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Aspen Headphone Amp

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#1,121
KoA,

There is always concern about offset. It's the last frontier before reaching Eldorado. If it's good, and it's stable, then we have ignition.

I'd now sit on your pcb design, doodle it for a couple of weeks to be absolutely sure, and then have it made. I use ourpcb.com, their service is good and they do excellent pcbs at moderate cost, and just get four done to begin. Your production run will inevitably need changes, so don't commit too early.

Finer points of pcb layout are very hard to detect at this stage. You really have to build it now, have the thing in your hand, turning it over and inspecting it whilst building, before you have the full, 3D picture.

Thanks for your hard work, nearly there.....

Hugh
 
#1,123
Here's something I've been thinking about, and I want to apply it to my speaker amps too;

Why not use a 3-pos switch to switch both main power and then connect your headphones? It's a small burden to have to wait a second before turning the power knob one more click 'round, and the time it takes you to turn from "ON" to the "Engage 'phones" might even be long enough for the amp to settle. Just make sure you buy a very nice switch.
 
#1,126
Here's an automatic way to do it (although there may be better ways).

The bottom half of this figure is a filament supply and automated mute switch. The 8.8V output is just a regular filtered DC. Substitute the rail supply for this.

Now look at the two FET's. These are in series and both must be on in order to open the mute relay (not shown in this diagram). The relay coil is connected from the 8.8V output to the relay common.

The gate of one FET is powered by the two diodes that are outboard of the diodes for the 8.8V supply. It's done this way so that as soon as the power is switched off, this FET stops conducting immediately. You can change the timing by adjusting the relevant resistors and capacitor.

The other FET gate is powered by the 8.8V supply, through the 100k resistor. It must charge up the 100u cap before the FET will conduct.

So, upon turn on, the mute relay doesn't open until the amp output has had time to stabilize. But the relay closes upon power off, before the main supply droops low enough to create a transient at the output.


http://www.diyaudio.com/forums/atta...nholy-alliance-phono-amp-3a5-phono-supply.jpg
 
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#1,127
Yes, and maybe something a bit more complete like a 'dc protection/delay' cct with a 'mute' option - probably require something more sensitive that the usual speaker protect ccts to enable a low 100mV trigger threshold - a Maxim 'Max 4236' chip could be adapted, for example, but many other ccts, probably simpler ....
 
#1,129
If preferred, you can ignore this post until any current issues you guys are working on get sorted out. Or, if anybody has a quick second they could be of great help to me. I have started practicing PCB design only maybe two weeks ago. I think I am getting the hang of it. I am pretty sure I want to build this headphone amplifier, and I do see that somebody is already cooking a PCB up for it, but I want a single layer one, so I will be making my own. Here is my attempt:

http://dl.dropbox.com/u/5430178/pro...lifier/AKSA_Aspen Headphone Amplifier PCB.png

The red traces are to symbolize jumper wires on the bottom of the board. Here is the schematic that I copied in order to make the pcb, in case I screwed up somewhere:

http://dl.dropbox.com/u/5430178/pro...er/AKSA_Aspen Headphone Amplifier Circuit.png

If this is not the first priority of you guys, I understand!

PS: I just want to know if this is OK. I know it probably isn't optimal or perfect, and that is fine. I'm not expecting anybody here to walk me step by step into optimising it and wasting you're time. Then again, if you have a real quick tip to throw at me, I won't mind.

Thanks,
Aaron.
 
#1,132
V4 is a means to assess the loop gain of the amplifier (Middlebrook analysis) and I1 is current source, which could be an LM317, or a DN2540 mosfet, or a two transistor 'ring of two' .

That was a long time ago, 8 years, I'd forgotten about that! It is two stages of my NAKSA power amplifier, in fact, and because it was single ended, sounds very, very good. You may reduce the CCS 150mA down to 40mA and drive high Z cans more than 150R, saving a lot of dissipation, only 520mW total.

Hugh
 
#1,134
Buzzy said:
I was searching for BJT headphone amplifier in this forum. This is the only other I found apart from JLH headphone amplifier. There don't seem to be as many transistor headphone amplifiers.
Click to expand...

Here is another of Hugh's concoctions at about the same time 2007/8 that sounds superb. I have been using it for about 10 years now since Hugh and I searched for the most simplistic class A headphone amps.

My philosophy is the simpler a class A amp the better it sounds, my best take was three transistors, Hugh used only two. I don't even think he recalls this.
 

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#1,136
Hi Hugh,
I hate getting old and lonely. Diane says that when we go out somewhere we are more out of place than two farts in a perfume bottle.

At least you still have the monster bike that is exhilarating and fun. I became a coach potato sitting day in and day out listening to music, while I could not give a rats *** what is happening around me.
 
#1,137
Nico Ras said:
Here is another of Hugh's concoctions at about the same time 2007/8 that sounds superb. I have been using it for about 10 years now since Hugh and I searched for the most simplistic class A headphone amps.

My philosophy is the simpler a class A amp the better it sounds, my best take was three transistors, Hugh used only two. I don't even think he recalls this.
Click to expand...

Wow that looks really simple and portable too. Is this amp meant to be run from 9v or 12 v ?
 
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