*Project* - CMOY Headphone amp

[peanutismint]

Ah right, so it's just about getting a better sound? i.e. one which probably only audiophiles will notice?

And if that's the case, do you have to access your PMP's sound before it reaches its own internal amp? Or does it just pass through both?

 

[Mansize_tissue]

Ah right, so it's just about getting a better sound? i.e. one which probably only audiophiles will notice?

And if that's the case, do you have to access your PMP's sound before it reaches its own internal amp? Or does it just pass through both?

Let's use the iPod as an example.

Running an amplifier from the headphone-out won't really be doing the music any favours, sound quality-wise, other than increase the volume. In this scenario, the user can adjust the volume on the iPod itself as well as on the amplifier.

Running the amplifier from the line-out on the device will mean that the user can no longer control the volume of the output from the device directly. Instead, all volume control will be done via the amplifier. However, this has the advantage of producing better sound quality as the not-so-good iPod amplifier is removed from the equation.

There are other PMPs which have a line-out, but a lot of them don't. Some even have a digital-out so the signal can be routed to an external DAC and then an amplifier for even better sound.

I hope that's answered your question.

 

[markiemrboo]

I did wonder what the purpose of R3 was. It seems like it would limit the current dramatically with any kind of load at the amplifier connected to it. If it does do that, it would probably cause the supply rails to go all over the place and sag lots.

Wouldn't the current limit, noise and a whole load of other specs of that opamp also affect things? For example, if the output of that opamp is noisy, that noise is then on your virtual ground, and since the rails are referenced to ground, the rails will be noisy? Then that noise, if of a high enough frequency / poor decoupling might make its way on to the actual amplifier output?

Then the current limit. Apparently it's 20mA for the 741. Doesn't all current have to return through ground? So would that limit the actual amplifiers current to 20mA, even if the output opamp is rated for [extreme example] 500mA? This would cause clipping if the load was nasty enough. If R3 does limit the current, surely this would just make matters a whole lot worse? Perhaps if it was a really low value, like 4.7R or something, but then I am still not sure what purpose it would have? To isolate ground from something possibly?

Some opamps do apparently need a resistor in the feedback loop with unity gain, but such a high value resistor shouldn't be in series with the output of this opamp I am sure.

Could this be the cause of the hiss you are hearing?



I'm quite curious, so if someone who knows could explain it to me, I would be grateful! I'm largely guessing.

 

[p4radox]

I agree with the question mark over R3. It was the first thing I went for when trying to eliminate the clipping effects I was experiencing, even after switching to the 741 circuit, and after removing it I don't hear any clipping anymore.

 

[Phil99]

Would it be possible for you to either draw a diagram of your final circuit plan, or perhaps upload a version of your handwritten plans that are readable? You sound like you've ended up with excellent results and I'm having a little trouble getting it to work properly with anything other than the reference design from the website. Unless I'm right in saying you went with this but with an extra two 10nF caps on the power circuit, 0.1uF instead of 0.47uF on the amp and a 220Ohm in series with the output?

 

[BigManBill]

Man those are some crazy diagrams.

 

[p4radox]

I'm pretty sure this is the exact design I went with in the end:

The 0.47uF caps were physically too big, so I stuck with the 0.1uF ones.

The key features that solved my problems were getting rid of the feedback resistor in the power supply's op amp circuit (see above: the 741's output feeds directly into the inverting input), and the use of an output resistor just before the stereo jack output (150ohm above).

 

[tebanski]

OK - a wee bit of topic here P4radox but i clicked your link from the Leeds/Wembley thread.

Simply to say, as a Leeds Lad, do you remember M&B Radio by the Dark Arches, shut down now unfortunately - I used to love going in there (late 80's) for component parts and looking at all the old retro gear (that will be worth a bomb now)

Given the chance (nowadays) I am still a pretty dab hand with a soldering iron.

Good memories, cheers

 

[Margaret]

I got my CMoy amp yesterday but I haven't got a friggin stereo jack lead yet, won't get one till next week either.

 

[p4radox]

OK - a wee bit of topic here P4radox but i clicked your link from the Leeds/Wembley thread.

Simply to say, as a Leeds Lad, do you remember M&B Radio by the Dark Arches, shut down now unfortunately - I used to love going in there (late 80's) for component parts and looking at all the old retro gear (that will be worth a bomb now)

Given the chance (nowadays) I am still a pretty dab hand with a soldering iron.

Good memories, cheers

Can't say I've heard of it unfortunately. How long has it been shut? I'm probably far too young to remember.

 

[HighlandeR]

I always wanted to hook up my Audio technic A900s to an headphone amp but frankly dont think there would be much difference with low impendance cans anyhow.

+ Got far too many sources id need a input for the pc/cable box/vcr etc etc

Mmm need a remote control headphone amp with 2-3 input jacks

 

[p4radox]

You obviously need to build one with multiple inputs then.

 

[MikeHunt79]

or a separate pre-amp with multiple inputs

 

[hardflipman]

hi, i wanted to make one of these a while back but managed to lose all my bookmarks relating to it!
where did you order the parts from? (if it's ok to say here...)

 

[p4radox]

Farnell and Rapid. I'm pretty sure they're okay to link to as they're always mentioned in the DIY audio thread.

 

[gloomygod]

P4radox, you mentioned that only one store in the UK had the opamp chip.

I'm trying to buy it somewhere, but the only online store that I know that has some of the required components is t2retail, and even they don't have everything needed.

Could you please tell me where did you buy the opamp, and the rest of the components???

I want to give it a try to this DIY if I find all the components.

Thanks a lot.

 

[moon man]

great thread ,i bought the german caffine ultra amp after reading some very positive reveiws ,I like the fact it has two gain settings and also a bass boost that dosnt add distortion just a very lush rich sound .it can also be ran on mains power via a dc adapter of course, and has a recharge circuit.

ok i am amping a headphone out but the cowon has a very clean hp out and the combination with my ultrasone hfi780s sounds amazing ,having said that it takes some burning in sounding a little grainy in the first hours.
http://www.penguinamp.co.uk