All things G1176 - the new "repost" thread.

[guitarguy12387]

I'm back with two questions:

1) According to mnat's page, the only thing to be tied to chassis is the xlr. How do i ground mains voltage?

2) Having trouble with VU meter lamp. I'm using VU's from PM 1000 and cannot get the lamps to light. I have been looking around and i see that it runs on 12V or so, and the VU lamp pads on the board supply ~32V. I have also seen gyraf's suggestion about wiring the lamps to be powered by the secondaries. But i tried applying 12V with a power supply and didn't get any response. Does anyone have any suggestions about something i might be doing wrong?

Thanks again.

 

[Echo North]

1) I believe what he is referring to there is the signal ground. The XLR is the only point where the signal is connected to the chassis. You should still connect your IEC ground to the chassis. That is your power chassis ground.

2) Are you connecting a ground to the other terminal on the VU?

Mike

 

[gswan]

[quote author="guitarguy12387"]I'm back with two questions:

1) According to mnat's page, the only thing to be tied to chassis is the xlr. How do i ground mains voltage?[/quote]

If you are using a metal chassis and your country's wiring rules require it to be earthed then you will need to bolt the mains earth wire to the chassis.

I think the mnats page is implying not to use multiple signal and power supply earth points through the chassis, as this will create loops and noise.

[quote author="guitarguy12387"]
2) Having trouble with VU meter lamp. I'm using VU's from PM 1000 and cannot get the lamps to light. I have been looking around and i see that it runs on 12V or so, and the VU lamp pads on the board supply ~32V. I have also seen gyraf's suggestion about wiring the lamps to be powered by the secondaries. But i tried applying 12V with a power supply and didn't get any response. Does anyone have any suggestions about something i might be doing wrong?

Thanks again.[/quote]

If it's an incandescent globe, measure it with an ohmmeter. If you get no reading then it's probably blown. If you stuck 32V through a 12V globe it will blow pretty quickly.

If you have 2 12V globes, wire them in series and use one of the 24V AC secondaries from the transformer to power them.

 

[guitarguy12387]

I believe what he is referring to there is the signal ground. The XLR is the only point where the signal is connected to the chassis. You should still connect your IEC ground to the chassis. That is your power chassis ground.

If you are using a metal chassis and your country's wiring rules require it to be earthed then you will need to bolt the mains earth wire to the chassis.

I think the mnats page is implying not to use multiple signal and power supply earth points through the chassis, as this will create loops and noise.

Perfect. Thanks.

Are you connecting a ground to the other terminal on the VU?

Yeah... i'm using a bench supply to test it. +ve from supply to +ve of the VU and gnd from the supply to -ve on the VU.

If it's an incandescent globe, measure it with an ohmmeter. If you get no reading then it's probably blown. If you stuck 32V through a 12V globe it will blow pretty quickly.

Yeah i get around 40M ohm. I tried the bench supply on another meter that hadn't been hooked up to the board before with no result on that one either.

 

[guitarguy12387]

Alright i figured 40M was pretty high... so i checked the others (i bought four used) and two of them don't get a reading for ohms and the other gets 13 ohms. That looked a little better. Tried putting 12v on that, but nothing.

 

[Echo North]

I have a PM-1000 meter here...it reads about 10ohms.

I attached 9V to the light terminals and she lit up fine.

-Mike

 

[guitarguy12387]

I double checked them. And lo and behold i get light on the one showing ~12v. I suppose i just have lots of broken bulbs hah. Thanks guys!

 

[guitarguy12387]

any idea how to get ahold of those bulbs? Is that even possible?

 

[Echo North]

I haven't seen them anywhere.

A better bet might be to mod it by lighting it with an LED strip. Better lighting and you won't have to search around for bulbs when they blow.

Mike

 

[gswan]

I've done that to quite a few meters now. Dead bulbs are a thing of the past, and they are a hassle to replace (usually involve opening the meter and poking around trying to avoid damaging the meter, faceplate and spring.

Don't run 'superbright' LEDs though, they tend to give a bright spot and not much else. Some highly diffused yellow LEDs give a nice warm glow.

 

[guitarguy12387]

Ok. I'll give that a try. I appreciate the help!

 

[Even]

Just finished a 1176 today - mnats REV J - oep in Lundahl out - all woking fine but getting a little hum.
I didnt have a 2x24 Power transformer at home , but a 2x18 1.3VA.
So connected it and getting the 10V and instead of the 30V about 26.9V.
Can it be that the hum is caused by that????
I tried all grounding possibilities but getting the same hum with or without grounding.
Rechecked everything - looks all fine to me

 

[Echo North]

I'm no expert to be sure, but this seems like a bad idea. This is a significant difference in the secondary that would surely cause your compressor not to function properly.

You're getting greater then a 10% dip in voltages which is too much.

I would definitely get the proper transformer in there before moving on.

Mike

 

[gswan]

A 3V drop is not that bad, provided the rail is clean. What's the ripple voltage on the DC rail? 1.3VA is not much, about 36mA per 18V secondary. If you are running VU lamps off it then I'd say you have power supply problems. I would suggest a 15VA or better transformer.

Failing that, most hum-related problems are created by a poor grounding scheme, so I'd check that if you are sure your power supply is OK.

 

[Even]

Yeah will change it - hope it works...

[quote author="gswan"]
Failing that, most hum-related problems are created by a poor grounding scheme, so I'd check that if you are sure your power supply is OK.[/quote]

What poor grounding scheme could it be?
Not too much possibilities with the mnats board....
I grounded the input as mnats recommended...then power ground with star grounding .... and then the output too...always exact the same hum...even with no ground connected at all.
When i disconnect the input pot i get a loud sizzle.
And when i disconnect the output pot from the Ratio board its completely quiet.

 

[gswan]

[quote author="Even"]Yeah will change it - hope it works...
What poor grounding scheme could it be?
Not too much possibilities with the mnats board....[/quote]
It's not just the board, it's the external wiring too.
[quote author="Even"]
I grounded the input as mnats recommended...then power ground with star grounding .... and then the output too...always exact the same hum...even with no ground connected at all.
When i disconnect the input pot i get a loud sizzle.
And when i disconnect the output pot from the Ratio board its completely quiet.[/quote]
Do you have a ground connection between the input and output sockets through the board as well as through the chassis? I would avoid connecting the input socket ground to the chassis and wire it to the module, allowing for the star point between the module PSU and the chassis.

 

[Even]

no difference at all whatever i do .....

 

[gswan]

Did you measure the ripple on the DC rails?

 

[glide 1]

I have a few questions.

I was wondering if it is possible to use 1 50VA toroidal transformer to power 2 of mnats rev j boards. I also have mnats' power supply boards but would like not to use it as the boards i have are already stuffed and taking the parts out would be a pita.

Are there any issues that i could encounter by just connecting the 2 secondaries and centre tap the each of the boards?

I searched and found this in the meta but not sure if it answers my q thouroghly. thanks in advance

CJ member wrote this: "maybe some additional pi filtering to eliminate cross talk" Anyone care to explain this?

http://www.groupdiy.com/index.php?topic=1086

specs for the toroid transformer:

Brand - Nuvotem Talema
Toroidal Tran 50VA
PRI: 0V-230V 50/60hz
SEC: 2 x 0V-25V

 

[gswan]

There should be no problem doing this. I am assuming you are using a single 50VA toroid and connecting it to two 1176 modules with onboard regulators. I don't think you'll have any crosstalk problems through the AC power rails doing this. Two 1176 modules draw less than 50VA so your power budget should be ample.