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SUPPORT FORUMS FOR ZKITS >> ZKIT 1 Support forum >> ZKIT1 Hum
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Message started by Mike B on 06/21/13 at 16:53:56

Title: ZKIT1 Hum
Post by Mike B on 06/21/13 at 16:53:56

All of the previous posts on this topic have vanished, so I will try again.
Just completed a ZKit1 and I have 5.5mv of hum at the speaker terminals.

I tried several input tubes, but no change.  I used tube rectification so I swap out the rectifier tube for new one, no change.

I removed the input tube, as per Steve D's blog, this eliminated the hum.  Voltage at the speaker terminals is 1.7mv. So this indicates the problem is in the input circuitry.

 I am going to isolate the chassis ground from the AC supply ground just to eliminate another source of the problem.

Any recommendations will be appreciated.  I'll try to post a picture when the forum allows me.

Mike B

Title: Re: ZKIT1 Hum
Post by Mike B on 06/21/13 at 16:55:46

Here is a picture of the components.

Title: Re: ZKIT1 Hum
Post by mboxler on 06/22/13 at 14:18:21

Hi Mike

I see you didn't use the 100 ohm CT resistors for the heaters.  Does your PT have a CT for the heaters?  Can the hum be created from the input tube heaters?  

Mike

Title: Re: ZKIT1 Hum
Post by Mike B on 06/22/13 at 15:25:50

Mike, the heater supply is center tapped.  The heater voltage is equal on both legs.  

The only voltage differences I found is the plate voltage on the 6n1p, pin 1 and 6, there is a 10 vdc difference, pin 1 reads 126 vdc pin 6 reads 136 vdc.  the voltage feeding the 47k resistor is the same, so one of the 47k resistors may be suspect.  This is just a swag (statistical wild ass guess) but it is and easy change so what the heck.

Mike B

Title: Re: ZKIT1 Hum
Post by Mike B on 06/24/13 at 03:40:20

Problem solved.  After much checking and verifying, I decided the hum was due to ripple on the mains.  I added a RC filter just after the rectifier tube.  After installing, the hum was inaudible and the voltage on the speaker outs went from 5.5mv to 1.7mv.  All is good.

Thanks for the comments.

Mike B

Title: Re: ZKIT1 Hum
Post by Lon on 06/24/13 at 14:03:15

Good news!

Title: Re: ZKIT1 Hum
Post by Raduschka on 05/01/14 at 02:28:12

Hello Mike and everyone else,

I'm about to rebuild the zen kit1 with new parts (and original trasnformers) in a metal chassis and I hope it will be hum free. Is it possible to please describe the RC filter you implemented so that I may use it?  just in case I have to... I'll be using a 5u4g rectifier and mimicking the youtube building instructions.

Thank you in advance


Title: Re: ZKIT1 Hum
Post by Raduschka on 05/01/14 at 02:29:55

...Greetings Lon!

Title: Re: ZKIT1 Hum
Post by Lon on 05/01/14 at 03:02:28

Howdy! Long time no see. Love that pic!

Title: Re: ZKIT1 Hum
Post by Raduschka on 06/01/14 at 01:45:23

Howdy, I have just completed a zenkit1 inside a metal chassis and have the eternal hum problem... I'm about to give it another listen with a 47uf in parallel with the 33uf C2, see if that changes anything... By the looks of it, do you think I'm doing something wrong?

https://www.flickr.com/photos/71648043@N02/14312934511

https://www.flickr.com/photos/71648043@N02/14314439792/

Title: Re: ZKIT1 Hum
Post by dank on 06/02/14 at 12:41:57

Raduschka

What jumps out at me is the VERY long runs from the input jacks to the volume control pots.  This is a very sensitive-to-noise area.  What kind of wire is that?  Is it coax?  just 2 straight wires covered with a plastic jacket?  twisted pair?  I would guess it needs to be coax and that might not even be good enough (may need to re-locate RCA's).

Do you have hum problems on both channels, with the hum still bad when the volume is all the way down and the source is unplugged?  If so, I'd try a few things:

1)  remove the input tube (6n1p?).  Does all the hum go away?  If so the problem is (probably) before or in the input stage.

2)  On one channel, remove the wires from the RCA to the pot AT THE POT and solder a temporary jumper to the pot where the 2 wires to the RCA use to be (so you are grounding the input signal on this channel AT THE POT after disconnecting the long wires to the input jack).  On the other channel, solder a temporary jumper to the RCA (so you are grounding the input signal on this channel AT THE RCA).  If the grounded at the RCA channel hums and the grounded at the pot channel doesn't you've found the problem.

Dan

Title: Re: ZKIT1 Hum
Post by Raduschka on 04/11/16 at 02:43:34

Hello Dan,

i browsed the forum for answers. ..again...and I noticed you had posted in this topic. I somehow missed it. Sorry!
I am still trying to solve the hum....


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