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

[Potato Cakes]

Got the VU meter issue sorted. It seems that the null adjustment trimmer that was sent with the kit was 5k and not 2k. I just so happen to have an extra one laying around from a previous build.

Thanks!

Paul

 

[Potato Cakes]

Once again, I didn't not clearly pay attention to the BOM and it even shows on the silk screen on the PCB that the tracking trimmer is 5k. I had it on my mind from my Rev D build that it was a 2k. Thanks to the Hairball audio guys for pointing this out.

So during calibration, I noticed that somehow the ratio buttons are reversed in how they actually affect VAC a the output XLR. I have the ratio board mounted as it shows in the build guide, and I've double checked continuity from the PCB pads to the pots to the ratio board and all seems fine. I was able to do the entire calibration process just fine and when I passed program material through it I could see and hear the compression working properly minus the ratios being reversed. I guess the fastest way is to mount the ratio PCB upside down, but would like to know what could be causing this. I thought it would have been amazing if I some how perfectly got all all the resistors backwards on the ratio PCB, but unfortunately that is not the case.

Anyone else come across this?


Thanks!

Paul

 

[Potato Cakes]

And done. For the time being I just flipped the ratio board upside down. everything seems to be working great.

Thanks to mnats and Mike! This is a fantastic project!

Paul

 

[Potato Cakes]

One more.

 

[hymentoptera]

I don't think the ratio assembly needs to be inverted.

It's been established that the output levels are seemingly a little "backwards" from one ratio to the next, but this is normal, and is because the ratio settings can be thought of as threshold/ratio presets. As you select higher ratios you are also selecting higher thresholds. See the dual resistor ladder in the schematic to see what I mean. One ladder attenuates the signal going into the GR amp, while the other tinkers with the negative control voltage coming out of the GR amp.

As seen while measuring AC volts at the output, this would appear that higher ratios put out a slightly louder signal.

 

[Echo North]

I don't think the ratio assembly needs to be inverted.

It's been established that the output levels are seemingly a little "backwards" from one ratio to the next, but this is normal, and is because the ratio settings can be thought of as threshold/ratio presets. As you select higher ratios you are also selecting higher thresholds. See the dual resistor ladder in the schematic to see what I mean. One ladder attenuates the signal going into the GR amp, while the other tinkers with the negative control voltage coming out of the GR amp.

As seen while measuring AC volts at the output, this would appear that higher ratios put out a slightly louder signal.

Yep absolutely what Hymentoptera is saying.  You probably have your ratio's backwards now.

The ratio in not an overall volume thing. It's a ratio, so you need two measurements to test it. In an ideal world, you measure your output at point 1 with GR OFF and have 1VAC. At point 1 with GR ON you have 0.5VAC.  Then you decrease the threshold and test again at point 2. GR OFF is 0.5V and GR ON is 0.25.

So with GR OFF you have a 0.5V change and with GR ON you have a 0.25V change.  2:1 ratio.

This is not exactly always true in practice because the compressor has a knee which lowers the ratio and saturation point at the other end that also lowers the ratio.  So to get the correct ratio in test you really need to hit the active region and stay in it.

Mike

 

[Echo North]

If you can't accomplish this, you probably have a circuit issue.  Check against the schematic with voltages.

Mike

Tried the hairball method this morning and still had the same issue where I cannot get the 0 to -10db drop on the meter.  Measured all my voltages and came up with the following (note... I flagged anything that was more than .5V off from the schematic):

Part:
(schematic voltage) - My Voltage reading

SIGNAL PREAMP

Q2

• (6.73V) - 7.28V
• (2.22V) - 2.52V
• (4.51V) - 4.38V

Q3

• (13.74V) - 13.18V
• (6.13V) - 6.70V

SIGNAL LINE AMP

Q4

• (13.72V) - 13.11V
• (6.6V) - 4.22V - off by more than 2V

Q5

• (3.42V) - 3.30V
• (2.7V) - 2.76V
• (25.15V) - 24.29V - off by almost 1V

Q6

• (27.58V) - 27.15V
• (2.2V) - 2.14V

GAIN REDUCTION CONTROL AMP

Q7

• (5.22V) - 5.16V
• (4.71V) - 4.63V

Q8

• (16.93V) - 17.02V
• (16.31V) - 16.38V

Q9

• (3.65V) - 3.68V
• (3.09V) - 3.11V

Q10

• (14.96V) - 14.41V
• (14.39V) - 13.82V

GAIN REDUCTION METER DRIVER

Q11

• (10.52V) - 9.21V - off by more than 1V

Q12

• (-0.81V) - -0.76V
• (-1.41V) - -1.35V
• (9.5V) - 8.14V - off by more than 1V

Q13

• (-0.88V) - -0.83V
• (-1.46V) - -1.40V
• (9.76V) - 8.46V - off by more than 1V

POWER SUPPLY

• (29.75V) - 29.79V
• (-9.85V) - -9.57V

Based on all of these readings, I'm under the impression that something is wrong leading into the GR METER DRIVER and possibly the SIGNAL LINE AMP.  However, in tracing through the schematic, I'm unsure of what could possibly be making these readings be off.  I also compared the voltages with those I read on my first 1176 that calibrated correctly and they are definitely not as close as the voltages on my first unit (with the exception of Q5... my first unit measured 24.35V at the same spot where unit #2 measured 24.29V for what should be, according to the schematic, 25.15V).  Thoughts on where to proceed from here? Thanks for the help thus far Mike!

I don't really see anything too concerning in there. Maybe the 2V one.

Have you tried measuring the AC at pin 22 and the DC at pin 21 at various ratios?

Let me find a link.

Mike

 

[Echo North]

If you're not getting correct compression check:

With in/out knobs mid way apply a 1khz 0dB signal and adjust the output to 0dB on the output
- that you see ac at pad 22 that starts larger and get's smaller as you move from ratio 20 to 4.
- that you have a negative DC voltage at pad 21 that starts larger and get's smaller as you move from ratio 20 to 4.

Post the values at each pad at each compression setting.

Mike

 

[Potato Cakes]

I don't think the ratio assembly needs to be inverted.

It's been established that the output levels are seemingly a little "backwards" from one ratio to the next, but this is normal, and is because the ratio settings can be thought of as threshold/ratio presets. As you select higher ratios you are also selecting higher thresholds. See the dual resistor ladder in the schematic to see what I mean. One ladder attenuates the signal going into the GR amp, while the other tinkers with the negative control voltage coming out of the GR amp.

As seen while measuring AC volts at the output, this would appear that higher ratios put out a slightly louder signal.

Thanks for clearing this up. If it isn't apparent already, I'm fairly new to the 1176 circuit characteristics. I can clearly see on the compressor curve graph that the higher ratios are at higher thresholds. I guess when I'm working past midnight my mind starts to play tricks on me and I arrive at incorrect conclusions when trouble shooting.

Thanks!

Paul

 

[keevhren]

If you're not getting correct compression check:

With in/out knobs mid way apply a 1khz 0dB signal and adjust the output to 0dB on the output
- that you see ac at pad 22 that starts larger and get's smaller as you move from ratio 20 to 4.
- that you have a negative DC voltage at pad 21 that starts larger and get's smaller as you move from ratio 20 to 4.

Post the values at each pad at each compression setting.

Mike

Okay... definitely onto something here. I measured pad 21 and 22 on my good/working unit and got the following:

pad 22
20:1 = .679vac
12:1 = .313vac
8:1 = .198vac
4:1 = .087vac

pad 21
20:1 = -5.82vdc
12:1 = -3.23vdc
8:1 = -2.42vdc
4:1 = -1.60vdc

on my non working unit, I'm reading 0.001vac at pad 22 on all ratios, and on pad 21 reading much lower values than my working unit... -.751, -.689, -.558, and -.329vdc from 20 down to 4 on the ratios.

I just looked over the joints and everything looks as though it's soldered well on the board and on the connectors leading to the ratio pcb and front panel knobs. II'm assuming a first step might be to reflow all of the joints around pad 21 and 22 as well as the places they connect to elsewhere? Or is this something that you've seen before and know the solution to already? Thanks for the patience and guidance!

 

[Echo North]

Are you should you had the GR ON when testing the non working unit?  If you have it in GR OFF mode you'll get 0VAC at pad 22.

Confirm.

Mike

 

[keevhren]

Are you should you had the GR ON when testing the non working unit?  If you have it in GR OFF mode you'll get 0VAC at pad 22.

Confirm.

Mike

confirmed, unit is powered on with gr selected for meter. 0.00vac at pad 22 and same readings as posted above for pad 21 vdc. 0.775vac reading at the output xlr

 

[Echo North]

Are you should you had the GR ON when testing the non working unit?  If you have it in GR OFF mode you'll get 0VAC at pad 22.

Confirm.

Mike

confirmed, unit is powered on with gr selected for meter. 0.00vac at pad 22 and same readings as posted above for pad 21 vdc. 0.775vac reading at the output xlr

What is your VAC with GR off, at PAD 15? (output pot)

 

[Potato Cakes]

Just finished a second Rev A and it worked right out of the gate. Thanks again to everyone for your help.

Mike, you're awesome. Can't wait to see what you guys come up with in the future.

Thanks!

Paul

 

[keevhren]

What is your VAC with GR off, at PAD 15? (output pot)

Just making sure I'm doing this right... when measuring pad 15, I should be doing it under the same circumstances as pads 21 and 22 (aka... unit is on, GR meter, 20:1, Input at 12 oclock, output adjusted to see .775vac at the output xlr, release full CW) except I should now turn my attack knob to the off position as opposed to fully CW... right?

 

[Echo North]

What is your VAC with GR off, at PAD 15? (output pot)

Just making sure I'm doing this right... when measuring pad 15, I should be doing it under the same circumstances as pads 21 and 22 (aka... unit is on, GR meter, 20:1, Input at 12 oclock, output adjusted to see .775vac at the output xlr, release full CW) except I should now turn my attack knob to the off position as opposed to fully CW... right?

Just turn GR OFF, 20:1, release fully CW, in and out midway.

1K 0dB signal.

What's your AC at 15?

Mike

 

[keevhren]

What is your VAC with GR off, at PAD 15? (output pot)

Just making sure I'm doing this right... when measuring pad 15, I should be doing it under the same circumstances as pads 21 and 22 (aka... unit is on, GR meter, 20:1, Input at 12 oclock, output adjusted to see .775vac at the output xlr, release full CW) except I should now turn my attack knob to the off position as opposed to fully CW... right?

Just turn GR OFF, 20:1, release fully CW, in and out midway.

1K 0dB signal.

What's your AC at 15?

Mike

VAC at Pad 15 is .885VAC with attack all the way off.

For comparison... my working unit is .341VAC at the same spot under the same conditions.

 

[Echo North]

What is your VAC with GR off, at PAD 15? (output pot)

Just making sure I'm doing this right... when measuring pad 15, I should be doing it under the same circumstances as pads 21 and 22 (aka... unit is on, GR meter, 20:1, Input at 12 oclock, output adjusted to see .775vac at the output xlr, release full CW) except I should now turn my attack knob to the off position as opposed to fully CW... right?

Just turn GR OFF, 20:1, release fully CW, in and out midway.

1K 0dB signal.

What's your AC at 15?

Mike

VAC at Pad 15 is .885VAC with attack all the way off.

For comparison... my working unit is .341VAC at the same spot under the same conditions.

I wouldn't worry too much about level at this point. The real issue is that with GR ON you have AC signal at pad 15 and none at pad 22. That's a problem.

Good news is that there isn't much in between.  Open the schematic:
http://mnats.net/files/1176REVA_125_VOLTAGES.pdf

Turn GR ON (must be on) and go into 4:1 ratio. Locate pad 15 at the top middle of the schem. The AC leaves the output pot by wire to pad 15 on the ratio PCB.  Then is travels though  R78->R19->R20-R21 on the ratio PCB and out a wire at pad GRN where it then connects via the switch to pad 22.

Trace that AC through that and see where is dies.

Mike

 

[JulienB]

Hi,
The resistor R32  smoke and it going hot. Any tip?
Julien
------------
Hi,

Make sure you have the output wired correctly.  It’s possible you have a damaged Q6, we could send a new one if you like.

Mike
------------
Hi, I finally had time to replace Q6 and also the resistor R32. The same problem occurs. I was able to adjust a calibrated null 0,00volt. For cons, I do not manage to adjust the meter has seen 0 Vu? I wonder why you have a possible solution. I check all the welds and wire, everything seems consistent.
Regards,

Julien
--------------
If you’re able to set the Q-bias, then you have an error in your meter section.
Mike
--------------
You're right, I try to calibrate the Q-Bias and notting really append. I applied 0,775 volts 0dBu to pin 2-3, I read the output pin is equal to 2-3 0,008volt. I tried to increase the output  0,012volts nothing significant. I adjust the machine exactly as the calibration section says:
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

Here (picture) the voltage that I found during my attempt.(orange colour)

I remplace Q4, notting change...

Can you help my?
Regards,
Julien

 

[dbonin]

for hot R32  make sure you have CR1 oriented correctly as well.