All things G1176 - the new "repost" thread.

[gswan]

thanks, this makes sense, and helps me to learn the circuit a bit more.

i've done the tests you suggested

The signal comes to the input pot pin 3, and goes out to pin 2. Turning the pot makes the signal on pin 2 louder, and it's distorted only when pot is at max, but i think is normal behavior.

No, this is not normal behaviour unless your input signal is overdriving the input buffer. If this is the case then reduce it. What input level are you using?

The voltage on the wiper of the input pot should be continuously variable from 0 to 2*Vin (6dB gain due to unbalancing summing).

With the FET Q1 out of the circuit, what gain do you measure between the signal at the wiper of the input pot (2) and the top of the output pot (15)?

I guess my problem is in the pre amp section, but i have replaced the transistor two times with no results. of course i even checked the solderings and the wiring, all is ok. Should i try replaceing the electrolytics too? What you suggest?

Randomly replacing components with no reason is clutching at straws. Unless you know what the problem is and have a solution you can't be guaranteed that you have fixed it or that it won't come back again.

If you have used undervoltage electrolytic caps or have them in the wrong way around then you should replace them. What reason do you have to suspect them?

 

[beatnik]

I'm sending a 1kHz 0dbU from the console.

So this sounds a normal distortion of the buffer with input at max. I think it's normal because my working channel acts the same.

What method can i use for calculating those gain levels?

I am using a multimeter and a simple audio probe with a cap connected to a shielded cable monitoring on a small loudspeaker.

Should i send the signal of the probe back to the console and then monitor the gain on the vu meters?

I was thinking about the polarized caps because maybe an inverted polarity or high voltage could have damaged them. If this really is not possible to happen we will find the real fault.

thanks again for your patience

 

[gswan]

I'm sending a 1kHz 0dbU from the console.

So this sounds a normal distortion of the buffer with input at max. I think it's normal because my working channel acts the same.

What method can i use for calculating those gain levels?

I am using a multimeter and a simple audio probe with a cap connected to a shielded cable monitoring on a small loudspeaker.

Should i send the signal of the probe back to the console and then monitor the gain on the vu meters?

I was thinking about the polarized caps because maybe an inverted polarity or high voltage could have damaged them. If this really is not possible to happen we will find the real fault.

thanks again for your patience

This is not really going to work. Without proper test equipment you can't possibly see what is going on. If you are building and maintaining audio gear you need a scope, signal generator and audio millivoltmeter. Is your multimeter AC range accurate for audio frequencies? Many are only accurate below 100Hz, you need to consult the technical specs to see. The problem will be that the loading presented to the circuit by your probe will alter the signal that you are measuring, it may be the probe which is creating the distortion that you hear.

To check the gain of the various stages you need to measure the output voltage level from the stage with a known sine wave input level. Then the gain is just Vout/Vin. To convert to dB, it is 20*log(Vout/Vin).

 

[kepeb]

yo! dual G1176 REV J BUILD:

I have no 5m pots. but i do have lots of resistors and some 1-12 way switches could i somehow make a stepped version of this without hunting some pots down?

any ideas, suggestions/solutions welcome

 

[gswan]

yo! dual G1176 REV J BUILD:

I have no 5m pots. but i do have lots of resistors and some 1-12 way switches could i somehow make a stepped version of this without hunting some pots down?

any ideas, suggestions/solutions welcome

You could try this if you can get a dual gang 2M pot:
http://www.axtsystems.com/index.php?option=com_content&view=article&id=47:1176lnreleasepot&catid=34:1176ln&Itemid=62

 

[beatnik]

This is not really going to work. Without proper test equipment you can't possibly see what is going on. If you are building and maintaining audio gear you need a scope, signal generator and audio millivoltmeter. Is your multimeter AC range accurate for audio frequencies? Many are only accurate below 100Hz, you need to consult the technical specs to see. The problem will be that the loading presented to the circuit by your probe will alter the signal that you are measuring, it may be the probe which is creating the distortion that you hear.

To check the gain of the various stages you need to measure the output voltage level from the stage with a known sine wave input level. Then the gain is just Vout/Vin. To convert to dB, it is 20*log(Vout/Vin).

Unfortunately I don't have the proper professional equipment. My multimeter AC frequency range is 40-400Hz. It's sufficient for doing the measurements?

I hope is possible to resolve the problem without the scope. I came across this thread and there are some instructions on how to proceed with the simple audio probe i''m using, but i can't go further at the moment. Many thanks for your help.

http://www.groupdiy.com/index.php?topic=4481

 

[gswan]

Unfortunately I don't have the proper professional equipment. My multimeter AC frequency range is 40-400Hz. It's sufficient for doing the measurements?

Probably not, unless you plan to do all your measurements at 100Hz.
Build yourself an audio millivoltmenter if you want to perform measurements across the audio band.

I hope is possible to resolve the problem without the scope. I came across this thread and there are some instructions on how to proceed with the simple audio probe i''m using, but i can't go further at the moment. Many thanks for your help.

These days you can get a scope capable of audio frequency analysis for less than $100.
Unless you can build a good probe with a high impedance ac coupled input (1M or greater) then there's not much you can do. Even with a simple probe there is a limit to what you will be able to diagnose.

 

[beatnik]

my electronics knowledge is very limitated, and money available too. I think an oscilloscope would be kind of overkill in my case.

it's not any way to go further with what i have on hands?

i read of many people like me with poor electronics knowledge and basic equipment succesfully debugging their units, this really makes me demoralizing.

if there is not something more you can suggest me to do, i will try desoldering all the components and starting again, but this sounds like ****.

what really makes me crazy is that the comp was working in a first time, but later died. i checked all the wiring and soldering, all is ok, so i guess it's a fried component somewhere. what else could be?

 

[kdawg]

I'm revisiting the Mnat 1176 Rev D that's been sitting on my shelf. I'm using it with t-pad input and an o-12 input transformer and cinemag output transformer. I was struggling with calibrating it, but now I thought I had it going OK. I ran through all the calibration procedures and the GR metering all seems correct.. but... I am not getting any GR on the output. Would this be a failed attempt at calibration, or is the metering circuit working but actual GR circuit not? I did make sure that pin 22 was not grounded after calibrating.

I can run music through it and the metering looks great, threshold seems to be right about where I'd expect on the input settings and changing ratios changes the threshold like it should, attack/release working. Now if I could only hear any what the metering is showing!

Thanks
-kdawg

 

[gswan]

Measure what is really happening and generate a transfer curve for the 20:1 ratio.

http://www.axtsystems.com/index.php?option=com_content&view=article&id=54:1176lnratios&catid=34:1176ln&Itemid=62

 

[kdawg]

Never mind, found an intermittent solder joint around the FET. Working now!

 

[seavote]

i'm building 1176 using mnats revision "j" boards. since i am using a lundahl EDIT  input tranny i have not installed the components in the section denoted by mnat (do not install these components if using transformer balanced EDIT input). i just hooked up my input pot and see the ground connected at the pcb . the middle lug connects to the circuit on the pcb. the 3 lug (hot?) attaches to the pad labelled 3 but this pad connects to a trace that only connects to an omitted component.   do i need to jump anything on the pcb or am i ok. i'll take a look at the schematic and try to understand.
also i have fets for Q8 and 9 but they are not matched. how big of a problem does this pose. is matching a necessity or just preferable? opinions?
thanks for any help

 

[gswan]

i'm building 1176 using mnats revision "j" boards. since i am using a lundahl output tranny i have not installed the components in the section denoted by mnat (do not install these components if using transformer balanced output). i just hooked up my input pot and see the ground connected at the pcb . the middle lug connects to the circuit on the pcb. the 3 lug (hot?) attaches to the pad labelled 3 but this pad connects to a trace that only connects to an omitted component.   do i need to jump anything on the pcb or am i ok. i'll take a look at the schematic and try to understand.

I think you are confusing the missing components with an input transformer, not an output transformer. If you don't have an input transformer you will need to fit the 5532 and its associated components.

also i have fets for Q8 and 9 but they are not matched. how big of a problem does this pose. is matching a necessity or just preferable? opinions?
thanks for any help

It depends on how closely you want the meter GR reading to match the real GR. If the trimmers can't compensate for the differences then what you see on the meter won't be exactly what is happening at the GR stage. Having said that, the GR meter is only a VU ballistic and is not really useful in showing instantaneous GR anyway.

 

[seavote]

yes my mistake. i meant input transformer . i got confused because of the components proximity to the output tranny.  the "hot" lug of the pot is supposed to be hooked up to the pad marked *1. (its near the input tranny by the resistors marked with an * as well). since i already have my pot(all 3 lugs) hooked up to the" input" pad i'll just jump the hot leg of the pot from the first uninstalled component on that trace to the *1 pad on the underside of the board.
as for the meters,i guess i'll know how mismatched the fets are when i fire the project up. thanks

 

[sr1200]

If anyone has completed the Rev-J with the Hairball "kit" for the J and has pics of the board/tranny please PM me.  Im having some god aweful issues with this thing and would like to compare.

 

[Le Roux]

Just finished my second Rev J 1176, using the board as input, and OEP output tranny.

Passes signal, but I'm getting a hum.
The hum is controlled by the output pot.
As I turn the output up, it gets quiet until about half way, then gets really loud.

I have both XLR's grounded to chasis, and using Mogami shielded cable.

Any idea's?
Thanks

Neil

 

[gswan]

Passes signal, but I'm getting a hum.
The hum is controlled by the output pot.
As I turn the output up, it gets quiet until about half way, then gets really loud.

I have both XLR's grounded to chasis, and using Mogami shielded cable.

Quite a common problem it seems.
1. Check the grounding of your front panel. I have seen ungrounded front panels cause this. Even though the rest of the chassis is grounded, unless the front panel is wired to gound it may have some resistance between it and ground. A quick check with a piece of wire.
2. Check the location of your mains transformer and its associated leads. Move them around and see if it changes amplitude. Find the quietest spot. If the contruction is really packed in you may need to add a metal shield in front of the transformer.

 

[Le Roux]

Excellent, I'll give it a try this evening.

Thanks
Neil

 

[kepeb]

I'm almost there with my 1176 rev j, just missing a few bits now, in the meantime... i was thinking of adding the option to choose either 1:1 or 1:2 on the output (i have oep's) before i solder them straight to the board.

can you see any issues?
or is this even worth it?
cheers

 

[jeid]

I've got a problem with my Rev J. I've double checked my power transformer and I'm getting the correct voltages into the board. When I test the board at the -10v and +30v points, I'm getting -10v and +10v. This obviously throws the values off around the rest of the board.

Any ideas what could be a possible starting point for fault finding? Would it be right to possibly assume that the voltage regulator could be the issue? Or am I well off?

Thanks for any possible responses. I appreciate it