Tubby56 Posted July 14, 2021 Posted July 14, 2021 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/forumet/attachments/diy-og-utvikling-ha-yttalere-forsterkere-etc/507300d1535893509-rotel-rq-970-bx-ve_rotel_rq970bx_hfw_nov_94.pdf&usg=AOvVaw3AeXdNNih-x87CkDBkt1ym There are also handy discussions of the mods below which have helped my understanding of audio circuits: https://audiokarma.org/forums/index.php?threads/rotel-rq970bx-phono-preamp-mods.420686/ https://www.diyaudio.com/forums/chip-amps/161301-dumb-op-amp-question-complete-newbie-3.html 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!!!
Tubby56 Posted July 14, 2021 Author Posted July 14, 2021 Here is the Technical Manual for the Rotel rotel_rq-970bx.pdf
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