Yes, that's fine and much better than running anything on the AC adapter side of the amp. Just make sure the pot/input/output wiring are twisted pairs. As mentioned in the article, pulling the pairs out of any sort of CAT5 ethernet cable works great. You can also twist together 30 AWG wire wrap wire.
If you don't have an oscilloscope I can only make "blind" suggestions. Make sure all the parts around U2 are the correct values and correctly soldered. Getting any of those wrong, especially C1, C16, C21, R4, R24, and R8, could make the turn on transient worse by "unbalancing" the circuit. I'm also assuming you didn't modify the amp in any way (use parts not on the BOM, etc.)?
This may sound weird, but try pushing the power switch in (with no front panel or just the bare board) at an angle from both the power jack side and from the volume control side and see if that makes a significant difference in the pop. Pushing it from the side will slightly rotate the sliding portion inside the switch. If one side of your switch is making contact much sooner than the other side that might make the transient worse. If so, you might have a marginal power switch.
You can also try making C1 smaller--say 0.1 uF or 0.22 uF but if it's too small, the amp may not turn on at all with partially discharged batteries and the transient associated with low battery shutdown might be worse. In my testing (see the scope photos in the O2 Details article) 1 uf was optimal.
With my amps, using "average sensitivity" headphones the turn on "tick" isn't very loud or objectionable. With my HD650's it's even softer. With my balanced armature IEMs, which are some 20+ dB more sensitive, the tick is more of a "pop" as it's 20+ dB louder.
What headphones have the loud pop?
Timpert, I am very interested in your guide. This is my first PCB board that I am soldering and I would greatly appreciate any help you can give. I was just going to go off my knowledge of soldering and looking at the pictures, but I know the current needs to flow between the pieces and I would vastly thank you for creating a step by step guide for people like me. I think it will help me a lot to take on future projects but I wanted to start with this Objective 2 Amp because it has awesome reviews and doesn't really look like a terribly hard thing to put together if I got all the right parts. So please if you have the time and energy make this guide. I think there will be a lot of people appreciative of this on here because it seems that tons of people have questions and it's their first or second project as well. I PM'ed you as well but I might even donate $5 to the guide if it's good enough. If I am allowed to do that I am not sure.
Guide
I will happily do a guide as it is really a straight forward build, all the information is on nwavguy's blog, there is a lot of information on the site but if you read through carefully it is pretty simple.
If there is enough interest for me to do a guide then I will order some parts and build another O2 taking pictures etc on the way.
You will have to wait a couple of weeks though as I need to order the parts.
I will happily do a guide as it is really a straight forward build, all the information is on nwavguy's blog, there is a lot of information on the site but if you read through carefully it is pretty simple.
If there is enough interest for me to do a guide then I will order some parts and build another O2 taking pictures etc on the way.
You will have to wait a couple of weeks though as I need to order the parts.
I twisted each channel together so I have 3 24AWG wires twisted together. Is that what you meant, or did you mean a pair for each tab on the PCB, so it would be 3 pairs per channel?
If you build the stock circuit using the BOM materials and put it in the recommended case, no wires are required.
Some folks are using different cases, different jacks, different layouts, so need some wires to make it all work.
Thank you very much for your effort, I'll be checking things out as soon as I get the opportunity.
The headphones are Sennheiser HD25-1, which are rather middle of the road regarding sensitivity. I'm not too worried about the headphones, they are some tough buggers, but the pop is truly physically painful.
I am pretty sure this is more than what there is supposed to be, I imagine it would be nearly ear damaging with IEMs, that is if the armatures don't snuff it.
I'm going to build an amp for my Beyer DT880 (600 ohms) and was curious as to what would be the best gain for them...
Presently I have built one of the amps for my other phones and it works very well with those but I want to optimize the gain for 600 ohms on a different amp.
any suggestions for the gain resistors... source will be Ipod LOD.
Thanks in advance..
Presently I have built one of the amps for my other phones and it works very well with those but I want to optimize the gain for 600 ohms on a different amp.
any suggestions for the gain resistors... source will be Ipod LOD.
Thanks in advance..
Did some audio testing a few days ago and the amp works great! Using ath-m50s, I couldn't even tell there was an amp because it was so transparent. I'm excited to test it with some more revealing headphones in the future. At low gain setting and when the pot is at a very low volume, I do notice channel imbalance even though I trimmed the bottom leg of the gain switch so it's not touching the via.
Do you turn down the volume before you turn the amp on/off. If I remember correctly, it was advised to do so.
I had the same problem on one of my amps... it was so bad that with the volume dial all the way down I was still getting some signal in the left side.
I put an omh meter on the volume pot and measured both sides.. they were way off... so I thought I had a bad pot... started to remove the solder with solder wick and just before I was going to use the solder sucker I decided to measure it one more time.. to my suprise the readings were now matching.
I know for a fact there wasn't any bridging going on as I looked at the back side of the board very carefully.. only thing I can think of is that I may have had some solder between the pot and the board, when I wick'd it maybe the solder
flowed better and fixed the issue...
I'd measure the resistance of the volume control all the way down and all the way up and compare the left/right numbers to see if they match...
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Buy the sockets for the gain resistors and buy a full set of gain resistors and then you can try them all out.. It'll cost you a whole $3.05 to do that, and if you want to change them later, you don't have to worry about desoldering them... (look under the "Gain Resistor" heading in the BOM spreadsheet)