Preamp with humming noise!

Matthewong · 18th May 2011, 10:51 AM

Hi, I have an old tube preamp which my friend sold to me. The problem with this preamp is whenever I plug in the CD player output to the preamp input, the humming sound start to scream. When disconnect the RCA from CD player, the humming sound will stop immediately, no matter whether the CD player is on or off. I did try other sources, like cassette player, DVD player... all also the same. What is the problem for the preamp and how to solve this problem????

rsumperl · 18th May 2011, 11:07 AM

Most CD players have a high signal level output (~2v) that is probably overloading the pre-amp. Most pre-amps were used as additional amplification for magnetic phono cartridges. My CD player as well as my Sirius satellite radio have output levels of ~2v which drive Pete's red board to full volume.

Ray

Chris Daly · 18th May 2011, 12:33 PM

Use a L Pad divider ie 4 resistors - 2 for each channel to reduce the CD output to an acceptable level .

Cheers / Chris

chrish · 18th May 2011, 01:38 PM

I don't think signal level is the problem. Matthewong stated that the humming is loud when the CD player is plugged in "if it is on or off". To me, this sounds like a ground loop problem. Does any other line-level signal source cause this same problem? Maybe you have an iPod or similar non-mains powered device you can plug in to help see if it is a ground loop issue.

Cheers,

Chris

Andy5112405 · 18th May 2011, 02:10 PM

A lot of older equipment had the input RCA connectors connected to GND. This, as CHRIS says, can cause GROUND LOOP problems. You could try disconnecting the input sockets from the chassis to see what happens.

Matthewong · 20th May 2011, 11:17 AM

I have checked all the RCA input and output, found one of the RCA touched the body, so changed to new RCA socket and the humming noise reduced a lot. Now the humming noise is low, but still audible when my ear near the speaker. When I turn my volume to max, then the humming noise is loud, would like to know how can I totally kill the humming noise which is quite anoying. One of my friend told me that tube preamp will surely have some humming noise especially when turning the volume past 12'o clock mark, is that true????

18th May 2011, 10:51 AM	#1
Matthewong diyAudio Member Join Date: Jun 2005 Location: KL	Preamp with humming noise! Hi, I have an old tube preamp which my friend sold to me. The problem with this preamp is whenever I plug in the CD player output to the preamp input, the humming sound start to scream. When disconnect the RCA from CD player, the humming sound will stop immediately, no matter whether the CD player is on or off. I did try other sources, like cassette player, DVD player... all also the same. What is the problem for the preamp and how to solve this problem????

18th May 2011, 11:07 AM	#2
rsumperl diyAudio Member Join Date: Oct 2009 Location: Binghamton, NY	Most CD players have a high signal level output (~2v) that is probably overloading the pre-amp. Most pre-amps were used as additional amplification for magnetic phono cartridges. My CD player as well as my Sirius satellite radio have output levels of ~2v which drive Pete's red board to full volume. Ray __________________ A great pleasure in life is doing what people say you cannot do.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
F3 - Small humming noise, how to get rid of it	Nicola	Pass Labs	9	31st March 2010 09:27 AM
Musical Fidelity P270 Humming noise!	TheRambler	Solid State	1	5th February 2010 10:44 AM
Humming Noise, Problem?	MorePower7701	Solid State	2	26th December 2007 05:49 AM
Rotel RX950 with humming noise	jorgens	Solid State	1	28th March 2007 08:34 PM
Humming Noise in my amplifier???	lock dogg	Chip Amps	29	23rd February 2006 11:33 AM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read

18th May 2011, 12:33 PM	#3
Chris Daly diyAudio Member Join Date: Sep 2004 Location: hobart tasmania	Use a L Pad divider ie 4 resistors - 2 for each channel to reduce the CD output to an acceptable level . Cheers / Chris

18th May 2011, 01:38 PM	#4
chrish diyAudio Member Join Date: Oct 2003 Location: Sydney	I don't think signal level is the problem. Matthewong stated that the humming is loud when the CD player is plugged in "if it is on or off". To me, this sounds like a ground loop problem. Does any other line-level signal source cause this same problem? Maybe you have an iPod or similar non-mains powered device you can plug in to help see if it is a ground loop issue. Cheers, Chris

18th May 2011, 02:10 PM	#5
Andy5112405 Banned Join Date: Nov 2006 Location: Torpoint	A lot of older equipment had the input RCA connectors connected to GND. This, as CHRIS says, can cause GROUND LOOP problems. You could try disconnecting the input sockets from the chassis to see what happens.

20th May 2011, 11:17 AM	#6
Matthewong diyAudio Member Join Date: Jun 2005 Location: KL	I have checked all the RCA input and output, found one of the RCA touched the body, so changed to new RCA socket and the humming noise reduced a lot. Now the humming noise is low, but still audible when my ear near the speaker. When I turn my volume to max, then the humming noise is loud, would like to know how can I totally kill the humming noise which is quite anoying. One of my friend told me that tube preamp will surely have some humming noise especially when turning the volume past 12'o clock mark, is that true????

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)