[paul3]

Amazing - Just finished my build, and it worked first time.
 
I was very worried about the SMs but I guess I pulled it off.
 
A few minor glitches - I ordered/ fitted incorrect R6s so the gain off.
 
I set the gain too high, as I expected iPhone LOD to give a lower signal than phones out, and am planning to fit a crossfeed later.
 
Not sure what bias current to set - guess in the 1-3 ma range - still to experiment with.
 
SQ is amazing, even on IEMs, iGrados, didn't expect much difference with such small drivers, and HD650s sound great.
 
Thanks all for a great design, and tangent for your tutorials. I've learned so much.
 
Paul

 

[tangent]

Thanks for the report, Paul!
 
I'd definitely wait to drop the gain until after you insert the crossfeed. It will change things considerably.

 

[mfueger]

With the default RBLIM of 1k and 24V PS, is is correct to only be able to dial in about 2.8mA maximum for the Bias?

 

[tangent]

Yes, you can "only" push the op-am into class A by about two orders of magnitude.
 
How much deeper into class A do you believe you need to go?

 

[mfueger]

I am not sure. I read through some articles which mentioned higher values based on volume and load. Driving higher impedance headphones, or so I understood, require a higher bias level. I am still studying this, so please excuse my ignorance.

 

[tangent]

I think you're confusing the PIMETA biasing with that for different amps where the adjustable bias is in the output stage. That changes everything.
 
For the bias on an intermediate stage op-amp as in the PIMETA, 3 mA is "lots".

 

[TheLaw]

Very nice soldering. Look's almost like a machine.

 

[mfueger]

Could you point me in the right direction on how to determine optimal bias current for a given opamp?

 

[tangent]

Use your ears.  If it sounds right, it is right.

 

[i_djoel2000]

what do you guys think about listing all opamps (LR & G) that has been known work well in pimeta v2 in the first post? some sound characteristic explanation would be nice too..
 
what do you think? not a bad idea, right?

 

[mashuga]

Hello
 
I have a pair of newly acquired Pimeta v2 boards and some of the parts from Tangent's shop, but I still need to pull the trigger on a Mouser and Digikey order.
 
I guess my dilemma is that I want to pick all the components at once and not have to place multiple orders to the same shop because I picked something incorrectly.
 
After studying this thread as well as Tangent's site, (and anything else that Google would pull down) I seem to keep coming up against the same brickwall questions.  Hopefully my newbishness will be forgiven, 'cause I really feel that the specific answers aren't out there ( at least not without being an EE! ):
 
First thing is the bass boost.  I am comparing the PPA schematic to the Pv2 and I just don't get it.  In the Pv2, the switch seems to bypass the cap and R4...  Wouldn't that break the Jung multiloop topology? ( I say that like I understand it...!)  So is the bass boost active when the switch is closed or open? It's gotta be when it's open, right?  I'm thinking that I should just use the PPA style boost because it makes more "sense" to me, but I'm still not sure how the values for R4 compare between the two designs..  Is it really just a case of picking whatever works for the desired amount of gain?  Also, a .1uF polypro cap of "acceptable" quality that will fit on the board seems hard to find.  Is the quality of this cap that important?  If I do the PPA I will likely use Tangents suggestion to have a small piece of perf board like a daughter card.  Maybe I should just leave the boost out for now....
 
Next thing is power...  The recommended Elpac PS is no longer out there so I'm inclined to use a cheap(er) 24v wall wart and a LM7818 to get linear, regulated, isolated power.  Is it really as simple as having a .33uF cap on the input side and a .1uF on the output to get a decent quality PS for the Pimeta?  I'm not interested in battery power or charging at this point.  An 18v PS works out to a 12k R11 as best I can figure..  Just hoping for confirmation on my math..
 
I'll also just mention that availability of the recommended quality of caps seems to be a major stumbling block.. I'm really surprised at the huge gaps in inventory that Digikey and Mouser seem to have.  Not much demand out there I guess?  
 
Those are the holes in my shopping list so any help from those who have dealt with these questions would be much appreciated..TIA

 

[tangent]

Quote:

In the Pv2, the switch seems to bypass the cap and R4...

Yes, that's why I call it "unity boost". It works fine if -- and only if -- you need current gain without voltage gain.
 
If you need both voltage gain and current gain, do what the docs tell you: build a PPA-style bass boost in the scratchpad area.
 
 
Quote:

is the bass boost active when the switch is closed or open? It's gotta be when it's open, right?

 
Yes.
 
 
Quote:

I'm still not sure how the values for R4 compare between the two designs..

 
If you build out a PPA-style bass boost, the equations you find in the PPA docs work for the PIMETA v2.
 
The default PIMETA v2 gain is lower than for the PPA, but you had that choice with the PPA already. They're just defaults, not commandments.

 

[i_djoel2000]

tangent, i'm now building my pimeta and i decided to use resistor values which are not the same as per your suggestion.
 
i read your assembly guide and i think i have followed the rules correctly. but can you confirm that this circuit is ok? just to double check. i'm going to use 9.6V "9V" battery for this project, if that matters..
 
nb: forgot to mention, the value of R6 is 390k ohm
 


 
what do you think? thanks

 

[tangent]

Your 9.6 V battery could be as high as about 11 V when fresh off the charger. If you charge the battery in the amp using the built-in trickle charging circuit, the V+ voltage can be even higher, so R11 should be higher, too. I'd recommend at least 7.5 K.
 
The other changes should be fine.

 

[i_djoel2000]

 
Quote:

Your 9.6 V battery could be as high as about 11 V when fresh off the charger. If you charge the battery in the amp using the built-in trickle charging circuit, the V+ voltage can be even higher, so R11 should be higher, too. I'd recommend at least 7.5 K.
 
The other changes should be fine.

how to predict, or calculate the voltage of the battery after charging using the built in trickle charging circuit?
 
also, i want to add extra LED instead of populating LED2. i want this LED to give indicator when the wall adapter is plugged in and the battery charging is running

 
is my LED implementation correct?