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The on/off time is around 10mS which would be slower than the H11F1M however should be negligible.

I have to kinda disagree here. The human ear can detect about .5ms of latency, and 10mS is enough to be perceived as "delay." The H11F1 is 25 MICRO seconds. It's 400 times faster! I realize that we probably deal with 10mS pretty often in digital recording without being too bothered, but I feel like you need a more compelling reason to put up with the poorer switching performance than saving a dollar on the chip when you're dealing with a latency that eventually you or someone else will be able to hear and will be bothered by. The H11F1 SMT is a little cheaper than the DIP package, too.

The good news is that there's no reason you can't make a board that could handle either, and then you could test them both. The pinouts are the same between all the optoisolator chips.

You should be safe going from 9V to 18V with the same CLR. If you were dealing with 30V or something, it might be worth worrying about. There should be some fudge room in your CLR regardless.

Oh, also, you need to worry about potential static protection with a CMOS chip, just like with MOSFETs, clock chips, companders ... and all those other components that blow up all the time. So you'll need an overvoltage zener at the input (which can also be a crude voltage regulator).

Where I would think about using these as a switch is in applications where an immediate on/off might produce a thump or scratching sound, like passive bias adjustment boosts. The question there is whether there aren't already better ways to handle such things.

For reference, here are estimated forward voltages of reasonably common parts:
Blue or White LED: 3.2V
Green or Yellow LED: 1.8-2.2V
Red LED: 1.7V
Typical silicon: 0.55-0.7V
Typical germanium: 0.25-0.38V
Typical Schottky: 0.2-3.5V

Diode datasheets are difficult to suss out this information, but diodes are mostly cheap, so just buy a wide swath and measure them with your multimeter.

Special stuff:
3.3v Zener: Fv is 3.3V in one direction and 0.7V in the other
BS170 or 2N7000 MOSFET: 1.2V+ softclipping (never hard clips) or 0.7V silicon body diode. Do a forum search for more information about using these

A resistor in series with the diodes reduces current and therefore raises the Fv. You can test the difference by putting the resistor in series with the diode and measuring the Fv again.

Also, you might consider just using single 1N914s on the symmetrical side instead of four germanium diodes. It's the same Fv.

Isn't this precisely the kind of situation where it's possible to hear a difference between silicon and germanium clippers of similar fv? (as you explained in a recent thread about 1n34A diodes — clippers are connected to ground with no extra cap post clipping)

Yes. I was just making sure the op realized that the Fv was the same. Without seeing the rest of the circuit, we can't know what else is going on here. In any case, you could also just adjust the limiting resistor instead of using two diodes. Then you could use one resistor for silicon diodes or a different sized resistor for germanium and save space on the board and cost on the final build. Basically, there's no overall benefit in using four germanium diodes instead of just two in the circuit shown.

Check out the way the LaVache does it http://www.madbeanpedals.com/projects/LaVache/docs/LaVache.pdf

The lavache is functionally identical to what the OP posted. The method the op posted is actually slightly preferable in one way: The limiting resistors can account for the reduction of the Fv by the LEDs in parallel with the other clipping options when the switch is on in either position.

OP: D4 has a higher forward voltage than the red LEDs, and therefore will not offer much of a change (that is, it won't have a higher Fv when you're in that switch position). You need to start with the highest forward voltage in the "always on" part, and allow the "on" positions to reduce the Fv further. In fact, you could omit D4 and it would sound almost identical. You also need to make sure that a blue LED will even clip the signal being produce. Their Fv can be over 3V, and many transistors and chips will being to clip at that point on their own, leaving nothing left over for the blue LED.

Also, you might consider just using single 1N914s on the symmetrical side instead of four germanium diodes. It's the same Fv.

Very much sounds like power whine.

You can improve the filtering at the power jack by increasing the resistance in the resistor-capacitor low-pass filtering network at the DC jack. You're probably like "What resistor?" Well ... most of the time, we just see a big cap from +9V to ground. Your power supply has a very small amount of resistance, so this forms a low-pass filter with the big cap. An additional 100nF film cap is usually used to filter higher frequencies because apparently film is better at that task than electrolytics. [Edit: there's no cap like this in the slambox, so you could solder it across the DC jack to add some filtering.]

Often, this is good enough, which is why a lot of your pedals work correctly. Sometimes, though, especially in high gain circuits, you need to increase the filtering. You can put a 47R in series with the +9v power and it will filter out more noise. Look at r24 in the mudbunny for an example. If you can still hear the noise -- if it just got higher pitched but didn't go away, use a larger resistor, like 100R. I'm suggesting the resistor in part because going any bigger on your filtering cap might involve a capacitor that's physically too large for the board.

There is a small price to pay for this, probably about a quarter volt, so you could lose a fraction of boost and headroom.

This is A+ work!

My kids friends are gonna be pretty ripped when they come to our house and see all the cool gear they get to use because their dad builds/hoards musical instruments...

Yeah, but once he's old enough for all his friends to play rock music, your kid's gonna be really embarrassed by his dad and all the electronics. 

Source: I used to be a kid and am still embarrassed.

I'm in NY, and I don't really want to pay 1.25 per... dang.

That's closer to the normal price for these. The BLMS price was outrageously low and I'm not totally convinced his were real Lumberg ones or just a clone. Note that the Musikding price is .95 euros, which is $1.27. Jameco was also close to that much. FWIW, these are totally worth it for 1590A builds. You can do side DC jacks with them with the body of the jack on top of 9mm pots.

Use the 5ka or the linear 1k. I don't,t think the tracers made a mistake, but I don't understand how a transistor can drive a 1k load. I doubt it matters what raper pot you use since anything below fully open is probably going to have a big, sudden volume loss. Figure 500ohms from the transistor, that's half the pot. I just don't see the need, especially given the absurdly large output cap. You could reduce that by a factor of 10 and use a 10k output cap and still have every subharmonic known to man coming out.

What a strange circuit.

Post a schematic. No way to tell without seeing it.

The gain pot has all the lugs wide open to ground when its turned fully clockwise. Could this be my problem? When the pot is tuned fully counter clockwise, lug 1 and 2 are open to ground, while lug 3 is not... Kind of puzzled here.

Look at the schematic. The gain pot connects to ground. This is not your problem. You need to inspect every connection to the base of Q1 to figure out where the short is. Remove them all one at a time if you have to, and if worst comes to worst, scrape off the solder mask with a knife and see if there's a fault in the PCB connecting something to the ground plane. Compare everything with the PCB image in the build doc.

Look for a solder bridge at R3 and R4 on the left side of the PCB.

Being "most desirable ones" has very little to do with whether the transistors will be "the most useful ones." What I'd do is look up the datasheets for the part numbers that the guy has. Meaning, take a smart phone with you if you have one and look them up on the spot. Look up the polarity and the gain range. Otherwise, just test a couple transistors out of each bag if you have a DMM that does that; if the gain is really low, like under 40, there are very few guitar pedals that will even work with them.

Your best bet for figuring out what the mot valuable part number is is to look at the schematics for a bunch of old fuzz pedals and then write down the part number. Not the series (like "OC"), but the specific part number. Then look up the equivalent transistor from other companies. New Market, for instance, is a brand name, but the same transistor construction as in the 213 and 275, which are very valuable, have different part numbers by RCA or Telefunken, for instance.

Here are the most useful "numbers":

PNP 40-80: Q1 in classic Fuzz Face
PNP 80-130: Q2 in classic Fuzz Face and Q3 in a MKII, Three-knob bender, or Buzzaround
NPN 40-50: Q1 in a low-gain NPN fuzz face
NPN 60-70: Q2 in a low-gain NPN fuzz face
PNP 40-60: Q1 in a Percollator
PNP 20-40: Q1 and Q2 in Tonebender MKII, but requires moderate leakage
PNP 70-80: classic Rangemaster, requires low leakage; Skreddy Screwdriver if moderate or high leakage

Also, a bunch of my projects are made to work with lower gain NPN Ge transistors 50-70hfe. I'd buy a handful of any NPN black glass transistors you see near that gain range, like 7113, or RCA metal can stuff like the 2N1304.

[Ghost Note - Afterlife with Sensitivity knob.]

Ghost Note - Afterlife with Sensitivity knob.

Brian suggested that fiddling with R7 could change the sensitivity. So I put a minimum resistance of 24K on a 50K pot. Stock settings are near the center. CCW is more dynamics and headroom before it squishes, and CW is squishier with a hint of bloom. I highly recommend this mod if you use multiple guitars with different pickup outputs.

Hi! First time poster here. I know this thread is very old but am hoping Jon or someone else can answer this as I am interested in building an Afterlife with the sensitivity pot mod:

Question is trying to understand how you "...put a minimum resistance of 24K on a 50K pot. "

I haven't found any clear answer to this after doing some googling and such. Thanks!

Use a 24k resistor in series with a 50k pot (just lugs 1 and 2). When the pot is at 0, the resistance will be 24k.

Try my Hamlet if you have major headroom concerns. Otherwise, all the Zero Points are awesome, and the Multiplex is amazing.

It's not so much the headroom that concerns me ( although I have been eyeing up the hamlet - who is selling the boards?) more the garbage noise that seems to be inherent with the pt2399. Companding seems to be the way to go ala pt80, but I really should check out the ZPs and mplexes. I guess the echo base just put me off PTs in general...

Like Forrest says, the PT2399 just doesn't have the bandwidth to do "clean." Companding only helps manage signal levels going into the chip -- if you avoid feeding it a signal that will exceed the 5v power rails, then you can avoid overdriving the PT2399, but you won't make it sound cleaner.

The Hamlet "cheats" in multiple ways ... it feeds the chip an attenuated signal (rather than what's done in something like the Deep Blue Delay where the signal is boosted before it goes to the PT2399), it has an LED cap on the current of the PT2399 itself (which prevents the audio signal in the chip from ever exceeding 1.7V but doesn't distort because it doesn't clip the audio), and it has severe filtering which is then reamplified and tone shaped by a stage that's completely separate from the dry path (getting around the issue most delays have where they mix the delay signal raw back in). I'm not trying to puff up my design, but it's WAY simpler than using a compander, uses a 2c indestructible diode instead of a $5 chip that blows up when you look at it wrong, and the topology allows a delay line that still SOUNDS bright but is clean for most of the dial.

Also, re bandwidth concerns, it's not like even MN3005s are that high fidelity to begin with. It takes two of them, preceded by a compander, severely band-passed, running on 15V, to put out a "reasonably" clean 500ms. The Zero Point SDLX's analog mode is astoundingly good, and it does all this other stuff, too ...