[BUILD] 1176LN Rev D DIY

[LHS]

Another chassis ground question:
I think I must've bought my kit before the screws for the chassis ground were included. Could someone provide a part number for that screw/washer as well?

 

[Echo North]

Another chassis ground question:
I think I must've bought my kit before the screws for the chassis ground were included. Could someone provide a part number for that screw/washer as well?

I include an 8-32 screw and nut now.

 

[mitsos]

I've had some issues with a dual/stereo unit I built ages ago... comes and goes, I've checked it multiple times, and my next step is to remove the stereolink boards to see if they are responsible.. In converting it to dual mono only, after removing the stereo link boards, is it only a matter of reconnecting the output pot wire to the ratio board?

or is there anything else I need to rewire? It's been a while since I've been in this thing and I'm a bit rusty on the wiring..

thanks!

Yes pad 15.

Are you using a switch?  In "non-link" mode it should be bypassed.

Thanks for the confirmation... working fine now.. I did have a toggle switch for the link, and it worked fine, but something was not right about the unit.  It actually worked fine at my place, but I had it at my friend's for a few months and it would act up there.  Once in a while the VU would go from 0 to about -3 and sort of fluctuate back forth a bit (like between -2.5 and -3.5 or so). This was with the meter in GR (of course) with or without signal, sort of like -3 was the new 0.  In the end, I think it was compressing, I'm waiting for my friend to send me a vocal he ran through this unit where it happened in the middle of it.

Anyway, I can't say for sure that it was the link circuit, but with so many wires in this box (2 channels in 2U), one less thing will at least make it easier to troubleshoot if it happens again.  So far though it's been on for a couple of hours and needles are set at 0. Fingers crossed.

thanks!

 

[Echo North]

Could it be oscillation?

See DMP's grounding post here:
http://www.groupdiy.com/index.php?topic=35656.msg481187#msg481187

 

[Sillen]

Hi
I now replaced my power transformer and the vu meter lit up and seemed to work in the different modes (not calibrated yet). One problem appeared though, capacitor c25 kind of got way too hot for some reason and a little smoke came from it. Any clue why this happened? Is it a grounding problem you think?

All the best
Sillen

 

[jplebre]

is the ground cable from C25 to chassis hooked up to the correct lug?
Diodes the right way around?
does C25 meet the minimum voltage requirement?

first things that come to mind

cheers

 

[Harpo]

I now replaced my power transformer and the vu meter lit up and seemed to work in the different modes (not calibrated yet). One problem appeared though, capacitor c25 kind of got way too hot for some reason and a little smoke came from it. Any clue why this happened? Is it a grounding problem you think?

Not grounding related.
The (once was a) 2200uF cap fitted with polarity reversed and/or insufficient caps voltage rating?
One of the 1A rated rectifying diodes CR7,8,9,10 might be blown as well from excessive current drawn by the blown cap.

 

[mitsos]

Could it be oscillation?

See DMP's grounding post here:
http://www.groupdiy.com/index.php?topic=35656.msg481187#msg481187

I don't think so. Well, could be anything I guess, but I used shielded cable as necessary for the link circuit, and, unlike DMP's problem, mine was unrelated to the output pot's position.  I started to think it was his mains because he did have some AC related noise way down there, or his UPS's because I'm not convinced they are true sine wave output. But most of his other gear is OK (has had some problems recently with some gear, but I'm not sure it's related).

I recently installed a balanced power trafo in my place and the 76 is running just fine on that right now (last night it was on regular mains, with some sort of shabby ground wiring, but it still was working fine).

Anyway, I'm not sure the issue is solved, because I was never able to replicate it here, only at my friend's studio.  I'm going to try to get to his place on friday and try it again. That will be the true test.

thanks for the tips!

 

[friesdan]

Thank you Mike and mnats. Stellar Job! Thank you so much for allowing me this awesome project and unit.
-Dan

 

[LHS]

Hey everyone, for some reason I can't get the my safety ground resistance reading below around 1.8Ω-2.4Ω.

I've checked that my chasis screws are secure and sanded and re-sanded the powder off where the lug meets the chasis. Scratching my head trying to figure out what's going on. Any ideas? Would I get a higher reading since I've installed some of the other components like the toroidal xfmr, meter, xlrs etc?

 

[Echo North]

Hey everyone, for some reason I can't get the my safety ground resistance reading below around 1.8Ω-2.4Ω.

I've checked that my chasis screws are secure and sanded and re-sanded the powder off where the lug meets the chasis. Scratching my head trying to figure out what's going on. Any ideas? Would I get a higher reading since I've installed some of the other components like the toroidal xfmr, meter, xlrs etc?

Could be a lot of things.  Solder joint quality, type of solder, flux residue, wire type, your DMM could be a little out of calibration, your leads.  What is the Ω reading if you just connect your leads directly together?

Mike

 

[LHS]

I'm getting 1.8Ω when I check just the leads directly together.

I'm using this hookup wire that I got from frys http://www.frys.com/product/1615731?site=sr:SEARCH:MAIN_RSLT_PG . Is that cheap wire bad news or is my DMM suspect (it's a fluke 87V)?

 

[sr1200]

so youre getting 1.8 ohms where you should be getting 0 and 1.8 ohms where you should be getting 0...  sounds right to me then. lol
maybe change the battery in the DMM?

 

[Echo North]

Ya, you're just slightly out of calibration or your leads have a little more R than usual.

Keep in mind there is always a little R in everything.

I think you're safe to move forward.

Mike

 

[mitsos]

I took the 76 to my friend's studio again, worked perfectly, sounded great... Unfortunately, the fluctuating VU problem came back after the unit was on for a few hours. I had already left but he did say that when he turned it off and on it came back to normal and the level jumped in one channel (he's not sure about the other channel). 

Again, when the problem happens, the VU fluctuates around -3dB with no signal input. 

My friend's comment about the level jumping when the VU was back to normal.... I'm thinking the VUs are working fine, and something is causing the unit to go into compression.  Can anyone think of what could cause this?  I have't been able to take voltage measurements because I didn't have a DMM with me when I saw it doing this.

I have visually checked component values multiple times, and all resistors were matched between the two channels while building, I may have been crazy and matched the caps as well, but I don't remember. In use, the two units follow each other perfectly. Not that that means anything here, just throwing it out there that I was fairly meticulous with the build.

Any ideas are welcome! thanks!

 

[Harpo]

You cleaned the pcb at the FETs from (hydroscopic) rosin ?

 

[mitsos]

Thanks harpo, I've gone over them a few times with isopropyl and small brushes. Can't hurt to try again. I'll probably get it back in a few days. 

 

[Echo North]

Ya the High Z parts of the circuit, like at the FET gate are super sensitive to flux.  Also get any wiring as far away as possible.

Mike

 

[Sillen]

Hi
Having some troubles to calibrate the q-bias adjustment here. The trimmer did  not work when i tried to get a -1 db allthough i turned it 20+ times. So I thought the trimmer was broken and de-soldered it, turned out it wasn't broken though. So maybe I mounted it wrong? It should just be mounted in a straight line right? Like on the picture from Hairball's stuff your pcb section. Does the position of the screw matter? I noticed mnats had it the opposite way from how it was shown in the "stuff your pcb sectioN". If it was mounted correct as well what do you think could be the problem?

Kind regards
Sillen

 

[jplebre]

the orientation (left to right/right to left) doesn't really matter.
What matters is that you don't use the extra wiper points. THese are the ones that go vertically through the round drawing. if you test them with a DMM, you'll see they check for continuity. Don't use these.