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post #181 of 556
Quote:
Originally Posted by H22 View Post

Yes, I was asking about biasing. I re-read the assembly notes and think I have a little beter understanding, I thought the CRDs could be part of the circuit, as in some other amps (B22, Lisa3). but as i understand it now, one would just use a CRD in place of a resistor to assure no LED dimming?

A CRD is a constant current source. If you check the documentation, there is already a discrete constant current source on board.  

Quote:

Any sugestions on good 1206 sized resistors? thick film or thin film or other? metal film in  1206 are very pricey, and i would use them in the audio path, but they are very limmited in what values are offered.

 

1206 versus through hole?  You'll same some height, but not a lot compared to some of the other taller components.

post #182 of 556
Quote:
Originally Posted by cobaltmute View Post



A CRD is a constant current source. If you check the documentation, there is already a discrete constant current source on board.  

 

1206 versus through hole?  You'll same some height, but not a lot compared to some of the other taller components.


Yes, But i like SMD, also, finding resistors that match the schem is proving to be difficult. Vishay has a metal film MELF, but some of the values are out of stock (digikey &mouser). Thin film 1206s are plentifull and have the right values. wanted to use the RN55 stuff, but again i was hit by a couple "out of stock 12 week lead time" issues.

post #183 of 556

 

Quote:
 No, the greater the resistor value, the greater the current limiting.  You may want to look at page 16 in the LMH6321 datasheet.

 Ok, Got it.  I will check out the datasheet.

 

So I am wondering, as this will be powered from a battery, would it be to dangerous to calculate it from the low batt voltage, in this case 12v? or play it safe and base it on the fully charged voltage ~16.8v? 8000k and 11.4k respectivly

post #184 of 556

I guess you're asking about the C2 cap voltage ratings and such?  Rate those for the highest voltage they will ever see.  If you're hacking some kind of external charging circuit into this, beware that this will have to put a higher voltage across the battery than their highest off-charger voltage.

post #185 of 556
Quote:
Originally Posted by tangent View Post

I guess you're asking about the C2 cap voltage ratings and such?  Rate those for the highest voltage they will ever see.  If you're hacking some kind of external charging circuit into this, beware that this will have to put a higher voltage across the battery than their highest off-charger voltage.


Tangent, thanks for all you help and designing a much loved amp. I was not concerned about C2 voltage, I plan to use 25v caps here. And the charge circuit I have for the lipo pack ensures that the voltage never exceeds the max volt per cell for li-pos (4.2v), so 16.8 is max, and the circuit also cuts the current flow round 12v (3v per cell) to avoid cell damage. 

What I was asking about was a safe yet unrestrictive (buffer current/audio quality wise) resistor velue to use for R11, as the V+ is dynamic, using your simple formula of 667xV+ will provide a range of resistor values. safest bet is to use a larger resistance to limmit current to 300ma at full voltage, but, if i understand it correctly, this will limmit the current at nominal voltages. I realise this is splitting hiars, as 300ma is WAY more current than will likelly ever be needed. But in e an effort not to hamper the performance, im wondering if the buffer can take momentary current surges of over 300ma (within reason). So, pick a R11 resistance that allows a full 300ma at 12v, and should the output be shorted (witch it most likely will at some point) the momentary >300ma surge wont hurt anything. You stated somewhere that the chip can handle higher momentary currents, so I am thinking it is not a huge deal....

 

Again I am splitting hairs here i think. As for the resistor dilemma I was facing (out of stock on some of the good resistors in the proper schem values), I found your wonderfull resistor calculator! so I can substitute more common and "in stock" values, and it only changes the gain by a tiny bit. But with that in mind, i have made up my mind to build 2 Pimetas, 1 lower gain for portable use (thinking a gain of 3-4) and a higher gain for home use with full sized cans.

 

post #186 of 556

 

Quote:
safest bet is to use a larger resistance to limmit current to 300ma at full voltage, but, if i understand it correctly, this will limmit the current at nominal voltages.

 

Yes, to about 212 mA, by my calculation.  That still sounds like enough to me.

post #187 of 556

Hey guys I'm just starting out.  This is my first pimeta build and I have a question.  The input power (v+ v-) for OPAG is still pin 4 and 8 right?  I'm getting correct v- from pin 4 but v+ from pin 7 and not pin 8 for OPAG. 

post #188 of 556

I was going to ask if there was a reason why you couldn't just check the schematic but it's easy to see how you could be confused after checking it.

post #189 of 556

Mister X you are right.  I do look at the schematic but at this point I'm pretty confused.  My v+ and v- readings are different from OPALR to OPAG so I'm a little concern.

post #190 of 556
Quote:
Originally Posted by evolo View Post

Hey guys I'm just starting out.  This is my first pimeta build and I have a question.  The input power (v+ v-) for OPAG is still pin 4 and 8 right?  I'm getting correct v- from pin 4 but v+ from pin 7 and not pin 8 for OPAG. 


OPAG is a single channel op amp and OPALR dual channel. They have different pin outs as the way you described.

post #191 of 556

Spacehead thanks for you answer.

post #192 of 556

Hi all. For my next project I wanted to build a pimeta v2 and grubDAC in the same enclosure.  I have a 24VAC wallwart transformer I planned to use with a TREAD for an 18VDC supply to the Pimetav2. However Tangent's shop no longer contains the TREAD kit? :(  

 

Otherwise I will just use amb's sigma25. 

post #193 of 556

Alright the amp is done.  Wow this is one sweet sounding amp.  I love it.

 

Any one using Lipo for power source?

post #194 of 556

Is a 2 cell LiFePO4 pack close enough?

 

 

P1010573.jpg

post #195 of 556

Yeah, LiFe are suppose to have really high discharge rate.  I just used 5000 4s lipo pretty crazy.

 

MisterX what opag and opalr are you using this that one?

 

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