All things G1176 - the new "repost" thread.

[seavote]

thanks that exactly the type of direction i need!! i have no bench psu. could i just hook up 3 9V batteries and introduce them to the circuit after the regulator??

 

[gswan]

thanks that exactly the type of direction i need!! i have no bench psu. could i just hook up 3 9V batteries and introduce them to the circuit after the regulator??

3 9V batteries do not have current limiting. They will also be shorted out, as is your regulator. Check with an ohmeter and see if there is a dead short on the rail first, indicating either broken components or wiring short. If not then it is likely that both your output transistors are being driven into saturation at the same time. Start there and check the active components, use your Hfe meter to get a reading for the transistors to see if they are still OK.

 

[seavote]

looks like a much easier fix than i expected. when i replaced the 7824 last time i connected wire to the pads and the wires to a 3pin female molex connector that accepts the regulator so i could mount it offboard on the case since it was getting hotter than i expected. i  always check my connections for continuity after i make them. but some how 2 of the connections failed. i used solid core wire as it was all i had on  hand. while moving the wires around they must have come lose. i resoldered  but did not get a chance to hook everything up and test. unfortunately i am sick and wont be back at work to test. hopefullythis was the only problem with the unit.
8) 8) 8) 8) 8) 8) 8) 8) 8) 8) 8) 8) 8) 8) 8) 8) 8) 8) 8) 8)
thanks for the help gswan... just took a look at your website perhaps it can help if i have other problems

 

[gswan]

when i replaced the 7824 last time i connected wire to the pads and the wires to a 3pin female molex connector that accepts the regulator so i could mount it offboard on the case since it was getting hotter than i expected.

This is a bad idea. You are moving the regulator away from its local decoupling caps and adding inductance to the pins. It could cause the regulator to become an oscillator.

 

[seavote]

duly noted.  2 pads for the regulator have lifted i repaired this and have the regulator installed. i will hook up.  check voltages and then check the audio. if i get some oscillation i will know where to look first, but for now id rather leave the regulator alone until i know it is a problem. thanks for the heads up its good to know for my next 1176.( which i start when this one is up and running.)

 

[kepeb]

just a quick one.
decided to use TRS connectors, should I normal my switched i/o's to ground?

probably no real reason it would make a difference because you have it connected if its switched on.. but are there any benefits or problems with this?

 

[gyraf]

Normal inputs to ground.

Do NOT normal outputs to ground - shorting output at high levels can probably seriously disturb the output stage.

Jakob E.

 

[kepeb]

thankyou
i better be careful when patching as well then.

 

[XeNoMoRpH]

Normal inputs to ground.

Do NOT normal outputs to ground - shorting output at high levels can probably seriously disturb the output stage.

Jakob E.

Another question about grounding; should the IEC be grounded to the chassis the same place as the input XLR/Jack is grounded to the chassis? I understood it so from your page, but I've seen conflicting messages about this.

I thought grounding these two the same place would be safest.

Thanks a lot for the G1176 project btw, I love building it!

 

[joshcamp]

hello - I am new here and want to build the G1176 clone.  I bought a rev J board set from Mnats.  I want to buy a kit from hairball audio.

They recommended the Rev F kit.  Does that mean I should also follow the Rev Schematic and get all of the componenets on the Rev F BOM ?

Also, I want to do the rotary switch for ratio selection - not the pushbuttons.  Does the Rev J board kit provide for this alternate?

 

[gswan]

I do not know if the Rev F kit uses the same schematic as the RevJ kit. If you are sourcing the components then you should use the BOM for the boards that you intend building. There may be different component designators between revisions.
The Rev J board kit would have come with some rotary switch PCB's for you to use for rotary switch metering and ratio selection.

 

[idylldon]

Well, I built six channels of Gyraf's F revision 7 a few years ago and all of them worked from the get-go until now.  Two of my units are dual mono and one of them has one channel that is now distorting when in bypass and it gets more distorted when compressing.  I used the IC input and Lundahl output (w/the higher gain mod), I've done the proper grounding fixes, I've replaced the ICs, the FETs, and a few of the transistors, and I've compared it to the other channel and it's identical; that is, all voltages are the same on every pin of every transistor and the scope shows the same pattern at every stage on each board when the controls are set the same.  One of the channels is distorting and one is fine.  I'm about to pull what's left of my hair out since I can't seem to find/see anything amiss.  When I built these, I stuffed both boards at the same time, piece by piece, to make sure everything was correct.  I'm starting to wonder if I have a leaky cap, but I haven't checked those yet.

Any ideas would be most welcome.

Cheers,
--
Don

 

[gswan]

What is the nature of the distortion? Clipping? Crossover? Harmonic?
Run a pure sine wave through the device and see if there is any distortion at the output under different signal level conditions. You need to do this with a scope and use subtraction to remove the input sine wave from the output to view the distortion artifacts.

 

[idylldon]

What is the nature of the distortion? Clipping? Crossover? Harmonic?
Run a pure sine wave through the device and see if there is any distortion at the output under different signal level conditions. You need to do this with a scope and use subtraction to remove the input sine wave from the output to view the distortion artifacts.

I'm not sharp enough with a scope to do the subtraction thing, so I can only report what I see using a regular old sine wave and looking at the output. 

The good channel and the problem channel start to clip on the input with the same level of signal; however, the problem channel's sine wave swings higher on the positive side than it does on the negative side.  Let's say the good channel has a completely symmetrical sine wave with equal parts above and below the center line.  The other channel has a sine wave that isn't symmetrical and the part of the sine wave above the center line hits a higher division mark than the part of the since wave that swings below the center line.  The ratio is about 2 divisions above the center line to one division below.  Also, the bottom of the sine wave is much more rounded off than the top part.  It's not flattened like it's clipping; it's just a gentler radius than on top.  Since this had a Class AB output, I'm wondering if there's something going on in the output section, but I've changed those transistors already and the results are the same.

Some pics, both channels with the same settings in bypass (not in compression mode):

Good channel output:



Bad channel output:




Cheers,
--
Don

 

[idylldon]

Update:

The incoming sine wave looks great at pin 1 of the 5532 IC but by the time time it gets to the drain of Q1 it's starting to exhibit the asymmetry that shows in the scope traces in my previous post.  All component values check out and match the other channel that's working flawlessly, so I'm going to pull the board up and have another look at all the soldering in this area to see if something is amiss there.

Cheers,
--
Don

 

[gswan]

Q2 is a BJT, it does not have a Drain. It has B, C and E pins. Q1 is a JFET and has G, D, S pins.
What signal do you have on the top of the Input pot?
If it is still looking distorted there then check the DC level at pins 3 and 5 of the op amp (they should be the same, around 15V). Check the signal at pin 7 of the op amp too.

 

[idylldon]

Q2 is a BJT, it does not have a Drain. It has B, C and E pins. Q1 is a JFET and has G, D, S pins.
What signal do you have on the top of the Input pot?
If it is still looking distorted there then check the DC level at pins 3 and 5 of the op amp (they should be the same, around 15V). Check the signal at pin 7 of the op amp too.

Q2 was a typo on my part.  I changed it in my post.

As for the rest, the signal is fine at the top of the input pot.

All voltages and wave forms look fine on the IC.

Thanks for the suggestions!

I've been tinkering with this now for so long I've about run out of ideas.  I'd sure like to know why the wave form is asymmetrical on the bad channel. 

Cheers,
--
Don

 

[gswan]

What is the value of the gate voltage?
Does twurdling R6 affect the waveform symmetry at Q1-D?
Can you pull the Q1 FET from the board and repeat the measurement?

 

[idylldon]

It ended up being a faulty C3 cap.  It's working 100% now and it's back in the rack.

Thanks for the suggestions.  They put me on the right path.

Cheers,
--
Don

 

[dagoose]

I have something strange going on..
The 1176 rev J (mnats board) was the first DIY project i did and i always enjoyed a lot but i didn't use it for 1 or 2 years no. So.. i thought to myself, let's start up the 1176 again!

But.. it passes audio fine, the meters are working fine and they respond to the various attack/release settings but there is no compression going on.
I checked voltages and it looks like everything is working fine.
It's a stereo unit and both channels behave exactly the same.. that's the strangest thing.
Any idea? Where to start searching?