High 3.4 amp for pedals

Frequently asked questions regarding powering your pedal.

High 3.4 amp for pedals

Postby j2sip » 17 Apr 2012, 08:05

Hi,

I'm planning to use a 19v 3.4amp laptop power supply for my pedals. I will use LM317 and/or 7809 for regulation to suitable voltages(18v and 9v). Won't the high current fry the regulators because I see 1amp as the common current for pedal supply sold and DYI'd.

Thanks.

Jordan
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Re: High 3.4 amp for pedals

Postby PokeyPete » 17 Apr 2012, 16:11

j2sip wrote:Hi,

I'm planning to use a 19v 3.4amp laptop power supply for my pedals. I will use LM317 and/or 7809 for regulation to suitable voltages(18v and 9v). Won't the high current fry the regulators because I see 1amp as the common current for pedal supply sold and DYI'd.

Thanks.

Jordan

Just because your power source can supply 3.4A doesn't mean it will. The load determines the current draw.
If you are drawing anything close to an amp (even 1/2A) you will want to incorporate a heatsink with your regulators.
A 'pass' transistor will be necessary if you want to be able to use high currents.....and this transistor will need
to be heatsinked as well. Another issue will be the 19V on the input of the 7809. It is common to supply a couple of volts
higher to the input of a regulator than will be output regulated. With 9 volts out, the regulator will have to deal
with the other ten volts.....it will generate excess heat and will need a large amount of heatsinking just for this,
not counting the heat generated by the current it will be supplying to the circuits.
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good counsel, and no man so wise that he may not easily err
if he takes no other counsel than his own. He that is taught
only by himself has a fool for a master.”
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Re: High 3.4 amp for pedals

Postby j2sip » 18 Apr 2012, 10:02

Thank you so much for the fast reply.

How about putting a 7812 first before the 9 volt regulator? That way only 12 vots will be handled by the 7809.
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Re: High 3.4 amp for pedals

Postby PokeyPete » 18 Apr 2012, 13:06

That's not necessary. Just trying to make you aware of using a heatsink. 19V input is well within specs,
just higher than normal for a fixed regulator of that output voltage. Typically pedal circuits have very
low current consumptions. You can power numerous pedals and only draw a couple hundred milliamps.
Unless you have some monster multi-pedalboard system that 3A supply will be way overkill. Still, it
wouldn't hurt to include a heatsink on that regulator with all things considered. If you plan on putting
this supply in an enclosure and wish to keep the ground floating, just use a mica insolator between the
heatsink and case, and secure it using a nylon bolt and nut. Who knows, if you're not powering that
many pedals, you may not need a heatsink at all. If you will be daisy chaining your stompboxes
using a single power source, be aware that you could be introducing some grounding issues. That's why
many use a transformer with several secondary windings, then rectify and regulate each winding separately.
This isolates the ground for each pedal and saves problems. The single source system can work, just depends
on the pedals.
“No man is so foolish but he may sometimes give another
good counsel, and no man so wise that he may not easily err
if he takes no other counsel than his own. He that is taught
only by himself has a fool for a master.”
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Re: High 3.4 amp for pedals

Postby j2sip » 20 Apr 2012, 03:53

pokeyPete,

Now that is the most informative response I ever got in a forum. Thank you so muCh!

Jordan
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Re: High 3.4 amp for pedals

Postby brianhujung » 14 Jun 2012, 04:39

I use LM338T for my Laptop PSU.. it the same as LM317 but it can handle 5A.. :thumbsup
just don't forget to use a proper heatsink.. :D
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