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

[rhythminmind]

Finished up my 1st 1176, All Cal'd up & sounds/functions great.

 

[MicDaddy]

Nice!  I like the different take on the front panel with the 'Army Green Stripe'

 

[rhythminmind]

Yeah I like the black/green look. Not a huge fan of silver/blue & thought this would be a interesting take hinting at the origins of the design.

 

[rhythminmind]

How do these specs look @ -10 db gain redection?

Frequency response +4 dbu (sharp cut off @ around 30khz was surprising)

Harmonics 1k tone +4 dbu

THD+N sweep & 1k tone +4 dbu

 

[MicDaddy]

Looking for some advice...

I've built 2x 1176 Rev A compressors.  They work GREAT in any signal chain, as well as with a TT patchbay at the studio.  

However, when used as an insert with my analog console (Dynacord PM2200) I'm getting a nasty 60Hz ground loop issue.  :'(

It seems to only be when the send from the console (trs tip/send ring/return split to XLRM/XLRF) is terminated to the input of either 1176.  If I come from a different pre into the 1176, XLRF into the console insert (ring/return) no hum...

Pin-1 on both XLR(F/M) of both compressors is tied to XLR chassis per Mnats wiring guide.  

My question, where do I lift the ground?  On the input XLR from the TRS/XLRM ?  Is this an unbalanced/balanced issue or impedance issue?  hmmm


Have I confused anyone yet?  

 

[Rob Flinn]

Frequency response +4 dbu (sharp cut off @ around 30khz was surprising)

Anything to do with the frequency response of your test set up ??

 

[dtrax]

Finished her up the other day, but I'm stumped. I'm getting no compression. I've rechecked all of my wiring and such, and I seem to have narrowed it down - at least for now - the ratio PCB. The BoM, which was the link provided from hairball.com for Rev A's, was missing some resistors. It seems that BoM was for mnat's ratio PCB (the rotary switch version), rather than the switching bank version that I got. In any event, I used this pdf to source the correct resistor values for the Ratio PCB:

http://hairballaudio.com/docs/FET_Compressor_PCB_Board_Info_V2.pdf

I then followed mnats wiring guide from that point on. Everything went smoothly and she passes audio wonderfully. But again, the unit is not compressing. Can someone please confirm these resistor values for me? Here's what I have installed on the Ratio PCB currently:

R1: 180
R2: 470
R3: 470
R4: 1K5
R5: 10M
R6: 56K
R7: 56K
R8: 130K
R9: 56K
R10: nothing

 

[Echo North]

For R10 you need a "link".  You basically need to install a resistor leg or wire. 

 

[dtrax]

For R10 you need a "link".  You basically need to install a resistor leg or wire. 

That did it! Thanks so much bro. I don't know how I missed that in the schematic. I guess I'm just a little burnt out. In any event, on with the rest of the calibrations.

.... Oh and it sounds phenomenal!

 

[dmp]

Has anyone successfully built the >s/n 125 version on a MNATS rev 1.0 pcb?
I have triplechecked all the components to match the schematic on this page:
http://mnats.net/1176_revision_a.html
I added the 3.3k/.001uf feedback path and triple checked it is connected correctly.
I get oscillations when the output pot is turned up more than about halfway, with the input grounded and the GR FET removed. Both the signal preamp and the output amp work correctly when tested separately with a function generator. I am seeing gain of 50 for the signal preamp and 10 for the line amp. Thought it might be shielding to the output pot, but even with the pot disconnected I get oscillations (with a jumper in place of the pot).
Anybody have an idea what's wrong?

 

[ilfungo]

I built two for each revision of 1176
only on one I have a similar problem
with outpot to zero (meter goes to full scale and low sound comes out)
I don't know what can be
for the rest the compressor work well....

 

[evilcat]

Same thing here, at about 2 or 3 o clock. Weird, but I never go so loud on the output pot so it doesn't bother me...

 

[Biasrocks]

Nothing like that here, clean output right to the top on my REV A.

I have mine terminated by a 620R resistor, try that.

Mark

 

[ilfungo]

Nothing like that here, clean output right to the top on my REV A.

I have mine terminated by a 620R resistor, try that.

Mark

???
???

 

[Biasrocks]

These limiters are supposed to be terminated @ 600 ohms if your not driving a 600 ohm input, like most modern inputs which are usually 10K and higher. Put a resistor across Pins 2 & 3 on the output. I'm not sure it will solve your problem, but it may help.

I suspect your getting oscillations, most likely caused by wiring. Try repositioning wiring or checking that you have adequate ground connections where they're supposed to be.

Mark

 

[Randyman...]

FWIW - I put switchable 600 Ohm termination on all of my gear with transformers designed for 600 Ohm Loads - this way I can feed one of these units into another unit that already has a 600 Ohm input impedance with the termination disabled (like API Preamp into LA2A into 1176) - or I can patch the Compressor or Preamp directly into my AD with the termination engaged and not have any sonic differences due to loading.

Sorry - not of any help with the other issues.  Still weeding out issues on my 2-1176 Rev D and D-LA2A that I can't seem to track down (noob alert!!!)...

8)

 

[dmp]

I added a 620R resistor at the output xlr and saw no change in the behavior. I am getting oscillations when I turn up the output pot about 1/4 of the way. I double checked that the signal preamp is working fine on its own (30 dB gain) and the line amp (20 dB gain).
I removed the pot, and installed a 270k resistor in its place as if the pot were at max (this is to make sure it is not caused by wiring to the pot). Still have the same oscillations.
Removing R17 stops the oscillations (which turns off the signal preamp), implying that there is positive feedback from the output to the input of the signal preamp.
I'm stumped for the moment but I would appreciate if anyone could confirm that the v1.0 Mnats revA board can work with the >sn125 schematic mods, because I am starting to suspect the feedback may be occurring through the ground or power layout.

 

[Biasrocks]

Hey Dan

My REV A has the AB mods applied and I've got no oscillations happening.

Have you verified all of your grounds or tried moving the transformers around?

I'll forward my REV A comparison chart that I did a while back so that
you can verify your parts changes.

Mark

 

[Andy Meyer]

Hi guys,

I have just assembled my Hairball + Mnats Rev A and have an issue.  I don't get anything.  I have checked the voltages at the 30v and -10v spots and both are showing 0v.  I also checked voltages at the two AC and CT points on the PCB both showing 0v.  I am getting 120v from the IEC power connector to the "Off" button on the meter board.

It seems like this leaves the transformer right?  I am a newbie and could use some help.

Thanks in advance.

Andy

 

[MicDaddy]

Hi guys,

I have just assembled my Hairball + Mnats Rev A and have an issue.  I don't get anything.  I have checked the voltages at the 30v and -10v spots and both are showing 0v.  I also checked voltages at the two AC and CT points on the PCB both showing 0v.  I am getting 120v from the IEC power connector to the "Off" button on the meter board.

It seems like this leaves the transformer right?  I am a newbie and could use some help.

Thanks in advance.

Andy

Post some pictures that follow the power from IEC to switch, to transformer, to pcb etc...  it may be something simple enough for someone to spot.

Can you take any measurements at the transformer primary/secondary?