Mystery EFT Compressor-EQ Unit

[sage]

EQ P300 scehmatics

 

[sage]

Ok so we recapped and cleaned and the units still acted weird - replacing the 5534 - both of them  - with new op amps they came ALIVE!

So far with a non-scientific test but just with a BASS track they seem to compress really nicely - the make up gain is loud - and they are not too noisy except for a strange interference i hear them pick up once in a while...

I tested the National 49710 and they react really well - plenty of character i hear and the controls after a good spraying seem don't crackle almost at all. Also tried the LT1357 that at first I seemed to prefer but they seem to react faster too fast - not sure yet I need further testing but definitely they do sound different with 2 opamps i have available here.

Now i do need a suggestion - I remember Jim Williams talking once of the importance of removing coupling cups if using more modern op-amps like the LT1357 or OPAs, so I wonder are the coupling these once in the picture? Shall I remove them?

sage

 

[sage]

oops here it is

 

[abbey road d enfer]

Now i do need a suggestion - I remember Jim Williams talking once of the importance of removing coupling cups if using more modern op-amps like the LT1357 or OPAs, so I wonder are the coupling these once in the picture? Shall I remove them?

I think you misunderstand something. 5534's have compensation caps across pin 1 5 & 8. Some opamps misbehave when they are put there and the cap is not removed. Anyway I don't think you can expect much audible improvement over a 5534.

 

[sage]

I found a couple of 5534s and i must say that this unit seems to sound best right now with the 5534 - so i might just get new 5534s and stay with the original configuration that way -

So If i am understanding right the caps I indicated in the photo should be removed if I decide to keep the National 49710 ?

all 4 of those?

I did put numbers on the pic to be more clear -

thank you

 

[Harpo]

all 4 of those?

only remove compensation caps #1 and #3, connecting to NE5534-pins 5/8 (both probably 22pF) for differing opamp.

 

[gyraf]

Strange way of doing gain reduction..

What component is U2 on the limiter card?

Jakob E.

 

[abbey road d enfer]

Strange way of doing gain reduction..

What component is U2 on the limiter card?

Jakob E.

Considering the way it is connected and the fact that the audio voltage is partially injected, I think it is probably a dual FET.

 

[sage]

You can probably look at the schematics I posted and probably understand a lot more than i do from those...
I think this is a FET type of compressor, the back can appears to be the FET component, I had never seen one in an encloser like that or OVEN like someone on this thread called it...
I cannot tell what type of FET it is and on the schematics it is listed as EFT LMX 2 - which to me sounds like they made this name up, could have they possible have built that?

A strange thing happened when recapping I noticed of the electrolitic caps axial had the + pointed on the different direction than what the PCB had marked on the opposite side, all the other caps had the + corresponding to the + on the PCB so I decided to put the new radial caps following the PCB markings. It's working great, so I guess polarity must have not be important in that position.

There is a very annoying thing : this unit picks up interferences, not radio but a strange electrical buzz that comes and goes... perhaps this could be cause it's wired unbalanced?

I really wanna try to include an output trafo and make this a balanced signal coming out, I hope that will take care of the interferences and clean up the signal.

I will try to remove the coupling caps as suggested by Harpo in 1 unit and see how the newer Opamps sound otherwise I might stay with the original 5534s as so far are  the ones that sound more open and natural at least at the moment, once I will have it in the studio I would be able to do a better test.

THE EQ has been recapped and WOW - it is a phenomenal EQ, very detailed, loads of options, the cuts are great, cutting the high and the lows completely results in NO sound at all. I think I will be really able to use this in the studio, I have a Focusrite EQ and it is detailed and very transparent, this seems to be having same precision but more character, truly impressed, perhaps I will make a little video and post some here to show the EQ in action. So far all tests are NOT scientific but just HEAR and TELL....

I also wanna put in  it the optional  1:1 output trafo in the EQ. The original design calls for it so since I have 3 of these units I can try on 1 and decide if it's worth changing all.

Thank you so much for following this tread!

sage

 

[sage]

SO I ended up inserting 2 type of Cinemag Output trafos in the EQ units I have - since i have 3 units I left 1 without and the other 2 I have 2 different types that David at Cinemag built for me, one has a 50/50 copper/steel (I think) and the other is 100% copper.

I wil do some testing now that they are in the rack and patched -

ONE IMPORTant thing I noticed right away is that those units are loosing 6 dBs in the path - any other unit in my rack what goes in dB wise comes out but all those EFT units loose 6 dBs even in Bypass -

I know they are unbalanced so could this be the reason? Is there anything that could be done, I know on the compressors it is easy to compensate but on the EQ I wonder if this will compromise the purity of the signal.

Is there anything else other than the UNBALANCED input that could cause this loss ?

sage

 

[abbey road d enfer]

all those EFT units loose 6 dBs even in Bypass -
I know they are unbalanced so could this be the reason?

Looking at the schemo of both the EQ and the comp, the input stage is unity gain. When the units are in bypass, the output comes directly from the input stage so you should not experience any loss, but make sure the negative input leg is connected.
The EQ gain structure is not correct. The post gain buffer has 5dB loss and the output stage has 5dB gain to make up for the loss, which may be correct maybe not, because it is correct only when the gain pot is at max or when the sum of EQ's result in overall gain - not good news for those who favour negative-only EQ.
The operating level is a compromise between signal-handling (headroom) and signal-to-noise ratio.
Reducing the operating level, as it's done here, is good for headroom but detrimental for noise.
You could increase the output gain by increasing the 47k in the FB or decreasing the 27k at the input of the output stage; that would increase headroom.
OR.
You could increase the gain of the buffer by increasing the FB res (27k) or decreasing the input res (47k); that would improve noise.
Personally I always favour the solution that gives the best noise figure, so I would decrease the input res to 27k, that would  make the input buffer unity-gain.
For the limiter, it's a slightly different situation; you can't increase the operating level because the FET(s) would distort - as it is, it already runs pretty hot, about 10dB hotter than in an 1176. So you can only increase the output stage gain, by decreasing the 2.2k at the foot of the FB loop. Make it 1.1k and you're done.

 

[sage]

WOW ! That is amazing !
That is why I love this forum - I would have never been able to come up with this solution!

I will certainly try this solutions - it might take me a minute but I will try them as it bothers me to have this significant signal loss.

In the meantime yesterday we tested the EQs extensivly on Accs Gtrs, Clean Electric, Bass, Vocals and Over Heads -

At the moment I have installed the Optional Output Trafo on 2 units, one has the Cinemag CMOB-2L, the other the CMOB-2H -
Sonically the one without trafo sounds very close to the CMOB-2L but it has incredible noise and interference, so the trafos really take care of all that junk making the signal really nice and clean.

I prefer the sound of the CMOB-2H , High NIckel 80% - round - full, beaitifulquality EQ for vocals and Over HEads sounds great -
This is no cheap unit, I think I have a acquired a real nice piece of equipment here and next time I will go to Italy i should look for more of these units! I can see using them in mixing a lot considering my MCI EQ on the board is nice but not has detailed.

Again thank you and I will post again once I test the compressors -

sage

 

[abbey road d enfer]

At the moment I have installed the Optional Output Trafo on 2 units, one has the Cinemag CMOB-2L, the other the CMOB-2H -
Sonically the one without trafo sounds very close to the CMOB-2L but it has incredible noise and interference, so the trafos really take care of all that junk making the signal really nice and clean.

That is a sign that there's something wrong in your installation, unless you have very long cable runs, which I doubt.
It seems the problem occurs when you connect the output of one of your units to something. Is this "something" unbalanced? Is this "something" powered from a different outlet? Tell us a little more about your setup.

 

[sage]

I have a MCI JH 636 board, my outboard gear is in 2 racks about maybe 25 feet run of cables -
I tested the other units of the rack and what goes in comes back to the board - no signal loss on the Neve or LA3A or LA4 or 1176 Rev A, D or H that i have...

Only the EFT have unbalanced inputs/outputs.

So I have installed the OUTPUT trafos to balance the signal out, as I said it is incredible that the 2 EQ units with Trafos now are super clean but the one EQ still without has quite a bit of noise. SO i have just ordered a 3rd transformer.

As far as the signal loss ONLY the EFT units (both the Compressors and the EQs) have this 6 dBs loss, all the same amount - , so there's something common on these units that make the signal be loss.

You mentioned the negative leg being connected - I think the way they are wired the negative is not connected to the PCB, it is a Unbalanced input on the PCB so there's + and Common I think only.

Same on the Output - does it show differently from the schematics? How would I connect the negative ? I have to check maybe it is already connected to Common but I am not sure now.

Again thank you!

sage

 

[abbey road d enfer]

Schemos show that neg leg is optionally connected to common (according to schemo, there should be an optional link). Seems like the normal operation is balanced in-unbal out. You should make sure that the neg leg (pin 11) is NOT connected to common in order to benefit from balanced in.
Then your connection should be signal + to pin 12, signal - to pin 11.
Shield may or may not be connected. Typical 70's manner suggests shield to common (0V), but we know better now (do we?). I would recommend first connecting shield to chassis. You also need to check if and how common (0V) is connected to chassis.

 

[sage]

HI
i wanna make sure i understand correctly... if i put signal in - to pin 11 than do i also put signal out - to pin 11 ?

Ground from XLR right now goes to chassis thru the xlrs and then to the main ground from power - as at right now ground from Common is not connect - only wire connected is RED to Trafo -

My only question is right now My OUTput trafo has a wire connected to 11, I assume that is the common to trafo but what do i do with it?

 

[sage]

or shall the RED wire that now is connected to common go to chassis ground?

 

[abbey road d enfer]

HI
i wanna make sure i understand correctly... if i put signal in - to pin 11 than do i also put signal out - to pin 11 ?

No. Don't change the output wiring.

Ground from XLR right now goes to chassis thru the xlrs and then to the main ground from power - as at right now ground from Common is not connect - only wire connected is RED to Trafo -

My only question is right now My OUTput trafo has a wire connected to 11, I assume that is the common to trafo but what do i do with it?

The output xfmr should be connected between pin 10 and common (pin9 - 3).

 

[sage]

Yes - that is the way I have it now but still I have a loss of 6 dbs... so strange - if i connect the cables from the patch bay NO LOSS of course. With the unit OFF it passes audio and still I have the 6 dBs loss.
Taking OFF the whole EQ card it does not pass audio so I wonder if this circuit is designed to load the signal down 6 dbs...

I am not sure where to look other than the wiring cause I am not a tech unfortunately.... but i know it is not a random thing cause i have 3 EQs and 5 compressors in these two units and they all do have the 6 dB loss - obviously with the compressor is not an issue as it has quite a bit of make up gain but for the EQs I am puzzled.

sage

 

[sage]

Also wanted to point out that at the bottom right of the schematics it says:

IN BIL (it means BALANCED IN) then some letters are crossed
IN SBIL (it means UNBALANCED IN) and other letters are crossed

not sure what that means but maybe that is the key?