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O2 Build Complete: Let the objective, subjective listening tests commence! - Page 10  

post #136 of 721

From the datasheet:-

 

The NJM4562 integrated circuit is a high-gain, wide-bandwidth, low noise, dual operational amplifier capable of driving 20V peak-to-peak into 600Ω loads. The NJM4562 is frequency compensated for closed loop gains greater than 10.
 
The NJM4562 is frequency compensated for closed loop gains greater than 10 - or to put this another way - the NJM4562 may oscillate at closed loop gains less than 10.
 
An amplifier can have audibly degraded performance due to oscillation without the oscillation itself being obvious to the senses. Such differences are sometimes perceived as improvements. (Any difference I can hear is a good difference.)
 
The driver stage in the O2 is a unity-gain buffer. The NJM4556 is unity-gain stable, i.e. it is unlikely to oscillate in this configuration. 
 
20V peak-to-peak into 600Ω loads.
 
The NJM4556 is rated 70mA into 150Ω.
 
The NJM4562 has a dissipation of 500mW in DIP8 as opposed to 700mW for the NJM4556.
 
The 4562 may be OK driving some phones but the 4556 is the preferred option for stability, power and almost certainly distortion and frequency response (gain flatness) and particularly versatility in terms of the phones it will drive well.
 
w

Edited by wakibaki - 11/6/11 at 11:00am
post #137 of 721
Thread Starter 


 

Quote:
Originally Posted by wakibaki View Post

From the datasheet:-

 

The NJM4562 integrated circuit is a high-gain, wide-bandwidth, low noise, dual operational amplifier capable of driving 20V peak-to-peak into 600Ω loads. The NJM4562 is frequency compensated for closed loop gains greater than 10.
 
The NJM4562 is frequency compensated for closed loop gains greater than 10 - or to put this another way - the NJM4562 may oscillate at closed loop gains less than 10.
 
An amplifier can have audibly degraded performance due to oscillation without the oscillation itself being obvious to the senses. Such differences are sometimes perceived as improvements. (Any difference I can hear is a good difference.)
 
The driver stage in the O2 is a unity-gain buffer. The NJM4556 is unity-gain stable, i.e. it is unlikely to oscillate in this configuration. 
 
20V peak-to-peak into 600Ω loads.
 
The NJM4556 is rated 70mA into 150Ω.
 
The NJM4562 has a dissipation of 500mW in DIP8 as opposed to 700mW for the NJM4556.
 
The 4562 may be OK driving some phones but the 4556 is the preferred option for stability, power and almost certainly distortion and frequency response (gain flatness) and particularly versatility in terms of the phones it will drive well.
 
w

 

That was very informative and helpful, thank you for the post!

 

Trying to compare data sheets with the different way companies spec and rate their products is a pain, but knowing just a few of the key pieces to look for is helpful.
 

 


Edited by cheapskateaudio - 11/6/11 at 7:02pm
post #138 of 721
Thread Starter 

Update: I swapped out the other two elctrolytics, C8 & C9 on the board, and while it results in a perceived reduction in bass, bass quality is improved while the body and richness of the mids was increased. This has a good effect on some types of music like old Kraftwerk which is not quite as robust sounding as modern synth music. It has a somewhat congesting effect on some other types of music, but it could just be an adverse reaction to more musical information as this amp has thin mids (with HD650's) by default. So to test things out in the extreme I went to youtube and searched for "bass", I listened to a hilarious song called "Speakers Going Hammer" that was Bass Boosted, I swear I could hear the license plate on a trunk rattling somewhere in the distance... Bass test your setup: http://youtu.be/nPUJwgZZiYM

 

 

 

 


Edited by cheapskateaudio - 11/7/11 at 6:48pm
post #139 of 721

what caps did you put it?  brand, series, values (farads, voltage, esr)?

post #140 of 721
Thread Starter 


 

Quote:
Originally Posted by samsquanch View Post

what caps did you put it?  brand, series, values (farads, voltage, esr)?


For C8 and C9 I used same value low esr Panasonic caps, http://www.mouser.com/Search/ProductDetail.aspx?R=EEU-FR1H221virtualkey66720000virtualkey667-EEU-FR1H221

 

I also swapped C2-C5 with 470uf Panasonics.

 

And C13 & C14 with Panasonic Polypropylene film caps, http://www.mouser.com/Search/ProductDetail.aspx?R=ECW-F2225JAvirtualkey99990000virtualkey667-ECW-F2225JA

 

Everything fits on the board if you bend the leads and surface mount the Polypropylene caps (the leads are too big for the through holes), but likely the 470uf Panasonics are too tall for the thin case and the Poly caps definitely are. I got the tall case though, yay!

 

I also got the beefier wall wart, WAU16-400.

 

The wall wart's effect was more noticeable at first, after adding everything else the wall wart's effect is diminished, but not entirely. I just did 3 blind tests again, between the two wall warts, and it took me about 5 minutes of comparing to feel confident the first time, but once I found what to listen for the other two goes took less than a minute. The difference was most noticeable on Tabla Beat Science's Tala Matrix CD. (A great recording for testing amps because it really stresses some of the more intangible qualities of rhythm and cohesion.) What you get with the bigger PSU is a fuller and smoother overall sound, more and better controlled bass, better separation between instruments, bigger broader dynamics. It's a subtle effect at this point, but completely 100% detectable.

 

The caps improved those same things to varying degrees. It was kind of weird how the sound came together. I'd describe it like this:

 

No mods: A bit thin and smeared with drum driven music, aggressively revealing. Great for classical.

WAU16-400: Fuller sound, HD650's starting to sound like HD650's, still harsh at times.

WAU16-400 + C13, C14: Smoother fuller sound, more cohesive.

WAU16-400 + C13, C14 + C2 - C5: More bass, more bass control, a more familiar dark tone, and a more full and smooth sound, was great with the uDac 1..

WAU16-400 + C13, C14 + C2 - C5 + C8, C9: More full in the midrange. After this change the uDac 1 dac output sounded more rolled off from the lower treble up. Switching to the PC line out showed the difference easily. 

 

I feel like it might be a little tipped up in the bottom end, or rolled off on the top end, but that is the basic shape of the HD650 FR curve, so based on this not so scientific ear test I'd say the above mods produce improvement across the board. 

 

I'm going to build another one, and build it 100% stock at first, just to compare the two and maybe measure the output before I mod it and give it away.

 

 


Edited by cheapskateaudio - 11/8/11 at 12:55am
post #141 of 721
Thread Starter 

Well, I think something got damaged with all the handling and soldering/unsoldering, and now the left channel is slightly lower in volume. Any ideas on what could have caused that? I have no MM so basically I can reflow the solder joints and thats about it. But I do have a few spare/upgrade parts here so I might try swapping them at random and seeing what happens. Could a bad resistor cause that? I touched a resistor with the soldering iron for a few seconds trying to surface mount the poly caps.


Edited by cheapskateaudio - 11/9/11 at 12:44am
post #142 of 721

How hard is the build this amp? Is it as easy as looking at the instructional, plugging parts into proper place and then soldering it? I want to try this amp but have never built an amp or anything before.

post #143 of 721

cheapskateaudio: Check between S2 [gain switch] and R21, its been reported that they're a little too close togeter and can cause a short, nothing harmful apparently... that's if you've been working in that area....

 

How about soldering thinner leads onto the thicker ones so you cant still mount through-hole!


Edited by Paul Blythe - 11/9/11 at 2:41am
post #144 of 721

It's an easy build, so long as you take your time you should be fine. The bits from Mouser are bagged individually & marked with the componant details which relates to the BOM, cross-refrence this with the pcb layout for part placment and you can't go wrong. If you've never soldered before, spend 20-30 minutes practicing beforehand and you should be ok.
 

Quote:
Originally Posted by snakeeater69 View Post

How hard is the build this amp? Is it as easy as looking at the instructional, plugging parts into proper place and then soldering it? I want to try this amp but have never built an amp or anything before.



 

post #145 of 721

Most you guys building the desktop version with 1/4mm plugs?

 

For portable one, has any been able to fit it with an altoids case? Just wondering because I'm cheap and want this be as cheap as possible.


Edited by snakeeater69 - 11/9/11 at 2:49am
post #146 of 721
Quote:
Originally Posted by snakeeater69 View Post

Most you guys building the desktop version with 1/4mm plugs?

 

For portable one, has any been able to fit it with an altoids case? Just wondering because I'm cheap and want this be as cheap as possible.



not possible. even the size of the pcb is already bigger than the outer dimension of altoids case

post #147 of 721

If you want to use a 1/4" output socket the NRJ3HF-1 socket and NRJ-NUT-B locking nut are the recomended replacement parts... this is mounted off-board and wired to P2.


Edited by Paul Blythe - 11/9/11 at 3:34am
post #148 of 721
Quote:
Originally Posted by cheapskateaudio View Post

Well, I think something got damaged with all the handling and soldering/unsoldering, and now the left channel is slightly lower in volume. Any ideas on what could have caused that? I have no MM so basically I can reflow the solder joints and thats about it. But I do have a few spare/upgrade parts here so I might try swapping them at random and seeing what happens. Could a bad resistor cause that? I touched a resistor with the soldering iron for a few seconds trying to surface mount the poly caps.


This sounds like 'bad amp karma"  :=)

 

After all, you have done everything to this amp that Voldemort said was unnecessary  to do. Indeed, he designed the amp to demonstrate that all your mods are a waste of time and money.

 

It has been entertaining though, and we thank you for that :=)

post #149 of 721
Quote:
Originally Posted by cheapskateaudio View Post

Update: I swapped out the other two elctrolytics, C8 & C9 on the board, and while it results in a perceived reduction in bass, bass quality is improved while the body and richness of the mids was increased. This has a good effect on some types of music like old Kraftwerk which is not quite as robust sounding as modern synth music.

 

WOW !!

Swapping caps to compensate for poor digital remastering of old analog tape-recordings, that's dedication :)

But it isn't HiFi . It is entirely possible that it sounds better to you for some reason but I would like to see some measurements

establishing the deficiency you claim and also of the fix . 

 

Regarding the RMAA debate :

Dedicated audio-analysis hardware costing thousands of dollars combined with math that adds up vs a more or less free PC-program, often using non-calibrated hardware ?

That's a tough one ..

 

Now excuse me, I'm working on a sensational report on the huge sonic differences between cables made from

South-African vs Russian gold .

 


Edited by AKG240mkII - 11/9/11 at 7:42am
post #150 of 721
Quote:
Originally Posted by snakeeater69 View Post

For portable one, has any been able to fit it with an altoids case? Just wondering because I'm cheap and want this be as cheap as possible.

The dimensions of the PCB alone are 8 cm x 10 cm. Too big, me thinks, for an Altoid tin.
 

 

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