choke filter inducing noise

[EETStudent]

Ive been to go with a choke filter so I can use lower voltage power tubes, but its just too noisy. Cap filter has minimal noise issues. With the choke, i tried troubleshooting various noisy suspects. My PPIMV did affect the noise some, but with that removed it was still there. As with the regular volume control. I dont know, maybe chokes(or mine in particular) are just noisier??

[tubeswell]

Hmmm.. I don't know why a chole would be 'noisier'.

Is your amp fixed- or cathode- baised?

[tubeswell]

Hmmm... I don't know why a choke would be 'noisier'.

Is your amp fixed- or cathode- baised?

[tubeswell]

Whoops! (two for the price of one )

[Enzo]

You don't mention WHAT noise. Hum? I tend to use hum for hum and reserve noise for things like hiss and crackle/pop.

I don't know why a choke would be noisy either, unless you mounted it so the transformer fields couple into it. Take out the screws and rotate it 90 degrees.

[Bruce / Mission Amps]

You don't mention WHAT noise. Hum? I tend to use hum for hum and reserve noise for things like hiss and crackle/pop. I don't know why a choke would be noisy either, unless you mounted it so the transformer fields couple into it. Take out the screws and rotate it 90 degrees.....

Or, possibly forgot to put the filter cap after the choke....

[Enzo]

Um, that wouldn't sound good.

[Paul P]

Ive been to go with a choke filter so I can use lower voltage power tubes, but its just too noisy.

Does your choke have a suitable current rating ? You can't just take
a choke from a capacitor input filter and stick it before the first cap
as the current requirements are quite different. With a choke input
filter the choke has to handle all of the current your amp uses whereas
with a capacitor input filter the current of the power tubes does not
go through the choke.

Paul P

[Steve Conner]

The choke in a choke input filter also runs with a much bigger AC magnetic field than in a capacitor input filter. That means a lot of acoustic buzz, and because chokes have an airgap, the magnetic field spills out easily and induces hum in everything else.

You don't have to worry about transformer fields coupling into it like Enzo suggested: it's the opposite, it induces crud into everything else. If the choke saturates, that makes everything even worse, with more acoustic and magnetic buzzing noises.

Have you tried attaching the choke on some 6 foot long wires and putting it over on the other end of the bench? I know this isn't practical for your finished amp, but if it cures the noise problem, you proved that it's caused by magnetic induction like I said above, so you know you need to go shopping for a better choke.

[Enzo]

Oh... Live and learn.

[Wakculloch]

Just been looking at some old MO valve stuff. Many of their higher powered amps used swinging chokes and they all had snubber networks across the choke, usually a 10n cap and a 10k resistor in series.
Don't know what these components do; -
but in trying to find out came across this little jem:-
"If series resonance occurs in L and C of the filter, large alternating voltages will build up and the reverse of smoothing will result. To avoid this, the product of the inductance in henries times the capacitance in uf should not be lower than 5..........a large safety margin is essential."

[Rob Mercure]

What MOV is getting at is the frequency of series resonant circuits which the inductor and the first capacitor would form across the rectified voltage. I don't know how to display a formulae here, but it is determined by dividing into 1 the 2 X pi X the square root of the product of the inductance (henries) times the capacitance (farads). Essentially you don't want to have this add up to a multiple of the power line frequency or probably a sub multiple either, I dunno.

If you've got a spreadsheet program, such as Excel, it's easy to set up it up to calculate this and other electronics stuff - but when I was a teenager a "calculator" was me and a slide rule and determining this stuff was much, much fun (yeah, right, and so are hemmoroids - or so I'm told <grin>).

Rob

[Rob Mercure]

What MOV is getting at is the frequency of series resonant circuits which the inductor and the first capacitor would form across the rectified voltage. I don't know how to display a formulae here, but it is determined by dividing into 1 the 2 X pi X the square root of the product of the inductance (henries) times the capacitance (farads). Essentially you don't want to have this add up to a multiple of the power line frequency or probably a sub multiple either, I dunno.

If you've got a spreadsheet program, such as Excel, it's easy to set up it up to calculate this and other electronics stuff - but when I was a teenager a "calculator" was me and a slide rule and determining this stuff was much, much fun (yeah, right, and so are hemmoroids - or so I'm told <grin>).

Rob

[Rob Mercure]

Poop, sorry for the double post - my machine locked up on sending the first on and I didn't realize that it had gone through - my apologies folks.

[Bruce / Mission Amps]

Poop, sorry for the double post - my machine locked up on sending the first on and I didn't realize that it had gone through - my apologies folks.

No. I don't think so.
IMHO it is not your machine... because the same thing happens to me frequently here on the MEF and nowhere else... I post at a number of other forums and never have that happen.
Something is going on here that causes that but I have no clue what it is, unless the server is shared with something else that puts the MEF on the far back burner with no gas for a minute or two.