The Objective2 (O2) Headphone Amp DIY Project - Page 334 - diyAudio
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Old 18th June 2013, 07:05 PM  
qusp is offline qusp  Australia
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not a chance DJNUBZ, not only will the gain and way to much noise be a problem. the very low, but not zero, source impedance (and inductance) presented by phono cartridges, makes it an even worse proposition. is your Cart MM or MC? i'm guessing MM

of course you are lacking any kind of RIAA at all

Last edited by qusp; 18th June 2013 at 07:13 PM.
Old 19th June 2013, 10:17 PM  
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Default Check out this site for a inexpensive amp

Here's the site:

Boozhound Laboratories: JFET Phono Preamp Kit

There are many other PCB's, both solid state, IC's, and tubes that do the
job much much better than an O2 every could. It would take a redesign.
Old 20th June 2013, 04:49 AM  
agdr is offline agdr  United States
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Default Phono amp

DJNUBZ - here is an implementation of the simple phono pre-amp in the LT1028 data sheet (opens PDF, picture top of page 18)

that would fit in the top slot of an O2 amp in the taller B3-080 case. The board goes updside down from the image so the two electrolytics point downward. The power and ground wires into the O2 power, outputs go to the O2 input PCB holes, and inputs probably should go to RCA jacks mounted in the O2 amp front panel (that would fit with the taller B3 case).

I know you have wanted that phono pre-amp for a while.
Attached Images
File Type: png LT1028 Phono amp circuit.png (15.0 KB, 372 views)
File Type: png LT1028 Phono amp layout.png (38.8 KB, 370 views)
Attached Files
File Type: zip 80x100mm 2 layer 1.6mm green (17.5 KB, 6 views)

Last edited by agdr; 20th June 2013 at 04:57 AM.
Old 20th June 2013, 05:13 AM  
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Originally Posted by proid View Post
Hi all! I want to make a custom o2 that is as small as possible (only using batteies) so i want to ask if the filter section for batteries is really need or can i omit it? Like in the Grado Ra1, there are no filter capacitors too.
Click the image to open in full size.
You can use SMD ceramic capacitors while still keeping the pcb size small.
If you are planning to omit PM ckt all together you will loose protection from low battery situation and power ON/OFF thump.

o2 inspired smd headphone-
Dual O2-Inspired, SMD Headphone Amp

Last edited by availlyrics; 20th June 2013 at 05:21 AM.
Old 22nd June 2013, 09:09 AM  
sallau is offline sallau  Finland
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Hello all,
I'm a starting diy-artist and building the o2 amp+dac. I'm trying to make it desktop version: RCA input +1/4" output + (both panel mounted). The AC-input will also be panel mounted (so that it can be placed into the backpanel). So, my problem is my inexperience and lack of good instructions. I've made the O2 ready excluding the RCA, 1/4" socket, power input and the DAC. But now I'm unsure how should I solder the wires between the sockets and the board.

Could some either give me direct instructions or a link or help me in some other way? I'm sure these things have been discussed over before but I can't find any.
I've got these O2 Headphone Amplifier Desktop Kit but I haven't got the panel mounted AC-socket yet. (The amp will be fitted into the bigger B3-080 case)
Thanks alot!
Old 25th June 2013, 01:42 PM  
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I've just assembled the O2 everything works fine however, when I increase and decrease the volume, some fuzz/static can be heard(only when nothing is playing though). Anyone know why this happens?
Old 25th June 2013, 08:00 PM  
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Location: Germany
Assuming you used all the parts as per BOM and have an AC coupled source, it's got to be a scratchy pot. Not sure whether there are any fakes of RK09s around, maybe just a bad apple.
Old 26th June 2013, 03:56 AM  
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Originally Posted by sallau View Post
....Could some either give me direct instructions or a link or help me in some other way? I'm sure these things have been discussed over before but I can't find any....
I can upload some more snaps of my O2 to help you out with RCA, 1/4 H/P, e.t.c. connection or PM you.
Attached Images
File Type: jpg IMG_0119.jpg (815.9 KB, 275 views)

Last edited by availlyrics; 26th June 2013 at 04:17 AM.
Old 26th June 2013, 05:02 AM  
JZatopa is offline JZatopa  United States
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Location: Chicago
Sorry if this is to OT but I broke down and ordered a VSPS 300 kit. I wanted to try playing with the 02 as an RIAA as I have a few extra boards laying around that I haven't decided what to do with just yet but you guys have convinced me to take the easier path.

AGDR thanks for posting that, I may still try playing around with that circuit at some point.

I think that the o2 circuit could be the basis a few other pieces. Considering it's measured performance, it would make a great preamp or phono preamp. Yes you would need to increase the gain and add the riaa filter but if you look at the VSPS, its not much more then an opamp and a few parts. With the o2 we have 2 gain stages to work with.
Old 1st July 2013, 06:51 PM  
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Default Steps for RCA connections

Before proceeding-remove any batteries / AC power.

Steps for RCA connections-

1. Carefully cut the GND track joining 3GND & 4GND using a sharp knife. Use continuity meter to verify that there is no continuity between points GND & 3GND or GND & 4GND.
2. Strip stereo shielded cable & solder one of the inner two wires to point 3GND & the other wire to 4GND. Usually RED is LEFT CH. & WHITE is RIGHT CH. The outer copper mesh /shield is common GND. The end result should be something like image01.
3. Solder the inner pin of each RCA connector to the respective RED & WHITE wire. The outer “ring” of the RCA connector is common GND.
Attached Images
File Type: jpg image 01.jpg (645.1 KB, 192 views)
File Type: jpg Soldered RCA connector.jpg (649.2 KB, 68 views)
File Type: jpg Soldered RCA GND ring.jpg (981.3 KB, 62 views)

Last edited by availlyrics; 1st July 2013 at 07:14 PM.


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