All things G1176 - the new "repost" thread.

[herrmann]

Unlikely to be a transformer, however that depends on what you've been doing to them.
Inject a signal and run the usual test diagnostics through the stages and see where the problem is.

Thanks for your response. I suppose you mean using a scope, but I don't have one.  :-\ Maybe there's a software (Mac) ?
So, where should I look for, a dead cap maybe? I have try to change transistor, without results.
Sorry, I'm newb...

 

[herrmann]

Found the problem, was a bad solder on input transformer...  :
Well, in my research, I found a software scope, Signalscope. There's a 30 day demo, I'll test it to calibrate my 1176.
Thanks

 

[a_)_i]

I am just putting the finishing touches to one of my G1176 projects.  It sounds great but I am having a problem with the balanced output.  I am only getting one side of the signal (-ve) from the transformer.  There is nothing coming from the secondary winding 'S1' for the +ve side.  I am using an OEP transformer in the 1:2 configuration with no modifications to the transformer part of the PCB. 

I have a signal probe which I have tested the surrounding circuitry with and everything seems OK. 

Does anyone have any suggestions?

 

[gswan]

Relative to what? GND?

The signal appears across the transformer, not relative to GND. If you have shorted one side of your transformer to GND then you will see what you have measured. Connect your floating measuring device across the transformer. The output XLR hot and cold pins are connected to the transformer outputs, not GND.

 

[a_)_i]

Thanks for the quick response gswan, I presume you're addressing my post and not the other transformer related posts earlier. 

Probe shield to XLR ground - it's just a DIY audio probe with a capacitor on a single core cable.  I can hear what coming off one of the secondaries (the one which goes to the -ve).  I can't hear what's coming off the other winding to the +ve.

You might have to put what you've said in simpler language - I am no expert. 

 

[gswan]

The XLR GND is not related to the transformer output unless you have shorted one of the transformer outputs to GND. The signal appears across the transformer output, not relative to GND.

 

[a_)_i]

I see.

So why can I hear a signal at the -ve XLR pin and not at the +ve? 

 

[gswan]

You should hear a signal between XLR+ and XLR-.
I don't know what you are doing with your GND. Maybe you have XLR+ shorted to GND.

 

[casrec]

Just an outsider looking in on this conversation, but I think you guys are confusing each other. I'm quite confused by the whole thing myself. On the primary, one winding should be hooked up to ground and the other hooked to C15. The secondaries should not be hooked up to any ground. One winding to the Hot and one to the cold of the XLR. The Ground of the XLR is just hooked to the the ground trace of the PCB. Hope this helps. If it's wired right sounds like you might have a bad transformer.

Brandon 

 

[a_)_i]

Hi Brandon,

Thanks for your input.  I think gswan might have a point as I tested the +ve and ground of the output connector and there is a short between the two.  I didn't have time to have too much of a look at it but I do remember that the positive side seems to go via the VU meter output and a resistor before it gets to the output.  I will check for mistakes in that area tonight. 

 

[a_)_i]

I've had a good long hard look at this and I can't figure out why the +ve output from the transformer (S1 on the OEP A262A2e) shorts to ground.  I have another g1176 board that I put together at the same time and that does not short to ground.  The only thing between the S1 secondary output and the output socket is the VU meter out and the 1K resistor R84.  

Anyone any ideas?

 

[waner]

Hi there

I have built an Mnats revJ but it won`t work properly. Something is leaky

If I put in a sine and watch the output (the tranny) on the scope it is slowly, slowly rising in amplitude. This only happens in gainredution mode. In bypass the outputsignal is stable.

Any tips?

ragards
Mattias

 

[a_)_i]

Solved one problem - created another.  I don't even know what I did!

There is no longer a short between +ve and ground.  Both +ve and -ve now have signals coming off the transformer secondaries.  However they are much weaker and lacking the low end of the signal that is going into the primary.  Is there some phase cancelation going on here, or is it something completely different?  I have searched the forum for a while and couldn't see anything.  This is really doing my head in.

On a second matter - where is everyone getting their festoon lamp power from?  I am taking mine from the -10V rail but as a result the LM337 which is regulating that rail is getting too hot to touch for anything over a second.  Surely a 1.2W bulb at 10V is only 0.12A?  The heatsink is cool as anything without the bulb attached but as soon as I add it things hot up really quick.

 

[V9977]

#Sorry to but-in#

But a_(_i , you have an answer in the Lexicon 224 thread! 

 

[gswan]

Solved one problem - created another.  I don't even know what I did!

There is no longer a short between +ve and ground.  Both +ve and -ve now have signals coming off the transformer secondaries.  However they are much weaker and lacking the low end of the signal that is going into the primary.  Is there some phase cancelation going on here, or is it something completely different?  I have searched the forum for a while and couldn't see anything.  This is really doing my head in.

This sounds like you are connecting your monitoring to the XLR+ and GND or XLR- and GND, rather than across XLR+ and XLR-. The GND plays no part in the signal, since the transformer is across XLR+ and XLR-.

On a second matter - where is everyone getting their festoon lamp power from?  I am taking mine from the -10V rail but as a result the LM337 which is regulating that rail is getting too hot to touch for anything over a second.  Surely a 1.2W bulb at 10V is only 0.12A?  The heatsink is cool as anything without the bulb attached but as soon as I add it things hot up really quick.

Using the -10V rail is a bad idea. This rail needs to be very clean or your gain reduction will suffer. Use a winding off the transformer wth a series resistor (the lamp will power from AC) or use a separate power supply.

 

[gswan]

Hi there

I have built an Mnats revJ but it won`t work properly. Something is leaky

If I put in a sine and watch the output (the tranny) on the scope it is slowly, slowly rising in amplitude. This only happens in gainredution mode. In bypass the outputsignal is stable.

Any tips?

ragards
Mattias

You've got a scope, start doing some probing around the GR amp section and see if everything is OK.

 

[a_)_i]

I'm afraid I've been a bit of an idiot and not plugged the output into a balanced input.  It does of course work perfectly now that I've done that.  Lesson learnt.  I didn't quite understand the way you had put it gswan until I disengaged my mind and started watching TV and realised that I'd need to complete the circuit by plugging the output into a balanced input.  I get it now.  Thanks

Just have to work on the grounding scheme now and try and get some 24V bulbs for the lamp so I can put it straight off the 25v power transformer secondary.

Thanks for your help.

 

[gswan]

Just have to work on the grounding scheme now and try and get some 24V bulbs for the lamp so I can put it straight off the 25v power transformer secondary.

Two 12V bulbs in series will work from the 25V secondary. I usually run the bulbs slightly under power since they don't need to be too bright and they last longer that way, so two 14-16V bulbs in series may be better.

 

[waner]

Thanks Gswan

I had forgotten to solder point 21 of the ratioboard. But when I did that, the compressor got wierd.
It`s like the smaller the ratio the more it compreses.

I have checked with the signals here (http://www.axtsystems.com/index.php?view=article&catid=34%3A1176ln&id=57%3A1176lnproblems&option=com_content&Itemid=62)and they are all the same, execpt from one thing. I don`t have any rectified signal att the junction of cr3/cr4. So I changed them, but it didn`t help. This is driving me nuts!!!

I wonder one more thing. When you set the Qbias you should turn it CCW before you begin. I get my smallest output when I turn the trimmer CCW, so I can`t get the output signal to drop 1dB it only increase as I turn it CW. I can adjust my bias voltage from 0 to -3V.

Please Help me!

Regards
mattias

 

[danjpiscina]

Hey Guys,

I'm in the home stretch of building my G1176.   the unfortunate thing is R36
100R resistor 1/4 Watt keeps frying... I have no idea what is causing this to happen..

any thoughts are greatly appreciated.

hi. i realize this post was from a long way back, but i figure i'll give it a shot.

i'm having the same problem with my rev F board. what did you end up doing to fix this? which transistors did you need to replace? if anyone has any ideas, they would be much appreciated! thanks,

Dan P.