All things G1176 - the new "repost" thread.

[mac]

for martin  ;D

 

[mrcase]

hey all!

I finished a dual 1176 mants pcb rev j. all seems fine except my ratios are way off! or all more or less the same except in slam mode.
Ihave mesaured the ratios according to this procedure: http://www.axtsystems.com/index.php?option=com_content&view=article&id=54:1176lnratios&catid=34:1176ln&Itemid=62

resulting in 4:1 - 18.2dB / 8:1 - 19.1dB / 12:1 - 19.7dB / 20:1 - 19.9dB / SLAM - 21.9 dB

now this seems way off and I am clueless where to look. I have built the mnats Slam mode switch as in his tutorial and I have calibrated the system like gyraf explains on his site (starting with the output fully CW, sending 0dB signal to input, rising the Input pot till signal out is +1db, trimming QBias till 1dB drop (after making sure its out off conducting range before).
So, am I doing something worng or is there a fault in my build? Ihave no clue! So please, HELP!  ???

thank you all

btw - I am not sure my fets are matched - I have ordered them matched at banzaimusic but dunno if the succeeded doing what I payed for. could this be an issue?

 

[mrcase]

ah and mac - is this your B11148 wiring?

 

[gswan]

hey all!

I finished a dual 1176 mants pcb rev j. all seems fine except my ratios are way off! or all more or less the same except in slam mode.
Ihave mesaured the ratios according to this procedure: http://www.axtsystems.com/index.php?option=com_content&view=article&id=54:1176lnratios&catid=34:1176ln&Itemid=62

resulting in 4:1 - 18.2dB / 8:1 - 19.1dB / 12:1 - 19.7dB / 20:1 - 19.9dB / SLAM - 21.9 dB

now this seems way off and I am clueless where to look. I have built the mnats Slam mode switch as in his tutorial and I have calibrated the system like gyraf explains on his site (starting with the output fully CW, sending 0dB signal to input, rising the Input pot till signal out is +1db, trimming QBias till 1dB drop (after making sure its out off conducting range before).
So, am I doing something worng or is there a fault in my build? Ihave no clue! So please, HELP!  ???

thank you all

btw - I am not sure my fets are matched - I have ordered them matched at banzaimusic but dunno if the succeeded doing what I payed for. could this be an issue?

You need more than one measurement to construct a chart showing the gain curves for each ratio.
So for each ratio setting, construct a plot of measurements from say +4dBu to -15dBu and you should see a straight line for GR off (ie output = input) and a gain reduction curve for each ratio setting.
The ratio value is calculated using two points on the compressed gain section of the curve, and examining how many dB the output changed for a certain dB change in input signal.
For example, say you changed the input signal from -6dBu to 0dBu (ie 6dBu), then for each of the ratios you should get the following changes in output signal level for this input signal level change:
4:1 => 1.5dBu
8:1 => 0.75dBu
12:1 => 0.5dBu
20:1 => 0.3dBu

You can see that the output changes are quite small relative to the input change, so make sure your equipment and technique are up to the job or you will get wildly innacurate results.

The matching of FETs will not affect this. Provided the qbias and metering calibration worked OK then your FETs are compensated for differences.

 

[mac]

ah and mac - is this your B11148 wiring?

yup...sorry I was a bit slow off the mark....

 

[mrcase]

hey all!

I finished a dual 1176 mants pcb rev j. all seems fine except my ratios are way off! or all more or less the same except in slam mode.
Ihave mesaured the ratios according to this procedure: http://www.axtsystems.com/index.php?option=com_content&view=article&id=54:1176lnratios&catid=34:1176ln&Itemid=62

resulting in 4:1 - 18.2dB / 8:1 - 19.1dB / 12:1 - 19.7dB / 20:1 - 19.9dB / SLAM - 21.9 dB

now this seems way off and I am clueless where to look. I have built the mnats Slam mode switch as in his tutorial and I have calibrated the system like gyraf explains on his site (starting with the output fully CW, sending 0dB signal to input, rising the Input pot till signal out is +1db, trimming QBias till 1dB drop (after making sure its out off conducting range before).
So, am I doing something worng or is there a fault in my build? Ihave no clue! So please, HELP!  ???

thank you all

btw - I am not sure my fets are matched - I have ordered them matched at banzaimusic but dunno if the succeeded doing what I payed for. could this be an issue?

You need more than one measurement to construct a chart showing the gain curves for each ratio.
So for each ratio setting, construct a plot of measurements from say +4dBu to -15dBu and you should see a straight line for GR off (ie output = input) and a gain reduction curve for each ratio setting.
The ratio value is calculated using two points on the compressed gain section of the curve, and examining how many dB the output changed for a certain dB change in input signal.
For example, say you changed the input signal from -6dBu to 0dBu (ie 6dBu), then for each of the ratios you should get the following changes in output signal level for this input signal level change:
4:1 => 1.5dBu
8:1 => 0.75dBu
12:1 => 0.5dBu
20:1 => 0.3dBu

You can see that the output changes are quite small relative to the input change, so make sure your equipment and technique are up to the job or you will get wildly innacurate results.

The matching of FETs will not affect this. Provided the qbias and metering calibration worked OK then your FETs are compensated for differences.

thanks for answering gswan + mac!
I am not in the studio anymore but I gonna check again tomorrow! I also think my threshold may be a little hefty if its compressing already -20db halfway...

 

[drumminkiger]

Well, Ive got a bit of a problem that seems kinda odd to me, but i am a noob so i might just be missing something totally arbitrary, I built two channels of 1176 rev J with IC input and the mnats power supply. Now, when i fire up the power supply it gives me about 29.5 volts on the +30 rail, when i plug it into one of the channels it works just fine and supplies the same power, the unit looks ready to calibrate. but when i unhook it and then plug it into the other unit the output drops by about 5v (even at the power supply itself). -10 seems to stay about the same from board to board. I tried to check over my board for shorts and couldnt seem to find any, though there always could be one im sure. What got me looking at this  is that Q8 and 9 are getting really hot, and its eating 250ma fuses for breakfast. Ive bumped up the fuse size to 500ma so i can at least turn it on and grab a voltage and then turn it back off. I kept my build really straight forward, used the BOM off the mnats page and a hairball output transformer. Any ideas where i should start looking for fixes? Ive been crawling the form looking for a similar issue but havent come across it yet. Thanks for any input

 

[drumminkiger]

Awww man, no hints?

 

[mica]

Im having a problem with my second G1176 (mnats rev j). The problem is that it works and (appears to be) compressing fine at 1:4 and 1:8, but if I turn to 1:12 or 1:20 there's no compression and the meter doesn't move in GR mode.. How are the ratios seperated and where should i look or measure to find the error? Any suggestions?

thx

Michael

 

[mica]

bump..

 

[airtech]

I'm having problems with my 1176 as well.  I have signal going in, the vu meter shows that, but the voltages are wrong throughout the unit as far as transistors go.  I triple-checked all resistor color codes to make sure they were correct and all were right.  I looked for solder blobs, but couldn't see any.  I'm using Mnats RevJ Board with NTE transistors.  My transistor voltages are as follows and way off what they should be:

          Pin B          Pin C          Pin E
Q2 -    1.36          1.76          0.53
Q3 -    1.75          16-25        1.15
Q4 -    16-25        29.84        14.07
Q5 -    4.83          28.1          4.41
Q6 -    28.11        14.36          28.6
Q7 -    28.67        14.36          29.3
Q8 -    4.9            29.84          13.74
Q9 -    3.74          0              4.31
Q12 -  15.14        14.39        14.39
Q13 -  14.39        29.85        13.85
Q14 -  2.65          4.6            2.10
Q15 -  4.6            29.85        4.1

Thanks for any troubleshooting ideas,
Nate

 

[gswan]

I'm having problems with my 1176 as well.  I have signal going in, the vu meter shows that, but the voltages are wrong throughout the unit as far as transistors go.  I triple-checked all resistor color codes to make sure they were correct and all were right.  I looked for solder blobs, but couldn't see any.  I'm using Mnats RevJ Board with NTE transistors.  My transistor voltages are as follows and way off what they should be:

          Pin B           Pin C          Pin E
Q2 -    1.36           1.76           0.53
Q3 -    1.75           16-25         1.15
Q4 -    16-25         29.84         14.07
Q5 -    4.83           28.1           4.41
Q6 -    28.11         14.36          28.6
Q7 -    28.67         14.36          29.3
Q8 -    4.9            29.84          13.74
Q9 -    3.74           0               4.31
Q12 -   15.14         14.39         14.39
Q13 -   14.39         29.85         13.85
Q14 -   2.65          4.6             2.10
Q15 -   4.6            29.85         4.1

These look completely wrong. In all sections of the circuit!
If you are confident of the wiring and component values then you should check the orientation of the transistors. Check the orientation of C2 and C8 as well.
What are you doing to make Q3/C swing about by so much?

 

[juni]

I'd think the problem should be in somewhere on the switch board - doublecheck the resistors and traces. You've had the unit calibrated ok, yes?

Im having a problem with my second G1176 (mnats rev j). The problem is that it works and (appears to be) compressing fine at 1:4 and 1:8, but if I turn to 1:12 or 1:20 there's no compression and the meter doesn't move in GR mode.. How are the ratios seperated and where should i look or measure to find the error? Any suggestions?

thx

Michael

 

[airtech]

Well, I found the problem.  I forgot to get clearance from Bosch to use their box for this project.  No, really though I just retouched all the connections with my solder iron.  I guess there was a cold connection somewhere.  All the transistors are pretty close to what they should be now.  Got a love it!  Now I need to plug in some audio to see what happens.  Thanks for the help here.

          Pin B          Pin C          Pin E
Q2 -    1.02          1.75          0.52
Q3 -    1.75          11.9          1.15
Q4 -    11.9          29.8          11.4
Q5 -    4.84          28.1          4.38
Q6 -    28.1          14.4          28.7
Q7 -    28.6          14.4          29.3
Q8 -    14.4          29.8          13.7
Q9 -    13.1          0              13.7
Q12 -  4.44          15.02          3.89
Q13 -  15.0          29.8          14.4
Q14 -  3.44          16.6          2.88
Q15 -  16.6          29.8          16.1

 

[gswan]

Well, I found the problem.  I forgot to get clearance from Bosch to use their box for this project.  No, really though I just retouched all the connections with my solder iron.  I guess there was a cold connection somewhere.  All the transistors are pretty close to what they should be now.  Got a love it!  Now I need to plug in some audio to see what happens.  Thanks for the help here.

No. You need to perform all the tests and calibration procedures.
Plugging in audio now is a complete waste of time.

 

[airtech]

I powered up the unit and connected some xlr cables to calibrate, but noticed hum in monitors.  Bypassing unit, the hum is gone.  It's not super loud, but it's there.  I've got the rev j Mnats board and read about a "hitchhiker cut."  That was done to a Gyraf board and didn't know if that could be done on the Mnats board or needed to be done.

All my ground points are wired to the xlr input ground lug.  Do I also connect xlr pin 1 to the ground lug?  This is how I have it connected know and was wondering if this may be causing hum.

Also, I don't have a mu-metal can installed on my oep transformer and was wondering if that's where the hum may be coming from.

Does the power transformer need shielding?

Here's a picture of the top inside of my unit.  Maybe things need to be moved around.  All cables/wiring are shielded where they need to be.

 

[Chrome Heart]

You should not need to shield the torroid.
I run a ground from the power connector to the chassis. And then run xlr ground to chassis and I have no noise.

 

[airtech]

So the xlr ground you are referring to is pin 1?  I have a ground lug on the xlr connector along with the pins 1,2 and 3.  I joined the xlr pin 1 to the ground lug on the xlr connector.

 

[Chrome Heart]

So the xlr ground you are referring to is pin 1?  I have a ground lug on the xlr connector along with the pins 1,2 and 3.  I joined the xlr pin 1 to the ground lug on the xlr connector.

I would not tie IEC ground to pin 1 on the XLR. I would tie it the case/chassis.

 

[airtech]

Alright, so I'll disconnect pin 1 of the xlr input from the grounding point.  That's where all my grounds go to.  Center tap and Power main.