Op Amp Advice – RQ970BX Phono Preamp Andy Grove Mod
Hi
I recently bought a Rotel RQ970BX phono preamp. I wish to try an upgrade of the Rotel based on the "Andy Grove Modification" which was printed in the Nov 1994 edition of HiFI World. Please bear with me as, although I am an engineer, I have a very rudimentary understanding of electronics. I can read a basic circuit diagram and can wield a soldering iron but I am very much a “monkey see, monkey do” hifi enthusiast.
I need help with the substitution of the op-amps. The mod called for replacement of the NE5534 op-amps and replace them with the AD744’s being used in the front end. The gaps left by the AD744’s were to be filled with AD743’s.
There is still a live link to the mods on:
https://www.hifisentralen.no/forume...w_nov_94.pdf&usg=AOvVaw3AeXdNNih-x87CkDBkt1ym
There are also handy discussions of the mods below which have helped my understanding of audio circuits:
Rotel RQ970BX phono preamp mods? | Audiokarma Home Audio Stereo Discussion Forums
Dumb op-amp question from complete newbie
I would still be able to use the AD744 but I believe the AD743 are expensive and hard to come by. Op-amp tech has also moved on. On another discussion OPA627’s (output) and LME49710’s (input) were also successfully used. I have researched some alternatives and the OPA627’s successor (which are eye-wateringly expensive) is the OPA828 but its specs are quite different eg
slew rate – OPA627 is 55: OPA828 is 150
GBW – OPA 627 is 16MHz: OPA828 is 45MHz etc.
I am way out of my depth here as I have almost no idea what would be appropriate. What characteristics are important and what should I be looking for?
I would like some advice on what op-amps I could use in the circuit that aren’t too expensive or do I bite the bullet and order original. I will be putting in DIP sockets so I can test alternatives. HELP please!!!
Hi
I recently bought a Rotel RQ970BX phono preamp. I wish to try an upgrade of the Rotel based on the "Andy Grove Modification" which was printed in the Nov 1994 edition of HiFI World. Please bear with me as, although I am an engineer, I have a very rudimentary understanding of electronics. I can read a basic circuit diagram and can wield a soldering iron but I am very much a “monkey see, monkey do” hifi enthusiast.
I need help with the substitution of the op-amps. The mod called for replacement of the NE5534 op-amps and replace them with the AD744’s being used in the front end. The gaps left by the AD744’s were to be filled with AD743’s.
There is still a live link to the mods on:
https://www.hifisentralen.no/forume...w_nov_94.pdf&usg=AOvVaw3AeXdNNih-x87CkDBkt1ym
There are also handy discussions of the mods below which have helped my understanding of audio circuits:
Rotel RQ970BX phono preamp mods? | Audiokarma Home Audio Stereo Discussion Forums
Dumb op-amp question from complete newbie
I would still be able to use the AD744 but I believe the AD743 are expensive and hard to come by. Op-amp tech has also moved on. On another discussion OPA627’s (output) and LME49710’s (input) were also successfully used. I have researched some alternatives and the OPA627’s successor (which are eye-wateringly expensive) is the OPA828 but its specs are quite different eg
slew rate – OPA627 is 55: OPA828 is 150
GBW – OPA 627 is 16MHz: OPA828 is 45MHz etc.
I am way out of my depth here as I have almost no idea what would be appropriate. What characteristics are important and what should I be looking for?
I would like some advice on what op-amps I could use in the circuit that aren’t too expensive or do I bite the bullet and order original. I will be putting in DIP sockets so I can test alternatives. HELP please!!!
To properly reverse engineer a circuit, there must be a complete schematic and BOM available.
Otherwise, "hit and miss" would be an understatement. And phono preamps are extremely
critical of design, layout, and parts.
AD743 | Octopart
Otherwise, "hit and miss" would be an understatement. And phono preamps are extremely
critical of design, layout, and parts.
AD743 | Octopart
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The opamp substitutions in that article don't make sense - the AD744 has a lot more voltage noise than the NE5534A, and represents a downgrade. Yes its got less current noise, but the 5534A is good enough, and adding a lot more voltage noise completely defeats the purpose!
There might be an argument for chosing a more modern JFET opamp with good voltage noise specs here, but its hardly worth the effort.
There might be an argument for chosing a more modern JFET opamp with good voltage noise specs here, but its hardly worth the effort.
At the very least I would suggest you install sockets for the op amps while you have the iron in hand to give yourself the opportunity to try alternatives and decide for yourself.
Used OPA627 is a bit of a crapshoot but there is a resistance test, details of which have slipped my mind but can likely be found with a search engine, and idle current can be measured. Passing both tests is unlikely for a fake.
Used OPA627 is a bit of a crapshoot but there is a resistance test, details of which have slipped my mind but can likely be found with a search engine, and idle current can be measured. Passing both tests is unlikely for a fake.
Unfortunately confirmation bias is very powerful and can easily account for this, the only way to avoid it is blind testing. This has been proved over and over and over again. The brain cheats, and subjective perception of audio is affected by many factors in the brain - witness the McGurk effect for instance - your brain lies to you about what it hears....
Quite often you see people claim they made a change to the circuit and it sounded better. But to do this you need to have
a very good auditory memory over significant time periods. The actual auditory memory in the brain lasts about 7 seconds,
which is why you need to do back-to-back blind testing of sound samples to reliably compare them - which requires both
the original and modified systems to be simultaneously available and switched between at random with an ABX test harness
or similar.
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