advertisement


Converting speaker level input to line level

JemHayward

pfm Member
I want to drive the bass bins of my ML Summits from a line level input, rather than from the output of my power amp so I can introduce an element of DSP without it getting anywhere near my panels. At present they accept a speaker level input, but I now have the schematic, and I think this is the input from the bass binding posts, and I'm thinking that the R1001 R1005 and R1006 are the attenuators, and that I'd be feeding it with a balanced output from my preamp, as the IC has a differential input.

Can someone confirm my thinking is correct, or tell me I'm an idiot, and point me in the right direction?

Summit bass input by Jem Hayward, on Flickr
 
Another sanity check on this project: If I'm using a miniDSP balanced board, which is 24 bit 48kHz resolution and I'm using it to process signals that are below 270Hz the digital resolution will be more than enough?
 
Sorry - another question: If I connect to the Op-Amp inputs directly, will I need to remove the R1005 and R1006 or could I leave them in place. I want to do the minimum amount if alterations so I can reverse it if I ever sold my speakers.
 
What precisely are you wanting to drive it from? Is it a low impedance line level signal? Is it balanced? If so the very simplest would be to remove R1001 and put 10 K across R1005 and R1006.
 
I would be driving it with a miniDSP Balanced 2 x 4 - so basically a standard balanced connection - hopefully fitting an XLR 'plug' on a flying lead, so yes low impedance line level.

When you say put 10k across R 1005 and R 1006 do you mean relplace R1001 with 10k, or put 10k in parallel with R1005 and 10k in parallel with R1006 - which would reduce the values of those resistors.
My gut feeling says lift R1005 and R1006 and connect the + and - of the balanced line direct to the op -amp - but I'm on the edge of my electronics knowledge here (which I assume is obvious anyway!)
 
I would be driving it with a miniDSP Balanced 2 x 4 - so basically a standard balanced connection - hopefully fitting an XLR 'plug' on a flying lead, so yes low impedance line level.

When you say put 10k across R 1005 and R 1006 do you mean relplace R1001 with 10k, or put 10k in parallel with R1005 and 10k in parallel with R1006 - which would reduce the values of those resistors.
My gut feeling says lift R1005 and R1006 and connect the + and - of the balanced line direct to the op -amp - but I'm on the edge of my electronics knowledge here (which I assume is obvious anyway!)

Don't go with your gut feeling then!! It makes no difference whether you lift R1005, 1006 or not. My "instructions" are how to do it with the least effort and least "messing with" the original circuitry... hence you could solder the 10K resistors across the originals from the top without removing the board... if it's accessible and not SMD... even if SMD then just use leaded resistors. These values give unity gain.
 
Brilliant - many thanks. So I remove the resistor between the +ve and -ve (R1001), and then solder 10k resistors piggy back on the 356K thus reducing their value and it is then no longer a L-Pad attenuator - that has now sunk in to the very small bit of my brain that gets electronics - I could then connect via the current binding posts which would be a bit weird but makes the whole thing easily reversed. Thanks for your expert guidance.

Just need to get my parts sorted out and I'm ready to go.
 


advertisement


Back
Top