All things G1176 - the new "repost" thread.

[kenrinc]

Got ya. Thanks. I went through the Qbias adjustment and that went perfect. The other calibration procedures are done in GR mode and my meter just pegs when switched into that mode, I'm going to need to figure out why. The meter adjust doesn't work. R54 does nothing on my unit. VU meter is always pegged in GR mode. I'll try swapping the trim pot.

Ken

 

[kenrinc]

Replaced the pot and no change. I do notice that the meter "slams" against the far side with less force when the pot is fully CW than when it is CCW. So when it's CW it's a gentle slam as opposed to a hard slam. 100k pot at that location.

ken

 

[gswan]

I doubt it has anything to do with the pot. It's more likely that the meter tracking has not been calibrated correctly.

 

[lofi]

can any body give me a quick pointer to the maths needed to turn a DMM reading into the meter readings or is it not possible? ive not got a meter yet so was hoping to set it roughly with a dmm. I will be using it within my DAW so the meters really not needed as the infos on the screen.

ho hum,

Iain

 

[kenrinc]

Jeesh, I know I'm going to get through this eventually :roll: I couldn't understand why it was telling me to turn CW on the output knob when the first instructions tell you max the output!! Anyway, I backed off on R55 and that allowed me to at least get the meter pin the ballpark. Done.

This is probably related to Ian's question, as I cannot get my function generator to output anything less than .600v per my DVM hooked up across the XLR (which may be an incorrect way of measuring). Tried measuring from the outputs of the generator, still only .6v lowest I can get. Can I somehow use a resistor to get it lower? You mentioned that DVM's aren't accurate to 250hz.

At this point things are looking might close to being finished.

Ken-

 

[lofi]

Ken, whats 0.6V in RMS?

 

[kenrinc]

Ok figured out my generator had 2 modes, needed to pull out the output pot. Now I can set it to .245v with the generator feeding the unit and me measuring at the XLR input. Is this correct? If so, the Attack control does nothing :sad:

Ken-

 

[gswan]

[quote author="lofi"]can any body give me a quick pointer to the maths needed to turn a DMM reading into the meter readings or is it not possible? ive not got a meter yet so was hoping to set it roughly with a dmm. I will be using it within my DAW so the meters really not needed as the infos on the screen.
[/quote]

Firstly make sure that your DMM actually works at the frequency you are trying to measure. Many cheap DMM work great up to 100Hz but are of no use after that.

You need to inject a sine wave, so the DMM will read RMS voltage correctly. The reading on the DMM will be RMS. If you need to convert this to dBu, then the reference is 0.7746V (ie 0dBu = 0.7746Vrms).
Conversion is then: dBu = 20*log(V/0.7746)
For dBV, where the reference is 1V, the conversion is:
dBV = 20*log(V)

Here's a site that will do the conversions for you onscreen:
http://www.sengpielaudio.com/calculator-db-volt.htm

 

[kenrinc]

Ian,

I'm assuming the meter does the math since that's what it's called, a true-rms DVM. So a read .6v (or whatever) is RMS.

Ken-

 

[gswan]

[quote author="kenrinc"]Ok figured out my generator had 2 modes, needed to pull out the output pot. Now I can set it to .245v with the generator feeding the unit and me measuring at the XLR input. Is this correct? If so, the Attack control does nothing.
[/quote]

If you are feeding a continuous sine wave into a compressor, what would you expect the attack pot to actually do?

 

[lofi]

i ask about the rms thing as i dont know if your DMM reads in rms or just volts, if its the latter it will be a highr reading than the 0.254 that gets mentioned. out of interest does it sound like its compressing?

Gain Reduction Meter Tracking

1. Set the controls as follows:
Control
Set to
Input middle
Output fully CW
Attack fully CCW (switched to OFF)
Release fully CW
Compression ratio 20:1
Meter mode GR
VR54 trimmer 1/4 turn from fully CCW



2. With no signal applied, adjust VR55 so that the meter reads 0VU.

3. Apply a 0.245Vrms (-10dB) 1kHz sine wave signal to the input.

4. Switch the meter mode to +4dB.

5. Turn the output level control CW until the meter reads 0VU.

6. Turn the attack control ON (CW) and observe the drop in the meter reading.

7. Adjust the input level control until -10dB is indicated on the VU meter.

8. Turn the attack control OFF (CCW) and re-adjust the output level control for 0VU meter reading if necessary.

9. Repeat steps 7 and 8 until the output drops 10dB whenever the attack control is turned ON.

10.Without adjusting the input or output controls, select the meter mode for GR.

11.Adjust VR54 until the GR meter reading reads -10dB when the attack control is ON.

12.Adjust VR55 until the GR meter reads 0VU when the attack control is OFF.

13.Repeat steps 11 and 12 until the results are consistent.

 

[kenrinc]

Ok guys, I'm a bit confused.

Gain reduction meter tracking:
I set the controls as mentioned on Geoff's site as well as those posted before (from manual) In=mid, out=full cw, attack full ccw, release=full cw, 20:1, GR mode

VR54 adjusted roughly 1/4 from ccw

No signal, adjust VR55 so that meter reads 0vu. Done.

Apply .245v rms 1khz sine to input. I'm assuming the DVm won't work well measuring level here even though I've used it to check for .245v

Switch meter to +4

"Turn output level CW until meter reads 0vu." The output level control is already at full per the instructions. How am I supposed to adjust CW if it's already full?? Are you saying adjust output to 0vu? I can do this but when after using input to set level to -10 I can't make up enough gain to bring it back to zero. Says to adjust attack cw and observe change on meter. My attack control does nothing.

PS: FWIW, I have it hooked up and passing audio. Mic pre -> 1176 -> DAW. Gain controls are working well. Signal is really clean and almost no noise! Maxing input and setting output to say 3 I can just barely make the meter move.

 

[lofi]

maybe it should be adjust input cw untill you get to 0 on the vu, then turn the attack to activate the meter in gr and adjust, leave the output alone, its post meter? just got up so my head is still fuzzy.

Iain

 

[gswan]

[quote author="kenrinc"]
"Turn output level CW until meter reads 0vu." The output level control is already at full per the instructions. How am I supposed to adjust CW if it's already full?? Are you saying adjust output to 0vu? I can do this but when after using input to set level to -10 I can't make up enough gain to bring it back to zero. Says to adjust attack cw and observe change on meter. My attack control does nothing.[/quote]

Turn the output control back a bit, say about half way, so you have some adjustment room. It's relative levels you are calibrating here. The attack pot has the GR bypass switch on it, so turning it CW activates the GR and turning it CCW switches GR off. If you aren't using a switch on the attack pot then you have to use your switches to engage/disengage the GR amp.

 

[gswan]

[quote author="lofi"]leave the output alone, its post meter?[/quote]
The level metering (+4, +8) is connected to the output directly. The GR metering is done using a FET and an op amp driven by the same GR amp as the compression FET.
The meter tracking adjustment is attempting to get the meter to show what is happening at the signal FET by calibrating out the differences between the two FETs. It's a bit easier when the FETs are reasonably matched.

 

[kenrinc]

Well all be. I didn't know the attack pot was supposed to have a switch I'll assume that was on the original. So, going with the process in the 1176 manual, meter switch at +4, adjust output/input to 0db THEN switch meter switch to GR and turn attack pot CW and observe drop in meter. Adjust input until -10db on meter, then turn attack CCW and meter switch back to +4 mode and readjust output control for 0vu. This sound correct?

Ken-

 

[lofi]

Ker nob head alert!!!

ive done something wrong, i am on page three of this but if some body can post the relevant page i would be appreciative.

it passes audio, but it doesnt sound like its working :?: i have oep in and out, i loaded a wave into my daw, then played it through the comp, and recorded it back in, it sounded the same, i would have imagined the oep's would have coloured the sound a little?

also i have made the slam switch but it only makes a difference when i put it into slam mode, then it gets louder rather than quieter, all other modes dont do any thing.

i have not got a vu meter, so i set the fet by playing my cable tester into my ada8000 and using digi check to set the gain to 0 (using the K14 system than i prefer in the studio) then setting the 1176 as stated in the vu calib instructions, but taking the meter as the digicheck to +1 then moving the trim to drop this back to zero.

im on the wireing check tomoz. but if this rings bells for anybody please post a link

Iain

 

[gswan]

First perform a measurement of your compression ratios to see if it's working as a compressor and also to see where the threshold it and how close the ratios are to what's marked on the panel.

Details here:
http://www.axtsystems.com/index.php?view=article&catid=34%3A1176ln&id=54%3A1176lnratios&option=com_content&Itemid=62

I'm not sure why you would expect 'colouration' from your transformers. The compressor should work fairly transparently using normal operating levels. There will be colouration when the circuits and transformers are driven hard.

 

[gswan]

[quote author="lofi"]i have not got a vu meter, so i set the fet by playing my cable tester into my ada8000 and using digi check to set the gain to 0 (using the K14 system than i prefer in the studio) then setting the 1176 as stated in the vu calib instructions, but taking the meter as the digicheck to +1 then moving the trim to drop this back to zero. Iain[/quote]

I'm not sure that this is going to work. You need to be measuring dBu, not dBFS (or at least find the relationship between dBFS and dBu for your system).

You need to feed a 1kHz sine wave into the unit at a voltage level of 0dBu (0.7746Vrms) and then use the input pot to get enough gain to show +1dBu on the meter. Then adjust the Qbias so that we are just into conduction at this point (ie starting gain reduction by 1dB). By using any other input voltage level, you are changing the threshold at which compression starts, which is probably not what you want. If your compressor does not have a VU meter on it then you might want to go and buy one, since they can be very handy to have around.

 

[kenrinc]

I went through the GR meter tracking process again tonight.

Although I get nice sounding signal through the amp sections I get no response using the Attack control. I apply the 1khz signal, switch to +4 mode on the meter and turn input and output to mid. Then use output to set meter at 0vu. Then it says "turn attack control on" I'm assuming since I don't have a switch on the attack control, I have to switch to GR mode. When I do this, turning the attack control does nothing on the meter.

Ken-