bernbrue

Re: [BUILD] NU FEDERAL AM-864 PCB OFFICIAL BUILD & HELP THREAD
« Reply #160 on: October 04, 2018, 04:35:36 AM »
Which output transformers do you use? How did you wire it? The 12ax7 could be bad as well. Can you measure the voltages around the output tube once again? Has your input transformer got a  centertap? Check for correct wiring.  Compare with the data sheet of your transformers.
Bernd


Re: [BUILD] NU FEDERAL AM-864 PCB OFFICIAL BUILD & HELP THREAD
« Reply #161 on: October 05, 2018, 12:53:57 AM »
I used the Edcor  XSM 10K/600 output transformers as recommended on the first page of the thread.  Input I used  Hammond 140QEX 1:1 600ohm transformers.  The Hammond has both sides centre tapped, so I connected it on the output side of the input transformers, and just blanked it off on the input side, as there is nowhere to connect it to the board.
Output transformer I connected the centre tap on the primary side (TO-OUT-TX on the board), and left it disconnected on the  secondary (FROM-OUT-TX) connection.

The bit that is annoying me, is whatever the issue is, it's the same issue on both channels, because they both have the same hum. To me that kind of rules out a bad tube.
« Last Edit: October 05, 2018, 11:04:26 PM by fiat_cc »

bernbrue

Re: [BUILD] NU FEDERAL AM-864 PCB OFFICIAL BUILD & HELP THREAD
« Reply #162 on: October 05, 2018, 03:32:51 AM »
The circuit itself is absolutely flawless. The pcb has been tested as well. So there must be a very simple, obvious mistake. Please double check the wiring of the XLRs and verify that hum is not introduced to the unit from an external source.
Bernd

Re: [BUILD] NU FEDERAL AM-864 PCB OFFICIAL BUILD & HELP THREAD
« Reply #163 on: October 05, 2018, 11:06:46 PM »
I'm not suggesting at all there is an issue with your product.  I'm just frustrated, as I feel as though I did a good job of building this, and I cant figure out where the hum is coming from. I'm not a tube guru, but I've built my share of tube circuits successfully, and feel as though I have a sound understanding of layout issues etc.  I'm always learning of course, but I thought this one would fire right up with no issue. 

I will partially disassemble and try a few things in terms of layout etc, and triple check my wiring.
Regards,
Reuben

scott2000

Re: [BUILD] NU FEDERAL AM-864 PCB OFFICIAL BUILD & HELP THREAD
« Reply #164 on: October 05, 2018, 11:47:35 PM »
Maybe a leaky cap?

Re: [BUILD] NU FEDERAL AM-864 PCB OFFICIAL BUILD & HELP THREAD
« Reply #165 on: October 08, 2018, 06:54:06 PM »
Maybe a leaky cap?

Not impossible, but given that it's a 2 channel unit, and both channels exhibit virtually identical noise issues I'm leaning towards something that is shared between both boards.  I have some sheet aluminium at home, and will try building a shield of sorts around the PT.  I've just been dealing with a guitar amp build that has all sorts of noise issues due to the OT placement too.  I'm feeling it's either a layout thing, or possibly something like meters.  I may have made a wiring mistake on both boards, but I was careful with this build, and it seems unlikely.

I've put it on the shelf to concentrate on another project for a few days, and will come back to it with fresh eyes soon.
« Last Edit: October 08, 2018, 07:26:31 PM by fiat_cc »

shot

Re: [BUILD] NU FEDERAL AM-864 PCB OFFICIAL BUILD & HELP THREAD
« Reply #166 on: November 17, 2018, 04:48:43 PM »
Hi!

I'm in the process of finding what's wrong with my one channel build.
I'll explain in the next post what is wrong and ask for assistance if I don't find the error in the meanwhile.

But I think I found an error on the pcb silkscreen!
It's in the section of output pad.
Labels on R23 and R19 are reversed.

I've drawn myself a diagram  of actual situation on the left and schematic on the right.
If you look at top left on my diagram you'll notice that R19 is connected to output pot CCW (that's supposed to be R23 on schematic) and R23 is connected to output transformer (that one is supposed to be R19 on schematic).

If you stuff the board following silkscreen labels you end up with wrong values. It works of course, but it's wrong!

I attached my hand drawn diagram (sorry for the lack of drawing skills  ???)

:)

Luka

zayance

Re: [BUILD] NU FEDERAL AM-864 PCB OFFICIAL BUILD & HELP THREAD
« Reply #167 on: November 18, 2018, 03:28:56 AM »
Yes you're correct shot, silk error there.
I surely have crossed the names while cleaning the board's silk...

Sorry for the inconvenience, will add a note for this error.

T.

shot

Re: [BUILD] NU FEDERAL AM-864 PCB OFFICIAL BUILD & HELP THREAD
« Reply #168 on: November 25, 2018, 09:13:17 AM »
Unfortunately, I'm struggling to find free time to work on this compressor more.
I don't have a clue what's happening with compression. I don't hear it!
Meter is showing that it's compressing, attack and release slightly change the way needle on the meter is moving, but when pushed I only notice more distortion. I don't hear the compression. Os should I say, I think I hear some compression but it may even be placebo when simultaneously watching the meter bounce.
Input potentiometer is definitely not behaving as it should since whatever I do it keeps the same level. I went to check if it's connected the wrong way but it seems fine. I'll double check. Maybe that's the root of all my problems.
I'll keep you posted as I go along when I get some time to work on it.
Btw, I have 10k:10k as input transformer and at the moment I'm using 10k:150R as output. I know that this output transformer may not be appropriate but I don't think it's got anything to do with my problems at this stage.

:)

Luka

bernbrue

Re: [BUILD] NU FEDERAL AM-864 PCB OFFICIAL BUILD & HELP THREAD
« Reply #169 on: November 25, 2018, 12:07:33 PM »
Hi Luca,
You might check the video I made from my unit and compare the compression you clearly can hear there with yours. Attack and release changes are subtle with this compressor.  I mentioned this before. Your input pot should cut down the input signal to zero when turned fully counterclockwise, whereas the output pot is just a 10dB attenuator.  Try to get the input pot wiring right, Im shure this is causing your problems.
Heads up!
Bernd