[BUILD] 1176LN Rev D DIY

[babaorum]

I removed these pins from the ratio potentiometer, like with the rotary version doc,
is that ok with the v2.2 rev D  version ?

 

[dmnieto]

I do, I see a significant drop in the meter when following the conditions above.  The needle drops to about "-4.5" when I switch it on.  I also hear a significant drop in sound level.

Then the issue is in the GR meter circuit, It could be that the FET is not properly polarized (check for cold solder points around the GR meter) or an issue with the differential amplifier.

Check R70 an other resistors for the correct values... did you actually close the jumper TP1 ?

 

[omribgr]

Hello there,
Ive just started to build my first 1176 rev d. (from Hairball audio)
on the PCB i have 2 testing points, 30v an -10v (DC)
the -10V shows -0.97 , but the 30V shows 37V...
does someone experienced the same problem ? what components do i have to check ?

 

[dmnieto]

Did you mount the Zener on the wrong way?

If you were reversing the Zener, that would made the difference between COM and -9 to be equal to the Vf of the Zener (which should be around 1.2V), which is similar to what you are getting.

 

[omribgr]

ohh sorry I wrote -0.97 but i meant -9.7V, my mistake ...the problem is with the +37V
I've checked the AC voltage that the PCB gets from the power transformer and it shows 28V (AC) for each AC input (there are 2 on the PCB)

can it be the problem ?  i think the power transformer suppose to supply 25V

 

[andyfromdenver]

ohh sorry I wrote -0.97 but i meant -9.7V, my mistake ...the problem is with the +37V
I've checked the AC voltage that the PCB gets from the power transformer and it shows 28V (AC) for each AC input (there are 2 on the PCB)

can it be the problem ?  i think the power transformer suppose to supply 25V

Hi, did you measure all the resistors prior to placing them?  I'm guessing 37vdc will be a tad too high, may not be a problem, not sure.

To clarify, just your power section is built, like the Hairball recommendation right?
Also, see what your wall is putting out. 

 

[omribgr]

first of all - thanks a lot !

so I've checked every resistor prior to placing them with two different multimeters ,i bought everything from hairball and did every step in their building guide..
i've added here the power supply section from  MNATS website.
i think as you say maybe a bigger dropping resistor will fix it ... but i'm not sure which resistor to change and what size  :\ so if you can tell me from this schematic what can i do , I'll really appreciate it

 

[andyfromdenver]

I wish I could say for certain, but I can't
My personal X factor is  the  vr1.  Hopefully another can help.  Just for fun, can you post an up close of that section for a second pair of eyes?  No solder bridges underneath etc?

 

[dmnieto]

first of all - thanks a lot !

so I've checked every resistor prior to placing them with two different multimeters ,i bought everything from hairball and did every step in their building guide..
i've added here the power supply section from  MNATS website.
i think as you say maybe a bigger dropping resistor will fix it ... but i'm not sure which resistor to change and what size  :\ so if you can tell me from this schematic what can i do , I'll really appreciate it

The only way to have 37V there is that you have a broken regulator or the wrong resistors.

VR1 should output 24V across its pins OUT and COM, so you should be getting ~24V across R87, measure it.

If you have 24V across R87, then check the resistors and measure again. You probably have the wrong ones.
If you don't have 24V across R87 then maybe you have:
-Interchanged R87 and R89
-Inserted VR1 the wrong way.
-Have a fucked up VR1

 

[omribgr]

O.K i think I'm getting closer so i bought 2 new VR1 and this is what I've found:
1)the legs of the first one shows 34.8V DC and the second one shows 36 V (which is better than 37 )
2)it shows the same voltage on the legs of the regulator and at the checking point, which means that
now the situation is better (34.8V)
so how bad is it ? can i live with 34.8?


thank you all

 

[dmnieto]

O.K i think I'm getting closer so i bought 2 new VR1 and this is what I've found:
1)the legs of the first one shows 34.8V DC and the second one shows 36 V (which is better than 37 )
2)it shows the same voltage on the legs of the regulator and at the checking point, which means that
now the situation is better (34.8V)
so how bad is it ? can i live with 34.8?


thank you all

What is the voltage across R87?

 

[cpeterson]

Hello!
Myself and a friend are lucky enough to be building three hairball 1176's between us...
One of them which is sort of completed, we've come to calibrating it and realised the following problems...

-The input knob only increases the gain until it reaches 18; after that nothing increases or decreases
-The +4/+8 metering jumps as I turn up/down the output knob; if it put signal through it usually stays fairly flat out
-When i plug an XLR into the output the meter jumps as well- goes crazy. That bit is random- sometimes it will sometimes it wont..
-Passes audio cleanly when the output meter jumping doesn't happen.
-Turning the q bias adjust for the first calibration seems to do nothing. :/

-I printed off the circuit diagram with the dc voltages AND HERE ARE THE RESULTS! *drum roll*...
Everything is correct except for the GR meter driver section.

q11- D= 17.37
        S= 1.668
        G= 1.815

q12- D= 1.68
        S= 17.34
        G= 1.669

q13- D= 1.64
        S= -1.63
        G= -1.03

99.9999*% everything is correct in terms of wiring AND pcb board... its identical to the other two.

Any response would be HUGELY appreciated...

 

[cpeterson]

Ok now this is weird...

Input knob is now fine, same with output knob.
But no compression and still no apparent change when calibrating with the q bias adjust...

 

[andyfromdenver]

Cpeterson, did you follow the Hairball build guide? 
If so, you likely put the bias trimmer in the opposite way of the mnats video for example.
One thing I noticed, and it's probably been stated, if you did the mike trimmer placement qbias starts fully ccw and turn clockwise until the drop, if placed per mnats it's opposite.
Also, the Hairball guide (as of last time I checked states to put it in gr mode, when it should be +4.

Hope that helps, two ways to skin the cat

Also, is your output pot scratchy?  I coulda swore up and down I didn't misplace a component, but low and behold I put c7 in backwards which puts DC on the output and made it scratchy and jumpy.

Good luck!!

 

[omribgr]

so that's where it stands now : (I took some pictures to make it easier )

1) the 28.1V is the AC power of input 2 ( one gets the same power)
2)the 34.7V is the DC power on the leg of the R87 (1.1k resistor) , this is the problematic value (suppose to be 30V) 
3)the -9.8V is the DC power on the leg of the CR6 Diode (which is a correct value )
4)the  12.12V is the DC power on the legs of the 220 ohm resistor (R89)
5) the 37V is the DC power on the leg of the CR7 Diode .

6) only that you'll see that everything else is ready except the PCB 

so my guess is that the problem is on the AC power that the PCB gets, I think it suppose to be 25V AC for each input .
i also think that the Diode (CR7 ) should be 35V DC  (you can't see it on the MNATS schematics but on the original schematics
on the dot between the C25 and CR7 )
what do you think guys? if you agree maybe i can drop it somehow with a resistor ! (before the PCB)
and dmnieto , thank you for the help , really, I'm hopeless!

the links for the pictures: (direct links to Dropbox)
https://dl.dropboxusercontent.com/u/83599022/1176/picture01.JPG
https://dl.dropboxusercontent.com/u/83599022/1176/picture02.JPG
https://dl.dropboxusercontent.com/u/83599022/1176/picture03.JPG
https://dl.dropboxusercontent.com/u/83599022/1176/picture04.JPG
https://dl.dropboxusercontent.com/u/83599022/1176/picture05.JPG
https://dl.dropboxusercontent.com/u/83599022/1176/picture06.JPG

 

[dmnieto]

so that's where it stands now : (I took some pictures to make it easier )

1) the 28.1V is the AC power of input 2 ( one gets the same power)
2)the 34.7V is the DC power on the leg of the R87 (1.1k resistor) , this is the problematic value (suppose to be 30V) 
3)the -9.8V is the DC power on the leg of the CR6 Diode (which is a correct value )
4)the  12.12V is the DC power on the legs of the 220 ohm resistor (R89)
5) the 37V is the DC power on the leg of the CR7 Diode .

6) only that you'll see that everything else is ready except the PCB 

so my guess is that the problem is on the AC power that the PCB gets, I think it suppose to be 25V AC for each input .
i also think that the Diode (CR7 ) should be 35V DC  (you can't see it on the MNATS schematics but on the original schematics
on the dot between the C25 and CR7 )
what do you think guys? if you agree maybe i can drop it somehow with a resistor ! (before the PCB)
and dmnieto , thank you for the help , really, I'm hopeless!

the links for the pictures: (direct links to Dropbox)
https://dl.dropboxusercontent.com/u/83599022/1176/picture01.JPG
https://dl.dropboxusercontent.com/u/83599022/1176/picture02.JPG
https://dl.dropboxusercontent.com/u/83599022/1176/picture03.JPG
https://dl.dropboxusercontent.com/u/83599022/1176/picture04.JPG
https://dl.dropboxusercontent.com/u/83599022/1176/picture05.JPG
https://dl.dropboxusercontent.com/u/83599022/1176/picture06.JPG

I really don't know how to make the point across, but your resistors NEED to be of the wrong value.

1. The voltage across R87 is 34.7-12.2 is 22.5 which is a tad bit low, but within the tolerance of the voltage regulator (as there is a dropout from the 25V rectified AC to the output of the LDO).
2. I am colorblind, so it is extremely difficult for me, but I believe that R87 is BROWN-BLACK-RED-GOLD which is 1.0k+/- 5%, not 1.1k. That should still give you still possibly good values.
3. Now, with extreme difficulty I can see that R89 is NOT 220 Ohm... (RED-RED-BLACK), but somehow something like GREEN-GREEN?-BRWN (from your picture 5).

If we take those resistors: R87 1K and R89 550R we get that assuming 22.5V across R87, there will be a drop of  (22.5V/1000Ohm0 = 22.5mA*550Ohm => 12.35V) which is very similar to what you are getting.


So please, unsolder R87 and R89 check their values, and put the right ones in and you will get the right voltage.

 

[omribgr]

actually its really hard to see the colors on the pictures..
but the colors are RED-RED - BROWN -GOLD - for the 220 Ohm
and the 1.1K is BROWN- BROWN - RED- GOLD ..
and of course the resistors checked before it was soldiered with a multimeter

you can see here:
https://dl.dropboxusercontent.com/u/83599022/1176/picture07.JPG
https://dl.dropboxusercontent.com/u/83599022/1176/picture08.JPG

 

[dmnieto]

actually its really hard to see the colors on the pictures..
but the colors are RED-RED - BROWN -GOLD - for the 220 Ohm
and the 1.1K is BROWN- BROWN - RED- GOLD ..
and of course the resistors checked before it was soldiered with a multimeter

you can see here:
https://dl.dropboxusercontent.com/u/83599022/1176/picture07.JPG
https://dl.dropboxusercontent.com/u/83599022/1176/picture08.JPG

Cannot see the pictures from my work, but I am going to assume your eyes are better than mine.

If the voltage drop across the leads of R89 is 12.12V, that means that your circuit feeds R89 with 55mA of current, but the voltage drop across R87 is 22.58, so the regulator is only feeding 20.53mA. The only place the missing 22mA can come from is the COM terminal of the 7824.

But that cannot be,
If you look at the specs http://www.onsemi.com/pub_link/Collateral/MC7800-D.PDF (page 17), the maximum current can be Ib which is 8mA.

So there is something really weird going with your circuit.

 

[omribgr]

do you think i should buy a new PCB or going to a professional lab will help me ?

 

[dmnieto]

do you think i should buy a new PCB or going to a professional lab will help me ?

I dont think so... Just checking... have you verified that you have soldered the voltage regulator the right way?