Just when you thought it was safe to go back to the work bench....
Here's 7 easy pieces for chip amps.
www.passlabs.com/np/GC-VAR-INV-FDBK-1a.pdf
You might find this a trivial circuit, but for those who
don't know it, it can be very important. Chip amplifiers
have enormous amounts of open loop gain (120 dB = 1,000,000)
which can create stability problems when the circuit is set
for low gain, say only 10 or 20 dB. This circuit places a
resistor to ground at the negative input, which throws away
some of the open loop gain, resulting in less feedback. In
fact you can put a variable resistor here, and tune the
amount of feedback to taste.
www.passlabs.com/np/GC-VAR-BAL-FDBK-1a.pdf
Does the same thing for a balanced input circuit. Generally
you want the pots at equal value, but for the most perfect
common mode input rejection, separate pots allow trimming.
www.passlabs.com/np/GC-OUTPUT-BIAS-1a.pdf
You say your chip amp needs more output bias? Here's an old
trick.
www.passlabs.com/np/GC-OUTPUT-BIAS-2a.pdf
Here we see the same thing as GC-SS-3a, but without the
SuperSymmetry jazz, just a pair of chip amps. The voltage
sources will be low values, as will the output resistors,
and additional output stage is provided by the DC difference
in the output voltages across those output resistors. The
load output sees the split value, so there's no DC seen there.
You also get the advantage of delivering about twice the
current as a single chip amp.
www.passlabs.com/np/GC-BOOTSTRAP-1a.pdf
What? You want your chip amp to behave as if it's seeing a
higher impedance and also deliver more current? You can
parallel chip amps equally, or you can set one up as a
current bootstrap, relieving the load on the first amp,
but also leaving it in control of the signal. Sort of
like power steering. Watch how you set the current gain
of the bootstrap. For this circuit, 50% is a good number.
www.passlabs.com/np/GC-BOOTSTRAP-2a.pdf
And of course you can go crazy and use a lot of them. In
this case, the current gain would probably want to be set
to divide the current equally between all the amps, including
the first one. In the case of 4 bootstrap amps, each would
probably want to be set at delivering 20% of the output
current.
www.passlabs.com/np/GC-ZEN-ALEPH-1a.pdf
How can we resist not making a Zen amp with such a current
source? Here we see that the Aleph current source is easily
duplicated by a chip amp.
😎
Here's 7 easy pieces for chip amps.
www.passlabs.com/np/GC-VAR-INV-FDBK-1a.pdf
You might find this a trivial circuit, but for those who
don't know it, it can be very important. Chip amplifiers
have enormous amounts of open loop gain (120 dB = 1,000,000)
which can create stability problems when the circuit is set
for low gain, say only 10 or 20 dB. This circuit places a
resistor to ground at the negative input, which throws away
some of the open loop gain, resulting in less feedback. In
fact you can put a variable resistor here, and tune the
amount of feedback to taste.
www.passlabs.com/np/GC-VAR-BAL-FDBK-1a.pdf
Does the same thing for a balanced input circuit. Generally
you want the pots at equal value, but for the most perfect
common mode input rejection, separate pots allow trimming.
www.passlabs.com/np/GC-OUTPUT-BIAS-1a.pdf
You say your chip amp needs more output bias? Here's an old
trick.
www.passlabs.com/np/GC-OUTPUT-BIAS-2a.pdf
Here we see the same thing as GC-SS-3a, but without the
SuperSymmetry jazz, just a pair of chip amps. The voltage
sources will be low values, as will the output resistors,
and additional output stage is provided by the DC difference
in the output voltages across those output resistors. The
load output sees the split value, so there's no DC seen there.
You also get the advantage of delivering about twice the
current as a single chip amp.
www.passlabs.com/np/GC-BOOTSTRAP-1a.pdf
What? You want your chip amp to behave as if it's seeing a
higher impedance and also deliver more current? You can
parallel chip amps equally, or you can set one up as a
current bootstrap, relieving the load on the first amp,
but also leaving it in control of the signal. Sort of
like power steering. Watch how you set the current gain
of the bootstrap. For this circuit, 50% is a good number.
www.passlabs.com/np/GC-BOOTSTRAP-2a.pdf
And of course you can go crazy and use a lot of them. In
this case, the current gain would probably want to be set
to divide the current equally between all the amps, including
the first one. In the case of 4 bootstrap amps, each would
probably want to be set at delivering 20% of the output
current.
www.passlabs.com/np/GC-ZEN-ALEPH-1a.pdf
How can we resist not making a Zen amp with such a current
source? Here we see that the Aleph current source is easily
duplicated by a chip amp.
😎
Anybody got a spice model for an appropriate opamp to simulate with?
Think I need a cup of tea.
Jens - already thinking a pot might be better
Think I need a cup of tea.
Jens - already thinking a pot might be better
Metalman - Already thinking pot might be better!
In the last 24 hours my head has chipped
exploded 
spun 
inverted 
balanced 
, bootstrapped 
and in true Pass fashion finished in a state of Zen 
I'm sure I hurt something in there but what a ride
Thanks Nelson!
Ok Nelson, i have to ask this, exactly how much time did you spend on those schematics? I knowing you, probably didn't take you long, but I'm curious 😀 later
-Matthew K. Olson
-Matthew K. Olson
Mattyo5 said:
I'd bet not long - about noon Nelson's time there were only 5 schematics in that directory. 😉
I use P-CAD, so I thought about them for 30 years and
drew them in about 15 minutes each.
I saved the 7th for last because it links the generalization
back to a specific. And it is cute.
drew them in about 15 minutes each.
I saved the 7th for last because it links the generalization
back to a specific. And it is cute.
In retrospect, they're fairly obvious, just like lots of stuff. Don't
get too impressed; I didn't invent most of it, I just applied it
to chip amps. 😎
get too impressed; I didn't invent most of it, I just applied it
to chip amps. 😎
Remember when there were only two kinds of gainclones?
Remember when the discrete know it alls said that there was no room for experimentation or circuit design with chips?
Jocko- what's that brown stuff on your nose?
Remember when the discrete know it alls said that there was no room for experimentation or circuit design with chips?
Jocko- what's that brown stuff on your nose?
will i need to add capacitors like C5 and C6 in description of aleph current source in Zen V2 to make GC Zen aleph, or do i missunderstand the schematic and it works without?
(C5 and C6 --> C5 to + pin of opamp and C6 in series with resistor from speaker output to neg. input of opamp)
(C5 and C6 --> C5 to + pin of opamp and C6 in series with resistor from speaker output to neg. input of opamp)
Isn't #6 the kissing cousin of my massively parallel small-signal amplifier idea?
For those interested in the idea, there is a calculator for parallel devices on the second page. I wrote it, so you may want to verify your results before powering up...
http://www.diyaudio.com/forums/showthread.php?s=&threadid=32991&perpage=20&highlight=&pagenumber=2
#7 is nice.
For those interested in the idea, there is a calculator for parallel devices on the second page. I wrote it, so you may want to verify your results before powering up...
http://www.diyaudio.com/forums/showthread.php?s=&threadid=32991&perpage=20&highlight=&pagenumber=2
#7 is nice.
What is it???
I think that I can safely say that it is the same stuff on my shirt, jeans, hands, glasses......and most everything else:
Mud. Good ol' Texas mud.
I spent around 3 hours repairing a 1-1/4" pipe break in an irriagtion system on a large commercial property.
"Glasses?""
Yes.....they fell into it many times.
Hmm......looks like mud........smells like mud........tastes like mud.
Better not get any on me.
Any other questions??
Jocko
I think that I can safely say that it is the same stuff on my shirt, jeans, hands, glasses......and most everything else:
Mud. Good ol' Texas mud.
I spent around 3 hours repairing a 1-1/4" pipe break in an irriagtion system on a large commercial property.
"Glasses?""
Yes.....they fell into it many times.
Hmm......looks like mud........smells like mud........tastes like mud.
Better not get any on me.
Any other questions??
Jocko
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