[Sinbios]

Looking at this thread, it seems the bass boost circuit in the PPA is simply a pot in parallel with R7. Now, where would this be in the PIMETA circuit?

 

[mono]

Not just a pot, you'd add the following portion in purple (mounted on a separate circuit board with jumper wires going back to the Pimeta PCB) to both holes, the solder points for R4L (and same for the other channel, R4R). Not sure it that makes sense unless you're already visualizing it...

You'd not put the Pimeta's R4R or R4L on the Pimeta board anymore. Instead, you'd use the points where you "would've" soldered the R4 L&R to solder jumper wires to the new bass boost circuit board that has both R4 resistors on it in addition to the rest shown in purple.

 

[nikongod]

the pimeta dosnt have this circuitry.

you can add it on a chunk of perf-board if you like. but it is not on the pimeta board.

 

[nikongod]

Quote:

Originally Posted by mono

note that it is the pot OR the switch, not both.

 

[silvalis]

Quote:

Originally Posted by nikongod note that it is the pot OR the switch, not both.

Isn't it the pot or R7? The switch just turns bass boost on/off.

 

[mono]

No it is a choice between the pot or the switch. With the POT turned all the way counter-clockwise you'd have (near enough to) 0 Ohms.

I simply copied that from the PPA schematic. See Tangent's PPA information for implementing the bass boost on the PPA, all of it still applies, the only deviation is how to get the circuit interfaced into the Pimeta.

 

[nikongod]

Quote:

Originally Posted by silvalis Isn't it the pot or R7? The switch just turns bass boost on/off.

nope.

1 or the other.

the pot turned all the way down (so that the circuit sees it as 0 ohms) is seen as a closed switch. bass-boost=0

when the pot is all teh way "up" it in parallel with the r7 in parallel with the cap sets the bass boost urn on, and max value. depending what values you uuse, the bass boost will level out at some frequency.

if you omit r7, bass-boost will never stop(well, whan the cap in parallel with the pot catches up with it..) , and at low frequencys you could (will) have very high gains.... bass boost will also extend further into the "midrange" if you do this. all bad stuff.

pot OR switch (or neither if you want it on all the time) and absolutely use r7.

 

[silvalis]

Hmm. ok. I don't believe you

There's just this little bit in tangent's tweaks notes that says to use one or the other as there's no point in using both.

I can't see myself why you'd use both - according to tangent's bass boost graphs using both in parallel would just lower the maximum bass boost you can have. Since the pot is already wired in parallel with itself (you have 50k resistance in parallel with the resistance from the middle terminal to the end), lowering the resistance on the pot will just decrease bass boost; raising it will increase bass boost to a maximum of 50K||50K=25Kohms (which, according to tangent's calculator gives ~10dB gain with default R3/R4/C1 values).

And yes, I can see how the switch is optional. I guess I like switches though

edit: I don't see why you can't have both. Closing the switch just bypasses the pot and the pot is there more for variable bass boost, rather than as an on/off switch. Costs more for an additional switch though.

 

[tangent]

You can install all the bass boost parts if you want to be bloody-minded. It'll still work.

Sane people will likely do one of two things:

1. R7 + switch + C7; or

2. Boost pot + C7 + optionally the switch if they want to disable bass boost while the pot keeps its position

Personally, I've been doing #2 without the switch, because toggles are ugly.

 

[silvalis]

haha. You're right, toggles are pretty ugly. I'm using a nice metal on/off push button switch.

 

[Sinbios]

What does C7 say there, 0.1uF? Would a polyester do?

 

[rreynol]

You could always socket the resistor bank on the pimeta PCB and add something like this to it.

It's the bass boost circuitry + R4 implemented on a dip20. The wires run to the pot. Since the the resistors on the pcb are socketed, you can remove it if you don't like it. Also, having the components on the bass boost circuit will let you tweak the values of the cap and resistor if you're not happy with the level of bass / frequency characteristics.

 

[Sinbios]

Quote:

Originally Posted by rreynol You could always socket the resistor bank on the pimeta PCB and add something like this to it. It's the bass boost circuitry + R4 implemented on a dip20. The wires run to the pot. Since the the resistors on the pcb are socketed, you can remove it if you don't like it. Also, having the components on the bass boost circuit will let you tweak the values of the cap and resistor if you're not happy with the level of bass / frequency characteristics.

Exactly what I was thinking of doing, except maybe not so neat

Just wondering if this will still fit into a serpac h65 9v?

 

[rreynol]

Quote:

Originally Posted by Sinbios Exactly what I was thinking of doing, except maybe not so neat Just wondering if this will still fit into a serpac h65 9v?

It won't fit in the manner in which I have set it up . I have another basic PIMETA in a H65 and the height restriction was a minor pain. I had to topple the power supply rail caps in order for it all to fit. Also, I don't think a board mounted with the favorite panasonic pot will fit either (I used the alps pot with built in switch that tangent sells). I'd bet that it would fit in the taller model, the H67. Then again, you might be able to make it fit in the H65. Just get creative.

 

[mono]

Space is pretty tight in a H65 case. If your switch were fairly small you could probably get it to work if you laid the caps flat on their sides thn remotely mounting the switch on leads, else a very shallow switch that protrudes through the side of the casing lid... which seems trickier to match up for hole-cutting but I find that a very thin piece of blue-tak allows one to make an impression of the spot where you'd drill a hole, then get a center point for the hole with a tiny drill-bit drilling through the blue-tak then later removing it for the final hole drilling.

It might be possible to make it "snap-in", by putting pins on a board that match up to the spacing of the holes for the R4 resistors, and then put low-profile socket header strips on both R4 positions. Essentially you'd be cutting the circuit board to drop in between the two film decoupling caps, or if you turned the caps sideways to mount, you might gain a little space and be able to put the board above it. It might be easier if you're using dual-channel L/R opamp rather than a pair of singles on a browndog.