[babyoh]

My Cary 300SEI has some background hum. I changed the output tubes and reduced the hum to a minimum. But it's still not completely silent with the volume turned all the way down. I can't hear it with full size speakers but I can hear it with headphones. Is this normal with tube amps?

 

[928GTS]

How bad is it with headphones? Some designs just hum due to their layout and sometimes the wire routing can be made to be a bit cleaner and tighter to reduce hum.

 

[Rob N]

IME the Cary does have some hum with low impedance Grados

 

[babyoh]

Quote:

Originally Posted by 928GTS /img/forum/go_quote.gif How bad is it with headphones?

I can hear it when there's no music playing. But I can't hear it as long as there's some music playing to mask the hum.

 

[928GTS]

Quote:

Originally Posted by babyoh /img/forum/go_quote.gif I can hear it when there's no music playing. But I can't hear it as long as there's some music playing to mask the hum.

Don't worry about it,I have a tube amp that does that to the same level. As I said its just a part of some designs be it from a combination of parts or chassis layout requiring some wires to be routed rather close to each other.

 

[hypoicon]

You might try lifting the ground to see if that makes it disappear. I've owned a lot of tube amps over the years that never hummed, including the Little Dot MK III. Several people have complained about hum in that amp, but I've heard that using a ground lift plug usually takes care of it.

 

[scootermafia]

The stock tube doesn't hum with my 336SE, but other 6SN7s so far hum.

 

[BigTony]

I found NOS tubes can take a while to settlr, much longer than i thought. Just leave it running for a few long spells, see if it clears up.

 

[babyoh]

Quote:

Originally Posted by hypoicon /img/forum/go_quote.gif You might try lifting the ground to see if that makes it disappear. I've owned a lot of tube amps over the years that never hummed, including the Little Dot MK III. Several people have complained about hum in that amp, but I've heard that using a ground lift plug usually takes care of it.

I don't think it's a good idea to float the ground given the lethal voltage running inside the tube amp. It's there to save you in case something goes very wrong. If it's a CD player, I'll give it a try.

 

[hypoicon]

Quote:

Originally Posted by babyoh /img/forum/go_quote.gif I don't think it's a good idea to float the ground given the lethal voltage running inside the tube amp. It's there to save you in case something goes very wrong. If it's a CD player, I'll give it a try.

I think that's mostly bull. Vintage tube equipment frequently has two-wire cords to begin with and the shock hazard is pretty minimal. The main reason for a ground lead is to accelerate the response of a circuit breaker in case of a failure-- there aren't generally stray voltages drifting around just for the heck of it, particularly lethal ones. That happens during a short that causes a failure (i.e. smoke).

 

[928GTS]

Quote:

Originally Posted by hypoicon /img/forum/go_quote.gif I think that's mostly bull. Vintage tube equipment frequently has two-wire cords to begin with and the shock hazard is pretty minimal. The main reason for a ground lead is to accelerate the response of a circuit breaker in case of a failure-- there aren't generally stray voltages drifting around just for the heck of it, particularly lethal ones. That happens during a short that causes a failure (i.e. smoke).

Have you ever heard of a floating ground? Back in the day manufacturers would "simulate" a ground using a relatively simple circuit involving a few capacitors known as "death caps" due to the reason that when they failed live voltage would often present itself across the chassis.

Ever wonder why so many vintage guitar amplifiers have been converted to a 3 prong plug?

 

[Skylab]

Quote:

Originally Posted by Rob N /img/forum/go_quote.gif IME the Cary does have some hum with low impedance Grados

>> MANY tube amps have some hum with low impedance headphones, especially OTL tube amps. I don;t know anything about the Cary, but this might be something that only high-impedance headphones would alleviate.

Quote:

Originally Posted by scootermafia /img/forum/go_quote.gif The stock tube doesn't hum with my 336SE, but other 6SN7s so far hum.

>> This is an issue unique to the DV336 - there is a fix for it, search "Fitz hum mod"

Quote:

Originally Posted by BigTony /img/forum/go_quote.gif I found NOS tubes can take a while to settlr, much longer than i thought. Just leave it running for a few long spells, see if it clears up.

>> Yep - very common. Usually clears up by 10-12 hours max though.

Quote:

Originally Posted by hypoicon /img/forum/go_quote.gif You might try lifting the ground to see if that makes it disappear. I've owned a lot of tube amps over the years that never hummed, including the Little Dot MK III. Several people have complained about hum in that amp, but I've heard that using a ground lift plug usually takes care of it.

>> This doesn't sound like the problem here, but it's possible. Does the hum increase as you increase the volume level?

 

[babyoh]

Quote:

Originally Posted by Skylab /img/forum/go_quote.gif >> This doesn't sound like the problem here, but it's possible. Does the hum increase as you increase the volume level?

No, it stays the same. The music just masks the hum.

 

[scootermafia]

Yeah, I don't have the guts to screw around with the internals of the 336SE anymore. Does anyone know why the stock tube doesn't hum but 3 other ones do? If this mod was really necessary then all tubes would hum with it. I guess it's something subtle, electrically.

 

[Skylab]

My 336SE hums with some 6SN7's, but not with others. Most for me actually have been fine. Not sure what the difference is in what works and what doesn't.