Federal Limiter AM864 thread

[skal1]

just have too wait for the tubes then..

 

[nielsk]

Do the Edcors have a DC center tap?

 

[skal1]

Need to get some Micromold capacitors for this project , has any one got a source for these caps 0.1 uf and the 1uf seal can paper.

thanks in advance

skal1

 

[pH]

Dredging up the ol' Federal thread here...

So I have a PTP prototype up and running, used Edcor for all the transformers for starters. First impressions: it works! I used to have a real one of these, so I duplicated the H-pad on the input XLR and wired in a 600R T-pad after the output transformer just like I did on my old one. It behaves a lot like I remember the real Federal.

But one thing that I'm battling is hum. I swapped the Edcor input for a UTC A-10 but it didn't help the problem. It's somewhat usable as it is, but hum is definitely there when the program material dies down. Hum disappears when the input pot is dialed down to zero. My real one was dead quiet, so I know that this isn't inherent in the circuit (as some have said).

The other problem that I'm having is the meter. I bought an old dB meter with a similar scale as the real thing, but it doesn't zero out (even with a variable resistor for R2) and it doesn't move the right direction for GR (barely moves at all), and doesn't move at all for output. I tried another old VU with the diode network removed and it added loads of distortion and hardly moved at all. What have you guys used for meters?

 

[cannikin]

Hahaha welcome to my world!

I have four Federal versions that I built all with the same hum problem.  I tried hum pots, DC heaters on the input, moving the transformers, shielding audio transformers, using more filter caps, dual chokes, insulated wire (shield to ground) etc.  Thats why I was drooling to see your real thing.  I was so bummed that you sold it before I could get my hands on it.  Currently, I'm reworking one AGAIN by taking the PSU out and putting it into its own chassis.   I'll let you know how that goes but its going to take a while.   IF you figure it out, I'm all ears.

funny thing is all my voltages were spot on correct.

Then theres the motor-boating on the 6SQ7...

About the meters.... I have 4 NOS original Federal Meters that I got a while back, when I dropped one in my clone it tracked perfectly, when I switched it GR mode it went right to Zero.   I paid a pretty penny for them but if you want one let me know.

Regardless we should have a Federal Hum party over some beer.

 

[pH]

Hey, Cannikin's back!

Nice to hear from you David. Sorry I had to let the real Federal go but last year I was really skint. I have a friend who has a nice one, I can borrow it if we have our Federal Hum party someday  ;D 

 

[emrr]

You guys get together on this and sort it out; buy me a plane ticket and I'll join the party!  Someday I'll get around to this one too, and have a few cents to chuck into the pool.   

 

[mushy]

Guavatone built one that sounded clean. He mentioned that he had to move his input tranny (Edcor) around till it went silent.

Did ya try the chopstick?

 

[cannikin]

You guys get together on this and sort it out; buy me a plane ticket and I'll join the party!   Someday I'll get around to this one too, and have a few cents to chuck into the pool.   

With the money I have thrown at this project - Not only could I have purchased a couple of originals,  I could have sent you a round-trip ticket to Seattle to fix it.    Someday, it will work......

 

[cannikin]

Guavatone built one that sounded clean. He mentioned that he had to move his input tranny (Edcor) around till it went silent.

Did ya try the chopstick?

I tried chopsticks, spoons, meat cleavers, you name it....  the only thing I haven't tried is the shooting it with 12 gauge but.....  ;D ;D ;D ;D

 

[cannikin]

I even sent it to P johnson but thats another story..........

 

[guavatone]

I tried chopsticks, spoons, meat cleavers, you name it....   the only thing I haven't tried is the shooting it with 12 gauge but.....   ;D ;D ;D ;D

But the instructions clearly say Kerosene, pick axes, and spades but no 12 guage. 

 

[lassoharp]

Guavatone built one that sounded clean. He mentioned that he had to move his input tranny (Edcor) around till it went silent.

Did ya try the chopstick?

I tried chopsticks, spoons, meat cleavers, you name it....   the only thing I haven't tried is the shooting it with 12 gauge but.....   ;D ;D ;D ;D

Does the input transformer you're using have a CT?

Have you checked the chassis for stray AC?

 

[guavatone]

You could go shielded input xfmr.  I tried cheap edcor and it must be in the far corner positioned at correct angle of a 14" deep par metal case.
his for $60 AU?

http://www.jlmaudio.com/shop/index.php?_a=viewProd&productId=26

This may do

or this 600:15K $30
http://diypartssupply.com/index.php?main_page=product_info&cPath=4&products_id=5&zenid=q9ebk4h9no059v4oj0tl88u4g1

or Lundahl LL1922  1:4 for $100 smackers

or Jensen.  I think they have a 1:4 shielded

I should be selling a PCB soon.  Look for the Feeler within a month.

 

[cannikin]

I used a Sowter 9045, Edcor, Chicago 600:20K, utc  600:15K

All with similar results 60Hz HUMMMMMMMMMMMMMMM  Lifted the grounded Heater and added a hum pot: that minimized the 120Hz residual hiss but thats it.   Heater wires were tightly twisted running in 90 degree angles from the rest of the circuit.

I built it with the field manual using the exact turret layout, like I said Voltages everywhere are dead on.

I'm going to pull the power supply to a separate chassis and I bet it will fix it.
every time I do that I have zero hum problems.... I build 4x tube stereos (christmas gifts for the family), and 3 tube limiters that way - result was absolutely zero hum.

 

[pH]

Okay, solved it. Coated the guts in mil-spec tropicalization shellac and now all is quiet on the western front.

Yeah, right 


So while I may not have conquered the hum problem yet, I've enjoyed checking out the mods in stages. Both Threshold and Current Control are on the front. Then added a 100k resistor between R1 and R11 and a .47 cap to ground at the juncture of the 100k resistor and R11. This adds a faster response on top of the 1uF/2Meg combo, but I could kind of hear both networks working independently with a bit of a hole between them.  Added a 370k resistor on V4 pins 4/5 to ground, and this last mod really smoothed out the two networks, now they seem more glued together.

We're getting farther away from what an original sounds like, especially with the nice UTC input tx, but this ain't a bad thing. It may not have that limited bandwidth mojo that did cool things in mix setting, but I could definitely imagine using this one to track with, something I never wanted to do with my un-modded original.

 

[johnnytoobad]

Hi, after years reading the most intersting things in this forum, i start to ask by myself.
 i'm planning to build the federal comp, but i got three questions i didn't find any answers...
the first one is how do i connect two of them for stereo-link? between R1 and 6SK7 cathode, seems to be the good place for me...
secon question: if i need an external sidechain, will an input and a switch before C5 will be good?
i was thinking about going fullwave rectifying (to be able to compress assymetrical signals) so using 6al5 à la Sta-level (with a 6sl7 to amplify signal if i take it before output stage, and i'd like to , so i'll be able to use design a louder output stage witg a gain make-up control)... but it seems i'll have to cool it down  because of current and voltage compared to 6sq7... maybe 2 6sq7 or 6H6 like ba6a?
i'm also planning not use vu meter but em84 for input and output control.
thanx for answers...
Jon

 

[mushy]

Since most people are adding pads to their outputs, I'm not sure why you would want an even hotter output stage.

 

[johnnytoobad]

that was not the main point of the post, anyway, i was thinking of a sta-level outputstage as i got all parts for something like that, and coupling to the comp/preamp with dual 500K pot and pad after the OT.
But any ideas about the other points from my first post?
side-chain, stereo link and goin' fullwave...
does any one got something to say about compression is 6sq7 enough for it??
i am an electronic musician (tapemusic/noise/industrial/power-electronic/ambiant/dub/creep-hop), and part time demo tech recorder for underground bands (from punk to free-jazz and noise, for friends and for fun) so i'll use it mostly on already distorted sounds. I'm also a singer so i'll probably end with it on my voice as i hope it will sound good.

 

[mushy]

Sorry.  Didn't mean to come off dismissive.

I'm in the process of putting together the parts for one of these myself.  My approach is to breadboard the entire thing first.  I'm spending the extra $25 its going to take to swap things out and experiment.  I'm mostly playing with the sidechain but possibly later the output stage as well. 

As as for external sidechaining/stereo linking, I was going to put my insert and switch between the CT and R1/C1 a la the VK1.  It's quick and dirty but seems to work for others.