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Old 22nd November 2013, 03:07 AM   #11
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Quote:
Originally Posted by xnor View Post


... and care to explain what's so bad about class D?
Class D has come a long way, with really nice commercial sound reinforcement class D amplifiers that are powerful, efficient, and remarkably affordable. I realize that many of us right here have worked very hard to optimize class D amplifiers for hi-fi. But..

Please don't try to tell me that you can get hi-fi with a patchcord from a cellphone to an amplifier. I've had people in my shop patch their cellphones and ipads into the sound system (I have a patch chord hanging right in front of the preamp), and it sounds OK. But it doesn't even sound as good as the tuner (I do have a nice Nakamichi tuner), and to my ears FM broadcast sounds "canned."

The comments about the power supply are right on the money. The "stiffer" and cleaner a power supply is, the better an amp will sound. Headphone amps have modest power supply requirements, so you can apply "overkill" power supplies without much trouble. An electronic regulated power supply (even a basic series regulator) will clean up the sound a whole lot, trust me. Of course this is impractical for anything but a balls to the wall design when designing a speaker power amp, but it can be done. With headphones you get a lot of bang for your buck out of a regulated power supply.

I have a box of modern switching power supplies from servers and computers. With electronic regulators and high bandwidth capacitors (like ceramic) in parallel with the electrolytic smoothing caps, they clean up real nice.
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Old 22nd November 2013, 03:14 AM   #12
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+1 - especially on the ceramic caps, they're a godsend to getting decent SQ from switching PSUs.

What I find surprising is how few transformers I've seen on headphone amp offerings. If you can't arrange a really low noise PSU, make an amp with a higher voltage output than you need and step the output down to the phones with a trafo. Has worked a charm for me so far....
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Old 22nd November 2013, 03:23 AM   #13
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To me, this should be such a non-issue in this day and age. Sound quality can be greatly improved for relatively little expenditure with an external amp, in nearly all cases. The improved, dedicated power supply. The improved match between output drive and load. The improved headroom. No matter what your volume control setting. It's a shame "amp" or "booster" have a narrow SPLs!! connotation when it comes to hpa's.
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Old 22nd November 2013, 04:56 AM   #14
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Originally Posted by abraxalito View Post
+1 - especially on the ceramic caps, they're a godsend to getting decent SQ from switching PSUs.
And all it took to find that out was just trying it. I thought it was a good idea, and it was.

I'm not exactly a state of the art engineer, but I have been dorking around with this stuff for over 40 years.
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Old 22nd November 2013, 05:06 AM   #15
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Originally Posted by sofaspud View Post
To me, this should be such a non-issue in this day and age. Sound quality can be greatly improved for relatively little expenditure with an external amp, in nearly all cases. The improved, dedicated power supply. The improved match between output drive and load. The improved headroom.
It's a no brainer to me.

Quote:
It's a shame "amp" or "booster" have a narrow SPLs!! connotation when it comes to hpa's.
People are clueless when it comes to electronics; especially audio electronics. Thank the marketing jackoffs for that.

I remember when I started building amplifiers. I was around 11 years old. My father was so against me building an "amplifier"- "isn't that s___ loud enough god d___ it Eddie!" But then he also thought that you could hook a speaker directly to a ceramic cartridge and I am not kidding. By the time I was 14 I had cobbled together a pretty decent home built "hi-fi" (not a transistor in it) and then my father finally got what I was doing - he was actually impressed (no easy task) and actually started to encourage me. But he still never really "got" what I was doing; he just knew that the results were pretty good.
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Old 22nd November 2013, 05:19 AM   #16
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Quote:
Originally Posted by Fast Eddie D View Post
I'm not exactly a state of the art engineer, but I have been dorking around with this stuff for over 40 years.
Don't worry, it was the 'state of the art' guys who came up with the 'Transwarp' drive which Mr Scott found so easy to sabotage 'The more they overthink the plumbing, the easier it is to stop up the drains'.
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Old 22nd November 2013, 07:42 AM   #17
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Originally Posted by Fast Eddie D View Post
I think you missed the part where it was pointed out that an external amplifier represents a much easier load to the "bad" amplifier, thus greatly reducing distortion. Also the explanation of the differing output impedances- built in amplifier usually has a higher output impedance compared to an external amplifier. All this makes a world of difference in the distortion profile.

Battery operated devices have amplifiers where the primary design parameter is low power consumption. Cellphones have nasty, nasty class D amplifiers. I don't know what's inside an ipod, but I doubt that it's optimized for audio.
I also missed the part where you explained how a nasty class-D output stage suddenly becomes all better by patching it into a completely different impedance than it was designed for.

In fairness, the (Class-AB) output stage in your average integrated codec chip will perform better driving the line input of an external amp, than it would driving the headphones directly. The data sheets of the codecs I've used actually state this.

But I wouldn't necessarily assume the same for a Class-D output stage.

Until recently, IPods had a line output from the dock connector that (as far as I know) bypassed the headphone amp. I have no idea what is in the new Lightning connector.
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Last edited by scopeboy; 22nd November 2013 at 07:45 AM.
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Old 22nd November 2013, 01:53 PM   #18
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Originally Posted by scopeboy View Post
I also missed the part where you explained how a nasty class-D output stage suddenly becomes all better by patching it into a completely different impedance than it was designed for.
That's because I didn't say that. In fact, I pointed out that the fidelity from a cellphone patched into a hi-fi amplifier is still quite inferior.

I'm aware that class D amplifiers sometimes don't work right when driving impedances outside of their design parameters.

Quote:
In fairness, the (Class-AB) output stage in your average integrated codec chip will perform better driving the line input of an external amp, than it would driving the headphones directly. The data sheets of the codecs I've used actually state this.
The reason for this is glaringly obvious, to me.

Quote:
But I wouldn't necessarily assume the same for a Class-D output stage.
I don't assume that and I realize why.

Quote:
Until recently, IPods had a line output from the dock connector that (as far as I know) bypassed the headphone amp. I have no idea what is in the new Lightning connector.
I'm not up to speed on ipods but since they're designed to work with docking stations as well as headphones, this would make sense.

Does anyone have a pinout diagram of the dock connector?
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Old 22nd November 2013, 02:21 PM   #19
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Originally Posted by abraxalito View Post
Don't worry, it was the 'state of the art' guys who came up with the 'Transwarp' drive which Mr Scott found so easy to sabotage 'The more they overthink the plumbing, the easier it is to stop up the drains'.
Haha now that's funny.

As someone that works on cars, I have the perfect example of this phenomenon. Subarus and Audis are very similar in function and performance. Both have "boxer"engines (the base Audis do anyway), both have full time symmetrical all wheel drive, both are head and shoulders above all the other competition for traction on ice and snow. Either brand will beat the pants off any of the competition on ice, snow, and mud.

But working on them is completely different. While Subarus are certainly more complex than everyday cars like Toyota or Ford, they are still simple to work on (to me anyway) because everything is made to be serviced, repaired, or replaced in the field. Audis on the other hand, are absolutely ridiculous. Evidently the engineers (those damn Germans ) thought that their vehicles would never require repair or service. Not only do you have to have special tooling to work on them, but you need proprietary electronic diagnostics too. I can use the same diagnostics on a Subaru that I use on Fords, Chevys, Hondas, and Toyotas. But I can't touch an Audi without completely retooling my shop.

The perfect example is what should be a routine repair: replacing the radiator. On a Subaru it's straightforward and routine; a gorilla could figure it out. But on an Audi, you have to remove the front clip, discharge the AC and remove the condenser, and you have to be Gumbie with hands the size of a gerbil's to reach the bolts. In other words, you have to partially disassemble the vehicle and perform a procedure that was intended for only a robot to perform. And that's just a stupid design.

Last edited by Fast Eddie D; 22nd November 2013 at 02:25 PM.
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Old 22nd November 2013, 02:44 PM   #20
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Originally Posted by Fast Eddie D View Post
Please don't try to tell me that you can get hi-fi with a patchcord from a cellphone to an amplifier. I've had people in my shop patch their cellphones and ipads into the sound system (I have a patch chord hanging right in front of the preamp), and it sounds OK. But it doesn't even sound as good as the tuner (I do have a nice Nakamichi tuner), and to my ears FM broadcast sounds "canned."
All relatively new iDevices have flat frequency response, output impedance <5 Ω, roughly >105 dB SNR, 0.00x% THD (0.0x% when driving 32 ohm headphones at full output) etc.

As such, your opinion seems to be quite biased. Are you seriously comparing those devices to a tuner? I just cannot take that serious and have to seriously question anything you write...
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