Jim Candela
2004-02-04 05:06:09 UTC
Hi guys,
Sometime ago I was looking at the Curcio web page concerning "The
Audibility of Power Supplies". I was also in the process of restoring my
Sherwood S8000 where I made a few posts on this group. My poor Sherwood sure
had lots of power supply ripple, and regulation issues that I did not like
at all. I decided to do something about the power supplies in my Sherwood.
I was reading the White paper by Joe Curcio, and although I dare not
disagree, I cannot understand the need to have a tight regulation loop with
DC to 1 Mhz bandwidth. I must be missing something. I am more comfortable
(maybe because it is easier) with a regulator that has DC to several
kilohertz bandwidth, and use sufficient power supply decoupling capacitors
that kick in to stiffen the buss before the regulator runs out of bandwidth.
That way the regulator does not need to be ultra sophisticated, and the bus
is clean and pure from DC to beyond the audio range. I also have a hard time
reasoning how to make a tight wide bandwidth regulator that can only source
current to a buss that is lightly decoupled with capacitors. Wouldn't this
require a totem-pole design that can both source, and sink to maintain rs=0?
Anyway, here is Joe's white paper that got me going on this:
http://www.curcioaudio.com/Audibility_of_PwrSupply.htm
My Sherwood has been evolving now for several months. The power supply
is about done. A re-cap of all those black "Good-All" audio coupling
capacitors is next. I was also thinking of beefing up the 7868 audio drive
by replacing the 12AX7 driver (1/2 voltage amplifier, other 1/2 a hot
cathode phase inverter) with a 6EZ8. This gives me three triodes (like 1.5
12AT7's) in a 9 pin bulb. That certainly opens up a few options. I have
three regulated power supplies in my Sherwood now. The regulated screens for
the 7868's are within 1/4 volt p-p of +375 DC when driving the tar out of
the amplifier with all sorts of program material. It's the prolonged bass
notes from rap music (I hate listening to that stuff, but good for testing
your amp!) that causes the worst dip in voltage (1/4 volt), and that is
because the voltage feeding the regulator is also dipping to sustain a full
power 5 second 20 hertz bass note. Why do I need a active regulator with 1
Mhz bandwidth? Below is a link to my circuits, and a brief description.
These circuits are my doing, and the product of lots of bread boarding, a
few arc's, a couple wisps of smoke, and a shock or two. It sure was fun
though!
http://pages.prodigy.net/jcandela/Sherwood_S8000/HV_REG/regulator.htm
I welcome your comments.
Jim Candela
Sometime ago I was looking at the Curcio web page concerning "The
Audibility of Power Supplies". I was also in the process of restoring my
Sherwood S8000 where I made a few posts on this group. My poor Sherwood sure
had lots of power supply ripple, and regulation issues that I did not like
at all. I decided to do something about the power supplies in my Sherwood.
I was reading the White paper by Joe Curcio, and although I dare not
disagree, I cannot understand the need to have a tight regulation loop with
DC to 1 Mhz bandwidth. I must be missing something. I am more comfortable
(maybe because it is easier) with a regulator that has DC to several
kilohertz bandwidth, and use sufficient power supply decoupling capacitors
that kick in to stiffen the buss before the regulator runs out of bandwidth.
That way the regulator does not need to be ultra sophisticated, and the bus
is clean and pure from DC to beyond the audio range. I also have a hard time
reasoning how to make a tight wide bandwidth regulator that can only source
current to a buss that is lightly decoupled with capacitors. Wouldn't this
require a totem-pole design that can both source, and sink to maintain rs=0?
Anyway, here is Joe's white paper that got me going on this:
http://www.curcioaudio.com/Audibility_of_PwrSupply.htm
My Sherwood has been evolving now for several months. The power supply
is about done. A re-cap of all those black "Good-All" audio coupling
capacitors is next. I was also thinking of beefing up the 7868 audio drive
by replacing the 12AX7 driver (1/2 voltage amplifier, other 1/2 a hot
cathode phase inverter) with a 6EZ8. This gives me three triodes (like 1.5
12AT7's) in a 9 pin bulb. That certainly opens up a few options. I have
three regulated power supplies in my Sherwood now. The regulated screens for
the 7868's are within 1/4 volt p-p of +375 DC when driving the tar out of
the amplifier with all sorts of program material. It's the prolonged bass
notes from rap music (I hate listening to that stuff, but good for testing
your amp!) that causes the worst dip in voltage (1/4 volt), and that is
because the voltage feeding the regulator is also dipping to sustain a full
power 5 second 20 hertz bass note. Why do I need a active regulator with 1
Mhz bandwidth? Below is a link to my circuits, and a brief description.
These circuits are my doing, and the product of lots of bread boarding, a
few arc's, a couple wisps of smoke, and a shock or two. It sure was fun
though!
http://pages.prodigy.net/jcandela/Sherwood_S8000/HV_REG/regulator.htm
I welcome your comments.
Jim Candela