[BUILD] 1176 Rev A - Back to the beginning...

[thomasdf]

I am SO in love with my Hairball Rev A old version. It's just plain incredible and does something awesome to any vocals I run thru it.

So here's my question : if I want a pair of them, are there any circuit changes between the old and new kits ?

 

[dribro]

hi.
cannot wrap my head around Igor's F76 LL1524 schematic and Rev.A output feedback. Maybe this traffo can't be used with Mnats 1.25 boards?
As i have a LL1524 pair, i might as well use them. They are so good.
As per Igors, primary + 12/7 and - 11/8; output +6/3 and 4/1 shunt. But then i have 5/2 not connected but i tested these are outs too.

any help is welcomed

 

[Potato Cakes]

I am SO in love with my Hairball Rev A old version. It's just plain incredible and does something awesome to any vocals I run thru it.

So here's my question : if I want a pair of them, are there any circuit changes between the old and new kits ?

I've built the old ones and the new ones. The only difference I know of is the board layout, which makes it much easier to assemble and has an integrated option to add an active stereo linking option.

Thanks!

Paul

 

[Poupignon]

Hi everyone.
I just finished my 1176 rev D,
But the sound is completely distorted.
And the unit, more precisely, the transformer make a strange noise like whistling like a radio…
If someone can help me…

 

[Ilya]

Hi. This is Rev A thread, not Rev D.
As for your issue, this sounds like an oscillation in high frequencies. Check for proper wiring.

 

[HerbertR]

Hi, ve built a pair of Mnats 1176 A's and I measured wrong DC Voltages on the two JFets J309. Also my Output Level feeding with an 1kHz Sine is very low.
So I ve measured the 309J's and have recognised that they are BJTs and not JFETs!!! Original Aliex Fairchild Quality........ Hell.... Five meteres before finishing the units...... I also made the expierence with BF245A's... Especially always with Fairchild brands... Cheap BJTs reprinted in China... I am such an Idiox........ Sorry for my words....

 

[mike_signo]

Hi everyone, I hope you're having a good day!
I just finished building a Rev A kit (V1.25 05/12/10) but I've encountered some problems during the calibration procedure.
There's clearly something wrong with it.

I started by trying to set the Q Bias with the procedure on the hairball website:
------------------------------------------------------------------------------------------
Input = "24" mid-rotation, Output = "24" mid-rotation
Attack = full CCW (switched to off position)
Release = full CW
Compression ratio = 20:1
Meter mode = "GR"
Q-bias adjustment = full CCW
Shorting pin in "normal position" connecting the two pins closest to Q13

Apply a 1 KHz O dBu signal to the input and confirm with your DMM between pin 2 and 3 of the input XLR. Now move your DMM to the output XLR and measure AC between pin 2 and 3. Adjust the output control to read +11dBu (2.75 VAC) on your DMM at the output. Slowly turn the Q-bias adjust (R59) CW until a drop of 1 dB occurs, and your DMM reads +10 dBu (2.44 VAC). This places your gain reduction FET Q1 slightly into conduction.
------------------------------------------------------------------------------------------

I'm not able to have enough gain to reach 2.75 VAC on the output and proceed with the calibration, I barely reach 1.4v (all of this with the Q Bias pot fully CCW, If I start to rotate clockwise I can reach a much higher output level).


I tried to examine the Bias voltage on pin 18 and I noted an excursion from 0 to -2.8V which doesn't coincide with the values on the troubleshooting guide for Rev A (https://help.hairballaudio.com/hc/en-us/articles/360045942974)
I strangely have the same values present on Rev D......

I checked all the voltages, Power supply, and all the other voltages indicated on the schematic (Revision A DC Voltage Chart). They all are in the +-10% range, mostly spot on.

I checked the ac voltages and there's clearly a problem

Test Point	Revision A (ideal)	My Rev A
TP1	0.100 VAC	0.100 VAC
Q2 Gate	0.084 VAC	0.003 VAC
Q3 Base	0.051 VAC	0.001 VAC
TP15	3.60 VAC	0.040 VAC

I already tried to change Q1,Q2 and Q3 with no success.

I believe the problem is related to the Bias voltage or something related to it. When following the procedure to set the Q Bias I noticed that the output level increases with turning the trimmer clockwise, the bias voltage will go more negative as well reaching -2.8 at the end of the pot.
I attached a video of the failed calibration procedure.

Thanks to everyone that will find some time to help me!!!
Michele

 

[corgan4321]

I'm not able to have enough gain to reach 2.75 VAC on the output and proceed with the calibration, I barely reach 1.4v (all of this with the Q Bias pot fully CCW, If I start to rotate clockwise I can reach a much higher output level).

you're looking for 0dBu or .775v AC signal on the input. Also, your q bias adjust should be in the position where you get most gain, then set output to +1dB on the meter. Then turn the trimmer so you get the meter showing 0dB. My experience if that the specific amount of signal you're putting in isn't important, just that your adjust is set to reduce the meter level by 1dB

 

[znjamznjam]

Hi everyone, I hope you're having a good day!
I just finished building a Rev A kit (V1.25 05/12/10) but I've encountered some problems during the calibration procedure.
There's clearly something wrong with it.

I started by trying to set the Q Bias with the procedure on the hairball website:
------------------------------------------------------------------------------------------
Input = "24" mid-rotation, Output = "24" mid-rotation
Attack = full CCW (switched to off position)
Release = full CW
Compression ratio = 20:1
Meter mode = "GR"
Q-bias adjustment = full CCW
Shorting pin in "normal position" connecting the two pins closest to Q13

Apply a 1 KHz O dBu signal to the input and confirm with your DMM between pin 2 and 3 of the input XLR. Now move your DMM to the output XLR and measure AC between pin 2 and 3. Adjust the output control to read +11dBu (2.75 VAC) on your DMM at the output. Slowly turn the Q-bias adjust (R59) CW until a drop of 1 dB occurs, and your DMM reads +10 dBu (2.44 VAC). This places your gain reduction FET Q1 slightly into conduction.
------------------------------------------------------------------------------------------

I'm not able to have enough gain to reach 2.75 VAC on the output and proceed with the calibration, I barely reach 1.4v (all of this with the Q Bias pot fully CCW, If I start to rotate clockwise I can reach a much higher output level).


I tried to examine the Bias voltage on pin 18 and I noted an excursion from 0 to -2.8V which doesn't coincide with the values on the troubleshooting guide for Rev A (https://help.hairballaudio.com/hc/en-us/articles/360045942974)
I strangely have the same values present on Rev D......

I checked all the voltages, Power supply, and all the other voltages indicated on the schematic (Revision A DC Voltage Chart). They all are in the +-10% range, mostly spot on.

I checked the ac voltages and there's clearly a problem

Test Point	Revision A (ideal)	My Rev A
TP1	0.100 VAC	0.100 VAC
Q2 Gate	0.084 VAC	0.003 VAC
Q3 Base	0.051 VAC	0.001 VAC
TP15	3.60 VAC	0.040 VAC

I already tried to change Q1,Q2 and Q3 with no success.

I believe the problem is related to the Bias voltage or something related to it. When following the procedure to set the Q Bias I noticed that the output level increases with turning the trimmer clockwise, the bias voltage will go more negative as well reaching -2.8 at the end of the pot.
I attached a video of the failed calibration procedure.

Thanks to everyone that will find some time to help me!!!
Michele

Ha i have precise same issue as you with build A. My cue bias voltage is same as in build D (0v til -2,9
v in place A revision at TP18. I can set cue bias calibration but second step for metering is no go....

 

[bobbriessinck]

Hey all!
A few years ago I traded this got this RevA. Though, it was very prone to static noise, hiss, interference. I've got a 10kVolts cabin about 8 meters away from where I've got my little studio, it is also located in a small industrial area and always thought that the extreme static noises were a result of this cabin/the heavy machinery close by. After 4PM it always completely disappeared, that's exactly when the activities around here stop for the day. In the weekends it's clean too.
Now I decided to started digging some more and trying out some DIY shielding to start with using tinfoil. After a lot of trying out weird stuff I noticed the static increased by 20dB whenever I held my hand above a certain spot. Turns out it's the C2 orange drop cap. Whenever I even come close the static increases by 20dB, and when I touch it it goes up another 10dB.
Is this simply a bad cap? Will replacing it fix this issue? Has anyone had a similar problem?

The has a PCB marked with 2010 v1.25, so if the unit was built around this time it might be due for a total recap anyway.

Here's a link with a little video where I touch the cap and you see the static increase on the computer.

Thanks!
Bob

 

[MiamiBoy]

Have you tried to desolder that orange drop and inspect it? Maybe there’s something stuck there or loose. Or maybe it’s defective.

 

[Ilya]

Hey all!
A few years ago I traded this got this RevA. Though, it was very prone to static noise, hiss, interference. I've got a 10kVolts cabin about 8 meters away from where I've got my little studio, it is also located in a small industrial area and always thought that the extreme static noises were a result of this cabin/the heavy machinery close by. After 4PM it always completely disappeared, that's exactly when the activities around here stop for the day. In the weekends it's clean too.
Now I decided to started digging some more and trying out some DIY shielding to start with using tinfoil. After a lot of trying out weird stuff I noticed the static increased by 20dB whenever I held my hand above a certain spot. Turns out it's the C2 orange drop cap. Whenever I even come close the static increases by 20dB, and when I touch it it goes up another 10dB.
Is this simply a bad cap? Will replacing it fix this issue? Has anyone had a similar problem?

The has a PCB marked with 2010 v1.25, so if the unit was built around this time it might be due for a total recap anyway.

Here's a link with a little video where I touch the cap and you see the static increase on the computer.

Thanks!
Bob

I’ve built this rev. A unit only once and quite some time ago.
What I found is it’s much more susceptible to EMI than rev. D and later versions. I had to screen an input section (don’t remember the exact components that I screened) with a grounded piece of nickel alloy. Why nickel? Because that’s what I had at hand and it’s a good shield against power transformer radiated interference as well.
This may help your unit as well.

 

[CalavoBob]

The 3 ferromagnetic metals are iron, cobalt and nickel. (actually hydrogen is a 4th but not usable at room temperature). Your choice of nickel was a good one. These 3 solid metal elements can reduce both the electric and the magnetic field of an electromagnetic wave until they are saturated. This means steel works well since it is an alloy of iron. For some reason that I don't understand, copper screen as in a Faraday cage can do it too. I think it is paramagnetic. Aluminum only blocks the electric field, but not tbe magnetic component of an EM wave. Its the same for tin, lead, and zinc. Can anyone explain to me why copper can block both the electric and magnetic field of an EM wave despite the fact that its not ferromagnetic? I've never understood that one.