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Need experts for vexing hum problem

I am sorry if this is slightly off-topic for this group. But you are
the ones I trust the most.

There is a guy who has built a tube-based preamp, from a commercial
DIY kit. The preamp causes significant hum at the main amplifier's
output, even when the preamp is NOT powered, and also when unpowered
and unplugged. (It also causes hum when powered.) Other signal
sources do not cause hum when connected to the amplifier. Other than
the hum, the preamp sounds good.

Some great minds at diyaudio.com have, so far, been unable to find a
solution. The discussion-thread is here:

http://www.diyaudio.com/forums/showthread.php?s=&threadid=116374

(Please ignore my embarrassing contributions to that thread.)

Here is a link to thumbnails of the preamp's schematics, pcb-layout
diagram, and photos:

http://home.comcast.net/~garyworld/site/?/photos/

[Please note that the filaments' (DC) supply's smoothing capacitance
is much larger than what is indicated on the power supply schematic.]

The grounding scheme is quite ugly, and IMO should at least eventually
be completely converted to a proper star-grounding scheme.

But my current thinking is that if we can solve the hum problem for
when the preamp is NOT powered, then we will probably have mostly
solved the problem for when it IS powered, probably with minimal
modifications.

Thanks, guys.

- Tom Gootee
 
M

MooseFET

Jan 1, 1970
0
I am sorry if this is slightly off-topic for this group. But you are
the ones I trust the most.

There is a guy who has built a tube-based preamp, from a commercial
DIY kit. The preamp causes significant hum at the main amplifier's
output, even when the preamp is NOT powered, and also when unpowered
and unplugged. (It also causes hum when powered.) Other signal
sources do not cause hum when connected to the amplifier. Other than
the hum, the preamp sounds good.

Some great minds at diyaudio.com have, so far, been unable to find a
solution. The discussion-thread is here:

http://www.diyaudio.com/forums/showthread.php?s=&threadid=116374

(Please ignore my embarrassing contributions to that thread.)

Here is a link to thumbnails of the preamp's schematics, pcb-layout
diagram, and photos:

http://home.comcast.net/~garyworld/site/?/photos/

[Please note that the filaments' (DC) supply's smoothing capacitance
is much larger than what is indicated on the power supply schematic.]

The grounding scheme is quite ugly, and IMO should at least eventually
be completely converted to a proper star-grounding scheme.

But my current thinking is that if we can solve the hum problem for
when the preamp is NOT powered, then we will probably have mostly
solved the problem for when it IS powered, probably with minimal
modifications.

Thanks, guys.

- Tom Gootee



Check your rectifier, use Inductance+Cap as your filter, and Do not overload
your final Tube.

The waving at the top of your DC supply is where you need to clean up.
Stick an AC volt-meter on DC line to check your progress. This tip brought
to you from the Retarded Community.
 
I am sorry if this is slightly off-topic for this group.  But you are
the ones I trust the most.
There is a guy who has built a tube-based preamp, from a commercial
DIY kit.  The preamp causes significant hum at the main amplifier's
output, even when the preamp is NOT powered, and also when unpowered
and unplugged.  (It also causes hum when powered.)  Other signal
sources do not cause hum when connected to the amplifier.  Other than
the hum, the preamp sounds good.
Some great minds at diyaudio.com have, so far, been unable to find a
solution.  The discussion-thread is here:

(Please ignore my embarrassing contributions to that thread.)
Here is a link to thumbnails of the preamp's schematics, pcb-layout
diagram, and photos:

[Please note that the filaments' (DC) supply's smoothing capacitance
is much larger than what is indicated on the power supply schematic.]
The grounding scheme is quite ugly, and IMO should at least eventually
be completely converted to a proper star-grounding scheme.
But my current thinking is that if we can solve the hum problem for
when the preamp is NOT powered, then we will probably have mostly
solved the problem for when it IS powered, probably with minimal
modifications.
Thanks, guys.
- Tom Gootee

Check your rectifier, use Inductance+Cap as your filter, and Do not overload
your final Tube.

The waving at the top of your DC supply is where you need to clean up.
Stick an AC volt-meter on DC line to check your progress.  This tip brought
to you from the Retarded Community

Thanks for the tips, MooseFET.

But none of that would explain why it also causes hum when it is not
even powered on.
 
M

MooseFET

Jan 1, 1970
0
I am sorry if this is slightly off-topic for this group. But you are
the ones I trust the most.
There is a guy who has built a tube-based preamp, from a commercial
DIY kit. The preamp causes significant hum at the main amplifier's
output, even when the preamp is NOT powered, and also when unpowered
and unplugged. (It also causes hum when powered.) Other signal
sources do not cause hum when connected to the amplifier. Other than
the hum, the preamp sounds good.
Some great minds at diyaudio.com have, so far, been unable to find a
solution. The discussion-thread is here:

(Please ignore my embarrassing contributions to that thread.)
Here is a link to thumbnails of the preamp's schematics, pcb-layout
diagram, and photos:

[Please note that the filaments' (DC) supply's smoothing capacitance
is much larger than what is indicated on the power supply schematic.]
The grounding scheme is quite ugly, and IMO should at least eventually
be completely converted to a proper star-grounding scheme.
But my current thinking is that if we can solve the hum problem for
when the preamp is NOT powered, then we will probably have mostly
solved the problem for when it IS powered, probably with minimal
modifications.
Thanks, guys.
- Tom Gootee

Check your rectifier, use Inductance+Cap as your filter, and Do not
overload
your final Tube.

The waving at the top of your DC supply is where you need to clean up.
Stick an AC volt-meter on DC line to check your progress. This tip brought
to you from the Retarded Community

Thanks for the tips, MooseFET.

But none of that would explain why it also causes hum when it is not
even powered on.




Then your suspected target is not the cause of the hummmmmmmmmm..........
 
F

Fred

Jan 1, 1970
0
news:f48586f1-db70-4a87-9f55-afcaf247d168@e25g2000prg.googlegroups.com...
I am sorry if this is slightly off-topic for this group. But you are
the ones I trust the most.
There is a guy who has built a tube-based preamp, from a commercial
DIY kit. The preamp causes significant hum at the main amplifier's
output, even when the preamp is NOT powered, and also when unpowered
and unplugged. (It also causes hum when powered.) Other signal
sources do not cause hum when connected to the amplifier. Other than
the hum, the preamp sounds good.
Some great minds at diyaudio.com have, so far, been unable to find a
solution. The discussion-thread is here:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=116374
(Please ignore my embarrassing contributions to that thread.)
Here is a link to thumbnails of the preamp's schematics, pcb-layout
diagram, and photos:
http://home.comcast.net/~garyworld/site/?/photos/
[Please note that the filaments' (DC) supply's smoothing capacitance
is much larger than what is indicated on the power supply schematic.]
The grounding scheme is quite ugly, and IMO should at least eventually
be completely converted to a proper star-grounding scheme.
But my current thinking is that if we can solve the hum problem for
when the preamp is NOT powered, then we will probably have mostly
solved the problem for when it IS powered, probably with minimal
modifications.
Thanks, guys.
- Tom Gootee
Check your rectifier, use Inductance+Cap as your filter, and Do not
overload
your final Tube.
The waving at the top of your DC supply is where you need to clean up.
Stick an AC volt-meter on DC line to check your progress. This tip brought
to you from the Retarded Community

Thanks for the tips, MooseFET.

But none of that would explain why it also causes hum when it is not
even powered on.

Then your suspected target is not the cause of the hummmmmmmmmm..........



Sounds like a "ground loop" to me. You must allow only one path
between your system and earth. Isolate all the round grounding pins on
power cords (green wire).
Not paying attention to this allows a.c. current to flow in your
signal return connections, inducing him, whether the "offending
unit's" power is on or off.

Fred
 
J

JeffM

Jan 1, 1970
0
tom@ fullnet.com said:
Thanks for the tips, MooseFET.
- Tom Gootee

Unless Ken had a brain aneurysm AND switched providers,
this is a hijacked identity.

I suspect this is the same 13 year old
who hijacked Mike Terrell's identity previously.
 
J

Jim Thompson

Jan 1, 1970
0
Unless Ken had a brain aneurysm AND switched providers,
this is a hijacked identity.

I suspect this is the same 13 year old
who hijacked Mike Terrell's identity previously.

And mine.

...Jim Thompson
 
I am sorry if this is slightly off-topic for this group. But you are
the ones I trust the most.
There is a guy who has built a tube-based preamp, from a commercial
DIY kit. The preamp causes significant hum at the main amplifier's
output, even when the preamp is NOT powered, and also when unpowered
and unplugged. (It also causes hum when powered.) Other signal
sources do not cause hum when connected to the amplifier. Other than
the hum, the preamp sounds good.
Some great minds at diyaudio.com have, so far, been unable to find a
solution. The discussion-thread is here:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=116374
(Please ignore my embarrassing contributions to that thread.)
Here is a link to thumbnails of the preamp's schematics, pcb-layout
diagram, and photos:
http://home.comcast.net/~garyworld/site/?/photos/
[Please note that the filaments' (DC) supply's smoothing capacitance
is much larger than what is indicated on the power supply schematic.]
The grounding scheme is quite ugly, and IMO should at least eventually
be completely converted to a proper star-grounding scheme.
But my current thinking is that if we can solve the hum problem for
when the preamp is NOT powered, then we will probably have mostly
solved the problem for when it IS powered, probably with minimal
modifications.
Thanks, guys.
- Tom Gootee
Check your rectifier, use Inductance+Cap as your filter, and Do not
overload
your final Tube.
The waving at the top of your DC supply is where you need to clean up.
Stick an AC volt-meter on DC line to check your progress. This tip brought
to you from the Retarded Community
Thanks for the tips, MooseFET.
But none of that would explain why it also causes hum when it is not
even powered on.
Then your suspected target is not the cause of the hummmmmmmmmm...........

Sounds like a "ground loop" to me. You must allow only one path
between your system and earth. Isolate all the round grounding pins on
power cords (green wire).
Not paying attention to this allows a.c. current to flow in your
signal return connections, inducing him, whether the "offending
unit's" power is on or off.

Fred

In the preamp, all circuit and signal i/o grounds now connect to the
chassis through only one point, and there is a 'safety disconnect'
network between that point and the chassis, consisting of 10R, 0.1uF,
and anti-parallel diodes, all in parallel. Only the earth ground
connects directly to the chassis. The chassis is steel, by the way.

The preamp causes hum even when unplugged.

But, when plugged in, the earth ground should stay connected to the
chassis, and to the circuit etc (only) through the disconnect network,
for safety (and maybe even legal) reasons, right?
 
S

Spehro Pefhany

Jan 1, 1970
0
And mine.

...Jim Thompson


Hijacking something that old is more along the lines of salvage. ;-)

Happy BD!

Best regards,
Spehro Pefhany
 
J

Jim Thompson

Jan 1, 1970
0
Hijacking something that old is more along the lines of salvage. ;-)

Happy BD!

Best regards,
Spehro Pefhany

Thanks! (I think ;-)

...Jim Thompson
 
Unless Ken had a brain aneurysm AND switched providers,
this is a hijacked identity.

I suspect this is the same 13 year old
who hijacked Mike Terrell's identity previously.

OK. But he has at least attempted to contribute to the on-topic
portions of this thread, which is more than can be said for all of the
off-topic posts about his alleged identity hijacking.

To MooseFET:

Dude! Since you do know something about electronics, why not use your
own unique identity?

If you're as young as they say you are, then your level of electronics
knowledge is quite impressive.

And you can think whatever you want. But I gotta say I don't think ID
highjacking is too cool.

- Tom
 
L

legg

Jan 1, 1970
0
I am sorry if this is slightly off-topic for this group. But you are
the ones I trust the most.

There is a guy who has built a tube-based preamp, from a commercial
DIY kit. The preamp causes significant hum at the main amplifier's
output, even when the preamp is NOT powered, and also when unpowered
and unplugged. (It also causes hum when powered.) Other signal
sources do not cause hum when connected to the amplifier. Other than
the hum, the preamp sounds good.

Some great minds at diyaudio.com have, so far, been unable to find a
solution. The discussion-thread is here:

http://www.diyaudio.com/forums/showthread.php?s=&threadid=116374

(Please ignore my embarrassing contributions to that thread.)

Here is a link to thumbnails of the preamp's schematics, pcb-layout
diagram, and photos:

http://home.comcast.net/~garyworld/site/?/photos/

[Please note that the filaments' (DC) supply's smoothing capacitance
is much larger than what is indicated on the power supply schematic.]

The grounding scheme is quite ugly, and IMO should at least eventually
be completely converted to a proper star-grounding scheme.

But my current thinking is that if we can solve the hum problem for
when the preamp is NOT powered, then we will probably have mostly
solved the problem for when it IS powered, probably with minimal
modifications.

Sounds (reads) like you've tackled a lot of issues, so far. There's
always a problem with iterations, that makes it possible to
accidentally pass over or defeat solutions.

First thong to fix is hum when off. Ignore all other issues.

With hum present, disconnect all other equipment. Leave disconnected
until powered-off hum is solved. This includes your 'computer scope'.

These connections will just complicate things. Use your ears to
measure the hum. When you can't hear objectionable levels, the problem
is on the road to being solved.

trannybox - the orange wire should follow the brown wire from the AC
line socket to the switch. Twisting uses the least hardware. You are
switching the neutral wire in this photo. This could explain a 60Hz
hum when the preamp is off.

You said that you reversed wires going to the switch. This wording is
subject to misinterpretation. The live terminal of the IEC inlet
(brown wire in your trannybox photo) should go through the fuse, to
the switch. From the switched terminal the returning connection should
run to the transformer primary.I am surprised that both transformer
primary wires are colour-coded brown. The orange wire on the polarized
neutral of the IEC inlet should follow the brown wire to the switch
and return unbroken to the transformer primary. Twisting it around the
live wire uses less hardware to accomplish this routing.

This is actually how the wiring is laid out in the 'preamp1' photo,
using printed wiring, but without the polarized inlet. The 2-pin 120V
hardware can also be polarized - the wider blade is supposed to be
neutral. Old Dynaco hardware may predate this convention.

There is no ground wire connection. Assuming plastic hardware, this
would still have connected to the transformer case, followed by a lead
to the chassis of the target load, to allow for leakage current return
to safety earth. If not present, connect the transformer case to the
chassis, anyways, even from a remote plastic box.

Check the line cord phasing of the power amplifier, it should match
that of the preamp, even if line and neutral are not properly wired
into your wall socket.

The power supply schematic does not use the same transformer you are
using. The original has a colour-coded primary, a grounded
core/screen. If you have an isolation transformer, use this
temporarily for the preamp, power amp and combined set to see if
there's a difference one way or another.

Ignore other issues until powered-off hum is defeated.

RL
 
news:f48586f1-db70-4a87-9f55-afcaf247d168@e25g2000prg.googlegroups.com...
I am sorry if this is slightly off-topic for this group. But you are
the ones I trust the most.
There is a guy who has built a tube-based preamp, from a commercial
DIY kit. The preamp causes significant hum at the main amplifier's
output, even when the preamp is NOT powered, and also when unpowered
and unplugged. (It also causes hum when powered.) Other signal
sources do not cause hum when connected to the amplifier. Other than
the hum, the preamp sounds good.
Some great minds at diyaudio.com have, so far, been unable to find a
solution. The discussion-thread is here:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=116374
(Please ignore my embarrassing contributions to that thread.)
Here is a link to thumbnails of the preamp's schematics, pcb-layout
diagram, and photos:
http://home.comcast.net/~garyworld/site/?/photos/
[Please note that the filaments' (DC) supply's smoothing capacitance
is much larger than what is indicated on the power supply schematic.]
The grounding scheme is quite ugly, and IMO should at least eventually
be completely converted to a proper star-grounding scheme.
But my current thinking is that if we can solve the hum problem for
when the preamp is NOT powered, then we will probably have mostly
solved the problem for when it IS powered, probably with minimal
modifications.
Thanks, guys.
- Tom Gootee
Check your rectifier, use Inductance+Cap as your filter, and Do not
overload
your final Tube.
The waving at the top of your DC supply is where you need to clean up.
Stick an AC volt-meter on DC line to check your progress. This tip brought
to you from the Retarded Community

Thanks for the tips, MooseFET.

But none of that would explain why it also causes hum when it is not
even powered on.
Then your suspected target is not the cause of the hummmmmmmmmm..........

But the amplifier hums when the preamp is its signal source, and
doesn't hum with any other signal source. And it hums with the preamp
as it source whether or not the preamp is powered, unpowered, or
unplugged.

As I said, it's 'vexing'.

Whoever solves this one will be given genius/hero credit, at
diyaudio.com .

- T
 
I am sorry if this is slightly off-topic for this group.  But you are
the ones I trust the most.
There is a guy who has built a tube-based preamp, from a commercial
DIY kit.  The preamp causes significant hum at the main amplifier's
output, even when the preamp is NOT powered, and also when unpowered
and unplugged.  (It also causes hum when powered.)  Other signal
sources do not cause hum when connected to the amplifier.  Other than
the hum, the preamp sounds good.
Some great minds at diyaudio.com have, so far, been unable to find a
solution.  The discussion-thread is here:

(Please ignore my embarrassing contributions to that thread.)
Here is a link to thumbnails of the preamp's schematics, pcb-layout
diagram, and photos:

[Please note that the filaments' (DC) supply's smoothing capacitance
is much larger than what is indicated on the power supply schematic.]
The grounding scheme is quite ugly, and IMO should at least eventually
be completely converted to a proper star-grounding scheme.
But my current thinking is that if we can solve the hum problem for
when the preamp is NOT powered, then we will probably have mostly
solved the problem for when it IS powered, probably with minimal
modifications.

Sounds (reads) like you've tackled a lot of issues, so far. There's
always a problem with iterations, that makes it possible to
accidentally pass over or defeat solutions.

First thong to fix is hum when off. Ignore all other issues.

With hum present, disconnect all other equipment. Leave disconnected
until powered-off hum is solved. This includes your 'computer scope'.

These connections will just complicate things. Use your ears to
measure the hum. When you can't hear objectionable levels, the problem
is on the road to being solved.

trannybox - the orange wire should follow the brown wire from the AC
line socket to the switch. Twisting uses the least hardware. You are
switching the neutral wire in this photo. This could explain a 60Hz
hum when the preamp is off.

You said that you reversed wires going to the switch. This wording is
subject to misinterpretation. The live terminal of the IEC inlet
(brown wire in your trannybox photo) should go through the fuse, to
the switch. From the switched terminal the returning connection should
run to the transformer primary.I am surprised that both transformer
primary wires are colour-coded brown. The orange wire on the polarized
neutral of the IEC inlet should follow the brown wire to the switch
and return unbroken to the transformer primary. Twisting it around the
live wire uses less hardware to accomplish this routing.

This is actually how the wiring is laid out in the 'preamp1' photo,
using printed wiring, but without the polarized inlet. The 2-pin 120V
hardware can also be polarized - the wider blade is supposed to be
neutral. Old Dynaco hardware may predate this convention.

There is no ground wire connection. Assuming plastic hardware, this
would still have connected to the transformer case, followed by a lead
to the chassis of the target load, to allow for leakage current return
to safety earth. If not present, connect the transformer case to the
chassis, anyways, even from a remote plastic box.

Check the line cord phasing of the power amplifier, it should match
that of the preamp, even if line and neutral are not properly wired
into your wall socket.

The power supply schematic does not use the same transformer you are
using. The original has a colour-coded primary, a grounded
core/screen. If you have an isolation transformer, use this
temporarily for the preamp, power amp and combined set to see if
there's a difference one way or another.

Ignore other issues until powered-off hum is defeated.

RL


"> First thong to fix is hum when off. Ignore all other issues."

First things first: I wouldn't want to fix 'thongs'. I'd want to
unfix them. And I always ignore all other issues when the thong is
off and there's a hum. :)) [Sorry. Couldn't stop myself.]

THANKS, RL! After first quick read, it sounds like you have
uncovered some significant-sounding issues that have NOT yet been
mentioned in the diyaudio.com thread! I will paste your post into
the discussion over there, if you don't object.

And I certainly agree that solving the hum problem for when the preamp
is unpowered is probably the key.
 
M

Michael A. Terrell

Jan 1, 1970
0
I am sorry if this is slightly off-topic for this group. But you are
the ones I trust the most.
There is a guy who has built a tube-based preamp, from a commercial
DIY kit. The preamp causes significant hum at the main amplifier's
output, even when the preamp is NOT powered, and also when unpowered
and unplugged. (It also causes hum when powered.) Other signal
sources do not cause hum when connected to the amplifier. Other than
the hum, the preamp sounds good.
Some great minds at diyaudio.com have, so far, been unable to find a
solution. The discussion-thread is here:

(Please ignore my embarrassing contributions to that thread.)
Here is a link to thumbnails of the preamp's schematics, pcb-layout
diagram, and photos:

[Please note that the filaments' (DC) supply's smoothing capacitance
is much larger than what is indicated on the power supply schematic.]
The grounding scheme is quite ugly, and IMO should at least eventually
be completely converted to a proper star-grounding scheme.
But my current thinking is that if we can solve the hum problem for
when the preamp is NOT powered, then we will probably have mostly
solved the problem for when it IS powered, probably with minimal
modifications.
Thanks, guys.
- Tom Gootee

Check your rectifier, use Inductance+Cap as your filter, and Do not overload
your final Tube.

The waving at the top of your DC supply is where you need to clean up.
Stick an AC volt-meter on DC line to check your progress. This tip brought
to you from the Retarded Community

Thanks for the tips, MooseFET.

But none of that would explain why it also causes hum when it is not
even powered on.


|------||-----|
| DO NOT |
| FEED THE |
| aioe.org |
| TROLL! |
|------||-----|
||
||
||
/|\\|/||||//|||/\???\\//\\\\/|?\/
--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
 
J

JeffM

Jan 1, 1970
0
Spehro said:
Hijacking something that old is more along the lines of salvage. ;-)
Jeez. Warn a guy so he can put down his beverage. :cool:

Have a happy day, JT.
 
J

Jim Thompson

Jan 1, 1970
0
Jeez. Warn a guy so he can put down his beverage. :cool:

Have a happy day, JT.

Thanks! Feels just like any other day... happy, happy ;-)

...Jim Thompson
 
R

Rich Grise

Jan 1, 1970
0
But none of that would explain why it also causes hum when it is not
even powered on.

Your preamp has a loose ground on its output, and is acting like an
antenna.

Good Luck!
Rich
 
And mine.

                                        ...Jim Thompson
--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus   |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat |
|      http://www.analog-innovations.com          |    1962     |

         America: Land of the Free, Because of the Brave

It's your birthday?! "To the wine!", then, Jim.

I hope that your birthday is as happy as possible.

- Tom Gootee
 
J

Jim Thompson

Jan 1, 1970
0
And mine.

                                        ...Jim Thompson
[snip]

It's your birthday?! "To the wine!", then, Jim.

I hope that your birthday is as happy as possible.

- Tom Gootee

Thanks! I won't disappoint you ;-)

...Jim Thompson
 
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