[BUILD] 1176LN Rev D DIY

[gemini86]

College101, I know how frustrating this is. I had bugs in my first revj build that I couldn't figure out for months.

At this point I would start looking at all your solder points in the metering section. Make sure that each component lead is actually touching each solder pad, as in bent over and touching copper (or silver, maybe) and not just solder blobbed into the hole. It's little tiny things like that we often overlook.

 

[college101]

Hey Gemini86...

I went back through the section, and All of my solder joints on the main trace side of the board are legit...

I used a brand new Weller soldering station at 700 degree's to solder my joints...Everyone is nice and shiney! I was thinking of adding more solder to the mapping side of the board to just take that out of the equation..but I doubt that is the problem...

I just got my second multimeter and I am going to try and match all the 2N3078's..as crazy as that sounds (atleast get them all close in range)

Add the dip sockets and add a 5k trimpot to R75

Its pretty comical to me at this point...once you get to this point of the build, your GR meter will show compression, it just wont be showing you the correct amount of GR...it works of course, the point of the third calibration step is to actually SHOW you the -10 amount in the 20:1 ratio...

I also just bought 200 2N5088's..same ones that Purple Audio use in their 76 clone...but 2N5088's have a different pin out then the 2N3078's.... get to know your pins

 

[college101]

Hey guys...Whats a good range on the HFE of the transistors for Q12 and Q13?

And how close is close to being matched... +/- 5?

Im getting around 380 to 420 Hfe on my 2N3708'S!

 

[Sparqee]

Total noob here.  Hoping to elicit some advice from those that know.  I just finished assembling my first Hairball Rev D with the MNAT board.  I powered the unit on several times for short durations.  It passed audio and a bad ground hum.  I scraped off some of the case coating around the output XLR housing and that seemed to solve the hum issue.  But the 5th time that I powered the unit up the fuse blew.  Visual inspection of the fuse didn't show any obvious indication it was blown but my multimeter says that it is.  I tried a couple of "non-slow blow" .250Amp fuses and each one blew instantly upon hitting the power switch.  I tried a .315Amp fuse and this one lasted once but the second time I turned the unit on the fuse blew.  The next .315 fuse blew instantly.

Any advice on how I should troubleshoot this issue?  I don't want to damage any of the other components but what can I do if I can't power the unit up?  What's the largest fuse I can use and still be safe?

Thanks for any help.  I've been looking through old posts since yesterday and haven't found anything that I can relate to my problem.  If it's here already I apologize for asking the question again.  It may be that I don't understand people's explanation.

 

[imo]

i would either try powering up with a variac, if you have one, or if you don't making a plug that has a lightbulb in series. This will prevent you from popping fuse after fuse. The plans for this can either be found on the site or by googling.
Probably one of the power rails shorting to ground, which i would imagine would be a solder blob or miswiring
Ian

 

[Sparqee]

There is a variant of Murphy's Law in which no matter how hard you try to solve a problem you will not.... until you ask for help.  The moment you ask you immediately see the problem, this usually followed by slapping your forehead.

I had been checking all my solder points on the back of each board but I neglected to note that the wire from the meter board to pin 2 of the output jack had broken right at the surface of the board.  I was probably over enthusiastic when I was stripping it and scored the wire.  Because this wire is twisted together with the wire for pin 3 it was being held in place and it took careful scrutiny to notice that it was actually broken.

Long story short: I fixed the connection and no more fuse blowing.  Now, time for calibration!

- Sparqee

p.s. thanks for taking the time to respond Ian.

 

[college101]

I wish I had your luck...I keep going back through and none of my connections are broken...

I just installed R75 5K trimmer and dip socket on R44 PLUS I put dip sockets for Q12+13

Im going to see a Tech next week...if this doesnt work, then I have to wait...

 

[college101]

BAD NEWS..no luck

Added the dip sockets to Q12+13 as well as R75 null adjust and R44

My observations are as follows...

Once I connect R44 into the circuit to perform the third calibration procedure, AS SOON AS I turn compression "ON"- the meter drops to Zero by -20 in the Black!!! No amount adjustment does anything...

SO I experimented...I pulled R44 out of the socket and the needle jumps to -3...I measure the trim pot to 2K, 1.5K, 1k, 500 ohms, and 250 ohms,-----NOTHIN...as soon as I put it back into the dip socket...the needle drops to -20....

I matched Q12 and Q13 to 392 Hfe...and my new measurements are the exact same as the non matched pair

HELP guys

 

[Hyder]

Hey guys, I just finished my REV D. The unit fired up fine, Test points read 30v, and -10. Setting up for Q bias. Placed controls in correct positions, turn input up until VU reads +1. Try turning R59 trimmer and nothing! No change, no drop or increase on VU meter. Checked everything at least three times. The only thing I have found is one of the lugs on the attack pot. ( Alpha RV24A02F-10-15S1-BF4 potentiometer with the SPDT switch) Is loose. I mean it can move, all other lugs are tight. The unit passes audio and VU shows gain reduction and input level, and looks fairly accurate with no calibration yet. getting a pretty hot signal if I push the unit very much along with some distortion. Could this loose lug be a problem? 

Sorry for the long ass question:
Thanks,
Hyder

 

[imo]

Hyder,
DO you have a voltmeter? I would use that to see if you are having any reduction when turning the trimmer. If the meter is not properly calibrated you might not be seeing what you need. check your input AC voltage to make what it is and then strap it across your output. You should see some voltage reduction after a few turns. If the trimmer is installer correctly you should have it all the way counterclockwise before you do this. Also, if you are using multiturn trimmers it may take many turns before you start to see any affect at all
Are you sure your fet is properly installed? do you have the compression sidechain shorted to ground as per the calibration instructions?
Ian

 

[sr1200]

Just finished my Rev D build.... WOW man, i cant thank you enough.  This thing ROCKS the soxxx off my bass tracks, and is SOOOOO clean.  Virtually no noise at all.  (the original 1176 I used at our other studio, used to have this "hiss" to it, and believe me, im not missing it)  Vocals are being run thru tomorrow, again, thanks so much for this awesome board!!!

 

[Hyder]

Hyder,
DO you have a voltmeter? I would use that to see if you are having any reduction when turning the trimmer. If the meter is not properly calibrated you might not be seeing what you need. check your input AC voltage to make what it is and then strap it across your output. You should see some voltage reduction after a few turns. If the trimmer is installer correctly you should have it all the way counterclockwise before you do this. Also, if you are using multiturn trimmers it may take many turns before you start to see any affect at all
Are you sure your fet is properly installed? do you have the compression sidechain shorted to ground as per the calibration instructions?
Ian

Thanks, yes I am using a volt meter. As far as the trimmers go, I checked them before installing them, they read 2K max value, and track all the way down.

My REV D. is a hairball kit with push buttons, so my attack pot turns off GR.

The FET's came matched from hairball (I hope), but  they are installed correct from what I can tell from all the pictures I compared. 3 pins, across 3 holes and with the image on the board.

When you say " If the meter is not properly calibrated you might not be seeing what you need" do you mean the 1176 VU meter? And to use my voltmeter to check for the 1 db drop for the Q bias instead?
Thanks again,
Hyder

 

[college101]

I used the 76 vu meter to calibrate the q bias...

I set the trimmer to be all the way open....at 2K, and then adjusted after setting to +1

 

[college101]

From Page 7- Mnats post
Since then I have purchased a batch of 2N3708 transistors and each and every one of these meets the specification needed for this part of the circuit.

I have my own board 90% stuffed but am still awaiting transformers from Purple, so I have not had a chance to test them yet. But the fix shouldn't be too difficult - if you use 2N3708 transistors or have 2N3707s that meet the 250 hFE spec, simply cut the track for the additional Base pads on the bottom side of the board. If you are going with the 2N5088 I'm afraid the fix is a little more difficult as you will have to carve around half the pad on the top side to separate it from the ground plane.

So maybe this is where I am going wrong? Mnats...are we supposed to be using 2N3708's in the 2N5088 position? OR are we supposed to mod the top base pad and then use the 2N3708's?

Just need some clarification on this issue...

 

[imo]

you can use your 1176 meter to do this, but it is better to use an external meter, and I always use a voltmeter(set for AC of course) to do the calibrations. The VU meter will work most of the time, but if your meter trimmers are way off when you put them in, you might not be seeing the drop in voltage.
Also, just as you are measuring resistance, i would always check pinout of transistors before you put them in. it is good practice. you probably have the fets installed correctly, but it is a simple check to see this, and that way of thinking is the best way to solve the problem; methodically go through your build looking at the pieces from most obvious first. Make sure all the components are right, then make sure all of the wiring is right, and then check for soldering mistakes. As has been repeated hundreds of times before, this solves 95% of all new build problems.
Good luck
Ian

 

[college101]

I checked pinouts of all my transistors...PLUS the boards have screen prints showing the correct location of the install

My question is referring back to page 7 info from mnats, where I am led to believe that I may have to adjust the top bas pad of the board...

If not, I have some fresh 2N5088's which I can use in place...

 

[edanderson]

as you've figured out, you can use either 2n3708 or 2n5088 by matching the correct legs into the correct holes, noting the different pinouts of the 2n3708 and 2n5088.

the problem referenced on page 7 was an issue with only the original run of PCBs (from 2007) where there was an extra bit of copper that had to be removed for the PCBs to work correctly.  all the subsequent runs of PCBs had this fix implemented.  unless you bought your PCBs second hand, this should not be an issue.

ed

 

[college101]

RATS..this means I geuss I have to pull Q7 thru 10 and add the new 2N5088's

 

[Hyder]

you can use your 1176 meter to do this, but it is better to use an external meter, and I always use a voltmeter(set for AC of course) to do the calibrations. The VU meter will work most of the time, but if your meter trimmers are way off when you put them in, you might not be seeing the drop in voltage.
Also, just as you are measuring resistance, i would always check pinout of transistors before you put them in. it is good practice. you probably have the fets installed correctly, but it is a simple check to see this, and that way of thinking is the best way to solve the problem; methodically go through your build looking at the pieces from most obvious first. Make sure all the components are right, then make sure all of the wiring is right, and then check for soldering mistakes. As has been repeated hundreds of times before, this solves 95% of all new build problems.
Good luck
Ian

Thanks again, I have gone over the board with a fine tooth comb, and everything seems to be correct. The unit passes audio and is showing gain reduction as well as input on VU meter. when I set up for Q bias and bring up the input to get +1 on VU meter. the trimmer is wide open, and I can turn it all the way down with no drop on VU meter. unit sounds good as well???

How would I best use my voltmeter to do this first calibration? Where is the best place to hook up?

Still trying,
Hyder

 

[sr1200]

bad trimmer?  can you sub it out?