All things G1176 - the new "repost" thread.

[kenrinc]

Appreciate all the help so far. Many of my shielded wires are only long enough to make the connection from board to destination so it's difficult to get in and at the board in order to measure or do things. I'm probably going to lengthen them all so I can lift the board up and check things. The tell tales signs were that everytime I went to turned the unit on it would behave differently. I initially had input and output working (no compression) so I know I did have some of it right :roll:

Ken-

 

[mtw]

Greetings,

This is my first post on the board. I've just finished my first project (building a Hamptone JFET pre) and have got the DIY bug. Im thinking the 1176 would be a great 2nd project.

Right now I am working on putting together a BoM for a mnats board.

What is the proper voltage to use for the poly and ceramic capacitors? The BoM from his site doesn't specify and I don't want to buy the wrong parts. I've found Greg's BoM but thought that going through the motions of actually finding all the parts myself would be a good learning experience.

Thanks in advance,

-mtw

 

[gswan]

Since it has a 30V supply rail, I'd suggest either 50 or 100V caps, which are very common and easy to get.

 

[mtw]

[quote author="gswan"]Since it has a 30V supply rail, I'd suggest either 50 or 100V caps, which are very common and easy to get.[/quote] Thanks for the reply! I was able to find all of the ceramic caps in 100V versions except for the 100p (C100, C101) which Mouser only had as 50V.

 

[kenrinc]

OK let's try this gain. I posted some new scope pics here: http://www.kenrinehart.org/1176/1176.html This is just the scope from XLR to input pot then output pot.

Ken

 

[gswan]

Looks good. Gain is about 25.5dB which is correct.
You can try the next stage as well. Measure the input to the next stage (wiper of pot) and the output (capacitor feeding the transformer). The gain should be about 10dB

 

[kenrinc]

Sweet. I've posted the scopes of the Q2, Q3 and Q4 bases. I don't get much of anything at the bases of Q5 - Q9. Nothing. Remember Q1 has been removed.

Ken

 

[gswan]

If you get nothing at the base of Q5 it's because your output pot is probably turned down. Turn it up a bit and measuer the signal there and also on either side of C15. If the signal's clean and the gain is around 10dB then it's probably working OK as an amplifier.

After that you can insert Q1 and start the calibration procedure for the compressor part.

 

[kenrinc]

Gotcha. Turned output pot up a bit and now have signal at base of Q5. Have signal at all the others too; C6 - C9. C15 also has signal although the wave form looks really wacked the further I turn it up (see webpage). The VU meter pegs within the first 1/4 turn of the output knob and I can hear a faint "hum" that get's louder the further I turn the output CW.

Ken-

 

[gswan]

Thta's because you have a lot of gain on the input stage. You can turn the input knob down a bit (say to halfway).

A faint hum is either power supply or most probably an earthing problem. I wouldn't worry about it yet. Get the basic operation of the circuit working first and then, after it's in the box, make sure your earthing scheme is correct.

 

[kenrinc]

Input was 1/2 way but I'll verify again later. I've verified grounding per mnats site but the actual wall socket I'm plugged into is not grounded (it's an old house). I'll see if I can swap for an actual grounded socket as I did hear hum in the unit initially.

Will insert Q1 and try calibration.

Ken

 

[kenrinc]

Yeah I see what your saying. Maybe input pot set 1/4 of the way up and output allows you to tailor it pretty well. The rest of the amp section looks like it's working well. Better than before, but I cannot figure out why I get output even though the input pot is full CCW. Using a small amp hooked up to the output connector I hear the test tone. There is some noise along with it.

Ken-

 

[gswan]

That sounds like you don't have the GND connected to the bottom of the input pot. Check that it is connected and also connected to the GND of the PCB, otherwise the input pot is not going to work correctly.

 

[kenrinc]

OK your right there. If I put my thumb over the gnd terminal (where the shields meet) the problem goes away and I can use the input pot as normal. Problem is I completely just re-soldered all the connections including preparing and installing new wire to/from the pcb to the input pot and it still does the same thing. It thought there was a short in one of the wires because when I moved it the problem went away but I replaced the wire checking for shorts with a meter before installing it and the same thing happens. Is there a specific GND connection for the PCB? I don't remember one in the mnats build info. Maybe I forgot it? Input XLR is grounded at that location. Power trannie grounded at it's location.

Is the pot body to be grounded to the chasis or should I isolate them? This wasn't apparent in the build instructions either. I noticed if I press the body aginst the chassis the problem also goes away.

Ken-

 

[adoucette]

Is there a pdf or psd file of the front plate of a G1176 available? Im thinking like a generic one with the markings for adjustments but then can be personalized.

Thanks
Andre

 

[kenrinc]

There are many GIF and JPG files. Jakob has one at his site. Probably best you head on over to NRG and check out his frontpanel files.

http://www.nrgrecording.de/html/schaeffer.html

Ken-

 

[kenrinc]

OK, found the problem with the input pot. No ground because the ground lug is either broke or come loose from it's substrate. If you bend the lug back it works. Replaced 10k input pot with new pot. Works! Made longer connections to the PCB too so now it's easier to move the board around for changes.

I went ahead and soldered in Q1. Did Qbias this way: input 250hz signal with DVM hooked up to 2 and 3 on output xlr. Output full CW. Attack full CW. Release full CW. Meter: No GR. Turned up input until I got 1.55v on meter, turned Qbias until I got .775 on meter. Wasn't sure how to "see" 1db drop on the DVM.

Meter still pegs when I set it to GR. I thought it was the trim pot but I replaced it 3 times to no avail.

Ken-

 

[gswan]

Sounds like you haven't calibrated it correctly or set the GR meter tracking.

How do you know your DVM is accurate at 250Hz? Most aren't.
Going from 1.55V to 0.775V is a 6dB drop. Why do you want to do this?

 

[kenrinc]

Probably because I'm not sure wtf I'm doing? :grin: I"m asuming I can't use the GR meter itself to do the calibration? I have some notes I took awhile back: 250hz signal .3v. Attack, release fully cw, 4:1 and output full. Get a readable reading on the DVM, say 100mv Adjust Qbias until 1db drop in output. DVM is reading volts. Don't know how I'm supposed to see a 1db drop.

Ken-

 

[gswan]

It's not just a GR meter, it's also a VU meter. It reads VU directly from the output signal level with the series 3.6K resistor. You can use this meter to read signal level directly. How well this works depends on the quality of the meter you have selected, however most meters are Class 2.5 or better which is acceptable here.

Use a 1kHz signal and perform the calibration the way it's supposed to be done. That way if something's out we'll be able to see where.

If you don't already have a calibration procedure, there's one here:
http://www.axtsystems.com/index.php?view=article&catid=34%3A1176ln&id=56%3A1176lncalibration&option=com_content&Itemid=62