Basic beginner questions

[Mattson]

Hi guys,
I'm new to FX circuits, so please be patient with some very dumb questions here.  I'm building a tube amp out of spare parts, and I've got a power transformer that has a winding that will give me about +16VDC at 1.5A once regulated/filtered.  I'm thinking about regulating this down to +9 or +12 and powering a solid state FX loop with it.  Being new to IC's and transistors, I've having a hard time spec'ing them. 
First question:
When a regulator, like an LM7812, states "works up to 1A" in the specs, does this mean my 1.5A input current is too high for it, or does it simply mean that it's fine to exceed 1A on the input but I'll only get up to 1A on the output?   Same with transistors.  I see specs like I(C) Max. of 200mA--does this mean an input over 200mA is too high, or does it mean it knocks anything over 200mA down to 200mA output? 

Also,
Would this circuit work as an internal effects loop?  http://www.aronnelson.com/gallery/main.php/v/BarcodeVeroLayouts/album120/buffnblendPCB.gif.html

Would I need to make any changes in order to run it at 12VDC? 

Thanks for humoring my questions. 

[anchovie]

The current specs are maximum ratings - anything over this on the input will fry it.

You say you're new to ICs and transistors - do you mean by this that you're not new to tubes? If you've got experience of tube circuits then fine, otherwise I would say that a tube amp is a dangerous thing to be working on as a beginner project.

I expect the Buff'n'Blend will work fine at 12 volts, but if the B+ voltage of your tube preamp is going to be higher than that then you'll need to attenuate the signal going into it to avoid hitting the rails of the buffer and any effects that you have in the loop.

[R.G.]

Hello mattson. Not bad questions, and common ones for newcomers.

...I've got a power transformer that has a winding that will give me about +16VDC at 1.5A once regulated/filtered.  I'm thinking about regulating this down to +9 or +12 and powering a solid state FX loop with it.  ...
First question:
When a regulator, like an LM7812, states "works up to 1A" in the specs, does this mean my 1.5A input current is too high for it, or does it simply mean that it's fine to exceed 1A on the input but I'll only get up to 1A on the output? 

It means that the regulator will self limit so that it will put out no more than 1A, usually (and in this case definitely) to protect both the regulator and the load against over currents or shorts in the load. The regulator will protect itself, in other words. The LM7800 series also shuts down when it gets too hot, and is a good example of thoughtful, self protecting electrical engineering.

Same with transistors.  I see specs like I(C) Max. of 200mA--does this mean an input over 200mA is too high, or does it mean it knocks anything over 200mA down to 200mA output? 

It's different in this case. For a transistor, FET, etc. That means that over 200ma and it may become a Darkness Emitting Diode (or DED  ). You need to develop the habit of looking up the manufacturer's datasheets on line and looking at the "Absolute Maximums" section, where they tell you what till kill the device.
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You can save yourself a lot of time by reading everything you have the time and patience for at GEO - http://www.geofex.com, as a lot of it is basic level instruction.

[anchovie]

Thanks for setting me straight on the regulators, R.G. -  I can stop being paranoid about blowing them up now!

[Mattson]

It means that the regulator will self limit so that it will put out no more than 1A, usually (and in this case definitely) to protect both the regulator and the load against over currents or shorts in the load. The regulator will protect itself, in other words. The LM7800 series also shuts down when it gets too hot, and is a good example of thoughtful, self protecting electrical engineering.

Thanks for the help.  Unfortunately, this is still unclear as it seems like the two of you are saying different things.  I understand the fact that its output is limited to 1A.  That is fine for my needs.  What is still unclear for me is whether I can safely operate a 1A LM7812 regulator with 1.5A current going into it.  I also found an LM7812 rated for 3A, so I can use that if necessary at 3x the cost of the 1A unit

It's different in this case. For a transistor, FET, etc. That means that over 200ma and it may become a Darkness Emitting Diode (or DED  ). You need to develop the habit of looking up the manufacturer's datasheets on line and looking at the "Absolute Maximums" section, where they tell you what till kill the device.

Thank you.  I looked up the absolute max for the J201 needed in the effects loop circuit I'm eyeing, and it's rated at 50mA.  That's obviously waay lower than the 1A I'll have working through this after regulation.  I need the current after the regulator to be in the area of 1 amp to help power preamp tube filaments.  So, what can I use to safely get the current down to an acceptable range for a J201 rated at 50mA?  Alternatively, is there a higher-current transistor that I can use instead of the J201?

I am quite experienced with tube circuits and know the proper precautions with high voltages, etc.  Transistors and IC's are a whole different ball game.  I totally understand how to control voltage and spec components' voltage requirements, but obviously I'm having a hard time spec'ing current handling capabilities of solid state devices. 

[R.G.]

Thanks for the help.  Unfortunately, this is still unclear as it seems like the two of you are saying different things.  I understand the fact that its output is limited to 1A.  That is fine for my needs.  What is still unclear for me is whether I can safely operate a 1A LM7812 regulator with 1.5A current going into it.  I also found an LM7812 rated for 3A, so I can use that if necessary at 3x the cost of the 1A unit

Ah. OK, that's beginner problem number two. Electronic loads can only pull as much current as they need, not all that the supply can give. A 100W light bulb is something under 1A. The 120V service to your house can supply 200A. The availability of 200A doesn't mean the light bulb has to take all of it. It only takes what it needs.

Same with linear regulators. A linear regulator only pulls a tiny amount more current than it puts out. So a 7812 running from a 16V supply that can supply up to 1.5A may put out - and draw - up to 1A. It quits pulling when it senses it's putting out 1A, saying, "no, thanks, that's enough" to the supply.

I looked up the absolute max for the J201 needed in the effects loop circuit I'm eyeing, and it's rated at 50mA.  That's obviously waay lower than the 1A I'll have working through this after regulation.  I need the current after the regulator to be in the area of 1 amp to help power preamp tube filaments.  So, what can I use to safely get the current down to an acceptable range for a J201 rated at 50mA?  Alternatively, is there a higher-current transistor that I can use instead of the J201?

And this is problem number 3. How much current does a transistor rated at 100ma use?
Only as much as you tell it to by setting the conditions on its control lead. A J201 is OK with any amount UP TO 50ma, at which point more current may destroy it. You control its current in exactly the same way you control a power pentode's current - by setting the gate bias to not let it pull too much. The absolute max warning is to you; it warns you not to tell the transistor to go over this much, because it will try, and will be damaged in the process.

[Mattson]

The availability of 200A doesn't mean the light bulb has to take all of it. It only takes what it needs.

Only as much as you tell it to by setting the conditions on its control lead. A J201 is OK with any amount UP TO 50ma, at which point more current may destroy it. You control its current in exactly the same way you control a power pentode's current - by setting the gate bias to not let it pull too much. The absolute max warning is to you; it warns you not to tell the transistor to go over this much, because it will try, and will be damaged in the process.

Thank you.  For some reason I thought there was more complexity to the way SS devices handled current that warranted greater sensitivity to current specs.  Sorry for the ridiculously basic questions.  This is the first time I've had to think about design rather than just copying the layout of an amp kit, and I just got a little off base with my thinking. 

[anchovie]

Unfortunately, this is still unclear as it seems like the two of you are saying different things. 

That's why I stood corrected after I'd finished bowing to R.G.