Question on Opamp upgrade on phono stage

[marchewd]

I have a Jolida JD9 (OPA37 opamps) and Rogue Stealth phono stage (AD797 opamps) and I would like to replace the Opamps in. I have decided on either the Burr Brown 627 or 637. The 627 has unity gain, but the 637 is only stable if the gain is equal to or greater than five. I admit, I do not know much about electricity and electrical circuits, so I thought I would ask one of you guys since there are many knowledgeable members here. I can pick up the 637 opamps much cheaper right now, so I would perfer to use those; however, I do not want to buy them and find out they don't work. Can someone please explain how the gain relationship works? I have searched the web and cannot find any good information. Or, would it be better to use a discrete opamp like this one: www.bursonaudio.com/burson_hdam_module.htm ?


Thanks for any and all help,
Dan

 

[h_a]

Hi!

If you don't have any experience in electronics, I would really recommend not replacing the opamps in an amp where nobody with more experience has done that before!

Especially the AD797 is a great chip - and expensive - and delivers its full potential only in circuits which were designed for this opamp.

Remember, it's not just changing an opamp for getting good sound!

Cheers, Hannes

 

[analog_sa]

I can only agree with Hannes.

Still, not much harm in some innocent swapping fun.
It's extremely unlikely an opamp in a phono stage will be used with gain < 5. If you post some pics of the boards there will no doubt be more suggestions.

 

[phn]

The AD797 is about as good as they get. I would leave it.

The OPA37 is a very good opamp, though not like the AD797. But to swap the OPA37 for AD797 could cause the phono stage to oscillate. You might need a bypass cap (see datasheet). This may not be possible to impliment.

The 637, as impressive as it is, should usually not be used in phono stages.

My

 

[Calvin]

Hi,

"The 637, as impressive as it is, should usually not be used in phono stages."

Well, it all depends on the topology of the phonostage what kind of OP-amp to use in which position, doesn´t it?
The 637 shouldn´t be used in every possible position, but can be used with very good results in the appropriate ones. As input stage for a MM-system or as second stage-amp it can be a very fine solution.

On the rest I agree with my forerunners. Successful tweaking needs more than just beeing able to order samples
When the circuit is designed properly, it will be very hard to beat the used OPamps OP37 and AD797 sonically, let alone to get better specs (like noise).

jauu
Calvin

 

[SY]

It's extremely unlikely an opamp in a phono stage will be used with gain < 5.

With active RIAA, the opamp must be unity-gain stable.

I admit, I do not know much about electricity and electrical circuits

Then, seriously, don't screw around with expensive gear until you've learned the basics and let the smoke out of cheaper stuff. Would you replace the pistons in your car without knowing anything about engines or how to use a wrench?

 

[analog_sa]

With active RIAA, the opamp must be unity-gain stable.

True with most active riaa networks.

 

[marchewd]

Thanks for the replies

Thanks for the replies. I know quite a bit about computers and popping out op amps is easy enough. What your your thoughts about discrete op amps instead of chip op amps?

Thanks,
Dan

 

[SY]

It's doubtful that you'll get significantly better performance in this application than the 797 using discrete unless you do some very exotic and complex tricks, i.e., build a new phono stage from scratch. Of course, one could use tubes...

 

[AndrewT]

a moderator referring to us as "tubes"!

Call them by their real name, "valves", and the ambiguity disappears.

 

[valveitude]

Call them by their real name, "valves", and the ambiguity disappears.

As soon as you stop calling your cars trunk the "boot"

 

[AndrewT]

at least we don't call you old boots.

What about the Burr Brown OPA227 (op27, lt1007, max427 replacement) or OPA228 (op37, lt1037, max437) in single dip8 or so8.
Also available in dual 2227, 2228 or quad 4227, 4228 (dip14/so14).

 

[peranders]

With active RIAA, the opamp must be unity-gain stable.

It is not necessarily so. It depends of how feedback you have.

 

[SY]

a moderator referring to us as "tubes"!

Call them by their real name, "valves", and the ambiguity disappears.

How about "big glowy hot things?"

P-A, if you follow the RIAA curve, at some point you have to hit unity gain, since the 75us time constant is the highest one. If you incorporate the 3.18us zero, you might be able to stay above unity gain, but that would mean enormous amounts of gain in-band.

 

[AndrewT]

Hi,
if the 75uS is passive (and last) then the gain can remain higher throughout the band.

 

[marchewd]

I will just contact Rogue

Thanks for the lesson and repsonses. I will call Rogue and and talk to the circuit designer for his opinion. I just thought about the OPA637 because I had some (bought them for next to nothing). But I didn't want to stick them in and either fry the chips or the Rogue!

Thanks again,
Dan

 

[SY]

Hi,
if the 75uS is passive (and last) then the gain can remain higher throughout the band.

That's right. But with an active circuit, you're almost certainly going to hit unity gain at some point. A circuit designed for a unity-gain-stable chip is very likely NOT to use a passive 75us, so willy-nilly opamp substitution could be problematic.

 

[pjpoes]

I don't really see what an OPA627 or 637 would be a poor choice in a phonostage, it is a very quiet opamp with low distortion specs.

I used them as the input of a MM phonostage and liked the results quite a bit. I've also compared them with some chips from Linear Technologies, the LT1115, which is recomended for phonostage use, and liked the Linear better. The AD797, as many have said, is a really good opamp, and is not worth upgrading.

Knowing rogue gear, the opamp is not the place to upgrade. More than likely better results will be had by replacing any coupling caps and the power supply caps. Minimaly bypassing them should offer some improvement. However, given that you said you don't know a lot about this stuff, I would probably leave it alone.

I just recently went through one of my phonostage, a Musical Fidelity X-LP and replaced every part on the board with better ones. I found that the opamps made the preamp quieter, but that was really about it. However, in the case of the MF, I went from a very cheap national chip to a BB chip, you are going from an already very good chip to an arguably better, but very possibly worse chip. Its a latteral move.

 

[marchewd]

Thanks

Thanks for the reply. The coupling and power caps upgrades were installed directly from Rogue before the unit shipped out. So, I guess the Rogue has hit it's ceiling. It sounds great, but I was just wondering if it could sound better. I bought a Jolida JD9 knowing I was going to mod it and I will keep the one that sounds better in my system. I had never heard anyone swapping out the opamps in a Rogue Stealth, but I figured it wouldn't hurt to ask the question since I had extra opamps lying around. I just didn't want to install them if it would hurt the phono stage or opamps.

Thanks again,D
an

 

[pjpoes]

I've never seen a rogue with particularly high end components inside. They aren't junk by any means, but I would say that if you really want to see what tweeky parts can do, I would more seriously look at the caps. What brand are they?

As for the film caps, that is often where the biggest difference is made, since they are almost always in the signal path. Tell me what brand they are? Even if they are using something as nice and highend as Solen, you could further improve the sound with Relcaps, Cardas, etc. Short of it having all teflon v-caps, you can argue that improvements can be made in that unit. Its not peeked out, I promise.

There are also things that can be done further with the power supply. What type of regulation does it use? Depending on your willingness to change things, you could probably add better regulation. Also the Rogue is tube correct, what type of tubes are in it, that of course would be another area to upgrade. Also the tube sockets and the wire connecting any of that. Some people claim they hear no difference, I personally do, and though I don't like spending tons of money on it, I do find that Silver sounds different than copper, and gold different from both, etc.