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bass boost on pimeta (just like ppa?)

post #1 of 5
Thread Starter 
I *think* the answer is obvious but just wanted to check.

looking at the schematics for the pimeta and the ppa series, they both use the same multiple feedback style topology and it SHOULD be easy to add the same exact bass boost circuit by pulling out R4 (or in my case, its already socketed) and adding that series network of the pot, parallel R and C and then add back in the R4 to that.

it should just work and be identical to the ppa style one, right?

the ppa series uses diff values for r6, the feedback R on the main op amps. pimeta uses 1M and ppa uses 470k (why are the different, btw?)

would this mean I need to scale values, somehow, on the pimeta style bass boost?

since the boost pot goes from zero to 'high R' and zero means having no effect at all (essentially out of the circuit) - I should be able to use almost any high value pot for this, 10k on up to 50k, right? the higher value will just give more boost, but if I happen to have 10 or 20k in pots, that will work just with less total effect, right?
post #2 of 5
I used a 10k pot || 0.22uF Wima MKP cap.
goes from normal to mega bass with decent travel. It's great for bassing out I just feel my pimeta is lacking a bit in resolution. I think its them BUF634s to be honest cause the AD8610/20s in there are detailed lil buggers.. anyway.. the BB works great
Here's the post that got me going..
I did a similar implementation as MisterXs, but far from as neat :P well.. that was a year ago..
post #3 of 5
Thread Starter 
update: here's my relay based pimeta bass-boost:










its similar to mr x's daughterboard method. mine mounts on one edge with a metal post and the other end of the board is supported by the wires from the yellow .15uF caps as well as the inline resistors (between 2 IC socket machined pins).

it took a bit of time to craft this together had to steal the pins from IC sockets, cut the perf board to size, figure out where the components would have to sit to have their leads extend down and hit the R4 holes (also IC socket pins).

apply 12v to the relay and it opens the NC contacts and the R/C are in series - adding the bass boost. remove power from the relay (its normal disposition) and you have flat response with the R/C combo shorted out and only the series R4 there for normal linear gain.

...sort of a lesson I learned from the gamma1 double-stack style!
post #4 of 5
Thread Starter 
update: new version.

I did a pc board for this (using eagle and laser printer toner etch) this time around.

the relays are 5v aromat style, dpdt. here's the circuit:



and my layout:



(power is not shown as that is wired in, or would use top traces if there were any).

some photos of the '2nd floor' board:









the idea is to use 2 different resistors and switch them in combos, in series.

with this I get 4 states:

0 ohms
low ohms (1 resistor; around 2 or 3k)
medium ohms (1 resistor; around 5 or 6k)
high ohms (both are in series, adding)

that gives me an 'off' (bass boost disabled) as well as 3 other settings. no pots needed! all wiring is 'local' and not traversing the case!

this is going into my preamp which has an IR remote control. this is why I wanted switchable bass-boost - I'll assign 4 buttons to the 4 states and switch the relays on based on the button pressed.
post #5 of 5
I know this is an old thread, but its all I could dig up in the search.

I'm adding bassboost to an amp im working on at the moment, it uses the alps RK097 pot with built in switch for the bass boost control.

I want to use the SPST switch built in to switch BB on and off, mainly for an uncluttered front panel. Could I use the relay idea like the one above or could I use transistors to switch both channels from the same switch?

I thought I might be able to use something like this but don't know how this effects SQ.

Evan
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