[BUILD] 1176LN Rev D DIY

[JdJ]

[quote author="nerd"]
JDJ: How are you hooking up the bypass? I put a resistor in the R-OPT1 spot and hooked the switch up to where the wiper would be. I figured that since this is for threshold adjustment, I would basically be swithing the threshold in and out (so high that it doesn't do anything). I don't know if this thinking was correct.[/quote]

Nerd: check your PM. Since there is a "bypass" position on the Meter board already (I believe it switches out the sidechain) I was going to do a hard bypass between the input/output jacks. That way I can use it as a line amp for flavor (meter switch bypass), or hard bypass to check between compressed and uncompressed signals.

-Josh

 

[nerd]

Since there is a "bypass" position on the Meter board already (I believe it switches out the sidechain) I was going to do a hard bypass between the input/output jacks.

Damn! I am an idiot. I just went back and re-read the Purusha case thread. Early on someone says that the bypass bypasses the meter only, then later on someone counters that saying that it does turn gain reduction off. So, the other bypass is for a hard bypass, direct xlr in to xlr out.

 

[shabtek]

how is that 600 ohm t-pad working out?? isn't that a pretty heavy load for modern gear...I've got the altran input and a 4 pole switch to build the attenuator and I'm wondering if 600 is going to be useful if somebody plugs in the output of an 002...

any suggestions?

 

[Stagefright13]

I am using the Mallory 600 ohm T-Pad and works perfectly as a send (Out Then Back In) With my 002r. Although I use it for tracking mostly I have run lots of other tracks thru it with the 002 out.

 

[Bri]

Been trying to calibrate GR tracking for the past few days.

Before I replace the fets(spent hours testing and matching), I wondered if anyone had any other ideas:

Unit is compressing.

Triple checked the wiring.

Meter seems to be okay...reads -4db running a .775VAC signal through it.

Following guidelines on Gyraf's site for GR tracking, I adjust the needle for the 6db of reduction, I remove input signal, and needle moves about 2db back toward 0, I'll zero the needle, apply input signal again and the needle only moves to -1db, so I adjust down to -6db again...and this process goes on and on without change in characteristic until my "0 Set" trimmer(R71) cannot be adjusted anymore(full CW).

All my fets were matched to within 4%

My ratio switch seems to be functioning backward.
I get the most gain reduction when it's switched fully counter-clockwise.

I had my ratio switch set for 6 positions for a while, before I realized it.
Strange things were happening when I switched to position five and six.
The compression level would drop and then slowly ramp back up...took about 6 seconds.

I had the unit running for about five minutes without the main board grounded.

For awhile, I had a piece of cardboard under the main board instead of standoffs...perhaps the fets didn't like this?

Well, any thoughts would be appreciated.

--Brian

 

[dissonantstring]

hi brian,
if you are using a lorlin-type enclosed rotary you might want to try removing the stop pin from it and turning the switch until it reaches it full CCW position (essentially the first position) then put back the stop pin to stop at 5 positions. you can do a search, i believe others here have had similar problems with the switch being off and jakob suggested it IIRC. this basically resets your switch so that position 1 is really position 1. not sure if this is the solution, but it at least will let you know if your switch is the problem.
regards,
grant

 

[Bri]

Hi Grant.

Yeah, I verified the switch/pin positions...seems correct.
I have the Lorlin 2-pole 6-pos.
Others have said the switch orientation didn't matter.
So as an experiment, I did configure the switch in the other positions...such as using only the last four positions.
However, the same thing still occurs, a couple db more GR when turned CCW.

I'm more concerned about not being able to set the GR tracking at all.
However, these two issues may be related, huh.

Any more ideas?

--Brian

 

[dissonantstring]

hi brian,
o.k. going back to you first post about this problem:

[quote author="Bri"]
Meter seems to be okay...reads -4db running a .775VAC signal through it.[/quote]

so this is after fet conductance calibration and in GR mode at 4:1 ratio?
so with no signal and in GR mode your meter is at 0dB and in +4 mode it rests at -20dB?

I had the unit running for about five minutes without the main board grounded.

if you're talking about the pad GND on the side of the board between pads 20 and 18 then do not worry about this. i forgot myself and powered up my board for longer than 5 minutes - no issues, though i haven't calibrated it all the way yet due to me wanting to mount my FPE front panel before calibration.

For awhile, I had a piece of cardboard under the main board instead of standoffs...perhaps the fets didn't like this?

naw, as long as it wasn't shorting on the chassis or anything the fets wouldn't be harmed.

check mnats site for the link the the JBL website and download the 1176 manual. the calibration procedure is on pg. 39-40. try calibrating to that instead. can't say that i can help much as i'm still quite a newb and have difficulties troubleshooting my own builds, but lets post away to see if anyone sees the problem.
regards,
grant

 

[Bri]

Yeah, I have those pages from the manual printed out...among others.
I've tried at least three different methods of GR tracking adjustment.

Yes, all after Fet adjustment (Q bias).

If I turn the meter switch to VU mode, and run a 1khz 0db(.775vac) signal into the unit, turn input control all the way down, and turn output control all the way up, I get a -4db reading on the unit's VU meter.
When I remove the input signal, yes, the meter drops to -20.

With meter switch to GR mode, with or without a signal, Meter reads 0VU...
Unless of course I turn up the input control...which it will show gain reduction.
However, with my skepticism about the ratio switch, I'm never sure if I'm at 1:4 or 1:20.
The meter does show a db or two more reduction when I turn the ratio switch all the way left....which I'm assuming shouldn't happen.
I assume 1:4 ratio should be the first stop of the switch...continuing on to 1:20(fully CW)....correct?

Thanks for the help....you're less of a newb than I.

--Brian

 

[Bri]

Given that others have mentioned the ratio switch and it's affect on threshold, I guess I'm not too worried about the ratio switch just yet.

What I would like to know is, what would be the cause for the unsuccessful GR tracking adjustments.

--Brian

 

[Bri]

Guess I'll just swap the relevant transistors....and note any changes.

--Brian

 

[mnats]

[quote author="Bri"]If I turn the meter switch to VU mode, and run a 1khz 0db(.775vac) signal into the unit, turn input control all the way down, and turn output control all the way up, I get a -4db reading on the unit's VU meter.
When I remove the input signal, yes, the meter drops to -20.[/quote]
If what you have written is correct, the result shows something is very wrong. Have a look at the schematic and try to follow along.

Whatever the signal you are feeding into the input of the circuit, the first thing it should hit is the input attenuator. If you have the input control all the way down as you describe, there will be little signal getting through.

Now looking at the output circuit, the X and Y points from the output transformer feed the meter switch. When switched to the +4 (VU) mode you are reading the output of the Signal Line Amplifier.

With not much going in to the compressor there should be not much coming out, so the meter shouldn't even register. By actual measure on my unit using the input signal you specify, the input control full CCW and with the output control full CW, the reading is -26dB...off the bottom of the scale.

Fix this problem first because without a good idea of the actual output you won't be able to accurately know how much gain reduction you're getting - therefore you won't know what you are trying to set your GR Meter Driver to show!

[quote author="Bri"]Given that others have mentioned the ratio switch and it's affect on threshold, I guess I'm not too worried about the ratio switch just yet.

What I would like to know is, what would be the cause for the unsuccessful GR tracking adjustments. [/quote]
Even though there appears to be a problem with your ratio control, no, it does not necessarily mean that you would not be able to calibrate your GR Meter Driver circuit. After all, you say you are getting gain reduction. Once you know how much gain reduction is happening (with the VU meter on the output or +4 setting) the goal is to calibrate the GR Meter Driver circuit to reflect that reduction in gain.

A common misconception, I think, is that the calibration procedure affects the compression action of the 1176. In fact, once you do the Q Bias adjust procedure your 1176 is compressing the way it always will. The calibration of the GR Meter Driver circuit is only so your meter will show how much gain reduction is happening in a way that is easily readable for humans. The compressor itself could care less about how the meter circuit is calibrated.

For calibration instructions, stick with the manual from the JBL site. As I've said elsewhere there doesn't seem to be any way to write it clearer than the original manual. Remember that this isn't a G1176 circuit. Some of the trimmer designations are different between the Rev C/D/E circuits than the F/G based G1176 version.

By the way, have you first calibrated the discrete meter circuit as described on page 40 of the big manual download?

 

[Bri]

Hey thanks mnats.

Yeah, I've got all those pages printed out in front of me.
I do get confused at the point where it says to trimpot to zero with the attack all the way CCW.
Because, this is our bypass mode correct?
My meter doesn't function in bypass mode...should it?

Been troubleshooting for quite awhile.
I thought maybe I had my t-pad wired incorrectly.
I've wired it a few different ways since....looking at the Purple schematic.
I'm still unsure how to verify it's correct.
When it seems to be wired correct, I still get the ".775vac coming through" problem, when input control is full down and output control is full up.

In fact that's what led me to believe I have it wired wrong since the "low wire" connecting to the t-pad seemed to be more or less a straight connection the the input transformer. I figured that's why the .775vac comes through when input control is full CCW and output control full CW.

However, there is a peculiarity I've noticed.
When I'm turning the input control CW, and I get to a little past 3/4 of the way to fully CW, the signal starts to suddenly and dramatically attenuate from then on.
This happens in bypass mode...actually, it didn't matter which meter setting.
Is this indicative of something obvious?

--Brian

 

[edanderson]

PLEASE DO NOT PM ME

sold out

ed

 

[Bri]

I'm not sure if my t-pad is working properly.
These are the resistances from mine...the two deck, group buy PEC.
Can someone verify if these are correct.
I arbitrarily numbered the terminals.

Full CCW
1-2: 2ohms
2-3: 37K
1-3: 37K

4-5: 18.5K
5-6: 96K
4-6: 87K


Full CW:
1-2: 43K
2-3: 13.5K
1-3: 37K

4-5: 87K
5-6: 1.6ohms
4-6: 87K

Thanks.
--Brian

 

[drpat]

...

 

[Bri]

Thanks Patrick! Very useful info.

I'll have to turn the input down fully when calibrating.
On this clone, the GR bypass is done using the meter switch, which also bypasses the meter.

Quick question.
Is that 0dbu and then -10 dbfs?"
What would the equivalent of -10dbfs on your Pro Tools system be in dbu or dbv?

I'm still unsure about wiring the t-pad.
I checked resistance continually while turning from CCW to CW, and it has strange characteristics.
Steady going, then sudden big spike, then sudden big drop, then up steady again until fully CW, for example.
This test was done bare, not in circuit and no resistors.
Didn't know if this was characteristic of a t-pad...or if mine is was "irregular."

--Brian

 

[Stagefright13]

Maybe your t-pad is a little scratchy? Is it an NOS? Try running the wiper up and down a bunch of times to get it cleaned up. Are you using an 0-12 input transformer or one of the clones? Mine was pretty finicky using a temporary 1:1 input tranny 'till I got the right one.

 

[Bri]

Hey John.

I'm using the group buy, PEC...along with a UTC-A20.
Should be cool...yes?

--Brian

 

[drpat]

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