Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Leevi on September 05, 2016, 10:55:46 am

Title: Relay causes hum
Post by: Leevi on September 05, 2016, 10:55:46 am

I have met this problem many times before. What is a good way to power a relay?


I have noticed that when taking voltage from the heater source there will be problems with hum especially
when the relay is energized. I think the hum will come through the heaters to the circuit?
This can be solved with big filter caps in power supply of the relay but not fully. I have even used voltage regulator
like 7805 but it does not help.


An optimal way is if the PT has two 6.3V secondaries.


One solution is to add a separate transformer for the relay.


Any other ways?


/Leevi

Title: Re: Relay causes hum
Post by: Tone Junkie on September 07, 2016, 09:01:08 pm

Leevi I think Geezer figured a way he hung a 100 ohm resister from one side of the reley and it killed the hum. I have one on an on off switch and when tracing a noise will clip then turn it on then off I have killed a few hums that way. Often hanging on the relay. some in other places.
Bill

Title: Re: Relay causes hum
Post by: jojokeo on September 08, 2016, 02:40:27 am

Quote from: Leevi on September 05, 2016, 10:55:46 am

Any other ways?

Using Doug's separate regulated power supply board from the relay board, then mind your lead dress and mine are dead quiet. Also certain relays are quiet and others are not. Using the type Doug supplies you can be sure this won't be your issue.

Title: Re: Relay causes hum
Post by: tubenit on September 08, 2016, 07:18:34 am

Doug's relay power supply boards and his relays are dead quiet in every amp I've used them in.  Dead quiet switching and at idle.


With respect, Tubenit

Title: Re: Relay causes hum
Post by: EL34 on September 08, 2016, 07:22:53 am

It can be several things

It can be the relay itself you are using - relay types do make a difference
Or where you have run the signal wires - too close to a hum source
Or where the relay is mounted - too close to a fuse holder, etc

Title: Re: Relay causes hum
Post by: Leevi on September 08, 2016, 08:53:31 am

Thanks for the replies and tips.
/Leevi

Title: Re: Relay causes hum
Post by: Leevi on September 08, 2016, 11:54:09 am

I usually put a diode and resistor across the coil which decreases popping


https://www.google.fi/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwihlvjCnYDPAhUFhywKHb7CB_MQjRwIBw&url=http%3A%2F%2Felectronics.stackexchange.com%2Fquestions%2F115857%2Fflyback-diodes-and-relays&psig=AFQjCNGXHtW67mjMLfQ0Ca0xTMAk-KfpJA&ust=1473439905347279 (https://www.google.fi/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwihlvjCnYDPAhUFhywKHb7CB_MQjRwIBw&url=http%3A%2F%2Felectronics.stackexchange.com%2Fquestions%2F115857%2Fflyback-diodes-and-relays&psig=AFQjCNGXHtW67mjMLfQ0Ca0xTMAk-KfpJA&ust=1473439905347279)


/Leevi

Title: Re: Relay causes hum
Post by: Merlin on September 14, 2016, 05:36:11 am

It is easy enough to feed clean DC to the relay using a resistor and a big cap.
However, if you still get buzz then it may in fact be due to running a rectifier off the heater supply, which will therefore corrupt the heater waveform (make it clipped and ringy). You can cure ringing with an RC combo across the heater supply (try 10n + 4.7k) and by using fast rectifiers. A humdinger is also worth a try.

Title: Re: Relay causes hum
Post by: EL34 on September 14, 2016, 02:47:45 pm

Note that the first time I added relay switching to my original Stout project, I had a bunch of hum
Look where the relay is in the pic
Right next to incoming AC
Power cord, fuse holder and switch


I added the brass shield around the relay and it became hum free
The shield is grounded to the chassis
That's why I said up above that hum can be other sources than what you may be thinking it is

The signal wiring coming to and leaving the relay can be a source also

http://el34world.com/projects/images/DSCN1697.JPG (http://el34world.com/projects/images/DSCN1697.JPG)


(http://el34world.com/projects/images/DSCN1697.JPG)

Title: Re: Relay causes hum
Post by: Leevi on September 15, 2016, 11:05:23 am

Quote

I added the brass shield around the relay and it became hum free

Good to know, that's definitely worth to try

I remember one case when I had similar problem.
Fortunately I had two 6.3V secondaries in the PT and after I had reserved the second one for the relay only the hum was totally gone.
Of course the root cause might have been wiring related in this case as well.

/Leevi

Title: Re: Relay causes hum
Post by: kagliostro on September 15, 2016, 03:00:16 pm

There are also relay with metal casing

(this is 24v but other voltages are available

http://uk.rs-online.com/web/p/reed-relays/2173318/ (http://uk.rs-online.com/web/p/reed-relays/2173318/)

(http://uk.rs-online.com/largeimages/F2173318-01.jpg)

Ciao

Franco

Title: Re: Relay causes hum
Post by: EL34 on September 16, 2016, 12:29:13 pm

In my case, it was only a problem because of where the relay was located

A shield is not needed if the relay is located in a proper spot

Title: Re: Relay causes hum
Post by: kagliostro on September 16, 2016, 03:13:59 pm

Of couse Doug

Franco