Need experts for vexing hum problem

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.

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ght

Thanks for the tips, MooseFET.

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

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..........

ht

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

tom@ fullnet.com wrote:

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

-- | 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 | |

..

ly

ught

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?

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

Happy BD!

Best regards, Spehro Pefhany

Thanks! (I think ;-)

...Jim Thompson

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

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

ht

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

"> 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.

|------||-----| | DO NOT | | FEED THE | | aioe.org | | TROLL! | |------||-----| || || || /|\\\\|/||||//|||/\\???\\\\//\\\\\\\\/|?\\/

Jim Thomps>>And mine.

Spehro Pefhany wrote:

Jeez. Warn a guy so he can put down his beverage. 8-)

Have a happy day, JT.

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

...Jim Thompson

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

Good Luck! Rich

=A0 =A0 ...Jim Thompson

=A0 =A0 | =A0 =A0mens =A0 =A0 |

=A0 | =A0 =A0 et =A0 =A0 =A0|

=A0|

=A0 =A0 =A0 =A0 =A0 |

=A0|

=A01962 =A0 =A0 |

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