All things G1176 - the new "repost" thread.

[gswan]

So ya, just like I mentioned before, R55 and R54 still do nothing.  I have gone through the calibration process for Q bias, which is also messed up and doesn't react like my other pushbutton units did, but I cannot continue without solving this.  There are currently bourns multi turn pots in there, is that a bad thing?  No matter how many turns, these 2 pots do absolutely nothing...likely due to the same issue I'm having with the metering when I do Q bias.  Something is just not right with the meter board, or meters.

I'm almost ready to pack it in on rotary versions, so far they suck to me.  Pushbuttons all the way.   

The shape and style of switches uaed to select parameters have no bearing whatsoever on calibration and testing of the unit. It's you own lack of understanding of what you are doing.

Did you perform the calibration of the GR FET bias correctly?
Did you verify the bias conditions on the BJT's?
Did you check that your supply rails are stable and correct?
Did you check that your components and wiring are correct?

Do your meters have internal diodes or do they require external circuitry to work as VU meters?
With GR displaed can you run a signal through the unit and observe that it is undistorted and that the gains of the input and output stages are correct?

 

[dustbro]

R81 is the Q bias, correct? Is this correct, or are you suggesting that I jumper something still?

yup
Jumper were the red line is

 

[Siegfried Meier]

The shape and style of switches uaed to select parameters have no bearing whatsoever on calibration and testing of the unit. It's you own lack of understanding of what you are doing.

Did you perform the calibration of the GR FET bias correctly?
Did you verify the bias conditions on the BJT's?
Did you check that your supply rails are stable and correct?
Did you check that your components and wiring are correct?

Do your meters have internal diodes or do they require external circuitry to work as VU meters?
With GR displaed can you run a signal through the unit and observe that it is undistorted and that the gains of the input and output stages are correct?

GR Fet calibration set correctly.
BJT's are good and matched.
Voltage is 100% perfect, +-0v.
Components and wiring as good as can be, I believe. 

Like I mentioned, I've built many of the pushbutton versions now with hardly any trouble, and got this one half built second hand, and it's just frustrating trying to sort out.  In bypass, the unit sounds very clean, with tons of gain.  It compresses, and sounds as good as is to be expected.  It's just the metering that seems off.  And it's a Sifam AL19, which is just a mini version of the AL29 (and expensive as ****) so it should most definitely be a working VU meter if I'm not mistaken.

Thanks,
Sig

 

[gswan]

GR Fet calibration set correctly.
BJT's are good and matched.
Voltage is 100% perfect, +-0v.
Components and wiring as good as can be, I believe. 

You mentioned in a couple of posts ago:
[quote author=Siegfried Meier]
I have gone through the calibration process for Q bias, which is also messed up and doesn't react like my other pushbutton units did, but I cannot continue without solving this.[/quote]

Which would seem to suggest that your GR FET calibration is not setup correctly.

The Sifam AL19 meters are indeed true AC voltmeters and do not need anything other than the series resistor for reading VU.

You will need to check the circuitry around the metering FET to ensure that it is inserted correctly and biased in the same way as the GR FET.

Once you have verified that the GR FET is operating you should see voltage swings at the S terminal when compression is occurring.

The actual voltage change will depend on the amount of gain reduction.

The tracking (R54) pot adjusts the amount of this signal which goes into the TL071 buffer and the zero adj (R55) is used to apply an offset to the non-inverting input, allowing for a 'zero' adjustment.

If you don't get any change on the meter when turning R55 then you need to check your TL071 output and also the orientation of CR11 (the diode in series with its output).

If you are getting signal out of this section (at least 'zero' adjust DC offset signal on terminal 29) then you need to check your switch and meter wiring.

 

[Luny Tune]

Ok, here's something odd.  With the ratio set to 20:1, as suggested when adjusting Q bias, I can't even get to 0VU on the meter with .775 in.  If I set it to 4:1, it's perfect.  Something is really odd with these little Sifam meters.

No no, why do you reason that the meter's wrong?? The strange stuff happens when you change ratio... The logical conclusion would point toward the ratio board and it's surrounding components.

Triple-check resistor values (in particular) on and schematically surrounding the ratio board. There are resistors setting the offset voltage for the threshold there and it's not uncommon that people accidentally puts in a 470KΩ where a 470Ω resistor should be.

And it's easy to miss if you you just check it by looking at color codes in a "Yellow, violet...yeah that's 470Ω alright! On to the next one..." manner. That's what I mean by "Don't assume ANYTHING!"

Another thing. When setting Q-bias. Start by turning the trimmer CCW. That detail is left out i the guides I've read...

 

[Siegfried Meier]

I never look at resistor colour codes.  I can't even SEE the damn things.  So I must always use a meter, sadly.  It takes forever, but I'm guaranteed that they're right values.  However, I did not populate the board, as mentioned several times, but things seem to be ok.

I think the problem lies in these multi turn bourns pots.  They've been twisted so far that they're all whacked out and it's hard to find the "normal" range in them.  I just got the first channel to zero properly.  Need to go back and finish calibration there, but the second channel is not so good.  The meter bounces all over, down then pins - I think the pot may be bad.  Will replace and check again.

Thanks for the hints guys!  I'll be damned if all it is, is these trimpots.

Sig

 

[Siegfried Meier]

Didn't have a 2k for R55, but I had a 5k, which is fine.  GR zero works perfectly now, turned out to be a bad pot on side, and mad tweaking on the other that showed all kinds of wacky stuff on the meters.

On to real calibration now, and hopefully they should be all good.

Need to buy some 470k trimpots (can't seem to find, may have to get 500k) to try that threshold mod thing, so hopefully that works out.  If that's the case, that will likely solve the problems with the level in my Rev D's as well, instead of the turning the Cinemag around thing, which didn't seem to work out so well.

Thanks a bunch guys!
Sig

 

[dustbro]

Need to buy some 470k trimpots (can't seem to find, may have to get 500k) to try that threshold mod thing, so hopefully that works out. 

500k will work fine. I think I actually used 200k in some if mine and they worked.

 

[skal1]

i have a problem with the mnatts psu .The negative side keeps burning out the 120 ohm res and their is no movement in the variable pot, everything is the same as the supply on his site . input dc to reg is -36v  

 

[s2udio]

i have a problem with the mnatts psu .The negative side keeps burning out the 120 ohm res and their is no movement in the variable pot, everything is the same as the supply on his site . input dc to reg is -36v  

Been a while since i finished a dual 1176 using mnats psu ..and i remember a similar problem with the -10 rail
I think I found an error on the pcb with the trimmer connections,
compare the diagram point to point with the pcb tracks.....im'sure that was where the problem lies

 

[skal1]

@s2udio  ,Just worked that out had to blow a reg to find that out. ;D

regards


skal1

 

[onlymeeee]

Hi,

For the pots, is it ok to use 0.1w rating?  I know for resistors it's 0.25w or higher but is that the same for the pots?

eg. http://uk.farnell.com/tyco-electronics/cp16sh10ip6103bif/potentiometer-10k-log/dp/1227599

 

[onlymeeee]

As for the meter zero adjust trimmer.  If I want to panel mount it like the original (to be adjusted externally with a screwdriver).  Do I use a standard pot? eg. http://uk.farnell.com/vishay-spectrol/249-7-10-2k5/potentiometer-2k5/dp/9609318  Do Urei use something like this?

Or will it not be sensitive enough?

 

[gg85]

Hoping someone can help me with a few 2-1176 problems...the main one i'm having at the moment is my left channel input pot when wound completely CW causes me to lose all bottom end and the level drops off and becomes very thin. As soon as i back it off a little the level and bottom end come back. I haven't yet attempted calibrating the unit because of this, and the other issues i'm having are all metering so I'm sure there's a good chance they will be sorted out once I've calibrated it.

Thanks,

George

 

[Luny Tune]

@Onlymeeee
These work!
http://uk.farnell.com/tyco-electronics/23-esb-103-mmf-50nf/potentiometer-log-10k/dp/350175

Don't know if 0.1W is too little. These are 0.2W and I've used them. I would however recommend using better ones. They work fine but they ARE cheap and you DO sense that when using the 1176 a lot...which you will! I would recommend buying good quality for the input and output pots. They cost several times more than these but I think it's a good investment in smooth operation...

 

[pstcho]

hi, is that possible to use without output transformer?

is there a simple solution?

thank you

 

[Luny Tune]

Why would you?

 

[onlymeeee]

@Onlymeeee
These work!
http://uk.farnell.com/tyco-electronics/23-esb-103-mmf-50nf/potentiometer-log-10k/dp/350175

Don't know if 0.1W is too little. These are 0.2W and I've used them. I would however recommend using better ones. They work fine but they ARE cheap and you DO sense that when using the 1176 a lot...which you will! I would recommend buying good quality for the input and output pots. They cost several times more than these but I think it's a good investment in smooth operation...

Hi, the reason for me choosing those was because I'm building a dual and every millimeter helps. So the smaller the better. 

 

[Luny Tune]

Ahhh, ok...

I think this one is a step up in quality and doesn't cost very much more:

http://uk.farnell.com/bourns/91a1a-b28-b15l/potentiometer-10k/dp/9357769

 

[gswan]

Hoping someone can help me with a few 2-1176 problems...the main one i'm having at the moment is my left channel input pot when wound completely CW causes me to lose all bottom end and the level drops off and becomes very thin. As soon as i back it off a little the level and bottom end come back. I haven't yet attempted calibrating the unit because of this, and the other issues i'm having are all metering so I'm sure there's a good chance they will be sorted out once I've calibrated it.

Thanks,

George

Test and calibrate it first. Then you will know if there are problems.
- check PSU rails.
- check DC bias conditions for each transistor.
- perform basic gain stage checks with 1kHz signal.
- perform calibration.
- perform GR metering setup.