#124 started

[norburybrook]

so when you say MV pot and OD relay which points am I grounding?


M

[martin manning]

The input (CW) lug of the MV pot, and the other end of the coax from there (at the OD relay). Then you have two paths, one for clean and one for OD. Does the hum occur in both modes now?

[norburybrook]

weird....

I've just rewired the send and return jacks as per the schematic and now have no sound whatsoever.

Wiring them as per the layout as I had before at least seemed to work.

which one is correct?

it seems the schematic has quite a few errors. I never used them in previous builds but as I learned more I decided to use the schematic this time and it's throwing me curved balls.

M

[martin manning]

I don't see any difference between the loop jack wiring in the layout and the schematic (the 1984 version in the #124 archive).

[erwin_ve]

Did you reverse the tip/ring wiring on the loop?
Maybe a close up pic for that location?

[norburybrook]

Martin,

Sorry, it's been another long day of staring at layouts/schematics and my amp searching for problems. It's quite intense!!!

the difference is that on the Dumble clone chassis the send and return are the other way round so to be correct with the schematic I put the switching jack on the return rather than the send. However as I'm tired I could have probably just switched the two sockets instead of rewiring in doing so I've managed to stop all sound!!! not sure how.......

anyway..

I'm finished now for the day.

I'll start again tomorrow


Thanks for your continued support.


so close......

Marcus

[norburybrook]

here's a photo of the newly wired sockets in case you can see my error.

M

[martin manning]

The jack wiring looks correct to me. Is the ground from the PI tail (390R and 1uF presence cap) connected to the sleeve lugs too? I think I see it (black wire) on the send jack. Can you verify that you have signal coming out of the MV/send jack?

[aflynt]

Are you sure that the switching jack is connecting and disconnecting as expected? The Switchcraft style shorting jacks can be flaky. Sometimes the tip connection can collapse and not allow the switch leg to fully disconnect when the plug is inserted. That can usually be fixed by carefully bending the tip loop out a bit so that it pushes further away when you plug the cord in. After time the jack can sometimes corrode too.

-Aaron

[amplifiednation]

I was looking at the pictures on page 5. Your OD relay should not have an unused eyelet. I cant tell exactly how you have the relay wired, but the connection from the clean channel and master volume needs to be made there - even when the relay isn't engaged 100% of the amp goes through it - so it needs to be hooked up right

The clean channel output is jumpered.

Overdrive in (220k)- master in - ground - clean out - clean out - Overdrive pot

If the clean channel isn't connecting with the master volume you will not get any sound.

[larsvictor]

Wiring of the jacks looks correct. Try with a patch cable to exclude a bad switching contact.

[norburybrook]

morning all.

1 step forward and 10 back

so last thing I did last night was to rewire the send return.

At that stage I had an amp that was humming and clipping but everything else seemed to be working i.e. relays OD/PAB tone stack, all front panel switches.


I then rewired the send return and found I had no signal at all.

I came in this morning and put my meter on the PI and I have 395vDC on ALL pins of the valve ?what's going on ??? all I did was rewire the send return how can that suddenly mess up the PI?


Obviously 396vDC on all the pins is NOT GOOD.


M


@Taylor the unused eyelet on the relay board is because I made the boards before I looked at how many eyelets I actually needed. two of the relay connections are connected underneath



edit.

Spent a few minutes staring at the now very familiar schematic and thought about what could have happened. Checked continuity with ground at the send/return sockets and found it wasn't there.??? then I realised; Anodised Chassis...I hadn't tightened the nuts as tightly as before. Nuts tightened , ground established and we're back to where we were.....the HUM.....so

i'm going to do as Martin requested last night and ground up the chain.......TBC

[norburybrook]

Martin.

Grounding the master volume center and the OD relay entrance has no effect on the hum. well in truth it has a very small effect but not like when I ground out the PI 0.1uf node which kills it stone dead.



M

[erwin_ve]

Marcus it is very simple, Just wire the sleeves of both jacks of the FX loop to the groundingpoint near the power tubes. For all other groundingpoints points: Make sure you grind the anodised material away. Just tightening isnt enough. You're almost there

[norburybrook]

Marcus it is very simple, Just wire the sleeves of both jacks of the FX loop to the groundingpoint near the power tubes. For all other groundingpoints points: Make sure you grind the anodised material away. Just tightening isnt enough. You're almost there

Erwin,

I did think about that. I might do it anyway because if an amp is on the road and being wheeled in and out of gigs, in trucks, vans etc vibration could loosen those nuts and that would not be good. I've had machine head/Bridge screws on my guitars vibrate out over time when touring.


I did Dremell all the earth points before I attached the screws and I have good continuity between ground s where necessary.

this Hum is really loud though, I've not heard a hum like it before.



Marcus