*Project* - CMOY Headphone amp

[p4radox]

That is literally as wide as it could be. There's one spare row down one side to sit on a shelf on the inside of the box and one spare row down the other side which I'll have to shave a bit off in order to get the battery in.

edit: it sounds immense. The bass is absolutely fantastic and voices are very, very crisp. That's about as well as I can describe it, not having trained ears.

 

[markiemrboo]

That is literally as wide as it could be. There's one spare row down one side to sit on a shelf on the inside of the box and one spare row down the other side which I'll have to shave a bit off in order to get the battery in.

Looks nicely compact Glad you got it working OK with minimal debugging needed. It's nice to create something that produces nice sound!

I might just be over reading in to the hiss problem really I would be annoyed if there was more than barely audible hissing at full volume personally. I can say that I have managed to get all of my DIY amp stuff with zero audible humming or buzzing, and only the very faintest of hissing at full volume, with my ear right against the tweeter, 90dB/1W/1M speakers. Granted, they are speakers rather than headphones though!

The noise floor of my DIY stuff is certainly *much* better than this Cambridge Audio A5 I am back to using, while I mess around with discrete class A/B / class B output stages

Anyhow, enjoy and congratulations!

 

[p4radox]

There's no hiss, even at max volume.

 

[Flibster]

The one I bought last week arrived from the USA yesterday.
Superb thing. I did go for a very well regarded BioScienceGeek one in the end.

Plus the Peppermint Penguin Caffinated sweetie tin rocks.

 

[Dr.EM]

Nice job, looks good! The track breaks are usually done with a drill bit turned by hand, producing a result like this:




But in your case this may have wasted too much space, a lot easier though if you can spare the space!

I haven't had tracks peel off before, but having to remove a component usually makes things a lot more difficult. You can get desolder wicks to remove the solder, but I've always just pulled the component while heating the joint; remember you'll need a "wet" tip to re-melt a joint (seems wierd applying more solder in order to de-solder, but it won't melt without doing this as the heat cannot be transferred to a large enough area of the joint with a dry tip).

If I need to insulate a lead of say a resistor, I tend to strip the insulation from a normal wire are place it over that lead rather than use heatshrink:



To hold things you can get a "helping hands" device. Its just an iron base with moveable arms and crocodile clips on the end, very useful to have though!

Sounds like your getting great results and i'm sure you had fun making this. So, whats the next project going to be

 

[p4radox]

Lol, I haven't finished this one yet! I'll be making a start on the container tonight hopefully.

Re the resistor insulation: that's what I did. What I mean in my post above was that the actual wire insulation I applied was shrinking significantly while soldering, so in some cases I added another layer of heatshrink over the top.

I'd also been advised that a drill bit was the best way of using stipboard, but as you said, there wasn't enough room for that!

 

[p4radox]

One more update for today.

Just some proof for all you naysayers and doubters: it does indeed fit in that tiny little enclosure:

 

[markiemrboo]

Looks mighty cramped on the back panel

 

[Dr.EM]

Pretty tight! Looks like the same box as I used for an coax to optical convertor, but I didn't need to fit a battery and pot in there! So long as your accurate drilling the panels it'll be fine

 

[MikeHunt79]

You should be able to get a smaller pot than that if you want a little extra room...

 

[Phil99]

Just finished my first one (in terms of circuit anyway, still need to find a case) going by the reference design as found on the net and it works perfectly first time

Going to try the suggestions posted here for my second amp a bit later

 

[p4radox]

Just finished my first one (in terms of circuit anyway, still need to find a case) going by the reference design as found on the net and it works perfectly first time

Going to try the suggestions posted here for my second amp a bit later

Good to hear someone else is giving it a shot! How's it going so far?

The best improvements I made were placing a 200ohm resistor in series with each channel output which reduced background hiss immensely, and changing the power circuit to the 741 buffered version which stopped distortion at high volumes.

 

[p4radox]

Okay, I finally found the time to get it finished!

To be honest I made bit of a mess of the front panel, the holes aren't quite lined up and there are a couple of scratches which the flash from the camera exaggerates.

I also ended up with a volume knob that's too big really, but it was the only one in stock at the shop I got it from.

But overall I'm really, really pleased with how it's turned out. It makes a massive difference to the sound of both my iRiver and my little 256mb flash player. I'm also very pleased that my planning paid off and I actually managed to fit the damn thing in that little box!

Mike - you've interested me in Class D amps now. Having read a little I think it might be my next project. In the meantime I've got some exams to pass, so it'll have to wait unfortunately.

 

[Phil99]

Good to hear someone else is giving it a shot! How's it going so far?

The best improvements I made were placing a 200ohm resistor in series with each channel output which reduced background hiss immensely, and changing the power circuit to the 741 buffered version which stopped distortion at high volumes.

Funnily enough I've found the direct opposite with the 741 version!! At high volume it distorts a lot and there's a noticable voltage drop on both sides as the volume increases with a 9v battery. Not sure if that's normal but I doubt it is as it creates quite an offset between the magnitude of each rail.

My first attempt at the standard amp is fine at high volume except for a bit of hissing - it doesn't distort at all and I can't really notice any hissing at low amplification (i.e. MP3 player turned right up, amp turned down). At the moment I've got no resistance on the output for that one though so might try putting in the R5 resistors (47 ohm) if that's what sorted it for you.

I've got a breadboard now at least though, was a pain soldering the first one on the protoboard just to test it!

Could the quality of the capacitors affect hissing by the way? I've got pretty standard film caps from ****** because the 'audio grade' caps they sell are online only.

edit: forgot they sold other stuff, good job it stars it out for us now

 

[p4radox]

It wasn't R5 that improved the sound for me. R5 is within the feedback loop, and I got best results without it. I added the 200R directly in series with the output.


As for the 741, are you using this power circuit?

Try ditching R3. It gave me loads of trouble with uneven rails.

 

[Phil99]

Turns out it's not a PSU issue at all, just shoved the original design PSU on there and it's the same issue with distortion at high volumes and loads of hissing.

 

[p4radox]

You check if it's a capacitor problem, just short out the input coupling capacitor.

But definitely give an output resistor a shot. It made the biggest difference to the hiss for me. Maybe try the star grounding system that was discussed on page 1.

 

[Phil99]

Just noticed you've got the same headphones as me; I only get distortion when I'm maxing out my MP3 player's volume and the amp's volume - I don't know if I'm simply expecting too much from the amp/headphones as the volume really is incredibly loud at these levels. I've still got 1k for R3 so might give increasing that a go.

 

[peanutismint]

Right, here goes....

What is the point of a headphone amp?

Let the flaming begin But I just don't understand it... I know what amps do in hi-fis etc, but I don't know of anything you can plug headphones into (MP3 players or handheld games consoles for example) which requires an amp in-between.... Somebody please enlighten me?!

 

[Mansize_tissue]

Right, here goes....

What is the point of a headphone amp?

Let the flaming begin But I just don't understand it... I know what amps do in hi-fis etc, but I don't know of anything you can plug headphones into (MP3 players or handheld games consoles for example) which requires an amp in-between.... Somebody please enlighten me?!

Without an amplifier there'd be no sound. However, often amplifiers build in to PMPs aren't so good which is why people use their own. Some headphones (in general those with a high impedance) require a beefier amplifier to reach acceptable volumes, more often than not however they're used to change the sound somewhat (making a cold, analytical-sounding headphone warmer, for example).