[BUILD] 1176LN Rev D DIY

[fluxofpinkindians]

I have abnormal voltage at Q13 (Gain Meter Driver). I tested all voltages with respect to ground. GR mode, "Calibrated (!)", No input, Left for 30mins.

Should be:
c:  9.75
b: -1.04
e: -1.63

Mine is:
c: -1.75
b: -0.99
e: -1.58

All other voltages (as per the 1176 REV D VOLTS schematic PDF) are within 10% tolerance. Any suggestions gratefuly received.

 

[beatnik]

I did some more measurements on my 1176. If you see a couple of posts before there is a primer description of what is happening.

I discovered other strange things.

Voltage on Q13 collector changes from 8.5V with meter on GR to -0.9V with meter on VU mode. Is this normal?

With audio through the unit, if I switch from ratio 20 to another ratio, there is a sudden volume burst, that quickly fades away.

I still got no answers. Please I need your help. I'll never be able to fix this by myself

 

[fluxofpinkindians]

I did some more measurements on my 1176. If you see a couple of posts before there is a primer description of what is happening.

I discovered other strange things.

Voltage on Q13 collector changes from 8.5V with meter on GR to -0.9V with meter on VU mode. Is this normal?

With audio through the unit, if I switch from ratio 20 to another ratio, there is a sudden volume burst, that quickly fades away.

I still got no answers. Please I need your help. I'll never be able to fix this by myself

Hi Beatnik! I just tested my Q13 voltages in both GR and +4VU mode.

In GR mode I have -1.57 volts at the Collector and in + 4VU mode I have +9.28 volts. The Base and Emitter remain the same, within 10% tolerance.

I don't know if this is normal though!

My unit also has a volume burst when changing ratios. I think this is normal.

 

[fluxofpinkindians]

Problem: Compressor compressing too much. Input has little effect on amount of compression. Output very high

Test: -21.7db peak 1khz sine wave from Avid IO = 0.775 AC RMS at pin 2 & 3 of 1176 input.

• With input fully CCW and output fully CW I get the following voltages at output. These build steadily from cold start to reach the following peaks after roughly 3 minutes. The voltages vary depending on the Meter selection as follows:

GR MODE: 29.70 VAC                 
+8 MODE: 29.46 VAC
+4 MODE: 29.33 VAC

• To get 0.775 VAC between XLR pins 2 & 3 at both Input and Output the input has to be fully CCW and the Output has to be at -50!

• With 0.775 VAC at both input and output I get the following voltages at output at the different ratios. These vary by 0.5 mV depending on GR, +8 OR +4 meter selection. The input attenuator is having little effect on the amount of compression:

          INPUT FULL CCW        INPUT FULL CW
20-1: 222 mVAC                      232 mVAC
12-1: 189 mVAC                      205 mVAC                   
  8-1: 176 mVAC                      198 mVAC                     
4-1: 154 mVAC                      190 mVAC

• I have an abnormal voltage at the Collector of Q13 (-1.75mV instead of 9.75mV in GR meter mode). Strangely this changes to +9.28 mV (normal) when in +4VU meter mode. I have read similar comments in other threads but have not been able to establish whether this is normal behaviour ?

• My input attenuator does not travel to infinity when turned fully CCW (with the knob set so that the dot is on 0 when turned fully CW). Is this normal ?

I have calibrated the Q bias and the discrete meter circuit and the GR reduction meter tracking adjust. It was difficult to calibrate the discrete meter circuit as I had to have the input fully CCW and the output at -50 to achieve 0VU on the meter.

Otherwise, I have checked my wiring and all seems ok. The unit sounds fine and is compressing. The problem is that to compress less I have to attenuate quite a lot (in the DAW) before the compressor. I think the input attenuator might be broken but I am concerned at the voltages at the output. Would really appreciate any help.

 

[Echo North]

Problem: Compressor compressing too much. Input has little effect on amount of compression. Output very high

Test: -21.7db peak 1khz sine wave from Avid IO = 0.775 AC RMS at pin 2 & 3 of 1176 input.

• With input fully CCW and output fully CW I get the following voltages at output. These build steadily from cold start to reach the following peaks after roughly 3 minutes. The voltages vary depending on the Meter selection as follows:

GR MODE: 29.70 VAC                 
+8 MODE: 29.46 VAC
+4 MODE: 29.33 VAC

Not sure what all of this means as these are not very helpful measurements. 

• To get 0.775 VAC between XLR pins 2 & 3 at both Input and Output the input has to be fully CCW and the Output has to be at -50!

Is this in bypass mode?

• With 0.775 VAC at both input and output I get the following voltages at output at the different ratios. These vary by 0.5 mV depending on GR, +8 OR +4 meter selection. The input attenuator is having little effect on the amount of compression:

          INPUT FULL CCW        INPUT FULL CW
20-1: 222 mVAC                      232 mVAC
12-1: 189 mVAC                      205 mVAC                   
  8-1: 176 mVAC                      198 mVAC                     
4-1: 154 mVAC                      190 mVAC

Again bypass?

• I have an abnormal voltage at the Collector of Q13 (-1.75mV instead of 9.75mV in GR meter mode). Strangely this changes to +9.28 mV (normal) when in +4VU meter mode. I have read similar comments in other threads but have not been able to establish whether this is normal behaviour ?

Not strange at all.  When you go into +4 your removing that part of this circuit.  This tells me you have an issue with your GR amp and get's getting loaded when in GR mode.  My guess is that this points to a wiring error.

• My input attenuator does not travel to infinity when turned fully CCW (with the knob set so that the dot is on 0 when turned fully CW). Is this normal ?

Normal.  They don't really make 320 degree pots anymore.

I have calibrated the Q bias and the discrete meter circuit and the GR reduction meter tracking adjust. It was difficult to calibrate the discrete meter circuit as I had to have the input fully CCW and the output at -50 to achieve 0VU on the meter.

Something is wrong.

Otherwise, I have checked my wiring and all seems ok. The unit sounds fine and is compressing. The problem is that to compress less I have to attenuate quite a lot (in the DAW) before the compressor. I think the input attenuator might be broken but I am concerned at the voltages at the output. Would really appreciate any help.

If you insert a AC signal into the unit measure it at the transformer input and rotate the tpad.  what do you see?

 

[sr1200]

the .775 is what you should have across the pins on the INPUT not sure why you'd need 0.775 at the output as well.

 

[fluxofpinkindians]

If you insert a AC signal into the unit measure it at the transformer input and rotate the tpad.  what do you see?

Thanks so much for helping me. Really, really appreciated 

With 0.775 VAC applied to the Input, at the transformer I get 0.752 VAC  (input fully CW) and 0.307 VAC (input fully CCW.)

For clarification of my last post. The below voltages (at the output xlr with 0.775VAC applied to input) were NOT in bypass. The compression was engaged.

          INPUT FULL CCW        INPUT FULL CW
20-1: 222 mVAC                      232 mVAC
12-1: 189 mVAC                      205 mVAC                   
  8-1: 176 mVAC                      198 mVAC                     
  4-1: 154 mVAC                      190 mVAC

best wishes

Flux

 

[fluxofpinkindians]

the .775 is what you should have across the pins on the INPUT not sure why you'd need 0.775 at the output as well.

I set the unit up like this in bypass in order to see the effect of the different compression ratios when the compressor was engaged. 

I really am grateful for any help. All the best.

 

[beatnik]

hey guys,

i have built one revD and i'm stuck with calibration!

i can set the qbias and the null adjustments (first and second video) but then i can't do the tracking adjustment.

when i switch the attack pot from compression on/off (i used the classic hairball components), there is not any drop on the vu meter.

i checked all the transistors voltages compared to the mnats schematic with voltages, and everything seems ok.
the preamp and output sections are perfect, as it's the gr control amp. the meter section is basically right, only lower about -10%.

i measured all the resistors before placement and checked capacitors value and every wire for continuity or shorts.

the fets are matched and i even tried with another pair.

it probably is something simple but i can't figure it out. i really need some help!

let me know if you need all the transistor voltages and i'll post them.

thanks in advance

I finally managed to solve the problem by myself.

The fault was caused by missing connection between R62 and R63 on the ratio pushbutton pc board. That was causing the gain reduction control amp to not work properly.

It took a long time to check every connection and then find that, but now I am happy to have the compressor working.

 

[kiopo]

Hello folks!

I'm mid-way through my build now. I literally can't think of a more fun project to be doing, and the excellent layout and information from mnats and hairball is invaluable for relative beginners like myself!

I have a couple of questions. What do you all do with the ground wire that is on the EA-5002 output transformer, for best result? Do you use that to connect to negative C25 instead of a wire from chassis, connect to shield of output XLR, or not use it, or do something else? Bit confused.

Also, my wire cutters snapped and pulled a pad from the ratio board (grey wire). Am I right in thinking this trace goes to the middle pin on the second row of the 20 switch (further of the two from the wire pads), and that soldering it directly to the leg is fine? I've soldered it to that leg but just want to check... easier than scraping away the trace.

 

[Trench Recordings]

The ground  wire that is soldered to the side of the transform can be wrapped around and tighten on the mounting bolt for the transformer itself. Make sure you sand off some of the paint at that point and have a good connection to the chassis. Check with your ohm meter.

As for the raised pad. Either study the schematic for a good alternative solder point or use your meter to figure it out. I had the same thing happen with the green wire. I ended up soldering to the switch contact.

 

[kiopo]

The ground  wire that is soldered to the side of the transform can be wrapped around and tighten on the mounting bolt for the transformer itself. Make sure you sand off some of the paint at that point and have a good connection to the chassis. Check with your ohm meter.

As for the raised pad. Either study the schematic for a good alternative solder point or use your meter to figure it out. I had the same thing happen with the green wire. I ended up soldering to the switch contact.

Thank you! I've seen pictures of people doing loads of different things with that ground wire so I was getting really confused by it. I think your way is better than using it for the negative c25 connection as the bare wire could touch a lot of things on the underside. I'll either do that or connect it to the chassis pin on the XLR, unless anyone has other suggestions.

Is there an overlay for the hairball ratio board online do you know? I can only seem to find the meter one (sorry if I'm being really dense..!). Without the pad there I can't continuity check to see... I'm fairly sure it's the right pin though! From the schematic I think it's fine too but it's a little hard to follow with the switch pinouts etc. It looks to me like as long as all of that row of pins are connected and going to 21 on PCB and R53 / C21 etc then it'll be okay.

Thanks again for the help 

 

[Trench Recordings]

you could just cut that ground wire or tie it to the ground post. As long as that metal transformer bracket is connected electrical to chassis you should be fine. As for the ground for C25 I would definitely use a insulated green wire. you dont want that shorting something out by accident

 

[fluxofpinkindians]

Just posting this again as I am stuck and can't work out what I have done wrong. I have searched in this thread for similar problems and come up with nothing.

I have calibrated the Q bias and the discrete meter circuit and the GR reduction meter tracking adjust. It was difficult to calibrate the discrete meter circuit as I had to have the input fully CCW and the output at -50 to achieve 0VU on the meter.

Something is wrong.

Otherwise, I have checked my wiring and all seems ok. The unit sounds fine and is compressing. The problem is that to compress less I have to attenuate quite a lot (in the DAW) before the compressor. I think the input attenuator might be broken but I am concerned at the voltages at the output. Would really appreciate any help.

If you insert a AC signal into the unit measure it at the transformer input and rotate the tpad.  what do you see?

With 0.775 VAC applied to the Input, at the transformer I get 0.752 VAC  (input fully CW) and 0.307 VAC (input fully CCW.)

thanks so much for your help 

 

[Echo North]

Just posting this again as I am stuck and can't work out what I have done wrong. I have searched in this thread for similar problems and come up with nothing.

I have calibrated the Q bias and the discrete meter circuit and the GR reduction meter tracking adjust. It was difficult to calibrate the discrete meter circuit as I had to have the input fully CCW and the output at -50 to achieve 0VU on the meter.

Tpad seems fine.

Probably a GR meter circuit issue.  What are you readings against the schem with voltages?

Something is wrong.

Otherwise, I have checked my wiring and all seems ok. The unit sounds fine and is compressing. The problem is that to compress less I have to attenuate quite a lot (in the DAW) before the compressor. I think the input attenuator might be broken but I am concerned at the voltages at the output. Would really appreciate any help.

If you insert a AC signal into the unit measure it at the transformer input and rotate the tpad.  what do you see?

With 0.775 VAC applied to the Input, at the transformer I get 0.752 VAC  (input fully CW) and 0.307 VAC (input fully CCW.)

thanks so much for your help 

 

[jwhmca]

What is the recommendation for grounding the Hairball audio powder coated case?

 

[fluxofpinkindians]

I have calibrated the Q bias and the discrete meter circuit and the GR reduction meter tracking adjust. It was difficult to calibrate the discrete meter circuit as I had to have the input fully CCW and the output at -50 to achieve 0VU on the meter.9

Something is wrong.

If you insert a AC signal into the unit measure it at the transformer input and rotate the tpad.  what do you see?

With 0.775 VAC applied to the Input, at the transformer I get 0.752 VAC  (input fully CW) and 0.307 VAC (input fully CCW.)

Tpad seems fine.

Probably a GR meter circuit issue.  What are you readings against the schem with voltages?

All voltages on the PCB check within 10% of the schematic except the collector of Q13. I have -1.57 in GR mode and +9.28 in +4VU mode. It should be +9.75 in GR mode. I have checked my wiring many times against the MNATS instruction. The unit sounds great and is compressing - just way too much. In BYPASS, with 0.775 VAC applied to the input I get +29VAC at the output with the input fully CCW (full attenuation). This can't be right!!

many thanks for your interest.

 

[dbonin]

Here are some calibration videos that I took yesterday (sorry about the web cam quality)  - they are the same steps as described in MNATS videos on a rev d, push button version.  Sometimes just seeing someone else do these steps can help make things a little clearer.  I hope this helps someone.

http://www.youtube.com/watch?v=0Uuk1Y7M2D8
http://www.youtube.com/watch?v=lRStwXwmBUw
http://www.youtube.com/watch?v=pgSWfsEzU40

Cheers!
-Don

Mike/mnats - thank you for your support and encouragement to this community!

 

[Echo North]

I have calibrated the Q bias and the discrete meter circuit and the GR reduction meter tracking adjust. It was difficult to calibrate the discrete meter circuit as I had to have the input fully CCW and the output at -50 to achieve 0VU on the meter.9

Something is wrong.

If you insert a AC signal into the unit measure it at the transformer input and rotate the tpad.  what do you see?

With 0.775 VAC applied to the Input, at the transformer I get 0.752 VAC  (input fully CW) and 0.307 VAC (input fully CCW.)

Tpad seems fine.

Probably a GR meter circuit issue.  What are you readings against the schem with voltages?

All voltages on the PCB check within 10% of the schematic except the collector of Q13. I have -1.57 in GR mode and +9.28 in +4VU mode. It should be +9.75 in GR mode. I have checked my wiring many times against the MNATS instruction. The unit sounds great and is compressing - just way too much. In BYPASS, with 0.775 VAC applied to the input I get +29VAC at the output with the input fully CCW (full attenuation). This can't be right!!

many thanks for your interest.

Depends on where your output is.  If you have -20dB or something at the PCB input with full attenuation and you're output is cranked up to 50 or 55dBu of gain you could see 30V on the output (maybe).

You've got an issue in your GR meter section.  Bad trimmer, R value, or pad 28/29 wiring.  Keep in mind when you're in +4 your by passing all of that.

I'm not sure you have an issue with your compressor, other than your GR metering.  I could be wrong.  If you're compressor is not passing/compressing signal properly it most likely NOT related to the GR metering issue unless you have the pad 28/29 wiring mixed with something else.  They would be separate.

Have a look at the meter PCB and follow where 28 and 29 come in and test continuity for a broken trace.  Keep in ming those 2 resistors are not in the circuit in GR so don't worry about them. 

That's all I think of right now.  Are you passing clean audio?  The Qbias when well?

 

[fluxofpinkindians]

You've got an issue in your GR meter section.  Bad trimmer, R value, or pad 28/29 wiring.  Keep in mind when you're in +4 your by passing all of that.

I'm not sure you have an issue with your compressor, other than your GR metering.  I could be wrong.  If you're compressor is not passing/compressing signal properly it most likely NOT related to the GR metering issue unless you have the pad 28/29 wiring mixed with something else.  They would be separate.

Have a look at the meter PCB and follow where 28 and 29 come in and test continuity for a broken trace.  Keep in ming those 2 resistors are not in the circuit in GR so don't worry about them. 

That's all I think of right now.  Are you passing clean audio?  The Qbias when well?

Mike, thanks so much for your continued patience with this. I am summarizing things here below as things are getting a bit spread out over the various posts. I am determined to fix this.

• Unit passes clean audio and compresses
• Q bias set but strange (see below), Discrete Meter set, GR meter tracking adjust set
• The Meter is tracking ok and seems to be representing correctly the voltage drops that I see between the input and output when compressing.
• Visual inspection of wiring correct. Trimers checked. R values of meter driver section ok. Continuity of pad 28/29/meter board pcb checked.
• All voltages ok except collector of Q13 which is negative (-1.56 )in +4U mode. Not sure if this is normal.

Problem: In +4VU mode, IN BYPASS, If I apply 0.775VAC to the input, to get 0.775VAC at the output, I need to fully rotate the input CCW (full attenuation) and rotate the OUTPUT CCW to -50 (huge attenuation)

It is as though the signal preamp is amplifying way too much. Or the input attenuator is not attenuating enough. This is what made setting the q bias "strange"

With compression engaged, it is pushing the signal into the "threshold" very early and thus compressing far too much.

I am a bit at a loss as to what to do next!

with best wishes,

Flux