The DT880-600 is on the edge of the O2's ability if you like your music loud (or listen to a lot of really wide dynamic range music). So it's important to at least come close maximizing how much gain you can run without overloading the input stage.
I used to assume all iPod LOD's were 0.5 volts RMS at 0 dBFS (max output). But I'm starting to wonder if the iPod Classic might be higher based on some posts I've seen. Does anyone know for sure? The Touch 3G and 4G are 0.5 volts and I assume (but don't know) the Nano is as well.
Assuming 0.5 volts from the iPod, and if you want to run on battery power, the math would be 4.5/0.5 = 9X gain. So the gain resistor value is 1500/(9 - 1) = 188 ohms. Always go with the next highest standard value such as 191 ohms or these 200 ohm Vishays:
CCF50200RFKR36
If you're only going to use AC power (no batteries), the smallest gain resistor it's 7/0.5 = 14X and 1500/(14-1) = 115 ohms or about 120 or 121 ohms to use the next highest standard value.
But if you have something besides an iPod Touch 3G or 4G you need to find out what the maximum output is and use that number instead of 0.5 in the math above. For more see:
O2 Gain Settings
O2 Maximum Input
All About Gain (article)
More Power (article)
If the balance shift is in the first 5% or so of the pot's rotation that should be at a level softer than most want to listen. If you find yourself using less than half the volume control's range you probably have the amp configured for too much gain for your application. Lowering the gain will let you use more of the volume control and the imbalance should disappear. See the links above.
Thanks... I've got them all...
also wondering about R3 and R7 ?? Notes say R3 and R7 are the same value as R19 and R23 (High Gain) upto and including a resistance of 274 ohms... for a max of 6.5X gain...
If I go up from there, say 12X, do I just change out R19/R23 to 133 ohms and leave the R3/R7 at 274 ohms???
At this time I'm thinking about setting the amp up for low gain of 4X and a high gain of 12X for the DT880...
Ok... just so I'm sure about this... if I want the upper gain to be at 12X
I put in 133 ohm resistors at R3,R7 and R19,R23 ???
presently I have R3,R7 with 274 ohms and the stock gain of 6.5x with the same
resistance of 274 on R19,R23..
one more question... if I run with a 12X gain with 600 ohm headphones, is there any danger to the source draw??
I put in 133 ohm resistors at R3,R7 and R19,R23 ???
presently I have R3,R7 with 274 ohms and the stock gain of 6.5x with the same
resistance of 274 on R19,R23..
one more question... if I run with a 12X gain with 600 ohm headphones, is there any danger to the source draw??
I'm not sure what you mean by "source draw"? The input impedance of the O2 doesn't change with gain changes, or unlike many amps, volume setting. It's always a constant 10K.
And yes, 133 ohms gives a gain a bit over 12X which limits the maximum input voltage to 0.375 volts on battery and 0.583 volts on AC power. iPod LODs are fixed output (the volume control on the iPod is disabled) so you'll be forced to use the headphone output and turn the volume down if you try to run the O2 on battery at 12X gain from an iPod.
I guess I'm having one of those days where I can't communicate...
I'll try again..
the question pertains to R3 and R7...
I change the resistance of R19 and R23 to 133 ohm's for ~12X...
Do I also change the value of R3 and R7 to 133 ohms..
sorry if this sounds stupid... but the notes sorta imply that...
I'll try again..
the question pertains to R3 and R7...
I change the resistance of R19 and R23 to 133 ohm's for ~12X...
Do I also change the value of R3 and R7 to 133 ohms..
sorry if this sounds stupid... but the notes sorta imply that...
@dixter, I should make the notes more clear. I agree it's a bit confusing. R3 and R7, for convenience, can be the same as any of the gain resistors in the range of 100 - 300 ohms. That way someone using say 214 ohm gain resistors doesn't also need to order 274 ohm resistors for R3 and R7. They can just order four of the same value.
Put simply, R3 and R7 can be anything from 100 - 300 ohms. In the stock amp I picked 274 ohms to be the same as the default 6.5X gain resistors only to have one less item for everyone to buy.
For the curious, the purpose of R3/7 is mainly to provide an RF input filter in combination with C11/12 and a bit of ESD/overload protection for U1. Too low a value doesn't offer much protection. Too high a value will cause some slight HF phase shift and loss of gain.
Put simply, R3 and R7 can be anything from 100 - 300 ohms. In the stock amp I picked 274 ohms to be the same as the default 6.5X gain resistors only to have one less item for everyone to buy.
For the curious, the purpose of R3/7 is mainly to provide an RF input filter in combination with C11/12 and a bit of ESD/overload protection for U1. Too low a value doesn't offer much protection. Too high a value will cause some slight HF phase shift and loss of gain.
Thanks... makes purfect sense now...
sometimes I think I just try to make the simple things into hard to understand things...
I think what also tossed me into that direction is I had seen a picture of a completed board and on the board it had the resistor sockets installed for R3 and R7 in conjunction with the actual gain resistors/sockets.... so I guess my
mind put the association together when I was thinking Gain options...
my bad for linking the two together...
thanks again.
sometimes I think I just try to make the simple things into hard to understand things...
I think what also tossed me into that direction is I had seen a picture of a completed board and on the board it had the resistor sockets installed for R3 and R7 in conjunction with the actual gain resistors/sockets.... so I guess my
mind put the association together when I was thinking Gain options...
my bad for linking the two together...
thanks again.
Would it make a difference if those two resistors are carbon film or metal? I made a mistake in ordering and didn't get those 2. I checked with the local radioshack and they only have carbon film. I did some reading and my understanding is that they introduce distortion. Since they aren't in the audio pass, would it make a difference to use carbon vs metal?
Which two resistors? R3 and R7? They're not super critical at gains of 6.5X or less. Even at higher gains while the noise will be measurably higher it will still be inaudible in most applications.
The gain resistors really should be 1% types, in part, for close channel matching and also for the lowest noise. But again, you could get by with 5% carbon films. If nothing else they're fairly easy to swap out later if you order parts for another project down the road.
In both cases because the volume control is after all of the above the noise of the resistors is far less important than it is in most amps with the volume control at the input jack.
@Alexium, with no load at all the bare minimum is 13.5 VAC but 13.7+ is better to allow for line voltage fluctuations. I have tried even 12 VAC and, despite the fact the regulators let through considerable ripple at such a low voltage, the O2 still performs nearly as well with as it does with a proper transformer (and still way better than any other headphone amp I've ever tested). That's because the audio circuits have very high PSRR and reject all but a tiny (about 0.00005) fraction of the ripple.
I haven't done any blind tests between the ODA and O2 yet partly because the ODA is still in pretty "rough" form waiting for the ODAC to stabilize before I order ODA PC boards. I don't expect there will be an audible difference due to the power supply but there is a measurable improvement in the ODA. And once the ODA is further along I do plan to run some blind tests.
No, acid flux will destroy the O2 over time. I would suggest you find some good tutorials on soldering electronics. Either your soldering iron is the wrong temperature, has a bad tip, you're using poor quality rosin core solder, or your technique is wrong. Others here may have some additional suggestions?
I'm afraid all of the abovementioned suggestions are true, my soldering skill is minimal and the materials and iron are most likely inappropriate. Still, I don't remember ever having such trouble as I had yesterday.
Thanks for the warning, I'll buy rosin solder instead of acid (don't know what kind of solder I used, but it has fairly high melting temperature).
Thanks for the warning, I'll buy rosin solder instead of acid (don't know what kind of solder I used, but it has fairly high melting temperature).
60/40 at least, I prefer 63/37. Both of these refer to lead/tin solder. That and a decent 25watt solder pencil should get you a nice basis for a good joint. Oh and a little practice never hurts, try to find some old and broken junk electronics and de-solder and re-solder a bit you'll get the hang of it in no time. Good luck!
