Guide to fix up a Cmoy 2

[jasonhanjk 0]

I did buy alkaline rechargeable once. Can only charge 10 times.....

At that time, Malaysia battery ex like hell, now also ex like hell.

 

Normally buy battery here and go back Malaysia and use.

[1bit 0]

Hi, I'd like to ask those who have built their cmoy2 amp: what's the gain setting you use?

 

I've just finished building mine and it uses the same part configurations such as listed in the guide (with gain=2) and found out that it's not enough for me. So any recommendation about this anyone?

[squalle 0]

Hi, I'd like to ask those who have built their cmoy2 amp: what's the gain setting you use?

 

I've just finished building mine and it uses the same part configurations such as listed in the guide (with gain=2) and found out that it's not enough for me. So any recommendation about this anyone?

I'm using 2 too

 

then I think you should just increase the resistor values

[1bit 0]

Do you think 2 is enough, squalle? what's the source you use?

 

I'm using the line out from my pcdp but even after maximising the pot on the cmoy2 the volume is smaller than what is possible coming out from the headphone out.

[squalle 0]

for me it's enuff.

which headphones are u using?

on my hd497, I'd need almost half. when using apple in-ear I'd need very little. maybe ard 15% vol pot.

I'm using ipod as source, taken from its line out

 

for ur pcdp, I think ur volume of your headphone out PCDP is the one that limit it. try put the volume to around 75% and see what happens next.

[1bit 0]

but, isn't the idea of using an amp is not to use amplification from the pcdp?

[squalle 0]

yes if there's a line-out on ur PCDP, but if there none, and putting the volume to 0 out of the headphone out, well it's impossible to get audible result out of any amp

the SNR would be way too low for the amp to amplify anything useful out of the signal of ur PCDP.

 

fyi, the line out of ipods is of way higher volume than the headphone out itself.

volume is not the only thing when we're discussing abt amps

I think u've mixed up volume and sound quality

[jasonhanjk 0]

Some PCDP volume control doesn't control their line-out. An increase of gain is necessary. It's on the first page of this thread.

 

It's always recomended to have a volume of 50% to 100% from the headphone out of a PCDP when using an amp. The idea of using an amp is TO drive your headphone. Which most PCDP can't.

[squalle 0]

just rolled to another op-amp

 

put in the AD8397

impression on me: nice, clear highs. the bass is tight

u guys shd try too

but be careful of it for the fact that it's bipolar

 

oh btw, the ground channel is still on MAX4166 as I havent been able to get its replacement so far

(need one that can run on lower voltages, yet can sink lotsa current, sounds like impossible tho' )

[kross 0]

hi, just wondering is there any difference in using the better pots (blue velvets)vs the cheapo pots found in koba, sound quality wise?

[1bit 0]

squalle: hi just wondering why we need to be careful as ad8397 is bipolar?

 

kross: well koba also sells a cheaper variant of the blue velvet for $15, i've been wondering how it compares to the one sold at farnell

 

in a high quality pots usually they are expected to have long life, smooth turning (doesn't contribute noise when you turn them while passing signals), true log taper, lower gang error for the entire range (differences in resistance between the right and left pots for dual gang pots)

 

i think the pot affects the sound quality by means of the taper and the gang error

[squalle 0]

1bit: bipolars have higher input offset current. this will cause higher DC offset voltage at input of the op-amp, as opposed to the FET op amp.

bipolars have something that's 300nA to 3uA. whereas the FETs have like 10nA.

read here: http://tangentsoft.net/audio/hs-opamp.html for more details. too lazy to re-type

 

kross: agree with 1bit. cheaper ones (like what I'm using ) cause slight noise when u turn, but luckily most of the times not. tracking is poor tho' especially at the two extremes. and I've measured some imbalance of resistance between the 2 channels.

[kross 0]

yup, i experience the distortion when turning and found some slight difference in resistance between the coupled pots. but what i am more concerned about is whether they will affect the sound quality. for example using the cheapo pots (set to 0ohm) vs not using at all.

[1bit 0]

kross:

well, i've just read this, the thing about potentiometer is that it can't give a true 0 ohm. from the article, analog pots will always have a wiper resistance, basically the contact resistance between the moving part (wiper) and the stationary part where the log taper is located. it is said this resistance can be around 100 ohm.

 

so if you compare a direct line and through a pot set at max, there bound to be a small attenuation for the signal through the pot.

 

as the value is around 100 ohm it shouldn't have a big effect for audio application i think. it'll do have an effect for delicate frequency tuning application or some precision continuity tester (lol tried to design this once using a couple of trimmer and failed lol).

 

other than attenuation another effect that i can think of to sound is noise, but it should be barely audible.

 

squalle:

thanks for the info about the input offset current, now need to look at the data sheet more carefully lol

[squalle 0]

1bit: np

 

yup, regarding any degradation due to the pot in signal path. errmm I cant hear any noise or watever induced by the pot. unless ur pot is mechanically broken. lol. I meant to say that the whole assembly is shaky or something, which in that case, you should just replace it with a new one.