On Mar 4, 12:54*pm, John Larkin
wrote:
On Thu, 3 Mar 2011 19:53:58 -0800 (PST), Fred Bloggs
wrote:
On Mar 2, 5:58 pm, John Larkin
wrote:
On Wed, 2 Mar 2011 14:55:18 -0800 (PST), Fred Bloggs
wrote:
On Mar 2, 4:33 pm, John Larkin
wrote:
On Wed, 2 Mar 2011 12:03:38 -0800 (PST), Fred Bloggs
wrote:
On Mar 2, 11:40 am, John Larkin
wrote:
I've always sort of liked the classic "GE" tape head/mic preamp
circuit:
ftp://jjlarkin.lmi.net/GEcircuit.jpg
but it occurred to me that it might also make a nice headphone amp...
ftp://jjlarkin.lmi.net/GE_headphone_amp.JPG
Audio tends to be nonsense, but at least the audio guys have fun
playing with circuits, whether they make a lot of sense or not.
John
Bizarre??? Just a standard buffered input CE with negative feedback DC
bias to stabilize the operating point against Vbe and reverse leakage
collector current change with temperature- a textbook circuit...
Which textbook?
John- Hide quoted text -
- Show quoted text -
Just about any textbook that goes into bias point sensitivity analysis
of transistor circuits- you remember the S- functions, mainly ICQ
stability. The big three were HFE, VBE, and ICBO. Then the rest of
your circuit is just ac-bypass and the shunt-series feedback for
signals. I've seen it dozens of times.
I bet you haven't seen the bipolar+mosfet version, with inductive
pullup, used as a power amp.
John- Hide quoted text -
- Show quoted text -
I don't see the MOSFET being all that much of a change. And as for the
inductor pull-up, this just doesn't make sense for low wattage high
impedance headphone loads. Your inductive reactance needs to be a good
few integer multiples of the load impedance, making these things
prohibitively large if not unobtainable for a headphone app- you would
use far less iron/ ferrite by boost switching your supply to
accommodate the output swing...guess that's why I've never seen the
inductive pullup here.
Of course you haven't seen this circuit befo I just invented it.
But inductors were widely used as plate loads in the tube days. Tubes
were expensive and had low gains, so transformers and inductors were
sensible. Early transistor amps used lots of transformers, for the
same reasons.
John- Hide quoted text -
- Show quoted text -
I thinking you are confusing your app with peaking coils which were
one of several techniques used to broadband the amplifier- that's a
totally different application and it was practical because the
reactance was only important in the 10's KHz band or higher- this is
not the case for a 20-20K Hz headphone circuit.