Bypass RIAA stage

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Hi!

I'm little noob with electronics so asking little help from you experts.

My intention is to bypass the RIAA stage and use the pre-apmlification only (if this is possible).

Here's a photo showing the layout of board and components (one channel):

An externally hosted image should be here but it was not working when we last tested it.


Which leads is needed to cut to get the RIAA stage totally bypassed?

Juha
 
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Its difficult to tell from the photo, but my guess would be that the leads where you've labeled the picture "out" is the output of the RIAA stage. It would be easier to identify the output with a schematic of the board.

The marked "out" lead goes straight to a RCA connector labeled as output and the "in" lead comes straight from a RCA connector labeled as Input. Picture shows only one channel and supposeingly those components (6-7 components) placed in column on the right side are for RIAA EQ.

I try to sketch the schematic.
 
Jiiteepee, I don't know if you're aware, but there's another option. Instead of bypassing the phono stage, you can build a little "inverse riaa" or "reverse riaa" filter. It basically takes a line level input and applies the inverse of the riaa curve and attenuates the signal so that the phono input can accept the signal, as if it were coming from a phono cartridge. The circuit is passive (needs no power) and can be made compact.

Check out the following:

Reverse RIAA

http://www.diyaudio.com/forums/solid-state/580-inverse-riaa.html
 
Here's the schematic:

10ztfds.png


I'm not sure 'bout pin order of those U1/U2 (probably wrong in my schema).
 
Jiiteepee, I don't know if you're aware, but there's another option. Instead of bypassing the phono stage, you can build a little "inverse riaa" or "reverse riaa" filter. It basically takes a line level input and applies the inverse of the riaa curve and attenuates the signal so that the phono input can accept the signal, as if it were coming from a phono cartridge. The circuit is passive (needs no power) and can be made compact.

Check out the following:

Reverse RIAA

http://www.diyaudio.com/forums/solid-state/580-inverse-riaa.html

In this case it's not an option because of this pre-amp is going to be used in computer setup where a digital RIAA EQ filter replaces this analog one. I need the flat pre-amplification just for to get input signal enough high. For me it would be easier to achieve the target by modifying this phono preamp instead of building a new one suitable for turntable input.
 
I suspect Q1 and Q2 are in fact transistors and not op-amps. The schematic as drawn makes little sense. You need to identify those transistors and make an accurate schematic.

It may be as simple as removing the caps you have identified as C5 and C6 or not..


For me it's maybe impossible to identify those Q1/Q2. I have to try what happens to the correction curve when one of them is removed.
 
I made a simulation from situation where caps was removed:

Original RIAA stage (LTSpice example):

An externally hosted image should be here but it was not working when we last tested it.


Caps removed:

An externally hosted image should be here but it was not working when we last tested it.


As suggested earlier, it looks like it could be one solution worth to check out (least in this LTSpice exaample).
 
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