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 25

post #361 of 568

quick question. how do we determine whether the LMH6321 is dying or broken?

 

my friend lent my pimeta this afternoon and before i was able to tell him how to use it he already switched headphones while the music was still playing, i left out the R11 to reach optimum sound quality (no current limiting). now i noticed there is some harsh/peak around upper mid-lower treble area, i don't know whether my brain is making this up, that's why i need to ask. any respond would be appreciated


Edited by i_djoel2000 - 7/9/11 at 11:15am
post #362 of 568

 

Quote:

how do we determine whether the LMH6321 is dying or broken? 

http://tangentsoft.net/audio/trouble.html

post #363 of 568

Check the supply voltage. You may not have fixed the battery problems as well as you thought you had.

post #364 of 568

Hey tangent, I have a question. You've seen my DIY pimeta v2 with BUF634s in WB mode, being fed with a dual 15v PSU. I don't think I'll be building another amp, so.. Is this amplifier powerful enough for high impedance headphones like the HD650? I'll get a pair in some years.. 

 

I suppose it's powerful enough with a high enough gain (other than the 3.5 I'm using right now) but you're one of the ones who designed this, so you know better.

post #365 of 568

I don't see what kind of guarantee you can be expecting. Yes, you used my information to build an amp, but in the end, it's DIY. You built it, yourself, so you are responsible for qualifying its behavior.

 

I will observe that PIMETA v1s were known to drive such headphones, using those buffers.

 

 

post #366 of 568

Now that I review what I've written, I think I should've worded my question in another way. My apologies.

 

What I meant is; is the pimeta design able to drive more demanding headphones, like 300 ohm models? Particularly the HD650. Yes I understand that this is all DIY and that I'm the one who is assessing what I've built, but putting it that way is more like what I wanted to ask in the beginning. You've said that yes, you've seen v1s driving such headphones, so my question is answered.

Thank you for your time!

post #367 of 568

Actually, higher impedance headphones are usually easier to drive than low-impedance headphones.

 

A typical 32 ohm headphone might require 0.5 V to sound "loud", which equates to ~8 mW. A typical 300 ohm headphone might require over twice as much voltage, but because the impedance is so much higher, the power to the headphones is much lower, more like 5 mW.

 

The only trick for driving high-impedance headphones is having enough voltage. I cover that on my site here.

post #368 of 568

Hi everyone! A quick q on the whole "needed parts" thing

 

How many DIP-8 sockets and op-amps do you need in total? and also, what would be the best op-amp to use in the pimeta for improving bass response?

post #369 of 568

 

Quote:

How many DIP-8 sockets

 

Either 2 or none for a Pimeta 2. .

 (dunno were the"1-5" suggested in the parts list came from)

 

 

 

Quote:

and op-amps

2 or 3.

3 singles or 1 single and 1 dual.

Obviously you would need an adapter if you go with 3 singles...

 

 

 

Quote:
what would be the best op-amp to use

Best would depend on how the amplifier is powered.........

 

post #370 of 568
Quote:

what would be the best op-amp to use in the pimeta for improving bass response?


Notes on Audio Op-Amps

Quote:
Originally Posted by MisterX View Post

 (dunno were the"1-5" suggested in the parts list came from)

 

Sorry about that.  It was a copy-paste holdover from PIMETA v1, where the buffers were socketable.

post #371 of 568

Tangent notes ... "Most headphones sound best when the amplifier's output impedance is as close to 0 as possible."

 

Not sure about this ... std. cans like Grado, beyer, and IEMs like ER 4P, IME, sound better at higher-impedance O/P (but not the newer 600-ohm versions of beyer). E.g., my Meier Corda II has both 120-ohm and 0-ohm O/P. I was a bit shocked to find that my 16-ohm Senn. IE-8 IEM -- my go-to can if there ever was one -- also performs better at 120-ohm. This makes more than 1/2 my cans inventory better suited for above-0-ohm O/P impedance.

 

Back OT ... what's your general experience here with Pimeta 2? I mostly couple the Pi2 with IE-8. So now I'm wondering ... build a  special  high-O/P-impedance jack? ... and how much/little/optimal O/P impedance I really require for this IEM, and IEMs in general.  (i.e., I only have experience with 0 and 120)

 

[ Note: Sorry if this topic is redundant. My lousy excuse: I'm too lazy to do research today. Just point to links as necessary. Thx!!  ]

 

 


Edited by alphaman - 9/3/11 at 10:11am
post #372 of 568
Quote:
Originally Posted by alphaman View Post

Tangent notes ... "Most headphones sound best when the amplifier's output impedance is as close to 0 as possible."

 

Not sure about this ... std. cans like Grado, beyer, and IEMs like ER 4P, IME, sound better at higher-impedance O/P (but not the newer 600-ohm versions of beyer).


You're welcome to stick series resistors in between the output pads on my amp boards and the output jack solder lugs.

 

 

Quote:

E.g., my Meier Corda II has both 120-ohm and 0-ohm O/P.

 

As does my original Corda, and I couldn't say I heard a worthwhile difference in 120 ohm mode. I'm not saying no difference, I'm saying none I wanted to keep.

 

The only two arguments I've heard for why there should be an improvement are:

 

  1. The German standard that says you should do this, quoted by Jan Meier in defending the high-Z output. This standard also says you should design headphones with the same 120 Ω impedance. That's a double failure, as far as I'm concerned. On one front, we have a bureaucracy trying to set standards for audio equipment; what next, oil-on-canvas brush stroke styles? On another front, we have the reality that the other half of the standard is largely ignored, so even if there is acoustic merit to this idea, shouldn't the output impedance change depending on the headphone?
  2. The fact that you get optimal power transfer to a load when the impedances are matched. This is probably the reasoning behind the German standard, but I consider it separately because it seems bogus in its own right. I'm not doubting the engineering, I'm doubting its applicability to headphones. The only time I've ever seen serious engineers bother with impedance matching is at RF, to avoid reflections. That's a complete non-issue at audio frequency. (Well, it is to those of us who can't hear green markers anyway.)
post #373 of 568

Tangent/ALL:

Not sure about the German std. I could very well get even better performance above or below the "politically-standardized" 120-ohm -- haven't tried. Also -- and as I speculated elsewhere in this forum recently -- better performance at higher O/P imp. may have more to do with operating the volume pot in its more-linear range.

The improvements I heard were subtle ... but noteworthy.

post #374 of 568

Hi,

 

In case you're interested, you can indeed build a Pimeta v2 handheld amp with the following features:

- Serpac H65 enclosure

- Li-Ion cell pack 14.8V 0.75Ah with protection circuit

- Integrated modified Linkwitz Crossfeed circuit

- Integrated Bass Boost and Volume Boost circuit

- Integrated battery level control circuit with bi-color led

 

For some of you this may be a bit over-engineered, but to me it was a good exercise.  The amp sounds brilliantly and qualitatively excellent, and the cells last for well over 10 hours.  As a proof, see the following pics.

 

DSC06090.JPG

Lots of cables for the filters and boosters, but eventually it will fit.  On the bottom see the bass/volume booster circuit as a piggi-back board to the R4 pins.

 

 

DSC06124.JPG

The 4 circuits all connected.  The Linkwitz circuit required the big caps to be soldered horizontally, while one of the C4 Wima caps had to be moved to the scratchpad area.

 

DSC06129.JPG

On the bottom of the pic see the battery control circuit, which goes as a vertical piggi-back board onto the sratchpad area.

 

DSC06134.JPG

All fits precisely into the enclosure.  The Li-Ion pack has been R&D'ed for this purpose - newest technology you can build these days.

 

DSC06154.JPG

Finally, the enclosure can be closed and the product is finished... happy listening!

 

Cheers.

post #375 of 568
Quote:
Originally Posted by mfuerst View Post

For some of you this may be a bit over-engineered

 

Actually, this sort of build was one of the drivers behind the PIMETA v2 design: the scratchpad area, Molexes everywhere...

 

Thank you for taking the PIMETA v2 in its intended spirit. :)

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