Pimeta Power + Other Questions

[cgrums]

I've spent quite a lot of time recently poring over these forums and others absorbing this vast amount of knowledge. I just completed my first amp (cmoy) and am hooked! I've got the pcb and most of the parts for a pimeta but am left with a few last minute questions. Any and all help is much appreciated as my background is in mechanical engineering and my poor brain struggles with this electrical stuff

I'm having a difficult time getting a hold of the TLE2426 (rail splitter) and as such am undecided as to how to power this amp. I've ordered the parts for both a TREAD and a STEPS power supply. I was planning on saving the STEPS for a m^3 or similar amp for home and using the TREAD in the PIMETA for work. If I understand correctly (which I don't claim that I do) I'll still need the TLE2426 with the TREAD as it is just a single voltage supply. Am I way off base here? I have no problem using this on wall power only which is why I'm looking into the power supplies (that and they look like a fun build)

Also, is it an either or situation when comparing the use of rled vs. the rfet/fet/znr combo? I'm not seeing how one would use them both at the same time.

Thanks in advance for the help. Truly awesome forum here.

 

[tomb]

Quote:

Originally Posted by cgrums I've spent quite a lot of time recently poring over these forums and others absorbing this vast amount of knowledge. I just completed my first amp (cmoy) and am hooked! I've got the pcb and most of the parts for a pimeta but am left with a few last minute questions. Any and all help is much appreciated as my background is in mechanical engineering and my poor brain struggles with this electrical stuff

There are a few of us ME's around here.

Quote:

I'm having a difficult time getting a hold of the TLE2426 (rail splitter) and as such am undecided as to how to power this amp. I've ordered the parts for both a TREAD and a STEPS power supply. I was planning on saving the STEPS for a m^3 or similar amp for home and using the TREAD in the PIMETA for work. If I understand correctly (which I don't claim that I do) I'll still need the TLE2426 with the TREAD as it is just a single voltage supply. Am I way off base here? I have no problem using this on wall power only which is why I'm looking into the power supplies (that and they look like a fun build)

It sounds like you are confusing the purpose of the TLE with the TREAD and the STEPS. They are not related. The PIMETA design is based on an amplified virtual ground. As such, the TLE provides the voltage division of whatever power is supplied (DC wall power or batteries), thereby creating the "virtual" ground between the two. You might read the original CMoy article Chu Moy has in the Headwize Libraries on this principle. The PIMETA takes it a step further by adding an amplified feedback loop to the virtual ground.

What all that means is that the biggest part of a "ground" in the PIMETA has nothing to do with the power ground, and everything to do with a TLE. The amp won't work without it. If you've checked DigiKey and Mouser, try Jameco. Also, Amb sells one on his M3 and Amb DIY Audio web site. If none of that works, you could try checking ti.com (Texas Instruments). They would be happy to send you a sample if they have it, especially if none of the major suppliers has them. (Delivery dates on backorders are often exagerrated - you end up getting things a lot sooner than they estimate. So, don't hesitate to put in an order somewhere if they only have a few weeks delay.)

Quote:

Also, is it an either or situation when comparing the use of rled vs. the rfet/fet/znr combo? I'm not seeing how one would use them both at the same time.

Yep - either or, but not both.

Quote:

Thanks in advance for the help. Truly awesome forum here.

A few ME's lurking around, too.

 

[cetoole]

TLE2426 is pretty easy to get right now. Mouser has over 800 of them in stock in the TO-92 package you need for the Pimeta. Alternatively, AMB carries them in his audio shop, and it may be the most economical way to get the part, especially if he is willing to ship it to you USPS First Class. With both the STEPs and TREAD PS, you will need a rail splitter.

Yes, you can use rled xor rfet/fet/znr to power the LED.

EDIT: Dang nab Tomb, couldnt ya have waited a minute to post that?

 

[tomb]

Quote:

Originally Posted by cetoole ... snip ... EDIT: Dang nab Tomb, couldnt ya have waited a minute to post that?

No - I got it in first, and typed a lot more to boot.

When are you going to do more work on that Millett layout?

 

[cgrums]

Thanks for the quick responses! I was able to locate and order the TLE2426 at jameco (even ordered a few extra). This is all starting to make more sense (slowly

)

 

[cetoole]

Quote:

Originally Posted by tomb When are you going to do more work on that Millett layout?

Not sure, probably when I get some more feedback, to give it direction where to go. If you wanna see more work done on it, the best way is to generate more discussion on it.

 

[tomb]

Quote:

Originally Posted by cetoole Not sure, probably when I get some more feedback, to give it direction where to go. If you wanna see more work done on it, the best way is to generate more discussion on it.

OK - I won't digress further here and hijack the OP's subject. See you on DIYForums.org.

 

[tomb]

Quote:

Originally Posted by cgrums Thanks for the quick responses! I was able to locate and order the TLE2426 at jameco (even ordered a few extra). This is all starting to make more sense (slowly )

Glad to hear it. Be sure to post your questions as you start to build. There are many here who can help, almost instantaneously - in many cases. The PIMETA is a fun build, and absolutely a perfect choice as your next amp after a CMoy.

If you are not too concerned with power demands, I would definitely opt for the stacked buffers, and for the Class A biasing transistors. That will really accentuate the difference between the CMoy's sound and the PIMETA's.

 

[cgrums]

So the build is coming along nicely...mostly in part due to this forum.

I've got the TREAD outputting 24v and I've been checking voltages at all of my DIP-8 sockets. I have exactly half the supply voltage (exactly what tangent said should be there) at pin 8 of each socket except for OPAG. I've got what I view as a decent solder joint and can't see anything weird...is this pin not supposed to be seeing the same voltage measurement as the others?

Other than this development I'm waiting on a few browndog adaptors to use with the AD8620/8610 combo I'm going to start with before I roll in different opamps. Beyond that it's just a little case work and I should be good to go.

 

[tomb]

Pin 8 is "NC" - "No Connection" on a single channel opamp, which is OPAG. Here is the pinout for the AD8620/8610 you propose to use (the same for any other opamp compatible with the PIMETA):

 

[cgrums]

Quote:

Originally Posted by tomb Pin 8 is "NC" - "No Connection" on a single channel opamp, which is OPAG. Here is the pinout for the AD8620/8610 you propose to use (the same for any other opamp compatible with the PIMETA):

I don't mean to sound ungrateful here...but the speed and accuracy of your responses is starting to scare me a little tomb

That makes much more sense...had a brain glitch and was just looking at the 8620 datasheet...forgot ground was only single channel.

Thanks again!

 

[vixr]

Isn't tomb great? Very smart and very kind. He also sticks up for the underdog in some of the lopsided battles on the forums, when most of the others just pile on... Stick around cgrums, you will see what I mean.

 

[tomb]

Very kind words, vixr - thank you for the compliment! The same can be said of you, too. Sometimes I mess up big time, though (ygpm at Headwize). Hopefully I notice it and apologize when that happens.

In any event, Tangent's PIMETA is almost as important as a CMoy in the DIY headphone journey. As a logical next step, having a good experience with it is important. It was a lot of fun building mine. So, if someone's having a problem with one, I want to help if possible.

 

[cgrums]

So Everything's in and wired up...got the buffers stacked, AD8620/10 mounted to browndogs and inserted and an input/output hooked up. Went to test it...nothing. I can get a very faint sound with the pot (Alps RK27) cranked all the way clockwise but other than that nothing. Any ideas on what I should check? I can provide pics as well.

 

[tomb]

Yes - pics, please.

Did you wire to the proper INputs? That messed me up once. The inputs next to the "PIMETA" text and smiley face only work for the RK097 pot. All others use the square-shaped set of pads over in the corner.

The other trip-up is leaving out the jumpers for R8. You won't get any sound unless you put a jumper in those positions (assuming you don't use the R8 resistors - most don't).