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

[hymentoptera]

This message is for KSeaton. Re: Post #1579, from January 2013.

Kevin, I know it's been 5 months, but did you ever get your trouble sorted out? Looking at picture posted in post # 1579 I noticed your output leads going to the meter switch run along side your mains voltage / transformer wires. This lends to inductive coupling of 60Hz onto your output. Try rerouting the blue/purple leads between output XLR and meter board somewhere else away from mains voltage.

Hope this helps. Looking fwd to starting my own bluestripe build soon.

edit:
Might also consider using shielded balanced cable for both the line from output transformer to output XLR, and the line from output XLR to meter board, soldering the shields of each to pin 1 of the XLR and the leaving the other ends snipped and unconnected to anything. The same grey kind of cable you used for the input would be fine here.

The output leads MUST be shielded if you to keep out the majority of interference. Good luck, and happy DIY'ing!

 

[Curran]

so I want to get the Q bias to read (-2.0vdc) off of the wiper then correct? and I should be able to move on to the VU calibration

 

[Echo North]

so I want to get the Q bias to read (-2.0vdc) off of the wiper then correct? and I should be able to move on to the VU calibration

You want your Qbias to read whatever it needs to cause a 1dB drop at the input.  You need to do the Qbias as your FIRST calibration step.  The start the calibration you want the QBias most negative, which it where it is now. 

Read here:
http://hairballaudio.com/docs/FETGUIDE/Section%20B%20-%20FET%20Intro.pdf

Set the QBias as described in the MNATS video.

 

[rainton]

I finished my Rev. A yesterday - and apart from the issue with my DMM running low on bat at the beginning of the build - showing me some kind of weird voltage drop in the power supply, which turned out not be there in the end -
that was an extremely smooth build and I have to thank Mike for putting this together and Mnats for the extremely good guide!

Also regarding calibration - the videos really made it a breeze! Thanks again you guys!

And the best of all - this thing sounds fantastic!!

One last question though:
I've installed a red power LED above the VU meter - like the original had.
I simply took the power off the +30V DC test point on the pcb and used a dropping resistor.

the LED is 12V/2W and so I calculated a 220 Ohms resistor would bring down the voltage to where it would give the LED a decent glow without making it to bright.

Now IT IS working -  but when measuring the DC voltage after the dropping resistor at the + pole of the LED against ground I still measure 19.5V...
shouldn't it be more like around 9V? (before the dropping resistor I measure +30V)

 

[Echo North]

I finished my Rev. A yesterday - and apart from the issue with my DMM running low on bat at the beginning of the build - showing me some kind of weird voltage drop in the power supply, which turned out not be there in the end -
that was an extremely smooth build and I have to thank Mike for putting this together and Mnats for the extremely good guide!

Also regarding calibration - the videos really made it a breeze! Thanks again you guys!

And the best of all - this thing sounds fantastic!!

One last question though:
I've installed a red power LED above the VU meter - like the original had.
I simply took the power off the +30V DC test point on the pcb and used a dropping resistor.

the LED is 12V/2W and so I calculated a 220 Ohms resistor would bring down the voltage to where it would give the LED a decent glow without making it to bright.

Now IT IS working -  but when measuring the DC voltage after the dropping resistor at the + pole of the LED against ground I still measure 19.5V...
shouldn't it be more like around 9V? (before the dropping resistor I measure +30V)

Is it an LED or a lamp? 

Seems like the current is 45mA (10/220).  If you want a 21V drop across the R maybe try a (21/0.045) resistor in the 470Ω area.  At least 2W.

Mike

 

[rainton]

Is it an LED or a lamp? 

Seems like the current is 45mA (10/220).  If you want a 21V drop across the R maybe try a (21/0.045) resistor in the 470Ω area.  At least 2W.

Mike

Thanks Mike!

It is an LED.
Why did you calculate 10/220?
I calculated I=P/U...was that wrong?

After measuring 19.5V at the anode of the LED your suggestion of 470 Ohms
makes much more sense!
I just want to learn why that is...

 

[Echo North]

Is it an LED or a lamp? 

Seems like the current is 45mA (10/220).  If you want a 21V drop across the R maybe try a (21/0.045) resistor in the 470Ω area.  At least 2W.

Mike

Thanks Mike!

It is an LED.
Why did you calculate 10/220?
I calculated I=P/U...was that wrong?

After measuring 19.5V at the anode of the LED your suggestion of 470 Ohms
makes much more sense!
I just want to learn why that is...

I calculated the current draw from the V and W but that didn't add up.  So I calculated the actual current by calculating the resistor Ω and drop across the R.  So you're dropping 10V across a 220Ω R which mean your current is 45mA.  Then I figures how much drop you need across the R to get the V to 9V (you need a 21V drop).  21V/0.045 for a 470ish Ω resistor.

All in theory of course.

 

[rainton]

I calculated the current draw from the V and W but that didn't add up.  So I calculated the actual current by calculating the resistor Ω and drop across the R.  So you're dropping 10V across a 220Ω R which mean your current is 45mA.  Then I figures how much drop you need across the R to get the V to 9V (you need a 21V drop).  21V/0.045 for a 470ish Ω resistor.

All in theory of course.

Now I see - thank you very much Mike - makes perfect sense!

Also - I built a couple of DIY projects already and not being an electrician - I kind of started from zero and I'm learning so much with every new project!
BUT since this was my first Hairball kit I have to say: I never had such a good quality case to work with - and to have all the holes pre-drilled is just awesome!!

Again thank you so much!

 

[hymentoptera]

...
I've installed a red power LED above the VU meter - like the original had.
I simply took the power off the +30V DC test point on the pcb and used a dropping resistor.

the LED is 12V/2W...

May I ask where you got your LED or a part number? I'm planning to do the same, and I'm overwhelmed at the number of different LEDs and bezels to choose from. I'd like to try one that's known to work with a given resistor and voltage.

Thanks!

 

[rainton]

May I ask where you got your LED or a part number? I'm planning to do the same, and I'm overwhelmed at the number of different LEDs and bezels to choose from. I'd like to try one that's known to work with a given resistor and voltage.

Thanks!

Sure!
This is the Mouser part-number: 607-2191QU1-12V
Good luck

 

[damian]

Hi,

I have calibrated my 1176 but my VU is way off, with a around 0db signal going in, compression turned off and adjusting the input and output knobs to get 0db back into the mixer the 1176 is only showing aound -15db

I tried calibrating again and still this happens, do you have an idea what is wrong or what I have done wrong?

Thanks,

Damian

Is it a digital mixer?  Are you looking at -15dBFS?  That is pretty close to 0dBu.

Hi,

Its an analog mixer, It has a meterbridge for each channel so I can see exactly whats going in.

What is your mixers metering calibrated to?  0dBu = how many V? 

If it's -10 metering and you 1176 is in +4 mode....

Measure the ACV across pin 2 and 3 of your output XLR and adjust your in/out so it reads 1.25VAC.  Your meter should then be at 0 in +4 mode.

Hi, yes when I did that I got 0 in +4 mode, so the VU is correct thanks, my mic preamp just gets distorted when the gain is all the way down and when I drive a signal of 0 from the 1176.
If I run it to the line in I should be ok.

Thanks,

Damian

 

[rainton]

May I ask where you got your LED or a part number? I'm planning to do the same, and I'm overwhelmed at the number of different LEDs and bezels to choose from. I'd like to try one that's known to work with a given resistor and voltage.

Thanks!

Just to give you a quick heads up: I tried a 470 ohms dropping resistor before the LED.
But measuring at the anode of the LED I still get 15V...strange, right?
I try further and keep you posted

One more (tiny) thing: Is it normal that I can't turn the input knob all the way up to "0"?
With the output pot it's no problem - can turn it from "infinite" all the way to "0"
But when adjusting the input knob to start at "infinite" it ends at around "6".

I mean in a real world scenario you would never turn the input knob up that much that's why I figured it might be supposed to be like that - just wanted to know for sure...

 

[Curran]

I think I am done?!?!?!?!?! The 3rd step was to easy, so easy it makes me worry I did not do something properly. The VU wa almost perfect with NO goofing around on the trimmer for R59. I get a 10db drop when I kick in the GR, I have the outpur set to +4 and reading on the VU 0db, then kick in the GR and it drops 10db. should it be this easy or am I monitoring the VU with an incorrect setting??

 

[hymentoptera]

Just to give you a quick heads up: I tried a 470 ohms dropping resistor before the LED.
But measuring at the anode of the LED I still get 15V...strange, right?
I try further and keep you posted

One more (tiny) thing: Is it normal that I can't turn the input knob all the way up to "0"?
...

Thanks for the tip, I'll try with 470 ohm first if that works for you.

As to why the meter still shows 15v, I know that's confusing, especially when we speak of a "voltage drop", you'd expect to see less potential on your meter, but it doesn't work like that. I've never been able to wrap my head around that, but you wont see an actual drop in voltage there with no load, it's actually a drop in current caused by the resistor when it's connected up and working. The drop is seen as heat from the resistor.

I feel like this is where the hydraulic analogy fails me and I'm left not understanding electricity. If we think of a resistor as a thinner piece of pipe in a closed circuit water system, you pressurize the system to a given psi with a pump (battery or other PSU) and cap the small pipe off so no water is flowing (open circuit), if you measure the psi at the other end of the thinner pipe you still show the full psi. It's not until you complete the circuit and water starts flowing that you realize you're restricting the flow of water due to the thinner section of pipe.

I believe it has something to do with volts = current / resistance.  Perhaps current is an integral part, according to Ohm's Law? And then there's Kirchoff's law, which starts talking about voltage drops, and I'm lost all over again. Er, I'm just rambling. maybe someone else can help us understand it better?

 

[baadc0de]

Guys... quick question, if anyone has an idea... at 20:1 and 12:1 the compressor works but is a bit too distorted. Sounding like 0.5% or more THD. But it compresses normally. Pressing 20:1 and 4:1 goes into "all buttons mode" and sounds like it, but THD feels like it *decreases* which is weird. At 8:1 and 4:1 there is no compression. Huh, what gives, any ideas on what to check, what could be a newbie mistake? Probably threshold is too high or something?

Built with hairballs switch PCBs, rev 1.25 main board I believe.

 

[MicDaddy]

I'd like to add the Red LED above the VU.  Anyone care to advise on lining up and drilling for the LED before I hack and destroy my beautiful front panel?  Thanks in advance!

 

[hymentoptera]

I'd like to add the Red LED above the VU.  Anyone care to advise on lining up and drilling for the LED before I hack and destroy my beautiful front panel?  Thanks in advance!

I plan to measure the blue stripe width, and divide by 2, and come off the edge of the stripe for my centers. Mine looks to be 3 19/32"(91mm) wide, so half of that would be 1 51/64" (45.1mm). Double check yours is the same width, and don't trust my math.

I plan to lightly scribe a vertical line at 45.5mm from one edge of the strip about how high i need it to clear the meter, etc, wherever i want my LED center, mark my horizonal center. Check same from other edge to make sure they are the same or touching (measure twice, cut once?). Then drill CAREFULLY where they meet. I'll probably do it in the drill press, starting with a small bit and moving up to the full size of whatever LED panel mount device I end up choosing.

it's aluminum so it should drill easily with a sharp bit.

 

[hymentoptera]

Using my calipers I'm getting 3.60" width on the blue stripe, so 1.8" should be the center of mine.

 

[rainton]

I'll probably do it in the drill press, starting with a small bit and moving up to the full size of whatever LED panel mount device I end up choosing.

it's aluminum so it should drill easily with a sharp bit.

I had some cnc engraving done to my front panel by frank at NRG in Germany and while he was at it he also did the hole for the LED for me -
otherwise I would also try it the same way as hymentoptera

 

[hymentoptera]

I had some cnc engraving done to my front panel by frank at NRG in Germany and while he was at it he also did the hole for the LED for me -
otherwise I would also try it the same way as hymentoptera

rainton, I would love to see a photo of your front panel. Is it a custom panel, or did you buy the full hairball kit w/ bluestripe enclosure?