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The Objective2 (O2) Headphone Amp DIY Project
The Objective2 (O2) Headphone Amp DIY Project
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Old 7th May 2013, 03:37 PM   #3271
agdr is offline agdr  United States
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The Objective2 (O2) Headphone Amp DIY Project
Quote:
Originally Posted by okim View Post
I make smallest version of o2, which smd transistors I can use as a replacement?

How look comparison o2 with triad l3 or Lisa III?
Here is kind of what you would get:

http://www.diyaudio.com/forums/headp...p-version.html

Like ybz90 says, the pot, batteries, jacks, etc. take up a lot more room than the chips and resistors. I stayed with 1206 SMD parts just to make it easy to solder, but electrically a lot of those could be 0805 or 0603.

I kind of ran out of motivation to build it once I learned about the JDS Labs C5:

http://www.jdslabs.com/item.php?fetchitem=70

If you do build a SMD O2, please post some pictures!

Last edited by agdr; 7th May 2013 at 03:42 PM.
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Old 7th May 2013, 05:20 PM   #3272
okim is offline okim  Poland
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I want to make combo (o2+wm8740+wm8804) everything will be powered by 4 li on cells (+7,4v and -7,4v)
I have already designed bigger part of pcb, some of capacitors will be leaded but I can't find replacement for this transistors, can someone help me?

P.S dimensions of the pcb 15x100x60mm (similar to ibasso db2 but with very good amp)
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Old 7th May 2013, 06:05 PM   #3273
agdr is offline agdr  United States
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Quote:
Originally Posted by okim View Post
but I can't find replacement for this transistors
The two power management mosfets?

Adding the DAC definitely makes it more interesting!

Last edited by agdr; 7th May 2013 at 06:07 PM.
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Old 7th May 2013, 06:21 PM   #3274
okim is offline okim  Poland
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Yes, mosfets (I make mistake)
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Old 7th May 2013, 07:35 PM   #3275
smudgeface is offline smudgeface  Canada
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Quote:
Originally Posted by availlyrics View Post
A couple of posts back, a member had reported O2 + ODAC in same case resulted in somewhat higher level of noise (analog+digital ckts. too close for comfort?) on some high sensitivity h/p as compared to just single stand alone O2. Also to see if your O2 is "dead quiet" you need to disconnect 3.5mm i/p connector (so the sockets short i/p pin to gnd) & then chk. for any noise, provided you have shorted i/p socket gnd. pin to case properly.
So I tested this a bit more: the noise disappears completely with the DAC unpowered, confirming once more that the DAC does cause noise. I have not ye tried removing the ODAC from the case to see if the noise is reduced. I'll try that later tonight. If this turns out to be the case, I wonder if additional shielding might work to isolate the noise, assuming it is radiated and not getting in on the LOD.
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Old 7th May 2013, 09:19 PM   #3276
okim is offline okim  Poland
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Sabre have charge pump for negative voltage inside, maybe this is the reason of noice

Wysłane z mojego Galaxy Nexus za pomocą Tapatalk 2
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Old 7th May 2013, 10:10 PM   #3277
agdr is offline agdr  United States
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Quote:
Originally Posted by okim View Post
Yes, mosfets (I make mistake)
The On Semiconductor NTZD3155CT1G might be an interesting part for your application. It has both the n-channel and p-channel mosfet in the same part, so they will be well matched for similar switching times.

http://www.onsemi.com/pub/Collateral/NTZD3155C-D.PDF (opens PDF)

20Vds which is enough for your +/-14Vdc rails. Rds = 0.5R, which is 10x larger than the O2 mosfets but still just 0.125V drop at 250mA. They have low threshold voltages, turning on hard at just 1.8Vdc. I see "single and dual cell lithium battery operated systems" listed as one of the applications. One problem, Vgs (max) is just 6V - logic level - so you would have to use a resistive divider on the gate of each with the O2 circuit.

Mouser #863-NTZD3155CT1G. Farnell has them in stock, #2101817.

Last edited by agdr; 7th May 2013 at 10:18 PM.
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Old 8th May 2013, 10:35 AM   #3278
okim is offline okim  Poland
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Thanks
I have a lot of space, so MOSFETs doesn't have to be small.

What's if I have for example 7v on positive and 7.5v on negative?
Is it have any effect?
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Old 8th May 2013, 04:26 PM   #3279
agdr is offline agdr  United States
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Quote:
Originally Posted by okim View Post
What's if I have for example 7v on positive and 7.5v on negative?
Yeah I typo'ed that. You have +/-7.5Vdc rails and 15Vdc rail-to-rail, which is what the mosfet gates see.

Here is an even better part that has +/-20Vgs. No resistive divider needed. You could use it in the O2 circuit just the way it is. Smaller Rds (on) too, around 0.1R. Fairchild FDS4559:

http://www.fairchildsemi.com/ds/FD/FDS4559.pdf (opens PDF)

Mouser #512-FDS4559, Farnell #1471052, RS Components #6710523.
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Old 8th May 2013, 08:15 PM   #3280
Knusperkeks is offline Knusperkeks  Germany
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Quote:
Originally Posted by okim View Post
I want to make combo (o2+wm8740+wm8804) everything will be powered by 4 li on cells (+7,4v and -7,4v)
I have already designed bigger part of pcb, some of capacitors will be leaded but I can't find replacement for this transistors, can someone help me?

P.S dimensions of the pcb 15x100x60mm (similar to ibasso db2 but with very good amp)
Hey, this sounds like a quite nice idea. I'm currently thinking about a SMD-O2 version powered by li-ion cells with an integrated dac (probably the odac). Because i only want to drive iems, the 2V rms from the odac would be totally fine so i can left out the gain part to same more room. Is there any easier way for the low voltage protection part than nwavguy's solution? None of the li-ion protection chips i found so far, are suited for a bipolar design. Greetings
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