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Old 22nd June 2006, 11:25 AM   #11
Pano is offline Pano  United States
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Quote:
Originally posted by BWRX
I'll have to butcher a cheap pair of headphones so I can hook them up to the bridged outputs of a T-amp and see what's going on
No need! Just connect both phone channels to ONE amp channel. That will be enough to let you hear the noise.
Connect before you put the headphones on your ears.

The CMOS gate idea is pretty cool. Most gates that I know can sink or source about 50 mA each, so a quad would get you where you need to be. There may be stronger gates out there, any ideas Tim?
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Old 22nd June 2006, 12:24 PM   #12
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I had a spare 3.5mm phone jack laying around so I decided to see how noisy my AMP1-B's would be through some headphones. I paralleled one 8ohm resistor on each channel to make the output filter happy, then I connected the phones. Result?................. .

HORRIBLE!!! Not only was there an overwhelming amount of noise, but it didn't even sound as good as the output of a MP3 player I have. Compared to the sound I get from my main speakers, it sounded like a completely different amp.

I recently sold my modded SI so I can't comment if it has any less noise, but I'm sure it can't be much less.
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Old 22nd June 2006, 12:39 PM   #13
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Has anyone tried a pair of headphones with their Hypex UCD modules? I'd be interested in hearing the results of such a test.
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Old 22nd June 2006, 02:52 PM   #14
BWRX is offline BWRX  United States
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Here's some SwCAD stuff I just did for the circuit.

The schematic.
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File Type: gif ucdheadphonesim.gif (80.7 KB, 367 views)
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Old 22nd June 2006, 02:53 PM   #15
BWRX is offline BWRX  United States
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1Vrms 1kHz sine wave was input and this is the output waveform.
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Old 22nd June 2006, 02:55 PM   #16
BWRX is offline BWRX  United States
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This is the FFT of the output waveform shown above.

Not bad for a very simple UCD implementation! The supply rails were 12V and the load was 32ohm. You can see that the switching frequency is right above 1MHz.
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Old 22nd June 2006, 03:42 PM   #17
BWRX is offline BWRX  United States
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Actually, the switching frequency of the comparator output is closer to 3.5MHz according to SwCAD. Is there any way to obtain better resolution with the FFT plots? Any suggestions on better component values? I just kind of picked generic values and tweaked them until the amp actually worked.

There is a little bit of cross conduction that is happening so the design could obviously be improved (like we didn't already know that!).
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Old 22nd June 2006, 04:12 PM   #18
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Quote:
Originally posted by theAnonymous1
I had a spare 3.5mm phone jack laying around so I decided to see how noisy my AMP1-B's would be through some headphones. I paralleled one 8ohm resistor on each channel to make the output filter happy, then I connected the phones. Result?................. .
If you used a phone jack you probably connected wrong because you bridged the amplifier. The headphones would have to be connected without a shared ground, i think...
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Old 22nd June 2006, 05:34 PM   #19
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Hello guy...

Why not simply use a LM319 and a TC4420 6A mosfet driver in your UCD configuration at +/-8V? I have made in the past ( about 8 years ago..) a class d car amplifier with a LM319, a TC4420 and a TC4429 mosfet drivers. They put about 45W into 2 ohms load with a very good sound in full range, at 14.4V. The only difference is that I have use it at fixed frequency, 250kHz. If you use it at +/-8V it should put out about near a watts into 32 ohms! Even at 12V with coupling capacitor, you should get nears 750mW...That lot enought for headphone! And at these voltage, you should have a very low ripple voltage at the output...

This design is very fast, about 90ns of delay from comparator input to output, so it should sound very good.

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Old 22nd June 2006, 05:46 PM   #20
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Quote:
Originally posted by nilsomat


If you used a phone jack you probably connected wrong because you bridged the amplifier. The headphones would have to be connected without a shared ground, i think...
The AMP1-B is not a bridged amp, both channels share a common ground.
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