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O2 AMP + ODAC - Page 302

post #4516 of 4525
Quote:
Originally Posted by lehoang15tuoi View Post

Guys I've never been in love with headfi as I am right now! It's all fine after I turn the volume on Windows to 45%. I feel that I need to update my audio knowledge immediately, so perhaps I'll spend more time on the nwaguy blog right now


looking that on my laptop, 45% is -11.8db(I changed the unit with a right clic like a boss ^_^)

now switching from 1X to 3.3X that's about +10.4db. you see where I'm going here? :wink_face:

 

 

@jseaber while trying to look for some specs on the revB in case lehoang was somehow reaching the limits with the K612. after all that thing seems a little horrible to drive, worst than an audeze http://www.innerfidelity.com/images/AKGK612.pdf  I noticed that on the rev B combo dac/amp you still give the same power output with different loads as nwavguy(for 33 and 150ohm at least), except that the default gain values are now different.

I'm very aware that you're doing epiphany's customer service when you try to help here, but because you're always so reliable, we now count on you for everything ^_^.

 

oh well, akg writes:  Max. Input Power 200 mW  on the specs of the k612... does that mean the headphone summons armageddon in a wild explosion after we pass 115db with it? @lehoang15tuoi how about selling that headphone?  that would solve a bunch of problems. (ok I know the way out, I'm leaving now... bubye..) :biggrin:

post #4517 of 4525

Would it work if I made the bottom of the case metal, but the rest of it some kind of plastic?

post #4518 of 4525
Quote:
Originally Posted by castleofargh View Post
 


looking that on my laptop, 45% is -11.8db(I changed the unit with a right clic like a boss ^_^)

now switching from 1X to 3.3X that's about +10.4db. you see where I'm going here? :wink_face:

 

 

@jseaber while trying to look for some specs on the revB in case lehoang was somehow reaching the limits with the K612. after all that thing seems a little horrible to drive, worst than an audeze http://www.innerfidelity.com/images/AKGK612.pdf  I noticed that on the rev B combo dac/amp you still give the same power output with different loads as nwavguy(for 33 and 150ohm at least), except that the default gain values are now different.

I'm very aware that you're doing epiphany's customer service when you try to help here, but because you're always so reliable, we now count on you for everything ^_^.

 

oh well, akg writes:  Max. Input Power 200 mW  on the specs of the k612... does that mean the headphone summons armageddon in a wild explosion after we pass 115db with it? @lehoang15tuoi how about selling that headphone?  that would solve a bunch of problems. (ok I know the way out, I'm leaving now... bubye..) :biggrin:

 

Gain of 1.0/3.3x is slightly rounded (try to find resistors that give exactly 7.0/2.1=3.33x gain). Actual gain is slightly higher.

 

Also, the O2 amplifier specifications are published separately from the DAC. It's possible to reach published Max Power = 613mW at 32 ohms with an O2+ODAC RevB:

 

P = ((gain*Vsource)^2) / 32 = (3.3*2.1*3.3*2.1)/32= 1500 mW...

 

O2 is current limited here, so max power is unchanged at ~600mW.

 

Max output is about 7.0VRMS from O2+ODAC, yielding:

 

Max power @ 600 ohm = 82 mW

Max power @ 150 ohm = 327 mW

 

O2 can achieve 7-8% more voltage with slightly higher gain, or stronger analog input. This is a small amount since volume increase are perceived on a logarithmic scale.

 

AKG K612 Pros are rated 92 dB/mW @ 120 ohm. Tyll's measurements show about 90dB/mW, so slightly more demanding than AKG's own spec.

Reply
post #4519 of 4525

oh yeah, I didn't think current was the limiting factor and stayed focused on voltage and power alone for some reason. that sure explains it all, thanks you for the clean explanation.

post #4520 of 4525
Quote:
Originally Posted by lehoang15tuoi View Post

Guys I've never been in love with headfi as I am right now! It's all fine after I turn the volume on Windows to 45%. I feel that I need to update my audio knowledge immediately, so perhaps I'll spend more time on the nwaguy blog right now
Your K612 doesn't get loud enough using 1x gain?
post #4521 of 4525

It does, at 1 or 2 o' clock. I'm just under the impression that the soundstage gets bigger on hi-gain.

 

@castleofargh Nah I'm starting to love it. With tubes these shine!

post #4522 of 4525
Quote:
Originally Posted by castleofargh View Post
 


how much the amp will heat up depends entirely on the headphone that will be used. in most cases it does not get warm TBH, but depending on the headphone that can happen.

 

With case open mosfets are heating up around 60C, also NJM4556 buffers have around 50C when listening to normal levels on 32ohms headphones. When using high impedance headphone even the 2207 is a bit hot (at most 50C). Placing small heatsink on every opamp will decrease temp with more than 5C; I did that myself and I can recommend you to do that if you want to cool down your opamps. Unfortunately, I was unable to add heatsinks to mosfets because lack of space. :(

 

Not so high temps here, but when placed inside a plastic case opamps and mosfets temps will be at least 10C higher. Most likely some small halls drilled into the plastic case will help moving the airflow a little bit.

post #4523 of 4525

The mosfets operate in switch mode and don't generate any heat.
 

Are you sure your not referring to the voltage regulators?

 

A.

post #4524 of 4525
Switching mode? Are we looking at the same schematic?
post #4525 of 4525
Quote:
Originally Posted by diamondears View Post


Many sources gives up bits when you turn the volume down.

 

ALL sources reduce the number of bits if you use the source itself to turn down the volume.

(To turn down the level you make the numbers smaller; smaller numbers are smaller and so use less bits.)

 

However, the Sabre's internal 32 bit digital volume control won't do this (at least not at normal levels).

Many DACs also have digitally controlled analog volume controls (not on the DAC chip itself).

 

However, in both of these cases, that will only help if the source can "talk" to the DAC and use that better volume control.

Unless they specifically say otherwise, the source device has no way to USE the better volume control in the DAC.

DO NOT assume this to be the case unless the manufacturer of your DAC SPECIFICALLY says that it is with the particular player you're using. (It's also possible for a USB DAC to "co-opt" the Windows system volume control, in which case the software volume control will be disabled and the better one in the DAC will be used no matter what player you use. However, if that's the case, they WILL tell you - since it's an important feature.)

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