Hi guys
I have an existing phono pre that I do not want to change or modify. So I did a search for pre-equalizer circuits for 78RPM records, something that would sit between the LP player and the phono stage and provide equalisation to modify the standard RIAA for 78RPM playback. The only circuits I found were add-ons to modify existing circuits (like the ESP circuit). I do not want to modify my existing phono stage, so I was hoping that someone could help me with a pre-equalizer circuit with unity gain that can do the needed additional equalisation, and then be plugged into my existing phono stage.
Thanks beforehand,
Deon
Edit:
PS. I was thinking about this. A post phono preamp equalizer could also be useful. So the EQ would be between the phono pre output and the linestage input, doing the needed EQ at line-level levels rather than the low levels direct from the cartridge. This design should be easier. I would appreciate any and all suggestions.
PPS. I hope be can come up with designs for both. The pre-phono stage circuit for people who have a pre-amp with a good built-in phono stage, and the post-phono stage circuit for those who have a separate phono stage. The circuit for the post-phono stage version could start with a reverse-RIAA circuit, then do the needed EQ after. I am not aiming for ultra audiophile sound here, just a good, usable circuit. For those requiring ultra premium sound there are units available at multi-$1k prices. I am not in that league. Thanks again to all that can contribute. Deon
I have an existing phono pre that I do not want to change or modify. So I did a search for pre-equalizer circuits for 78RPM records, something that would sit between the LP player and the phono stage and provide equalisation to modify the standard RIAA for 78RPM playback. The only circuits I found were add-ons to modify existing circuits (like the ESP circuit). I do not want to modify my existing phono stage, so I was hoping that someone could help me with a pre-equalizer circuit with unity gain that can do the needed additional equalisation, and then be plugged into my existing phono stage.
Thanks beforehand,
Deon
Edit:
PS. I was thinking about this. A post phono preamp equalizer could also be useful. So the EQ would be between the phono pre output and the linestage input, doing the needed EQ at line-level levels rather than the low levels direct from the cartridge. This design should be easier. I would appreciate any and all suggestions.
PPS. I hope be can come up with designs for both. The pre-phono stage circuit for people who have a pre-amp with a good built-in phono stage, and the post-phono stage circuit for those who have a separate phono stage. The circuit for the post-phono stage version could start with a reverse-RIAA circuit, then do the needed EQ after. I am not aiming for ultra audiophile sound here, just a good, usable circuit. For those requiring ultra premium sound there are units available at multi-$1k prices. I am not in that league. Thanks again to all that can contribute. Deon
Attachments
Last edited:
It would certainly be simpler to just build a new preamp. Inverse RIAA is notoriously difficult to achieve precisely, and then you’ve got to implement your five replay curves anyway, not to mention the many dozens of other possibilities. Have a look at Gary Galo’s Archival Preamp in Linear Audio for one approach.
You could put a miniDSP between your phono preamp and amplifier to modify the response with whatever EQ was desired.
I built a flat response phono preamp and then applied whatever EQ was desired digitally. The EQ is perfect and the channel matching is perfect once the gain of the two channels are matched. It can be done in real time using a miniDSP or other stand alone box or using a USB audio interface and running filters on a PC. As I use a PC as my digital source this works well for me. I just used a few op amps and some proto board. I used the balanced TRS line level inputs on my MOTU USB interface. There is no apparent line noise above the preamp noise floor.
I only built the first stage shown in the schematic with the LT1037 and went to the MOTU from there.
I built a flat response phono preamp and then applied whatever EQ was desired digitally. The EQ is perfect and the channel matching is perfect once the gain of the two channels are matched. It can be done in real time using a miniDSP or other stand alone box or using a USB audio interface and running filters on a PC. As I use a PC as my digital source this works well for me. I just used a few op amps and some proto board. I used the balanced TRS line level inputs on my MOTU USB interface. There is no apparent line noise above the preamp noise floor.
I only built the first stage shown in the schematic with the LT1037 and went to the MOTU from there.
There is countless used line level Graphic EQ units around already built.
Anything from Technics to Sansui.
Anything from Technics to Sansui.
Why do you think that? The required equalization is the same either way. Multiplication is commutative.