All things G1176 - the new "repost" thread.

[kenrinc]

OK here we go. I measured the output of the function generator with a dc voltmeter to get .775. Is that cool? I've posted pics to a page:

http://www.kenrinehart.org/1176/1176.html

Ken

 

[gswan]

Do you see any change to the Q2-E waveform when you adjust the Symmetry pot (R16)?
What do you see on Q3-C/Q4B?

 

[kenrinc]

R16 does nothing. Added pic of Q3c and Q4b

Ken

 

[gswan]

You'll need to turn the vertical down to 1 or 2 V/div to show the complete waveform. It's off the screen.

 

[gswan]

Looks a bit like you have too much gain in the amplifier. Check R19/R20, C8 and R11. Also R21.

 

[kenrinc]

R19, R20, R21, R11 check out. C8 has 1.093v across it.

Ken

 

[gswan]

Measure the signal at the wiper of the input pot and also at the top of the output pot. What is the gain of this stage? It should be around 26dB.

 

[kenrinc]

I'm assuming the wiper is the middle terminal. It goes from nothing to about .5v pp at full CW rotation; less signal than the input signal at the transformer.
The middle terminal on the output pot goes from nothing to way off scale. Not sure how I can determine what signal level is in db.

 

[gswan]

Set the input pot wiper to some value you can measure at the input, around 0.1Vp-p (call this Vi). Now measure the output p-p voltage (call this Vo).
You will need to turn down the vertical of your scope so that it does not go off-scale.

Now, to work out the gain in dB, use the following:

Gain (dB) = 20 * log(Vo/Vi)

So for 0.1Vp-p at the input wiper, and a 26dB gain, you would expect to see about 2Vp-p at the output pot.

 

[kenrinc]

I must be getting tired because my brain is mush. I can set it so I measure .1v pp on the scope at the input then moving to the center term on the output pot measure quite a huge amount of output. It's way off scale and I can reset the vertical but unfortunately I'll need to do a bit more research on reading the scope because I'm totally lost there.

Ken

 

[gswan]

Measure the top of the output pot, not the wiper. To see more waveform, turn the V/div knob on the scope anticlockwise. Now read how many divisions the waveform takes up and multiply that by the V/div setting on the knob. That's the Vp-p reading.

 

[kenrinc]

Sorry for the confusion on this. OK so the "top of the pot" is what terminal? I I guess if your looking from the front with the terminals pointing down it's the right or left terminal?

I figured out the wiper is the center terminal.

Ken-

 

[gswan]

The top of the output pot is the terminal conected to C9.

 

[kenrinc]

I think I've got bigger problems. Whenever I move the board the scope output changes (get's bigger then smaller). I've got wires everywhere and i think either cold solder joints or something is just plane broken somehwere. When I did get a measurement at that pot it took 2 div at the 5v setting so I'm guessing a little over 10v. But the output pot actually doesn't do anything: there is signal present at the output even when the input is fully ccw.

ken

 

[3nity]

Geez i'm 90% done with mine and i'm worried about all the problems people have!!

 

[gswan]

[quote author="3nity"]Geez i'm 90% done with mine and i'm worried about all the problems people have!![/quote]

Most problems are due to people rushing construction, incorrect component values and a lack of understanding about how it works and calibration methods.

Post any problems you have here and we'll see if we can guide you to completion.

 

[kenrinc]

I agree. And this is only one side of a dual 1176 so I'm actually thinking of stuffing the 2nd board and wiring it up just to verify that there is actually a problem with the other board. I always measure my resistors before soldering in so I'm fairly confident there but for me the complexity of the ratio board/switch was tough for me. I'm guessing it's somewhere in those shielded wires going to from the pots.

ken

 

[MartyMart]

You'll get it working, don't worry
The G1176 was my second "proper" studio project,( SSL9k's first ) after a couple of valve
amps and lot's of 9v stompers and it worked pretty much right off the bat !
Some patience and careful construction is all it takes.

MM

 

[gswan]

Ken,

From the symptoms you describe here I'd suggest going over the wiring carefully and tidying it all up a bit. If you are confident about the resistor values then that is good. You may need to check soldering and termination of the wiring carefully, particularly that concerning cable screens.

Geoff

 

[3nity]

i'm waiting for the rotarys, case and transistors to be done!
:thumb:

Actually i did fixed one 1176 way far more complex so i'm pretty confident and almost all my builds worked the only problems i had were you know like pin 2 xlr to ground..... :roll: :thumb: