Power supply magic

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Power supply magic

balazs.bencs
So.. I built two power supplies based on the geofex schematics (http://geofex.com/article_folders/oldspyder/oldspyder.htm), and they are working great with the pedals that I built from this site - stable 9V, plenty of power. I used a 12V 2A transformer to power two 7809 regulators (9v 1A). I measured it, really stable 9.00V is coming out on both outputs (even when I'm using a daisy chain).

But yesterday I bought a Boss TU-3 tuner, and it is always blinking, shows me like.. something is wrong with power, even if it's the only thing that is running on one these power supplies (but the lights are bright, how they should be)

But... I also have another power supply from eBay (http://www.ebay.com/itm/RAAD-EURO-regulated-power-supply-DC-9V-adapter-guitar-effect-pedal-negative-tip-/171573999380), which is a simple regulated 9V/500mA power supply - but for some miracle, when I use this there's no blinking, no problems, everything is fine.

Did you folks had an issue like this? I'm going crazy about this, cause every other pedal I have is working, and producing a really good sound, and I don't want to carry another power supply cause of this.
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Re: Power supply magic

Neil mcNasty
I've had the same issue with the Boss TU-3, and it is a result of it not getting enough current.
The tuner draws quite a lot, and it sometimes maxes out the power supply's capability when it is added to the same power supply as the rest of the pedals on the board.
Use a bigger power supply and it is ok...
Or do like I do (yes, I know it not the answer you are looking for): give the tuner it's own power supply.
I use the small Boss one-spot for the tuner, and run the rest of the pedals from my DIY power supply.
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Re: Power supply magic

balazs.bencs
yeah, I ended up with the same conclusion, but I am still confused because this happens when I only plug the tuner into the 1A regulator. That should be enough current for everything!

So this should be something else that we can't figure out..!?
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Re: Power supply magic

Neil mcNasty
Maxing out a 1 amp regulator is no problem on a large pedalboard.
Specially if the board has a lot of modulation pedals.
These often draw quite a bit of current (sometimes in the 100mA or more, range), compared to dirt pedals that hardly draw any current at all...

As far as I can remember the TU-3 draws about 300mA (guessing from memory , since the bottom where that info is located, is covered with velcro).
My Chorus draws pretty much the same as the tuner.
Many reverb and delay pedals draw about 100mA or more each...
With just 3 pedals and the tuner on the board, we are now potentially drawing over 800mA.
Throw a couple of more modulation pedals in there as well, and we have now reached the limit.

BUT!: if you get the same result when only running the tuner from the supply, without any of the other pedals connected, I would conclude that the TU-3 is a bit picky on the power supply filtering, and maybe reacts badly to ripple currents, or some similar issue.
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Re: Power supply magic

balazs.bencs
Yeah, I think I'll try to add some more filtering and I'll try again with the tuner alone.

oh.. and I included a 100ohm resistor, 9V is coming through on that because it eliminates that high pitched noise with some fuzz circuits - that can't be an issue, right?
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Re: Power supply magic

balazs.bencs
ok, so... I was debugging in the last 30 minutes and got some weird stuff.

First I tried to do some more filtering with like from 1000uf to 100nf, nothing changed.
Then I got the feeling that maybe voltage isn't right, so I got my multimeter hooked up on the daisy chain and voila I got something!

When nothing is plugged in, voltage is 9.00V how it should be. But when I start to put pedals on it (remember, 12v/2A transformer and 7809 1A regulator), the voltage starts to drop right away. I tried with 4 different 7809 transistors, but every one of them is doing the same thing. Even if I put some really simple pedal onto it like the Lovepedal Kalamazoo.

When I tried with the tuner, first it dropped to 7.3 volts, then when I engaged it, dropped to between 6.5 and 7 volts (depending on how many LED was on). When I put other pedals onto the daisy chain, it just dropped even more. (without turning them on)

But there should be a way out of this, cause when I used the RAAD power supply, the voltage was dead on 9.6 volts, even with all the pedals and the tuner turned on (it was ts808, phase90, Kalamazoo, zvex distortron, jhs morning glory and king of tone). Everything was working great!!! This little power supply is only capable of putting out 500mA, so I am so sure that the problem is the 7809. I got them in the local shop, they are a very big and reliable store, so I don't think the transistor is fake or anything like that.
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Re: Power supply magic

balazs.bencs
OK so update: I solved it, the 100R resistor is the "bad" part of the circuit... I took it out, and everything started to work like it should.

Now I'm going to try and find some book about this, cause I don't really understand why is this causing a voltage drop.
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Re: Power supply magic

Travis
Administrator
Google "Ohm's Law"
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Re: Power supply magic

Neil mcNasty
This post was updated on .
In reply to this post by balazs.bencs
Cool!

I think I might have an idea about what is going on here:
If your 100r resistor is located directly after the regulator output and then feeds all your DC outputs, it will drop the voltage more and more as you add pedals, since the amount of voltage drop is dependent on how much current you are drawing as a total.
Meaning: The higher the current draw/mA, the more extreme the voltage drop becomes.

If you intention for adding the 100r resistor is to make a "Huminator style" decoupling, you need to add a resistor (and a cap) for each output.
A single resistor for all the outputs is not a decoupling, but just a current reduction that reacts to the total load of your power supply.
It results in huge voltage drops when you connect all your pedals/increase the amount of mA that is being drawn from the power supply.
A decoupling only happens when there is a resistor for each DC output.
Meaning: there is a resistor running from the regulator's output point to each of the DC outputs, followed by a filter cap, like a 10uf.
So if you have 8 DC outputs, there will be 8 resistors running from that point to each their outputs, followed by a filter cap for each of them.

If all your DC outputs are being fed directly from the regulator output, it will actually function just like a regular one-spot with a daisy-chain.
There will be no difference, since all outputs are sharing the same current feed coming out of the regulator and interference between pedals might occur.

If you want to decouple the outputs, I would recommend that you use a lower value resistor (example: 10-33r for each of the outputs), specially if you are using a lot of modulation effects with high current/mA draw.
100r is ok if you are using it with dirt pedals that just draws tiny amounts of current, since the voltage drop then becomes tiny and is hardly noticeable.

You could of course ignore the whole decoupling stuff as well, keep the power supply as it is now, and then rather just build a single decoupler/Huminator circuit in a tiny format/box that you put between the power supply and the pedal that is troublesome.
This way you do not have to modify your power supply again, or worry about how much each pedal's current draw will result in a voltage drop.

I hope this makes sense, and helps you understand what is going on.

I know that I repeat myself a lot when writing my responses, but I do this intentionally in order to explain stuff in several different ways, so that it potentially becomes clearer and hopefully one of these explanations matches your way of thinking/talking.

If there is anything confusing in my statements or if it is still unclear, let me know, and I'll do my best to make sense of it with my limited knowledge...
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Re: Power supply magic

balazs.bencs
No, everything is very well explained, I learned a lot from this post. Thanks, man I really appreciate it!
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Re: Power supply magic

balazs.bencs
Now that I understand that I was a complete idiot, I figured out that I have to isolate the tuner anyway, because of the digital noise that it generates.
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