[BUILD] NU FEDERAL AM-864 PCB OFFICIAL BUILD & HELP THREAD

[dogvoid]

Hi!!!
I'm testing the first channel, it sounds lovely, but there are some strange things, the input attenuator, the transformer is a 8540 sowter (600 / 10k) with the same h-pad configuration as the output. Attenuates to the middle, from the center to the ccw seems to expand the sound (I do not know if it's a problem, the result I like) I've reviewed and everything is correct unless something happens with the H-Pad, you may not need it, any ideas? I have not clarified with the H-Pad calculator, which I put in Required Attenuation In DB (1 to 40)?
The VU, I used a Vintage-Meters VM-B10R https://www.don-audio.com/Vintage-Meters-VM-B10R-LED-Retro-VU-Meter-LED-Illuminated
and I can not put it to 0, it does not exceed -5, but it moves, indicates compression (and I hear it !!!) any help with this?
the release is noticeable and seen in the movement of the VU, the much more subtle attack
The voltages are OK.
Still sounds great !!! I think it was worth the investment in tubes
For 6ba6: 4 paired manleys
6av6: Heintz and Kaufman (nos) matched
12AU7: CC803 S matched tube amp doctor.

Great project !!!

 

[Eliani]

Hi guys!

I've been building my very own NU Federal compressor this week, and I have some questions. First of let me show you guys my progress! I need to cleen up my wiring, but I'm waiting for cable sleeves to show up! I've done my own frontpanel, since I own a CNC, I bought the power transformer and in/out transformers from Don-Audio.

So as for voltage I get a few strange things?
Voltages from Power transformer: 2x197VAC, 2x10.36VAC and 7.12VAC.
I had to put 1K on both R1 and R2 to get exactly 200V DC for B+ here are my voltages measured after 10 minutes power-on.

B+ 200V

A 93.5VDC
B 51.1VDC
C 109.3VDC
D 156.9VDC
E 0.59VDC
F 0.59VDC
G 200VDC
H 200VDC

So A voltage should be around 8V? This one comes right after the the 15K 10W resistor (R27.) wich takes it's power from B+ so it's right that this voltage is around 90V instaid of 8V.
B/C are off because I think one of my 6BA6 tubes is not ok, it lights up rather hot when powered on and when switched with the other 6BA6 tube the B/C voltage switch places, I can only trim them slightly with R9 and somehow they burn R3/R4 (12K 1/2W)

note! I've only connected one ground connection to the ground of my power connector, are there any more seperate groundings I should make?

 

[rock soderstrom]

Hi, I can't answer your questions but I got one suggestion. The distance between your power transformer and the unshielded Edcor transformers are pretty close. This could lead to hum problems. I would maximize this distance and move the power transformer to the right corner of your case.

Nice build, keep up the good work! 

Cheers!

 

[Eliani]

Hi Rock,

When I'm cleaning up my wiring I might do so. First I'll need to get it running propperly. Did you build a Federal? And you remember your voltage at point A?

 

[Eliani]

I just don't get this,

Why is point A at +/-90VDC?  And why are R3/R4 burning up? I think the tube that isn't flashing when powering up the compressor is faulty, because it's that resitor (closest to that tube) that's burning up.

to be sure, all voltages ar measured with tubes in and all pots wired? because I fired it up before I got the rest wired and voltages for B+ where higher then!

By the way, my 1mA DC meter just crashes to the right wall when power is on! Audio passes trough, all pot's seem to work, like they have audible features like louder when turning output-pot, more compression when turning input pot, attack and release works to! Just that meter doesn't show anything.

is it maybe because these tubes are not matched? I can tell they are not even the same model/brand because they look different!! Maybe this guys just sold me fake 6BA6 because there's no markings on the tube... I'll just get a couple new ones!

 

[bernbrue]

Hi there,
Nice built and nice frontpanel. The specs of your power transformer are for a stereo version, where each channel has got its proper winding and power supply. For your mono version you only need 1x200VAC and only 1x 6,3V ( not 10,36VAC !!!) for the heater (wires underneath).  The 7,12 VAC are for the onboard 5V psu provided for the relays and lights. So check your heater voltage and the transformer wiring.
Cheers
Bernd

 

[Eliani]

Hi Bernbrue,

I’m using the transformer you put in the First post of this thread, it has (stated on the transformer) 2x180, 2x 6.3 for heaters and 1x 9V. But all the voltages are a bit higher when connected to my main power.

I thougt the 9V was for the relays, 6.3V for heaters and 180V for B+.

When measuring heater voltages I get 3,4V

 

[bernbrue]

Hi,
for a single channel use only one 180V and one 6,3V winding.  9V is for the relays.  Heater voltage must be 6,3 VAC, measured at the screw terminal FIL/AC. Check your transformer wiring.
Bernd

 

[Eliani]

Ok,

So i mixed up my potmeters!! I had threshold and current control on the wrong potentiometer!!

These are my measurements:
B+ = 216V

A = 16V
B = 208V
C = 212V
D = 138V
E = 1.27V
F = 1.23V
G = 215V
H= 215V

Better check my other pots... ;-)

Edit: all potentiometers are in the right positions and now my meter is up and running too!
However, I experienced the same problem with the input attenuater as Dogvoid. No attenuation in the middle, and less signal to the cw and ccw position. So I figured out that one deck of the input pad should be reversed and now I have a proper working input attenuator, and a clean signal and a working compressor! Now I need to calibrate the voltages and maybe add this resistors to the threshold and ratio-pots!

Here's a small video of me turning knobs!

 

[Eliani]

Not to brag but i'm kind of proud of this build!

At least of how it looks because wiring could have been a bit cleaner, but I'm sure I'll get it next time. I'm waiting for new 6BA6/EF93 tubes to arrive, I've bought like 10 and hope to good pair out of them. I'm not totally aware of how one would match tubes, or if I even need to, but I'm guessing it wouldn't hurt as I can't seem to get C and B to the same voltage! This might explain that the input get's distorted when cranking the input?

I've yet to do the threshold/ratio range reduction mods

 

[jefflehiress]

Nice work,
I have to finish mine in 2 weeks, the time that my input transformers arrived.
I did not put any PAD in entries...
I would tell you if I have the same kind of values when I measure.
What did you get in as audio for now? and what do you think?

 

[bernbrue]

Hi,
What a superbly built unit!! The wiring is fantastic. Maybe I'm  wrong , but there is nothing connected to the "from Output tx" terminal ? You'll get pleasant harmonic distortion when cranking up the input.  Did you use ecc83 as output tube?
Congratulations!!!
Bernd 

 

[bernbrue]

Cool video!! Your unit works as it should!! Enjoy it!!
Bernd

 

[rock soderstrom]

Very good work! Where did you buy these fabric hose? 

 

[Eliani]

Hi,
What a superbly built unit!! The wiring is fantastic. Maybe I'm  wrong , but there is nothing connected to the "from Output tx" terminal ? You'll get pleasant harmonic distortion when cranking up the input.  Did you use ecc83 as output tube?
Congratulations!!!
Bernd

Hard to see, but the output TX is connected and thank you for your kind words!
I do have a couple of questions though.

Question 1: I'm having trouble adjusting the voltages between B and C, seems like the R9 (500R) trim pot is working, but it does nothing to the voltage difference between B and C.
Question 2: Do I need matched 6BA6 tubes for this build or is R9 supposed to make up for the difference?
Question 3: Are all voltages supposed to be measured with all tubes in place and how close should I have to get to  your voltages?
Question 4: My heater voltage is 6.9V in stead of 6.3V is this going to be a problem? 

Very good work! Where did you buy these fabric hose? 

It's MDPC-X sleeve bought at Highflow.nl for €1 per meter.

 

[bernbrue]

1) try to find a nice pair of 6BA6 tubes where the voltages of B and C are quite close. Trim small deviations with the pot. Otherwise replace the 500 ohm pot with a 1 K
2) see 1)
3) yes, all tubes in (within 10%)
4) no

Bernd

 

[iampoor1]

Hi guys!

I've been building my very own NU Federal compressor this week, and I have some questions. First of let me show you guys my progress! I need to cleen up my wiring, but I'm waiting for cable sleeves to show up! I've done my own frontpanel, since I own a CNC, I bought the power transformer and in/out transformers from Don-Audio.

This might be better in another thread, but what CNC are you using? Are you just engraving anodized aluminum? Love the look of your panel.

 

[rock soderstrom]

It's MDPC-X sleeve bought at Highflow.nl for €1 per meter.

Thanks!

 

[djfatum]

;D ;D ;D

 

[bernbrue]

Baaamm! Very nice!!
Bernd