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Old 22nd September 2009, 12:36 AM   #11
Bigun is offline Bigun  Canada
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Aspen Headphone Amp
Quote:
Originally Posted by MJL21193 View Post
Nice one Hugh!
Simple, easy to build and I'd guess as good (or better) than most out there.
Will Gareth work up a board for this?
As you know I've enjoyed designed a few boards in the past, but I think Hugh needs something professional here so I'm going to lean on Aspen for some help with boards, take advantage of their supply chain
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Old 22nd September 2009, 12:41 AM   #12
MJL21193 is offline MJL21193  Canada
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Could be a group buy in the offing? Sign me up!
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Old 22nd September 2009, 01:15 AM   #13
GK is offline GK  Australia
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This small amp has lots of phase margin, 75 degrees at 12MHz, the dominant pole.


12MHz??

The unity loop gain frequency is actually closer to 1.1MHz and the dominant pole frequency is a bit under 50kHz.
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Old 22nd September 2009, 01:20 AM   #14
Bigun is offline Bigun  Canada
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Aspen Headphone Amp
Let's see if a simulation file is helpful here (attached - my recreation of the schematic - Hugh, perhaps you can post your original file including the device models). I've opted for the infamous Vbe multiplier for now - can swap out for diode's later.

To use the sim, download it and change the file extension from .txt to .asc (LTspice). You may need to go into file options to view the file extensions.
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File Type: jpg AspenHDamp.jpg (85.5 KB, 1154 views)
Attached Files
File Type: txt Aspen_hdph_with2.txt (7.1 KB, 80 views)
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Old 22nd September 2009, 01:29 AM   #15
Bigun is offline Bigun  Canada
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Aspen Headphone Amp
Default Power supply

I see this as a desktop unit so my first thought was not batteries despite the noise benefits because I don't want to be worrying about re-charging etc.

If we want to keep this simple I'm leaning towards a 20VA trafo, anything too small will have poor regulation ? IF it is to drive small monitor speakers as well, I'd want 50VA.

Current draw on the rails is small, perhaps we can get away without dual supplies, put some fairly stiff CRC or CLC filtering in place on the rails if current draw is limited to headphone use only.

Another option would be a capacitance multiplier. It's a bit crude, but does the job well. The downside is some loss in headroom since you have not just the Vbe drop but Vce under load and the drop across the base resistor.

I'd like to keep it really simple - my dream would be a single pcb for both channels and power supply - how fussy should we be, can we achieve -100dB cross-talk on a single pcb ?

What are you thoughts ?
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Old 22nd September 2009, 01:32 AM   #16
iko is offline iko  Canada
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Hi Ikoflexer (should that be Harley, or Buell?),
It's just a plebeian wee-strom, but I love it.
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Old 22nd September 2009, 01:36 AM   #17
GK is offline GK  Australia
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.
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Old 22nd September 2009, 01:43 AM   #18
MJL21193 is offline MJL21193  Canada
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Quote:
Originally Posted by Bigun View Post

I'd like to keep it really simple - my dream would be a single pcb for both channels and power supply - how fussy should we be, can we achieve -100dB cross-talk on a single pcb ?

What are you thoughts ?
I think so but where the amp itself is simple, I'd like to see extra effort on the PS. For a low current draw amp like this going with a fully regulated supply makes sense.
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Old 22nd September 2009, 02:06 AM   #19
AKSA is offline AKSA  Australia
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Here's the Bode plot from LTSpice:

Looks like unity gain is at 11.6MHz, 3dB point is at 1.6MHz.

I noticed GK's plot showed a gain of near on 34dB, which is very different to the CLG of 15dB.

?

Hugh
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Old 22nd September 2009, 02:07 AM   #20
MJL21193 is offline MJL21193  Canada
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Maybe a variation on the Jung super reg. Make things a bit more challenging for us older hands.
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