bernbrue

Re: [BUILD] NU FEDERAL AM-864 PCB OFFICIAL BUILD & HELP THREAD
« Reply #200 on: August 30, 2019, 03:12:43 AM »
Huh, now you’ve got me. It’s more than 10 years ago :-)
Bernd


scott2000

Re: [BUILD] NU FEDERAL AM-864 PCB OFFICIAL BUILD & HELP THREAD
« Reply #201 on: August 30, 2019, 06:48:16 AM »
Quote

What would happen with a stereo unit if I used one B+ supply for both sides?

Collins 26U-2 has a similar thing as well I believe....

Mmt50816

Re: [BUILD] NU FEDERAL AM-864 PCB OFFICIAL BUILD & HELP THREAD
« Reply #202 on: November 21, 2019, 01:55:33 PM »
Im just starting my build. I am slightly confused as to the wiring of the Attack, Release and Meter trim pots. are the two terminals CW and W or CCW and W?
Thanks

bernbrue

Re: [BUILD] NU FEDERAL AM-864 PCB OFFICIAL BUILD & HELP THREAD
« Reply #203 on: November 21, 2019, 02:11:05 PM »
Honestly, I can’t remember anymore. Best think is to try out and change later if it’s wrong. It won’t do any harm. Good luck with your new compressor.
Bernd

Mmt50816

Re: [BUILD] NU FEDERAL AM-864 PCB OFFICIAL BUILD & HELP THREAD
« Reply #204 on: December 11, 2019, 04:10:54 PM »
I am attempting to wire up the power transformer. I got the Don Audio Toroid with 2x 180v, 2x 6.3 and 9v. I am guessing that one each of the 6.3v goes to the " Fil AC", but then do I wire up the 2x 180v in parallel to the B+ AC on one of the boards? Also, which values for R1 and R2 should I try?
Thanks

madreza

Re: [BUILD] NU FEDERAL AM-864 PCB OFFICIAL BUILD & HELP THREAD
« Reply #205 on: April 17, 2020, 07:56:42 PM »
Hi guys.
What voltage for C9 C10 and C11 ?
Thanks
Knight 1: We are now no longer the Knights who say Ni.
Knight 2: NI.
Other Knights: Shh...
Knight 1: We are now the Knights who say... "Ekki-Ekki-Ekki-Ekki-PTANG. Zoom-Boing. Z'nourrwringmm.

bernbrue

Re: [BUILD] NU FEDERAL AM-864 PCB OFFICIAL BUILD & HELP THREAD
« Reply #206 on: April 18, 2020, 09:40:32 AM »
35V or more.
Bernd

shot

Re: [BUILD] NU FEDERAL AM-864 PCB OFFICIAL BUILD & HELP THREAD
« Reply #207 on: April 19, 2020, 01:51:57 PM »
Fortunately, my over a year long voyage with this build is finally over!
I a mysterious problem with the unit not compressing and barely reacting to anything. In the process, I went through checking all the things I could think of. I even found mislabeled resistor numbers on the input pad part of the pcb.
Since this corona s**t got me with too much time to spare, I went back to troubleshoot the unit.
Finally I've found that there was a broken trace from triode grid of the 6AV6 (pin 1) and wiper pin of the current control pot. Since I've been checking wiring if it was faulty and it always checked fine, I didn't go through testing what is going on on the pcb. Well, problem of my unit was actually on the board itself. How that happened I don't know! Probably I overheated it when stuffing components, since I doubt it was manufactured with this error. I fixed it with a wire link and it works now!

I also made a few modifications. I've lowered C16 to 0.5uF and R12 to 500k. Those two values sped up the release. And also I lowered R13 to around 5k to speed up the attack time. I've tried many combinations of those three values and this is what I most liked. They all depend on each other so it's not possible to modify attack without affecting the release and vice versa.

I'm happy now! It is packed and ready to be installed in studio rack!

:)

Luka

bernbrue

Re: [BUILD] NU FEDERAL AM-864 PCB OFFICIAL BUILD & HELP THREAD
« Reply #208 on: April 19, 2020, 01:56:39 PM »
Glad to hear that you finally sorted out the problem. Enjoy the compressor.
Bernd

Re: [BUILD] NU FEDERAL AM-864 PCB OFFICIAL BUILD & HELP THREAD
« Reply #209 on: April 30, 2020, 07:05:02 AM »
Hi,

This looks like an interesting build! I have to try something like this.

I've been studying the stereo link on vari-mu units like this. I'm trying to read the schematic, and is the stereo link on this unit simply a matter of connecting the center taps together on input transfomers' secondaries ?

Cheers!


bernbrue

Re: [BUILD] NU FEDERAL AM-864 PCB OFFICIAL BUILD & HELP THREAD
« Reply #210 on: April 30, 2020, 07:16:15 AM »
Hi,
linking the sidechains of both channels at the input secondaries ensures that both channels have the same time constants. You still need to match the input/output levels on both channels.
This project quite complex and certainly not a tube beginners project. All in all it’s worth the time and effort you have to put in this project.
Bernd

dribro

Re: [BUILD] NU FEDERAL AM-864 PCB OFFICIAL BUILD & HELP THREAD
« Reply #211 on: July 27, 2020, 01:57:41 PM »
Hi there

Can I use this trafo for a Stereo version ?

https://www.tube-town.net/ttstore/toroidal-62va.html

Using only one psu?

Or is it better to go with recommended DonAudio trafo?

Although I have the feeling im answering myself...
« Last Edit: August 01, 2020, 05:00:54 AM by dribro »

Mmt50816

Re: [BUILD] NU FEDERAL AM-864 PCB OFFICIAL BUILD & HELP THREAD
« Reply #212 on: October 16, 2020, 11:07:06 AM »
So I have been messing with this thing a lot lately.
It seems to me that the input pot is not input volume but rather a balance between the two 6BA6 tubes. There is only one position for the input pot that doesnt sound like crap. is that how everyone elses units work?
Also, R9 doesnt do anything for my meter. The meter trim pot gets it in the right range though. What is the purpose of R9?
Lastly, my voltages at E and F are 1.7v while everything else is matched to the recommended voltage. Is that ok?

Thunbo

Re: [BUILD] NU FEDERAL AM-864 PCB OFFICIAL BUILD & HELP THREAD
« Reply #213 on: November 17, 2020, 05:11:30 AM »
Hi guys

Fully on with this project.
I have ordered the Sowter 8540 input transformers, but they have a huge delivery time, so meanwhile I went on searching for other alternatives that would work.

I have found the Cinemag CMOL-2X600T2 600:600.
Technically it's an output transformer.. But otherwise it seems to me, that it shoud be working just fine..?
Has anyone tried this, with this project?

Because it's a 600:600, and not a 600:10K, will I have less-than-spec'd total-system-gain?

https://cinemag.biz/line_input/PDF/CMOL-2x600T2.pdf
Mathias Thunbo - Denmark

PermO

Re: [BUILD] NU FEDERAL AM-864 PCB OFFICIAL BUILD & HELP THREAD
« Reply #214 on: March 11, 2021, 04:41:44 AM »
Old topic, but I'm going to do an attempt to build this thing  :-\

I have a Dizengoff D864 and I really like the way it compresses, though I also feel there's room for improvement as it comes to sound quality, it's a bit too dark for my liking.


As I was on the hunt for a spare set of tubes for this compressor I found these to be really cheap, so I got a bunch of them. 6SK7 and 6SQ7, I'll be using Sylvania 7n7 as my output tube as I allready got a bunch of these for cheap from Jaques (Highly recommend these !)

So having these tubes I figured I could do a stereo version and that's how I found this topic. Being on a tight budget I decided to do a point to point version on a upside down 2HE case with a 4HE blankpanel for a front as I allready had these sitting around.
Don Audio is still stocking this transformer, so, it's a go !
Also got a great deal on a pair of XSM10K/600 from the black market and will be using a pair of Jorgen Schou CT input transformers from an old broadcast unit.


(ah..now it shows)


I guess these could be the real deal from the right era ?

I'm now in the process of collecting all the bits and pieces and figuring out how to put it all together.

I really like the design you guys did, in function it's the same as the Dizengoff unit, but listening to the youtube clips I think you did a better job as it comes to sound quality of this unit.


The info in this topic is quite amazing, thanks for this !
I've printed the original manual and all the schematics.
« Last Edit: March 13, 2021, 06:38:39 PM by PermO »
"It's very important that you run trough the door, not trough the wall" - Sadhguru

Thunbo

Re: [BUILD] NU FEDERAL AM-864 PCB OFFICIAL BUILD & HELP THREAD
« Reply #215 on: March 16, 2021, 10:02:28 AM »
The project is going really well here..
After waiting 5 months for the Sowter 8540 transformers, I am now "done".

It still doesn't compress.. -so there is a bug somewhere I have not yet resolved.

Here are a few notes I made along the way:

In terms of power, I eventually ended up using 2x 1K ohm resistors in R1 and R2, to get the same values as Bernbrue.
R8 I had to switch to 100ohm instead of 240 to make E and F fit.

The 12ax7 tubes I had required 12 VAC, so surprisingly enough I had no luck with them.
I have switched to some Russian 6N2P tubes. They have the same pinout as the 12ax7 but runs of 6.3 VAC.

One last thing that teased me was that you MUST have the transformers installed to be able to measure E, F, G and H. Otherwise they show no value.

I drew the front panel, with inspiration from DonnieDarko. Produced by Frontpanels-Frank.
Mathias Thunbo - Denmark

PermO

Re: [BUILD] NU FEDERAL AM-864 PCB OFFICIAL BUILD & HELP THREAD
« Reply #216 on: March 17, 2021, 07:08:54 AM »
Well, it's hitting hard on the scale of awesomeness.

That's a very cool build !  8)

If I understand this thing a bit, there should be a DC control voltage at the input transformer CT controlling the gain reduction.
If it's not there, work down the line from there to find it.

I've just started looking into this thing as I am planning to build it, I'm defenitely not an authority on this.
"It's very important that you run trough the door, not trough the wall" - Sadhguru


 

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