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

[Echo North]

You are getting this behavior with gain reduction off?

Most common cause of that is org-yel not connected on the output transformer, but yours looks connected.  Make sure all of your output transformer connections are solid and correct.

 

[KSeaton]

You are getting this behavior with gain reduction off?

Most common cause of that is org-yel not connected on the output transformer, but yours looks connected.  Make sure all of your output transformer connections are solid and correct.

Yes, with GR on and off. I will triple check those connections and see if that solves it. Thanks!

KS

 

[KSeaton]

  Make sure all of your output transformer connections are solid and correct.

Double checked all the connections and they are solid and correct. Still having the same issue. Any other suggestions? Could it be a calibration thing? Thanks again

Kevin

 

[Echo North]

  Make sure all of your output transformer connections are solid and correct.

Double checked all the connections and they are solid and correct. Still having the same issue. Any other suggestions? Could it be a calibration thing? Thanks again

Kevin

The only calibration step that affects your audio signal in a rev A is the QBias.  It's important that be done correctly.  Were you able to complete the QBias step with no issues?

Mike

 

[KSeaton]

Thanks Mike,

I had a tech calibrate to make sure it was done correctly, but he admittedly had some trouble with the Q bias adjustment. He said after trying a few different things he finally got it to drop 1db. I just tried to redo it myself and couldn't even get the meter up to 0db or +1 with a 1khz tone so i could try to adjust it. The highest I could get it no matter what I tried was -10 and then i would hear an audible squeal somewhere in the circuit and it wouldn't go any higher. Could it be a bad trimmer resistor? I did test all the resistors before then went on the pcb...

Thanks again

KS

 

[Echo North]

Well start by keeping your compressor in the GR Off position at all times.  That'll make it so only the signal and line amps are active and that seems to be where the issue is so we can isolate it.  The Qbias shouldn't be hard to set at all.

For setting the qbias try this:

If you have a version with the "off" switch on the attack pot, you can just switch that.  That will ground pad 22.  Feed a 1khz signal into the input at about 0dBu.  You can put your DMM across input xlr pin 2 and 3 and look for 0.775VAC which is about 0dbu.

Now put your DMM across pin 2 and 3 on the output xlr and turn the qbias (in and out knob mid way).  You should see the output moving up or down.  Turn the bias until it gets to the max and doesn't get any higher. 

Then adjust the output knob so you see +11dbu (2.75VAC) at the output.  Now pull the qbias back until you get a 1dbu drop 10dbu (2.45VAC).  That will set you bias.

If you have problems with this, check your voltages in the signal and line amp against the MNATs voltage chart:
http://mnats.net/files/1176REVA_125_VOLTAGES.pdf

Mike

 

[KSeaton]

Thanks, my tech said he did almost exactly what you outlined and we still have the problem. I'm going to run through it all again to verify. In the event the voltages are correct is there anything else it could be?

Kevin

 

[mnats]

In the event the voltages are correct is there anything else it could be?

How many things in the first answer of my 1176 FAQ (linked from the first post of this thread) have you checked so far? If there isn't a wiring problem it is extremely unlikely that all of the voltages will be correct.

 

[Che_Guitarra]

My Rev A is almost complete now, just waiting on a few Wima caps to arrive with my latest Mouser order.

Just doing some continuity checks, I notice I have a 5Ω resistance from the lid of my input trafo to ground.  But from the hex standoffs/screw tops it's 0.2Ω.  I recall reading you're ideally looking for a figure less than 1Ω.  Will this be an issue?

 

[Echo North]

My Rev A is almost complete now, just waiting on a few Wima caps to arrive with my latest Mouser order.

Just doing some continuity checks, I notice I have a 5Ω resistance from the lid of my input trafo to ground.  But from the hex standoffs/screw tops it's 0.2Ω.  I recall reading you're ideally looking for a figure less than 1Ω.  Will this be an issue?

Probably not that big of a deal for the input transformer can.

 

[meltingpat]

I am a newbie unsure if I have correctly solder the Orange Sprague on C10...If you look at the picture I have , am I suppose to solder a bridge on the right pads to R26? Or are they already connected? Everything seems to be working but I just want to be sure.

 

[Majestic12]

I am a newbie unsure if I have correctly solder the Orange Sprague on C10...If you look at the picture I have , am I suppose to solder a bridge on the right pads to R26? Or are they already connected? Everything seems to be working but I just want to be sure.

You don't need to solder the empty holes in the pcb, they already connected (you can even see the small copper traces inbetween).
But I often fill empty holes with solder just for optical reasons.

 

[Dr Gris]

I noticed on mnats build page that he has a State Electronics T-Pad on his input. Does anyone know the part number?

Some nice Clarostat´s for sale in the Black Market at this moment.

Best
Magnus

 

[Chrome Heart]

On the Hairball BOM it lists R19 on the ratio board as 68K. On the Mnats build its listed 130K. Anyone know?

 

[Echo North]

On the Hairball BOM it lists R19 on the ratio board as 68K. On the Mnats build its listed 130K. Anyone know?

130K is for the 1st revision REV A PCBs V1.0-V1.2.  The 68K is for the V1.2.5 PCBs which is based on the serial number 125-216.  These are the current Rev A's he sells.

 

[Chrome Heart]

Thanks for clearing that up Mike. I have a ver1.2 I bought a couple years ago that Im just getting around to.

 

[Chrome Heart]

Interesting problem... my unit passes audio but if the ratio board is connected the meter drops to -20 in GR mode when no signal is passing through. If I disconnect wires on pads 18, 19 and 21 the meter comes back up. Looks like its wired correctly at the ratio board but something is wonky.

 

[Chrome Heart]

Seems to be intermittent. With the ratio board disconnected, sometimes when I power up the meter goes to 0 VU in GR mode and sometimes it doesnt.

 

[Echo North]

If not a bad solder/pad, maybe a wonky switch/PCB.

Email me if think you need a replacement. 

 

[Chrome Heart]

I dont think its the ratio pcb. Problem seems to be in the GR circuit. If I remove Q11, it zeros fine at every start. I put it in, nuthin. Could it be bad?