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

[haystack]

Hi dbonin
Thanks for your reply.

Just to be clear- are you saying ground the bare wire by attaching it to the bolts with a connection to sanded chassis?

Or, ground the trans by having a connection to sanded chassis via bolts and cut bare wire short?
Sorry to be a bit dippy here!

Thank you Hay

 

[dbonin]

Hi dbonin
Thanks for your reply.

Just to be clear- are you saying ground the bare wire by attaching it to the bolts with a connection to sanded chassis?

Or, ground the trans by having a connection to sanded chassis via bolts and cut bare wire short?
Sorry to be a bit dippy here!

Thank you Hay

Yes: "...ground the trans by having a connection to sanded chassis via bolts and cut bare wire short"

Cheers mate,
Don

 

[haystack]

Don

Thank you

Hay

 

[peartplus]

Hi Everyone,
I've finished my rev. a, and started to calibrate.  I completed the qbias, though I could get no where near 2.75 VAC at the output xlr. I figured something was wrong, so I listened to what was going on. Super distorted, thin, and only any output if input/ output is cranked.  Someone here had a similar issue, and Mike asked for some voltages... so here they are.
1k  input @.775V
Controls midway, no gain reduction, black lead to CT
XLR in pin 2: .473V
+ in tpad: .473V
+out tpad: .136V
+input trans.: .136V
+out input trans: .09V
+pcb: .09V
C7: .027V
+output XLR: .009V

Thanks for the help!

 

[dbonin]

Start at the point where the input transformer enters the PCB - apply your .775V / 1khz input test signal as usual and measure the voltage as you increase the input pot (t-pad) from full ccw  to full cw  - (if you used terminals for the wiring, disconnect them)
- you should be seeing somewhere around .340 AC coming OUT of the input transformer, with t-pad turned full cw with the leads disconnected from the pcb - this should fall to ZERO volts as you turn the input knob fully off.
-  let us know what you find.

also, make sure there is good ground continuity from the input xformer metal case to the chassis.

Hi Everyone,
I've finished my rev. a, and started to calibrate.  I completed the qbias, though I could get no where near 2.75 VAC at the output xlr. I figured something was wrong, so I listened to what was going on. Super distorted, thin, and only any output if input/ output is cranked.  Someone here had a similar issue, and Mike asked for some voltages... so here they are.
1k  input @.775V
Controls midway, no gain reduction, black lead to CT
XLR in pin 2: .473V
+ in tpad: .473V
+out tpad: .136V
+input trans.: .136V
+out input trans: .09V
+pcb: .09V
C7: .027V
+output XLR: .009V

Thanks for the help!

 

[Timh]

Alright, dudes. I finished my 1176 the other night and did calibration and everything seemed to be working fine. VU was acting accordingly to the 10dBu drop and what not. I just plugged it in to my signal chain and it was definitely not working fine.
1.) There is a very loud hum no matter the setting
2.) I could get the signal to pass through (I could hear the mic), but it would distort and make all kinds of funny noises.

Of course, I patched my signal without the 1176 and everything was working fine and clear, so I know there aren't any other problems in my signal chain besides the 1176.

This is only my 3rd or 4th build, so I am somewhat of a newbie. I don't know where to start with trouble shooting. To me, it sounds like loose wiring or a fried component or something, but what do I know.

Any ideas where to start? Is there a similar problem/solution somewhere else in this thread? Thank you.

 

[dbonin]

Did you test for ground continuity all around the case, from front panel to back panel chassis, from the input xformer metal case to the chassis,  did you grind/scrape away the black powder coat down to bare metal to assure good connection? 
If your grounding is proven solid you should get no hum.  These units are extremely low noise when grounded well.  No wiring is passing over the PCB ?
What kind of noise?  Scratchy noise may be DC getting into the signal  chain.  Check your caps for orientation - check that C7 is in the correct way.

Alright, dudes. I finished my 1176 the other night and did calibration and everything seemed to be working fine. VU was acting accordingly to the 10dBu drop and what not. I just plugged it in to my signal chain and it was definitely not working fine.
1.) There is a very loud hum no matter the setting
2.) I could get the signal to pass through (I could hear the mic), but it would distort and make all kinds of funny noises.

Of course, I patched my signal without the 1176 and everything was working fine and clear, so I know there aren't any other problems in my signal chain besides the 1176.

This is only my 3rd or 4th build, so I am somewhat of a newbie. I don't know where to start with trouble shooting. To me, it sounds like loose wiring or a fried component or something, but what do I know.

Any ideas where to start? Is there a similar problem/solution somewhere else in this thread? Thank you.

 

[Timh]

Did you test for ground continuity all around the case, from front panel to back panel chassis, from the input xformer metal case to the chassis,  did you grind/scrape away the black powder coat down to bare metal to assure good connection? 
If your grounding is proven solid you should get no hum.  These units are extremely low noise when grounded well.  No wiring is passing over the PCB ?
What kind of noise?  Scratchy noise may be DC getting into the signal  chain.  Check your caps for orientation - check that C7 is in the correct way.

Yeah, I did not sand the paint off the output transformer mount, and somehow that solved both problems! It sounds amazing!

 

[JustDavid]

So, I've finished the build of my REV A, everything went together pretty smoothly. I started the calibration stage with qbias and when I set the unit up for calibration and put in the 0.775 dBv test signal the meter is pinned to the right. I get signal at the output but the q bias doesn't seem to have any affect. I turned the trim pot fully ccw, and the meter is still pinned. Any thoughts?

 

[dbonin]

So, I've finished the build of my REV A, everything went together pretty smoothly. I started the calibration stage with qbias and when I set the unit up for calibration and put in the 0.775 dBv test signal the meter is pinned to the right. I get signal at the output but the q bias doesn't seem to have any affect. I turned the trim pot fully ccw, and the meter is still pinned. Any thoughts?

Check your wiring closely.  For now ignore the meter and measure AC output voltage on pins 2/3 - does the voltage change when you are full CW the decrease as you back off the pots to full CCW?

Make sure your pots are wired correctly.

 

[JustDavid]

So, I've finished the build of my REV A, everything went together pretty smoothly. I started the calibration stage with qbias and when I set the unit up for calibration and put in the 0.775 dBv test signal the meter is pinned to the right. I get signal at the output but the q bias doesn't seem to have any affect. I turned the trim pot fully ccw, and the meter is still pinned. Any thoughts?

Check your wiring closely.  For now ignore the meter and measure AC output voltage on pins 2/3 - does the voltage change when you are full CW the decrease as you back off the pots to full CCW?

Make sure your pots are wired correctly.

I have check the wiring which looks too be correct . The output voltage is changing with movement of the pots as expected. Although I an not getting anywhere close the the 2.75 VAC at the output stage. Even with both pots fully CW.

 

[dbonin]

I have check the wiring which looks too be correct . The output voltage is changing with movement of the pots as expected. Although I an not getting anywhere close the the 2.75 VAC at the output stage. Even with both pots fully CW.

see my reply here about testing the input transformer output and let me know what you see:
http://groupdiy.com/index.php?topic=29981.msg731607#msg731607

 

[JustDavid]

Well, I think I just experienced a valuable lesson in test gear. I was using a my daw for a test tone and I was using the headphone out because my line level it wasn't giving me enough voltage.  Don't know what was going on, but I went out and grabbed an actual hardware oscillator and then all the pieces fell together. Works and sounds great!

 

[haystack]

Hi

OK, all finished on the rev A and calibrated fine I think.  Strange thing is, my DMM ( not an expensive one), didn't detect much of an AC signal from input xlr but v.healthy one on output, all trims worked fine etc . Also, tried to get a signal direct from the xlr cable from the DAW without luck. But I followed Hairball instructions carefully. I was using a signal generator software prog from macbook pro.

So, was having cup of tea and a bite with the rev  on, GR meter in, then glancing and admiring the meter etc noticed that the needle very occasionally dipped from 0vu to just below then back very gradually.  Any one else have this?

Hay

 

[rdp42089]

Hi All,

I just recently completed packing the PCBs and wiring up my first Rev A board.  The unit passes audio but I cannot get the unit to compress.  The attack potentiometer doesn't seem to be responding to any changes full CW / full CCW.

After building the power supply, R87 showed a reading of ~30Volts.  Now for whatever reason, it shows a reading of 24Volts.

I checked all the wiring resistor values, even re-soldered all of the components to ensure that there were no cold solder joints.

I am now in the process of building a second PCB in order to do a diagnostic between the two boards.

Any further suggestions would help.

Thanks,
Danny

 

[Echo North]

Hi All,

I just recently completed packing the PCBs and wiring up my first Rev A board.  The unit passes audio but I cannot get the unit to compress.  The attack potentiometer doesn't seem to be responding to any changes full CW / full CCW.

After building the power supply, R87 showed a reading of ~30Volts.  Now for whatever reason, it shows a reading of 24Volts.

I checked all the wiring resistor values, even re-soldered all of the components to ensure that there were no cold solder joints.

I am now in the process of building a second PCB in order to do a diagnostic between the two boards.

Any further suggestions would help.

Thanks,
Danny

Sounds like a misplaced component to me.  I've seen this a few times.  Something is dragging the voltage down.  I'd check all resistor values.

 

[dbonin]

So you are saying that you are seeing this behavior  when the unit is sitting idle, with no input signal, in GR mode?

Hi

OK, all finished on the rev A and calibrated fine I think.  Strange thing is, my DMM ( not an expensive one), didn't detect much of an AC signal from input xlr but v.healthy one on output, all trims worked fine etc . Also, tried to get a signal direct from the xlr cable from the DAW without luck. But I followed Hairball instructions carefully. I was using a signal generator software prog from macbook pro.

So, was having cup of tea and a bite with the rev  on, GR meter in, then glancing and admiring the meter etc noticed that the needle very occasionally dipped from 0vu to just below then back very gradually.  Any one else have this?

Hay

 

[haystack]

Yes.

I re- did the calibration couple of days ago. I got the .75 Voltage at input this time. Calibration went well - I followed the
youtube videos this time.

I put the unit on yesterday - no input signal- just let it warm up. The needle started to drift into 1db area from 0db in GR mode very gradually and fall gradually back. I thought it may be as the unit heated up or something??
cheers
Hay

 

[Echo North]

Yes.

I re- did the calibration couple of days ago. I got the .75 Voltage at input this time. Calibration went well - I followed the
youtube videos this time.

I put the unit on yesterday - no input signal- just let it warm up. The needle started to drift into 1db area from 0db in GR mode very gradually and fall gradually back. I thought it may be as the unit heated up or something??
cheers
Hay

There is some drift in the meter circuit.  Is the unit working otherwise?

 

[dbonin]

Yes.

I re- did the calibration couple of days ago. I got the .75 Voltage at input this time. Calibration went well - I followed the
youtube videos this time.

I put the unit on yesterday - no input signal- just let it warm up. The needle started to drift into 1db area from 0db in GR mode very gradually and fall gradually back. I thought it may be as the unit heated up or something??
cheers
Hay

There is some drift in the meter circuit.  Is the unit working otherwise?

I believe he is saying, even after warm up, it drifts up and down over and over again...  which is not typical. 
Please correct me if I'm wrong, haystack.