pins and it is only 0.6mv and -0.5mv there. Why is it that much higher at the phones output? could the buffer add offset ?
 
yes i´ve done distortion cancelling, although i had no 50pf cap. I only used a 22pf , but it definitely changed the sound for the better.
 
I noticed that the higher i went with the class a biasing resistors the more stable it got. Best results so far are with 10k. Less heat than unbiased and more slam. Maybe it needs more load impedance? I think i will try some JFETs.
 
I thought about exchanging the adapter, what do you think is the best for a picky ic like Ad797? I found this one:
http://cgi.ebay.de/10pcs-Dual-SOIC-to-DIP-8-Convert-PCB-Adapter-SMD-OPA627-/230408616394?pt=LH_DefaultDomain_0&hash=item35a56c79ca
 
Or maybe browndogs ? Mine came with rather cheap ebay adapters.

 

[Mad Max]

Those may be better.

 

[Charminbaer]

Quote:

Those may be better.

which ones? the browndogs or diyinhk ?

 

[Mad Max]

diyinhk

 

[Charminbaer]

Okay i bought them. Hope it does not take too long.

 

[Charminbaer]

Tried biasing again, this time with 15K. Another improvement. From what i have measured the m-stage uses +/- 14.15V. If i´ve not made an error bias must be at 0.943mA now.
 
Edit:
 
I found a schematic of the m-stage or some other BCL Clone:
http://i774.photobucket.com/albums/yy29/davidlouis1983/_.jpg

 

[T.B.N.]

I have a quick question about the OPA2227 that I need for an Apheared 47 amp that I'm building. It is meant to drive low impedance cans like Grados. Does this alter the requirements for the 4 opamps in the schematic? Why does it require two dual channel opamps on the left and right sides of the schematic? http://benfeist.com/a47/
 

 
 
EDIT: Nevermind, I guess the two opamps in the schematic are simply the 8 pins of one opamp.

 

[mencargo]

Hi everyone!
 
I want to make a DIY project with a Creative Sound Blaster Live 24bits, SB04100
 
I found this thread, great info, but I would like recommendations for opamps and capacitors, and I saw this opamp thread, but since it started more than a year ago and has 222 pages, I got desperate after some reading.
 
My current favorites based only on reviews and recommendations are:
 
 
LM4562
AD8066
OPA2211A
ADA4627-1
 
But I don't even know if I can place all of them at my card, open for suggestions.
I think I enjoy, in decreasing order, soundstage, detail, mids, bass, treble.