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

[Mr.Franky]

You need to trace the signal to see where is stops.

Feed a 1K 0dB signal into the input.  Set your controls mid way, no GR, and test the signal referenced to ground at the XLR pin 2, + in t-pad, +out tpad, + either side of the input transformer, + at PCB input, - side of C7, and positive of out XLR.

Don't worry too much about the AC value they'll go down then back up.  Just look for the point where you get no reading (less than say 0.050 VAC).

Mike

Hey,

The signal seems to stop at the output of the input transformer. It is installed correctly though. How could this be broken?



Regards,

Damaged winding if anything.  Check it at the output side + pin to confirm it's not a lifted trace.  Check the DC R  (ohms) between the + and - out put pin.

Hey, I am in fact getting signal at the output of the input xfo. 070 VAC when the input control is mid way. When input is fully CW, I get a value of 0.394 VAC. I thought the value of 0.70 VAC was too low, but I suppose it's not. I'll keep on seaching

cheers

 

[Echo North]

You could also pop your D transformer in there and if that fixes the problem we know you have a bad input.

 

[Echo North]

That's pretty low but I think it's within spec for a 0dB input.  Try the D transformer to confirm.

 

[Mr.Franky]

Hey,

I brought the kit in by a good friend of mine who is a great tech. A twisted/bent transistor leg (Q6) was the cause of all trouble. How could I've not noticed that?!  :-[ Anyway that created a short and killed R32. He took out the transistor, fixed and tested it. Lucky enough it wasn't dead. He also replaced the R32. He was pretty sure the unit would work fine now, so we didn't really test it as he had to leave as well. So I took it home and tried to calibrate it, because now I did finally get a healthy voltage between the output XLR pins 2 and 3. On Step 3 though, I noticed some issues. I couldn't get the 2.44VAC value at the output XLR with the input control. That didn't feel right so I decided to take it to the studio and have a listen. I sent a vocal trough it and unfortunately it sounded distorted with the attack 'off' as well as with the gain reduction engaged. So there's got to be something else that died under the short. I can't find what it is, so I'll most likely take it back to my friend. He doesn't bother as I do favors for him too, which is nice. Maybe you guys have any idea which components could have died down as well? caps? resistors? I hope its not the output transformer, as it sounds distorted in bypass as well?


Thanks in advance and I'll keep you updated when the kit works.
Regards,

EDIT: THE FIX FOR MY PROBLEM IS ON Reply #2263

 

[rhythminmind]

Question: I have a 1:1 Jennsen output transformer laying around. I had the thought of using this as an alternate output color... If I leave the 5002 in place & attach the jenny to the brown & wht/blk terminals with the transformer outputs on a switch, would this be a correct way to go?

 

[Mr.Franky]

Hey,

So my tech friend measured the kit and said he found no direct wrong values. He is not 'specialized' in audio gear though.
Does anybody have any idea where the distortion might be coming from? Would be helpful..
The distortion, as I already said, is audible all the time, wether in 'bypass' or not. I was thinking maybe it's the output transformer?



Regards,

EDIT: THE FIX FOR MY PROBLEM IS ON Reply #2263

 

[Echo North]

Hey,

So my tech friend measured the kit and said he found no direct wrong values. He is not 'specialized' in audio gear though.
Does anybody have any idea where the distortion might be coming from? Would be helpful..
The distortion, as I already said, is audible all the time, wether in 'bypass' or not. I was thinking maybe it's the output transformer?



Regards,

Though is does happen from time to time, transformer errors are very rare and not where I would start.

Have you checked your voltages against the schematic with voltages posted on the MNATS site?

Mike

 

[Mr.Franky]

Though is does happen from time to time, transformer errors are very rare and not where I would start.

Have you checked your voltages against the schematic with voltages posted on the MNATS site?

Mike

Hey,

Thanks for the reply.
My friend said he measured the entire kit compared to the MNATs schematic. He said he found no errors, everything was within range.


Greetings,
Peter

EDIT: My friend is going to bring his gear to my place. This way we can check together, and I can let him hear what it sounds like.

 

[bach]

Kind of at a loss on what to do. Need some help from the brain trust.

If I switch ratios from high to low (e.g.12:1-8:1) the meter shots to the right showing an influx of current then resets to 0. When I select a ratio from low to high (e.g. 4:1-20:1) the meter sags then resets to 0. The greater the difference between the ratios the greater the needle jumps. I used the the voltage test chart and found Q4 source and drain voltage to be low. Source is 4.15 should be 6.6. Drain is 12.92 should be 13.72. All other voltages test just fine.

Additionally, when I turn the output knob clockwise at some point the meter pegs. However, in Pro Tools it isn't recording noise (like in the FAQs) it instead shows a spike at the point that the meter pegs and when it is turned back down past the breaking point.

Here is what I've already done:
-checked solder joints & re-soldered any questionable ones
-checked all components values
-checked cables & none are laying over or close to the board
-tried a new meter
-removed from board and tested R27, R28, R31, R34, C9, C13, C16, & CR1

Any clues on what to try next?

 

[Jase_Sanderson]

Hi,

I know it must be in here somewhere cause i'm seeing a few posts with problems with r33, sorry for being a newb but can't find what i'm looking for.

Having built my Mnats/Hairball 1176 revA, my heads spinning out that there's smoke coming from r33 (panic). I built it slowly and took extra care following all the instructions from the Hairball and Mnats site.

I checked each component with a DM before soldering and although its not the neatest cable job (need to tidy them up) they all seem fine.

I've been googling all day and I've started reading all this amazing long thread but there's a lot to take in, it's my first DIY build and I'm thinking i should have tackled something easier.

First off is this a common situation, if so i couldn't see it in the FAQ?

In a google search i saw someone saying they had a similar thing and it was q6 to blame but when i looked for the rest of the guys post i couldn't find it.

Any pointers

 

[mnats]

Hi,

I know it must be in here somewhere cause i'm seeing a few posts with problems with r33, sorry for being a newb but can't find what i'm looking for.

Having built my Mnats/Hairball 1176 revA, my heads spinning out that there's smoke coming from r33 (panic). I built it slowly and took extra care following all the instructions from the Hairball and Mnats site.

I checked each component with a DM before soldering and although its not the neatest cable job (need to tidy them up) they all seem fine.

I've been googling all day and I've started reading all this amazing long thread but there's a lot to take in, it's my first DIY build and I'm thinking i should have tackled something easier.

First off is this a common situation, if so i couldn't see it in the FAQ?

In a google search i saw someone saying they had a similar thing and it was q6 to blame but when i looked for the rest of the guys post i couldn't find it.

Any pointers

Since that resistor is in series with a capacitor, there isn't any way for DC to pass through and cause this resistor to smoke. It's equally unlikely that there is enough AC signal to cause damage.

Check for shorts and confirm you are referring to the correct resistor. Most seem to have problems with R32, normally caused by ignoring the output transformer legends printed right on the PCB.

 

[mnats]

If I switch ratios from high to low (e.g.12:1-8:1) the meter shots to the right showing an influx of current then resets to 0. When I select a ratio from low to high (e.g. 4:1-20:1) the meter sags then resets to 0. The greater the difference between the ratios the greater the needle jumps. I used the the voltage test chart and found Q4 source and drain voltage to be low. Source is 4.15 should be 6.6. Drain is 12.92 should be 13.72. All other voltages test just fine.

I'm not clear about this - is there an issue with the operation of the unit?

Selecting a ratio alters both the amount of signal the gain reduction circuit sees as well as the bias to the FET. So some needle deflection when selecting a new ratio is normal.

Additionally, when I turn the output knob clockwise at some point the meter pegs. However, in Pro Tools it isn't recording noise (like in the FAQs) it instead shows a spike at the point that the meter pegs and when it is turned back down past the breaking point.

The FAQ refers to oscillation that is commonly reported as audible "noise". On further thought it is unlikely that any current DAW could record and display the frequencies in question so I have removed that part from the FAQ. I'm not sure what is meant by "spike".

Did you check your wiring as suggested?

 

[Spencerleehorton]

Hi Guys,

Im getting a boost in volume and more hum when i switch it into slam mode, is this normal?
also havnt got to the bottom of the hum problem, have posted this a few times but no ones has replied, so sorry to be a pain.

regards

Spence.

 

[bach]

I think I found a few problems, but I still am having issues.  First, the two victories.

Did you check your wiring as suggested?

It is wired correctly, but I just found that one of the Avel-Lindberg power transformers secondaries came lose. So that's one thing fixed.

I'm not sure what is meant by "spike".

By spike I mean is sounds like pulling the xlr out of a live mic.  This is not audible from the unit.  Rather, it is heard when recording in Pro Tools.  I found that if I move the output transformer farther from the xlr output this problem is solved.  So one more problem down!


Now the two problems.

Selecting a ratio alters both the amount of signal the gain reduction circuit sees as well as the bias to the FET. So some needle deflection when selecting a new ratio is normal.

This is A LOT of needle deflection.  watch this youtube video to see what I mean larger difference between ratios larger needle deflection. http://youtu.be/Nn6xTpYFxUk

Lastly, Q4 source and drain are still testing with a larger than normal voltage.  Source is 4.15 should be 6.6. Drain is 12.92 should be 13.72. All other voltages test just fine.

 

[TNO73]

Hi,

I ´ve finished my 1176 rev a built from hairball a few days ago - everything went smooth till i got to the 3. calibration step.
I don´t get the -10 db drop. There is no db drop!?

I went back and forth, checked wiring, Pcb´s for components, solder joints, voltages referenced to mnats rev a schematics - one faulty voltage at Q4 which measures 4.1V instead of 6.6V?

Apart from that the unit is sending audio through it - works as a pre amp well.
And curiously when no ratio button is pressed and i switch the attack pot on , compression takes place, even metering is showing that in GR mode.

What i´ve done wrong? Where should i look out for ?
Thanks
T.

 

[electrisizer]

hello,
i finished my build but have some problems.

first - all voltages are good...

BUT

my output pot does not work... its boosting only around 1-2db max

at GR meter setting the needle stays always at left not in/around 0 position

i cant do calibration because (feeding the input with 1,8 vac + setting input pot to 24 + ccw qbias) it lets the whole unit distort. vac between output xlrs is around 21 vac (!). with a non working output i cant reduce... thats a nice microphone preamp 


i checked wiring (i think its the problem) and i dont have connections on the lower meter board points: 22, grn, blk. was there a connection mentioned in the rev a wiring page text?

when i look a this wiring diagram there are connectins to do... http://img534.imageshack.us/img534/1859/1176wiring.jpg

do the rev a kits have other meter PCBs? do i have to connect this points?

 

[electrisizer]

hey guys i got it working...

by checking grounds i found a 5mega ohm resistance between the output pot and the case ground...
this causes my pot not to work...

i soldered a copper cable between the ground lug of the pot (with its two ground wires) and the pots housing...

now after proper calibration my unit is completley working 

dont know what causes this fault...

 

[bach]

I went back and forth, checked wiring, Pcb´s for components, solder joints, voltages referenced to mnats rev a schematics - one faulty voltage at Q4 which measures 4.1V instead of 6.6V?

It seems that we've got similar problems. I've done some looking and it appears that there are several posts of people with a lower than normal voltage on Q4... Still not sure why though.

Do you also have exaggerated needle deflection too? Check out my youtube video in the previous post. What mine is doing in the video doesn't seem normal to me and I'm wondering if your having the same issue.

 

[Spencerleehorton]

HI All,

I think i may have worked out a few things that maybe wrong in my version by reading all the mnats version builds.
Its looks like it may point to an earth loop which is the source of my hum.
I have a chassis earth from the IEC and also from that point i have an earth going to pins 1 on both XLR, as well as also having the screens from both input and output wired from XLR to pcb board.
If it turns out not to be this it maybe a hum coming from the pcb board which is generating 18v for the balancing board as i have heard a very similar hum in my U47 psu using the LM350 regulator when using fixed bias so might need to filter the AC more.
Mains frequency in UK is 50Hz so any hum will be 100Hz or 50Hz.
Earth-loop hum is usually 50 Hz and PSU hum is usually 100Hz.

regards

Spence.

 

[TNO73]

I went back and forth, checked wiring, Pcb´s for components, solder joints, voltages referenced to mnats rev a schematics - one faulty voltage at Q4 which measures 4.1V instead of 6.6V?

It seems that we've got similar problems. I've done some looking and it appears that there are several posts of people with a lower than normal voltage on Q4... Still not sure why though.

Do you also have exaggerated needle deflection too? Check out my youtube video in the previous post. What mine is doing in the video doesn't seem normal to me and I'm wondering if your having the same issue.

Yes indeed, the metering in GR mode is behaving the same way, than what is shown in your video....?
Is you unit compressing the audio signal like it should, but just not showing the correct metering?
My unit is only compressing audio signal noticeable when no ratio button is pressed,
if any ratio button is pressed there no compression at all noticeable!? I find this to be very strange, cause it should work the other way round, i guess?

Can anybody tell what a fully working unit is supposed to do, when no ratio button is pressed?

Thanks&regards
Tom