[pp312]

I posted this on an Oz forum but they all appear to be asleep down here so I thought I'd try Head-Fi. It's a sort of DaVinci Code mystery, electronics style:

 

 

I'm looking for more info on this little amp:
 

http://cgi.ebay.com.au/NE5532op-amp-Power-tube-HIFI-Headphone-Amplifier-/320668221495?pt=LH_DefaultDomain_0&hash=item4aa950c037

It's the same amp as is discussed here:

http://rockgrotto.proboards.com/inde...nt&thread=6013

which is almost certainly based on the same circuit as Onkyo use in their upmarket integrateds and receivers (5532 op amp, BD139/140 transistors, 2200uf power caps), which is discussed here:

http://www.head-fi.org/forum/thread/...s-onkyo-a-9555

and favourably compared to a well-respected $800 dedicated HP amp. Why am I interested in this? Because I own an Onkyo 9555 integrated which uses this circuit and I'd like to know more about it--plus it would appear to be something of a real bargain if published impressions are any guide. It certainly sounds the business through the Audeze LCD-2, but I just wondered if anyone had bought one of the Ebay amps and if so what they thought. If not, maybe someone would like to invest $50 and let us all know.

 

Here's the circuit for the separate HP amp in the Onkyo 9555:

 

 

[fubar3]

>>I'm looking for more info on this little amp:
 
It is potentially good for low-impedance phones.  The unbuffered opamps typically have a series resistance of 47 or more and the 5532 has that.  But the buffer transistors also have a 47 ohm series resistance. So you probably get a bit more voltage out but little additional drive power. Perhaps you will also notice slightly better high frequency response.