Hum on ITT/KB KP040 - UK Vintage Radio Repair and Restoration Discussion Forum

BUSHVHF · 5th Sep 2018, 12:31 am

I have a very nice KP040 record player, everything seems fine but there is a very loud hum at full volume and it is quite pronounced at normal volume, also on turning off the volume knob there is a very loud CRACK and humming, what is the best way to eliminate this hum? seems to me there must be something in the amp as the hum increases dramatically as you turn up the volume. thnaks BUSHVHF

19Seventy7 · 5th Sep 2018, 12:56 am

This should help:

http://best-turntables.com/how-to-fix-turntable-hu/

Edward Huggins · 5th Sep 2018, 7:14 am

Probably an electrolytic capacitor failing in the power supply. What experience do you have of fault finding and repair on (transistor) amplifiers?

BUSHVHF · 5th Sep 2018, 11:10 pm

Hi Edward, well I havent any really, I normally send my stuff to a great audio engineer in Stockport, but I thought that this transistor amp has a very loud hum, I cant upload a vid here to show it working, with the volume knob turned right up it hums very louds then comes down as you tunr it down, but on normal playing vlume it is still a bit too audible, and then this HUGE Crackle/BANG when you turn off the volume, thats probably the pot itself but as the hum increases the higher you turn it up does seem to indicate a faulty cap somewhere. thnaks BushVHF

BUSHVHF · 5th Sep 2018, 11:12 pm

thanks but its not a turntable hum, I cant post a vid of how the volum knob increases an amplifier hum to a very loud hum at full volume but even are normal level the hum is still too noticable, such a shame as its a lovely ITT KP040 set otherwise, the Acos cartridg seems fine with a new flipover LP/78 stylus. thanks BUSHVHF

Grubhead · 6th Sep 2018, 12:56 am

If this is a stereo record player then if the hum is both channels it will be the largest capacitor in the unit, which gets rid of the 50Hz mains hum.

On a mono amp, it could still be that one, or a speaker output capacitor, hence the crackle when you switch off. The capacitor is leaking voltage into the speaker.

unitaudio · 6th Sep 2018, 1:22 am

If the hum decreases with volume, that should rule out the smoothing cap shouldn't it?

Regards,
Paul

crackle · 6th Sep 2018, 11:28 am

If the smoothing caps are faulty there will be hum on all of the supply line, including to the preamp stages.
When you turn the volume down you are putting a near short on the base of TX1.
I dont remember having problems with the smoothing caps in my KP040.
So I think I would check out the wiring to the pickup and deck first.
This record player has a separate mains transformer but you can get a lot of induced hum off the motor attached to the record deck and the wiring to the pickup is not normally screened.

Mike

BUSHVHF · 6th Sep 2018, 1:23 pm

OK thanks for those, I dont really what what it can be but I think the guy who fixes my things will be able to check the wiring from the tapping off the motor to the tone arm/cartridge and amp if it isnt screened and that is what is causing this loud hum, or the cap which could be leaking and causing the voltage to leak into the speaker, Im a bit of a dunce for repairs but I dont understand a bit about circuit diagrams and voltages and how caps and resistors are used to reduce and smooth out voltages. thnaks BUSHVHF (its a lovely looking KP040 with a garrard 2025 deck, tried to post a little vid. of the humming but it wont accept videos.

crackle · 7th Sep 2018, 6:39 am

You need to post your video on somewhere like Youtube, then put a link to that in a post here.
Mike

BUSHVHF · 24th Sep 2018, 11:08 am

Hi Crackle, I did post the video of the humming on my KP040 on youtube under my same name Bushvhf.

5th Sep 2018, 12:31 am	#1
BUSHVHF Tetrode Join Date: Oct 2014 Location: Manchester, UK. Posts: 71	Hum on ITT/KB KP040 I have a very nice KP040 record player, everything seems fine but there is a very loud hum at full volume and it is quite pronounced at normal volume, also on turning off the volume knob there is a very loud CRACK and humming, what is the best way to eliminate this hum? seems to me there must be something in the amp as the hum increases dramatically as you turn up the volume. thnaks BUSHVHF

5th Sep 2018, 12:56 am	#2
19Seventy7 Octode Join Date: Jun 2018 Location: Essex, UK. Posts: 1,307	Re: Hum on ITT/KB KP040 This should help: http://best-turntables.com/how-to-fix-turntable-hu/

5th Sep 2018, 7:14 am	#3
Edward Huggins Dekatron Join Date: Sep 2015 Location: Southwold, Suffolk, UK. Posts: 8,338	Re: Hum on ITT/KB KP040 Probably an electrolytic capacitor failing in the power supply. What experience do you have of fault finding and repair on (transistor) amplifiers? __________________ Edward.

5th Sep 2018, 11:10 pm	#4
BUSHVHF Tetrode Join Date: Oct 2014 Location: Manchester, UK. Posts: 71	Re: Hum on ITT/KB KP040 Hi Edward, well I havent any really, I normally send my stuff to a great audio engineer in Stockport, but I thought that this transistor amp has a very loud hum, I cant upload a vid here to show it working, with the volume knob turned right up it hums very louds then comes down as you tunr it down, but on normal playing vlume it is still a bit too audible, and then this HUGE Crackle/BANG when you turn off the volume, thats probably the pot itself but as the hum increases the higher you turn it up does seem to indicate a faulty cap somewhere. thnaks BushVHF

5th Sep 2018, 11:12 pm	#5
BUSHVHF Tetrode Join Date: Oct 2014 Location: Manchester, UK. Posts: 71	Re: Hum on ITT/KB KP040 thanks but its not a turntable hum, I cant post a vid of how the volum knob increases an amplifier hum to a very loud hum at full volume but even are normal level the hum is still too noticable, such a shame as its a lovely ITT KP040 set otherwise, the Acos cartridg seems fine with a new flipover LP/78 stylus. thanks BUSHVHF

6th Sep 2018, 12:56 am	#6
Grubhead Heptode Join Date: Dec 2016 Location: Sheffield, South Yorkshire, UK. Posts: 539	Re: Hum on ITT/KB KP040 If this is a stereo record player then if the hum is both channels it will be the largest capacitor in the unit, which gets rid of the 50Hz mains hum. On a mono amp, it could still be that one, or a speaker output capacitor, hence the crackle when you switch off. The capacitor is leaking voltage into the speaker.

6th Sep 2018, 1:22 am	#7
unitaudio Heptode Join Date: Sep 2013 Location: Manchester, UK. Posts: 862	Re: Hum on ITT/KB KP040 If the hum decreases with volume, that should rule out the smoothing cap shouldn't it? Regards, Paul __________________ ...No, it's not supposed to pick up the World Service, it's not a radio!

6th Sep 2018, 11:28 am	#8
crackle Rest in Peace Join Date: Mar 2011 Location: Basildon, Essex, UK. Posts: 4,100	Re: Hum on ITT/KB KP040 If the smoothing caps are faulty there will be hum on all of the supply line, including to the preamp stages. When you turn the volume down you are putting a near short on the base of TX1. I dont remember having problems with the smoothing caps in my KP040. So I think I would check out the wiring to the pickup and deck first. This record player has a separate mains transformer but you can get a lot of induced hum off the motor attached to the record deck and the wiring to the pickup is not normally screened. Mike

6th Sep 2018, 1:23 pm	#9
BUSHVHF Tetrode Join Date: Oct 2014 Location: Manchester, UK. Posts: 71	Re: Hum on ITT/KB KP040 OK thanks for those, I dont really what what it can be but I think the guy who fixes my things will be able to check the wiring from the tapping off the motor to the tone arm/cartridge and amp if it isnt screened and that is what is causing this loud hum, or the cap which could be leaking and causing the voltage to leak into the speaker, Im a bit of a dunce for repairs but I dont understand a bit about circuit diagrams and voltages and how caps and resistors are used to reduce and smooth out voltages. thnaks BUSHVHF (its a lovely looking KP040 with a garrard 2025 deck, tried to post a little vid. of the humming but it wont accept videos.

7th Sep 2018, 6:39 am	#10
crackle Rest in Peace Join Date: Mar 2011 Location: Basildon, Essex, UK. Posts: 4,100	Re: Hum on ITT/KB KP040 You need to post your video on somewhere like Youtube, then put a link to that in a post here. Mike

24th Sep 2018, 11:08 am	#11
BUSHVHF Tetrode Join Date: Oct 2014 Location: Manchester, UK. Posts: 71	Re: Hum on ITT/KB KP040 Hi Crackle, I did post the video of the humming on my KP040 on youtube under my same name Bushvhf.