Holy Roller

[Charlie]

I'm a newb, nuff said right?

I loath asking questions, but here I am. I've searched high and low for a good, not so terribly difficult schematic for a DIY compressor. The Holy Roller seems to be just the right one for me. My question is many fold my friends so sit back and enjoy the newb nonsense, and hit me up with some kind of answer. I appreciate it. Anyway, I want to use the Holy roller as a vocal/bass guitar compressor, since it is an "La2a style" limiter/compressor. My questions only arise from wanting to up the voltage to between 18 and 20v for headroom with the vocals. I've already decided to use the 2sk117 Jfet from the Baja man version, and I've read that they're interchangeable. I'm going to assume that that first indicator LED will explode immediately if I don't lower the voltage for it. Now, I'm a country kid so bare with me, but if I'm doing the math right; I would need 895 ohms of resistance between power rail and 5mm Blue LED. Is That right? Is there such a beast? I have some LM317 voltage regulators, so would that be better? Overkill? More chance for noise? Alright, first five questions down, and you're still with me.. Sweet! I'm going to use two LME49860NA ICs that are rated at 22v, so I should be good there. I'm not using the chip for any other reason than it being the highest rated that I have around, so I don't know much about that. I do Know that I'm down to my final question. Is it as easy as doubling the Capacitor, and resistor values? Thanks for hanging with me, and Thanks for any help.

Charlie

[mjg]

You can always put more resistance between your power supply and LED.  You might find with a blue one that you'll burn your eyeballs out if it runs at full brightness. 

I'd suggest trying it out on a breadboard if you can, and try something like a 10k or 4k7 to start with.  If your maths is right, just don't go below the value you calculated, but you can go higher.

I think that answers one of your questions!

[Charlie]

Thank you mjg. That does answer a question, and I appreciate it. I will give it a go very soon.

[alanp]

If I'm understanding what you're doing (increasing the supplied voltage), then the LED current limiting resistor should be the only thing you'd need to change, as long as all the parts in the circuit are specced to deal with the increased voltage. (ie, not trying to stuff twenty volts into a nine volt rated capacitor.) The actual values (ohms, microfarads, etc) for everything else should remain the same in most circuits. There are some exceptions to this, but they aren't common, especially not in stompboxes.

[m-Kresol]

Welcome to the forum.

*2sk117: watch the pinouts!!! The 2SK117 has S-G-D, while the MPF102 D-S-G. you'll have to twist the legs, if you want to use that (or redesign the pcb).

* blue LED: like the others said, they are generally very bright. with 9V supply, I use 10k minimum as CLR. I would therefore suggest to try 20k-50k.
** 895 Ohm resistor: I haven't checked your math, but I think it will be hard to get anyways. Every value resistance can be produced, but it's only a matter of demand. My guess would be that if you find it, it will cost you big time.
** LM317 voltage regulator: overkill. If it's only for the indicator LED, you will never see the fluctuations in supply voltage.

*LME49860NA: The stock LF353 used in the project is rated for Vcc,max = +18V, Vee,max= -18V. Max difference = 30V. If I read this correctly, you could use +30V on Vbb and 0V on Vee (=gnd). Generally 30 % safety margin should be planed for all components, i.e. 25V electrolytics, when you plan 18V operational voltage. Components deteriorate much faster close to their limits. The LME49860NA has a range of 46V, so that works for sure. I can not attest to it's sonical properties though.

[Charlie]

Wow! I think I have found a new home. I was expecting damnation, but I got helping hands. Haha! Gearslutz turned me off of forums years ago, but you guys are awesome. I've learned more from the three answers here than a whole day of google.

Welcome to the forum.

*2sk117: watch the pinouts!!! The 2SK117 has S-G-D, while the MPF102 D-S-G. you'll have to twist the legs, if you want to use that (or redesign the pcb).

* blue LED: like the others said, they are generally very bright. with 9V supply, I use 10k minimum as CLR. I would therefore suggest to try 20k-50k.
** 895 Ohm resistor: I haven't checked your math, but I think it will be hard to get anyways. Every value resistance can be produced, but it's only a matter of demand. My guess would be that if you find it, it will cost you big time.
** LM317 voltage regulator: overkill. If it's only for the indicator LED, you will never see the fluctuations in supply voltage.

*LME49860NA: The stock LF353 used in the project is rated for Vcc,max = +18V, Vee,max= -18V. Max difference = 30V. If I read this correctly, you could use +30V on Vbb and 0V on Vee (=gnd). Generally 30 % safety margin should be planed for all components, i.e. 25V electrolytics, when you plan 18V operational voltage. Components deteriorate much faster close to their limits. The LME49860NA has a range of 46V, so that works for sure. I can not attest to it's sonical properties though.

Thank you! I'm quickly changing my mind about the blue LED. I'll be running this through an insert on my mixer, and it will be sitting on my desk. The last thing a I want is a laser to the eye. Haha! Good info. Hell, I may not even need an indicator LED just for myself. Also, thanks for the pinout advice. I would not have noticed that.

If I'm understanding what you're doing (increasing the supplied voltage), then the LED current limiting resistor should be the only thing you'd need to change, as long as all the parts in the circuit are specced to deal with the increased voltage. (ie, not trying to stuff twenty volts into a nine volt rated capacitor.) The actual values (ohms, microfarads, etc) for everything else should remain the same in most circuits. There are some exceptions to this, but they aren't common, especially not in stompboxes.

Thank you Alan, I was thinking I would have to up the uf too, but just the voltage rating is even better.

[stringsthings]

** 895 Ohm resistor: I haven't checked your math, but I think it will be hard to get anyways. Every value resistance can be produced, but it's only a matter of demand. My guess would be that if you find it, it will cost you big time.

Mouser gets us pretty close ...
https://www.mouser.com/ProductDetail/Vishay-Dale/RN65C8980BB14?qs=sGAEpiMZZMu61qfTUdNhGy2XqlsoYCVGZKS9Wj2xZdY%3d

[Charlie]

Well guys, I'm moving ahead with this build. I essentially want to make an outboard compressor that has some high headroom for vocals at 24v, but I'm going a different route first. I'm planning on adding one to my console (Tascam M3500) master bus and using the 15v power rail from the console to power the compressor. I don't have a way to test a 24v circuit yet, but I do have a way to test it at 15v. while I was testing 5mm yellow LEDs, the 560R resistor got hot, so I moved up from there. That was at a constant 15v, so I know that won't be the case, but I'd rather be safe.  I also noticed with a 560R and 1k resistor didn't make any change in brightness from 10v to 15v, so I opted to use 1k5, and it was consistent all the way up. I could get the LED brighter, but I want subtle compression on my mix bus anyway, and I figure the 24v (outboard) version will slam it brighter. I will have to test more LEDs when I get a 24v power supply, but the 1k5 should work well with 15v. I know I could just rely on ohms law, but melting resistors is way more fun. Haha! Anyway, I'm populating two boards for the stereo bus, and everything is looking good. If you guys have any more suggestions, please let me know. Also, one thing that I ran across that might be helpful. I'll admit that I've bought some cheap stuff from China, and solder was one of those things. I've been testing out different kinds, but one brand that I bought was like trying to melt a led musket ball to an ice cube. it wasn't working out. It was called JINHU. I don't know who Jin is, but they suck at making solder and now I'm like.. Jinwho? Moving on, I decided to try American Solder and I'm pretty sure that it's not made in America, but it has changed my mind about solder. It's cheap and probably not as good as what you guys are using, but it falls right into place and flows like the T1000 from Terminator. Also, it's cheap and that's what I like. I've also gotten some strip board that I think had cancer causing agents on it. I hope that helps somebody. Thanks again.

[Aristatertotle]

You could use something like a 1k trimpot as a variable resistor with an 820 ohm resistor in series with that to give you an adjustable range of 820 to 1820 ohms. That way once you have it at 24v, you can just trim to find your ideal brightness for the led. Also if you're worried about burning out the resistor you could bump it up to a 1/2 watt component to give you some peace of mind.

Interested to see what you think about the holy roller because I've been thinking about doing one of those for myself.

[m-Kresol]

P = U*I = U^2/R = 15*15/1500 = 0.15 W

--> a 1/4W resistor will do just fine 

[Charlie]

You could use something like a 1k trimpot as a variable resistor with an 820 ohm resistor in series with that to give you an adjustable range of 820 to 1820 ohms. That way once you have it at 24v, you can just trim to find your ideal brightness for the led. Also if you're worried about burning out the resistor you could bump it up to a 1/2 watt component to give you some peace of mind.

Interested to see what you think about the holy roller because I've been thinking about doing one of those for myself.

This is the reason for the internet right here. That's a brilliant idea, and with the pot, you can change the sensitivity of the compression. Nice! Thanks!