Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › the Pimeta-V2 thread
New Posts  All Forums:Forum Nav:

the Pimeta-V2 thread - Page 21

post #301 of 551
Quote:
Originally Posted by alphaman View Post

BTW: (Mostly a query for Tangent, I guess, tho' anyone's reply is welcome) ... how important is it to have "matching" OPAs for BOTH gnd and main L/R? E.g. AD8610/8620; OPA132, 2132; etc.?


Tangent already answered that, in the docs. Quoting:

 

 

Quote:
Some argue that you should use the single-channel version of the chip you used for OPALR in OPAG; the theory goes that because the ground channel must counteract the currents created by the left and right channels, using the same type of chip in all three channels is likely to give the lowest distortion since they all react to the signal in the same way. What we find in practice is that because both contribute to the sound of the amp, using dissimilar chips in OPAG and OPALR lets us fine tune the amp’s sonic signature more finely than if we always use the same chips for all channels. There is no practical limit on how widely different your OPALR and OPAG chips can be, as long as each is compatible with the PIMETA v2 circuit as a whole.

 

 

post #302 of 551

While not a PIMETA, here is a good example.

My amp uses 3 LT1363 with OPA633 buffers on the channels

and BUF634 on the ground.

post #303 of 551


 

Quote:
Originally Posted by i_djoel2000 View Post
have you tried to upgrade your resistor?

as for the ad8620, i just found it too bright for my current setup, that's why i switched to opa827

 

It has been a while since I built the unit, but I'm pretty sure I chose HQ metal film Rs ... mostly Panasonic and Vishay. But, since you brought it up, I may experiment with other brands.I agree that signal-path Rs must be of v. HQ.

Did you mean the AD827 (and not OPA827)?
 

 

post #304 of 551
Quote:
Originally Posted by alphaman View Post


 

It has been a while since I built the unit, but I'm pretty sure I chose HQ metal film Rs ... mostly Panasonic and Vishay. But, since you brought it up, I may experiment with other brands.I agree that signal-path Rs must be of v. HQ.

Did you mean the AD827 (and not OPA827)?
 

 


no, i really meant opa827: http://my.element14.com/texas-instruments/opa827aid/ic-op-amp-jfet-30mhz-ln-8soic/dp/1684749?Ntt=opa827

 

post #305 of 551

What are you folks using for C6 (which Tangent suggests as NP0 or C0G)? I'm using CAP CERAMIC 10PF 50V NP0 1206 (Digikey 399-1192-1-ND; Kemet C1206C100J5GACTU), which is a $0.14 part. 

 

Not sure whether upgrading this to something better will make much of a diff. I noted Styroflex above, but I have none that go this low in capacitance value, e.g., 10pF. Any thoughts?

Thanks!


Edited by alphaman - 4/19/11 at 12:52pm
post #306 of 551

I would suggest discussion of gnd channel op amp/buffer choice fine tuning the sound are evidence of conceptual failure of the whole "3-channel" idea

post #307 of 551

My nonsense to English translator must be broken again. :(

post #308 of 551

you must have broke it, it had to have worked at one time if you build, sell, advocate for  "3-Channel" headphone amps as having technical justification and measureable superiority to good dual supply amps with layout by people who actually understand grounding

post #309 of 551

Now testing Ready-to-use NiMH batteries and I must say that Pimeta v2 excels so well in producing purest sound for a battery powered device!

post #310 of 551

just thought i should share my recently cased and perfected pimeta. it's not the most beautiful looking one, though

23042011382.jpg

23042011381.jpg

 

23042011383.jpg

 

i use 4x aaa batteries and dc-dc step up converter (stepped up to 12V). i already anticipated that the sound will not be as good as i would like it to be, but i was wrong! there is no noise at all even though i cranked up the volume to maximum (no music playing)

 

this configuration gives me almost 20 hours of run time. much better than using 9v battery wink.gif

 

next plan: install dc socket to make the battery rechargeable without taking it out of the case. then buy this: http://store.curiousinventor.com/tenergy-universal-smart-charger-for-nimh-battery-packs-2-4v-7-2v.html

post #311 of 551

 

Quote:
i use 4x aaa batteries and dc-dc step up converter...no noise at all

 

Cool! Which one did you use?

post #312 of 551
Quote:
Originally Posted by tangent View Post

 

 

Cool! Which one did you use?


this one: http://my.element14.com/jsp/search/productdetail.jsp?SKU=1818377

 

by the way, i noticed some annoying buzzing sound after the batteries are almost out of juice. i was wondering what is the problem?? i thought it's broken opamp or soldering. but then i measured the dc offset at the ouput jack, it went to 0.5V!

 

how could this happened, tangent? the dc-dc converter requires a minimum of 4.5V supply voltage, and the battery goes to 3.6V when it is out of juice. do you think the problem is because the battery is running out?
 


Edited by i_djoel2000 - 4/23/11 at 7:57pm
post #313 of 551

Quite possibly. I don't see a reason to expect a DC-DC converter's performance to degrade gracefully when not given enough voltage to operate.

 

If you search the archives, you can find low-battery voltage indicator circuits that will warn you to turn the amp off before you get to that point.

post #314 of 551
Quote:
Originally Posted by tangent View Post

Quite possibly. I don't see a reason to expect a DC-DC converter's performance to degrade gracefully when not given enough voltage to operate.

 

If you search the archives, you can find low-battery voltage indicator circuits that will warn you to turn the amp off before you get to that point.

 

is it in here? http://tangentsoft.net/audio/pimeta2/tweaks.html

 

i couldn't find it
 

 

post #315 of 551

It's here.
 

Quote:
Originally Posted by i_djoel2000 View Post



 

is it in here? http://tangentsoft.net/audio/pimeta2/tweaks.html

 

i couldn't find it
 

 



 

New Posts  All Forums:Forum Nav:
  Return Home
Head-Fi.org › Forums › Misc.-Category Forums › DIY (Do-It-Yourself) Discussions › the Pimeta-V2 thread