[BUILD] 1176LN Rev D DIY

[Lowfreq]

Ok chaps,

I've nearly finished my RevD, but having a weee problem thats baffling me a bit. :?

The problem is that when i turn up the output pot (say a little more than a third of the way up) i get some nasty oscillation going on. The whole unit goes into some crazy static................. :shock: It works and sounds great with a low ouput.

So i did some basic (note very basic :roll: ) signal tracing with one of those home jobby things from Mark Burnley on the diyfactory page http://www.diyfactory.com/data/mbsignaltracing.htm, and when I got up to the drain of Q1, I was getting some strange noises coming through my test speakers. I checked Q11 to compare and that had good signal coming out of its drain leg.

I replaced Q1, and checked all the surrounding components but still had the same issue.

I think I'm looking in the wrong place???? Does this sound more like an issue with my 3053??? Maybe I've damaged a leg when i was trying to squeeze the heatsink on....... I'll buy a new one tomorrow and try.....

The weird thing is that when i use my signal tracer the oscillation dissapears....................... :shock: and i can turn the output up.
Actually if you touch some of the pads on the board with a wire thats not even connected to anything it stops the oscillation.............but starts to pick up radio at high gain............ is it a capacitance thing??

The gain control section seems to work ok, and i can really get this thing to pump. The problem still happens in bypass mode, so I'm thinking all is good in the gain control area.

I have used 2N5088 instead of 2N3707 in the the signal amp, and I've swapped the legs around, so I'm not sure if that would be the problem.......

Anyway, as you can see, I'm confused, and I've been going over this board all day...........................................................
so please any suggestions would be great. Just guide me in the general direction, and I'll get to it. :green:

 

[wmb]

Thanks for all the great tips. I printed them out and added them to my collection of notes I've taken from the Rev D page and this thread.

I abbreviate all the time in my private emails but rather ironically can never figure out the ones others use in emails to me. This line included...
[quote author="Stagefright13"]... And GL is a great diy project!

[/quote]

Cheers, Wm

 

[Stagefright13]

GL = Good Luck

 

[mnats]

[quote author="Lowfreq"]
The problem is that when i turn up the output pot (say a little more than a third of the way up) i get some nasty oscillation going on. The whole unit goes into some crazy static................. :shock: It works and sounds great with a low ouput.[/quote]
I'm no good at this distance troubleshooting unlike Jakob and others but I'll try to help. It seems as though there might be feedback happening between the Signal Preamp and Signal Line Amp. You could confirm that the Line Amp is OK by disconnecting the output pot at pad 15 and feeding an unbalanced signal directly into the pot between the wire you removed and ground. Crank up the pot and see if you can get it all the way up without oscillation. If not, then you have isolated the problem to the Line Amp.

I seem to remember having a similar problem when I first hooked up the Cinemag output transformer to my prototype board. The problem seems to have been the lack of shielding (no cabinet) and/or poor grounding. Tell or show us how you've done your grounding. How is the main board grounded? Have you used shielded cable where the audio leaves/returns to the board?

 

[Lowfreq]

Thanks Mako,

Ok, I think I've located the issue. My wire (solid strand cat5) from star ground to the ground pad on the main board, had snapped close to the board (maybe from being moved around), but the outer wrapping was still intact.(Talk about decieving....... no wonder I couldn't see a fault :twisted: )
I've replaced the wire and the oscillation has vanished!! :green: :thumb: :thumb: :green:

[quote author="Mnats"]Tell or show us how you've done your grounding[/quote]Ok I'll try my best to describe things, in case there is a better way or I'm not quite doing it right.
I have one earth point near the IEC connected to the chassi, and from there I have star ground to pin 1 on the xlr input, pin 1 on the xlr output and to the ground pad on the main compressor board. And that's it.
Just like the picture. If I'm missing anything let me know.

While I'm here I'll double check to see if I'm wiring up my t-pad correctly too. After looking at the pruple schem, I did this............

[quote author="Mnats"]Have you used shielded cable where the audio leaves/returns to the board?[/quote] Yep, I kinda cross referenced to your G1176 instrusctions on sheilded cables and did the same wth the revD.

Anyway, I'm off to bed, and then tomorrow It's time to calibrate this sucker. :green: :thumb: :thumb: :green:

Thanks again for the help!!! :sam: :sam:

 

[gevermil]

How wild , just having the same problem :wink:
im working to find the cause
heres some pics

http://i133.photobucket.com/albums/q47/gevermil/667.jpg
http://i133.photobucket.com/albums/q47/gevermil/IMGA0534.jpg
http://i133.photobucket.com/albums/q47/gevermil/IMGA0535.jpg

 

[kazper]

My wire (solid strand cat5)

You would be allot better off using some 24-28 gauge multi-stranded wire. for this.

 

[JdJ]

Hey Lowfreq-

What T pad are you using? I'm wondering what the proper way to wire it is myself.

Cheers,

Josh

 

[kazper]

JdJ which one do you have?

I have 2 types of the NOS ones that have been floating around. I actually have 4-600 T-pads with 2 Omeg's on the way.

I'll try and remember my photo web hosting and figure this out and post some pics of how to hook up the ones I have access to.

 

[Lowfreq]

Josh, I'm using the PEC from the group buy organised by ap123 a while back.

http://www.groupdiy.com/index.php?topic=21817&highlight=

 

[mnats]

[quote author="Lowfreq"]Ok I'll try my best to describe things, in case there is a better way or I'm not quite doing it right.
I have one earth point near the IEC connected to the chassi, and from there I have star ground to pin 1 on the xlr input, pin 1 on the xlr output and to the ground pad on the main compressor board. And that's it.
Just like the picture. If I'm missing anything let me know.[/quote]
This page says it better than I ever could:

http://rane.com/note151.html

[quote author="Lowfreq"]While I'm here I'll double check to see if I'm wiring up my t-pad correctly too. After looking at the pruple schem, I did this............

[/quote]

Look at the schematic again. Notice there is a common wire between the source and load side of the bridged T attenuator? See that the two resistors connect to one end of the pot, not the wiper? Fix it and show us how you did it.

 

[JdJ]

I came across this the other day-

[quote author="edanderson"]1. if that meter is a real VU meter, you should be able to use it without any additional circuitry. try hooking the two terminals up to any line level audio source, and see if the meter moves as you would expect. if so, it will probably work, and you can connect it as shown in the MC76 schematic. if it doesn't work, then yes, you may need to make an external rectifier, using some diodes and a piece of perf board. you don't NEED a meter for the compressor to work, however it is useful sometimes.

2. yes, input xlr to t-pad to o-12 pins 1 and 5. if you use the attenuator we supply (the three deck black clarostat modpot), then use this diagram i stole from newyorkdave (thanks!):

connect the input xlr hot (pin 2) to the "IN" and input xlr cold (pin 3) to "COM." connect the "OUT" to pin 1 of the O-12 and the "COM" to pin 5 of the O-12. the input xlr ground (pin 1) should connect to the cable shield on the way to the attenuator. connect it to the shield of the cable going from the attenuator to the O-12, and dont connect the other end of that shield. connect the xlr ground (pin 1) to the chassis ground.

ed[/quote]

I'm using the 3 deck T's from Purple.

-Josh

 

[nerd]

I've got my PEC wired like this...

I have not tested it though.

 

[mnats]

I had faith Lowfreq could figure it out for himself. Oh well, back to painting by numbers...

 

[gevermil]

Hey Mnat -
what voltages am I suppose to see off of the otuput transformer
My 2N3053 is smoking hot .
:roll:

 

[mnats]

[quote author="gevermil"]Hey Mnat -
what voltages am I suppose to see off of the otuput transformer
My 2N3053 is smoking hot .
:roll:[/quote]
"Off" the output transformer? Do you mean from the output? Zero DC volts.

If you look at the schematic there's 30 volts across the black wire (on the Cinemag) and ground and a small amount of DC across the White/Black and White/Red leads. I'm not sure if this will help you if your transistor is smoking though.

What is the actual temperature of your transistor while running? What sort of heat sink are you using? We discussed the operating temperature of the '3053 just on the previous page...

 

[Stagefright13]

3053 transistor rated to 200 C

50 C is very hot bath water

100 C is boiling water.

As long as ya got a heat sink on it you are prolly ok.

 

[gevermil]

Thanks mnat , well - I do see the voltages you speak of . My output pot jumps to distortion very quickly so Im trying to find the source of that .
I just mentioned the transistor because I thought it was odd that I couldnt touch it it was so hot .

 

[gevermil]

thanks stage , Its just a matter af figuring out the crazy output level .
As usual with me its something stupid .

 

[nerd]

Regarding JdJ's post in the thread "Yawn...another 1176 (pics)"

I was curious about that too. I am trying to get 2 D's into Purusha's dual 1176 case and I'm thinking about stacking the boards. I suppose I'll just wire everything up and try moving around a bit to see what'll work. My case is 2 high, but a bit shallower than Mako's.

This is how I finally decided to do the two boards in a purusha case. It doesn't look that tight in the picture, but I spent hours trying to come up with a layout. Will noise be a problem? I don't know. I still have to find the time to finish wiring the thing up. My thought was to put the input transformers as far away from the power transformer as possible.

JDJ: How are you hooking up the bypass? I put a resistor in the R-OPT1 spot and hooked the switch up to where the wiper would be. I figured that since this is for threshold adjustment, I would basically be swithing the threshold in and out (so high that it doesn't do anything). I don't know if this thinking was correct.

Anyone: Also, and this is strange, one of the LEDs on my mnats little psu is blinking, but there does not appear to be any change in voltage on my meter. Any thoughts? If you exceed the operating range for an LED, but not enough to blow it up, would it do this?