[Conan]

I just built 2 amps today, and they both sounds almost EXACTLY like my IPOD 5g's headphone out. Have I messed up horribly somewhere?

The first amp I built was using the LM4881 (the pa2v2's chip). Pretty much followed the datasheet except for the input/output caps (used 2200mf caps for both). Ran it off a regulated 5v wall wart.

The 2nd amp I built was a CMOY using 2 OPA134s. Followed the original CMOY spec for all parts. Instead of a 9v battery though, I used the same 5v wall wart.

Anyhow, everything's on a breadboard, and both circuits work fine, but I just don't notice any difference at all from the IPOD headphone out when I match the volume.

(The only headphones I have right now are the beloved ksc75s and a pair of ATH PRO5s).

- Are my headphones not 'good enough' to benefit from an amp?

- Am I severely underpowering the CMOY?

- Is there a big quality difference soldering the circuit instead of breadboarding it? (reduced cap/resistor trace lengths?)

Any other thoughts?

 

[phergus_25]

Quote:

Originally Posted by Conan I just built 2 amps today, and they both sounds almost EXACTLY like my IPOD 5g's headphone out. Have I messed up horribly somewhere? The first amp I built was using the LM4881 (the pa2v2's chip). Pretty much followed the datasheet except for the input/output caps (used 2200mf caps for both). Ran it off a regulated 5v wall wart. The 2nd amp I built was a CMOY using 2 OPA134s. Followed the original CMOY spec for all parts. Instead of a 9v battery though, I used the same 5v wall wart. Anyhow, everything's on a breadboard, and both circuits work fine, but I just don't notice any difference at all from the IPOD headphone out when I match the volume. (The only headphones I have right now are the beloved ksc75s and a pair of ATH PRO5s). - Are my headphones not 'good enough' to benefit from an amp? - Am I severely underpowering the CMOY? - Is there a big quality difference soldering the circuit instead of breadboarding it? (reduced cap/resistor trace lengths?) Any other thoughts?

did you get a line out of the ipod or just jump from HP jack to amp to phones/

 

[rsabo]

You're running the OPA134 (as well as the LM4881) at minimum voltage. Try replacing the 5v wall wart with a 9v battery.

 

[Conan]

I'm using a line-out for the IPOD.

The max voltage for the LM4881 is actually 5.5v, so I'm near the max already for that chip.

I will try the 9v for the CMOY. Hopefully, that'll make a difference.

 

[rsabo]

Quote:

Originally Posted by Conan I'm using a line-out for the IPOD. The max voltage for the LM4881 is actually 5.5v, so I'm near the max already for that chip. I will try the 9v for the CMOY. Hopefully, that'll make a difference.

On the original CMoy schematic, parts R2 & R3 form a voltage divider that creates a virtual ground. Your 5V wallwart actually provides +/- 2.5V to the chip.

 

[Garbz]

Two things come to mind. Firstly the CMoy isn't really a fantastic beall and endall amplifier. It's still very entry level but that said you should notice the difference.

The other thought is to do with ear training. If you have never heard two amplifiers side by side then you may not have any idea how to pick the differences. This is just like my inability to pick very subtle changes <2db changes in an EQ. The ear needs to be trained to pickup these sort of things. Consider yourself lucky it's cheaper if you can't hear a difference

Listen to the dynamics in the bass. This is the most prominant change from a portable headphone out to a dedicated amp, mainly because the iPod is underpowered.

 

[mono]

Conan, run!

Run, run, run away from us as fast as you can. In a brief moment of what you can look back upon years later and call "sanity", you believe they sound the same. This is a great thing. Right now you have the chance to escape all this madness, avoid untold hours/days/years playing Don Quixote and spending untold volumes of $$$$. This might be your last chance, don't let them trick YOU like they did me.

Quote:

Any other thoughts?

Welcome to Head-Fi, sorry about your wallet.

 

[Uncle Erik]

Did someone say vacuum tubes?

You seem to have a pretty good grasp of what's going on, so I'd recommend some tubes. You should hear a difference.

 

[69CamaroSS396]

Quote:

Originally Posted by Conan I just built 2 amps today, and they both sounds almost EXACTLY like my IPOD 5g's headphone out. Have I messed up horribly somewhere? The first amp I built was using the LM4881 (the pa2v2's chip). Pretty much followed the datasheet except for the input/output caps (used 2200mf caps for both). Ran it off a regulated 5v wall wart. The 2nd amp I built was a CMOY using 2 OPA134s. Followed the original CMOY spec for all parts. Instead of a 9v battery though, I used the same 5v wall wart. Anyhow, everything's on a breadboard, and both circuits work fine, but I just don't notice any difference at all from the IPOD headphone out when I match the volume. (The only headphones I have right now are the beloved ksc75s and a pair of ATH PRO5s). - Are my headphones not 'good enough' to benefit from an amp? - Am I severely underpowering the CMOY? - Is there a big quality difference soldering the circuit instead of breadboarding it? (reduced cap/resistor trace lengths?) Any other thoughts?

Are you talking about a difference in sound quality or volume? Even though the Cmoy is "entry level", so to speak, unless you used the wrong resistors for the gain, there should be oodles of volume capability, especially using a line out. So, if you still notice problems after changing the voltage input, maybe check those resistors.

 

[tomb]

I think Rsabo nailed it. If he's using 5V adapter with a virtual ground circuit, then, +or- 2.5V is what's driving the opamp. That's less voltage than any portable, except some of the more recent ones running a single AA. It's a little surprising it works at all.

Still, all the other comments are good ones. The difference with a CMoy are subtle, at best. Even against the worst sound card, you have to educate your ears to understand that the "swish" or "phhhh" is because the sound card is clipping. It's also true that except for the iPod Mini, the iPod's amps are consistently among the best on the market.

 

[Conan]

Alrite fellas, I just ran out and got a couple of 9v batteries. After hooking it up to my breadboard and about a good 1.5 hours of A/B testing, I still don't hear any difference (in quality).

The A/B testing using the 5v wallwart and 9v alkaline had no audible difference either. (Some of Xin's portable amps run on 5v btw, maybe this is why?)

As for loud, yes, the cmoy can go plenty loud, but so can the IPOD. As for which one is clearer at the permanent hearing loss levels, I'm not sure because I'm too busy cringing from the "this can't be safe for me" thoughts.

I wanted to try an amp because I thought it would improve the quality at normal listening levels, not damage my hearing.

I ordered a good amount of stuff for this project, and still have a couple more things to try: the OPA2227, OPA2134, and a TLE2426 rail splitter, and lastly soldering the thing together on protoboard (to eliminate thoughts that maybe the extra leads from the resisters/caps or breadboard contacts are not optimal), but my initial results are not good.

 

[jarthel]

try tubes.

 

[tomb]

Quote:

Originally Posted by Conan Alrite fellas, I just ran out and got a couple of 9v batteries. After hooking it up to my breadboard and about a good 1.5 hours of A/B testing, I still don't hear any difference (in quality). The A/B testing using the 5v wallwart and 9v alkaline had no audible difference either. (Some of Xin's portable amps run on 5v btw, maybe this is why?) As for loud, yes, the cmoy can go plenty loud, but so can the IPOD. As for which one is clearer at the permanent hearing loss levels, I'm not sure because I'm too busy cringing from the "this can't be safe for me" thoughts. I wanted to try an amp because I thought it would improve the quality at normal listening levels, not damage my hearing. I ordered a good amount of stuff for this project, and still have a couple more things to try: the OPA2227, OPA2134, and a TLE2426 rail splitter, and lastly soldering the thing together on protoboard (to eliminate thoughts that maybe the extra leads from the resisters/caps or breadboard contacts are not optimal), but my initial results are not good.

a. Your headhones are already quite efficient.
b. The iPod's have some of the best amps of any portable, as already mentioned.
c. Minimum source quality at 128bps compression will limit CMoy results.
d. You have the output from the iPod turned up too loud, over-driving the CMoy.
e. Your ears still aren't educated (volume isn't the difference).

Xin, in fact, uses a buck-boost circuit that raises the internal voltage for the opamp. Also, tubes will only change the sound, not make it better - as compared to a solid-state amp.

 

[]|[ GorE]

Conan,i am like you in terms of hearing a difference . My + and - 6.5 V CMOY super regulated out of a 14V Wallwart doesnt improve the sound quality over either the ipod or my audigy 24bit sound card.Sure,it provides way more volume but otherwise it sounds dead same....and to think i wasted 2 weeks over building the cmoy.
I can hear even 1 db differences when EQing , dont have tinnitus and can hear upto 18Khz.So atleast my ears arent damaged.

Moral of the story for me : No more amps to build or purchase.

 

[robzy]

5v is fine, increasing it may lead to an increase in quality - but its doubtfall.

I would definetly explain this as being the KSC75's "fault". With my PX100s i can hear a difference between headphone-out and my cMoy, but thats only because ive learnt what to listen for.

The KSC75's dont really need all that much more than the ipod offers (especially if the listener hasnt spent a while mucking around with various amps and headphones).

Rob.