All things G1176 - the new "repost" thread.

[buschfsu]

[quote author="gswan"][quote author="buschfsu"]ok i removed fets and get these
DC votages C B E
Q1 out out out
Q2 1.78 1.21 0.52
Q3 23v 1.54 0.92
Q4 30.25 12.1 11.67
Q5 -28.5 -4.97 3.07
Q6 -13.61 -28.53 29.11
Q7 9.5 20.88 29.74
Q8 30.23 13.61 13
Q9 1mv 12.3 12.92
Q10 out out out

should i measure again with fets in or is this a good place to start?[/quote]

It's a good starting place, since a few things look wrong here.
Q2: Vbe seems a little high.
Q3: Vc should be about 12V. R18 is probably wrong.
Q5: Your measurements are wrong here. You should not have a -30V rail anywhere. Vbe is completely wrong. Check your resistor values.
Q6: Measurements are wrong.
Q7: Vbe way out. Vc should be around 14V. The B of Q8 is connected to the C of Q7 and Q6, so they should all read the same. Yours don't.
Q9: Vb and Ve about 0.4V low. Check again after fixing the other problems.[/quote]


thanks for looking

Q2 i assume fixing other things will lower this as i can't lower the Vbe?
Q5 multimeter says its -30v im using the center tap for the black probe. also should the center tap also be connected to case/power ground or is this not necessary.

 

[sonores]

Do you think that some components may be broken because of my stupidity when i forgot the CR1 & CR2....I was just tapping some of the components and when i touched Q5 some strange things occur. The Hum level raised, before the hum level was low in the "background" but when i tapped it raised very much...like when i wired PSU output 0 to chassis....Also the VU started moving when i tapped Q5. Should I remove all those and the FET's?

 

[gswan]

Did you go through and check the components and fix the other problems? Or do you think that tapping transistors will magically produce a result?

You have several construction errors, start around Q3 and work forward.

 

[buschfsu]

gswan,
may be confusing posters here. I had the wacked out voltages but did not try any tapping. bad resistor values solved the voltage issues. using a multimeter under the influence accounted for the negative voltages. Im happy to say all voltages are spot on. now time to trace signal to find out why i have no output. then on to the GR (fets are socketed and are not installed yet)

thanks for your help!

 

[gswan]

[quote author="buschfsu"]gswan,
may be confusing posters here. I had the wacked out voltages but did not try any tapping. bad resistor values solved the voltage issues. using a multimeter under the influence accounted for the negative voltages. Im happy to say all voltages are spot on. now time to trace signal to find out why i have no output. then on to the GR (fets are socketed and are not installed yet)

thanks for your help![/quote]
Woops! Too much coffee and a 2-track conversation! Great to hear that you've solved the DC steady-state problems.

Now trace a sine wave throught the unit to check the operation of the amplifiers before doing the compression checks.

 

[maxheadroom]

hi all,

i finished the component placing on the main board of my mnats 1176 Rev J board. i don't use any input transformer.
after checking the DC voltages from the schematic from gyraf, all is fine and the voltages are in range.
the next step was checking the amp stages. for this i took out both FETs.
connect the input pot wiper to the output stage of the input stage. (=CW inputpot)
for the output-pot i disconnect the wiper.
all wirepoints of the print to the other prints (ratio and meter print) are disconnected.
so i put 1 a signal of 1VRMS on the input (HOT to COLD).
measured after C35 and i have my 1V. input stage is OK.

then i measured the output of the pre-amp stage and i measured ~0,48V.
something wrong on this!
i measured the DC voltages on the three BC107B (Q2,Q3,Q4):

Voltages of C B E
Q2 1,7V 1,07V 0,55V
Q3 12,7V 1,7V 1,11V
Q4 30V 12,7V 12,2V

for me this voltages are OK.

i tryed out to replace all the tree BC107B, but its the same.

BTW, for the caps a used the NK series, they are non-polar.
see here http://docs-europe.electrocomponents.com/webdocs/0649/0900766b806497fe.pdf
but i think this can not be the problem...
can someone help me?

 

[gswan]

Check the 1K signal at the base of Q2, Q3 and Q4 to see where it disappears.
Also check R15, R21 and R16 trimmer.

 

[gswan]

[quote author="maxheadroom"]
BTW, for the caps a used the NK series, they are non-polar.
[/quote]

Why on earth would you do that?
Electrolytics are better in supply decoupling.

 

[maxheadroom]

ok i solved the problem. i'got less voltage on the base of Q2. i checked the value of R11. it was 560R instead of 560k. there was to much feedback!
so, i replaced R11 and now :green:
the gain of the preamp stage is +26dB.
the next step is to check the line amp stage.
does anybody know the ~gain of this stage?

 

[maxheadroom]

[quote author="gswan"][quote author="maxheadroom"]
BTW, for the caps a used the NK series, they are non-polar.
[/quote]

Why on earth would you do that?
Electrolytics are better in supply decoupling.[/quote]

i don't know anything about these caps. i want to try it out.
but when anybody can't recommend them, maybe i will replace it.

 

[buschfsu]

As I said my dc v are ok so I traced a 1k sine through. Wave form gets strange after r6 (looks rectified) but I could see it until the emitter on q4. That's were I lost it. Voltage at q4e is a little hi, 16 vs 11.5. R17 and r18 check out so I'm stumped. Fets are out but pots are not disconnected th way maxheadroom did his. Any thoughts?

 

[dustbro]

Does the schematic on Gyraf's site with voltage reference work for a real unit? I have a unit down and wonder if I can reference these numbers.

 

[maxheadroom]

[quote author="buschfsu"]As I said my dc v are ok so I traced a 1k sine through. Wave form gets strange after r6 (looks rectified) but I could see it until the emitter on q4. That's were I lost it. Voltage at q4e is a little hi, 16 vs 11.5. R17 and r18 check out so I'm stumped. Fets are out but pots are not disconnected th way maxheadroom did his. Any thoughts?[/quote]

do you checked the resistor R11 for correct value? (560k)
check only the input stage, without R6.
what kind of waveform dou you mean with rectified? without neg. wave or mirrored neg. wave. or maybe a DC offset? then i would check the caps around the pre-amp stage.

 

[buschfsu]

ill post images. i cant do much without R6, audio wouldn't get to C1-R10-Q2base. ill check R11

 

[maxheadroom]

what i mean is the input-stage, not the preamp stage.
put R6 out and measure after C33

 

[mischa]

Hi,

just finished re-wiring 2 1176s that i finished already a year ago or so. The problem with one unit persist:

when i reduce the attack (turn cw) all the way, i get a clicking or crackling noise that comes in the peaks of rythm of the music. Only one click per peak, and no differences between the clicks. All loud sounds like drums seem to trigger it. It disappears only if i turn the knob just a tiny bit to the left again, even less than half a mm, it seems.

On the same unit, if i turn the output pot all the way up, i get a heavy noise, which doesn't appear on the other unit...

It's particularly strange because i compared the two units, and both seem to be equally stuffed... I have done no calibration though...

Also i have an issue with both meters. I use the flashstar meters from jlm. Compression is not indicated by the needle pushing to the right, starting at -20 or whatever, but starting at around -3, and pushing to the left. Both meters essentially behave the same, no matter what polarity i have (which is unimportant as i read...) Sad

other than that, a great project. looks cool, too thanks mnats for the board, which is really (almost) self-explanatory. i'll post pictures as soon as the thing works alright...

Any suggestions?

 

[gswan]

[quote author="mischa"]Hi,
when i reduce the attack (turn cw) all the way, i get a clicking or crackling noise that comes in the peaks of rythm of the music. Only one click per peak, and no differences between the clicks. All loud sounds like drums seem to trigger it. It disappears only if i turn the knob just a tiny bit to the left again, even less than half a mm, it seems.

On the same unit, if i turn the output pot all the way up, i get a heavy noise, which doesn't appear on the other unit...[/quote]

Since the unit is uncalibrated, you need to start with this problem. Disable the compression entirely and start tracking through the signal path to check that the amplifiers are behaving correctly.

Then enable compression and calibrate the unit. There's no point putting signal through the compressor until you know you can calibrate it and have the GR stage working correctly.

 

[gswan]

[quote author="buschfsu"]As I said my dc v are ok so I traced a 1k sine through. Wave form gets strange after r6 (looks rectified)[/quote]

What does "looks rectified" mean? Are you clipping the peaks? Are you losing the bottom half of the sine wave? The junction of R6 and C1 should have your sine wave on it, amplified by the input amplifiers and attenuated by the input pot.

[quote author="buschfsu"]but I could see it until the emitter on q4. That's were I lost it. Voltage at q4e is a little hi, 16 vs 11.5. [/quote]

That's a clue. Why is Q4Ve so high? I'm guessing that Q4Vb is also high (about 16.5V) and also Q3Vc. You have assumed that your "DC V are OK", when they appear not to be. How about Q2?

 

[mischa]

Since the unit is uncalibrated, you need to start with this problem. Disable the compression entirely and start tracking through the signal path to check that the amplifiers are behaving correctly.

I did that already before, and now again. It seems that as soon as I have compression, the clicking sets in.

Both units have very similar voltages on all parts...

I do have to admit though that i had some difficulties regarding the 3 different q-bias adjustment instructions. The last i used was the on page one of this thread. To me it seems that the start-off point for this trimpot is in a way arbitrary, because the q-bias pot can be set to achieve a 1db reduction from any position, right? wrong, i'm afraid, but i don't know why.

also, this one is the only one that should influence compression, right? So if i just turn it around without target, as soon as the compression sets in, the clicking also starts. :?

I use the mnats-J board, and there are 3 places where bridges can be applied, but only if i should use input transformer, which i don't (only for output): 1*r and the q8 and 9. Those are unfitted, since they shouldn't have any effect at all... other than that i can't find ANY wrong wiring, bad soldering, even the voltages all behave the same as in the other unit, which doesn't click...

by the way, the clicking intensifies when i short the two left lugs of the attack pot.

i'm not entirely sure if the thing compresses at all, but through all the noise when the qbias is ccw it seems like it.. if that's it, it sounds beautiful.

i already went through half of the post, but no similar problem there.

thanks for listening

 

[Echo North]

Does anyone have a digikey or mouser part number for an 1176 power transformer?

The one on Greg's list is back ordered until summer.

Thanks,

Mike