[BUILD] 1176 Rev F/G - new board, new transformer!

[frazzman]

Please open up the schematic on the first page of this thread.  Locate pad 22, it's near the middle-bottom.  You'll see a "22" near C17, that is pad 22 and everything to the right of it is your main PCB.  If you follow the trace up you'll see it leads to the GR odd switch (back of the attack pot) then to 1/2 of your ratio switch and eventually to your output pot.

So in a nutshell, the audio output (AC) of the first amp stage is tapped off the output pot and sent through a simple resistor ladder (the ratio switch) where the AC is decreased depending on the ratio selected (it goes through more resistors as the ratio gets higher) and then fed to pad 22 which is at the start of the GR amp. 

So you have no AC at pad 22 with GR on?  But you are passing signal which means you have AC at your output.  So you're losing it along that path.  Let's look at the schematic and trace your audio from the output pot to the GR amp and see where is stops. Make sure GR is on. 

1. There is a wire that goes from the output pot to pad 15 on your ratio PCB.  Your AC at output pot and pad 15 should be the same. Check?  If not the wire is messed up.
2. Pad 4 on the schematic is where your audio exists the ratio PCB.  This pad is listed as GRN on your ratio board.  Check your AC here.  It'll be smaller depending on the ratio selected but it should still be strong.  Check?  If not there is a problem on the ratio PCB.  This is my guess for your issue.
3.  With GR on the GRN pad should be connected to your wire connected to pad 22 via your switch.  Check for audio at GRN on your attack switch and pad 22.  Check?  No signal here means your switch is wrong.

Mike

Hey Mike,

I ended up ordering ratio and meter PCBs from you so I rebuilt this build using push button ratio and meter PCBs and wiring. This seems to be more thoroughly documented than the rotary builds. Anyhow, I wired everything up as per the wiring pages on mnats page. All the push button assembly is working fine, however I still have the same issues I had before (no GR) so I've ruled out the ratio board as a point of failure.

Following your troubleshooting tips, its apparent that theres no AC at GRN on ratio PCB, and obviously as a result none on attack s/w or point 22 on mainboard.

I've gone over all the wiring between meter & ratio PCBs and wiring between all pots - everything appears correct as per mnats well documented guide.

So theres obviously something a miss on my mainboard, after checking all resistor values and obvious things like shorts etc, I can't pin point anything. Are there any other points you could suggest I check which might explain why theres no AC at GRN?

Once again appreciate your patience and assistance!

 

[Echo North]

Have a look at the schem on the first page.  Feed a 1K 0dB(ish) signal into your unit and get 0dB on the output?  Are you passing signal?  if so see where the AC is not getting to your sidechain.

-You should have AC coming out of your first amp stage and it should be present at both sides of C9.
-You should have AC at pad 15 of the ratio and the output put lug it connects to.
-in ratio 4, check for AC at R22,24,25,26.
-check for AC at the pole of your GR off switch
-check for ac at pad 22.
-check for AC on both sides of C17

If you look at the schematic, you'll see the path I'm following.  Where does the AC die?

Mike

 

[frazzman]

Have a look at the schem on the first page.  Feed a 1K 0dB(ish) signal into your unit and get 0dB on the output?  Are you passing signal?  if so see where the AC is not getting to your sidechain.

-You should have AC coming out of your first amp stage and it should be present at both sides of C9.
-You should have AC at pad 15 of the ratio and the output put lug it connects to.
-in ratio 4, check for AC at R22,24,25,26.
-check for AC at the pole of your GR off switch
-check for ac at pad 22.
-check for AC on both sides of C17

If you look at the schematic, you'll see the path I'm following.  Where does the AC die?

Mike

Thanks Mike will check that tonight, I've got signal passing in each of the meter modes (and needle moves correctly) and audio passing in GR but no compression obviously.

Just to clarify - with audio passing, and measuring GRN at each ratio - I should be seeing strong AC and going up incrementally as ratio increases ? What I mean to say is with no AC at GRN is this an indication that there is definitely an issue with a resistor on ratio board ?

 

[Echo North]

Ya so your AC comes off the pot and passes thorough one of the resistor ladders on the ratio PCB.  The lower the ratio, the more resistors the AC passes through and the smaller it gets.  It should still be pretty strong though, above 0.1 VAC at 4 and closer to .4 VAC at 20.  Roughly and depending on settings...basically it should be way more than 0.002 VAC or something like that.

If your passing signal and not getting AC at pad 22 you either have an issue on that ratio PCB (again follow it through the ladder to see where), or your GR off switch is wired wrong (make sure 22 isn't shorted to ground).  Remember GRN is not ground , BLK is ground.  GRN just means they used a green cable and it should be connected to 22 with GR on.

Mike

 

[Echo North]

Also just for clarification. 

On the Rev F schematic:

GRN=4 (signal)
BLK=23 (ground)

So if your switch (S1) is correct 4 is connected to 22 for GR on.

 

[frazzman]

Also just for clarification. 

On the Rev F schematic:

GRN=4 (signal)
BLK=23 (ground)

So if your switch (S1) is correct 4 is connected to 22 for GR on.

Hi Mike,
I've been through all of your notes, looks like there is something up with the attack pot / gr switch wiring. I have continuity between GND and "22" when I shouldn't. I've attached diagram of my attack pot switch wiring and measurements as follows:

1) AC at both sides of C9?
-  Leg closest to terminal block around .290VAC
- Leg away from terminal block ranging from 2-5VAC
2) AC at Pad 15 and output lug it connects to
- Yes, same AC reading at lug and at "15"
3) In ratio "4" - check AC at R22, R24, R25, R26]
- R22 = .136VAC, R24 = .056VAC, R25 = .069VAC, R26 = .055.VAC
4) AC at pole of GR off s/w?
- Yes, ranging between .100VAC - .150VAC on both A and C lugs
5) AC at pad 22?
- No
6) AC at both sides of C17
- Yes, and strong VAC reading on both legs.
7) "22" shorted to ground? YES
- On a DMM I get continuity between switch lugs B ("Ground"), and C ("Connection to "22") - is this normal?
- As a result it means that there is continuity between "22" and "23" on the mainboard

Thanks once again

 

[Echo North]

C on the switch should have continuity to ground/4 in the off position and none to 23.  In the on position it should be opposite.

Is this true for you?

 

[frazzman]

Argh! Problem solved! I didn't take into account different pinout of 2n5088 transistors compared to 2n3707 in GR section. Feel like such a dumb ass!

Mike - thanks so much for your help, you got me onto the right track

Lesson learnt - observe component orientation if substituting components!

 

[frazzman]

In the process of calibrating this unit.... got the Q-Bias adjustment down. The unit seems to show that its compressing and the attack and release pots affect the level of compression, but it doesn't 'sound' like its compressing, I am guessing due to calibration not being completed fully.

I'm stuck trying to complete the GR meter tracking adj.

I'm not getting the required meter 'drop' on the VU meter when enabling GR. The meter barely moves when turning attack pot from off position (enabling GR)

I'm generating a 1Khz sine wave from Cubase, i've got a DMM across input XLR pins and i'm measuring .746 VAC (aiming for the required .775)

Any suggestions?

 

[Echo North]

In the process of calibrating this unit.... got the Q-Bias adjustment down. The unit seems to show that its compressing and the attack and release pots affect the level of compression, but it doesn't 'sound' like its compressing, I am guessing due to calibration not being completed fully.

I'm stuck trying to complete the GR meter tracking adj.

I'm not getting the required meter 'drop' on the VU meter when enabling GR. The meter barely moves when turning attack pot from off position (enabling GR)

I'm generating a 1Khz sine wave from Cubase, i've got a DMM across input XLR pins and i'm measuring .746 VAC (aiming for the required .775)

Any suggestions?

Sorry I'm confused.

Are you able to get a 10dB drop at the output XLR or meter with the jumper in the correct position.  Not sure if your issue is with actual compression, the meter displaying it, or both.

Mike

 

[frazzman]

In the process of calibrating this unit.... got the Q-Bias adjustment down. The unit seems to show that its compressing and the attack and release pots affect the level of compression, but it doesn't 'sound' like its compressing, I am guessing due to calibration not being completed fully.

I'm stuck trying to complete the GR meter tracking adj.

I'm not getting the required meter 'drop' on the VU meter when enabling GR. The meter barely moves when turning attack pot from off position (enabling GR)

I'm generating a 1Khz sine wave from Cubase, i've got a DMM across input XLR pins and i'm measuring .746 VAC (aiming for the required .775)

Any suggestions?

Sorry I'm confused.

Are you able to get a 10dB drop at the output XLR or meter with the jumper in the correct position.  Not sure if your issue is with actual compression, the meter displaying it, or both.

Mike

Hi Mike,

Sorry I might not be explaining it very well.

Problem 1:
Basically i'm trying to complete Step 3 of the calibration - the meter tracking calibration as per mnats video: http://www.youtube.com/watch?v=IOzaWP8ACLs

For this adjustment - As I understand it - you feed in your 0.775v 1khz sin wave , put the unit into +4 and disable GR using attack pot switch (or jumper b/w gnd + pin 22), then adjust input & output pots until the meter ends up at 0db VU. You then enable GR again via attack pot switch and observe the meter drop. The aim is to achieve a -10db drop when these settings are satisfied. This is the point in which nothing happens for me, when I enable GR again via attack pot switch there is no drop. I've been following some feedback on the Rev D thread where people have had simular issues.

Problem 2:
As a side issue - now that i've corrected the orientation issue with the transistors in the GR circuit - everything appears to work as it should - i.e. all the knobs and ratios affect the signal, at least visually on the VU meter - but It doesn't "sound" like the unit is compressing.

I was thinking problem 2 is linked to problem 1, or vice versa?

The finish line is drawing closer but still some way to go....

 

[frazzman]

I'm starting to think that I must be going deaf, or insane or maybe both.
The 1176 isn't known for its transparent compression but that said and done.... I haven't a rev F before.

I was convinced I was getting little to no compression despite the meter telling me I am. As I said before, I haven't been successful in completing the tracking calibration, so its safe safe to say that the GR reading on my meter is most likely pretty off. Q Bias calibration was successful however.

That said and done, I did a test by running some drum overheads through the comp - and to take my ears out of the equation I did a comparison of the original and uncompressed wav's in TT Dynamic Range Meter and found that the original untouched wav had 13db of dynamic range and the compressed file with the most aggressive settings set on the 1176 came out with only 6db of dynamic range, so clearly compression is working.

It still doesn't feel right though, can I attribute this to lack of calibration?

Everyone knows what the all-in ratio button sound sound's like, but I don't seem to be able to replicate that yet!

Thanks! and end of rant

 

[Echo North]

like using a decent DMM fr calibration.  One that can handle 1K signals.  Most do, they may say they are rated for 500Hz but most +$30 DMM's can handle the measurement of a 1K sine reasonably enough.

-Start by setting you meter to "0" in GR mode with no signal applied.
-Set you input and output to 12 o'clock, attack fully CCW (GR off), release full CW, 20:1, GR mode
-Inject a 0dBu (0.775VAC) into the input.  Confirm that you have 0.775 VAC between pin 2 + 3 of your input with your DMM.  Increase your signal as needed to get to 0.775 (impedance loss and all that).
-move your DMM to pin 2 + 3 of the output.
-Adjust your input pot so it reads +10dBu (2.45 VAC) on the output.  On a D and A this is usually around roughly 3-4o'clock.  Not sure about the F.
-Now turn on GR by turning your attack full CW.
-Adjust your output pot so you get 0dBu (0.775VAC)
-Now play with both so you get roughly +10 with GR off and 0 with GR on.  That's 10db of compression and you'll then know for sure you are compressing
-Make the tracking adjustment so your meter jives with it.

Mike

 

[frazzman]

like using a decent DMM fr calibration.  One that can handle 1K signals.  Most do, they may say they are rated for 500Hz but most +$30 DMM's can handle the measurement of a 1K sine reasonably enough.

-Start by setting you meter to "0" in GR mode with no signal applied.
-Set you input and output to 12 o'clock, attack fully CCW (GR off), release full CW, 20:1, GR mode
-Inject a 0dBu (0.775VAC) into the input.  Confirm that you have 0.775 VAC between pin 2 + 3 of your input with your DMM.  Increase your signal as needed to get to 0.775 (impedance loss and all that).
-move your DMM to pin 2 + 3 of the output.
-Adjust your input pot so it reads +10dBu (2.45 VAC) on the output.  On a D and A this is usually around roughly 3-4o'clock.  Not sure about the F.
-Now turn on GR by turning your attack full CW.
-Adjust your output pot so you get 0dBu (0.775VAC)
-Now play with both so you get roughly +10 with GR off and 0 with GR on.  That's 10db of compression and you'll then know for sure you are compressing
-Make the tracking adjustment so your meter jives with it.

Mike

Hey Mike - getting there... but still not quite able to do this final Calibration . My DMM can do 1K signals no worries.

-Start by setting you meter to "0" in GR mode with no signal applied. - OK Here
-Set you input and output to 12 o'clock, attack fully CCW (GR off), release full CW, 20:1, GR mode - OK Here
-Inject a 0dBu (0.775VAC) into the input.  Confirm that you have 0.775 VAC between pin 2 + 3 of your input with your DMM.  Increase your signal as needed to get to 0.775 (impedance loss and all that). - OK Here - confirmed 0.775 VAC at pins 2 + 3 of input XLR
-move your DMM to pin 2 + 3 of the output.
-Adjust your input pot so it reads +10dBu (2.45 VAC) on the output.  On a D and A this is usually around roughly 3-4o'clock.  Not sure about the F. - Measured 2.45VAC across output XLR - its about 3-4o'clocl on this too.
-Now turn on GR by turning your attack full CW. - Done - but is this the part where I am supposed to witness the elusive meter drop that I can't seem to get? Turning on GR doesn't make the needle move much at all.
-Adjust your output pot so you get 0dBu (0.775VAC) - You mean unity gain so 0.775vac on output and input xlr pins? If so - done.

I'm able to follow all steps up until here. By 'playing with them both' do you mean adjust input and output pots until I get 0VU when GR is off and -10db when GR is on?

-Now play with both so you get roughly +10 with GR off and 0 with GR on.  That's 10db of compression and you'll then know for sure you are compressing
-Make the tracking adjustment so your meter jives with it.

Unless I have misinterpreted I think i'm getting stuck since my meter isn't behaving as expected when turning GR on and OFF via attack switch, what do you think? Cheers Mike

 

[Echo North]

So it sounds like you're getting your 10dB drop at the output but GR metering is not working?

Check EVERYTHING in the meter portion of the PCB.  Are you getting a - DC at your meter FET gate?

 

[frazzman]

So it sounds like you're getting your 10dB drop at the output but GR metering is not working?

Check EVERYTHING in the meter portion of the PCB.  Are you getting a - DC at your meter FET gate?

Hi Mike,

Following your suggestions and checked everything in meter portion of PCB - it all checks out. All resistor values are correct.  As are the other component designations. The only thing I could think of was maybe something was up with the trim pots but they appear to be working fine in that they move the meter needle intuitively. I could remove them to verify their values but I checked them and all resistors with a DMM before soldering them. I've visually verified every resistor value on the entire board. I get - DC at the meter FET gate, I can't recall the exact reading as I'm not in front of the unit right now.

The compelling thing is that when in GR mode and with some audio going through, say a snare track for example, the gain reduction meter seems to work fine, it responds to all changes on the attack, release and ratio. I don't have much confidence in the actually GR reading (i.e. it might say its 20db of GR but it really sounds like about 5db for example).

I've attached a quick snapshot of how the meter board section looks incase you can see anything that I might have missed? You can also see the transistor orientation in the GR circuit section, i'm using the alternate pinout due to using 2N5088 transistors, i'm confident that the orientation of these is now correct.

Yours sincerely.... mr confused

 

[Echo North]

Wacky.

So what you're saying is:

1. The meter doesn't move in GR metering when you're trying to do the tracking adjust and you actually see a 0dBu to 10dBu on the output between GR on and off
2.  When you just use it on say drums, the meter behaves like it should in GR metering (although not calibrated)
3.  Moving the zero adjust and tracking adjust do change the meter position in GR metering?

Mike

 

[frazzman]

Hey again Mike - need to commend you ... hairball support is great so many thanks.

To answer your points:
1. To clarify - no... turning on and off GR does nothing to the output. I guess that's why the needle stays put. The only way I get those measurements is by inputting 1khz sine wav then putting DMM across output xlr and adjusting output pot until I get 2.50vac. But again, GR on/off switch does nothing to output!
2. Yes exactly
3. Yes both can move needle left or right

Confused as I am ?

Apart from the above it behaves like a compressor for most part

Wacky.

So what you're saying is:

1. The meter doesn't move in GR metering when you're trying to do the tracking adjust and you actually see a 0dBu to 10dBu on the output between GR on and off
2.  When you just use it on say drums, the meter behaves like it should in GR metering (although not calibrated)
3.  Moving the zero adjust and tracking adjust do change the meter position in GR metering?

Mike

 

[Echo North]

It's your input you want to adjust for 2.44 (10dBu) with GR turned off.  And adjust the output to get 0.775 (0dBu) with GR on.

Like the Purple Audio method:
4. Set controls as follows:
Input = "24" mid rotation
Output = "24" mid rotation
Attack = full CW
Release = full CW
Compression ratio = 20:1
Meter mode = "GR"
5. Apply a signal (1 KHz, 0db).
6 Set output control for 0db as read on an external meter.
7. Set attack full CCW (off position). Set input control for +10db as read on an external
meter.
8. Turn the attack control OFF (CCW) and readjust the output level control for "0" if
necessary.
9. Repeat 7 & 8 until the output drops 10dB whenever the attack control is turned ON.

If you're not getting that we'll need to step back and look in other places.

Mike

 

[frazzman]

It's your input you want to adjust for 2.44 (10dBu) with GR turned off.  And adjust the output to get 0.775 (0dBu) with GR on.

Like the Purple Audio method:
4. Set controls as follows:
Input = "24" mid rotation
Output = "24" mid rotation
Attack = full CW
Release = full CW
Compression ratio = 20:1
Meter mode = "GR"
5. Apply a signal (1 KHz, 0db).
6 Set output control for 0db as read on an external meter.
7. Set attack full CCW (off position). Set input control for +10db as read on an external
meter.
8. Turn the attack control OFF (CCW) and readjust the output level control for "0" if
necessary.
9. Repeat 7 & 8 until the output drops 10dB whenever the attack control is turned ON.

If you're not getting that we'll need to step back and look in other places.

Mike

Mike, you're the man! I'm stoked... within 15 minutes I got this calibrated perfectly after following your steps and understanding where I was going wrong.

I feel like a noob having got this whole calibration procedure completely confused. But on the bright side I am now in a position to give others a hand with this calibration.

So all in all, for the record and for anyone else who might ever read this thread and find themselves in the same boat as me:
Problem 1 - No gain reduction in GR mode
Solution: Check orientation of transistors in GR section of PCB - if using 2N5088 - make sure you use the alternate pins! ( I didn't at first and this oversight sent me chasing my tail for weeks wondering why I had no compression when in GR mode). I also ended up using sockets for these transistors so I could swap out as required, unless you like desoldering over and over.

Problem 2 - unable to complete meter tracking calibration - no 10db drop when turning on GR with attack s/w
Solution: Sine wave signal from cubase was too weak, and I had the whole procedure messed up. Follow Mike's step above and you can't go wrong.

Mike - thanks again. Compressor sounds great, rev A next....