[BUILD] 1176LN Rev D DIY

[sage]

could i t be that your attack pot is wired in reverse?

 

[RichardM]

I have gone through the wiring info again and everything is as it should be. I have gone over it several times and the alpha pot looks exactly like it does in the wiring diagram. The wiring to the pot also looks correct. Could there be a problem somewhere else that would cause this problem or does it have to be in this pot wiring? I also went back and tested the first revd  I built that I couldn't calibrate and it does the same thing but it also looks correct. Any ideas?


Rich

 

[jplebre]

seems it's really as Sage said. The common and the ground are reversed at some point.
The switch literally jumps the GR circuit to ground (pad22).

That will ground pad 22.

Pad 22 on main board to single pad on the back of the attack pot
Ground next to pad 22 on main board to lug B - top pad on the back of the attack pot (the top one on the side that has 2 pads)
Top pad (B Lug) to connection 2 on the Hairball ratio board. This to ensure grounding scheme throughout
Bottom pad (Lug A) to connection 4 on the hairball ratio board

best of luck
I would bet it's there. Check the lugs for continuity if you are still unsure how to proceed to understand the off (GR circuit grounded) and on (pad 22 on main board to pad 4 on ratio board) positions

 

[RichardM]

Thanks for you help. This does make sense to me that the attack pot or something related to it has to be wired backwards for it not to switch off and begin the qbias procedure but I have gone through it so many times and everything looks exactly as it does in the wiring guide. I am also using the wiring colours as used in the wiring guide to avoid confusion but still can't find a wiring mistake with the attack pot. Could something anywhere else in the unit cause this same problem? Would there be a simple way to diagnose this?Thanks


Rich

 

[zekester]

Just figured my issue to be as mentioned earlier in the thread, funky power transformer. It seems to be sensitive to a little movement. I read through and found a few people with issues with these, is there a high failure rate on the avel lindbergs?

Shouldn't be.  Maybe 3% at the most.

I put in an order for a new one, so that should get me back up and running again. Hopefully, I'll be in the 97% on this one 

If the new one works fine (confirming the first one you got was bad), let me know and I'll refund your second order.

Will do. I appreciate it.

Forgot to get back on this in case anyone else was searching for a similar issue on here. The transformer swap took care of it. I was able to play with the old transformer, putting pressure on it in one area was causing a short. Everything has been working great for the past month since I swapped it out.

 

[Zackster]

Hi Again,

I just can't seem to get any change from moving the q bias trim pot. I have tested some of the voltages and the 30v at the side of r79 tests exactly as it should but many of the others I think are too high. G at q11 = -1.8 vdc    D at Q11=18.3 vdc and S at Q11= -2.3 vdc.  I am really unsure what to do because I thought that the voltages in this region would not read as they should until the unit is calibrated properly. The o adjust trimmer that is accessed in the front works as it should and I am sure that I am following the calibration steps properly. Do you have any suggestions? My only other concern at the moment is that the output knob raises the level as it should when being turned up but as it nears the max, it makes a bit of a clunk and enters a hiss zone. Maybe this has to do with the calibration, but I am unsure. Thanks for all your help!

Rich

I am having the (almost) exact same problem on the second channel of my build, although bypassing gain reduction does nothing for me. Adjusting r59 either way for  5 minutes shows no difference. The voltage on Q12 is

GR Off: D=17.7 V
GR On: D=9.5 V
VU:  D= 17.7 V
Q11 is also off (don't exactly remember the values), but all other transistors have correct voltages and +30V and -10V are as they should. On the succesfully calibrated first channel the voltage of Q12 is around D=9.5 V  for all switch positions.

The voltage behaviour in channel 2 is also quite random. It shifts when adjusting the other nearby trimpots, but resets when power is turned off and turned back on. Occasionally the voltage decreases on its own to about 12 volts (once even to 4V) when left on for a few minutes, but this is not constant behaviour. I would therefore imagine that Q11, Q12 and/or R59 is faulty. I can not think of an easy way to test these components in cirquit and would appreciate if someone with superior knowledge could share some advice. Otherwise I quess I will get replacement parts for all these components and hope I don't brake any traces.

Zack

 

[jplebre]

Zackster

Pull one leg out of the resistor you want to test, lift it slightly, and use a multimeter (dmm or ohmeter). A member of this forum usually works at our place and he cuts the legs from the top of the PCB to test the components out and solders them back this way for quick diagnostic and replacements (eg. the resistor-fuse types used in SSL's)

For Q12 TBH I use one of the atlas peaks recommended in the forum. Would imply pulling the 2n out completely.

For Q11 have no idea did not investigate into J-Fet

However, Q12 and Q13 should be pretty similar in voltages. Have you done the null voltage and where's your jumper?
That could be an easy indicator if Q12 is fine or not

 

[Zackster]

jplebre,

Thanks for the quick reply.  R59 is the q-bias trimpot and it is fitted flat on the PCB, so to my understanding pulling a leg is not an option. I did do the null adjustment, but have since then tinkered with all the trimpots in an attempt to understand the surrounding circuit.

If you mean the jumper between R44 and node with Q13 and R69, yes it was fitted. Could you explain how this diagnoses Q12, as I am not that good at analyzing circuits?

Happy New Year!

Zack

 

[RichardM]

Hi Guys,

I have gone through the wiring of the attack pot/release pot many times on both of my rev ds and both are wired and look exactly like the wiring page. Just wondering if there could be any other cause for the function reversal? (The bias trim pots work when the attack knob is on but don't work at all when off). Has anyone else experienced this problem and not been able to trace it to the pot wiring? Thanks!

Rich

 

[sage]

Hey Richard

is the pot the one provided in the BOM or by the kit ?

 

[RichardM]

Hi,

The Alpha Pot came with the kit(mouser cart link). I took a magnifying glass to it and the 2B4 part number on my Alpha pot is different than the one on the wiring page. I can't clearly make out what it is on the wiring page but it looks slightly different. Could the A and B be opposite on this pot?

Rich

 

[sage]

it would be safe to look at the specs for this part... easily on line nowadays you can find the info on each component.

also as DIYer I would try wiring opposite and if it works... it works! 

 

[RichardM]

HI Guys,

Thanks again all for your help. I am trying to expose a problem I am having with the Attack pot. I have tried a few things and what I have found is that removing the shield from lug b of attack pot (this goes to ground pad beside pad 22) allows me to use the qbias function when the attack knob is in the off position. The qbias also functions when the attack pot is in the on position which it shouldn't. My first goal was to get the q bias to work in the attack knob's off position which I believe is correct. I have gone through the wiring several times and cannot find a problem with the attack pot wiring. Everything appears to be working as it should but now the unit has slightly decreased gain when the ground is off of lug b. I am not trying to "wire it my own way" but I am hoping that a little more info might help expose the real problem. Any ideas?

Thanks

Rich

 

[RichardM]

Hi Guys,

Thanks for all of your help during this first build! I thought I would pass along my discovery/mistake for anyone else who encounters the same issue. I was having so much trouble setting the q bias and I thought that there was a problem with the attack pot which was prohibiting the q bias adjustment. I couldn't find a problem with the attack pot wiring, because there wasn't a problem. I didn't understand that the qbias will appear like it isn't working at all if it is too many turns away from it's operating area. This is something that I really didn't pick up on in the calibration video and I was concerned about damaging the pot by turning it so many times.  Once it is in range, half a turn makes a huge difference , but it might take 5 or more full turns to get it to that point. These things sound fantastic!

Rich

 

[sage]

Rich I am glad you sorted it out 'cause it can get frustrating not to get to the solution.... and indeed these pots I think they have a 25 turn range !!! So it can be tricky...
I also had to go online and pull the specs as I kept turning and nothing happened... that's when i discovered how many turns they could take!

I just did a mix and used the unit on the kick and oh boy it's phat !!!

Since the wiring is the same for REV A I found a good idea to do one after the other if you have time and budget...

 

[thesystem]

Hi guys, I just finished my 2nd 1176 rev D. The first one works perfectly, the second one has a problem. After I finished the wiring I turned on the 1176 to see if it worked. There is power but I get a very high pitched, squeaky sound. This is only when I turn up the output pot. When turned up the needle moves upwards, starts shaking at it's highest point and then falls back and the squeaking stops. When I leave the pot down for a couple of seconds and turn it up again, there is the high frequency sound again.

What could be the problem? Bad cap? Bad output pot? How can I find out?

Thanks for the help!

EDIT: the sound seems to occur in equal intervals when I turn up the output pot. The high pitched sound sounds for 1 second, then it's silent for a second or 5 and then it happens again. I can't seem to find out very well what part is making the sound since it's such a short sound.

 

[sr1200]

ossilation?

 

[thesystem]

ossilation?

Hi sr1200, what do you mean with oscillation?

 

[sr1200]

from what i remember if the unit isnt grounded properly it can go into ossilation.  Someone with more knowledge than me should comment on it, as I dont really understand WHY it exactly happens.

 

[jplebre]

refer to mnats wiring pages http://mnats.net/1176_reva-d_hairball_wiring_power.html and doublecheck your wiring.
Make sure you use shielded cable where pointed out and to cut the shields where indicated (eg. connect the shield only on one side of the cable, snip on the other).

If you have a new rev PCB and follow this to the letter, you should be completely hum free and oscillation free.

Also, check for continuity on your enclosure, with the DMM on the earth lug of the IEC. If a panel does not have continuity, try scrapping the pain on the screw lugs

let us know if this helps