All things G1176 - the new "repost" thread.

[spacecho]

Hey Gswan, good point you make - I'm not getting voltage on the output (for the reason you mentioned) just voltage on the input pins 2 and 3. Probing the metal can transistors with a multimeter shows voltage on them as well.. I will remove the bottom panel from the case next and see if my voltages correspond to the check plot..

 

[spacecho]

Got the 1176 on the bench today,

checked the voltages of all the transistors as described here:
http://www.axtsystems.com/index.php?option=com_content&view=article&id=57:1176lnproblems&catid=34:1176ln&Itemid=62

all of the voltages match the ones described..

I'm not sure how to proceed at this point as the unit functions normally and all transistors appear to be at the right voltage.

Is it possible that t is normal for the unit to have 15v of DC voltage on the hot and cold pins of the xlr input (or)
Is it possible that the unit is not grounded properly and 'floating' - note - the pcb is connected to ground via pin 1 of the xlr input.

 

[Chrome Heart]

Im switching my Rev J from the IC input to OEP input transformer. Is it possible to use a T-pad between the input xlr and the trafo input instead of using the *1 wiring option as described here?  http://mnats.net/1176-wiring.html

 

[s2udio]

Is it possible that t is normal for the unit to have 15v of DC voltage on the hot and cold pins of the xlr input (or)

NO

Is it possible that the unit is not grounded properly and 'floating' - note - the pcb is connected to ground via pin 1 of the xlr input.

If your wiring and measurments are correct ....or not ..Yes it could and no it should'nt !

As sugested ...disconect the meter part of the circuit,...just to make sourcing the fault easier
You most likely miswired the meter switch somewhere, introducing dc onto the output ,
Or the metering circuit is outputing DC
Recheck the metering circuit and associated wiring

Edit ...+/- 15V ,....30v diff,....disconect the meter amp output and see what v is present with respect to 0v

 

[spacecho]

Thank you for replies,

I will start double checking the metering circuit...
Not sure how to disconnect it? maybe ill start by lifting all the wires that connect to the meter rotary?

Thanks guys,

will check and double check and report back

 

[spacecho]

Did some more checking,

All of the wires connect to the meter rotary board as they should - checked twice.

I did notice that near the meter IC (TLO71) i have not put in c16 (which is a 33pf ceramic) It said in mnat's notes that it is a legacy item (not needed)

perhaps this is it?

s2udio - do you mean 'disconect the meter part of circuit' by say disconecting points 28.29 from the meter pcb (i'm guessing they are what comes out of the tlo71 ic?

 

[Chrome Heart]

So. does anyone know? Can the Rev J be wired with a T-pad and trafo input like the Rev D?

 

[Chrome Heart]

The answer to the question is "no". You cant wire the Rev J like the Rev D with the input transformer.  You have to use the *1 wiring option. I also found the 2:1 stepdown configuration the most useful on the input.

 

[seavote]

im looking to calibrate my comps but am a bitconfused by some conflicting and/or nonspecific info thats out there on the web.  im using mnats g1176 revj.  to adjust the q bias gyraf says to bypass the unit and adjust input and output to set the meter at around +1db. if i bypass my unit the meter is out of the circuit. should i be bypassing the compression section by grounding it out as/per mnats video on calibrating the rev d version.  or should i be calculating what a+1db signal will read in mVs and monitor the input and output of the unit??  help??? myhead is spinning (granted ,it doesnt take much to get that  going)
8) 8) 8) 8) 8) 8) 8)

 

[Chrome Heart]

Just short pad 22 to ground and adjust the input/output according to the video. Once you set the Q bias slightly into conductance according to the video, your Q bias is adjusted properly. It is not necessary to monitor the output of the unit. I think the video mnats has on youtube states that the I/O settings are not really that important on the Q bias adjustment as long as your in the ballpark

 

[seavote]

im using the rev j pcb.  is pad 22 on the d revision the equivalent  of pad 22 on the ratio select switch pcb?

 

[Chrome Heart]

If your using the rev J, short pad 22 to ground and follow the procedure. The adjustment is the same no matter what rev your using.

 

[seavote]

thanks. 8)

 

[spacecho]

Hello All,

I'm still unable to figure out my problem as described in previous posts - 15v present on the hot and cold of the xlr input..
As mentioned earlier - the unit seems to function normally - (all controls function as expected, meter works correctly, tested voltage of every transistor and they are good)

It was suggested that i might be having issues with the meter circuitry introducing dc into the audio path - looking at the schematic i cant see how it would introduce it into the xlr input - have double checked every connection appears to be good.

Would adding a 1:1 isolation input transormer between the xlr and +/- input pads be a good way of isolating this voltage from other gear (afraid i might destroy any gear that connects to the input) until i figure this out?

Cheers

Dying to use this comp on a session i'm doing as it sounds really good!

 

[Danny1107]

Hi to all,

I've a little problem with my G1176 with mnats rev. J board, Lundahl Input and Output. Input 2:1, Output 1:2 connection.
When I send a balanced 50mV signal in the unit (50mV Pin 1+2 and 50mV Pin 1+3), and set the Output to unity gain, so my DMM shows me 50mV at Pin 1+2 at the output, but only 36mV at Pin 1+3 at the output instead 50mV too. So I lose 14mV somewhere. Is this correct? Has somebody an idea?
Thanks for your help!

Cheers Danny

 

[living sounds]

I've build another pair of identical G1176 using the MNATS Rev J boards. I've substituted the FHD333 with BF245 using source as cathode and gate as anode and leaving drain open. I've also temporarily used 4,7uf caps for the two timing caps C19, C20. Input is electronically balanced.

Now both boards show the same behaviour: They pass audio beautifully, but distort at a certain input level - and the q-bias pot has no effect at all. With compression dialed in both units show dynamic behaviour, but incorrectly (weird pumping depending on constants) and of course distorted. There's no way to calibrate them properly with the q-bias not working. I had the FETs soldered in wrong (2n5457) at first, but they measure OK with an hFE meter.

I've measure the voltages of all transistors for one channel. All values are EBC except where denoted otherwise:


Q1 GSD
0 0 -8,1

Q2
0,5 1,0 1,9

Q3
11,9 1,9 1,2

Q4
11,3 11,9 30,2

Q5
4,4 4,9 28,5

Q6
29,1 28,5 14,5

Q7
29,5 29,0 14,4

Q8 ECB
13,9 30,1 14,4

Q9
13,7 0 13,1

Q10 GSD
-7,0 -8,5 20,2

Q12
4,0 4,5 15,0

Q13
15,2 16,0 30,0

Q14
2,9 3,4 17,0

Q15
16,5 17,0 30,0


The wiper off the Q-bias pot set at the extremes measured as follows:
-8,5 / -5,4



Thanks for any help in advance!

 

[living sounds]

Any idea where to start looking at least? Thanks.

 

[Echo North]

Well you have a qbias issue for sure.  If you have 0VDC at the Q1 gate then your FET is wide open (compressing fully).  This would probably explain why as you increase the input you hear saturation.  You should be seing something like -0.5 to -1.5 at your gate.

Have a look around R82 and R83 (I'm looking at the Gyraf scem).  They form a voltage divider and set the V for the one side of the qbias pot (around -8.5V).  The other side should be a short to ground and give you 0VDC.  Check you PAD 18, release wiring, and R7.  Using the schematic see if you can get a qbias adjustment (-0.5 to -1.5 ) to your Q1 gate.  Then calibrate and try the comp again.

Mike

 

[living sounds]

Thanks alot, Mike, this really helped! "18" was not connected to the wiper, on the Mnats board there are two connectors, and the correct one was under the pot. Unfortunately there is no picture of the PCB availible for the Mnats version, but that solved it. Works great now.

 

[mnats]

Unfortunately there is no picture of the PCB availible for the Mnats version, but that solved it.

There is a PDF of the overlay posted on my site. The topic of the two pad 18s is also covered in my troubleshooting FAQ.