The Objective2 (O2) Headphone Amp DIY Project - Page 307 - diyAudio
Go Back   Home > Forums > Amplifiers > Headphone Systems

Headphone Systems Everything to do with Headphones

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 23rd January 2013, 02:25 PM   #3061
diyAudio Member
 
Join Date: Aug 2012
Can anyone tell me where I can find detailed assembly instruction for the O2, sort of a walk-through guide, I searched Google but didn't find any. Is there something around here that resembles that?

Thanks for your help
  Reply With Quote
Old 23rd January 2013, 06:21 PM   #3062
adydula is offline adydula  United States
diyAudio Member
 
Join Date: Aug 2010
nwavguy.com

NwAvGuy: O2 Details

Alex
  Reply With Quote
Old 25th January 2013, 03:12 AM   #3063
diyAudio Member
 
Join Date: Oct 2011
Quote:
Originally Posted by DevilsRightHand View Post
Can anyone tell me where I can find detailed assembly instruction for the O2, sort of a walk-through guide, I searched Google but didn't find any. Is there something around here that resembles that?

Thanks for your help
Building the O2 Headphone Amp
  Reply With Quote
Old 25th January 2013, 06:23 AM   #3064
diyAudio Member
 
Rullknufs's Avatar
 
Join Date: Mar 2010
Location: Sweden
Send a message via Skype™ to Rullknufs
There's some info over here as well: ?music: Objective
__________________
My audio and DIY blog: http://phimusic.blogspot.se/
  Reply With Quote
Old 27th January 2013, 02:28 AM   #3065
diyAudio Member
 
Join Date: Apr 2012
Location: Harrisburg, PA 17111
Default gain switching/resistors questions

Hi guys- I have almost got my O2 put together.

I am confused about the configuration of the gain switching resistors.

My build is for an AC only desk unit. I decided not to buy a gain switch. My thinking was to have a fixed gain and to use the SIP pin sockets for the gain resistors.

From the nwavguy resources page: "NO GAIN SWITCH: You can jumper around the gain switch and leave out two of the gain resistors if you want only a fixed gain amp. But testing shows the gain switch does not hurt the performance and it adds a lot of versatility for future sources and headphones. There are jumper marks on the PC board along the sides of S2 showing where to install jumpers if you leave the switch out."

Well, I guess I'm not interpreting that correctly. I thought he means to place two jumpers on the board where marked and then I can use just two resistors for a fixed gain.

However, regardless of what I do, I get 1X gain.

Attached is a photo of my board.

Initially, I soldered in jumpers as shown in the photo. When I found that doesn't work, I cut them- no change. I even shorted in the opposite driection (vertical instead of horizontal, looking at the photo)- no change.

What am I dong wrong?

Thanks,
Keith Ostertag
Attached Images
File Type: jpg o2_gainswitch.jpg (80.6 KB, 272 views)
  Reply With Quote
Old 27th January 2013, 06:01 AM   #3066
ericj is online now ericj  United States
diyAudio Member
 
ericj's Avatar
 
Join Date: Dec 2008
Keith, I suggest that you clean the back of the board (with alcohol - isopropyl or ethyl, and a brush) and check your solder work on the gain stage opamp.

Failing that, more and bigger pictures. both sides.

Last edited by ericj; 27th January 2013 at 06:04 AM.
  Reply With Quote
Old 27th January 2013, 03:15 PM   #3067
agdr is offline agdr  United States
diyAudio Member
 
agdr's Avatar
 
Join Date: Sep 2010
Quote:
Originally Posted by keithostertag View Post
I thought he means to place two jumpers on the board where marked and then I can use just two resistors for a fixed gain
You almost had it! Wrong two resistors. The resistors go in the R19 and R23 sockets, with the R17 and R21 sockets where you have the resistors now left blank. So just move your resistors to the other two sockets and it should work.

I've attached a diagram below. Red are the switch jumpers, which look OK on yours. Green is where the gain resistors should go, and purple are the holes or sockets that are left blank.
Attached Images
File Type: png O2 no gain switch jumpers 1.png (23.0 KB, 249 views)
  Reply With Quote
Old 27th January 2013, 03:48 PM   #3068
diyAudio Member
 
Join Date: Apr 2012
Location: Harrisburg, PA 17111
Thanks ADGR!

Yea, I spent a good hour figuring this out before I got your message... it's not obvious (at least to me) from the PCB markings or the text. Also, I'm not particularly good at following PCB traces, especially double-sided ones...

Turns out, after all that, I've decided to leave the gain resistors out- 1X seems to work fine for me. Easy to install them in the future- that's why I used those SIP sockets.

BTW- how to put images inline for these board posts? I'd like to post some photos of my completed project.

Thanks,
Keith Ostertag
  Reply With Quote
Old 27th January 2013, 08:33 PM   #3069
agdr is offline agdr  United States
diyAudio Member
 
agdr's Avatar
 
Join Date: Sep 2010
Quote:
Originally Posted by keithostertag View Post
BTW- how to put images inline for these board posts? I'd like to post some photos of my completed project.
I've never been able to figure out the magic to get inline images to work on DIYA. I would be curious myself. I've just used the attachments so far.
  Reply With Quote
Old 27th January 2013, 11:11 PM   #3070
diyAudio Member
 
Join Date: Apr 2012
Location: Harrisburg, PA 17111
Default O2 project report- rack mount unit

OK, here's what I've put together.

For my O2, I wanted to put it in a rack mount unit, and provide an extra set of paralleled inputs as a "pass through". This so I can put it in my rack unit we use for our entertainment center- one input comes from the DVD source, the other goes to an EQ and the rest of the stereo system. This way my wife can use the headphones while we watch a movie, and I can turn the sound up as loud as I want without affecting her headphone volume. We had been using the "monitor output" on my Crown amp- not bad sound, but no separate volume control (I don't use a preamp with my system). Using this with a BeyerDynamic DT880 (250 ohms).

I have a fair amount of junkbox parts I wanted to use, and most of my work on this project was in fitting them. Populating the O2 board was trivial, other than my poor eyesight and a few mis-identified traces/routings.

I put in a switch to the headphone output: just a precaution to use when plugging in-and-out of the amp.

Here's a photo of the major parts:

http://www.strucktower.com/o2_sections.jpg

The rack unit was bought at a local yard sale for $5 last year. I just spray painted it and replaced the guts with the O2, drilling holes where needed for remote inputs, etc. I used a sheet of old copper-clad (PCB) board for the base.

Here's a photo of the inputs:

http://www.strucktower.com/o2_input_outside.jpg
http://www.strucktower.com/o2_input_inside.jpg

The power transformer I got for $1 at a hamfest a few years ago- puts out about 17VAC and comes with it's own little circuit board with line conditioning and fuse. I dropped this and broke the board- then the repair slipped after I had clamped it and walked away... oh well.

http://www.strucktower.com/o2_ps.jpg

I happened to have a dual section military grade 5-position switch, always wondered what I could do with it. So I decided to turn it into a 5-step attenuator for the volume control. I couldn't find much info on how to make one- all the info I saw gave db values but no resistor values- maybe I didn't look hard enough? Anyway, I decided we didn't need low volume, and I limited myself to resistors I had on-hand, and I assumed (maybe wrongly?) that I should keep total values across each to 10K. The values I came up with are (wiper in the middle):

5.7K + 4.5K
6.8K + 3.9K
7.6K + 2.5K
8.2K + 1.8K
9.4K + .9K

Even though I had no idea how these would work out, happily it turns out just fine. Though I am only using the O2 at 1X gain, there's more than enough volume, and in fact one change I might make is replace the lowest section to reduce the volume further.

I etched a quick and dirty PCB with two concentric circles for the wipers: here's a look at how it turned out:

http://www.strucktower.com/o2_vol_side.jpg

http://www.strucktower.com/o2_vol_rear.jpg

You can see I used twisted pair as cable for it.

One of the more dumb things about this build was how difficult it was to install my 1/4 phone jack for headphone output. It has a large diameter shaft- plus I needed space for an insulator. I didn't have a drill bit that big- 3/4 inch. So I had to punch through the rack unit's aluminum front plate- 3mm! Took a lot of effort and a long torque bar. Then, I spent hours fabricating an insulator to fit because the shaft was just barely long enough. Oh boy, was that a lesson in choosing standard components!

Here's a photo of the remote power connections. Sloppy job with those, sorry. Notice- for strain relief I use a strong fiber string, similar to what they use for parachutes.

http://www.strucktower.com/o2_power_connections.jpg

Here's a photo of the gain resistors- taken before I corrected their placement (thanks agdjr) and eventually just removed them.

http://www.strucktower.com/o2_gain_resistors.jpg

I used good quality shielded audio cables (made by Amp) that I salvaged from a vintage stereo years ago.

Here's the final product:

http://www.strucktower.com/o2_final.jpg

Due to the size of the box around the transformer the whole thing takes a little more than one unit height, but I room have for it. If I come by a full size single rack unit in the future I can swap it easily.

In the future I will try to put more emphasis on better soldering and aesthetics. My soldering skills are not bad- I just have trouble seeing that close. Also, the smallest tip I have is 1/8", not really small enough for this type work.

So, to leave you with something humorous, let me show you a classic example of a really bad soldering job:

http://www.strucktower.com/o2_mistake.jpg

Hey, at least I was able to find it!

I hope this post helps give ideas to someone, or at least makes some of you laugh.

If any of you want to comment, thanks. Especially re the attenuator.

A special thanks to Eric who took the time out to help me with a part.

Keith Ostertag
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Headphone amp project grahamfocal Headphone Systems 7 21st June 2011 05:28 PM
My latest project - DAC + headphone amp gmarsh Digital Line Level 105 13th December 2010 02:31 PM
My headphone amp project trifidmaster Headphone Systems 2 22nd December 2008 03:52 PM
Mini Ipod headphone amp DIY project Nordic Headphone Systems 14 11th March 2007 02:35 PM
Need help for a battery headphone amp project dismalonyx Headphone Systems 1 15th April 2004 11:22 PM


New To Site? Need Help?

All times are GMT. The time now is 12:16 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2