[BUILD] 1176LN Rev D DIY

[Che_Guitarra]

The switch has continuity, and the on/off function works as it should.  I have a feeling i've perhaps received the wrong fuses - fast blows rather than slow blows.  No matter either way - they're all gone now and I need to get some more.

I spotted that fuse rating on the Mnats guide, but consensus seems to be that most are using 250mA fuses... split that in half for 240V operation = 125mA.  I can't even source 63mA fuses locally - 100mA is as low as I can find.


When the shops open i'll go get some more, and if a different batch doesn't solve the problem I guess i'll have to start looking at the PSU.

 

[Harpo]

The switch has continuity, and the on/off function works as it should.  I have a feeling i've perhaps received the wrong fuses - fast blows rather than slow blows.  No matter either way - they're all gone now and I need to get some more.

I spotted that fuse rating on the Mnats guide, but consensus seems to be that most are using 250mA fuses... split that in half for 240V operation = 125mA.  I can't even source 63mA fuses locally - 100mA is as low as I can find.


When the shops open i'll go get some more, and if a different batch doesn't solve the problem I guess i'll have to start looking at the PSU.

Fuse rating required is dependant on your transformers VA rating and local AC mains voltage, maybe 240V AC in your case (measure this AC voltage at your wall outlet. AC mains isn't a constant and might vary +/-10% depending on location and time of day).
You might have a 30VA toroid with maybe 92% efficiency due to core and copper losses. Your transformers efficiency might be listed on your transformers datasheet and will be in range of 85%-95% for assumed VA rating. Substitute the '30' in following formula with your transformers VA rating and the '92' with your efficiency number. If not listed, assume 90 for 30VA, lower% for less VA, a little more for higher VA.
Fuse rating required would be 30/240*(1/(1-2*(1-92/100))) giving 0.149A. Next avail standard fuse rating will be 160mA for this example value.
For your toroids higher inrush current you want a slow blow fusing characteristic, so your fuse will have the letter 'T' for time lag next to its current rating stamped on.

 

[jplebre]

The switch has continuity, and the on/off function works as it should.  I have a feeling i've perhaps received the wrong fuses - fast blows rather than slow blows.  No matter either way - they're all gone now and I need to get some more.

I spotted that fuse rating on the Mnats guide, but consensus seems to be that most are using 250mA fuses... split that in half for 240V operation = 125mA.  I can't even source 63mA fuses locally - 100mA is as low as I can find.


When the shops open i'll go get some more, and if a different batch doesn't solve the problem I guess i'll have to start looking at the PSU.

Fuse rating required is dependant on your transformers VA rating and local AC mains voltage, maybe 240V AC in your case (measure this AC voltage at your wall outlet. AC mains isn't a constant and might vary +/-10% depending on location and time of day).
You might have a 30VA toroid with maybe 92% efficiency due to core and copper losses. Your transformers efficiency might be listed on your transformers datasheet and will be in range of 85%-95% for assumed VA rating. Substitute the '30' in following formula with your transformers VA rating and the '92' with your efficiency number. If not listed, assume 90 for 30VA, lower% for less VA, a little more for higher VA.
Fuse rating required would be 30/240*(1/(1-2*(1-92/100))) giving 0.149A. Next avail standard fuse rating will be 160mA for this example value.
For your toroids higher inrush current you want a slow blow fusing characteristic, so your fuse will have the letter 'T' for time lag next to its current rating stamped on.

This informatino is GOLD! thank you Harpo

 

[wlambert]

This is a rather simple question... didn't find anything in my search efforts...

I am wanting to put an on/off power status LED above the meter on my blue stripe but want to clarify some details first.  I notice in the picture of mnats completed 1176 on his wiring page there is indeed a status LED powered from the 30VAC secondary taps at the power connecting block and no pad resistor.  From my research at Mouser there are no lamps that are rated at 30 volts exactly.  The closest are at around 28V.  My question is, if I use a lamp rated at 28V with my power at around 30V, does this mean my lamp will burn brighter (and potentially not as long over time) since I am "overpowering" it?  Is this OK?  Or, might the LED pictured be overrated, above 30V, that would burn a bit more dim since it's "underpowered"?  In some of these lamp specs it looks like many of them have a range of power handling.  With this being said, does power affect the lamp's luminosity?  Can someone please explain this relationship?

Also, in regards to finding a pad resistor value (if need be) to use with a lamp...

mnats explains this in the wiring page when he's going over the VU lamp wiring.  However, I don't fully understand how he got the .089mA measurement?  I understand this measurement is taken in series, and I understand that the .089mA value is how much current the lamp is drawing... but how exactly was that measurement taken? Straight from the secondaries to the the meter without a pad resistor!?  How can you justify hooking up the lamp straight to the power source to measure the amperes (in series with a DMM) knowing that there is too much voltage in the first place for the lamp?  I hope I'm articulating this question for everyone to understand.  In other words... I'm simply trying to figure out how I can find the current to calculate what value power resistor to use to feed my lamp the proper voltage. Does this mean I would simply measure the current between the connecting block and all of the corresponding wires since my lamp circuit will be in parallel with those other circuits?

 

[mnats]

I notice in the picture of mnats completed 1176 on his wiring page there is indeed a status LED powered from the 30VAC secondary taps at the power connecting block and no pad resistor. 

This isn't the case. There is a 0.6 Watt resistor under the bulge in the heatshrink.

However, I don't fully understand how he got the .089mA measurement?  I understand this measurement is taken in series, and I understand that the .089mA value is how much current the lamp is drawing... but how exactly was that measurement taken?

The measurement was taken by feeding the lamp from a bench supply at the rated voltage. I measured 89mA, not .089mA!

 

[Che_Guitarra]

First things first, a 200mA T fuse has fixed my blow outs.

Now, it seems I can't get my meter to respond.  I've followed Mnats calibration guide to the tee (input = ∞, output = 12, attack = off (tried on too), release = 7, ratio = 20, meter = +4, attack knob jumped to ground)... but my meter just sits bang on -20 on the left side of the VU without moving.

I've got a 1kHz signal going in at exactly 0.775 VAC, the signal coming out of the 1176 is extremely weak, but just enough to hear this test tone.  Q bias trimmer is working, output dial is working, no response from the input dial.


Gun troubleshooters, please offer your advice 

 

[sr1200]

If youre doing the hairball kit with the switched attack knob, i dont think you still need to short the pad to ground.  Turning it off should suffice.  If your input is all the way down, you're not going to see anything coming into the unit. (which is correct)  Check those instructions again and pause them frequently as you move from step to step.

 

[Che_Guitarra]

I've tried both with and without the attack pot short, and have tried every setting possible under the sun but I can't get the VU to budge from -20... not even a millimetre.  VU only moves during startup/shutdown.  I have been following Mnats video to the letter, but a lack of results i've also toyed around to try pin-point an area of concern.

My guess is that something is awry with the input circuit -  spin the dial from ∞ to zero and it's not affecting the test tone in any way, it's a steady output which is only slightly above the noise floor.  Play with the output dial however and I can hear a volume change and an increase in noise floor hiss as I dime the control, so I suggest this is working as it should.  Attack and release controls are too hard to observe at this point... too hard with a test tone anyway. 

I've tweaked for a 0.77 VAC output from my RME UFX so I know it's the ideal signal level for calibration, but still a bug to iron out before I can progress.  Hmmm....

 

[Che_Guitarra]

I'm getting a continuity to ground at both these terminals.  Is that to be expected or cause for concern?

 

[Echo North]

Is your Qbias calibrated correctly?

 

[sr1200]

Dont see a jumper on the tracking adjust short either... depending on what step you're up to, you need that on.  And I dont think you should have short to ground on those two.  Check the schematic for that one.

 

[Che_Guitarra]

Is your Qbias calibrated correctly?

I've wound the Q bias both in and out with no change in the meter.  I currently have it set where signal seems the loudest.

Dont see a jumper on the tracking adjust short either... depending on what step you're up to, you need that on.  And I dont think you should have short to ground on those two.  Check the schematic for that one.

This is a good point.  I don't fully understand what I need to do with the jumper piece and the tracking short.  I did have it on but at the time of this photo I had taken it off trying for results.  An explanation on what to do here would be great.


PS - still up to the very first stages of calibration: trying to adjust for +1 from the VU.

 

[Echo North]

Is your Qbias calibrated correctly?

I've wound the Q bias both in and out with no change in the meter.  I currently have it set where signal seems the loudest.

Dont see a jumper on the tracking adjust short either... depending on what step you're up to, you need that on.  And I dont think you should have short to ground on those two.  Check the schematic for that one.

This is a good point.  I don't fully understand what I need to do with the jumper piece and the tracking short.  I did have it on but at the time of this photo I had taken it off trying for results.  An explanation on what to do here would be great.


PS - still up to the very first stages of calibration: trying to adjust for +1 from the VU.

You need to adjust your Qbias properly before you do anything.  I believe I posted a procedure using a DMM (as opposed to the on board meter) earlier in this thread.  Don't do anything else until you are able to complete this adjustment.

 

[Che_Guitarra]

You need to adjust your Qbias properly before you do anything.  I believe I posted a procedure using a DMM (as opposed to the on board meter) earlier in this thread.  Don't do anything else until you are able to complete this adjustment.

That leaves me stuck then, as I can't get any AC voltage variation from the 1176's output, no matter the Q bias or output knob setting.

 

[Echo North]

Does your DC change at the gate of Q1 as you rotate the Qbias.

 

[Che_Guitarra]

Measured at 'G' on Q1, the DC is changing as I trim the Q bias.

 

[Echo North]

Measured at 'G' on Q1, the DC is changing as I trim the Q bias.

It's a negative DC value correct?

Check your voltages in the signal and line amp against the mnats schematic w/ voltages.

 

[Che_Guitarra]

All the values seem pretty close - within 5% of Mnats schematic voltages anyway. 

 

[Che_Guitarra]

This is driving me crazy... but no doubt it's going to be an incredibly simple fix.  Oh the joy of DIY  :'( ;D

Due to the symptoms i'm beginning to suspect the T-pad, or perhaps a cold solder on the T-pad, as I can't fault my loading of the PCB and all components were tested prior to install.  Is there a way of testing the T-pad as it sits with a DMM?

And in regards to the picture I posted above - can I get a confirm from someone with a working 1176 that I should be getting continuity to ground at both points of that terminal?

 

[Echo North]

This is driving me crazy... but no doubt it's going to be an incredibly simple fix.  Oh the joy of DIY  :'( ;D

Due to the symptoms i'm beginning to suspect the T-pad, or perhaps a cold solder on the T-pad, as I can't fault my loading of the PCB and all components were tested prior to install.  Is there a way of testing the T-pad as it sits with a DMM?

And in regards to the picture I posted above - can I get a confirm from someone with a working 1176 that I should be getting continuity to ground at both points of that terminal?

There would be some continuity/low DCR.  The transformers secondary connects to those two pads.  The transformers secondary is one lone piece of wire.  You should see a low DC resistance there.  Off the top of my head I'm not sure what it would be.

Trace your signal through the circuit.  Feed a 1khz 1VAC signal into the input and set the in/out knobs to the middle.

Measure the AC voltage at these points using GROUND as the reference.

1. Input XLR pin 2
2. + input at the PCB (by C1)
3. - of C7
4. Output XLR pin 2