Pearce BC-1 Limiter Section

[bobbass4k]

I've been meaning to do this for a while, not my first layout but my biggest so far and first one I've shared with the world.

It's the limiter section from the Pearce BC-1 Bass Pre-Amp, a now pretty legendary bass pre-amp (Used by Billy Shehann, though his is heavily modded). I used one once and I can only describe the experience as transcendentally spiritual. I've been hankering for a high ratio comp/limiter recently so this seemed like a no-brainer.

It's based on the service manual schematic here -. I've used half a 13700 instead of the 3080, I managed to keep it down to only 2 standing resistors, which i know is still 2 too many for some of you, but I make no claim to my stripboard skills being any good, I couldn't see a way around it and still keeping it 1590B friendly. It might be a push as it is, as you'll need a charge pump board too, I was going to put one on the main board, but I actually prefer separate boards.



I realize a bass limiter isn't the most exciting of pedals, but I've done the work, so not sharing it seemed pointless, I'll be building it tonight/tomorrow.

Image updated 07-01-17, I've built it and this layout works, but the circuit itself will need tweaking, see below.

[Ciaran Haslett]

Hi Bob.  Nice share!

Before you start building have another look at your +15V.  The 353 and 4558 are not connected to it.  Adding a double link to the long one on the right will sort that.

Also, the 33K at IN>GND assumes (I think) an input from the "Mixer Out" at all times.  I might be worth upping this to the usual 1meg seen as pulldowns on guitar effects.

Lastly the Limiter Out is always connected to a buffer.  Pretty sure this won't matter as a standalone circuit but just making note of it incase you experience any weirdness when hooked up to other pedals.

Anyway, good luck and looking forward to your progress.

[bobbass4k]

D'oh... Well spotted thanks, I shuffled those links around at the last minute to shave a column out and I forgot to mark the double link...

With the input pulldown, yeah I figured 33k might be a tad low, I was gonna see how it was after building, but yeah that may well become a 1m. I suspect the CLR for the limit LED will change too, 1k seems a tad low.

Started building last night, just got the electrolytics to put on.

[bobbass4k]

Finally got round to finishing this last night, it works! Kind of...

The layout is sound but the circuit itself will need some adjustments to make it useable, as it's designed for a much hotter signal the lower limit of the threshold was way too high even with an active bass, I ended up jumpering the 470R which brought a lot more life out of it, but the useable range is still well at the low end of the pot, i think a lower pot value and making the 470R a trim-pot would be the best solution, ad it will need to be tweaked for different output levels. With a makeup gain stage at the end I think this would make a great heavy compressor, which I might get round to eventually...

I'll put a new layout up tonight in case anyone feels like tinkering with the circuit themselves.

[Ciaran Haslett]

Looks like increasing R131 should give you more gain.  Maybe try increasing to 100K?

[bobbass4k]

Yeah I was looking at that, there's probably more to be coaxed out of the circuit as it is, I've updated the main image, gained a couple of rows to accommodate the trimpot, though Thresh 2,3 is just connected to ground, so you could lose the bottom row and take it from another ground point, or snip the unused leg 3 off the trimpot and take it from there.