That would work, but then you have a DC coupled amp with all the inherent fun - mainly the DC offset issue (possibility of frying the headphones). An alternative modification suggestion would be to actually add another C13 and C14 sized cap in series with R3 and R7 on the input to the amp, to keep any input DC offset voltage (from the source) from clipping the first stage. Like C13 and C14 those should make an inaudible difference on the low end, but prevent clipping.
Longer answer... if you do try shorting C13 and C14, some things to keep in mind:
* Before connecting any headphones to the O2, unplug the input jack, so it shorts the inputs to ground, and measure the DC offset voltage on both channels of the O2. With those caps shorted the DC offset of the O2 first stage, caused by U1 input bias current through the input resistors, will reflect to the second stage and may add or subtract from the nominal 3mV. 5mV or less offset voltage on each O2 output would probably be OK.
* The gain switch setting may affect the O2 output offset voltage now too, since any DC offset voltage in the first stage also gets multiplied by the stage gain, then added/subtracted from the output stage offset voltage. Try measuring the O2 output offset voltage on both channels with the gain switch in both positions.
* With the headphones still unconnected, plug in the source and re-measure the O2 DC offset voltage. Any DC on the source will now reflect back to the output.
* The O2 offset voltage may now vary a bit with the volume control. The two caps kept the second stage input bias current out of the pot (RocketScientist says that also causes a rustling sound when turned, too, which you now may get). Now the pot is in parallel (DC circuit model) with R12 and R13, so the voltage drop caused by the U3 & U4 op amp input bias current will vary slightly with pot position.
* If the input stage starts clipping against one rail due to too large of an input signal, then even if there is no DC on the input signal a net DC offset voltage (additional) may be generated by the first stage due to the asymmetric signal and fed to the second stage. Try to make sure your input signal is going to be well within the O2 input specs.
In summary.... not recommended to short C13 and C14.
They are doing many good things and really should have zero effect on the sound. For some further proof that they really don't make any audible difference in the signal, buy 8 more of them or so. Solder 4 in parallel to give a total of 8.8uF, then attach leads and solder that right over C13 for a total of 11uF, 5 times the capacitance which would drop the 3bB point of the highpass filter being created down to just a few Hz. Then do the same on the other channel with C14 and give it a listen. You could even do an A/B test by using a DPST switch to run one lead to C13 and C14 through, switching that extra 8.8uF in parallel on each channel in and out while you listen.Hope this helps!
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That helps a lot. I know that they are doing more good then bad and should be inaudible but every piece of equipment I have heard, without caps in the signal path, I have noticed a difference. I wasn't sure if DC offset would be so terrible it wasn't worth trying but I may play around with it. I just finished my first amp and love it so far, now it is time to build a second one and play around a bit.
As a tinkerer and skeptic I am always curious if things couldn't be made even better, even if it is more for academic purposes and not useable real-world improvement. Because of this I am curious if there are improvements that could me made to this amp. I may try some other opamps with the only goal being to improve the slew rate (or make it worse) so I know how that affects the sound of devices. I fully admit there may be nothing to gain by this but knowledge.
As a tinkerer and skeptic I am always curious if things couldn't be made even better, even if it is more for academic purposes and not useable real-world improvement. Because of this I am curious if there are improvements that could me made to this amp. I may try some other opamps with the only goal being to improve the slew rate (or make it worse) so I know how that affects the sound of devices. I fully admit there may be nothing to gain by this but knowledge.
The O2 mods thread has great improvements. On my list are DC coupling caps on the input and DC offset correction (tricky but doable). The reason I'm not interested in changing out the OpAmps is because the other ones I've found that look like they could be a drop-in without having changes to the feedback circuit also have a nasty ringing in positive feedback designs... if I remember correctly. Anyway, I disqualified everything out there for this circuit, so if I want something different, I'm not even going to be using the O2 board to do it. That's how integrated this is. There is room for improvements but they come with cost and complexity.
I do hope the ODA has the following improvements:
-three or more gain positions, one potentially a voltage divider circuit for <1 gain
-preamp output option
-DC coupling caps
-on/off relays for pop-free transients
-tunable DC offset correction (because ultra-sensitive IEMs are very affected)
-choice of three input sources constantly connected
I do hope the ODA has the following improvements:
-three or more gain positions, one potentially a voltage divider circuit for <1 gain
-preamp output option
-DC coupling caps
-on/off relays for pop-free transients
-tunable DC offset correction (because ultra-sensitive IEMs are very affected)
-choice of three input sources constantly connected
ditto except I tried the O2 as my preamp and it sound amazing as well. I am going to A/B it against my aleph 1.7 when I get some more time.
hi diy forum peeps hope to get a useful tip here....
help!
i need to ground the input jack to the case...i looked a t a couple of pictures
..
can i use a thin wire from a resistor cap thingy to ground the case from the white 'ground' that is labeled in the second picture?
help!
i need to ground the input jack to the case...i looked a t a couple of pictures
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
..
can i use a thin wire from a resistor cap thingy to ground the case from the white 'ground' that is labeled in the second picture?
sorry here's the pudated pics the previous post was too smalll
pic 1
http://img29.imageshack.us/img29/212/o2groundlead4.jpg
pic 2
http://img827.imageshack.us/img827/8351/o2odacinputjackwiring5.jpg
the scond picture it shows the ground..is that where i'm supposed to solder in the wire to ground it to the case?
fyi, nwavguy's article says its important to ground it to the case to reduce noise and humm
pic 1
http://img29.imageshack.us/img29/212/o2groundlead4.jpg
pic 2
http://img827.imageshack.us/img827/8351/o2odacinputjackwiring5.jpg
the scond picture it shows the ground..is that where i'm supposed to solder in the wire to ground it to the case?
fyi, nwavguy's article says its important to ground it to the case to reduce noise and humm
I'm intending to do this one day myself but so far I've rarely been troubled by noise or hum, ungrounded.
There seems to be something wrong with my ODA/ODAC combo since there is quite some hiss accompanying the music :-( It's as a radio station slightly out of tuning.
I just got the ODAC last evening so I haven't had any opportunity yet to troubleshoot.
My first move will be to get the combo out of the box to eliminate ground problems...
Only hissing, no hum.
Brgds
I just got the ODAC last evening so I haven't had any opportunity yet to troubleshoot.
My first move will be to get the combo out of the box to eliminate ground problems...
Only hissing, no hum.
Brgds
Is your 'ODA' using RS specified parts or modded? And have you done the grounding as described by RS?
You want to solder it to the ground post on the underside of the audio jack like RS did it. Electrical tape won't give you what you want. Also, you want to scour the part of the case it will contact as well as the wre end that's touching the case. The screwed in front plate will apply enough pressure... much better than electrical tape. So don't solder that part.
It would be OK to use the lead wire from a resistor or capacitor as you previously questioned, but beware that you only get a few bends out of that kind of wire before it snaps.
Hi, I am new here.
I am putting an O2 parts list on mouser.com. I have a couple questions.
For J1, Is 163-7620E-E the replacement for the obsolete 163-7620E?
For transformer, is 412-218054 better than WAU16-400 because it higher in voltage and amp?
Thanks.
The replacement power receptacle you listed is your best option, but beware that the blades are a bit larger so they will need to be filed or vertically crimped to fit in the PCB holes.
Also, the unloaded voltage of that Xicon AC adapter is 21V. Just think about that for a bit.
OK.
1: Take out your O2 PCB from the box. Get rid of the front panel.
2: Take the batteries out.
3: Find something as thick as the slots in the box.
4: Take whatever measure you like to keep the odac connected to the space below the batteries with component side down. I used tape that is adhesive on both sides. The tape is made for rugs/mats I believe.
5: Now this is the tricky part... We need new front and back panels that fits a O2/odac combo where the box itself has been turned upside down and the oda goes into slot 2 and the odac into slot 1 counted from the new bottom. I got rid of the Al structure in the middle of the box not to interfere with the inductor which is othervise in contact with the box.
6: The frontplate - all holes must move 2mm's up.
7: I have done this on my own but I don't have the measurements at hand. Just Put the odac into slot 1 and measure the distance to the usb hole...
I will buy a few If anyone else is interested in a fitting combo and someone wants to get this happening... Otherwise I'll make my own but since the ones for O2 was much better than I'll ever could produce I'll rather see that someone made a GB out of this!
This way you will have it all - O2 and ODAC in a B2 enclosure with batteries
Brgds
BTW: I confess - I took some electricians tape to be sure the regulators won't shortcut to the lower top in the box...
1: Take out your O2 PCB from the box. Get rid of the front panel.
2: Take the batteries out.
3: Find something as thick as the slots in the box.
4: Take whatever measure you like to keep the odac connected to the space below the batteries with component side down. I used tape that is adhesive on both sides. The tape is made for rugs/mats I believe.
5: Now this is the tricky part... We need new front and back panels that fits a O2/odac combo where the box itself has been turned upside down and the oda goes into slot 2 and the odac into slot 1 counted from the new bottom. I got rid of the Al structure in the middle of the box not to interfere with the inductor which is othervise in contact with the box.
6: The frontplate - all holes must move 2mm's up.
7: I have done this on my own but I don't have the measurements at hand. Just Put the odac into slot 1 and measure the distance to the usb hole...
I will buy a few If anyone else is interested in a fitting combo and someone wants to get this happening... Otherwise I'll make my own but since the ones for O2 was much better than I'll ever could produce I'll rather see that someone made a GB out of this!
This way you will have it all - O2 and ODAC in a B2 enclosure with batteries
Brgds
BTW: I confess - I took some electricians tape to be sure the regulators won't shortcut to the lower top in the box...
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