[kin0kin]

you are overly worried. As long as the rail splitter is working, you can hook the tread to it and power it on. you don't need 24v precisely.

as for replacing vset for a resistor, you have already been told in post #14. you can replace R2 and jumper the two points(2 and 3, or 1 and 3), or just simply get another resistor of the value (1685 - R2 = Resistor you need) and solder it on the two points (2 and 3, or 1 and 3....it is the same anyway) and you will get close to 24V output.

 

[n_maher]

If it were me (and warning I have nuked stuff before) with the opamps and buffers out I'd hook the TREAD up to the PIMETA and measure the voltage at the opamp sockets. If you're getting anything over 12.5V (+/-) try adjusting the TREADs output and see what happens. If you can dial it down closer to 12V (24V total supply voltage) and then test it with the opamps and buffers in. If you find that the voltage falls mcuh further then adjust it again, if it looks fine still let'er rip and enjoy the amp.

I wouldn't bother with the resistor shenanigans until you're sure that the pot isn't working.

Nate

 

[darkisz]

What a day.

I tested the Tread hooked up to the Pimeta with no IC's. There is some good news...nothing exploded!

I was getting +/- 13.2-13.4v across the OPA sockets. Adjusting the Vset would not the get voltage any lower than +/- 13.1v. Since this is still above the recomended 12.5v I was looking for, I disconnected the Pimeta from the Tread and figured it was time to start messing the the Tread's R2 value.

First, took the vset and r2 off (ugh, I suck at desoldering) and jumpered the vset connection. Then, I tried to make a resistor close to the 1685 ohm mark. I used a 1k+470+150 for 1620 ohms. I was expecting 1.6 to give ~23v, but I was still getting over 25v, so I dropped the 150 ohm off the series for a 1470 ohm resistor. I still got >25v.

I ended up sticking in various resistors, here are the results:

2k - 25.8v
1.47k - 25.8v
1k - 25.6v
470 - 24.7v
220 - smoked

I just don't understand. The only one that dropped the voltage to under 25v, the 470 ohm resistor, got finger blistering hot during the minute I had power to the board to test the voltage. The next lower resistor I tried started smoking within a few seconds of power being applied. I may have grabbed it out of the 1/8watt bag, though. All the other one's I tried were 1/4w.

I had the harsh realization today, while reading Tangent's Tread guide for the upteenth time, that understanding how to put the parts of a circut together, and actually understanding how a circut works, are two entirely different things.

Finally, I checked the schematics for the AD823/843 opamps. From what I can tell, they are both rated for up to 18v. If I can impart on someone to comfirm this, things might be lookin up.

 

[kin0kin]

lol, no idea what's wrong. you are suppose to get 22.x V with 1.6kohm resistor.

here is the simplified formula, assuming your R1 is 100ohm:

V = (1.35R2 + 125) / 100

like I said earlier, you don't need 24V precisely. And yes, the AD823 and AD843, and many other commonly used Opamps work within +/- 18V. Just hook up the tread and fire it up. Use (470ohm - 24.7V) since that gives you the voltage within your cap's limit.

um btw, higher R2 = Lower V, so it's not abnormal that 1.4k ohm gives u > 25V

 

[n_maher]

Quote:

Originally Posted by kin0kin Just hook up the tread and fire it up. Use (470ohm - 24.7V) since that gives you the voltage within your cap's limit.

I think he said that the 470ohm resistor got seriously hot in a short amout of time. That sounds like a recipie for badness to me.

Honestly, I'd wait a day and see if Tangent chimes in again. Always good to get the designer's opinion on things like this if you can. Perhaps some of whatever knowledge that comes from this can be incorporated into the TREAD docs. It would seem like either a bunch of us are building these wrong (i.e. no adjustment while unloaded) or that a different approach needs to be taken during adjustment (create a dummy load or something). Just a thought.

Nate

 

[kin0kin]

Im sure he hooked something wrong, and I have no idea how a 470ohm gives <24v while 1.6k gives 25v+. anyway, you can just hook your ac->dc adapter to your pimeta and fire it up and take your time to troubleshoot your tread.

at the mean time, mine posting up a picture showing how you connected the resistors in series? Btw, if 1/4W is too hot, get a 1/2W resistor.

 

[darkisz]

Quote:

Originally Posted by kin0kin Im sure he hooked something wrong, and I have no idea how a 470ohm gives <24v while 1.6k gives 25v+. anyway, you can just hook your ac->dc adapter to your pimeta and fire it up and take your time to troubleshoot your tread.

Ugh, I think I've been wasting alot of people's time....

I found it. Chalk it all up to user error.

D2 is backwards.

 

[kin0kin]

is everything working fine now? I thought you removed the pot?

 

[rreynol]

This is why I said to make sure all components were placed properly and of the correct value. A lot of the time, that is what the problem is.

It wasn't a waste because I'm sure a lot of speople will use this thread as a learning experience.

 

[n_maher]

Quote:

Originally Posted by darkisz Ugh, I think I've been wasting alot of people's time.... D2 is backwards.

Bah, no worries. Just report back how things go when you do get it hooked up. You're not the first and surely wont be the last.

Nate

 

[darkisz]

Since I've now destroyed the 3 parts I've tried to remove from the Tread (R2, Vset, and just now, D2) and considering the ammount of damage I've done to the board itself (lots of scratches, scorch marks, and stray solder), I'm starting over. I'm ordering a new Tread kit. Hopefully, I won't screw this one up.

I figure I can get some much needed practice desoldering on the mangled Tread.

At least I'm learning a lot!

 

[kin0kin]

Quote:

Originally Posted by darkisz Since I've now destroyed the 3 parts I've tried to remove from the Tread (R2, Vset, and just now, D2) and considering the ammount of damage I've done to the board itself (lots of scratches, scorch marks, and stray solder), I'm starting over. I'm ordering a new Tread kit. Hopefully, I won't screw this one up. I figure I can get some much needed practice desoldering on the mangled Tread. At least I'm learning a lot!

dude, wanna mail me your dead tread?

 

[n_maher]

Quote:

Originally Posted by darkisz I figure I can get some much needed practice desoldering on the mangled Tread. At least I'm learning a lot!

What are you using to desolder parts? If you're just using a wick do yourself a favor and get a half decent, maybe even static-free desoldering pump. It makes things SO much easier.

Nate

 

[Teerawit]

Quote:

Originally Posted by n_maher What are you using to desolder parts? If you're just using a wick do yourself a favor and get a half decent, maybe even static-free desoldering pump. It makes things SO much easier. Nate

You mean a vacuum pump? Or a desoldering bulb?

BTW those parts are cheap...$1.50 at most to replace

 

[n_maher]

Quote:

Originally Posted by Teerawit You mean a vacuum pump? Or a desoldering bulb? BTW those parts are cheap...$1.50 at most to replace

Desoldering Pump . It uses a short burst of vacuum to suck the solder away from the joint. I couldnt' live without it. Not cheap, but it's saved more money than it cost for sure. See Tangent's DIY guide for more examples of desoldering pumps.

N