[kin0kin]

load or not, most likely you will be getting 25.x V as measured from the thread. the only time an unregulated wall wart would output at it's rated voltage is when the current draw is near the maximum rated ampere on the wallwart. My 24v wallwart, regulated with lm317 with similar circuit as the tread measured 18.36V from the regulator output, and again measured 18.36V when loaded.

btw, caps generally could take voltage surge for a short period of time(I can't recall how many secs), so if you feed a 25V cap 25.x V for a few sec it should be fine, you probably would have enough time to determine if the loaded voltage will drop below 25V which I highly doubt, before it explodes.

 

[n_maher]

Well I certainly wouldn't go doing ANYTHING based only on my advice

. And yes, there is some load on the TREAD but I was just passing along information someone else had offered in a different thread. If you populated everything per the schematic the LED is probably drawing only a couple of mA. Not much load for a power supply that's probably rated for a couple hundred.

Here's the other thing. If your PS is putting out 25.7V it's likely that just the diode on the PIMETA is going to drop the voltage to almost 25V. Based on the data sheet at mouser it'll drop it nearly .5V. Now the bigger question (and more $$$) would be what your opamp is rated for. If you're using the AD8620/10 combo you're operating pretty near the peak voltage (+/- 13V) so I'd suggest making sure that the voltage comes down a bit more before putting anything in the sockets.

Bottom line, I'd make sure that the TREAD is working correctly before proceeding. Waiting sucks, but blowing stuff up sucks worse - trust me!

Nate

 

[kin0kin]

wait, I just looked at the pimeta psu's schematic, the caps are after the TLE2426, at that point the power has already been splitted

even a 16V* cap would do fine

so go ahead and power it on dude. The only time the cap would explode is when the virtual ground fails to work so that the whole 25.xV drift to a single rail(even so, you still have a few secs to power it off before it explodes). But you can easily verify if the virtual ground is working by feeding a lower Voltage to it and check if it had been splitted properly. Use a 9V batt to test it, if it splits up to +4.5V, -4.5V then you are good to go

Edit: *What......misread the value

 

[n_maher]

Quote:

Originally Posted by kin0kin wait, I just looked at the pimeta psu's schematic, the caps are after the TLE2426

That's a dangerous game you play - if the TLE ever goes bad caps go BOOM! I don't like cleaning up after caps.

And one more note to darkisz, check your TREAD calcs after you get everything set up, I was just messing with mine and burned my finger nicely by asking the reg to drop too much voltage while pulling too much current. Ouch, that'll leave a mark, seriously.

Nate

 

[kin0kin]

Quote:

Originally Posted by n_maher That's a dangerous game you play - if the TLE ever goes bad caps go BOOM! I don't like cleaning up after caps. And one more note to darkisz, check your TREAD calcs after you get everything set up, I was just messing with mine and burned my finger nicely by asking the reg to drop too much voltage while pulling too much current. Ouch, that'll leave a mark, seriously. Nate

Apparently Ray Samules like dangerous game too

my sr-71 is using boarderline rating caps. Takes in 18V, power caps are all rated 10V, if the virtual ground fails, BOOM! sweet juicy sauce all over the amp. But nope, they hardly fail when done properly.

Just make sure the amp is tested with a 9V before powering it up.

 

[darkisz]

Either my meter is reading high, or the wallwart is overvolted.



I read 9.45v from a fresh 9v battery.

I get 30.34v straight from the jack of the 100ma 24v wallwart.

I'm beginning to wonder if it's the meter?

 

[rreynol]

In that case, its what was mentioned earlier. The adaptor is rated for 24v, 400mA at full load. Measuring the voltage unloaded will be a lot higher which is what I think you're reading in that pic.


As an aside, how are the batteries in the multimeter?


p.s. thats the same ac/dc adaptor I used with my TREAD kit.

 

[n_maher]

Quote:

Originally Posted by darkisz Either my meter is reading high, or the wallwart is overvolted. I get 30.34v straight from the jack of the 100ma 24v wallwart. I'm beginning to wonder if it's the meter?

Well, I just checked the Wallwart that I've been using with my TREAD, it puts out over 29V without a load on it. Hooked up to the TREAD that drops to 25.5V. I'll try to check it hooked up to my M3 later tonight and let you know if I can adjust the voltage.

Nate

 

[sbelyo]

Quote:

Originally Posted by darkisz Either my meter is reading high, or the wallwart is overvolted. I read 9.45v from a fresh 9v battery. I get 30.34v straight from the jack of the 100ma 24v wallwart. I'm beginning to wonder if it's the meter?

That's all normal. It's pretty common for an unregulated or unloaded power suppy to read higher than it's spec'd voltage

Your meter is just fine

 

[darkisz]

The 9v in the meter was fine (still 9.2v), but I replaced it anyway.

I am still getting 27v across test points 1 and 2, and I'm now getting 25.5v across 2 and 3. I have tried readjusting the vset very carefully. I can adjust voltage up, but I can't get it lower than 25.5v.

Should I take kin0kin's advice and try to increase the resistance of R2 on the tread to try and drop the voltage some? I have some 10, 47, and 100 ohm resistors laying about, but no 83.

Many thanks again to those helping out a neurotic noob

 

[Teerawit]

Quote:

Originally Posted by darkisz Should I take kin0kin's advice and try to increase the resistance of R2 on the tread to try and drop the voltage some? I have some 10, 47, and 100 ohm resistors laying about, but no 83.

Why don't you try that just to be on the safe side...that way you can evaluate how much the voltage will drop in the circuit. Then later you can decide if you want to up the voltage to be just under the 25V threshold.

 

[tangent]

Quote:

Originally Posted by darkisz I've tightened it about 50 turns

You can kill trim pots by turning them past their stops too far.

Next time, listen carefully for the clicks. They're very faint.

Quote:

I can adjust voltage up

That's good. It means the pot hasn't been killed.

Quote:

I double checked the resistor values for R1/R2. They are 120/2k, which should put my voltage in the 22-27v range, according to the graph on the schematic.

The table on the schematic assumes a 500 ohm pot for VSET, as shown on that schematic. I ship a 1K pot with the TREAD kit, so the range is 22-32V.

 

[kin0kin]

did you hook your 9v to the pimeta? you're suppose to hook it up and power it up, then check if the volatge is splitted. if it does, then it is safe to say that the rail splitter is working and you can run 25.x V into your pimeta without problem. If you did hook it to your pimeta and it still measures 9v then your tle2426 isn't working properly.

btw, you can take the measurement from here. measure the pins of the caps, the first one on the left would give you -4.5 and the second one would give you +4.5.

 

[The Monkey]

This is a great thread, folks. I'm about to embark on a very similar journey and really appreciate the guidance here. My DIY skills are somewhat in line with yours, darkisz, so your worklog is really helpful.

Cheers!

 

[darkisz]

Morning update

I hooked a 9v up the the Pimeta, and got +/-4.4v on C2/C3. Looks like the TLE2426 is on the job.

For some reason, I'm reading higher voltage on the Input and Output voltages of the TREAD this morning. I haven't made any adjustments to it. The input is reading 27.6v and the output is now 26v. I can understand if I damaged the VSET, why the output voltage might change, but should it be affecting the input voltage as well?

Now, I've spent some time trying to adjust the VSET. It doesn't seem to be having any affect on the voltage, either up or down. So, now I'm worried (I'm always worried about something, right?) that the VSET is just borked. Which of the vset pins should I measure across to test it's resistance?

If the VSET is bad, can I take it off and substitute a standard resistor instead of jumpering to try to get the voltage down? Or should I only add another resistor in series with R2? OR am I getting overly fixated on the TREADs voltage problems and, seeing as the TLE is functioning properly, I should just hook the durn thing up and see if it works?


I'm glad you're getting good info out of this thread, Monkey. I was starting to feel like an annoyance with all my noob type questions, but if it's gonna help other people, I'll keep asking dumb questions! Like this one :

Is the metal in the mounting holes tied to the circut? I only have metal standoffs and don't want to short anything out mounting in an aluminum chassis. (It looks like the metal is just there for self threading purposes)

Thanks again and in advance!