Kel84 Hum

[Rocky]

Hi all, as you can see I am a newbie to this forum and I am also a newbie to valve amplifiers although I have been into Hi-Fi for some 35 years.
I have just finished building a Kel84 amp that I bought some two years ago and would like to ask you experts some questions.
The mains transformer on the amp is humming quite loudly and I would like some advice on how to maybe eliminate/reduce this. There are two plastic spacers on the top and bottom of the transformer which should isolate it from the chassis but it still hums.
Secondly, I am driving Quad 10L speakers which have an sensitivity of 84dbs and 8 ohm impedance. This is not the optimum I know but the room is not too large and I get a reasonably loud sound. I am however a little worried that I may drive the amp into clipping and damage my speakers. What is the audible effect of clipping so that I may recognise it when it happens?
Thirdly, to be a pain, another question. I have a slight hearing problem in that my right ear is not as good as my left and on other amps use the balance control to adjust the output. There is no balance control on the Kel84 and was wondering if I could add a resistor somewhere in the left channel to give the same effect.
Thanks in advance for any advice forthcoming.

Allen

[Rob042]

Allen
welcome to this 'mad' world.

transformer noise - is there humming coming throught the speakers? if not and all the noise is comng ftom around the tx I would - 1. check the incoming voltage and the voltages leaving the tx, the transformer could be worked to hard. while at it I would double check all the test point voltages to ( I find this best done with the amp plugged into where it will live as the voltages to the workshop are on ave 5% higher than in the house ).If that fails to show any problems check the rectifiers and earth wiring. Once you have done all that and you still get noise ... hmm

2. clipping - you'll know when you hear it, distorsion , a nasty sharping of the sonics. you'll know.

3.I have tinitus in one ear but have found that adjusting the angles of the speakers to be more effective than adding a balance control.Try that first, just in case it helps. Then maybe a balance pot.

hope this helps
Rob

[Rob042]

Allen
welcome to this 'mad' world.

transformer noise - is there humming coming throught the speakers? if not and all the noise is comng ftom around the tx I would - 1. check the incoming voltage and the voltages leaving the tx, the transformer could be worked to hard. while at it I would double check all the test point voltages to ( I find this best done with the amp plugged into where it will live as the voltages to the workshop are on ave 5% higher than in the house ).If that fails to show any problems check the rectifiers and earth wiring. Once you have done all that and you still get noise ... hmm

2. clipping - you'll know when you hear it, distorsion , a nasty sharpening of the sonics. you'll know.

3.I have tinitus in one ear but have found that adjusting the angles of the speakers to be more effective than adding a balance control.Try that first, just in case it helps. Then maybe a balance pot.

hope this helps
Rob

[Rocky]

Hi Rob

Thanks for the welcome and response to the post.

There is no hum coming through the speakers and I did check all the test voltages when I had completed building the amp and they were well within tolerances. However, I will check them again and look in the area you have suggested.

I will also try adjusting the angle of my speakers to see if I can alleviate the balance problem.

Allen

[John Caswell]

Hi Allen,
First the level problem, is the amplifier a plain amp or does it have input selection?

Regards

John aka Dr John

[Rocky]

Hi John

The amp has input selection.

Regards
Allen

[Richard]

Hello and welcome Allen,

There's a balance control here, you just need a 250k linear 2 gang pot,

http://www.world-designs.co.uk/forum...read.php?t=148




Rich