All things G1176 - the new "repost" thread.

[mac]

Hey Chromeheart,
I put it down to Eds output transformers that I have on the outputs of my dual 1176. And I am not in anyway saying that there is high end "drop". They have more of a top end smoothness which is all class. This makes the transformerless GSSL sound a bit bright or harsh by comparison. Because my 1176 front end is switchable (op amp or lundahl input) and this same character exists, I was assuming it to ed's trafos.
I have another "j" board kicking around with a lundahl output. One of these days I shall A - B them to see.

I love Eds outputs on mine - all class!! I have embarressed a number of higher budget studio compressors owned by some friends with mine.

Mac

 

[Janus Audio]

So, now I checked all the voltages of the transistors and they are pretty much like those on the first page of this thread.

Two other things I observed:

- When I change the ratio the sine wave on my pc scope changes to another level just as intended and then jumps back to its former level after half a second or so. So is the gain reduction not stable or something? What can be the reason?

- When I switch between GR and VU meter the sine level on my scope changes a little, too. The metering should not affect the gain reduction, right?

 

[Chrome Heart]

Hey Chromeheart,
I put it down to Eds output transformers that I have on the outputs of my dual 1176. And I am not in anyway saying that there is high end "drop". They have more of a top end smoothness which is all class. This makes the transformerless GSSL sound a bit bright or harsh by comparison. Because my 1176 front end is switchable (op amp or lundahl input) and this same character exists, I was assuming it to ed's trafos.
I have another "j" board kicking around with a lundahl output. One of these days I shall A - B them to see.

I love Eds outputs on mine - all class!! I have embarressed a number of higher budget studio compressors owned by some friends with mine.

Mac

Oh, maybe I misunderstood your post. Ive been considering switching one of my 1176's to a Lundahl input and one of the Hairball input pots. As it is, the input in very sensitive. There has been some discussion about a mysterious resistor value for the input threshold, but I have not been able to make any sense of it.

 

[mrcase]

hi all!

I´m finishing my dual  mnats g1176 and I´m having an issue with my sifam meters.
after powering on and the meter switch set to GR the needly rises very slowly to zero. once it´s there its fine, even if I change the meter switch position forth and back...
Is this like it should be? or is there something wrong with the voltage rising to slow?  ???

thanks for the help!!

 

[Chrome Heart]

hi all!

I´m finishing my dual  mnats g1176 and I´m having an issue with my sifam meters.
after powering on and the meter switch set to GR the needly rises very slowly to zero. once it´s there its fine, even if I change the meter switch position forth and back...
Is this like it should be? or is there something wrong with the voltage rising to slow?  ???

thanks for the help!!

seems normal to me.

 

[beaversaber]

Hi all,
Quick question,
I'm finishing up one of MNATS revision G 1176s with the IC input stage.  I wasn't getting signal, so I built up one of Mark Burnley's signal probes to trace and find where the error was.

I tested at the input XLR and signal came through just fine.  I then tested at the output of the IC input stage (going to the input pot) and the signal was significantly lower.  I also probed at the middle terminal of the input pot. Here the signal was just as low, and the input pot had no effect on the level.

Any idea what might be causing this?

 

[beaversaber]

Also,

My previous post was using ground at the input XLR as my 0v reference.  When I use pad 16 on the PCB as my 0v reference, I don't get any signal after the IC input stage

 

[gswan]

Hi all,
Quick question,
I'm finishing up one of MNATS revision G 1176s with the IC input stage.  I wasn't getting signal, so I built up one of Mark Burnley's signal probes to trace and find where the error was.

I tested at the input XLR and signal came through just fine.  I then tested at the output of the IC input stage (going to the input pot) and the signal was significantly lower.  I also probed at the middle terminal of the input pot. Here the signal was just as low, and the input pot had no effect on the level.

Any idea what might be causing this?

A wiring error to the input pot perhaps?
Or maybe a wiring error between the input XLR and the PCB.
I assume you do have the power turned on and the PSU has been tested.

 

[beaversaber]

everything is plugged in, PSU has been tested, although the voltages at the 2 reference points on the PSU were +29.71v and -8.17

 

[gswan]

everything is plugged in, PSU has been tested, although the voltages at the 2 reference points on the PSU were +29.71v and -8.17

These voltages look adequate for operation.
I assume you are using a balanced input (ie ignore the XLR GND pin) and are measuring the values on the PCB wrt PCB GND?

 

[beaversaber]

Yes and yes.  The ground pin on the input XLR is not connected to anything except the chassis. Pin 2 on the input XLR is connected to "+" at the input circuit on the pcb and pin 3 is connected to "-" at the input circuit on the PCB.

The output wire from the IC circuit is connected to the clockwise contact of the input pot, the middle contact of the input pot is connected to the signal pre amp, and ground from the pcb is connected to the counter clockwise contact of the input pot.

I am measuring these values using pad 16 on Mnats PCB as my ground reference.

 

[gswan]

OK, that all sounds good.
You should be able to take a measurement from the GND connection on the pot and the top connection on the pot, which is the balanced input summing amp output.
BTW, when taking this measurement, make sure that the wiper of the pot is turned all the way down, so that it is shorted to GND. That way your FET, if conducting, won't be attenuating the signal.
If you are getting nothing here then check what is coming out of pin 1 of the IC, and also pin 7.
What kind of signal are you putting in to this stage? Can you look at the output with a scope? What kind of measuring instrument are you using?

 

[beaversaber]

I am injecting a 1k -18db sine wave at the input XLR. I don't have a scope.  I followed Mark's suggestions that he posted here:

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

and just have the probe hooked up to a guitar amp.  the shield of the cable is connected to PCB ground and the hot of the cable is soldered to a .02uf polyester cap.
I tested this probe at the input XLR and it does work (heard the sine wave come out of the amp, not distorted), but while probing around in the unit I lose signal after the IC input stage.

When you say to take a measurement across the input pot I assume you mean with a multimeter? ie the negative lead from the multimeter on GND and positive lead on the top connection on the pot?

Pin 1 on the IC: 14.78v
Pin 7 on the IC: 14.75v

 

[gswan]

I am injecting a 1k -18db sine wave at the input XLR. I don't have a scope.  I followed Mark's suggestions that he posted here:

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

and just have the probe hooked up to a guitar amp.  the shield of the cable is connected to PCB ground and the hot of the cable is soldered to a .02uf polyester cap.
I tested this probe at the input XLR and it does work (heard the sine wave come out of the amp, not distorted), but while probing around in the unit I lose signal after the IC input stage.

When you say to take a measurement across the input pot I assume you mean with a multimeter? ie the negative lead from the multimeter on GND and positive lead on the top connection on the pot?

Pin 1 on the IC: 14.78v
Pin 7 on the IC: 14.75v

It's a crude test, but will suffice for tracing signals.
The measurement across the input pot is your signal trace, wrt GND. This is where you would expect signal to be if all is working OK. Otherwise go back a bit and check the signal at pin 1 and pin 7 of the IC. The fact that it is already at half rail DC is comforting, since that's it's quiescent point.
You need to check multimeter specs before measuring audio AC signals with them. The cheapies are not much good at AC above a couple hundred hertz.

 

[beaversaber]

No signal on pin 1 or pin 7 of the IC, the only place I get anything is Pin 2?

 

[gswan]

No signal on pin 1 or pin 7 of the IC, the only place I get anything is Pin 2?

Have you got the IC plugged in (the correct way around)?
Check the resistor values for R1, all should be 10K. You have no signal on pin 6?

 

[beaversaber]

Signal on pin 6 is very low.  About to try replacing all the R1 resistors

 

[beaversaber]

Replaced all R1 resistors, double checked to make sure they were 10k, still same problem.

I then replaced the NE5532, and now I have signal on the middle contact of the input pot, and it is affected when I turn the pot =] input stage works!  Good signal on pin 1 and 7 of the chip


However, the signal coming out of the unit still seems to be low, I need to have both input and output pots almost all the way up for unity gain, with compression bypassed. 

 

[beaversaber]

Did some more probing around the line amp section,

On R34, the 3.9k resistor, the signal is really strong on one side, and on the other side is very weak.  Is this to be expected?

 

[beaversaber]

With the FET Q1 removed, gain staging appears to be more normal.  I get unity gain with both input and output knobs about midway