Discrete Opamp Open Design

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#2,242
Mr. Marsh, finally figured out the thread is Marsh Headphone Amp Linear Audio

May I commend you on keeping this modest (?? 😱) 50 page thread in good order and contributing loadsa good stuff on PCB layout & PSUs too. I very much like your 'modest base requirements' in #279.

If I may be so bold .. Is the full circuit this one?
Amp & Auto EQ for Headphones

It's not clear if this little pic on the Linear Audio page is just the output buffer or the full circuit. I can't see any provision for 12dB gain. It is indeed examplary in its simplicity & effectiveness. 🙂

I believe my own modest effort with FET990 may meet your requirements list but at a cost of nearly double the active devices. 😡 In return, all I can offer is a reduced Iq of 3mA for the same performance and a less stringent need for matching devices.

I'm sorely tempted to treat myself to a beach bum's X'mas present as I see Guru Wurcers 'Supa Dupa Mike Preamps pt 2' is in the same issue of Linear Audio ... and I wanna know wat dis Auto EQ for headphones is too.
 
#2,247
RNMarsh said:
gads. Did I write all that? And, I only came here in May this year. I just wanted to help DIY headphone amp builders make the headphone amp and enjoy it. Now here I am spilling my life's guts out to a bunch of strangers on this social medium! 🙂 Am I that desperate!? [not really]. Wasnt I breast fed?

Kgrlee--- I'll see if I have any better luck finding it. -RNM
Click to expand...

You posted the schematic in this thread instead of your headphone amp thread. 😉
 
#2,248
PMA said:
That DB headphone circuit might be a good candidate for potential VHF oscillator 😉
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Which circuit Pavel?

If you are referring to Marshy's circuit, that's easy enough to solve without affect the performance. 2 resistor values.

You posted the schematic in this thread instead of your headphone amp thread.
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Got a link homemodder? I'm exhausted from looking through 50 pgs of the Headphone Amp thread.

Do you know if the small pic on the Linear Audio website is the full circuit?

Apologies to those who would have me buy the book. I am counting my pennies.
 
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#2,250
PMA said:
I mean the circuit you have linked,

A Headphone Buffer/Amp and Auto-EQ for Headphones
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Could you elaborate? Have you had a bad experience?

Any circuit with Complementary Feedback / Sziklai Pair followers may oscillate if designed badly but the cure is usually simple. In this case, IF there is a problem, the solution is to change 2 resistor values. In a VERY BAD case, you may have to add 2 resistors.

There are millions of amps with CFB pair O/Ps which aren't VHF oscillators. I'll concede there are thousands, mainly Golden Pinnae, which do oscillate at VHF from time to time.
 
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#2,254
Somewhere in last days BT thread posts.
 

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#2,256
PMA said:
I have documented the problem in another thread (250MHz oscillations, Agilent spectrum analyzer measurement). Output CFP of DB is prone to UHF oscillations triggered by RFI impulse sent to the output.
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Pavel, I could only find this
http://www.diyaudio.com/forums/analog-line-level/146693-john-curls-blowtorch-preamplifier-part-ii-2996.html I can't believe I've just looked through more than 350 posts to find it.

But Marshy's headphone amp, neither the pic at http://www.linearaudio.net/index.php?option=com_content&view=article&id=161:a-headphone-bufferamp-and-auto-eq-for-headphones&catid=44:volume-3&Itemid=108
OR
#522 on this thread
are standard 'Diamond Buffer".

So are the Agilent plots of some other evil Golden Pinnae device?
__________

As Mr. Marsh is at pains to point out, he is not putting forward this design to compete with SW-OPA. But for it's intended purpose, and also for a simple buffer or amp, it's elegantly effective if you can select devices and don't mind running 50ma Iq.

I for one am impressed and jealous cos he gets his performance with half the active devices that I need. 🙂
 
#2,259
RNMarsh said:
Output 'buffer' circuits vary in their isolation ability to minimize the affects.
...
But it clearly can affect performance .... such as, power amp and loudspeaker reflecting back any nonelinear Z.

...which topology in the output stage has the greatest isolation from output to Av stage...
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Though developed as a power chipamp, the Mauro Penasa MyRef uses a nested Howland Current Pump within a global voltage-series feedback loop to address precisely this issue - the effect of a nonlinear load-Z on audible sonics.

There are huge active threads in the chipamps forum on the MyRef and its derivatives. I've built several, and can attest to its outstanding sonics.
 
#2,260
kgrlee said:
...
unlike certain pseudo Messiah's that shall remain nameless ...
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Lol - bad-hair day?

BTW, I've preferred simplicity from the beginning of this thread, which is why I picked up on the Kaneda initially, and later played around with the single-ended versions of SWOPA, with various output stages.

IMHO, all have various pros and cons, but if I had to build yet another line-level discrete-opamp to actually listen to music, I'd probably go with a Kaneda/Constellation derivative, despite the fact that it's not an ultra-low THD contender. Why? Because it's simple and only requires a few parts to be matched, and by most accounts, has clean wide-open soundstage and resolution.
 
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