[BUILD] 1176LN Rev D DIY

[TijuanaKez]

Hey there peoples.
So I got jack of the meter bulbs always blowing on my (old version) FET RACK and decided to fit some yellow LEDs and a 5W resistor to the 30VAC out of the transformer.
As I was testing adding more leds to even out the light, wire slipped and found itself falling precisely onto the only tiny piece of exposed terminal on the mains plug that wasn't completely covered by heat shrink.
Sparks flew, circuit breaker flipped, fuse in the mains plug on the unit blew.
As one might expect, now it's not happy. Meter reacts to turning the knobs with nothing plugged in and only faint signs of audio at the output.
All voltages seem within range as per the schematic (with voltages added)
What's my next best bet?
Shotgun replace all the transistors except the matched pair and hope for the best?
Or is there something else I should try first?

 

[sjdowo]

hi, does anyone have a full part number for the GR meter function switch? need a replacement. rotary 3-position switch.

 

[zzzzz]

hi, does anyone have a full part number for the GR meter function switch? need a replacement. rotary 3-position switch.

Alpha SR2612F-0304-18R0B-D8-N fits

 

[TijuanaKez]

...coming back to this and reaching out to anyone with a bit of intuition here...
1176 RevD mnats 2.2:
- Passes clean audio with R23 (output) in the first %5 of travel, then cuts out into hissy distortion after that eventually nothing but DC offset.
Compression works as expected if R23 is within this %5
- Input knob can actually drive the level fairly high at the output still with compression off, so it's the position of R23 matters, not the level going into line amp.
- Looking for dry solders and warm components probing with my finger, I noticed there's a test point up above C10. Contacting this with a solid finger press and creating some good old body capacitance earthing fixes the problem entirely.
- It's not likely a dry solder because pushing around on the pcb with no electrical contact does nothing.

Can anyone care to have a stab at such a riddle? Should I just replace all the transistors in the lineamp and go from there?
thanks in advance!

 

[TijuanaKez]

...coming back to this and reaching out to anyone with a bit of intuition here...
1176 RevD mnats 2.2:
- Passes clean audio with R23 (output) in the first %5 of travel, then cuts out into hissy distortion after that eventually nothing but DC offset.
Compression works as expected if R23 is within this %5
- Input knob can actually drive the level fairly high at the output still with compression off, so it's the position of R23 matters, not the level going into line amp.
- Looking for dry solders and warm components probing with my finger, I noticed there's a test point up above C10. Contacting this with a solid finger press and creating some good old body capacitance earthing fixes the problem entirely.
- It's not likely a dry solder because pushing around on the pcb with no electrical contact does nothing.

Can anyone care to have a stab at such a riddle? Should I just replace all the transistors in the lineamp and go from there?
thanks in advance!

Okay well don't I feel silly now. Scraping away the paint at the points where the XLR connectors earth to the chassis turns out to be quite important!

 

[leo-666]

According to schematics Mnats Rev A has Chassis Ground and Second Ground.
Where second ground is connected to a chassis ground ?
Or they are completely isolated ?

 

[TijuanaKez]

According to schematics Mnats Rev A has Chassis Ground and Second Ground.
Where second ground is connected to a chassis ground ?
Or they are completely isolated ?

View attachment 140933

If it's same as REV D, it's a wire from the -ve leg of that cap to somewhere close by on the chassis.

 

[leo-666]

I already found it.

 

[maxwall]

Anyone try running a Antek-0230 25VA ( 2x30v secondaries in parallel ) power transformer with their 1176 Rev A-D,F build , would like to hear your results ? Dont have the time to filter thru numerous posts, searches not turning up anything meaningful , like dead links or current material parts lists. This transformer is reasonably priced. Seems a popular one is 30va with 2x25 secondaries , but not much is the way of low cost alternatives like this Antek.

 

[zzzzz]

Anyone try running a Antek-0230 25VA ( 2x30v secondaries in parallel ) power transformer with their 1176 Rev A-D,F build , would like to hear your results ? Dont have the time to filter thru numerous posts, searches not turning up anything meaningful , like dead links or current material parts lists. This transformer is reasonably priced. Seems a popular one is 30va with 2x25 secondaries , but not much is the way of low cost alternatives like this Antek.

View attachment 146217

That antek will prob give you around 40vdc ish rectified if using 1N4003 but the 7824 reg has a max Vin of 40vdc I think. Might be pushing your luck with the on board PSU scheme. Why not use the AN-0225?

 

[maxwall]

Thanks, looks about right , the high voltage will run that regulator too hot for practical use. Was trying to find a design calculator to determine the transformer requirement with voltage and current rating , but could not locate one that was easy to use. The typical rule 30v * 1.414 is probably the best guess however I could not pin down load requirement , guessing 250ma draw from the 1176 circuit is close.

Was thinking the rectified 40v ( 30v * 1.414 ) would get pulled down by the circuit load a few volts so the 7824 would be in the voltage margin for regulation, too close to the upper end as suggested and the device on the small heatsink runs hot or goes into thermal shutdown. Any problem running the heatsink remote on the chassis with wires for better heat dissipation. May have seen this before, but not sure if the 7824 device is required to be next to power supply on pcb. May be better off with the 50vct in the long run.