Bipass RIAA in Doug Self pre-amp - diyAudio
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Old 29th November 2012, 02:21 PM   #1
athanor is offline athanor  Portugal
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Default Bipass RIAA in Doug Self pre-amp

Hello all,

I've just bought the Elektor magazine, and the Doug Self pre-amp seems amazing! I've also have followed the thread about it, but I have one question related with the phone preamp in particular (the MC/MM board). Maybe someone could help me, since I'm not that good in circuit analysis.

I do vinyl restoration, so sometimes I use digital filters to correct the response of different manufactures of old discs (where RIAA filters don't apply streakily). So, is there a way to bipass the RIAA filter of this design (I want to place a relay somewhere, so I can choose to use it or not).

I'm not shure if I am allowed to upload Elektor magazine schematic, because of copyright issues...

It would be great if someone (or Doug, to which I kindly thank for the work), could help me in some way!

Cheers,

Isaac
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Old 29th November 2012, 02:31 PM   #2
DF96 is offline DF96  England
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As any equalisation is unlikely to radically depart from RIAA, and digital equalisation of large changes can create problems, I would leave the RIAA in place and then digitally adjust the result.
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Old 29th November 2012, 04:35 PM   #3
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Actually quite easily done by having this relay You want to use disconnect the capasitors in the feedback network.
But then You have a amplifier wich is amplifying some 20dB less in the mid-frequency area, and 40 dB less in the deep bass.
More or less no amplification one could say.
If You also disconnects one of the resistors (or "replaces it with one of another-Higher value) You have a amplifier with flat response and suitable amplification all over.
I believe the resistor in question here would be the one in paralell with the bigger cap in the feedback. PLEASE correct me if I'm wrong here folks.

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Old 29th November 2012, 06:34 PM   #4
Mooly is online now Mooly  United Kingdom
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Quote:
Originally Posted by athanor View Post
I'm not shure if I am allowed to upload Elektor magazine schematic, because of copyright issues...

It would be great if someone (or Doug, to which I kindly thank for the work), could help me in some way!

Cheers,

Isaac
Hi Isaac.

The Elektor material is all under copyright so no uploading I'm afraid

I think the other replies have pretty much covered it for you although one other option might be just a totally separate gain stage to use when needed feeding into a line level input.

It just seems a shame to hack the PCB around really.
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Old 29th November 2012, 08:21 PM   #5
athanor is offline athanor  Portugal
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Hello all,

and thank you for all the help provided! This place (aka forum) is filled with amazing people!

In fact, it is a shame to mess the wonderful pcb work. Anyway, since there is always more knowledge around here (I'm totally outside my expertise), someone could tell me a "just bypass this, do that, and you're done" kind of thing. I'm starting to fell the best way is, in fact, leave it as it is...

Once again, thank you for the help!

Cheers,
Isaac
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