[ozshadow]

What a Tread can do depends primarily on the wallwart power supply you use. A tread just regulates it and cleans up the signal.

 

[Teerawit]

Quote:

Originally Posted by ozshadow What a Tread can do depends primarily on the wallwart power supply you use. A tread just regulates it and cleans up the signal.

Depends also on the regulator...

 

[mono]

Quote:

Originally Posted by Heady I've got a question which is related. How much current can a Tread supply? Can it be used for a power amp with the appropriate bridge rectifier and voltage regulator?

The general topology can be used, but you have to accomodate the typically higher current and (often) voltage of a power amp. Some may be pretty miserly, I put a linear tread-like stage on a Sonic Impact T-Amp, but it is only rated for 15W, 12V.

For another amp you might be able to use another regulator but you'd need consider the bridge current, regulator heatsinking (and current of course), cap and other parts' voltage specs. Some parts like Tantalum caps are best used when derated from their voltage spec and less common, more costly in same uF values but higher voltage. The electrolytic after the bridge rectifier would also be increased in size, often people cite a generic rule of thumb like at least 1000uF per amp of current.

Generally with a tread-like supply you'd change it around a bit so you had a pass transistor handling a large % of the current if you wanted very far above 1A, unless you had a very closely matched transformer so heat wasn't so much of an issue. Beyond a certain point it may even be cheaper to start adding a transistor to (half?) the heat rather than a more expensive and larger heatsink that a single TO220 regulator would need (ignoring active, fanned sinks since it's not often people want to put a fan on one).

 

[tomb]

One common upgrade is replacing the LM317 with an LM338. In fact, that is the recommended option for the M3. The LM338 can handle up to 5A, whereas the LM317 is limited to 1.5A. If memory serves, the inrush has been estimated at over 3A. Steady state operation is still well below 1000ma, but somewhere above 500ma, I think. Regardless, the inrush is high enough that several LM317's have been blown on TREAD's and STEPS' supplying M3's - lots of power in that amp.

 

[ozshadow]

Yes, I was referring to the tread layout. Tangent gives lots of options for customizing it to fit your needs.

 

[ozshadow]

I guess the end result was all that matters - it powers the amp with no noise whatsoever, puts me almost at max for the amp, and has plenty for charging the batteries. But the taped wires are quite ugly - I'll get some nylon for them eventually, but all but a foot of it hides behind my desk anyhow.

 

[Teerawit]

Quote:

Originally Posted by tomb Steady state operation is still well below 1000ma, but somewhere above 500ma, I think. Regardless, the inrush is high enough that several LM317's have been blown on TREAD's and STEPS' supplying M3's - lots of power in that amp.

It really depends on how high your bias settings are. Also, the inrush on my LM317-equipped STEPS has never killed the LM317 when using the M3. I don't think anyone should be worried about the M3 causing their STEPS/TREAD regulator to blow up.

The real issue is what happens when you turn off the amp.

 

[tomb]

Quote:

Originally Posted by Teerawit It really depends on how high your bias settings are. Also, the inrush on my LM317-equipped STEPS has never killed my M3. I don't think anyone should be worried about the M3 causing their STEPS/TREAD regulator to blow up. The real issue is what happens when you turn off the amp.

Bias settings are steady-state (if not the definition of). It adds a component to the load, but inrush current is largely determined by the need to charge capacitors.

There is a lot of documentation of this problem, and the LM338 was specifically recommended by Amb. I'll agree in one respect, though - if you haven't noticed something immediately upon powerups, you probably aren't going to have the problem.

 

[Teerawit]

Quote:

Originally Posted by tomb Bias settings are steady-state (if not the definition of). It adds a component to the load, but inrush current is largely determined by the need to charge capacitors.

Um, I was referring to the bias settings determining what your current draw would be. 500 mA is way up there. I think the default config draws more around 300-350 mA.

 

[tomb]

Quote:

Originally Posted by Teerawit Um, I was referring to the bias settings determining what your current draw would be. 500 mA is way up there. I think the default config draws more around 300-350 mA.

OK - we are in agreement, but talking about two different things: steady-state vs. inrush current.

I only cited the steady-state as evidence that it may be much less than the inrush current. So that, if sizing for plenty of power supply safety factor for the steady-state case, it may be not be enough to prevent component failure (LM317) for inrush current.

The point I was trying to make, that even with a conservative safety factor in sizing a power supply for the M3, it may not be enough to prevent failure of the LM317 on account of inrush current, which may be up to 3-4 times as much as the maximum steady-state power draw.

This will sometimes result in blowing the LM317, and the LM338 is recommended as an upgrade that will handle up to 5A. This is documented on Amb's M3 site (he says something that will handle 3A, but references the LM338). Some have even suggested making it standard for the STEPS and TREAD.

In any event, it was a digression from the subject of the thread, and only mentioned as a possible upgrade.

 

[mono]

Quote:

Originally Posted by ozshadow Yes, I was referring to the tread layout. Tangent gives lots of options for customizing it to fit your needs.

The tread layout itself is not appropriate for much over 2A, because the spacing is to accomdate the small bridge rectifier (only so much bending of a larger bridge's leads or separate diodes would be reasonable) plus the pre-regulator capacitor is space constrained as well. Tangent's Steps is more appropriate for a moderate power amp but even it is going to be insufficient once you get up to the common wattage ranges (and associated power consumption) many target for power amps.