Shared Ground Capacitor wiring

[Champ81]

Hi everyone

Here we are having the may 24 weekend. Hope all are enjoying it.
I hope this is the correct thread considering it feels with wiring.
I am building a modulus amp kit and they have a shared ground for a 33uf cap circled in red.  Still learning so I'd like to ask.  At the moment the amp has a very low frequency hum with the master volume pot at zero and it goes away as you turn it to max. So I tried everything to ground the way it describes in TUT. I'm sure that's not the issue. But.. after all possible ways I pulled out the preamp tubes to see if it goes away. Still there. The low frequency hum (I'm guessing 60HZ) is definitely from the power section somewhere. 
Also I tried reorienting the output transformer and moving it away but still there. 

Now the only culprit I could think ofnow is this shared 33uf capacitor. Is it still a good idea and good practice to just get two 33uf caps and seperate their respective grounding? Or in this case would it not matter so much in terms of reducing noise.

[K O'Connor]

Hi Guys

Please DO NOT use inline images. Add them as an attachment that the reader clicks on to open. We cannot tell anything from the portion of the image available.

TUT3 shows thew correct way to ground an amp. Shared ground caps can be used as a single parallel cap for a single stage.You could "get away with it" as a SECOND Va cap + Vs cap, where a separate cap is used for the first-Va cap off the rectifier.

One detail that is important which can be gleaned from your drawing is that this amp is cathode-biased. There is no means added to huim-balance the output stage.

Apart from that, we cannot see how many tie points there are between the chassis and circuit ground - there should be only one. See TUT3.

[Champ81]

I think I have now removed the image inline.

As for the grounding I rewired it as best as I could to ground to each respective stage as per the galactic grounding. So my actual build does not reflect the layout. And that is all connected to only one point in the middle of the chassis. And the other main ground is connect separately.

Yes. This amp is currently cathode biased and I have ordered a two tube bias kit from London power. The pair of el84s are "matched" by the supplier. Shouldn't they be balanced? I checked the cathode on the meter and they measure very close in current.  

As for the common cap I am planning on cutting one lead to positive and adding another cap in place of the cut positive lead and adding a separate ground to the respective stage. Is this what you mean?

[K O'Connor]

Hi Guys

Champ81: What is the dual cap related to? It is best to use both sections since they are present, but do so as described previously and/or as described in TUT3.

Also,, I hope when you say "grounds" you are referring to points along the wired ground bus and NOT separate points on the chassis.

BMK2 will need to be wired a bit differently than its notes show to be applicable in a cathode-biased amp. I will make a drawing and post it here tomorrow.

[Champ81]

Thanks Kevin

I see what you are saying. The other half of the dual cap will tie together the positives with its own ground then add another cap seperate from the dual beside it and wire its ground separate. I posted the dual cap where one half filters the 100k plates of v1 and the other half filters the plates of v3? Sorry I'm still learning the proper identification of the circuits. I have attached a layout but hopefully it posted OK.

I am incorporating galactic grounding which I used on every build as best as I can. Where I run one buss wire across the board and all grounds are tied to its points along the buss.

The buss is then contacting the chassis as one point midway along the board. If I didn't screw in the point all grounds would be floating.  I didn't tie the one contact point near the input jack.

[K O'Connor]

Hi Guys

The input jack ground should go to the ground node for the input stage along the ground buss NOT to chassis. The tie between the bus and chassis should NOT be at the input.

Please add images as clickable attachments rather than inline.

[Champ81]

Yup. In all my builds there is a buss that connects to chassis only midway and not the input jack. The input ground connects to the buss. 

I am not sure how to make it click able for images. There is an option at the bottom for attachments and I upload it to that. There was another option where there is a bracketed link in the message. But that seemed to have the image that is not cliackable. Am I missing something?

[Champ81]

This a a shot in the dark. 
I received the bmk kit and drew up a rough layout.
The amp I am trying to work on is currently cathode biased.

For the potentiometers marked "o" is going to v-. But I'm not sure exactly where it should go.

   

[K O'Connor]

Hi Guys

I created a new thread in the London Power Kits section titled "BMK2 used to hum-balance cathode-biased output stage" since you are using that kit to do so. There is a DF attached that shows the correct connections. DO NOT use the wiring shown above.

Note: Regarding adding attachments: When you use the big black "New Reply" button, you have the full-featured reply window. At the bottom is the Attachments area which has a dotted outline box. Click in the box to browse where you might pull your image from. A button will appear in the box saying "Add to post"

DO NOT press that button.

Instead, just go below to "post reply" and the link for the image will appear as it should simply as a link.

Have fun