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Newbie checking in, K-12G pics.
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Author:  mwhouston [ 20 Sep 2010, 20:44 ]
Post subject:  Re: Newbie checking in, K-12G pics.

Chuck good build. To stop mechanical hum, which these amps will do some times, slice in half rubber grommets and sandwich the power tranni mounts between them. So completely isolate the power tranni. Having a big thin top plate acts like a sounding brd. for the power tranni's mechanical hum. I do it to my OPTs also to reduce resonance and microphonics.

Make sure you have an earth wire electriclay connected to the power tranni in case it goes live. The earth wire can aslo help cut down noise in the PS.

This works.

Author:  cmetzner [ 20 Sep 2010, 22:17 ]
Post subject:  Re: Newbie checking in, K-12G pics.

Mark -

Thanks for the advice. But, I am so unknowing of this whole thing. I am not sure of exactly what you are instructing me to do. I put rubber washers under the OPTs and then anchored the OPTs to the top plate. I didn't think I had to do that to the power tranni but I will.

Re the ground wire: Are you telling me to run a wire from the power trans to the PCB? The instructions had me run a ground wire from the PCB to each of the OPTs.

Re the chassis then: Given that metal top plates can accentuate hum, I suppose it's better to make the entire chassis of wood or some non-resonating material.

-- Chuck

Author:  mwhouston [ 21 Sep 2010, 01:08 ]
Post subject:  Re: Newbie checking in, K-12G pics.

cmetzner wrote:
Thanks for the advice. But, I am so unknowing of this whole thing. I am not sure of exactly what you are instructing me to do. I put rubber washers under the OPTs and then anchored the OPTs to the top plate. I didn't think I had to do that to the power tranni but I will.

Re the ground wire: Are you telling me to run a wire from the power trans to the PCB? The instructions had me run a ground wire from the PCB to each of the OPTs.

Re the chassis then: Given that metal top plates can accentuate hum, I suppose it's better to make the entire chassis of wood or some non-resonating material.

With the OPTs I just use one half of one grommet between the top plate and the OPT mount. With the power tranni put half a grommet above and below the top plate. You may need big washers to stop the soft rubber grommet being pinched.

Just ensure the metal of the power tranni is electrically connected to the common earth. So if the tranni goes live it will blow the fuse. When you isolated them on rubber grommets they may not be electrically connected to the mains earth.

Author:  cmetzner [ 26 Sep 2010, 18:43 ]
Post subject:  Re: Newbie checking in, K-12G pics.

You will see how little I know about this subject by this question.

Here is when the hum is loudest:

Amp is on; my mp3 player is connected to the amp but not on; the hum is annoyingly loud; I touch the RCA inputs with my finger; the hum is very loud. Once I turn on the mp3 player, the hum is reduced to almost nothing.

I know one answer is why sweat it since once I turn on the player, the hum almost disappears but I am hoping to eliminate all hum in the amp.

Thanks for any assistance anyone can offer since I have no diagnostic ability.

-- Chuck

Author:  mwhouston [ 27 Sep 2010, 05:33 ]
Post subject:  Re: Newbie checking in, K-12G pics.

Put a 100K 1/2 watt resistor from the input to ground. So from the hot wire or pin (centre of the RCA socket) run a 100K R to ground.

Author:  cmetzner [ 12 Oct 2010, 16:19 ]
Post subject:  Re: Newbie checking in, K-12G pics.

Can someone explain one of the modifications to the K12 kit that is described by Voltsecond on his site describing the changes he made to the K12. Bruce Heran (on this site) made the same changes and showed some of them in his "Photo 1".

The part I don't understand is where they add one cap and one resistor to three soldering points as Voltsecond describes below:

"Next, on the tube side of the 0.01 uF, we add a 0.1 uF (400V or 630V film). From the other side of the 0.01 uF, we add a 620 ohm 1/4 resistor to the free leg of the 0.1 uF."

From the pictures, I cannot what part is soldered to which point on the board. What's a "tube side"? Thanks in advance for any help you can lend.

-- Chuck

Author:  Gio [ 13 Oct 2010, 18:54 ]
Post subject:  Re: Newbie checking in, K-12G pics.

Hi Chuck,

The mods are shown on the VoltSecond page under the heading "HV Snubber Version 2, C-RC, Last update 20-Feb-05"
Image
The C-RC snubber goes after the HV secondary of the transformer and before the rectifier. On the PCB board this is where the high voltage secondary from the transformer is attached. Might be best to use "X" rated capacitors. I know I used 400V film types without problems but if I was to do it again I would use a "X" rated cap.

Cheers

Author:  gofar99 [ 14 Oct 2010, 16:59 ]
Post subject:  Re: Newbie checking in, K-12G pics.

Hi Sorry for the delay in responding (I did get the email). I have been ill for several days. :sick: To follow on to the above response.... It is generally ok to place parts both on top (tube side) of the PCB and underside as well. Often it makes for easier building. Sorry for the confusion. You mentioned hum problems with your amp. When do they occur, how bad, what is hooked up at the time, does it do it at all volume levels?

Again welcome to diy tube audio.

Good listening
Bruce

Author:  mwhouston [ 14 Oct 2010, 19:03 ]
Post subject:  Re: Newbie checking in, K-12G pics.

gofar99 wrote:
Hi Sorry for the delay in responding (I did get the email). I have been ill for several days. :sick: To follow on to the above response.... It is generally ok to place parts both on top (tube side) of the PCB and underside as well. Often it makes for easier building. Sorry for the confusion. You mentioned hum problems with your amp. When do they occur, how bad, what is hooked up at the time, does it do it at all volume levels?

Bruce: didn't know you were crook? What got you?

Author:  cmetzner [ 14 Oct 2010, 21:26 ]
Post subject:  Re: Newbie checking in, K-12G pics.

Gio -

Thanks for the reply. I am new to all of this. So, I was looking for directions more geared to an 8 yr old - such as "connect the cap to the hole that you connected the green wire to...". Once again, I understand if you think I am beyond help.

Bruce -

Re the hum. When I first completed the amp, I connected my mp3 player wirelessly. MP3 connected to an Audioengine AW1 wireless transmitter; the wireless receiver was connected to the inputs on the amp. I had virtually no hum. Later, I connected the mp3 player through an ordinary wired connection to the input. I have hum in that configuration.

The hum does not increase in volume and stays at the same pitch. I have not yet run a ground wire from the input to the ground on the power cord. I have read a number of things on grounding and all seem to tell me to do that.

I have the ground from the power transformer case and a ground from the speaker output to the center connection on the power cord. I still need to add a ground from the input to that same ground.

I suppose the wireless connection filtered out most of the hum. Also, I do not notice the hum when the music is playing. My son did. I have a good case of tinnitus. So my constant ringing in the ears masks alot of noise. For me to hear the hum, I have to put my ear to the speaker while the music is not playing. When I do that, I can tell why it would be noticeable to normal hearing.

-- Chuck

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