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

[beaversaber]

isn't that what the bypass switch does? shorts 22 to ground?

 

[evilcat]

I don't know, certainly. But if you do it with the switch, you disable the vu-meter. As you need it for the calibration, you have to do it manually with a wire.

 

[beaversaber]

I don't know, certainly. But if you do it with the switch, you disable the vu-meter. As you need it for the calibration, you have to do it manually with a wire.

To do the calibration you don't need the meter to be showing gain reduction.  just output level.

 

[evilcat]

Yes, exactly.
So your q bias calibration procedure is right, isn't it ? You achieve it but still no GR  after that ?

 

[Echo North]

If your Q Bias is correct and your not seeing compression when you measure the output I would think you have a bad component somewhere in your GR section.

Check the transistor voltages in that section.  If your voltages are odd, check the resistor values, check for solder bridges, change out the transistors...

Geoff's page is for the J board, but it still applies:
http://www.axtsystems.com/index.php?option=com_content&view=article&id=57:1176lnproblems&catid=34:1176ln&Itemid=62

Mike

 

[jordan s]

I "finished" my build last night. First, thanks to Hairball Audio and mnats for the awesome kits, boards and docs, you guys rule! Now to my problem.
I was able to do all the calibration procedures but I couldn't really get the gain reduction meter calibrated properly. While it sounds awesome, it was bugging me that the meter probably wasn't reading exactly what it was supposed to. I've been messing with it all night, going through all the calibration procedures again and now I've got myself to a point where I can not zero the meter in GR mode using the zero adjust pot. When the tracking adjust trimmer is bypassed with the shorting pin, it sits at -10 with no signal and moves below that when compressing. When the tracking adjust trimmer is put back into the circuit, the meter drops down to -20 and stays there. I can't figure out why I was able to get it close last night but now it's way off. Would it be a bad idea to reduce the value of r72 at the end of zero adjust pot to be able to boost it more? Could a component have gone bad somehow? Any ideas?

 

[Echo North]

With the tracking trimmer bypassed, is the null adj trimmer doing anything?

You should see it adj a DC voltage between the test points.  You want that to read 0.00V DC with the meter zeroed.  If the null adj is not effecting the DC or the meter, that is a problem.

Mike

 

[jordan s]

Yes, the null adjust does affect the voltage across the test points. I had it calibrated before when the zero adjust pot was able to get the meter at zero. Now for some reason, the test points read exactly 0V when the zero adjust is all the way down. I remember, at first when I would turn the unit on, it would take a minute for the needle to slowly rise up to zero. Now it doesn't do it at all. Is that normal?

 

[Echo North]

Normal for it to take a second to rise, but if it's not rising at all that is an issue.

Something is fishy in your GR meter section.  Those multi-turn pots break easily if you over rotate them.

Also make sure they are inserted correctly.

Mike

 

[jordan s]

Hmmm. Could a broken tracking adjust trimmer cause this? I still can't get the meter to zero with the zero adjust pot even when the tracking adjust is taken out of the circuit with the jumper, although I am able to get it higher. I guess the suspicious areas are around the tracking adjust and null adjust trimmers. Is there any way to test Q11, Q12 and Q13 to make sure they're ok? The only things that I could think of that I did to break this would be to over turn one of the trimmers, also I shorted pad 22 to ground as it says in the calibration videos to see if it would make a difference and found that it does something different than turning the attack pot off. This is pretty frustrating because it was working nearly perfectly before I decided to obsess about getting the metering absolutely perfect. I was amazed that I was able to finish it without spending days troubleshooting. Guess I was wrong. I have more work to do tonight.

 

[Echo North]

Any of those trimmers being damaged/creating a short would hurt the meter.

You could test the trimmers, check your transistors for DC oddities, replace the transistors, check you resistor values, check you GR FET, lifted pads, cold solders.

Are you convinced everything else is working fine?

Mike

 

[jordan s]

Ok, figured it out. For one, I did not have the bypass lug of the attack/bypass switch connected to ground. This made calibration procedures a little weird. Also, I guess the null adjustment was way out of whack. Once I tweaked it a bit, I was able to the the meter back up and re-run the calibration with no problems.

While it seems to be properly calibrated and sounds great, I have some remaining anomalies that I'm still not sure about.
The input stage is highly susceptible to clipping when gain reduction is bypassed. When I'm compressing, it sounds great, then i bypass and it's clipping like crazy and I have to turn down the input knob. Is this normal?
Also, I was trying to find a good point to draw current for my meter LED and noticed that when measuring across R87 (between the out and com of the voltage regulator) I only get around 14V DC. I'm also measuring 15V at the input. I measure the power transformer putting out about 15V AC, did I wire this incorrectly? On the primary I have brown at hot, blue at cold, grey and violet tied together. On the secondary I have red and orange tied together at CT and yellow and black separately at the AC pads.

 

[Echo North]

The input stage is highly susceptible to clipping when gain reduction is bypassed. When I'm compressing, it sounds great, then i bypass and it's clipping like crazy and I have to turn down the input knob. Is this normal?

Well it's not a "bypass" technically it's a GR off which means the signal will get hot when you have it off.

Also, I was trying to find a good point to draw current for my meter LED and noticed that when measuring across R87 (between the out and com of the voltage regulator) I only get around 14V DC. I'm also measuring 15V at the input. I measure the power transformer putting out about 15V AC, did I wire this incorrectly? On the primary I have brown at hot, blue at cold, grey and violet tied together. On the secondary I have red and orange tied together at CT and yellow and black separately at the AC pads.

You're in the US?  If so, that's wrong.  You want the primary in parallel.

http://www.diyfactory.com/data/transformer_connections.gif

See lower left and refer to the side of your transformer.  Your secondary sounds right.

Mike

 

[jordan s]

Wow, you're fast. Well, I fixed the transformer wiring to have the primaries in parallel and recalibrated. I'm getting the voltages I would expect now. Still sounds awesome. I noticed the heat sink on Q6 gets kinda hot. Hot enough to where I wouldn't want to put my finger on there for more than a few seconds. Normal? Maybe an upgrade to the regular heat sink in the BOM is in store.
Just one more query and I promise you I'll shut up, start smashing some signal and sing your praises. My VU meter has an LED instead of a bulb. I know now that it's not really typical to put an LED lighted meter in here but I think at the time I purchased the kit, it was an option. Where should I pull current for the LED? I've read that the 30V rail across R87 is ok, should I use a 5V voltage regulator to bring it down? I guess that would require another heat sink. Ideas?

 

[Echo North]

Q6 will get hot.  I'll have to check one of my builds to see just how hot it normally gets.

For the LED there are a million ways to do it.  You could use a rectifier from the AC sec and a regulator set up as a constant current source or do something as simple as hook the LED directly to the AC sec with a limiting resistor and have your LEDs flashing very quickly for a cool retro vibe.

Personally I would just grab the DC from your +30 rail/test point and use a limiting resistor.  Here is a handy calculator:
http://www.hebeiltd.com.cn/?p=zz.led.resistor.calculator

Mike

 

[jordan s]

Looks like a 1K, 1Watt resistor is the way to go. I'll try it out. Hopefully I get this thing done and post some awesome pictures in here.

 

[Stagefright13]

Max temp for the 3053 transistor is 392 degrees Fahrenheit. Mine run about 150 degrees measured with an infrared thermometer. Which "feels" real hot to the touch but WELL within spec. So I am sure you are fine.

Congrats on your build! Have fun these compressors sound awesome!  ;D

John

 

[jordan s]

I finally did it. It's looking and sounding great. Again, thanks to Mike from Hair Ball Audio for the wonderful kit and forum help and thanks to mnats for the boards and documentation. I'm a very happy man right now. Enjoy the porn:

 

[Echo North]

Nice!  ;D

 

[beaversaber]

If your Q Bias is correct and your not seeing compression when you measure the output I would think you have a bad component somewhere in your GR section.

Check the transistor voltages in that section.  If your voltages are odd, check the resistor values, check for solder bridges, change out the transistors...

Geoff's page is for the J board, but it still applies:
http://www.axtsystems.com/index.php?option=com_content&view=article&id=57:1176lnproblems&catid=34:1176ln&Itemid=62

Mike

Got it! R41 was 270K instead of 270  8)

Unit works and sounds sweet