All things G1176 - the new "repost" thread.

[al_p]

Brad,

So I strapped the compressor across a pair of busses, applied a 1k tone, and with matched knob positions the 5457 channel was showing 3 dB of gain reduction, while the 245 channel was showing just about 6 dB. I know it's kind of an un-scientific way of examining this, but practical application is what I'm building this for. With program material the difference was more sublte, but noticable for sure.

 

[bradb]

imo, that sounds like it makes sense, as you go clockwise resistance should decrease. on a side note, i think the 10k resistors should be 12k according to lundahl.


Al, did you match both of the new FETs so that the meter tracks? Did you observe this difference in compression on the unit's meters or on the input to a DAW or board or whatever?

are we getting close?


sorry i havent been contributing, i'll have some time this weekend.

 

[imo]

I wonder if you can make earings out of the 245's>? I've got a lot of them.
I popped one in and had only a couple of moments, but it did seem a little lighter on the compression than the 245..Need for time, must have more time..
Thanks for the tip on the 1540. I looked at the pinout on the specs, but didn't notice the resistance change. I will try a couple of 12's
Ian

 

[gyraf]

This is a bit wierd - my original tests for compatible FET's showed that the BF245A's (at least the three different samples that I got hold on) to be spot-on compared to our Real1176'es.

Could it be sloppy marking, or different manufacturing process messing up? I know too little about real-life FET behaviour to be sure of where this problem comes from..

For now, I don't really know how to get around this - obviously we've run into some non-trivial component tolerances and/or specifications.

A possible simple solution could be to reduce sidechain signal feed level - that will have the same effect as raising the threshold.

We can do this by lowering signal level at the first half of the ratio switch - this part adjusts threshold to match up with different ratios:

Look at the schematic and layout - find R26 - which is 56K - connected to Point15 and the top of the "out level" pot. You will find it on the ratio switch subboard.

If you increase the value of this, you increase the ratio of the voltage divider, and in effect reduce the level going to the rectifier amplifier circuits.

Try with a value of say 100K or 220K in stead of this 56K - or better, try soldering in a 470K trimpot in series with the 56k, which would allow you to find and set a threshold value that suits you. (Maybe it's time for an upgrade of this old-old design - adding a front-panel control for variable threshold? :grin: )

Jakob E.

 

[al_p]

Thanks for the comments Jakob. I'll investigate this, but I'm pretty happy with where my 5457 channel is at right now.

Roger, just to recap, I agree, this compressor sounds GREAT. I spared no expense on components and I think it might even outperform the other 1176s I have. My problems were getting the controls to respond the way I am used to. It was really disorienting before I started all my jiggering, but I'm almost there.

 

[imo]

amen..It is such a gift to be able to build units of this quality, and i agree that they are really beautiful sounding. There are so many resources and people with knowledge that are willing to share their design knowledge.
It has really helped me as well to understand a lot of the other gear that i have been using in my studio, as well as the general sonics of a lot of things that i have just taken for granted for years.
Cheers Jakob

 

[jlearman]

Hey gents, I'm just a few steps from getting the mnats boards of my dual 1176 stuffed. I have some noobie questions about parts & part numbers...

first of all, on the mnats psu, does anyone know what those thingys for attaching the input/output wires are called (i.e. wire from toroid & wire to main board)? Even better, does anyone know a part number for mouser/digikey?

Also...I don't think mnats has a diagram for the power supply, so I don't know which cables to attach where. The wires from my toroid are different colors than the one in his picture, and since I don't even know what the hell a toroid does, it's kinda hard to figure out.

Big thanks for entertaining my questions guys...here's a picture of the psu for reference:

 

[mnats]

does anyone know what those thingys for attaching the input/output wires are called (i.e. wire from toroid & wire to main board)? Even better, does anyone know a part number for mouser/digikey?

Here they are just called PCB Mount Screw Terminals or Terminal Blocks. A quick scan of the Mouser catalog turned up this: 571-2828373 but check out the specs before ordering it to make sure it will clear the components around it. You could also simply solder the wires to the pads as usual by passing them through the holes in the top and soldering them underneath.

Put some heat sinks on the voltage regulators!

Also...I don't think mnats has a diagram for the power supply, so I don't know which cables to attach where.

The pads that are marked AC-CT-AC go to the transformer secondary. The ones that are marked V+ and V- are the Positive and Negative DC pads that power the main boards. There is a Ground pad in between the positive and negative that isn't marked.

The wires from my toroid are different colors than the one in his picture, and since I don't even know what the hell a toroid does, it's kinda hard to figure out.

It's been discussed many times - do a search (hint: I have linked to one explanation on my wiring page). There doesn't seem to be any standard for wire colors on the transformer secondary so you will have to learn to read the symbol and possibly connect two wires to make the center tap.

 

[gyraf]

:thumb:

 

[rbaker]

I'm finally getting around to finishing my 1176 which has been sitting for almost 2 months untouched.

I have 2 questions. on the gyraf site it says to make sure the center tap of the power transformer is connected to ground---I assume that only means via the 0v on the board, not the chassis ground or iec ground? input xlr ground goes to chassis then to iec and that's it right?

secondly I have to hookup the lamp for my sifam meter.

I've done some reading and it looks like the lamp connection is giving 36v. I know there's the gyrad board and the mnats and most of them seemed to be talking about mnats, I'm using gyraf. Still 36v?

Can someone check my math? this is new to me.

12 volt lamp, 1.2 watts. (.1 amps)

I need a 24 volt drop

resistance is = 24v/.1A = 240ohms?

power = 240 x .1 x .1 = 2.4 watts?

So I assume I need a 240 ohm 2.4 watt or greater resistor. The place I'd buy it lists a 220 ohm 3 watt, or a 300 ohm 5 watt. Should I shoot for a higher resistance to keep the light burning longer or does the 22o ohm sound ok?

Thanks

 

[imo]

YOur math is right. I would go with the bigger resistance and the longer bulb life. It worked great for me

 

[bradb]

Ok,

First of all, thank you to Jakob and Mnats, a very experienced, compressor maniac, engineer friend of mine prefers my 1176 to his reissue 1176. Thanks for making this project available to us here and for consulting and troubleshooting with us.

Jakob, I'm trying your idea of replacing R26 and its definitly working. After trying different values, I found that 760K is about right for me...

HOWEVER, the ratios are messed up, I'm doing the meter track calibration and I get a higher compression now at lower ratios. 20:1 is the lightest compression. I verified this also by looking at input and output in PT metering.

I am now sticking with a R26 of 270k. I thought I was getting a bit extreme, but still my ratios are screwy. Maybe try 100k?

If we change the input to the voltage divider, don't we also need to change every other resistor in that circuit?

 

[jlearman]

Since mnat's boards have the two optional inputs, is it possible to install a switch that toggles the input from the transformer input to the electronically balanced input? Similarly...if I'm going through the transformer input, and I install the parts in the "optional" section...will it screw anything up? I'm assuming that if you go into the transformer input, that the entire path of the other input is bypassed....

not sure if that makes any sense...but I'm curious if anyone has done something like this.

thanks,
joe

 

[gyraf]

Brad,

Yes, I see that now.

Unfortunately I do not have a G1176 around to experiment on.

A better approach will probably be to install a 100K trimmer pot at the input to the sidechain, as a simple attenuator/voltage-divider (from the top of the output level pot at the ratio subboard) and keep the 56k as-is.

If you try this, please let us know how it turns out!

Jakob E.

 

[bradb]

Jakob,

Something like this?

i'll post results as soon as its complete.

 

[gyraf]

Nope - rather input (from out level pot's top) to top of the trimmer pot, output from viper (to the 56K), bottom to ground.

Ya'know - a standard attenuator - like the output level pot..

Jakob E.

 

[Dr nEon]

Hi All!

Very quick question...

A have been given a couple of panel mount leds (satin 14mm red) that rs sells . They are rated 24-36v dc , 17mA , and look ideal for power indicators on my G1176s which I've almost finished.

Question is, would it be best to feed one of them from just after the bridge rectifier , before the voltage regulator?

I am already using up the vu lamp feed for the meter leds , so I can't see any other place where I could feed this new indicator from..

I assume this type of indicator has dropping resistor built in,and that I shouldn't need to put anything else in series with it ?

Many Thanks!

nEon x

 

[bradb]

Jakob,
Thanks, will try it ASAP!

 

[gyraf]

Question is, would it be best to feed one of them from just after the bridge rectifier , before the voltage regulator?

Take it before regulator.

I assume this type of indicator has dropping resistor built in,and that I shouldn't need to put anything else in series with it ?

If the mentioned specs are correct, it's a drop-in. But you never know - consult data sheets for the item..

Jakob E.

 

[Dr nEon]

Ok will do!

Thanks very much , Jakob! :thumb:

nEon.