[Igor]

Hi guys, we carefully checked all kits and almost ready to send them.....



BTW, maybe, there will be some kits available again

Meanwhile, please take a look at the documentation here:
http://twin-x.com/groupdiy/thumbnails.php?album=417

Update: last version docs, everything is here:
http://ij-audio.com/downloads/51XF76.zip

Download the files, take 10 min to meditate on all this, than,
after you catch the logic, take some time to read schems.

As an educational reading, schematic redrawn in the way it is easy to understand how 1176 works.

I tried to make this unit 1176'is much as possible, however, if I have a choice, will never use "original" 1176 amplifiers of any version.
Yes, OK, this kind of compression did many great music, and this sound wrote history.
Anyway, kill me, the 1176 amps are out of my taste after building of some clones, comparing with "original", etc....
I had to make it more versatile, and to have more options with sound color.

You have some really nice surprises here. This unit can run at +/-16V, as well as on both +/-16 and +/-24 rails of 51X,
try my cascode topology input stage amp, with API output amp and Ed Anderson's 11148 replica for 500 format,
and tell about sound; yep, lot of color, all you freaks will like it 
My taste is my input amp, LL1524 and my own out amplifiers (with all DOA's are running on +/-24V), it is less colored,
but the color itself is way more "pedigree", well, leave my fubaru English, back to stuff!


The next 2 posts will be reserved for assembly guide, FAQ, some howtos, and test procedure.

[Igor]

/reserved for assembly guide/

Full assembly procedure will be posted, but please take a look, here are some very important bits.

Grayhill switches stoppers:



Put them as shown than attach stickers over it.

Meter LED's:

To have a very neat look, we using flat top LED's. There is a little trick.



First, see where + and - goes,  (check twice, put LED on PCB and put a dot on led's pins with a marker), than cut.



Than, solder first and last LED's. They should be very close to PCB.





Than, put the rest of LED's at their holes at front panel:



Line them up and solder...










Another freaky but same easy moment is RATIO and SLAM.

First, put RATIO switch and catch it with 2 pins:



Than, CUT the pins which at the side of SLAM pushbutton at the level of PCB and solder:



Well, more coming soon. Prepare to see really neat and easy assembly pictures !

   

[Igor]

51X-F76 test procedure.

Important.
1). When running on +/-16V, in 500 format, install jumpers JP1, JP2
and cut pins 17/18 of card edge connector.

2). When running at +/-16 and +/-24V, !DO NOT! install these jumpers,
they can cause damage to power supply.

3). After running many audio tests, the best sounding FET's here, IMHO, are 2n5457,
BUT the PCB was designed for BF245.
Stereo kits were supplied with matched within 0.5dB in gain reduction range 2N5457 FET's.
IF using 2n5457, they have pinout GSD instead of DSG like BF245.
They won't be damaged if installed wrong way, but compressor will not work properly.
The right way to install 2N5457 in sockets:




After PCB's stuffed and everything checked, every component in place-

http://i251.photobucket.com/albums/gg291/diy33609/51F_X76/51xf76_assembly/P1050847.jpg

Step 1. Audio (sound path).

Do not install audio and gain reduction FETS (2N5457 or BF245, Q1 and Q10).
Do not connect RATIO/ATTACK/RELEASE board.

Current draw.
Do not install input/output amps and chips in sockets; check if no smoke and current draw;
check -10V at LM337 out.

On FP (10 pin, dual raw) connector on motherboard,
short pins 9 and 10 to switch relays from BYPASS state to COMP IN.
(PC jumper will work fine).



Install input/output amps. Check if current draw is less than 70mA each +/-16 and +/-24V.
If don't have lab power supply, measure voltage on R91, 92, 93, 94 resistors (10R),
it should be maximum 0.7V at any resistor.


Now, we can check the amplifiers.

Input amp.
Close input and output pots, and, if my version of input opamp is used,
put DC voltmeter between amp's out and ground adjust amplifier's output
for +0.3...1V with trimpot located on amplifier's PCB.



Note 1: let amp heat up 5-10 min.
Note 2: to get VERY tasty sound from this amp, connect 1...2k, 1/4W resistor between its out and gnd.



Scope shows here transformer's, FET's and amp's residue on hot signal, COMP=OFF.
(For those who knows what is real cool harmonic signature)))

http://i251.photobucket.com/albums/gg291/diy33609/51F_X76/51xf76_assembly/P1050930.jpg

If "original" amp used at 24V power supply, check its output is in range +12V +/-10% ref. to gnd.

Output amp.
Check DC offset is in range few millivolts ref. gnd for DOA or is +12V +/-10% for "original" amp.
Same way as with input amp.

Let's check input/output pots, maximum gain +37db and distortion.
Feed -20dBV (0.1V RMS) to input of 51XF76, input pot=max, output pot=max,
with 2:1 input transformer or balanced line receiver, and 1:2 output transformer,
maximum gain should be 36...37dB (output shows +16...17dB).

Feed 1V RMS to input, put input/out pots somewhere in the middle, check the distortion is less than 0.02%.
Check max. undistorted output is +24db at least.

Let's adjust 0=+4dB on meter.
Put GR/OUT switch in OUT position;
Connect AC voltmeter to output, adjust input/output pots for 1.23VRMS output and turn MTR_OUT pot untill yellow led
(0db) lits on; than, turn it back a bit to let LED go OFF, again, slightly turn to lit the yellow led ON.
This way, we can have more precision in multiple channels (the led meter is not linear thing, but we want
to catch the same threshold to light on the leds).


Step 2. Compression (sidechain, GR metering, BIAS, etc).

Connect RATIO/ATTACK/RELEASE board (and remove jumper between pins 9 - 10).
SLAM is OFF, LINK=OFF, RATIO at pos. COMP OFF, ATTACK=MIN, RELEASE=MAX.
Feed -20db to input, INPUT=MAX, adjust output for 0db.
Put FET's in sockets (Q1, Q10; mind, silkscreen is for BF245, 2N5457 are reversed).

Adjust BIAS for -1db.
If building stereo pair, adjust second chan. for -1dB BIAS as well.

Than, LINK=ON. Both should remain in same level. If no, adjust a little bit BIAS of one of channels.
+/-0.2db is fine.

BTW, don't forget to connect wire at back side of PCB if use LINK.





Back to Channel 1.
Distortion cancellation circuit.
Adjust DIST (R16) to get minimum of distortion on sinus wave.
Or, misadjust a bit for color, but mind, too much will not sound good.
0.01....0.04% THD is fine.
This step requires audio analyzer or PC soundcard.

GR meter.
!AA
Remove input signal, put METER to GR, and adjust 0 with 0GR trimpot.
Yellow LED should light ON. Light ON the +1 RED LED, than, turn the pot back, just to leave yellow LED.
Repeat this step 1-2 times.

Apply input signal 0db, and put INPUT approx. at 14.00 pos.

Set RATIO to 4:1 and check the output.
Find input potentiometer's position which has output change
between COMP.OFF and 4 ratio setting of 10dB gain reduction.
Adjust GR_SCALE trimpot just to turn ON -10 db LED, turn it back,
and find the threshold of -10 LED.
!BB
Repeat from !AA to !BB till you get nice meter reading
with and without 10db of gain reduction.

Apply audio and listen.

Have a fun!

[culteousness1]

Hey all.

I am almost done with the control board. Now I found that R76 seems to be mislabeled on the board.
Printing says 470R but BOM says 470K. I guess the BOM is right. Igor? Help!

Cheers,
Carsten

[Igor]

R76, according to schematic, is resistor at attack switch assembly, in parallel with 22nf; it is 470 Ohm.
Am I missed something:

1   470R        1/4W METAL FILM 1%   R76

[culteousness1]

Ok. Thanks for clearing that up.

[zmgwg]

Igor, will a EA-2623 work on output with this?

[edanderson]

electrically, it "should" work, but the 2623-1 is a smaller transformer than the b11148 or 2503, so mechanically it might be a little flimsy -- only one of the screw holes will line up with the PCB.  you could make a little riser for it to sit on, out of PCB stock or plexi, that fits the cutout on igor's PCB.

ed

[reanimatorstudio]

The next 2 posts will be reserved for assembly guide, FAQ, some howtos, and test procedure.

good idea!!

[culteousness1]

Hi team,

I am almost done with this thingy. I only need to figure out what pot values are suitable for the I/O amps.
I am planning to use the provided IC amps and gar2520s.

Could someone please give me a hint?

Cheers,
Carsten

[briomusic]

Hi all,
I bought Igor's pcbs for this project, but not the kit.
I would like to start with a 'poor man's' version, so thats the lorlin/pot front and the IC amps I guess?
I am a bit confused - do I need to buy additional DOA's or do the little extra PCBs for the various in and out amps already constitute those DOA's?
The front panel in all the photos is for the grayhill version, and i need to make my own front for the lorlin/pot version, correct?
thanks
briomusic

P.S. I am also confused about what blocks go together and which are alternatives. Using the picture of a 4 course menu (with coffee and cognac  ) is the following correct:

INPUT TRANSFORMER
or
BALANCED LINE RECEIVER
--------------------------------------------
ORIGINAL INPUT AMP
or
IJ INPUT AMP
or
GENERIC DOA
--------------------------------------------
MAIN BOARD inc. METER
--------------------------------------------
1RU FRONT (LORLIN&POTS)
or
3 GRAYHILL FRONT
or
1 GRAYHILL AND 2 POTS FRONT
--------------------------------------------
ORIGINAL OUT AMP
or
IC OUTPUT AMP
or
GENERIC DOA
--------------------------------------------
OPTIONAL OUTPUT TRANSFORMER

[AudioGimmer]

I don't know if I can answer all your questions re lorlins and pots, but if you want the lowest cost options then you are right:

Thats balanced line receiver [ no input tranny ] with pot

IC input amp JFET
IC output amp

The choices are then determined by power supply:

ONLY +/- 16 [ 500 series rack] use AD711 etc for input amp and 5534 for output
511 rack with additional +/- 24 use OPA 604

You can only use the orig amps if you have the +/- 24 as well as +/- 16

Hope that helps a little

The Gimmer

[briomusic]

Thanks, this does clear things up a bit for me.
I do have a 51X rack and plan to check out the original amps at some later point.
So the line receiver replaces the input tranny, but I will need the output tranny in any case?

as for the controls, I think the cheapest 5xx style option is 1 grayhill (ratio) and two pots. the lorlin options is for rackmounting, it seems.

[culteousness1]

Hi all,

my question remains. So, please, give me a hint!

Cheers,
Carsten

[AudioGimmer]

Hi Igor, the F76s are coming together. Couple of questions:

1.) The output pot, what value is good here? I've used the grayhill switches so I have two pots over as part of the kit. Either of those any good? Otherwise a quality Bournes maybe, but suggested value?
2.) The link wire for stereo on the bottom of the board, is that needed for the stereo link to work, or just for calibration purposes?

I've gone with hairball's input tranny and  T-pad attenuator [not cheap, but I wanted the tranny input ] and Lundhal 1524 on the output.

I'll have to drill the bracket and faceplate for the attenuator, but you can't make an omelette without cracking eggs!!!

The Gimmer

[AudioGimmer]

Ok progress reports, how are people getting on with their F76s?

I'm about done with soldering number 1, got number 2 to start, then testing, adjustments and final assembly.


These things are crammed! how Igor fitted it all together is impressive:


Some observations.
If you are using T pad input w tranny, you need to drill out the aluminium bracket to accommodate the attenuator [ approx 10mm in my case] Need to find a way to pack out the rear of the bushing so only the nut is on top of the bracket, otherwise the faceplate won't sit flush.

I also needed to very gently open up the holes in the faceplate for the Grayhills and output pot. [I did it with a 6.5mm drill bit just held in my fingers]

Igor's input amp is TINY My optician won't be pleased next time I go see her.

Igor's tip for lining up the LEDs worked a treat, very neat

I bought some extra op amp pins so I can try some different options, like 2520 for output

I just have one question: I haven't put a zobel network in for my output tranny, do I need one for the LL1524?

Anyone else?

The Gimmer

[Igor]

Hi Igor, the F76s are coming together. Couple of questions:

1.) The output pot, what value is good here? I've used the grayhill switches so I have two pots over as part of the kit. Either of those any good? Otherwise a quality Bournes maybe, but suggested value?

The pots supplied with the kit are 10k log. Citec is high quality, I use them for years.

They can be used as input with balanced line receiver (THAT1246/INA137) and as output.

To get more smooth curve, take into account I don't need more than -40 db at neither in or out pot,
I connect the bottom (by schematic) pin of these potentiometers to ground via 100R resistor.

2.) The link wire for stereo on the bottom of the board, is that needed for the
 stereo link to work, or just for calibration purposes?

Rev.1.3 has this connection (trace) at PCB; at rev.1.4 I fixed some mech. issues, and this link has gone somehow.

To make a pair working in stereo link, you NEED this wire.

I've gone with hairball's input tranny and  T-pad attenuator [not cheap, but I wanted the tranny input ] and Lundhal 1524 on the output.

More distortion (iron); sounds nice as well.
Possible to use Elma 14mm, with line, grey, 6mm edit: 6.3mm shaft knob for Hairball T-PAD.

I'll have to drill the bracket and faceplate for the attenuator, but you can't make an omelette without cracking eggs!!!

The drill in bracket is for Citec pots, diam. 6.3mm. For 600 Ohm attenuator, you need to make hole bigger (9.5 or 10mm).

[Igor]

Some observations.
If you are using T pad input w tranny, you need to drill out the aluminium bracket to accommodate the attenuator [ approx 10mm in my case] Need to find a way to pack out the rear of the bushing so only the nut is on top of the bracket, otherwise the faceplate won't sit flush.

Yep)

I also needed to very gently open up the holes in the faceplate for the Grayhills and output pot. [I did it with a 6.5mm drill bit just held in my fingers]

Yep)

Igor's input amp is TINY My optician won't be pleased next time I go see her.

I have -7.5 on both eyes) But hey, this amp DOES sounds, aye?

Igor's tip for lining up the LEDs worked a treat, very neat

Thanx)

I bought some extra op amp pins so I can try some different options, like 2520 for output

That's funny. I tried about 15 different amp options, all have bit different sound.

I just have one question: I haven't put a zobel network in for my output tranny, do I need one for the LL1524?

O! That's important. Zobel network for LL1524.

Datasheet says nothing. However, I had some of these trannies used on SEEM AUDIO equipment;
they used 150R in series with 10nF (Wima, 100V, MKS-3) capacitor, without load (probably, the trafo was loaded at another stage).

For me, it is bit over-cut;
I used 1k...2k 1/2W resistor as load; 150R (1/4W) and (4n7...8n2) poly, 50...100V capacitor as Zobel.

Who finished the build? Have some time, at least this week, post questions now.

[Igor]

I am almost done with this thingy. I only need to figure out what pot values are suitable for the I/O amps.
I am planning to use the provided IC amps and gar2520s.

10k, log

IMPORTANT

For use with input line receiver, DO NOT INSTALL R5' = 270R!!!!

For use with input IC amp, INSTALL R11' = 560k.

This resistor IS installed on "my" or "original" input amp PCB.

[Igor]

So the line receiver replaces the input tranny, but I will need the output tranny in any case?

100% right.

as for the controls, I think the cheapest 5xx style option is 1 grayhill (ratio) and two pots.

Right. But, getting 5meg lin pot is not easy, so...
the difference in price between attack/release pots/Grayhill switches is approx. USD12-15.

the lorlin options is for rackmounting, it seems.

Yep)

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