Please Recommend an AD8397 Pocket Amp Schematic
Mar 13, 2013 at 5:56 PM Post #16 of 23

wakibaki

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Quote:
Originally Posted by Beftus /img/forum/go_quote.gif
 
The pad doesn't need to be soldered in order to function

 
No, the pad doesn't need to be soldered to function, but the amplifier will be less robust and less versatile. My recommendations are designed to produce the best amplifier possible with that chip.
 
Removal of a faulty AD8397 is barely more problematic when fitted as I recommend. Simply cut through the chip legs one by one close to the chip using a scalpel. Apply heat to the soldered hole on the reverse. The chip will drop off. Collect the cut legs with a hot soldering iron and clean up the pads with solder wick. Job done.
 
w
 
Mar 13, 2013 at 6:37 PM Post #17 of 23

Beftus

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Hmm less robust is debatable... My Mini3 with ARZ still going strong after nearly 3 years. The opamp doesn't get really hot in use either. Running form the line out of my iPod with volume knob @ 12 o'clock into a 32 ohm Sennheiser PX-100ii (= pretty loud, borders on the uncomfortable for me) I measure 12 degrees above ambient. Yeah I know, totally unscientific. 
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Mar 13, 2013 at 6:55 PM Post #19 of 23

Misterrogers

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Wakibaki is right. The projects of this past year have really impressed on me the importance of following design guides whenever possible. I've had components fail when I've ran them on the thermal edge too often. Do it right the first time (or next time :) and save yourself some future grief.
 
Mar 14, 2013 at 8:46 AM Post #20 of 23

Seidhepriest

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Quote:
 
Current is measured in Amps. 
 
Have you applied* whatever you are measuring to an actual headphone to determine what you need, or is that 6-12v someone else's number? I have heard as high as 45 (what units, I dont know, I'm quoting someone else's number) is necessary for 600ohm headphones.
 
 
*Start off at low levels and work your way up slowly. People have destroyed headphones with less than 5V of current before. Pay attention to clipping. 

 
Current is measured in volts. Current power is measured in amperes. Watt being a combined power measurement, V*A.
 
AKG K-240 Monitor (600-ohm) off a CMoy on a ~7.2V rechargeable minibrick battery don't get much of a fill. They sag slightly and don't quite sound that full. The higher the impedance, the more the current required, and the less the efficiency (higher impedance=less power gets through). AKG's own number for 600-ohm headphones is about 6-12 V (11.4 or so max. methinks). That's a number mentioned in general 600-ohm literature linked to from the K-240 Monitor profile on AKG's website. The number makes sense, while K-141 1st-gen., being supra, may still work with about 4-7 V. max, it's not enough for any K-240 make. This is why the AD8397 looks like one of the very few op-amps suitable, everything else either doesn't have the SNR, or the current/power capacity.
 
Mar 14, 2013 at 10:04 AM Post #21 of 23

nikongod

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Quote:
Current is measured in volts. Current power is measured in amperes. Watt being a combined power measurement, V*A.
 
AKG K-240 Monitor (600-ohm) off a CMoy on a ~7.2V rechargeable minibrick battery don't get much of a fill. They sag slightly and don't quite sound that full. The higher the impedance, the more the current required, and the less the efficiency (higher impedance=less power gets through). AKG's own number for 600-ohm headphones is about 6-12 V (11.4 or so max. methinks). That's a number mentioned in general 600-ohm literature linked to from the K-240 Monitor profile on AKG's website. The number makes sense, while K-141 1st-gen., being supra, may still work with about 4-7 V. max, it's not enough for any K-240 make. This is why the AD8397 looks like one of the very few op-amps suitable, everything else either doesn't have the SNR, or the current/power capacity.

 
Potential is measured in volts. 
Current "intensity" is measured in amperes. Current is just current until you have other things to compare it to. 
Normal convention is to use the letter I for current when writing formulas. 
 
I hate it when people quote MFR's specs to me, and since you have indicated that you have AC measuring tools, could you measure how many volts you actually use to drive these headphones to your desired level and report back? 
 
You say they sag and don't sound that full but that could come from any number of causes. Could you elaborate on your use of the word "sag?" Its kind of a broad term. Regarding fullness - again, this could mean so many things, but I would not really say that the K240 fit in any of the more common definitions of full. I'm drawing a bunch of inferences here - but you want K240 to sound like different headphones. That's fine, the best way to achieve that goal is by getting different headphones. For sure it is fun to design amplifiers, and fun to build them too, but you may find yourself VERY disappointed if you expect your new cmoy to change what is essentially how the headphones sound. 
 
Mar 14, 2013 at 10:37 AM Post #22 of 23

Seidhepriest

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The K-240 Monitor work fine with a stationary amp, even off a mixer's (or monitor speakers') headphone socket. A CMoy amp doesn't have the same amount of current available, and hence it doesn't even make the headphones cut external noise off as well with the same kind of music. It just can't drive the K-240 to the same volume/frequency coverage. Harmonics sag, dynamics lack, it's not a good lively full-range frequency coverage. It's that simple, and the K-240 being a serious power hog, it cannot be driven by anything less than pro gear or a stationary stereo system amp's headphone output.
 
The newer AD8397 CMoy amp isn't specifically meant to drive K-240 Monitor, though that'd be a nice plus. It's the DAC headphone out that has to be capable of driving 600-ohm headphones, and it'll still need a step-up stage (8-12V off USB 5V). As it's been said, Wakibaki has an interesting AD8397 circuit, and there's a Swedish DIY fellow's AD8397 design too which ought to work. Both are rather complex, which is a minus as the cheaper and simpler the DAC output stage, the better, but hey, looks like that's the tradeoff of using AD8397.
 
Current measurements aside, just stacking a few AA rechargeables ought to do the trick of measuring how much current the K-240 Monitor really need.
 
Mar 14, 2013 at 11:35 AM Post #23 of 23

nikongod

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Quote:
It's that simple, and the K-240 being a serious power hog, it cannot be driven by anything less than pro gear or a stationary stereo system amp's headphone output.
 

 
If the headphones are volume matched the same amount of current is going into them regardless of what kind of amp you are using. It is so easy to verify this experimentally that I wont bore you with details. 
 
You should probably look into other attributes of your home stereo that may not be reflected in the portable. I'd start by measuring output impedance.
 

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