The Objective2 (O2) Headphone Amp DIY Project

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MGeeOne

Member
Joined 2013
Brilliant thanks zoidbergslo!

This is probably a stupid question for a beginner, but is there any benefit to upgrading any components from the standard kit? Better pot? Higher spec caps?

Also, how long to the batteries last? Is there a DIY PSU one can make too? Or does this bring down the quality? I'm going to be using it at my desk, since my AKG K702's are not that portable now I've upgraded the cable to Cardas L-4E6S!!

Thanks again
 
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keithostertag

Member
Joined 2012
A few questions- BOM, schematic, gain switch, etc

Hey guys-

Where is the high resolution schematic? And the xls version of the current BOM? All I find is the googledocs version.

Also, one note I jotted down while reading through the many NwAvGuy web pages (whew!) is this:

"The only thing I would not remove from the PCB is the gain switch."

Why is that? I was thinking to have a remote gain switch so I could wire up more than two choices. Wouldn't whatever resistance in the wire be miniscule/irrrelevant compared to the resistors values? Or is something else going on?

Thanks, Keith Ostertag
 
ericj

ericj

Member
Joined 2008
MGeeOne said:
Thanks Eric... I'm new to this so was just thinking if those caps had been spec'd to achieve a price/quality balance then there may be alternatives that could improve sound but may cost more.

I understand that there are compromises in any design.
Click to expand...

Really you should read the blog posts about the design choices, but basically an increase in capacitance would likely decrease performance. Lower ESR may not have a positive effect either.

I wonder if a desktop version might be better with a 4562 instead of a 2068 but this has already probably been discussed.

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qusp

qusp

Member
Joined 2009
keithostertag said:
Hey guys-

Where is the high resolution schematic? And the xls version of the current BOM? All I find is the googledocs version.

Also, one note I jotted down while reading through the many NwAvGuy web pages (whew!) is this:

"The only thing I would not remove from the PCB is the gain switch."

Why is that? I was thinking to have a remote gain switch so I could wire up more than two choices. Wouldn't whatever resistance in the wire be miniscule/irrrelevant compared to the resistors values? Or is something else going on?

Thanks, Keith Ostertag
Click to expand...

because by moving the gain switch to the panel you are taking the feedback loop out to the panel with it and thus increasing the length of the loop and decreasing stability, increasing noise pickup etc.
 
ericj

ericj

Member
Joined 2008
MGeeOne said:
Thanks for the blog headsup...will digest over the next few days. Then straight to HnH!

Will look out for a suitable PSU too...in fact that might be another good DIY maybe? ;)
Click to expand...

The o2 has a very good on-board psu. It just needs ac voltage. I recommend something like the antek an-0109 toroid with it's dual secondaries wired in series for 18vac. Costs $10 and they have 76 of them in stock. Other than that, you could use a filtered ac inlet.

Sent from my DROID4 using Tapatalk 2
 
K

keithostertag

Member
Joined 2012
qusp said:
because by moving the gain switch to the panel you are taking the feedback loop out to the panel with it and thus increasing the length of the loop and decreasing stability, increasing noise pickup etc.
Click to expand...


OK, thanks. Could you elaborate a little more? As long as the wires I use are shielded, how does that decrease stability? If properly shielded, how does the length affect it?

I'm new to this so I'd like to understand a little more about it.
 
K

keithostertag

Member
Joined 2012
A few parts substitution questions- LED, NJM2068DD, C1, C6, C7

Hey guys-

For those who have mounted the power-on LED on a remote panel, what did you use? I see the cautions about it requiring an HE led, etc. Mouser part number?

Mouser is out of NJM2068DD for the next three months. I can order the "noisier" NE5532AP for now and substitute later, but wondered if any other options have emerged.

Also, for C1, C6, and C7 the 1uF 25V cap which is stated as a "non-critical part", any problem using a tantalum? I know tantalums sometimes get a bad rap, but AFAIK they are OK as long as they are voltage rated properly. I happen to have a bunch of tantalum 1uf 35V.

Thanks,
Keith
 
ericj

ericj

Member
Joined 2008
keithostertag said:
OK, thanks. Could you elaborate a little more? As long as the wires I use are shielded, how does that decrease stability? If properly shielded, how does the length affect it?

I'm new to this so I'd like to understand a little more about it.
Click to expand...

Shielding adds capacitance that could make it worse.

There are electromagnetic waves all around us that can induce signals into the feedback loop and cause distortion or even cause the chip to oscillate. Longer wires are bigger antennas, and the gain switch is a particularly sensitive area.

Sent from my DROID4 using Tapatalk 2
 
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ramsfan6239

Member
Joined 2011
Guys - I need help.

I'm doing an amp and I have a problem I can't fix.

so here is the problem - at low volumes, and at full volume on the potentionmeter, both left and right cups sound the same, anywhere in between, the right channel is very quiet, off balance.

I have tried - Replacing all mosfets, replacing the 2068dd opamp, potentiometer, replacing gain switch, checked all resistors, all diodes are in correct position, re soldered the whole board... I can't figure out what's going on.
 
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