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Old 11th January 2007, 04:43 AM   #1
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Question Question on Opamp upgrade on phono stage

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
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Old 11th January 2007, 07:27 AM   #2
h_a is offline h_a  Europe
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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
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Old 11th January 2007, 08:23 AM   #3
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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.
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Old 11th January 2007, 11:26 AM   #4
phn is offline phn  Sweden
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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
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Old 11th January 2007, 11:53 AM   #5
Calvin is offline Calvin  Germany
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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
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Old 11th January 2007, 12:06 PM   #6
SY is offline SY  United States
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Quote:
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.



Quote:
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?
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Old 11th January 2007, 02:36 PM   #7
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Quote:
Originally posted by SY


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


True with most active riaa networks.
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Old 12th January 2007, 03:18 PM   #8
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Default 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
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Old 12th January 2007, 03:25 PM   #9
SY is offline SY  United States
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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...
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Old 12th January 2007, 03:51 PM   #10
AndrewT is online now AndrewT  Scotland
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a moderator referring to us as "tubes"!

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