You're saying that it won't turn on at all, using batteries or AC power? No light at the LED? Have you gone through the "post build" testing steps on NwAvGuy's blog? Can you measure voltage at any of the test points he specifies?
It will probably be a long, slow process to find the issue, but it can be done.
I'm using a desktop DAC, the yulong D100, which outputs standard 2v RMS. I've noticed the same behavior on wall and battery power. My friend is using an ipod lineout as his source so that certainly should not be saturating.
Adding a series resistor is the same thing as increasing the amp's output impedance, which lowers the dampening factor. 75 ohms in series with say 16 ohm IEMs is a very large decrease in dampening factor. That will definitely be audible with most low impedance loads. The correct way to do it is to properly set the gain resistors. One of the nice design features of the O2 is the two gain settings, I'd definitely use them to get rid of the need for a series resistor for any load I was using regularly.
If it is clipping of the gain stage, it will be much worse running off of battery power than off of the wall wart. 6.5 gain seems too high to be usable on my O2's and I settled on 3x and 1x as the best compromise for the two gain switch positions. To avoid gain stage clipping you can do any combo of the following: lower source voltage ( source volume pot if available or software volume), raise amp rail voltage by running off the wall wart, install gain resistors to lower O2 gain.
So I should have read closer because I found a note on the schematic that mentions the maximum input voltage for a gain at wall and battery power and it does point that I would indeed be clipping with 6.5x gain and I tried lowering the input voltage and the distortion did go away.
So I think I may want to switch the gain resistors out with something a bit more functional for my purposes. It does not seem like there is much mention of gains lower than 2x anywhere in the O2 documentation. Are there any negatives to using a gain somewhere between 1-2x?
So I think I may want to switch the gain resistors out with something a bit more functional for my purposes. It does not seem like there is much mention of gains lower than 2x anywhere in the O2 documentation. Are there any negatives to using a gain somewhere between 1-2x?
Low gain is 1 + R16/R17 (1 + R22/R21) and high gain is 1 + R16/R19 (1 + R22/R23). R16 and R22 are 1.5k.
There seems to be no problem using low gains. RS recommends using 1x for IEMs and mentions just removing the resistors (so making R17 and R21 infinite) to do so.
Even with fullsize headphones (relatively insensitive at around 100 dB SPL / 1V) and a 1V rms source I usually use 1x gain and leave the volume pot between 9 and 12 for most music.
So in that case if I would prefer to switch the 6.5x to 1x I can do so by simply cutting R19, R23 and the switch would effectively be 2.5x and 1x? And now the out position would be high gain and the in position would be low.
I think you should start with the standard check-out procedures, as though you had just built it. Take out the batteries, switch off, plug in AC, start measuring.
Also, if the board didn't short against the case anywhere then the problem cannot have anything to do with inserting it in the case. Are batteries in it? Are they both securely attached and fully charged? Could one of them have moved while you inserted the board in the case?
I know it's too late now. In the future, it would be a good idea to build unfamiliar circuits in stages. Start with one section like the PS and add the resistors for it. Then the sockets and transistors. Then the capacitors. Verify that the section is working before you proceed. Doing things this way, at least the first time I build something, has saved me from bigger problems later. It has also found the demons before they could cause problems. Like you know you have done everything perfectly but it still isn't working. You reflow every joint and peer at the board through a 30x loupe. Only to find out two days later that you had a bad op-amp or mosfet the entire time. You can't say just try another mosfet or op-amp because you never know if the part came to you dead or your circuit killed it. Measure everything as you go. I have found mislabeled resistors, just plain bad tolerances, etc. Those are the kinds of problems that make you rip your hair out.
Hope someone can help with this...
I'm using a pioneer dv-757ai as a source for my O2 and have it's gain set to 2.25 & 3.5 based upon 2V output, I've managed to find the pioneer manual and it lists its output as 200 mVrms (1kHz, -20dB)!?
Err... no idea what that works out to...
Currently, even the x2.25 with ac power is loud and I'm only able to us the volume between 9 & 10 o'clock positions. It's easy enough to get the x1 gain, but it'd be nice to know the proper output voltage of the source and set the gain accordingly.
Thanks, Paul.
I'm using a pioneer dv-757ai as a source for my O2 and have it's gain set to 2.25 & 3.5 based upon 2V output, I've managed to find the pioneer manual and it lists its output as 200 mVrms (1kHz, -20dB)!?
Err... no idea what that works out to...
Currently, even the x2.25 with ac power is loud and I'm only able to us the volume between 9 & 10 o'clock positions. It's easy enough to get the x1 gain, but it'd be nice to know the proper output voltage of the source and set the gain accordingly.
Thanks, Paul.
I figured that Rocket Scientist would have logged back in by now! He must be busy doing the DAC reviews and the desktop version design.
BuildMeSomething- To do some math it would also be necessary to know the model of your cans or IEMS you are using to lookup the sensitivity.
But... all math aside there is an easier way. If you are "loud enough" with most music at the 10:00 position, and it doesn't sound distorted with the 2.25x gain setting, and if you are using the originally specified Alps RK097122008T control, then from the first page (pp 350) of the Alps data sheet
http://www.alps.com/WebObjects/catalog.woa/E/PDF/Potentiometer/MetalShaft/RK097/RK097.PDF
you can see from that chart you would have a "3B" resistance taper. The taper is the distribution pattern of resistance across the control. In other words, how high the resistance goes for a given amount of turn of the control. A given amount of turn might double the resistance for one taper, but might triple it, etc., for a different taper.
Going down to the chart at the bottom of page 359, on the left, you can see that a "3B taper" is essentially linear from 20% rotation to 80%, but the slope of the line is greater than 1:1. 10:00 would be about 40% of the rotation. Follow that up to the 3B curve and you get about 35% of the applied voltage. So if you were to cut your gain in half to about 1.15x (change the resistors in the O2) you would need 70% of the control's applied voltage to compensate for it (half the gain, double the control output cancel out). But from the chart that only gives you about 62% rotation for the 3B curve due to the greater line slope. Ideally it would be nice to use more of the control's rotation than that for "loud enough".
So... probably best to go all the way to a gain of 1x. That would need somewhere around 80% of the applied voltage out of the control, which would be 70% rotation, or about the 4:00 position or so. You can see from the 3B taper curve that you don't want to get up around 80% of the control's rotation because the resistance is nearly flat from there to 100%. In other words, after 80% rotation, you are turning and nothing more is happening.
If you are using a different control than the Alps RK097122008T just follow the steps above to look up the taper from the first chart and go to the second chart to convert control position to output. If you are using the Bourns control option just pull up that data sheet. It will have similar charts.
That is the low gain setting. As for the high gain setting maybe 2.0x or 2.25x. Your headphones and source won't be changing, of course, but that takes care of the case of music recorded at very low levels.
Good luck!
Rocket Scientist can post corrections whenever he next logs on, in case I've mucked something up here.
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Well, if -20dB gives 200mV then full scale (0dB) will be 2V. So you are fine if you calculated gain based on 2V.
Ian
Ian
agdr, thanks for the walk through, yes it's built with the standard pot and I'm using HD650's. About 70% of the music I listen to would fall under the compressed Pop banner, the rest is well recorded Classical. I'll snip the legs on the resistors used for x3.5 gain, giving me x1 & x2.25. Thanks.
ianrt, thanks
ianrt, thanks
This may not be the right place to ask for help. If not please suggest where would be appropriate. The O2 is my first DIY project. I have had great difficulty in seating DIPs in their sockets but everything else seemed to go well. Playing 1000hz test signals I get following results: INPUT OUTPUT
both left only
left only no output
right only left only
In other words it appears that only one channel works and channels are reversed. When I play music there is obvious distortion. All components are oriented correctly. Can anyone work out from the circuit what the problem could be?
both left only
left only no output
right only left only
In other words it appears that only one channel works and channels are reversed. When I play music there is obvious distortion. All components are oriented correctly. Can anyone work out from the circuit what the problem could be?
I'm thinking about ordering some batteries and found some that look good: 2 x Tenergy Centura 9v Low-Self-Discharge NiMH Rechargeable Batteries | eBay
Any opinions on them?
Any opinions on them?
I think it depends on how long you want it to operate. My understanding is that it'll run just fine on the 200 mAh batteries. In fact, I seriously doubt there would be any downsides to it (other than run time).
Mine will run on batteries for the vast majority of the time, so run time was important. I really like the idea of low-discharge batteries, but they tend to have lower capacity, so I went with Tenergy's standard NiMh.
It's neither good nor bad...just depends on your needs and what is most important for you.
Mine will run on batteries for the vast majority of the time, so run time was important. I really like the idea of low-discharge batteries, but they tend to have lower capacity, so I went with Tenergy's standard NiMh.
It's neither good nor bad...just depends on your needs and what is most important for you.