All things G1176 - the new "repost" thread.

[gyraf]

So the DC levels change at point7 with ratio, and stays changed?

The second part of the ratio switch, with R42-43-44-45-46-87 and C21, adds different negative bias'es to the anode (-side) of the FD333 diodes. This is the "threshold" to be overcome before the two FD333 diodes conduct and start gainreduction.

Check your DC voltage at point 21 with no signal. It should be between 0 and -10V, but in any case below 0V.

Try lifting one end of both the FD333 diodes, and recheck if ratio alters gain (it will change a little, but not much). If so, then the ratio setting affects the "Q-bias" - possibly because of an error around R74-75 and C21. Check orientation of C21.

Also, this could be because of an error in either C19 or C20 - if one of these are leaking DC, then you'll have constant over-threshold DC at the input of the diodes.

Jakob E.

 

[orson whitfield]

Maybe I have the incorrect value at C21. The schematic shows a 100/+25V. I have a 100uf 35V there. I think I remember asking if this was ok but I'll make sure now. Is it?

 

[orson whitfield]

[quote author="gyraf"]Check your DC voltage at point 21 with no signal. It should be between 0 and -10V, but in any case below 0V.
Jakob E.[/quote]

I haven't done the other things yet but this did result in voltage below 0V in every setting of the ratio switch with no signal passing.

 

[orson whitfield]

[quote author="gyraf"]So the DC levels change at point7 with ratio, and stays changed?[/quote] YES

[quote author="gyraf"]Check your DC voltage at point 21 with no signal. It should be between 0 and -10V, but in any case below 0V. [/quote] YES IT IS.

[quote author="gyraf"]Try lifting one end of both the FD333 diodes, and recheck if ratio alters gain (it will change a little, but not much). If so, then the ratio setting affects the "Q-bias" - possibly because of an error around R74-75 and C21. Check orientation of C21.[/quote] YES IT DID CHANGE. I checked the orientation of C19, C20 and C21. All were o.k.


[quote author="gyraf"]Also, this could be because of an error in either C19 or C20 - if one of these are leaking DC, then you'll have constant over-threshold DC at the input of the diodes. Jakob E.[/quote] So I guess the thing to do at this point is to get new caps for C19, 20 and 21? Does the fact that the meter changes with the ratio setting change the performance of the unit?

 

[orson whitfield]

:shock: Oh boy! Here I am about to resolder the FDH333's back into place and I notice a hole in the PCB not filled by the leg of anything. After a careful look I see that I have the 1000/35V electr. cap with both legs near each other when it appears that one of them needs to be in that open hole. Before I change this could some one tell me if I am not seeing this right? It's cap to the immediate right of BD517.

 

[gyraf]

If the gain/meter changes with different ratios even when the two diodes are lifted, then the problem must come from a point later than this.

So C19-20 are probably alright.

C21 100u/35V is fine. You can always use higher voltage rating - it's a maximum rating.

The only thing I can think of that would provoke this error, is shorts or wrong resistors around the ratio switch. That is, the second part of it, where the negative offset is added to the rectifier. Somehow this influences your "Q-bias" backwards, and it should'nt.

The voltage at point21 SHOULD change between some -5V and the voltage set with "Q-bias", when you adjust ratio. Check that this happens.

Jakob E.

 

[gyraf]

Orson,

That 1000u/35V is just an extra reservoir cap for the +30V. You could get a bit more noise if it's not there, but I don't think that this is your problem. There are two pcb holes - to accomodate wierd-size caps.

Jakob E.

 

[salty]

Hi I'd like to say a big thankyou to everyone on this board most definitely including the people asking questions!!

I'm making a G1176 at the moment and I'm currently at the stage of fitting all the wiring to the board and mounting it into the box. To be honest I'm stuck here, I don't know which of the 3 legs of the potentiometers to put to which hole on the board. Can anyone help me please?

BTW I couldn't get a 4.7m pot anywhere, so I bought a 2.5m pot and a 2.5m resistor and a switch. Which leg of the pot should I fit the switch/resistor to?

thanks,

Nick Salt

 

[Svart]

where are you from salty? in the USA, mouser sells 5M pots. let me find the part number...31VA605. it's made by alpha. they are 1.25$usd a peice. all the other pots can be purchased from the same series too so they all match.

 

[salty]

Hi Svart,

I'm in Newport, South Wales, UK. Farnell has been my supplier so far. I'm quite happy to go with the switched release pot, in fact I'm quite proud of my humble solution, it's making the thing more mine

If this unit goes well I will definitely be building another 2 or 3 of them as I would like a 1176 on snare and room mics simultaneously, and I needed to order 10 of most of the resistors from Farnell leaving me with a surplus.

Anyway to the point eventually - If my switch thing turns out to be a pain in the neck I'll need to find a 5m pot, and Farnell only seem to have the trimmer type, so I may have to order from the US - cheers for the info mate.

Salty

 

[gyraf]

Salty,

Page1 in the G1176 layout .pdf has a description on how to mount the pots.

For the resistor in series with the release pot, are you thinking of using a potentiometer with integral switch? In that case, connect the resistor across the switch, connect one end to the start of the pot, and use the other end of the switch as potentiometer end. This way you have the resistor in circuit only when you turn release speed all the way down to the click.

Jakob E.

 

[orson whitfield]

Jakob,

Does the problem I have with the meter effect the operation of the compressor itself? If not, I would like to call it quits on this. I really don't care anymore if the meter is accurate. I just want a compressor that sounds good. At this point, I am burned out and don't think I will make my next project one that needs to be calibrated in any way.

 

[Rob Flinn]

Jakob or anyone who has built this,

When the meter switch is in bypass mode should the meter still display the output signal ?

 

[mnats]

I never could find the stereo link diagram from the old forum on my HD. Does anyone have the modified stereo link that Jakob altered to make work?

 

[deanp920]

I never could find the stereo link diagram from the old forum on my HD. Does anyone have the modified stereo link that Jakob altered to make work?

Hi,

It is really simple: just put the series resistor(82k) on the other side of the pot; the circuit will still work the same but will allow you to adjust up to zero offset, say, if your FET's are perfectly matched...although with the matched FET's you can simply connect the two points without the circuit and be just fine. Rig the circuit on the JBLservice schematic like I've explained here and you'll have no problems.

Jakob or anyone who has built this,

When the meter switch is in bypass mode should the meter still display the output signal ?

No, the meter is OFF in bypass mode.

Dean

 

[Rob Flinn]

Quote:
Jakob or anyone who has built this,

When the meter switch is in bypass mode should the meter still display the output signal ?
No, the meter is OFF in bypass mode.

Dean

Thats interestng because both sets of calibration instructions tell you to set the unit into bypass mode & put a signal into the unit that shows 0dB on the meter, when adjusting q Bias. It also looks like it should work on the original diagram, but I`m getting nothing ?

 

[deanp920]

Dean

Thats interestng because both sets of calibration instructions tell you to set the unit into bypass mode & put a signal into the unit that shows 0dB on the meter, when adjusting q Bias. It also looks like it should work on the original diagram, but I`m getting nothing ?

The G1176 has the meter grounded in Bypass mode. You'll need to use an external meter for Q-bias setup.

I did a little diagram a while back that gets meter function in bypass mode: http://www.home.earthlink.net/~deanp920/id1.html

Dean

 

[Rob Flinn]

Thanks Dean.

Its a bit weird that it cuts off in bypass , because it it works in by pass on my real 1176.

 

[gyraf]

Yes, but there's changed quite a lot around the metering/bypass in order to use a standard rotary switch, available anywhere..

Jakob E.

 

[deanp920]

Jakob's meter switch design also excels in the fact that the VU meter is completely out of the circuit in bypass mode as well as GR mode.

For the purist wanting the G1176 as a line amp only, I've heard that this is a good thing. Apparantly the VU's rectifier sans buffer amp causes some distortion when placed in parallel with the audio path, although I have yet to hear it myself.

All in all, I decided not to use my meter mod. I just don't pay much attention to the meter. The thing is almost always in 'Nuke' mode, with the needle banging all over the place, or even in normal mode the meter is flying out of it's range by the time I get the kind of smooth pressed sound I like. For levels, I look at my DAW's input meters.

The Sifam makes a very impressive power indicator light, however. :grin:

Dean