Messages

OK I think I may have figured out #2 as well, and also why removing C3 doesn't seem to make any difference.  I had thought that C3 was responsible for powering the LED, but I'm now guessing that C3's only role is as a smoothing capacitor in the rectifier stage; the voltage presented to the LED is actually a heavily rippled DC voltage, and C3 smooths out the ripple.  R6 protects the LED because it controls the current flowing through the diode network.  Removing C3 just feeds the LED the raw, rippled DC voltage, with current still being determined by R6.  Maybe the ripple is just fast enough that I didn't notice it when I took out C3.

Please do correct me if I'm completely wrong though!  I promise I didn't set out intending to talk this through with myself in a public forum.

I thought of another question: I notice that there are two power-filtering capacitors, C4 and C6, of values 100uF and 100nF respectively.  I've seen this in other circuits as well.  Shouldn't their capacitances simply add up?  Is 100.1uF really that different from 100uF?  Something else must be going on; what is it?

Actually, let me rephrase that -- I should really stop using the word "signal", haha.

The voltages produced by the outputs of both op amps create a voltage difference across C3, and R6 and C3 are connected in series between the voltage difference.  Thus the magnitude of the voltage difference (dictated by R7) determines the voltage achieved by C3, while the current (dictated by R6) determines how fast it gets there.  Does that sound right now?

After thinking about it a little bit longer, I think I may know the answer to question 1: the signal coming out of the inverting op-amp doesn't actually build any charge in the capacitor, per se; it simply creates a voltage difference relative to the signal coming in through R6.  Thus R6 really does control the current flowing into C3, and thus controls how fast the charge accumulates in C3, while R7 increases the amplitude of the voltage appearing across C3.  Am I way off base here?

Hi all,

I'm pretty new to building pedals and have been lurking around the forum for a while taking stuff in.  I got started through the DIY club on tonefiend.com and have built all five of the entry level projects (Electra distortion, Bazz Fuss, FET clean boost, Rangemaster, Fuzz Face), and have just finished building a five-knob Orange Squeezer, with mods lifted from Mark Hammer's Tangerine Peeler and GGBB's Orange Smoothie, and with some advice/explanation from Mark Hammer via personal message.

Next up on the docket, and currently on the breadboard, is an Afterlife/Flatline; actually, it's a Ghost Note, as I copied Jon Patton's threshold control mod.  Because I'm a sucker for punishment, and because I'm trying to learn all I can from each circuit, I'm attempting to make a five-knob version, trying to figure out what I can do to adjust attack and release.  The Afterlife already includes a "sustain" control but it seems to me that that's really a ratio control.  Jon kindly answered some of my questions via personal message and suggested the following:

• replace R6 with a small-valued pot to adjust the attack
• add a 1M pot (plus series resistance) across C3 to shorten release

I replaced R6 with a 1K trimmer, and it seems quite effective.  I haven't tried #2 yet, but I did try adding a trimmer in series with vact_1A (the LED) to lengthen the decay, and it seems to work.  Jon mentioned that the release in the Afterlife is already quite long, but I've noticed that the LED pretty much instantly turns on and off (I don't have a Vactrol so I rolled my own with shrink tubing, an LED, and an LDR, which allowed me to see how bright different types of LED got before they went into the shrink tubing) unless I turn the trimmer up, and the release feels pretty quick to me unless I do that.  In fact, I can't really tell any visual difference in the behaviour of the LED if I just straight-up remove C3 from the circuit.  The LED still just lights up when I play and turns off when I don't.  Thus, my questions:

1) If I'm not misunderstanding the circuit, R6 controls how hard the signal gets "pumped" to C3, much as the 1k5 resistor before the diode in the Orange Squeezer controls the attack in that circuit.  But, that's also what adjusting the gain of IC1_B does (i.e. Jon's threshold control), albeit from "the other side" of the signal.  So, are the effects of these adjustments completely conflated, or do they actually have any distinct effects?  It does seem to me that adjusting R6 changes the attack while changing R7 adjusts the threshold, anyway, but I would need to fiddle around with it more to try and identify if they're doing the same thing.

2) Should I be worried that there is by default no resistance protecting the LED?  I'm not sure of the kinds of voltages we're feeding the LED, but from my rudimentary knowledge of diodes and Kirchhoff's laws, I don't quite follow why we don't see an unbounded current across the LED when the voltage of C3 exceeds Fv.  Moreover it seems like C3 is either instantly dissipating its charge across the LED if I don't put in the series resistance, or just not doing anything.

As a side note, I found that I'm getting really good results (i.e. strong compression) using what I think is an MEC MLG5547 LDR (http://leeselectronic.com/index.php?id_product=7363&controller=product&search_query=photo+resistor&results=11).  I started off with an old LDR (marked NSL-32 CANADA, if that means anything to anyone) that I got from a friend, and thought "really subtle effect, can't quite tell if it's on but it seems nice" but then when I tried the MLG5547 it clamped down really hard.  I can't compare it to a Vactrol VTL5C3 but the datasheet tells me that its turn on time and turn off time are pretty snappy (20ms and 30ms respectively), and its light and dark resistances are in the same realm as the VTL5C3.  So don't lose hope if you're rolling your own!  Actually, that brings me to another question:

3) The datasheet says I should be using a green LED, but my green LEDs aren't even close to as bright as my orange ones, so I'm getting better results with an orange one.  I looked it up and saw that green LEDs have a very wide range for Fv; does that mean that their turn-on voltage also varies?  Should I shop around for a brighter green LED?

Apologies if these questions have been addressed somewhere that I haven't already looked!