All things G1176 - the new "repost" thread.

[imo]

Brad,
Please post results when you do.
Ian

 

[mdrenthen]

Hello I'm new here and the proud owner of a DIY 1176 with Mnats boards.
I don't have the time to read al the threads, so if I ask a quistion thats already been asked, i'm sorry.

Here's my first problem.
With no signal on the input and the meterswitch in GR mode, the meter walks slowly around the zero point and never is steady, not even after an hour.
Adjusting it with the zero pot. does not help.(onley for a minute)

Second problem.
With the same singal, input and output settings my 1176 shows the same gain reduction in all the ratio settings.
I also checked this on a external output meter.
Maybe the 1176 react in a other way than a 'normal' compressor?

Please help me out with this one....thanks....many thanks..

Michel

 

[gyraf]

For the meter moving around slightly, try cleaning the pcb board area around the meter fet and related circuits. It's very high impedance, so even a little dirt can disturb it.

With the same singal, input and output settings my 1176 shows the same gain reduction in all the ratio settings.
I also checked this on a external output meter.

Normal, and has been discussed before. If you look at the schematic, you'll see that the threshold is altered with ratio to acheive this. But if you set it to just 1dB of GR, the ratios should give you different results.

Jakob E.

 

[Gustav]

first of all - any way to search within this thread? (I read through a lot, but not everything to look for my problem)

Second. - I have a G1176 that seems to be fine electronicly, and the compression seems to work like it should - however - it only outputs hi-end. I have tried running it both balanced and unbalanced pin3-ground shorted, with no change.

Would it be totally idiotic to try switching the lundahls? Any other suggestions?

Gustav

 

[Gustav]

[quote author="gyraf"]Andre,

Look for a balancing issue on cabling. I'm pretty sure that's it.

Jakob E.[/quote]

Found an answer to a similar problem on page 46....Ill check up on it

Gustav

 

[gyraf]

Gustav,

Yes, searching is becoming a bit hard within the posts. There is a good, but not simple way to search in long forum threads:

(from meta-meta)

-----
About searching:
As you have probably already found, the integrated forum search-engine can be a pain to use when searching for information in some of the long-long threads. Mike (user insideout) has come up with an elegant solution to this - involving the browser "Firefox" and a plugin called "ScrapBook". This really enhances searches over many-many pages, like the giant error-fixing threads.

Mike has put together an easy-to-follow howto, found at: http://mikeinak.googlepages.com/home

And yes, I'm pretty sure that you have a balancing issue. Make sure that both your + and - outputs has connection to the output transformer secondaries, and make sure to connect - to ground (on both input and output) when interfacing to unbalanced stuff like your new patchbay :razz:

Jakob E.

 

[mdrenthen]

[quote author="gyraf"]For the meter moving around slightly, try cleaning the pcb board area around the meter fet and related circuits. It's very high impedance, so even a little dirt can disturb it. [/quote]

Ok I'll try that.
Can it be that some of my components are of he wrong type?
I use BC107MC instead of the BC107A/B/C
And for the TL071 I use an TL071CN version.
The rest is the same as dicripted in the partlisting.

Normal, and has been discussed before. If you look at the schematic, you'll see that the threshold is altered with ratio to acheive this. But if you set it to just 1dB of GR, the ratios should give you different results.

The gain reduction stays the same at all ratio settings.
The meter is moving towards the right corner when switching the ratio and than returns. I checked the wires and they are all connected to the wright pads.

Michel

 

[gyraf]

[quote author="mdrenthen"]
Can it be that some of my components are of he wrong type?
I use BC107MC instead of the BC107A/B/C
And for the TL071 I use an TL071CN version.
The rest is the same as dicripted in the partlisting.[/quote]

..Shouldn't be a problem at all..


[quote author="mdrenthen"]
The meter is moving towards the right corner when switching the ratio and than returns. I checked the wires and they are all connected to the wright pads.[/quote]

..It's normal (also on originals) that meter misbehaves when you operate the ratio switch..

Jakob E.

 

[mdrenthen]

Normal, and has been discussed before. If you look at the schematic, you'll see that the threshold is altered with ratio to acheive this. But if you set it to just 1dB of GR, the ratios should give you different results.

I tried again but the gain reduction stays the same at every ratio setting.
I put a signal to the input, turn the input level on the 1176 up adn stop at a GR of app. 1 dB.(at ratio 1:4)
Then I switch to ratio 1:8 and 1:12 and 1:20 and the gain reduction stays arround 1 dB.
That should be more at a higher ratio..or am I mistaking?
If yes.....what could be wrong then??!!

..It's normal (also on originals) that meter misbehaves when you operate the ratio switch..

Thats a relieve then. :grin:

Michel

 

[gyraf]

You need to make up a complete input/output level chart for the different ratios in order to verify that they work correctly - simple tests are probably not revealing enough.

If it turns out ratio'ing the same on all settings, the only place where you could have gotten this wrong is at the resistor-ladder divider at the ratio switch - which you may want to double-check for solder blobs and right wireing and resistor values.

Jakob E.

 

[mdrenthen]

[quote author="gyraf"]You need to make up a complete input/output level chart for the different ratios in order to verify that they work correctly - simple tests are probably not revealing enough.

If it turns out ratio'ing the same on all settings, the only place where you could have gotten this wrong is at the resistor-ladder divider at the ratio switch - which you may want to double-check for solder blobs and right wireing and resistor values.

Jakob E.[/quote]

I am testing it with some protools tracks with different ratio settings and in/out settings, and now I understand the 1176 a bit more.
It's indeed not like other compressors...it's better. :wink:

Thanks Jakob, for helping me out so far.

 

[bradb]

I did some brainstorming this weekend on the input power transformer issue. I don't think the 1:1 to 2:1 is going to help.

Think about it like this.

If we drop a signal that input into the 1176 by 3dB (cutting it in half, basically 1:1 to 2:1) does that change the threshold? No.

The input threshold is a function of the FETs, not the input tranny.


Jakob, when I swapped out different FETs to try to raise my input threshold, all of them were basically the same. Do you think we need to pursue different FETs or different biasing? Any ideas we can pursue?

thanks!

 

[gyraf]

The BF245A should be in the right area.

Are you absolutely sure that your input level potentiometer is the correct type, i.e. a log one, not a lin? A linear pot at the input level would behave like you describe.

Jakob E.

(ps: ½voltage is -6dB)

 

[bradb]

Jakob,

I think I posted somewhere on prodigy about the Log / lin pot issue (ok just found it). I know I have an audio pot in my 1176, BUT what if I and everyone else with this problem bought audio pots with the WRONG characteristic.

take a look at this:
http://www.efunda.com/math/exp_log/images/exp_log_plot.gif

Sounds crazy, I know, but if you have an exponential characteristic instead of a log characteristic maybe you end up with this "you must have a linear pot in there" problem.

I'll try to get some time to investigate this.

EDIT: by the way, here is the input pot I ordered (from Mouser.com)


Mouser P/N Alpha P/N
31VJ401-F RV24AF-10-15R1-A10K Alpha (Taiwan) Audio 10K

 

[gyraf]

Taiwan-Alpha "A10K" should be the right type!

To check if a pot is Log or Lin:

Try measuring pot resistance from viper to either end with the pot in (more or less) centre position - if it's a log, there should be a big difference in resistance, if it's a lin, the resistances will be approximately the same..

Jakob E.

 

[al_p]

Hey Brad, Ian and others with this problem,

I tried using the 2N5457 in place of the BF245. It's what Purple Audio is using in theirs, and what was used the original...

I built a dual unit, so I kept the BF245 in CH 1, and popped the 2N5457s in CH 2. After matching and calibration I'm getting about half as much compression as the channel with BF245, with the same input settings. Promising. It's reacting much more like I am used to.

Jakob, do you have any comments on using this FET in your circuit?

So that's the good news. the bad news is the my input arrangement isn't quite right. The ganged pots I pulled from those UA routing modules aren't quite the right values.

Does anyone know any details of the original dual ganged 600 ohm T bridge attenuator? What makes it so special? Can you not just use a dual 600 ohm audio taper pot with tight specs? I was thinking about ordering a couple from Precision.

Also, a question for those who have built a dual unit. I have a slight noise problem which seems like an interaction between the 2 channels. If I listen to channel 1 cranked, I have a little hum. If I disconnect the output XLR of channel 2, the hum clears up same result with this test on channel 2. The same thing happens if I disconnect the AC power to the other channel. I have the secondary of the power TX paralleled to both channels.

thanks for any input.

 

[imo]

I built the "SL1176", which is Eddie Cilleti's and Scott Liebers version of the 1176. They use the 5457 as well, and i am able to get quite a bit more headroom with it. The specs don't look that different, but who knows.
I have an audio 10k input as well, but i am going to measure just to be sure there isn't anything funky going on

 

[bradb]

Al,
Thanks for pursuing this, this does sound promising:

You say it has half as much compression as the BF245 channel. What do you mean exactly, like the compression ratio is different, or are you talking about the input threshold?

If 0 on input is 7 o'clock, where is the threshold point with these new FETs?

Regarding the 600 Ohm T attenuator. All I know is that originally it was installed before the transformer and always presented a 600 ohm input impedance.

Thanks!
bb

 

[imo]

I measured the input pot and found that at about 75% of the way clockwise the resistance starts to lessen. It gets to about 2.7k and then goes back down to about 1.2k with the knob turned fully clockwise. The 2 10k resistors on the output of the input transformer are measuring a bit above 700r a piece in circuit. Does this sound funky?
I am curious to know how you guys wired your input section. I used the Lundahl 1540, and used Mnats wiring guide in hooking it up.
From the input pot (10KA):
clockwise tab goes to pin*1( output of input transformer)
wiper goes to pin 2 of the input gain
couterclockwise tab ties the shield of both the clockwise and wiper tabs together, and goes to pin 3 of the input gain

 

[imo]

I measured the input pot and found that at about 75% of the way clockwise the resistance starts to lessen. It gets to about 2.7k and then goes back down to about 1.2k with the knob turned fully clockwise. The 2 10k resistors on the output of the input transformer are measuring a bit above 700r a piece in circuit. Does this sound funky?
I am curious to know how you guys wired your input section. I used the Lundahl 1540, and used Mnats wiring guide in hooking it up.
From the input pot (10KA):
clockwise tab goes to pin*1( output of input transformer)
wiper goes to pin 2 of the input gain
couterclockwise tab ties the shield of both the clockwise and wiper tabs together, and goes to pin 3 of the input gain

Ian