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

[Echo North]

From Glorious to..... :-[
I made it through the first 2 calibration steps. But the third one, yikes. It turned into a bit of a mess. I couldn't get the R44 trimmer to decrease the meter. I couldn't get it to do anything. It seemed dead. So, having bought a spare, I swapped it out. Nothing. I stuck my DMM on the original 5k and it read 3.6 or so, twisted the knob and it actually seemed to be working. Desolder again. (Yeah I know but that's anll hindsight, regrets, etc) And now I see that the uppermost lead pad and the wiper pad seem to have the trace covering scraped off. Is that an issue or non-issue, they are connected in the circuit, right? Also, yes there's more, the lowermost lead pad is partially lifting. Yes, here's where the yikes comes into play. What I'm thinking is, (with my excessive or misguided proactiveness) with these pads in a bit of a mutilated state, there's an alternate trimmer with its own pads to the left of this. Can I find that one at mouser or somewhere and pop it in there? I'm here asking for guidance because I know that my poking around is good for my bravado and desire to learn but at a possibly severe detriment to the success of this build.
So, war and peace later, is this a good idea and what is that alternate trimmer?

So q-bias when without a hitch, so that is good.  You were able to null adjust with R44 out of circuit and got 0V DC across TP10 and TP11, good.

Now for the next step make sure R44 is put BACK IN CIRCUIT with the jumper.

Are you saying the solder mask is scarped away?  That generally is not an issue.  Just follow the trace to the next pad and then test the two pads at either end of the exposed trace with your ohm meter to see you still have continuity (less than 1Ω resistance).  If so you're fine.  If not you need to fix it with a wire jumper.

Lifted pads generally happen with excessive heat/desolder.  It happens to all of us "tinkers" at some point.  I would stick with the trimmer you have and just solder a short peace of wire from the trimmer lead at the bad pad(s) to the pad the trace connects to.

Keep with it!  You'll get it.

Mike

 

[MountCyanide]

Excellent. Soldered a wire jumper in and R44 is now successfully moving the meter. Thank YOU.
Now, to figure out how to get 10dB of compression as I'm only getting 5 in this 3rd step. I'm so on the cusp....

 

[Echo North]

Excellent. Soldered a wire jumper in and R44 is now successfully moving the meter. Thank YOU.
Now, to figure out how to get 10dB of compression as I'm only getting 5 in this 3rd step. I'm so on the cusp....

When you say you're only getting 5dB of compression, do you mean on the meter or on the output XLR?

 

[MountCyanide]

Yes, at the XLR. Actually, I think the main crux of the situation during this GR Meter Adjustment step is that after I set up the output control for 0dB thru the output XLR with compression on, I can't get my input to crank out +10dB with compression off.  The other day when I posted and was seeing only 5dB reduction at the XLR I was fudging the output and input knobs around to get the 0dB and +10dB during their respective steps. In other words, not starting at the 24 mid rotations but being mindful that I would run out of gain. So, hmm, a problem with the preamp perhaps? BTW I just ran a drum track through it and all compression sounds like it's working.

Edit: I've found a troubleshoot post from February and I'll see if that helps me out.

 

[MountCyanide]

Ok so my final issue and thread contribution will only serve to reiterate the most important lesson in building. DON'T BE A BONEHEAD.
I checked all voltages again and they were indeed low. Naturally, that's why I couldn't get +10 with the input gain. But it wasn't for anything other than boneheadedness.
When I installed the replacement meter I didn't fasten the power wires firmly enough to the terminal. The center tap was unhooked. Duh.

Well it's all working now and sounding frickin badass.

Thanks Hairball. Time to record.

 

[Raul]

Hy, can you help me with a problem. on step 3 i cant get the 10 db drop off, when i turn the input in the gain goes up insted of down...Is ther maby problem whit gr?? i can only get -4 db of gr.. im using the rev a 05.12.10 pcb. also when i turn the realas pot to slow the gr meter does down without a signal put in. I checkt the voltages and seems fine, when i process audio it shows compresion and have compression :/ im confused. :/ 
+ when i move the realase pot the volume goes down when i move to slow settings.
EDIT: when a blow the meter and gain dops off, the 3053 and voltage regulator hawe heat sink and are not hot, i can touch whit fingers, it is sensitiv when i blow from the down side of the pcb, i checked the soldering and seems fine :/

EDIT 2: when the attack is bypass the release  is stil afecting the volume when it turned to slow :/

 

[Timh]

So I got my power section all wired up yesterday (very scantily), and I couldn't get a good reading so I went back to the wiring pages and I think my connections were switched on the IEC tabs. Big mistake, I know. I switched them and still got nothing. So today I went out and bought terminals (I had soldered wires straight to pcb before) and I bought a plastic terminal strip for the secondaries. I wired it up nice and pretty, and...still nothing. I'm actually getting a -0.08 and then it slowly drops to 0. Did I fry my transformer for having the connections switched the first time? I have no idea why it's not working.

 

[samguaiana]

Hi guys! I recently had a handy friend from far away build me two 1176 Rev As. For a while one was making noise whenever I hit my hand on my desk. I opened it and realized the audio transformer was barely hanging on by its screws, and after I tightened it, all my problems were solved.

Now in the last few days, my other one has been acting up. It sounds like slight rumbling occasionally coming from it. I checked the transformer and it's not the cause for it. What are some quick ways to diagnose this problem?

Thanks in advance, I love this forum and all the support!

Sam

 

[zylvia]

hello,

i am new here and building my  first Rev A  fet comp.

i think i am doing good on the wiring but got a stupid question ...

i found that i couldn't  fix  the pots on the front panel...

there are exposed angles on the pots as shown on the picture

plz help?

 

[Studio Mollan]

Hi guys.
I just thought I'd share my experiences.
I've used my pair of rev A a while now and they sound great. The stereo link from hairball makes them a super drum bus comp.
I did two mods to them that I can recommend:
1) Replace the attack pot with a larger value. I chose 250k with a push/pull to deactivate compression. This really adds to versatility as the dirty nature of this comp together with a super fast attack really whack transients. Works a lot better for drums now.
2) got rid of the 12 ratio and added a 2 so now it's 2-4-8-20. Just like a limited edition from universal audio. The mod is really easy and available here. Just search the forum.
/
Emil

 

[MountCyanide]

Zylvia,
Chop that piece off. (Carefully, of course.) You don't need it.

 

[zylvia]

got it, thanks !

and it doesn't come with enough double inductor cable,  can i use some normal mic cable instead?

thanks

Zylvia,
Chop that piece off. (Carefully, of course.) You don't need it.

 

[Harpo]

So I got my power section all wired up yesterday (very scantily), and I couldn't get a good reading so I went back to the wiring pages and I think my connections were switched on the IEC tabs. Big mistake, I know. I switched them and still got nothing. So today I went out and bought terminals (I had soldered wires straight to pcb before) and I bought a plastic terminal strip for the secondaries. I wired it up nice and pretty, and...still nothing. I'm actually getting a -0.08 and then it slowly drops to 0. Did I fry my transformer for having the connections switched the first time? I have no idea why it's not working.

You couldn't be more vague.
Maybe start with updating your profile with your location data or at least continent, so we could get an idea of your local AC mains voltages.
There will be a maybe blown or missing fuse in between your IEC connector, the units mains switch and your whatever_type_and_rating_it_might_be transformer. The fuses rating and fusing characteristic needed depends on your local AC mains voltage and VA rating of your transformer. When you say, you are measuring a "-0.08 and then it slowly drops to 0", you say exactly nothing without mentioning what dimension (volts, amperes, ohms, bananas, ..., AC or DC) you are measuring in respect to whatever reference (probably/maybe 0V reference voltage, could as well be a different circuit node) and where you measure.

 

[Timh]

So I got my power section all wired up yesterday (very scantily), and I couldn't get a good reading so I went back to the wiring pages and I think my connections were switched on the IEC tabs. Big mistake, I know. I switched them and still got nothing. So today I went out and bought terminals (I had soldered wires straight to pcb before) and I bought a plastic terminal strip for the secondaries. I wired it up nice and pretty, and...still nothing. I'm actually getting a -0.08 and then it slowly drops to 0. Did I fry my transformer for having the connections switched the first time? I have no idea why it's not working.

You couldn't be more vague.
Maybe start with updating your profile with your location data or at least continent, so we could get an idea of your local AC mains voltages.
There will be a maybe blown or missing fuse in between your IEC connector, the units mains switch and your whatever_type_and_rating_it_might_be transformer. The fuses rating and fusing characteristic needed depends on your local AC mains voltage and VA rating of your transformer. When you say, you are measuring a "-0.08 and then it slowly drops to 0", you say exactly nothing without mentioning what dimension (volts, amperes, ohms, bananas, ..., AC or DC) you are measuring in respect to whatever reference (probably/maybe 0V reference voltage, could as well be a different circuit node) and where you measure.

Sorry, Im in the US. Obviously it's DC since I'm measuring at the 30 and -10 points like the "instructions" say.

edit- Nevermind. It was the fuse. Thanks!

 

[Raul]

Hy, can you help me with a problem. on step 3 i cant get the 10 db drop off, when i turn the input in the gain goes up insted of down...Is ther maby problem whit gr?? i can only get -4 db of gr.. im using the rev a 05.12.10 pcb. also when i turn the realas pot to slow the gr meter does down without a signal put in. I checkt the voltages and seems fine, when i process audio it shows compresion and have compression :/ im confused. :/ 
+ when i move the realase pot the volume goes down when i move to slow settings.
EDIT: when a blow the meter and gain dops off, the 3053 and voltage regulator hawe heat sink and are not hot, i can touch whit fingers, it is sensitiv when i blow from the down side of the pcb, i checked the soldering and seems fine :/

EDIT 2: when the attack is bypass the release  is stil afecting the volume when it turned to slow :/

Solved the 10 db step, but the release problem is still mistery :/, when i turn the release to slow the gain dops down and stays forewer, Can anyone hel me please

 

[dbonin]

This sounds so much like a short to ground or a wiring issue or both. 

Hy, can you help me with a problem. on step 3 i cant get the 10 db drop off, when i turn the input in the gain goes up insted of down...Is ther maby problem whit gr?? i can only get -4 db of gr.. im using the rev a 05.12.10 pcb. also when i turn the realas pot to slow the gr meter does down without a signal put in. I checkt the voltages and seems fine, when i process audio it shows compresion and have compression :/ im confused. :/ 
+ when i move the realase pot the volume goes down when i move to slow settings.
EDIT: when a blow the meter and gain dops off, the 3053 and voltage regulator hawe heat sink and are not hot, i can touch whit fingers, it is sensitiv when i blow from the down side of the pcb, i checked the soldering and seems fine :/

EDIT 2: when the attack is bypass the release  is stil afecting the volume when it turned to slow :/

Solved the 10 db step, but the release problem is still mistery :/, when i turn the release to slow the gain dops down and stays forewer, Can anyone hel me please

 

[MLAudio]

I just built a Rev A (mnats V1.2.5 05.12.10 PCB). Q-Bias adjustment went well. Gain Reduction Meter Tracking Adjustment worked well. Got stumped at Discrete meter/null adjust (VDC across R74 constant at 0.46 V). I tried it several times but couldn't get the VDC to 0. Zeroed the meter and moved on.

I ensured that R44 was out of circuit. The voltage across R74 stays constant either way (R44 in or out). The compressor sounds fine at all ratios. All buttons in gives the famous "nuke" character. It seems to be working, but I am unsure about the null adjust. Any ideas?

Thanks in advance.

{UPDATE} I pulled Q13 and it was bad. Conducting between E and B both positive and negative. I will update this as soon as a get a new 2N3708 and replace it on the board.

{UPDATE} Replaced Q13. Same issue. Both R71 and R44 will move the needle on the VU, but the VDC across R74 still remains constant at 0.46 V. Double/Triple checked all component values in this section, solder joints, etc.

{UPDATE} [FIXED] Found a link after hours of searching: http://groupdiy.com/index.php?topic=29981.msg705541#msg705541 explaining to use TP10 and TP11, not R74. The poster summed up my frustrations: "This has been covered extensively in this thread and elsewhere". Lesson learned. Don't search for the obvious. You won't find it.

 

[Mr.Franky]

I don't have a D yet, but your "D" file sounds good; the sort of high freq loss I would expect from a lot of compression with just about any comp. Maybe someone who's build a D or owns a real on can comment on that.

I did notice something unique about the "A" file... a distinct asymmetrical distortion on the top half of the waveform. Zoom in on it in any wave editor (I used WaveLab) to see what I mean. I'm gonna say this is either happening in the signal amp or the line amp, either Q3, Q5, or Q6. Also make sure CR1 is the right way around, with the line (negative "cathode" side) towards the outside edge of the board. Something is causing the positive swing to be clipped or something. Could be a bad transistor, or maybe (someone tell me if this is wrong) a decoupling cap nearby not providing enough current and dragging the +30 rail down on loud notes. And I know it sounds redundant, but double check all of your voltages per the volts schematic. Check every gate, source, drain, base, collector, and emitter to be sure, because that would have been my first guess. Like an improperly biased transistor. Sort of like the way a fuzz pedal distorts half the waveform.

If all the voltages check out, fire up the scope and feed the 1176 a strong input. 1kHz sine is best, 1v or there abouts, but anything will do really. My old wavetek puts ou 1v and I know this can sometimes be too much, and I have to pad it down. Square wave can be useful in situations like this too, but here you should start with a sine wave since we're looking for asymmetrical distortion and it will show up best as an asymmetrical sine wave.

Inject the signal with the 1176 on and in/out at 12 o'clock or less (less on the input? maybe 9 o'clock, you'll adjust as you go, you'll know when it's too hot or too quiet, the scope will show you), or wherever typical operating ranges are, ground the scope probe's ground clip to PCB ground (any ground, just make sure it's ground!) and probe the input XLR pin 2 to see signal coming in. It should be clean and sinusoidal. Use this opportunity to set up and tweak your timebase and volts settings on your scope, focus, intensity, position, volts/div, timebase, trigger, ac couple, etc, bringing the picture into view until it's stable and clear.

Now follow the signal step by step, next moving to where the signal exits the input attenuator, then moving to the input transformer's output, and using the schematic to probe off componant legs (or underside of board, which ever is convenient) step by step tracing the path though the signal amp, output pot, line amp, and finally through the output transformer and output XLR.

At some point the waveform should become distorted, one half of it looking weaker or filtered looking. This should give you a better idea of which section is in question.

All comments and corrections welcome (i'm still pretty noobish here too )

Hey,

I just noticed your reply, sorry

A few days back, me and my tech friend opened up my Rev A again to look for the problem. We spent several hours checking the kit for faults by eye, checked the wiring, checked the voltages etc.. but still it looked (and sounded) very strange on the oscilloscope. We fed the input with a 1K sine wave. The sine was fine until it hit the input to the PCB, there it started to take weird, distorted shapes. So we suspected the input transformer would've been the issue. We took it out, decoupled it, checked it, put it back in correctly (not that it was wrong the first time) and checked again. Still, the scope showed the same,  distorted signal (wasn't even anything near a sine anymore). So we decided to open up my working revD kit and put its input transformer into the faulty RevA kit to check if the input xfo was really the problem. So we did that, but STILL we measured the distorted signal on the header going into the PCB. He decided to continue his search,  checking voltages etc.. but really, we couldn't find ANYTHING that was odd or out of tolerance. We didn't really check the resistors though, as they are unmeasurable in circuit.

He proposed to buy a second revA kit (which I was planning to buy soon anyway  ), populate the PCB very carefully and correct, put it in the faulty unit and see what it does. If it still has the strange distortion, at least we know we don't have to look at the PCB anymore. If it doesn't have the distortion, we'd have to check the PCB completely. Anyway, we'll find the problem no matter what.. it has to be somewhere.. One thing I can say is that I'm always really focused and patient when stuffing PCBs, I'd be surprised if I had put a resistor in the wrong place, but.. mistakes happen. I've built several other outboard pieces without any issue at all. Really not loving the feeling of this I'm confided we'll get the kit running and kicking some vocal's butt pretty soon! 


Enjoy your day,
Mr.Franky

EDIT: THE FIX FOR MY PROBLEM IS ON Reply #2263

 

[zylvia]

I found some weird response on my 5k trim pot on R44, tried to unsolder it out for a clearer test,  but then I see 2 of the 'legs hole' are somehow 'connected (please look at the picture..  I don't know how to describe....) , I'm not sure if I broke the board?

 

[Echo North]

Nope that is supposed to be connected.

That's how you make a variable resistor with a potentiometer.

Mike