About polarity protection (when things go wrong)
- Duckman
- Opamp Operator
It's a TS808 I built for him as birthday gift and now is working again, but I can not forget that I lost a nice sounding 4558 for failing to put a simple diode, so I need to learn more.
I saw the 1N400x's are the most common diodes for polarity protection in so many stompboxes , so I assume to be the most appropriate, but what about the configuration: is better to connect the diode from the 9v line to ground, as in the Rat, or added in series in the 9v input, as in the Blues Breaker (just to give a couple of examples) or is exactly the same? What about 18v or higer voltages? Same 1N400x's or need something different?
Thanks to all who are interested in this subject and want to help
- salocin
- Resistor Ronker
Very interested to hear peoples thoughts on this. I've just been wondering the same thing.
I've not really bothered with it in the past but have recently had friends wanting to buy/trade pedals I've built so I've had to add it in so they don't come back to me with the pedal looking like the one in your post.
To this point I've just been sticking a 1N4001 in series with the voltage input. The first issue that comes to mind with that is the voltage drop.
The polarity protection in the Barbershop intrigues me, but what are the merits of it?
I've not really bothered with it in the past but have recently had friends wanting to buy/trade pedals I've built so I've had to add it in so they don't come back to me with the pedal looking like the one in your post.
To this point I've just been sticking a 1N4001 in series with the voltage input. The first issue that comes to mind with that is the voltage drop.
The polarity protection in the Barbershop intrigues me, but what are the merits of it?
- Duckman
- Opamp Operator
Nice trick! Seems like the MOSFET does the work, but without burning any component, just disables 9v, uh?The MOSFET is indeed for polarity protection, works like a charm. D1 is a 15V zener diode, it shuts off Q4 when the user plugs in the wrong voltage power supply.
- mictester
- Old Solderhand
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The 1N400X series are chosen because they're rated at 1 Amp, and can therefore carry quite heavy "wrong way" current.Duckman wrote:Ok, here's what a good friend can do with a chinese wall wart (those 9v to 12v w/ polarity selector)
It's a TS808 I built for him as birthday gift and now is working again, but I can not forget that I lost a nice sounding 4558 for failing to put a simple diode, so I need to learn more.
I saw the 1N400x's are the most common diodes for polarity protection in so many stompboxes , so I assume to be the most appropriate, but what about the configuration: is better to connect the diode from the 9v line to ground, as in the Rat, or added in series in the 9v input, as in the Blues Breaker (just to give a couple of examples) or is exactly the same? What about 18v or higer voltages? Same 1N400x's or need something different?
Thanks to all who are interested in this subject and want to help
I prefer a series diode - the effect just does nothing with a reversed supply - but there is a voltage drop. If you avoid the use of a conventional silicon diode, and use a Schottky type instead, you can keep the voltage drop down to 0.2V. With a modern Alkaline battery, you'll still have 9 Volts! I mostly use NiMH rechargeable batteries in my effects, and can just put in enough cells for whatever voltage I want, though I tend to design for 9 Volts so that users can use ordinary Alkaline batteries, in a pinch.
Remember - most effects are designed to work from batteries, so their current draw will be very small (just a few milliamps), so almost any Schottky diode will do. However, for compatibility with all circuits, it's a good idea to choose one capable of (say) 1 Amp.
"Why is it humming?" "Because it doesn't know the words!"
- Duckman
- Opamp Operator
Something like that, I guess... any preference?However, for compatibility with all circuits, it's a good idea to choose one capable of (say) 1 Amp.
- Attachments
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- 1N5818.pdf
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- Hides-His-Eyes
- Tube Twister
I tend to use the parallel 1n4001 in the opposite direction- is the main disadvantage to that the fact that if someone doesreverse it you lose the diode and have to put a new one in?
Testing, testing, won too fwee
- IvIark
- Tube Twister
Information
I've found that classic shorting diode protection going between +9V and ground in many non effect circuits often seems to be used in conjunction with a fuse, which I've never seen in an effect pedal. The series diode acting as a blocker seems like a much better option to me than putting in a component that you expect will blow.
"If anyone is a 'genius' for putting jacks in such a pedal in the only spot where they could physically fit, then I assume I too am a genius for correctly inserting my legs into my pants this morning." - candletears7 - TGP
- Duckman
- Opamp Operator
But if you have the chance to use a diode in series is not going to blown and has a lower voltage drop as the Schottky, why are most popular silicon diodes? Schottky Diodes cost the same...
- Duckman
- Opamp Operator
Perhaps the secret of using a MOSFET is that it does not cause voltage drop?Duckman wrote:Nice trick! Seems like the MOSFET does the work, but without burning any component, just disables 9v, uh?The MOSFET is indeed for polarity protection, works like a charm. D1 is a 15V zener diode, it shuts off Q4 when the user plugs in the wrong voltage power supply.
- mictester
- Old Solderhand
Information
You can get a very low drop with an FET, but a MOSFET wouldn't be my first choice. I sometimes use the HexFETs from International Rectifier. These have very low RdsOn.Duckman wrote:Perhaps the secret of using a MOSFET is that it does not cause voltage drop?Duckman wrote:Nice trick! Seems like the MOSFET does the work, but without burning any component, just disables 9v, uh?The MOSFET is indeed for polarity protection, works like a charm. D1 is a 15V zener diode, it shuts off Q4 when the user plugs in the wrong voltage power supply.
"Why is it humming?" "Because it doesn't know the words!"
- Hides-His-Eyes
- Tube Twister
Schottky diodes cost 20p each whereas 1n4001s cost about 2p each, at least from one of my main smaller suppliers.Duckman wrote:But if you have the chance to use a diode in series is not going to blown and has a lower voltage drop as the Schottky, why are most popular silicon diodes? Schottky Diodes cost the same...
Even on tayda schottky are 5c each compared to 1c.
Testing, testing, won too fwee
- mictester
- Old Solderhand
Information
Exactly! You have to remember that commercial effects manufacturers always use the cheapest components available. That's why the "legendary" 4558 was used in the Tubescreamer - not because it was best for the job, but because they cost almost nothing when bought in big quantities!Hides-His-Eyes wrote:Schottky diodes cost 20p each whereas 1n4001s cost about 2p each, at least from one of my main smaller suppliers.Duckman wrote:But if you have the chance to use a diode in series is not going to blown and has a lower voltage drop as the Schottky, why are most popular silicon diodes? Schottky Diodes cost the same...
Even on tayda schottky are 5c each compared to 1c.
"Why is it humming?" "Because it doesn't know the words!"
- RnFR
- Old Solderhand
Information
here's an explanation of the MOSFET protection. nothing blows up, and very little (.15V) series voltage loss with the BS250P. best way i've found to do it yet. of course i don't have a clue about HexFETs. (hint, hint.)Duckman wrote:So what's the advantage of the MOSFET used in the Barbershop? Why not to use a simple Schottky instead of the MOSFET-Zenner-resistor combination?
http://www.geofex.com/article_folders/m ... switch.htm
there is also this way to do polarity protection without having to use expensive MOSFETs. it takes a few more components, but should be easier to get a hold of the parts for the average DIYer.
http://www.geofex.com/Article_Folders/cheapgoodprot.htm
now if you can deal with the .3V drop, just use a series schottky or Ge diode. many people will remark that there will be little difference in the sound of a distortion circuit anyways.
if you haven't yet, i would read everything that GEOFEX and AMZ have to offer. they are really excellent resources.
"You've converted me to Cubic thinking. Where do I sign up for the newsletter? I need to learn more about how I can break free from ONEism Death Math." - Soulsonic
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- Duckman
- Opamp Operator
I usually do, but not on this occasion. Thanks for your commentsRnFR wrote:if you haven't yet, i would read everything that GEOFEX and AMZ have to offer. they are really excellent resources.
- RnFR
- Old Solderhand
Information
no biggie. i'm still finding things on RGs page. there is all kinds of stuff hidden all over that site.
"You've converted me to Cubic thinking. Where do I sign up for the newsletter? I need to learn more about how I can break free from ONEism Death Math." - Soulsonic
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- Hides-His-Eyes
- Tube Twister
I tried a pedal using a 9v1 zener as protection today and it was no harder than my old hopeless way except for a 220R series resistor where the power joined the board. So I think zener is the future for me? Or is there a special reason to use schottky instead? I mean zener offers overvoltage protection as well as reverse protection right?
Testing, testing, won too fwee