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# Speaker amps for headphones - Page 102

Quote:

Originally Posted by potterma

If the maximum output voltage (peak) of the MG3 is 20 volts (just a tad conservative, based on the MG3 specs, and if I remember correct that is about what I measured at clipping with the MG3) then the best you can do for attenuation is -5 dB.

The amp in question is just a 25 watt amp? Then I wouldn't even bother with any resistors. If you want to get that "1 watt" into the LCD-2s, then just use a single 50 ohm series resistor.

se

Quote:
Originally Posted by zilch0md

OK, I'll just work on the unquantifiable hiss and ignore all the other criteria that are quantifiable.

I'll just add series resistance, right?  Starting low and working my way up until the hiss is gone?

At that point, I'll have as much voltage as possible in the absence of hiss.  Then I can do the math and see if I've got more than 124mW into 50-Ohms (as I do currently, with the TBI box).

Thanks again,

Mike

If you add series resistance, as you say, until the hiss is gone, the remaining question to answer is "do you have the dynamics you want" which will be at least partially answered by how much peak voltage you have to work with.  Its a good experiment.  I can work up some test values, if you'd like.

Quote:
Originally Posted by zilch0md

OK - that's a plan I think I can execute. Thanks!

If this MG3 amp that's being talked about is a 25 watt amp and only does 20 volts peak on its output before clipping, then I wouldn't even bother with any resistors. At 20 volts peak, that's about 4 watts RMS into 50 ohms.

se

Quote:
Originally Posted by Steve Eddy

The amp in question is just a 25 watt amp? Then I wouldn't even bother with any resistors. If you want to get that "1 watt" into the LCD-2s, then just use a single 50 ohm series resistor.

se

30 watts.  I trimmed off 1.9 V for a little headroom.  Mean, I know....

Quote:

Originally Posted by zilch0md

In truth, I don't even know whether I'll start hearing hiss from the MG3 at an output of 1000mW.  To state my goals as succinctly as possible, I want to get as close as possible to 13Wpc into 50-Ohm without hearing hiss - but I doubt there are any formulas that can predict the hiss, even if there are formulas that can predict the power output with various combinations of resistors.

Are you hearing hiss now without any resistors? As it stands, that amp will only give you about 4 watts RMS into the LCD-2s without any resistors. So if you need some attenuation to reduce the amount of hiss, you don't have much room to work with if you don't want to go below 1 watt.

se

Quote:
Originally Posted by potterma

Sure that will work, but with the ability to only push 250 mW peak into the LCD-2.  Maybe not enough for transients.

Let me throw out the disclaimer that I'm just working from specs, here.  I've never been fortunate enough to hear a pair of LCD's of any flavor...

Yes, didn't know at the time he was working with such a low powered amp and only used it as an example to show you can get the same attenuation with a 250 ohm resistor.

se

Quote:
Originally Posted by potterma

30 watts.  I trimmed off 1.9 V for a little headroom.  Mean, I know....

Yeah, but 25 watts versus 30 watts doesn't really make a whole lot of difference anyway.

se

So what exactly is this MG3 amp that's being talked about? Not familiar with it.

se

Quote:
Originally Posted by Steve Eddy

So what exactly is this MG3 amp that's being talked about? Not familiar with it.

se

Here you go:  Millenia MG3

@zilch0md, I remember Jan mentioning that you could get a bit more voltage swing out of the MG3 with a higher supply voltage.  I don't remember the specifics or if it was significant.  Do you know?

Edited by potterma - 11/28/13 at 7:02pm
Quote:
Originally Posted by potterma

Here you go:  Millenia MG3

@zilch0md, I remember Jan mentioning that you could get a bit more voltage swing out of the MG3 with a higher supply voltage.  I don't remember the specifics or if it was significant.  Do you know?

Thanks. Never heard of it before.

se

Quote:
Originally Posted by potterma

Interesting....  You built one yet?  How's it sound with headphones?  Come on, we need a review!

No, I haven't built this one...yet :P However, I have supplies for the headphone amp version of the "The Wire" in BAL-BAL form. It's designed to be driven directly from a DAC preout, eliminating the need for an actual preamp, but your DAC needs to be up to the task. In which case the DA8 will do fine, so I went ahead with it. Total damage was under \$200 for all parts shipped, including case and other fancy bits. It's a unity gain amp, using high quality OPA1632 and LME49600. The PSU is using the newer TPS7A3301 regulators and distortion is greater than -130dB down. It's a wideband amp, flat FR from DC-100khz, no phase shift, and no caps in the signal path. Oh, and it's smaller than a credit card with SMD parts lol.  I might go dual mono PSU in the future for further reduced crosstalk, we'll see. I'll also be hardwiring a DIY pure silver HD-800 cable to it!

Edited by brunk - 11/28/13 at 7:06pm
Quote:
Originally Posted by Steve Eddy

Are you hearing hiss now without any resistors? As it stands, that amp will only give you about 4 watts RMS into the LCD-2s without any resistors. So if you need some attenuation to reduce the amount of hiss, you don't have much room to work with if you don't want to go below 1 watt.

se

Hey Steve,

Thanks for the help.

Yes, when my 50-Ohm LCD-2 rev.1 are connected directly to the amp, I can hear hiss - as have others with the LCD-3 and the HD800, for example.  I love the sound of the MG3 with the LCD-2, but want more power than the 124mW I've calculated I'm suffering with the resistor network built by the amp's designer, Jan Plummer:

I understand that I might not have much room to play with, given that the amp is rated at only 32W into 8-Ohm (when running on 24VDC power).

Thanks,

Mike

Quote:
Originally Posted by brunk

No, I haven't built this one...yet :P However, I have supplies for the headphone amp version of the "The Wire" in BAL-BAL form. It's designed to be driven directly from a DAC preout, eliminating the need for an actual preamp, but your DAC needs to be up to the task. In which case the DA8 will do fine, so I went ahead with it. Total damage was under \$200 for all parts shipped, including case and other fancy bits. It's a unity gain amp, using high quality OPA1632 and LME49600. The PSU is using the newer TPS7A3301 regulators and distortion is greater than -130dB down. It's a wideband amp, flat FR from DC-100khz, no phase shift, and no caps in the signal path. Oh, and it's smaller than a credit card with SMD parts lol.  I might go dual mono PSU in the future for further reduced crosstalk, we'll see. I'll also be hardwiring a DIY pure silver HD-800 cable to it!

Unity gain?  So, no driving the HE-6, then....

Quote:
Originally Posted by zilch0md

Yes, when my 50-Ohm LCD-2 rev.1 are connected directly to the amp, I can hear hiss - as have others with the LCD-3 and the HD800, for example.  I love the sound of the MG3 with the LCD-2, but want more power than the 124mW I've calculated I'm suffering with the resistor network built by the amp's designer, Jan Plummer:

I understand that I might not have much room to play with, given that the amp is rated at only 32W into 8-Ohm (when running on 24VDC power).

Personally I think 1 watt's fine with the LCD-2's, but if you don't want to go lower than that, using a 50 ohm series resistor is as much as you can get away with and will only reduce the noise by 3dB SPL.

Just how significant is the noise?

@potterma, do you happen to know what the input sensitivity of the MG3 is?

se

Quote:
Originally Posted by potterma

Unity gain?  So, no driving the HE-6, then....

Oh, you can with as little as a gain of 2. The designer of the amp is doing this very thing with HE-6. Only need to switch out 2 resistors

Amp is no joke lol!

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