Pre-amplifier modules to add gain level adjustment to 1,000W MosFet amp to drive 18" subwoofers

Hi All

I am looking to swap my 500W sub amps for 1,000W amps on my 18" subs as I want to build some additional 15" but the BK Electronics BPSP 500 amps (which are great) are no longer available, so will use the 500W on the 15" and 1000w on the 18". I have the work horse amps but these don't come with control plates and preamps, I do all the EQ and time alignment with DSP and this has a 560 Ohm output impedance (mini DSP 10x10). My 18" run from 8 Hz - 38Hz, I have no high pass filter just a low pass.

I'm looking for a small perhaps 12V (I have some fleabay 12V supplies) mono preamp circuit or kit that I can use as a gain control. I will also try a passive pot but do want to try active as well as I often find passive is perhaps more resolving but less dynamic and these are all about transients and dynamics so I want them to be as dynamic as possible so will try a cheap pre amp to make sure I'm not missing out

Any recommendations, I just want a nice small volume pot with perhaps a buffer and gain control. It has made me think that perhaps the 500W Subwoofer plate amps might sound better with a nice naim circuit (I use old naim preamplifiers in the AV set up) feeding the other sub power amps as I don't need the controls for EQ and phase. But after thinking about 24V power supplies and recommissioning an old naim HiCap I reminded myself the 500W are superb sub amps and the internal small and obviously cheap pre amps is fine with these !

Thoughts appreciated (By the way having replaced the internal Cremona Subwoofer amplifiers with external 500W amplifiers I am very aware that low frequency subwoofers are not immune to what drives them like some believe)

Any small DIY pre-amp board the input sensitivity of the amp is 500mV, but I can change the sensitive resistor to 775mV as I have the circuit schematic if any more information would be helpful. Any recommendations for small boards that I can build in appreciated

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@IWC Doppel

Adrian - if it helps, at 10Hz that input stage schematic has an effective AC input impedance of about 5kohm, give or take. The R3 value of 4K7 value dominates, and the 100K ..simply voids clicks/pops by ensuring input side of C1 has a path to 0v.

So - quite a low input impedance.

The simplest thing that could work really well would be say a single 10K linear pot on its own - the parallel 4K9 AC input impedance will effectively give the control a nice semi - log control curve. Easy, and cheap - providing your DSP pre source is happy driving loads down to say 2.5Kohm range. If not - a simple opamp buffer can be added.

ATB!
 
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That's just the maximum output voltage which you will never reach (or need).
Exactly; 2Vrms would be ABS max line-level input to this; and at that - have already driven the 1kW amps way past clipping/sub meltdown ... so never going to happen
[- and if it did - since IWC & I live in the same city - I'm sure I'd hear it :0 ]

Yet - even at that signal-level, the NJM opamps can drive 100ohms, from the datasheet linked.

So - seems to me , simple passive input attenuation along the lines suggested first by batteryman - will work.just.fine.
 
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Martin, thanks I have listened to a 24" Ascendo driven by 6KW and that had some rumble ! Made me think perhaps building a 24" at some point might be interesting 🙂

I do have a 10K pot I did use with Crossovers some time ago - a big Ohmite, I am also looking at where to fit these units as my rack is a bit jammed, thinking perhaps under the sofa with a cover and a temperature controlled fan. They did have fans fitted permanently on and they are AC fans so wanting to avoid sitting on a hot amp or hovercraft....

Thinking of 40-50 team sensor. Sat ticking over the heatsinks get to about 34-35 degrees
 
Yes.
Because the input impedance is defined by R3 so is around 4k.

So this will severely load a 100k pot, hence why 5k has been suggested and also, in this case, his DSP has a low output impedance of 500r which won't have a problem driving into the 5k pot in parallel with R3.

A 10k pot would work equally well.

Another minor point is that lower series resistances generate less noise.