[BUILD] 1176LN Rev D DIY

[vineyardgray]

Well, I've got my first build done and mercifully everything appears to sorta operate the way it should.  I have yet to do a proper calibration, but I'd say I'm in the ballpark. 

A couple questions persist which I'd like your help to allay. 

1. Selecting different ratios via the ratio switch does not appear to reduce the amount of gain reduction being applied.  This is using a 1kHz 0dBU sine wave. Is this right?  I was assuming that, for instance, if 20:1 reduced the gain by X dB, then 12:1 should reduce the db by Y - a lower amount.  This is not the case on my unit - all ratios finally settle on the same gain reduction amount for a given input value.

2. This question has more to do with test gear loading - I'm using a NTI minirator as my source.  0dBU gives me a .781 Volts value on my DMM.  As soon as I plug it in, testing that same unit on the backside of the panel mounted XLR gives me .5XX Volts.  Am i witnessing input transformer/circuit load or is some other phenom at work (i.e. shite signal generaor?)

Thanks to all - this site is a wealth.

MR

 

[Echo North]

Well, I've got my first build done and mercifully everything appears to sorta operate the way it should.  I have yet to do a proper calibration, but I'd say I'm in the ballpark. 

A couple questions persist which I'd like your help to allay. 

1. Selecting different ratios via the ratio switch does not appear to reduce the amount of gain reduction being applied.  This is using a 1kHz 0dBU sine wave. Is this right?  I was assuming that, for instance, if 20:1 reduced the gain by X dB, then 12:1 should reduce the db by Y - a lower amount.  This is not the case on my unit - all ratios finally settle on the same gain reduction amount for a given input value.

2. This question has more to do with test gear loading - I'm using a NTI minirator as my source.  0dBU gives me a .781 Volts value on my DMM.  As soon as I plug it in, testing that same unit on the backside of the panel mounted XLR gives me .5XX Volts.  Am i witnessing input transformer/circuit load or is some other phenom at work (i.e. sh*te signal generaor?)

Thanks to all - this site is a wealth.

MR

1.  Incorrect.  What you're seeing on the meter is overall GR not ratio.  Ratio can only be seen by measuring at least to points. In the case of the 1176, as you go to higher ratio's 4 -> 20 the threshold actually raises so you see less GR on the meter at higher ratio.  The ratio is increasing however.  Here is is visually:

http://arpjournal.com/wp-content/uploads/2012/05/a_moore_arp2011fig11.jpg

If you were to feed a 1dBu signal into the unit and get an output of 0dBu, then feed an input of 2dBu and get 1.25 dBu on the output, that would be a ratio of 4:1.

2. This is a load issue.  Completely normal.  The 1176 has a nominal 600Ω input impedance.  Unless you sig gen output impedance is significantly lower, like 50Ω, you're going to get some loss.  Just increase the generator till you get your 0dBu level at the input.

Mike

 

[benlindell]

Hey Ben,

I've got +40DC and +30DC w/ 8VAC.

Mike

Can someone with a working unit check out the voltages on the left side of CR7, CR8, CR9, CR10. I'm getting +32Vdc from CR7 and CR8. I'm getting -25Vdc from CR9 and CR10 but also 11Vac, are these normal?

Thanks Mike, I've tried isolating the board (unplugged everything but the connection to ground) and also tested all caps and resistors for shorts, I'm still getting a rise to about -4Vdc on the -10V rail then a slow and steady drop that continues down to -2Vdc or so (moving 10mV/sec approx). Like I said I've already replaced all the powersupply capacitors and the 4740 diode, do I need to replace the 4001s? what would cause the voltage to slowly drop like this?

 

[benlindell]

Thanks Mike, I've tried isolating the board (unplugged everything but the connection to ground) and also tested all caps and resistors for shorts, I'm still getting a rise to about -4Vdc on the -10V rail then a slow and steady drop that continues down to -2Vdc or so (moving 10mV/sec approx). Like I said I've already replaced all the powersupply capacitors and the 4740 diode, do I need to replace the 4001s? what would cause the voltage to slowly drop like this?

Ah Ha! Went and perused the 1176A thread, and someone with the same problem, ended up have a cap backwards, I decided to check mine make sure I didn't do such a simple mistake, and of course... C26 was reversed *whoops*

rocking -9.8V now. sorry for all the hassle guys.

 

[Echo North]

Thanks Mike, I've tried isolating the board (unplugged everything but the connection to ground) and also tested all caps and resistors for shorts, I'm still getting a rise to about -4Vdc on the -10V rail then a slow and steady drop that continues down to -2Vdc or so (moving 10mV/sec approx). Like I said I've already replaced all the powersupply capacitors and the 4740 diode, do I need to replace the 4001s? what would cause the voltage to slowly drop like this?

Ah Ha! Went and perused the 1176A thread, and someone with the same problem, ended up have a cap backwards, I decided to check mine make sure I didn't do such a simple mistake, and of course... C26 was reversed *whoops*

rocking -9.8V now. sorry for all the hassle guys.

Glad you got it sorted!

 

[chipss36]

so I have began my 1176 ln rev D journey, what a well thought out kit,thanks to all who made this happen about the only way I could afford a 1176...lol anyway
i have built the power supply sections first, I am building 2 so
#1 i read 29.89 VDC  and -9.74 VDC @ there respective test points ,
#2 reads 29.92 VDC and -9.60
seems in the ballpark to move on?

 

[Echo North]

so I have began my 1176 ln rev D journey, what a well thought out kit,thanks to all who made this happen about the only way I could afford a 1176...lol anyway
i have built the power supply sections first, I am building 2 so
#1 i read 29.89 VDC  and -9.74 VDC @ there respective test points ,
#2 reads 29.92 VDC and -9.60
seems in the ballpark to move on?

Yep...looks good.

 

[rockmonkey731]

So, anyone have any ideas as to what may have caused my c25 to blow? I just got my replacement from mouser, but before I put it in and start it up again, hopefully I can fix whatever caused it.

 

[RichardM]

I thought I would take a little time away to educate myself and make sure that I wasn't asking questions that I could easily solve myself .You guys at hairball have been excelllant! I had enough parts here to build another pcb board so I did so carefully and inserted it to see if I could eliminate the no input problem. I thought that maybe I had messed up on the pcb. All of the voltages test out better than the previous pcb (except for the GR meter Driver section)because I had 2 sets of mouser parts to pick from and I used the most accurate parts for the build. I still have no input/output so I did take the readings that you had asked for before.

.64Vac xlr pin 2
.07 Vac by c1
.07 Vac - of c7
.07 Vac pin 2 output xlr

Would this mean that the signal is not making it to the board? The same problem that occured with the old pcb occurs in the GRM driver with the new pcb. The values are off but this time they are higher. On the other board they were lower.Would this improper voltage in this area on both boards be the result of a problem elsewhere? I have gone through and checked all of the parts on both boards and everything appears to be the same. I did not use the original pcb as a reference at all while stuffing it. Only the mnats bom

My only other question is about the trimmer pots. On board one that I built I had them inserted horizontallyl as shown in one of the older rev D pics on the hairball site with the black side was facing the little semi circle. On board 2 I had the black side out because that how it is shown on the site now with the mouser parts. Should the blue side always be in?

Thanks again for your help!

 

[Echo North]

I thought I would take a little time away to educate myself and make sure that I wasn't asking questions that I could easily solve myself .You guys at hairball have been excelllant! I had enough parts here to build another pcb board so I did so carefully and inserted it to see if I could eliminate the no input problem. I thought that maybe I had messed up on the pcb. All of the voltages test out better than the previous pcb (except for the GR meter Driver section)because I had 2 sets of mouser parts to pick from and I used the most accurate parts for the build. I still have no input/output so I did take the readings that you had asked for before.

.64Vac xlr pin 2
.07 Vac by c1
.07 Vac - of c7
.07 Vac pin 2 output xlr

Would this mean that the signal is not making it to the board? The same problem that occured with the old pcb occurs in the GRM driver with the new pcb. The values are off but this time they are higher. On the other board they were lower.Would this improper voltage in this area on both boards be the result of a problem elsewhere? I have gone through and checked all of the parts on both boards and everything appears to be the same. I did not use the original pcb as a reference at all while stuffing it. Only the mnats bom

My only other question is about the trimmer pots. On board one that I built I had them inserted horizontallyl as shown in one of the older rev D pics on the hairball site with the black side was facing the little semi circle. On board 2 I had the black side out because that how it is shown on the site now with the mouser parts. Should the blue side always be in?

Thanks again for your help!

Sounds like the signal is dying before it hits the PCB.  Either at the input transformer or T-pad.  You need to re-check all of this wiring.  Test the signal at the + of the input primary, + of the secondary side, + of the T-pad input, + of the tpad output.  Then you'll see where it dies.

The GRM section values listed on the MNATs schematic are for a calibrated unit.  If your unit is not calibrated you will see different values.

The trimers will work facing "left" or "right".  The rotation of the calibration will just be reversed.

Mike

 

[Echo North]

So, anyone have any ideas as to what may have caused my c25 to blow? I just got my replacement from mouser, but before I put it in and start it up again, hopefully I can fix whatever caused it.

Maybe inserted wrongly or a bad cap.  Hard to say.  Make sure all of your caps and diodes in that power section are inserted correctly.  Seems like something is shorted.

 

[rockmonkey731]

Alright, so the issue was that I'm an idiot, and C25 was indeed backwards. Wow. So the unit now turns on (and stays on)!

Which brings me to my next issue. I'm a little confused about the Q Bias procedure. In the video, he says turn the wiper fully away from ground. Is the "wiper" the blue component? Because if so, I'm not sure what position is furthest from ground. The trimmer on the top doesn't stop at any position, it just spins forever. Am I doing this incorrectly?

 

[Echo North]

Alright, so the issue was that I'm an idiot, and C25 was indeed backwards. Wow. So the unit now turns on (and stays on)!

Which brings me to my next issue. I'm a little confused about the Q Bias procedure. In the video, he says turn the wiper fully away from ground. Is the "wiper" the blue component? Because if so, I'm not sure what position is furthest from ground. The trimmer on the top doesn't stop at any position, it just spins forever. Am I doing this incorrectly?

The wiper is the element in a potentiometer that moves beween the two set polls making the resistance variable.  The wiper is controlled by the screw or turning a panel mount pot.  Typically (not always) it's the middle lug or pin.

What I do is feed in the signal and monitor the output at the output XLR with a dmm (pin 2+3).  Turn the trimmer until you get the highest output and it no longer increases (out of conduction/pinched off).  That is where you start the adjustment.  Then you turn it back the other way until you get the 1 dBu drop setting it just into conduction.

 

[websoul]

Alright, so the issue was that I'm an idiot, and C25 was indeed backwards. Wow. So the unit now turns on (and stays on)!

Which brings me to my next issue. I'm a little confused about the Q Bias procedure. In the video, he says turn the wiper fully away from ground. Is the "wiper" the blue component? Because if so, I'm not sure what position is furthest from ground. The trimmer on the top doesn't stop at any position, it just spins forever. Am I doing this incorrectly?

The blue component with a little screw on top, R59, is what you need to use for the Q bias.  Don't turn too much as you could damage it. What I tend to do is leave the unit on for a couple of hours before any sort of calibration.

Then, get the audio passing through as explained, +1 on the VU meter.  Then gently start turning the screw CCW about 15 turns max.  If nothing happens, I'll turn back 15 turns CW (roughly back to the start), and then the do the same, but in the other direction. So, 15 turns CW. Just keep an eye on the VU meter to see what happens.

If the VU goes up, then decrease the input a touch, then keep turning R59 in the same direction until it stops increasing the VU.  That means its in the correct point to start the calibration.  Then get +1 on the VU and turn the other way to set the Q bias.

I found that you need more patience and time to calibrate than you do for the actual build. Not a bad thing. Also a bit of trial and error to.

Just take your time.

 

[rockmonkey731]

Ok, so I'm putting .775 Volts AC into the unit, and I'm getting about .4 out, and turning the q bias trimmer isn't changing anything. Another weird thing, on the inside of the input xlr, I'm reading about .4 volts. Is that normal?

 

[Echo North]

Ok, so I'm putting .775 Volts AC into the unit, and I'm getting about .4 out, and turning the q bias trimmer isn't changing anything. Another weird thing, on the inside of the input xlr, I'm reading about .4 volts. Is that normal?

You're experience a voltage loss from source/load impedances.  I've posted about this here on in the A threat in the past 2 days.  Look there for an explanation.  It's normal.

Check the DC voltage between your Q1 gate and ground.  Rotating the qbias should alter this value between 0VDC and -3VDC or higher.  If you're not seeing a DC change here you have an error in this part of the circuit. 

 

[rockmonkey731]

If I'm doing it right, the voltage at Q1 is .14 volts AC, and it doesn't move at all when I adjust the q bias trimmer. My attack/release pots all seem to be wired correctly. What other problems should I check for?

 

[Echo North]

If I'm doing it right, the voltage at Q1 is .14 volts AC, and it doesn't move at all when I adjust the q bias trimmer. My attack/release pots all seem to be wired correctly. What other problems should I check for?

Measure the DC.

 

[Echo North]

Do you have negative DC on pad 18?

 

[rockmonkey731]

Ah, whoops. I think i'm measuring it wrong, as I'm seeing 0V DC on Q1 and pad 18. Q1 has the labels G, S, and D, which one of those am I measuring? And to measure the voltage on pad 18 using my multimeter, which probe (positive or negative) would I put on the pad?
Sorry for all the (probably dumb) questions, I'm pretty new at this stuff. But thanks for the help!