All things G1176 - the new "repost" thread.

[Aleguitarpro]

Do you have your FETs socketed?
I read somewhere else about this "blow test", in that case it turned out to be caused by dirt/contamination in the sockets causing problems (I think it caused capacitance in between the pins and the socket) - problem went away by soldering in the FETs.

Or maybe it could have to do with cooling, but I don't think the FETs should be running hot at all...

You're right man! I've the FETs socketed!
Today I've made another one "main" pcb (from 11am this morning to 6pm a complete new board, including the pcb itself...) and the new one it's ok.
My eighth 1176...
No problem with release and with "blow" test.
This new board has the socket, too, as the previous couple.
The strange thing is that this new one and the one of the other working channel are made in the same way...

I'll try in the old BADworking pcb to solder directly the FETs and I'll post the results for future DIYers.
Thank you very much for support!

A.

 

[Soundcraft]

Done!
I've built my first. I just need a 5k trimpot.
Thanks to the people who share all these projects!

 

[Spencerleehorton]

HI Guys,

I am getting hum in about the 120hz region, when the input is low its kind of manageable but still there, when i change ratio from 20:1 down to 4:1 the hum gets worse, also when i put it in slam mode hum gets worse, when i switch slam mode off the hum level goes down.
The hum goes when i disconnect the input, anyone got any ideas?
such a great sounding unit its such a shame it has this hum.

regards

Spence.

 

[gyraf]

I'm pretty sure we've had this several times before.

What pcb do you use?

have you done proper grounding?

Are your supply voltages alright?

Have you tried rotating/moving away your power transformer?

 

[Spencerleehorton]

HI Guys,

I have tried moving the toroidal and no difference, i have proper grounding scheme, i have have rev #8 pcb from pcb grinder so dont need to cut trace.
Will check supply voltages but im up for any other ideas.

regards

Spence.

 

[Bozo]

thank you, here is my issue with this procedure. i forgot to mention that i do not have matched FET's and until now wasnt clear on the necessity of this. im new to solid state devices. so i dont know if this meter tracking adjustment thing is going to work until i get matching FETS's.
i can get through the Q-bias adjustment just fine, but the compressor sounds on the muddy side and i cant get it to heave at all.

when i start the meter tracking i get to step 5 when i get confused: when i switch to +4 the needle drops all the way to the left. and given that on step 1 it tells me to set the output control all the way CW, i cannot turn the output control further to get the meter to read O VU. Is this a typo or something? The only way i can raise the needle at all is with the input control, but only a little bit.

are my fets just so far out of whack that i am fighting a futile struggle? i have some matched ones coming from hairball and i guess i should wait for any further testing?
thanks,
mike

Hey
A friend and I have built a G1176 rev J each and we seem to have the same problem as this poor guy, who, unfortunately enough, never has been answered. The Q bias is done nicely but the the meter tracking adjustment is not doing the 10dB drop it's supposed to, refering to the axt-guide modified for rev J. http://www.xenoworld.org/wp-content/uploads/2011/07/g1176ln-calibration.pdf


Furthermore, i have an issue with the recifier output. Refering to this guide,
http://www.axtsystems.com/index.php?option=com_content&view=article&id=57:1176lnproblems&catid=34:1176ln&Itemid=62
my rectifier output seems quite wrong, because of the fact that i have no DC signal at all, at this stage. All base signals at the four transistors was good.

I should note that i have made meter and ratio boards of veroboard, using some interlocking 6pin schadow switches. I checked these several times and they should be identical with Mnats pushbutton boards, but the ratioswitches doesn't seem to step up/down. 4:1 appears to be different from the others which seems very similar, but this might as well be the first issue stated.
We have been struggeling with this build for some time, I really hope somebody is able to help us.

Best regards
Bo

 

[Spencerleehorton]

HI All,

I think i may have worked out a few things that maybe wrong in my version by reading all the mnats version builds.
Its looks like it may point to an earth loop which is the source of my hum.
I have a chassis earth from the IEC and also from that point i have an earth going to pins 1 on both XLR, as well as also having the screens from both input and output wired from XLR to pcb board.
If it turns out not to be this it maybe a hum coming from the pcb board which is generating 18v for the balancing board as i have heard a very similar hum in my U47 psu using the LM350 regulator when using fixed bias so might need to filter the AC more.
Mains frequency in UK is 50Hz so any hum will be 100Hz or 50Hz.
Earth-loop hum is usually 50 Hz and PSU hum is usually 100Hz.

regards

Spence.

 

[Spencerleehorton]

Hi All,

I have put in a adjustable psu and getting some distortion, no more hum but very distorted, played around with the bias control and distorted at all points?
I have removed the 1000uf caps c24, c25, c26 and 4 x 1n4004 diodes and the 2 x 1k resistors R85, R86.
i have left in C23, R87, R89 and CR6 diode.
I have put 2 jumpers from the diode points, the + point form the diodes to the pin 3 of where the 7824 was
the negative diode point connected to R85.

should i need to put the psu up to +30v in or +24V?

and i don't understand where the distortion is coming from any ideas?

regards

Spence

 

[Harpo]

I have put in a adjustable psu

an adjustable bipolar PSU, set for +30VDC in respect to 0V reference voltage and to -10VDC in respect to 0V reference voltage ?

I have removed ... the 2 x 1k resistors R85, R86.
i have left in ... R87, R89 and CR6 diode.
I have put 2 jumpers from the diode points, the + point form the diodes to the pin 3 of where the 7824 was
the negative diode point connected to R85.

Expect the CR6 zener diode to be blown from removed current limiting resistors R85+R86 as main cause of your distortion.
With your external connected bipolar power supply, R87 and R89 only draw additional power, heating up your room. Out they go.
Instead the external +30VDC connects to the rightmost/output pin of the removed 7824 voltage regulator.
External 0V connects to center pin of your AC-in connector on pcb.
External -10VDC connects to anode side of removed CR6 (where once fitted CR6, C24 and R85 connected).

should i need to put the psu up to +30v in or +24V?

to +30VDC for the positive rail and to -10V for the negative rail and adjust external psu output voltages before connecting to G1176.

and i don't understand where the distortion is coming from any ideas?

Hopefully only coming from blown zener CR6. Depending on failure mode (short or open) and amount of your negative supply voltage (you didn't tell) this might have caused follow ups.
Good luck

 

[Spencerleehorton]

Hi Harpo,

yeah +24v and -10v from adjustable psu.

so blown zener then?

regards

Spence.

 

[Spencerleehorton]

HI Harpo,

so i still want to leave in C23(6.8uf), R87(1k 1W) and R89(220R) but remove everything else?

regards

Spence.

 

[Bozo]

Hi All
My friend and i, finally figured out what was wrong. My friend had some bad connections and i missed one. But most important of all,  the famous 10dB drop occured after we stopped strickly following the calibration guide. Besides  some typos, the input and output should not be fully CW we concluded. After we both succesfully finished the calibration, the units sounded just like it should be. Very nice. Hours and hours of frustration finally over. Now the frontplate is the only thing left to finish.

Best regards and good luck
Bo Zølner

 

[Spencerleehorton]

Hi guys,

removed the zener and upped to +30v and unit works without distortion.
Slight hum as high levels but hiss there as well, havent earthed the new +30v/-10v pcb yet so slight hum could be this.

regards

Spence.

 

[pedroplanet]

Hello diyers!
I built a G1176 3 years ago and just finished a Rev D.

Comparing both units, I liked the REV G better so I decided to build another one.
Reading the rev G docs on MNATS pages he doesn't mention anything about matching the FETs.

I know it seems very important o REV D because of the discrete meter circuit, but I'm not sure on how important it is on the G1176.

I don't care much about the meter to be very precise,  but maybe adjusting the Q Bias wouldn't be precise without matching the FETs??

Please help me!!

 

[Spencerleehorton]

HI Guys,

putting together a stereo version of Mnats 1176 Rev J pcbs and have come across a few bits i'm unsure about and don't seem to be documented:

C* is not mentioned in the BOM? what value is it?
C*1, C*2, C*3 ?

or are they left out? seems that way in the pictures, very strange?

regards

Spence.

 

[Spencerleehorton]

think i get it now, leave out those components.

Spence.

 

[Spencerleehorton]

HI Guys,

hum turned out to be from gyraf g9 which was in line with the 1176, i now have correct grounding scheme and silent 1176.
still havent quite finished the stereo version but will need a bit of assistance doing the correct link for them as i know there are a few options, which is the best option for doing the link?

regards

Spence.

 

[Olegarich]

Sorry if this bee n asked but your answer could be  just yes or No

1.  C1, C10, C17 capacitors are 1.0uf (what voltages should it be?) can I use 63v Wima? Should i go for a 100v at least?

2. can I use 2N5457 instead f bc245 in g1176? (if Im using bc107 and others by Gryraf)?

 

[gswan]

It's only a 30V power rail, so 50V or 63V caps are fine.
2N5457 work just as well. You don't have to use BC107, BC547 are equivalent and readily available.

 

[Olegarich]

Thanks a lot and couple more questions.
In my place it's hard to find 1K1 1W resistor, can I use 1K2 or 1K instead, is it gonna be tragic?
c23 what value? on layout it 10uf on schetmics it's 6.8uf 35V? what should i use?
c30 c31 c33 are 6.8uf 35v (near NE5532), are those tantalum or electrolitycs?

thanks guys!!