new opamp

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goodguy

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Hi and thanks for taking the time to read this post.

I have purchased a nice dac which uses an Burr Brown opa2604 opamp.

Can anyone suggest a good upgrade. I was thinking of the ever popular BB opa627ap but have been told this is quite old and should really consider a modern one.

Can anyone please advise, something which works well in the opa2604's current environment (voltage, current, etc)

Many thanks in advance. John.
 
The only op amp I've ever used for audio projects is TL07x, but it seems 2604 is higher performance than that, so I don't know what ti recommend. To me it looks like the 2604 is a really, really good amplifier. Why do you want to change it?
 
Hi. Many thanks for the reply. I did hear on a few of the forums that the opa2604 is an older opamp and a little noisy. I was thinking of trying the newer opa827 on browndogs, it is only going to cost £15 for this upgrade so was wondering if it would be worth it, the only difficulty is that i would have to import the goods from US (ebay) as there are no sellers over here in the UK.

Many thanks. John.
 
It has been so long since I've done real electronics engineering that I don't remember how to do the math to prove it, but I'd bet a couple of boxes of chocolate donuts that the 2604 op amp, with a noise spec of 10nV/roothz at 1khz (vs the marginally better 827 at 4nV/roothz), is not going to be the source of whatever microscopic noise there may be in your ADC. Either of these op amps (or the TL07x for that matter) is capable of better signal to noise ratio than you're going to come anywhere near in the rest of your signal chain, especially as an input buffer for an ADC. I'd be very, very surprised if you could even measure any difference without some really expensive lab equipment. I'd be even more surprised than that if you could actually hear any.

Just one opinion, but if it were me, I wouldn't waste the solder, nevermind the £15, or the time it would take...
 
Hi. Thanks for the reply.

The reason i want to change the opa2604 opamp is that it does not work well at low volumes, i noticed increasing the volume on my media player caused the dac to sound better, the more i increased the volume the better it sounded, a few other people have reported the same. I agree with what you are saying that the opa2604 is a good opamp but only at high volumes. The result of this is i have some very annoyed neighbours, plus whenever someone comes to visit me he always says: "I knew you were in, i could hear your muic at the bottom of the road."

Many thanks. John.
 
Op amps are just op amps, they don't sound better at high volumes or low volumes. If you're getting distortion at low volumes but not at high volumes it probably isn't the op amp, it could be a leaky capacitor, or instability, or any number of digital reasons. By the way I recommend the ADA4841-2 op amp which was recommended to me by mshilarious before he retired. It has the very low noise of 2.1nV/root Hz, is low distortion, runs at up to 12V and only takes 1.1mA current. I made a mic pre amp using it and I'm very happy with it. It's more than quiet enough for any condensor mic.
 
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Okay , there is one small issue when trying to replace an OPA2604 , the OPA2604 is a very good opamp but it has a feature that makes it pretty hard to replace in some cases and that is that the OPA2604 has a Max supply voltage of +/-24v which is higher than pretty much any other opamp , so if your DAC uses a Supply voltage of +/-24v for the 2604 and you replace it with something like a TL072 for example then the TL072 will fry .......

so if you can confirm the Supply voltage that you are useing it would be easier to recomend a suitable replacement .... the OPA2604 is a very good opamp though and just because it is old doesn"t mean that it isn"t good ....
 
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