All things G1176 - the new "repost" thread.

[Siegfried Meier]

Ack, I'm a dolt.  Thanks for the tip 3nity, but this is actually what was wrong.  After reading this statement on Mnats site:

5k Trimmers - Optional (in place of R3, R5)

Duh, I also added in the resistors.  Cut them and it's perfect now!

Thanks,
Sig

 

[Siegfried Meier]

Ok, so both sides pass audio and are very quiet.  However, one side has no audible compression, and one does.  The zero adj pot (R55) doesn't seem to do anything to either side, and my ratio's (rotary) appear to be reversed from the labelling of the front panel??  Seems that whatever I've done, it's been done to both sides...

Pretty vague, but...any tips?  Working on a pair of Mnats Rev H here.

Thanks,
Sig

 

[Luny Tune]

I am building a mnats 1176 J and would like to get it to sound as close to the orginal H rev as possible.  I will be using a reissue B11148 output transformer which I'm hoping will get me closer than the Lundahl.
...
Anyone have any opinions on what I should use to get closer to the original?

I can't comment on mnats' boards and which revisions which boards are supposed to replicate but I can inform you that after some thorough testing I put a Cinemag CMMI-2C input transformer and a CMOQ-2S output transformer in my G1176's and sonically I can't tell them apart from the UA 1176LN.

I've got a little less input now since the CMMI-2C is stepping the signal down a bit. But the sound character is right on the money when compared to the re-issue in my opinion.

 

[Siegfried Meier]

How is it possible to see compression on the meter, albeit a small amount (R55 still doesn't work for zero adjust, no clue why), but not HEAR any compression?  This compressor is driving me nuts.  The rotary version is a huge pain in the ass.  I've made 4 pushbuttons with no problems at all and I can't even make 1 rotary that works.

 

[3nity]

make sure the wiring is right....for some reason my wouldnt compress and meter wouldnt track right because pad # 18 wire was missing.
Take your time and just make sure everything is just fine.

 

[Siegfried Meier]

Thanks for the tip again 3nity.  Pulling the boards out is a huge pain in the ass, even with the matrix pins, but I noticed that the Q bias pot wasn't soldered in !!!!  I bought these boards used and partially built last year, and had to replace/add some parts to them.  I have identical behaviour now in both channels regarding compression and metering - in GR, the meter shows -15dB and R55 does nothing to influence that.  Bypass works great, and +4 seems accurate as well.

Now why would that R55 do nothing...

Thanks!
Sig

 

[Siegfried Meier]

BTW, I'm using the Sifam AL19 meters, same as in the orginal dual UA's.  Don't think this should matter though...

Thanks,
Sig

 

[3nity]

I used this instructions to calibrate my 1176:
http://www.axtsystems.com/index.php?view=article&catid=34%3A1176ln&id=56%3A1176lncalibration&option=com_content&Itemid=62

 

[Siegfried Meier]

Can't even touch the calibration yet until I figure this GR problem out.  Both R55 and tracking do absolutely nothing to the meter visually...

 

[3nity]

you cant hope to track well if its not calibrated.....you shouldnt even pass audio before calibration....its not me who said that but everyone says that....

 

[Siegfried Meier]

Ok, I'll go through it, but I don't think it's going to help my meter problem...

Back at it tomorrow.

Thanks!
Sig

 

[gswan]

Did you check that your DC bias conditions for all your transistors appears sensible? This is a good start to weed out any obvious faults with reversed or incorrect parts.

Make sure your PSU rails are in order and perform the calibration of the gain reduction stage. Meter tracking is pointless until this is done.

Verify your compression ratios for a range of settings and input amplitudes.

Adjust the meter tracking to track what the GR FET is doing and disply it on the meter.

 

[Luny Tune]

How is it possible to see compression on the meter, albeit a small amount (R55 still doesn't work for zero adjust, no clue why), but not HEAR any compression?

That's easy enough. There are two FET transistors in the 1176. One for the signal path and another for the meter. One (and it's surrounding circuitry) could easily be out of order and the other working fine in which case you would hear compression but not see needle movement or vice versa.

Remember that these are well tested boards. You simply made an error somewhere and since you have the same error on both boards odds are that you are actually assuming that you did everything correctly. See? You repeated the error... That's why you have to go through everything methodically like it was someone else's work, not assuming anything at all. Check and recheck ALL(!!) component values and orientation as well as all wiring. And don't assume that you did ANYTHING right what so ever.

Also check if the Q-Bias trimmer is turned fully CCW. I think that would pretty much disable the machine or at least give you very little/light compression...

 

[Siegfried Meier]

Thanks, but that's long been fixed as mentioned above.  I'm on to new issues now haha.

I didn't build the boards, they came from someone else.  Lesson learned, always build up your own boards, and then you know what went into them and what could be wrong.  I've been very successful with nearly every build I've done.

Thanks,
Sig

 

[Luny Tune]

Sorry, I was homing in on your post just below mine where you asked about how you could "see but not hear" and I didn't see anyone answering that question...

 

[skal1]

It might be a stupid ?, is    the ratio board set up the slam mode with the rotary switch, or do i have to do some soldering pins together.

regards

skal1

 

[dustbro]

Both R55 and tracking do absolutely nothing to the meter visually...

If you used a small trimmer for R81, make sure you jumper pads for the center pin.

But now that I look at it, I guess either square pad can be used (depending on trimmer size) for point 18.

 

[Siegfried Meier]

R81 is the Q bias, correct?  My pot connects to the centre of your red line, and then the other 2 points where it says R81.  Is this correct, or are you suggesting that I jumper something still?

Q bias works fine now, it's just the GR that isn't reading or being affected by R55 and R54.

Thanks!
Sig

 

[Siegfried Meier]

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. 

Thanks,
Sig

 

[Siegfried Meier]

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.

Thanks,
Sig