OpAmp Resonance?

[Stew]

I'm thinking about trying the original JRC2068DD's in the balancing circuit with the AD826's for output buffers to see what happens. If it still "motorboats", I may try the OP275 or AD825 for output buffers per George's suggestion.

Are the JRC2068's decent for the balancing circuit? If not, what would be a good replacement?

 

[primalsea]

Stew,

Davidsrsb is correct. I should have said put a small capacitor between the opamp OP and - input, not the 2 inputs which will actually make this worse.

Apologies about that.

 

[Stew]

OpAmps to Consider?

I'm looking at several opamps that may be worth trying: OP275, OPA2132, opa2134, OPA2227, and AD823. Are these generally more stable than AD826? I'm especially interested in trying OPA2227 and AD823. Any success (or failure) stories with these?

 

[Stew]

I've narrowed down my list and am most interested in the AD823. I'd like to try them for both the balancing circuit (replacing JRC2068DD) and the output buffers (replacing JRC 5532D) but would appreciate some feedback on whether or not these should work.

Is this opamp unity gain stable? Looking at the datasheet, I think it is. Also, the output current (15 mA) is lower than most. Is this an issue?

 

[georgehifi]

15ma is pityfull, the AD825 will give 50ma all day and 100ma if asked for, use them if you want good drive, 8ohm output impedence as well.

Cheers George

 

[Stew]

15ma is pityfull, the AD825 will give 50ma all day and 100ma if asked for, use them if you want good drive, 8ohm output impedence as well.

Cheers George

George - These won't be used to drive headphones. The output buffers are for the analog outputs to the amplifier. Is 15ma adequate for this purpose?

I'd love to try the AD825's but would need 8 + 4 adapter cards. $$$$. I'm hoping to get similar sound from the AD823 without breaking the bank. What do you think?

Thanks for the advice!

 

[georgehifi]

I don't consider 50ma to be over the top, just good for cd output opamp to have that kind of head room.
If you look at the circuit of my dac in the link from my previous post, it is discrete, and can give 6watts out if asked for, now that's excessive, but also it is so far the best sounding dac i've heard, and I've heard quite a few, I do use a passive volume control though (because I don't belive in preamps), and it aways helps to have a strong output from the dac to drive through them.

Cheers George

 

[poynton]

............ If you look at the circuit of my dac in the link from my previous post, it is discrete, ...............

Hi George,

Wheres the link?


Andy

 

[georgehifi]

Sorry Andy it was in another thread, here it is just go down a bit and there's three diagrams, power supply, front end, and rear end.


http://www.diyaudio.com/forums/showthread.php?s=&threadid=57887

Cheers George

 

[Stew]

Problem Solved!

I checked the output current on the original opamps and they're around 15-16 ma, which is the same as the AD823. I put four AD823's in today and they sound great with no oscillation! The sound is pretty close the AD826's, maybe a little smoother. Thanks for all the advice!

 

[Stew]

After some more listening, I realized that with four AD826's, my system had more punch and detail (but oscillated ocassionally). With four AD823's, mids and highs were a little smoother but I lost the punch and bass response. I tried two AD826's for balanced to unbalanced and two AD823's for output buffers. This combination gives me punch, bass, detail, and smoothness - with no oscillation.

 

[Stew]

After spending some time with AD823 output buffers, it became obvious that the upper mids and highs were overemphasized and lower mids and bass were lacking. It's a shame; best vocals I've heard!

By the way, I feel stupid after a discovery I made recently. When I pulled the AD826's due to oscillation I noticed a capacitor between two of the opamps bent over with one lead close to, but not touching, a resistor lead. I straightened it and didn't give it a second thought. The next time I changed opamps I started wondering if the leads were close enough to cause the oscillation problem. I put the AD826's back in and No Oscillation!

The AD826's are the clear winner for the balanced to unbalanced converter but I'm still searching for the right output buffer. I like the AD826 dynamics but they sound a little sharp as output buffers.

I'm considering AD843's or OPA627's with brown dog converters. Will these work OK with +-5V rails? The datasheets say they will but how do they sound with +-5V's?

 

[namcir]

hi have you ever tried the LM6172?