Hello Folks

Just completed the build, all test points are good as per instructions. Sounds good, however there is strong hum noise from the speakers. Can someone please help me how to trouble shoot this issue? Checked ground points on the circuit board to frame all read zero. To note the signal coming in is balanced, so I connected pin 1&3 ends to board; pin 2 is signal.? I used another amp previously in exact same system, same wiring, etc. no hum so I know it's the ZKit amp for sure. Speakers are Lii-Audio F12


much appreciated

https://drive.google.com/file/d/1qVxc7ft_8eXCNkvSlKFrYHY7FHxXM7Y_/view?usp=drive...
https://drive.google.com/file/d/1BWsC9XHDGzEW6hqbUF1MThJf9hIU3HBV/view?usp=drive...

..

Hello,

Sorry your having problems. The only thing I can see on your photos is your running the amp wide open and the trannys are oriented in a way that any flux that might be leaking from the cans might be introduced into the inputs/output.

I would suggested fully enclosing the output trannies in a metal base along with the circuit board leaving the power transformer(with laminations positioned 90 degrees as compared to the output transformers) outside with the tubes. Your hum is most likely aggravated because the amp is shorted in the full volume setting.

John

OK, I'll just ask some basic questions because I'm an idiot about this kind of stuff.

Can you move your power cord to another outlet?

Is it both channels?

Is it the tubes that you have plugged into it?

I believe that JBzen meant turning your transformers 90 degrees clockwise from where they are and placing them on top of some simple steel shielding. At least that is how I read his post.

Look at Steve's other designs, the transformers are 90 degrees from each other.

Like I said, I'm pretty unschooled in such matters, but usually if you take a problem and break it down into it's basics something stands out.

seb,

Amuse me by trying different outlets.
As the old saying goes, "it don't cost nuthin".
Different amps, different results.

Remember, don't assume that anything is 100% right now.

Turn the PT 90 deg. so Edcor faces the side.

The blue/white wire is the UL tap not used in this amp.
Even with a preamp I really like a volume control on Decware amps.
Still a good idea to turn the power transformer.

You didn’t post if it hums without the input cables attached and I see you are unbalancing the signal at the pcb without an input transformer. That unbalances the entire length of the line to the source and removes the balanced line noise (and gain) advantage. Try shorting the input and see if the hum goes away, at least that would isolate the source of the noise.

You should measure and test the hum of the amp with inputs shorted to ground. If it hums in this configuration it is the amp. If you have volume control and hum changes with volume could be a ground loop/grounding. Input cables shield should be connected to board, and left floating at jacks.  Shield the input cables. If it isn't it is either a small hum due to ripple, or a loose solder joint. Typically ripple, which you can help resolve by doubling up second PS cap, is small consistent hum independent of volume close to speaker cones. If it is offensive eg hear loud from chair, then you have a might have a loose solder joint? The ripple hum can be annoying,  but you shouldn't hear it from your listening position. As things heat up sometimes a tenuous connection can cause hum.

Also, it appears you added a cap for CCE mod. Shouldn't this be connected between 3 and 6? Looks like you have 1 and 3 connected? I'd double check that too....

Best I got.

1 and 6 are internally connected, so 1 and 3 or 3 and 6 can be used.

Discovered The hum noise is much less when the preamp 6922 tube is removed

Well after of couple weeks of playing around, fixed some grounding issues and rotated the transformer.. a bit better but not perfect still a slight hum. I guess my conclusion it's a tube amp, not solid state class A and some noisr is expected


https://drive.google.com/file/d/1Fe2Syfc34T_UhXDmpv66qGamWp_tBk8c/view?usp=drive...

https://drive.google.com/file/d/1FFszxMNXWAVP1YsmA_mAROgR8EpyUuq_/view?usp=drive...

Thank you

If I wanted to upsize the power capacitors to quiet the ps down, which ones should I do and values?

I like the concept of it very mucj

What size would be needed and where does it go on this circuit? Would have to be a Edcor!

I used this choke: https://www.mouser.com/ProductDetail/Hammond-Manufacturing/158L?qs=sGAEpiMZZMsWX...

I also replaced the 1K/5W resistor with a 500 ohm one since the choke has a 400 ohm resistance.

The choke should mount inline and after the wirewound resistor between the two 33uF PS capacitors. In other words left of where you have it in your drawing.

DECWARE ZKIT #1 Hum/Buzz issue as well

Having similar, possibly related hum/buzz problems as you.  I do not want to hijack your thread and I have questions related to your experience (as it relates to mine).  Hoping for help, thanks

A. Transformer hum with or without inputs connected (heard at power transformer) - annoying, but not horrible

B. Mild hum heard through speakers when nothing is connected to the RCA inputs

C. Loud “harsh sounding” hum/buzz through the speakers in both channels
- 1 - Harsh buzz goes away when no RCA input is attached
- 2 - Loud when RCA is attached of either aka no difference with shorting RCA plugs
   - 2a - RCA cable (to preamp) - loud buzz/hum
   - 2b - RCA shorting plug (no cable/no preamp) - loud buzz/hum - maybe modestly quieter
- 3 - volume of hum/buzz grows louder as volume pot is turned up
- 4 - Hum/buzz not reduced by hum buster plug into wall (brand - Ebtech HumX)
- 5 - Hum/buzz not reduced by balanced/isolation transformer (brand - DECWARE)
- 6 - Hum/buzz not reduced by RCA based hum reducing transformer (brand - Rolls)
- 7 - Hum/buzz not reduced by power conditioner (Brand - PS Audio PPP)
- 8 - different tubes - no change
- 9 - Loud Hum/buzz reduced by putting mu metal around power transformer

Solutions:
For A - I will pot the power transformer

For B - I think this might be a grounding problem
     - The ZKIT instructions say to “Also don’t forget to install a jumper between the circuit ground and the board shield (ground plane).  There is no specific location marked for this jumper”. Am I missing something?  Or is the “chases ground” on the circuit board connection to the chassis at the same place as the power line ground (as a ‘star ground’) sufficient?

For C - I think this is a problem of interference of the power transformer with the RCA inputs (and thus cables) due to placement proximity.  The RCA jacks are on the top of the enclosure on either side of the power transformer with the decor labels (bells) facing the RCA jacks. So, I think the RCA plugs/cables are acting like an antenna.  In hindsight, this is a terrible choice of locations of the RCA jacks.  Plan to pot the power transformer in an iron transformer enclosure.

Questions:
- Feedback on my thoughts above
- In your build - you put a 100ohm resistor across the input (since no vol pot was used) - is that similar to having the vol pot turned to ‘zero” aka fully counterclockwise or turned to ’10’ aka vol pot turned all teh way up (clockwise)?
- You also tried a choke - did this help? Would this help my problem?  I don’t know how to test for ‘ripple’ related noice?

Thanks

Regarding #1 Transformer Hum

- I tried my PS Audio Power Plant Premier - the hum was made worse than it was when plugged directly into the wall.

 - on my digital multimeter - the Wall is 119 VAC
 - the the PPP it was 118 VAC in and 118 VAC out.

 - the PPP says 3.5% THD from the wall

Additionally the hum/buzz was also present through the speakers and again louder with the PPP in the chain than without.

I do not have an explanation for worsening of hum/buzz with the PPP - it could be faulty but I did just have it in for servicing (all caps replaced) and it showed a clean sine wave on my oscilloscope (safety precautions taken).

Thanks

Thanks - I tried that.  I used the Rolls box to isolate the RCAs from preamp to ZKIT amp.  Aka RCA from preamp in to Rolls isolation box RCAs out to ZIT.  Sadly, no change.

Any thoughts on my question about the ground plane connection form the KIT instructions?

Rob

FWIW there are "serious tube amp builders" that use circuit boards.
Turn key and kits.

I will give that a shot.  And, I am far from a serious tube amp builder.  This is my first attempt and i thought i would start with something relatively easy (aka a circuit board design).  I have Decware made amps and they sound wonderful, so I was simply learning on this one.  I am currently trying to translate this circuit into a point-to-point one that I will soon start to build.