TAPLFO PWM output + transistor PWM buffer issue - can't go above 5V?

[midwayfair]

and the indicator works much better in the four LED setup than the three.

Wait, really? I must have missed that early. Damn, two indicators is really kinda inconvenient for my layout ... I'll see if I can make the dual work.

Yeah, sorry about that. I mentioned it in my response to Dave. I hadn't realized that you were using the other LED(s) as an indicator.

Okay, I guess it's take it straight from the pin or figure out how to get the dual going. I definitely can't do two LEDs, it would just be horribly awkward on this layout.

[midwayfair]

Found out something today: When referencing the transistor in the datasheet to +9V instead of +5V, flipping the NPN so that its collector is at ground instead of at the +9V/LED side makes it work spectacularly well. There's more depth than doing the +5V reference (like what's in the datasheet), and I think that the waveform is actually a little smoother than when the transistor is the "right" way around (i.e. emitter to ground).

I don't understand why that is, but I guess today's lesson is don't be afraid to stick parts in the wrong way around.

Oh, and I solved the "can't fit two LEDs in this layout" issue by using a dual/common anode LED. Rare bird, but worked perfectly.

I'll have the enclosure for what I made here in a few days.

[drolo]

I had the same feeling when trying the transistors reversed once, but did not feel comfortable leaving it like that, not sure what long term effect the reversed polarity can have on the transistor ... maybe it's ok, maybe not ...

Here is an article from RG that left me doubting:

http://www.geofex.com/circuits/when_good_opamps_go_bad.htm

[midwayfair]

I had the same feeling when trying the transistors reversed once, but did not feel comfortable leaving it like that, not sure what long term effect the reversed polarity can have on the transistor ... maybe it's ok, maybe not ...

Here is an article from RG that left me doubting:

http://www.geofex.com/circuits/when_good_opamps_go_bad.htm

Interesting read -- but is the base actually reverse biased just because the transistors are upside down? The LFO signal is AC at all times, not DC, and the transistor ought to be just a variable resistor. What I can't understand is why it makes a difference which direction the transistors face.

RG's last couple of paragraphs seem to suggest that in a 9V circuit a transistor should be okay. The PWM is AC and no larger than +-5V, so I would think that the base isn't being reverse conducted outside of the range of the transistor ... but I don't know what effect it would have even if it did, since the transistor is not being used for audio.

[Mike]

That little transistor buffer in the datasheet was originally drawn up in my living room back in 2008 (I think) by an EE friend of mine. I was a struggling newbie trying to hack together the VCLFO (predecessor to the TAPLFO) and the Tremulus Lune. Tom ended up using it in the datasheet, even though it (and my amateur power supply filtering) is not essential. Taylor used it in his Tap Tempo Tremolo boards, too. Kind of cool.

Regardless, I emailed two questions to my friend:

1. Any problem connecting the transistor's collector to a higher voltage, particularly 9V (keeping in mind that the PIC is still running at a regulated 5V)?

2. It was reported that turning the transistor around works better-- Collector to ground, Emitter to V+. Why does this even work, and is it bad for the transistor?

I'll let you know if / when I get an answer.

Mike

[midwayfair]

That little transistor buffer in the datasheet was originally drawn up in my living room back in 2008 (I think) by an EE friend of mine. I was a struggling newbie trying to hack together the VCLFO (predecessor to the TAPLFO) and the Tremulus Lune. Tom ended up using it in the datasheet, even though it (and my amateur power supply filtering) is not essential. Taylor used it in his Tap Tempo Tremolo boards, too. Kind of cool.

Regardless, I emailed two questions to my friend:

1. Any problem connecting the transistor's collector to a higher voltage, particularly 9V (keeping in mind that the PIC is still running at a regulated 5V)?

2. It was reported that turning the transistor around works better-- Collector to ground, Emitter to V+. Why does this even work, and is it bad for the transistor?

I'll let you know if / when I get an answer.

Mike

Hey, thanks!