[SpaceTimeMorph]

 
Quote:

 
This is a real problem in this design, particularly on battery power.  Dual 8.4V batteries are specified, let's say that batteries are charged and does not fall below the rated voltage, we have 16.8V total spread, minus the forward drop of the two 1N5818 schottky diodes (0.5V each), this reduces the available voltage down to 15.8V.  And let's assume no further voltage drops in the power supply -- in fact there is some drop across the MOSFETs, but probably small enough to ignore for this discussion.  The NJM2608 opamp is not rail-to-rail.  It could only swing to about 2V above the negative rail and about 1V below the positive rail.  The signal's negative peaks will therefore clip first and effectively we have a maximum output voltage swing of 11.8Vp-p.
 
The volume pot is not at the input to attenuate the input signal, so the input opamp "sees" the full output voltage from the source.  Let's assume a standard Redbook audio CD player's output voltage at 0dBFS of 2Vrms, which is 5.7Vp-p.  Even at the lowest gain setting of 2x, the opamp output will be swinging 11.3Vp-p which is right at the verge of clipping.  If you switch the gain any higher, it will clip rather severely.
 
The designer states on the schematic "Input 4V RMS max".  If that was true, we'd need to be able to swing 22.6Vp-p at the output of the opamp for a gain of 2x (and more for higher gains).  Neither a battery-powered nor a wall-powered version of this amp could do that without clipping.
 
This is irrespective of the headphone sensitivity or volume pot position.  While similar concepts have been used in commercial gear, the input stage in them would be powered by much higher supply voltages in order to avoid clipping, but that is clearly not an option here due to the batteries.

However, 2 Vrms is not the standard for portable line input voltages.  Most portable players are ~1 Vrms, some significantly lower at around .5 Vrms.  2 Vrms is more likely for home usage.  Speaking of home usage, the power supply while running off of AC line voltage is rated for 24 Vpp.  Even accounting for .5V drop across the Schottky's you are dealing with 23.5 Vpp, which is 8.3 Vrms.  With a gain of 2x through the opamp that leaves you with a 4.15 Vrms input.  These leaves you with about 4% headroom here, which is cutting it awefully close.  However, the specified 4 Vrms max input was a design rating for input voltage, not a typical value.  With a 2 Vrms input and 3.1x gain you are dealing with 6.2 Vrms, which leaves you with a 33.9% headroom here; more than enough.  So, in short, you cannot compare the max output level of this for portable usage with a home source.  This is actually all explained within his articles.  Correct me if I'm wrong, but are there normal sources out there that would put out 4 Vrms or higher?
 
Here is a link to the datasheet for the NJM2068.  I'm not sure what the performance of the 2608 is, but since it isn't used in his design...
http://www.datasheetarchive.com/NJM2068%2A-datasheet.html#datasheets

 
 

 

[The Monkey]

Is this a portable or a desktop amp?

 

[khaos974]

Portable, but still able to output 0.5W on battery (33 ohm load, 1 kHz, inferior to 0.01% THD+N), on AC it has maybe 15% more power, it should be able to drive the HE-6 at 110 dB.

Still waiting for independent confirmation of the measures.

 

[Steve Eddy]

Quote:

2. No links to NwAvGuy's website, or resources maintained directly by him.

 

This needs to be modified to include no links to threads on other forums not directly maintained by him but where he may address critiques of the design (a link I posted previously to such a thread was subsequently deleted).
 
Allowing a thread for the discussion and critiquing of a particular individual's design without that individual being able to respond to any of it is eminently unfair in my opinion and to that end I think this thread should be removed.
 
se
 

 

[odigg]

Quote:

 
This needs to be modified to include no links to threads on other forums not directly maintained by him but where he may address critiques of the design (a link I posted previously to such a thread was subsequently deleted).
 
Allowing a thread for the discussion and critiquing of a particular individual's design without that individual being able to respond to any of it is eminently unfair in my opinion and to that end I think this thread should be removed.

While I do agree that it's unfair that NvAwGuy cannot post in this thread, I don't think deleting this thread is the answer as Head-Fi is a popular site.  Many people who have the engineering know-how to comprehensively review and critique the O2 are on Head-Fi, not on the other mainstream forums.  Average Joe types (like me) are not on audio engineering forums and don't care to be since we can't much all that much sense of what is said.  Head-Fi is probably one of the few sites (that I know of) where the average Joe can make some sense of stuff said in the DIY section.
 
Maybe NvAwGuy should be allowed back onto Head-Fi with the restriction that he can only post in this thread?  That makes the most sense to me as I'd like to hear what he has to say about critiques of his amp design.
 
Anyway, I know I'm not supposed to discuss bans and what not so I'll leave it at that.
 

 

[Steve Eddy]

Quote:

While I do agree that it's unfair that NvAwGuy cannot post in this thread, I don't think deleting this thread is the answer as Head-Fi is a popular site. 
 

 
So you agree that it's unfair, but that's ok because HeadFi is... popular? Really?
 
Quote:

Many people who have the engineering know-how to comprehensively review and critique the O2 are on Head-Fi, not on the other mainstream forums.

 
And it's also ok because some people here aren't on other forums? Really?
 
Quote:

Maybe NvAwGuy should be allowed back onto Head-Fi with the restriction that he can only post in this thread?  That makes the most sense to me as I'd like to hear what he has to say about critiques of his amp design.

 
How 'bout just sticking to the rules as posted?
 
"No links to NwAvGuy's website, or resources maintained directly by him."
 
The link I posted was not to his website or to any resources maintained directly by him.
 
Edit: I posted the link in response to another post which was also deleted suggesting that the thread be moved to someplace where NwAvGuy could respond.
 
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[khaos974]

"No links to NwAvGuy's website, or resources maintained directly by him."
 
The link I posted was not to his website or to any resources maintained directly by him.

Actually, it's no links direct or indirect to nwvaguy, so let's stick to the design.

 

[fishski13]

Steve,
while i have plans to build this amp for someone, i have to agree.  he's been banned here and elsewhere.  he has his own blog and diyaudio.com where anyone is free to join in on the discussion. 

 

[kevin gilmore]

Lets assume that the amp is running on AC power, the voltage drop across the diodes and fets is zero and the
input amplifier is rail to rail. At least according to the schematic, the voltage gains are 3.1 and 7.17
So  1.2 VRMS is the maximum input voltage at a gain of 7.17 where the input amp is already clipping.
And 2.76 VRMS is the maximum input voltage at a gain of 3.1 where the input amp is already clipping.
 
Run it off of fully charged batteries and you get
.83 VRMS at a gain of 7.17  and
1.93 VRMS t a gain of 3.1
 
practically after the diode and pass fet and the fact that the opamp is not rail to rail take
about 20% off of those numbers.
 
Over the years many manufacturers put the pot in the middle after the gain stage.
Lots easier on tube gear where the power supply rails are in the hundreds of volts.
The benefit is slightly lower noise. While its unlikely that this amp is going to be
used with a cd player with a tube output stage, those typically put out well in excess
of 5 VRMS.
 
The pass fets and comparators are not a power supply, they are a under voltage
kickout circuit. The pass fets are either very hard ON, or very hard OFF.
 
 

 

[Steve Eddy]

Quote:

Actually, it's no links direct or indirect to nwvaguy...

That's not what the posted rule states.
 
Quote:

so let's stick to the design.

 
You say "the design" almost as if it somehow materialized out of thin air. But it didn't. It was designed by someone. So I don't see how the design can be discussed without it having implications for the person who designed it.
 
se
 

 

[Steve Eddy]

Quote:

Steve,
while i have plans to build this amp for someone, i have to agree.  he's been banned here and elsewhere.  he has his own blog and diyaudio.com where anyone is free to join in on the discussion. 

Yes, but the point is, he's not free to join in on the discussion here. And as I said above, you can't really separate the design from its designer.
 
se
 

 

[Anaxilus]

Quote:

And as I said above, you can't really separate the design from its designer.

You must be kidding, it's done here all the time.  This is not unique.  If I had a dollar for everytime Spritzer went to town on Rudistor I'd have a 009 by now.  

 
I'm also not sure I'd agree the designer isn't or can't be represented here.  I see quite the contrary tbh.  To ask the thread to be removed on your grounds is over the top and unprecedented IMHO. 
 

 

[fishski13]

 
Quote:

Yes, but the point is, he's not free to join in on the discussion here. And as I said above, you can't really separate the design from its designer.
 
se
 

i agree, but he made his bed with his petulant behavior and refusing to desist.  he has a blog where he is free to act in any way he feels like and discuss whatever he wants.  i am surprised HF allowed this thread in the first place.
 

 

[Shike]

Quote:

i agree, but he made his bed with his petulant behavior and refusing to desist.  he has a blog where he is free to act in any way he feels like and discuss whatever he wants.  i am surprised HF allowed this thread in the first place.

 
Two sides to every story.
 
 
Either way, you can say he's rude but it doesn't change the fact that his measurements and design are good for the community.

 

[fishski13]

 
Quote:

 
Two sides to every story.
 
 
Either way, you can say he's rude but it doesn't change the fact that his measurements and design are good for the community.

 
good for the SS community, fine, but i would disagree wholeheartedly for the DIY community.