[BUILD] 1176 Rev A - Back to the beginning...

[Echo North]

Hi,

i just finished my revision a unit and it does what it should and sounds all good with ratios 2, 8 and 12.
when changing to ratio 20 it does not compress anymore AND the vu meter does not show gain reduction, its clearly audible and sounds like when its off.

when testing continuity on the ratio board everything seems to be right, the switch works, the tracks are fine and the resistors on the ratio board all have the right values (v. 1.2.5).

is it possible that the error is not on the ratio board? i thought i only switch a ladder of resistors and when the others work the 20 should work, too, right?

its not calibrated yet, because i don't have a oscilloscope but all trimpots are measured to middle position.

do you have any ideas where to look?

thank you

malu

Ya you're switching a ladder.  The 20 ratio has a much higher threshold so it's possible you don't see compression until you calibrate.  YOU MUST CALIBRATE before testing the compressor.  The calibration, specifically the qbias, is needed.

You don't need an oscope to calibrate.  Just a signal and a DMM.  Checkout the videos.

Thanks,

Mike

 

[mrtomcat]

So after about 2 weeks of using the new Rev A, and it's sounding great, I have come across a bit of a strange issue.
The unit is in my rack and I am using a Furman Power Conditioner. Today when I switched the rack on the fuse blew on the 1176, I replaced it and all was well again, this has happened twice now, once last week and once today. I checked the wiring to see if there was anything weird going on but everything seems fine.

Any ideas what could cause that and how to check on this?

 

[Echo North]

So after about 2 weeks of using the new Rev A, and it's sounding great, I have come across a bit of a strange issue.
The unit is in my rack and I am using a Furman Power Conditioner. Today when I switched the rack on the fuse blew on the 1176, I replaced it and all was well again, this has happened twice now, once last week and once today. I checked the wiring to see if there was anything weird going on but everything seems fine.

Any ideas what could cause that and how to check on this?

Not all slo-blo fuses are created equal.  They vary in the amount of "slowness".  I think the ones in the mouser cart might be too quick to blow.  I might need to try some different ones.

Mike

 

[malu]

Hi,

i just finished my revision a unit and it does what it should and sounds all good with ratios 2, 8 and 12.
when changing to ratio 20 it does not compress anymore AND the vu meter does not show gain reduction, its clearly audible and sounds like when its off.

when testing continuity on the ratio board everything seems to be right, the switch works, the tracks are fine and the resistors on the ratio board all have the right values (v. 1.2.5).

is it possible that the error is not on the ratio board? i thought i only switch a ladder of resistors and when the others work the 20 should work, too, right?

its not calibrated yet, because i don't have a oscilloscope but all trimpots are measured to middle position.

do you have any ideas where to look?

thank you

malu

Ya you're switching a ladder.  The 20 ratio has a much higher threshold so it's possible you don't see compression until you calibrate.  YOU MUST CALIBRATE before testing the compressor.  The calibration, specifically the qbias, is needed.

You don't need an oscope to calibrate.  Just a signal and a DMM.  Checkout the videos.

Thanks,

Mike

hi, i could calibrate everything but the ratio 20 still behaves very strange.
so when i calibrated and used ratio 20 for calibration i thought it would work at the end, but i think it isnt right...

when i switch from ratio 12:1 with 20dB of gain reduction ration 20 slowly fades to gain reduction zero and it gets quite loud. sometimes the needle is moving for a few milliseconds but no usual compression...

 

[frazzman]

Hello fellow DIY friends,

So I've taken a second stab at fixing my 1176 rev A today. We have made some progress but it still has me beat. I fear I may never sleep until I find whats wrong with my sick 1176.

Anyway, my wiring was suspect so I started again following Skylar's rev A/D diagram to the letter.

Since this diagram uses the meter pushbutton to enable/disable GR, I cut the tracks as indicated in the hairballaudio guide.

As it stands, the unit is behaving erratically but is passing audio in metering mode. In GR mode, the meter pegs far right. Audio is still passed but uncompressed (indistinguishable from meter mode). I noticed that my 2n3053 transistor seemed to have been over heating resulting in garbled audio, since fitting a heatsink it seems to have helped.

When I turn the output pot to full the volume drop significantly and the meter pegs in metering (and GR mode). When I wind it back slightly in metering mode it behaves again. It is always pegged right in GR mode.

+30 and -10V are both good so PSU is working properly.

In metering mode the audio is obviously quite loud with output near full, however the meter only moves a little bit. It will move in time to snare drum for instance but it doesn't move near as much as it should (meter not calibrated???)

Input and output pots work in some fashion but attack and release have no impact on the signal.

Questions:
1) Referencing skylars diagram - where is wire from release CCW lug "To Ratio - REL POT" supposed to go? There is no "REL POT" pad on the ratio PCB. At the moment I have 2 brown wires coming off the CCW release pot lug - one to pad 18 on mainboard, the other to pad 18 on ratio board. Is this correct?
2) What could be the cause of the output pot causing the meter to peg and volume to drop/breakup?
3) Any pointers for lack of compression and meter pegging in GR? All resistors in gr control amp section are correct. I am using 2n5088 transistors, using alternate base pad.

I've been over the rudimental check points over and over - component orientation, polarity of caps, resistor values etc. Can't find any probable issue. Caps have correct polarity and I've hand checked every resistor.

I've read nearly every page in this thread and followed any suggestions picked up on these pages, calling Mike or any other 1176 elite for assistance

Damn the rev F was a lot easier to build. Thank you

 

[frazzman]

Just observed according to the hairball page:
http://hairballaudio.com/shop/fetguide.php

-Confused about the resistor and capacitor values for the attack and release pots? The current revision A (1.2.5) has a 1.2K/0.012uF on the attack pot and a 270K on the release. However, for the Rev A (1.2.5) we have subsitiuted a more common value of 0.015uF in the mouser cart. All other revisions (D/F/G) and the older Rev A (1.0-1.2) use a 470/0.022uF on the attack and 270K on the release.

My PCB is 1.2.5. so it seems I am using the wrong cap and resistor values on the attack and the release pot, could this explain the odd behavior? Time to track down a 0.015uF cap

UPDATE: Own question answered... changing attack pot values to the correct ones for PCB 1.2.5 had no impact on problems in my previous post. I guess its time to call it a night... rev A evades me again 'til tomorrow

 

[Echo North]

Do you at the very least have your QBias calibrated?  It's important that this is set before attempting to pass any audio.

Do you have your power supply ground pad (attached to one of the neg of one of the big filter caps) attached to your chassis ground with continuity to the whole case?

 

[Curran]

Ok So I have finally been able to make the time for a voltage reading on my new rev A build from a month or so ago. I already have one of these beasts working so it is a little odd to me that I have succeeded in failing at this second build of the same thing. here are the voltages

Q2 6.71-3.99-1.44

Q3 6.70-12.85-6.21

Q4 12.87-4.08-0.86

Q5 2.93-24.1-2.7

Q6 26.3-2.7-2.2

Q7 4.6-16.4-4.5

Q8 16.4-28.8-15.9

Q9 3.5-13.7-3.0

Q10 13.8-28.8-13.6

Q11 (-.80)-8.5-(-1.4)

Q12 (-.80)-7.95-(-1.39)

Q13 9.2-(-.70)-(-.22)

My power supply tested out fine at 37v-0-28v and (-9.4v)

it seems to me all the voltages are a little off from the schematic, Q8 is wayyy goofy if I am doing this right. so NOW what.

the unit passes signal but has no head room and sound clanky or thin. I have checked and double checked all the wiring and i believe I have it right. so any help would be wonderful so i can gegt this beast running for some upcoming sessions at the studio

 

[mnats]

it seems to me all the voltages are a little off from the schematic, Q8 is wayyy goofy if I am doing this right. so NOW what.

From the FAQ: "Any voltages that are grossly different from the ones that appear in the schematic corresponding to the revision you're working on will point to the problem area. It may be a problem with the transistor itself or some other component, solder bridge, poor joint or mis-wiring as stated above."

Start by testing the transistor, if good then start checking the other items suggested.

 

[frazzman]

Do you at the very least have your QBias calibrated?  It's important that this is set before attempting to pass any audio.

Do you have your power supply ground pad (attached to one of the neg of one of the big filter caps) attached to your chassis ground with continuity to the whole case?

Hi Mike, thanks for your response. The unit isn't racked yet, it's on my work bench at the moment so it's not properly grounded. I figured there was something seriously wrong with it given the way it's behaving aside from the lack of grounding. So no the neg leg of the big filter cap isn't tied to chassis. I don't know if I'd be able to calibrate the q bias with the way the unit is at the moment. Touching the output pot impacts the audio , either causing the signal to distort or cut out.

Edit: I should have mentioned that fiddling with the output pot can also make the meter peg or "unpeg" in metering and gr mode. The wiring and soldering is solid as a rock ...

 

[Echo North]

Do you at the very least have your QBias calibrated?  It's important that this is set before attempting to pass any audio.

Do you have your power supply ground pad (attached to one of the neg of one of the big filter caps) attached to your chassis ground with continuity to the whole case?

Hi Mike, thanks for your response. The unit isn't racked yet, it's on my work bench at the moment so it's not properly grounded. I figured there was something seriously wrong with it given the way it's behaving aside from the lack of grounding. So no the neg leg of the big filter cap isn't tied to chassis. I don't know if I'd be able to calibrate the q bias with the way the unit is at the moment. Touching the output pot impacts the audio , either causing the signal to distort or cut out.

Edit: I should have mentioned that fiddling with the output pot can also make the meter peg or "unpeg" in metering and gr mode. The wiring and soldering is solid as a rock ...

That's grounding issues.  You need to ground properly using the MNATS guide and definitely do the power supply filter cap or you'll get exactly what you're describing.

It will also never compress properly with out the qbias set.

 

[frazzman]

Do you at the very least have your QBias calibrated?  It's important that this is set before attempting to pass any audio.

Do you have your power supply ground pad (attached to one of the neg of one of the big filter caps) attached to your chassis ground with continuity to the whole case?

Hi Mike, thanks for your response. The unit isn't racked yet, it's on my work bench at the moment so it's not properly grounded. I figured there was something seriously wrong with it given the way it's behaving aside from the lack of grounding. So no the neg leg of the big filter cap isn't tied to chassis. I don't know if I'd be able to calibrate the q bias with the way the unit is at the moment. Touching the output pot impacts the audio , either causing the signal to distort or cut out.

Edit: I should have mentioned that fiddling with the output pot can also make the meter peg or "unpeg" in metering and gr mode. The wiring and soldering is solid as a rock ...

That's grounding issues.  You need to ground properly using the MNATS guide and definitely do the power supply filter cap or you'll get exactly what you're describing.

It will also never compress properly with out the qbias set.

Thanks Mike... you are a legend. The proper grounding (particularly from the filter cap) has made a huge difference. The unit is now stable and appears to be working as expected. Now to calibrate... I've built a number of rev Fs in the past , had no issue not grounding them for the "pre enclosure test"... this unit though was clearly not happy without being properly grounded. Thanks again I feel like a dumbass having wrecked my brain over what seemed to be a pretty obvious thing....

 

[Echo North]

Do you at the very least have your QBias calibrated?  It's important that this is set before attempting to pass any audio.

Do you have your power supply ground pad (attached to one of the neg of one of the big filter caps) attached to your chassis ground with continuity to the whole case?

Hi Mike, thanks for your response. The unit isn't racked yet, it's on my work bench at the moment so it's not properly grounded. I figured there was something seriously wrong with it given the way it's behaving aside from the lack of grounding. So no the neg leg of the big filter cap isn't tied to chassis. I don't know if I'd be able to calibrate the q bias with the way the unit is at the moment. Touching the output pot impacts the audio , either causing the signal to distort or cut out.

Edit: I should have mentioned that fiddling with the output pot can also make the meter peg or "unpeg" in metering and gr mode. The wiring and soldering is solid as a rock ...

That's grounding issues.  You need to ground properly using the MNATS guide and definitely do the power supply filter cap or you'll get exactly what you're describing.

It will also never compress properly with out the qbias set.

Thanks Mike... you are a legend. The proper grounding (particularly from the filter cap) has made a huge difference. The unit is now stable and appears to be working as expected. Now to calibrate... I've built a number of rev Fs in the past , had no issue not grounding them for the "pre enclosure test"... this unit though was clearly not happy without being properly grounded. Thanks again I feel like a dumbass having wrecked my brain over what seemed to be a pretty obvious thing....

I only know because I went down this same road not long ago

 

[frazzman]

Do you at the very least have your QBias calibrated?  It's important that this is set before attempting to pass any audio.

Do you have your power supply ground pad (attached to one of the neg of one of the big filter caps) attached to your chassis ground with continuity to the whole case?

Hi Mike, thanks for your response. The unit isn't racked yet, it's on my work bench at the moment so it's not properly grounded. I figured there was something seriously wrong with it given the way it's behaving aside from the lack of grounding. So no the neg leg of the big filter cap isn't tied to chassis. I don't know if I'd be able to calibrate the q bias with the way the unit is at the moment. Touching the output pot impacts the audio , either causing the signal to distort or cut out.

Edit: I should have mentioned that fiddling with the output pot can also make the meter peg or "unpeg" in metering and gr mode. The wiring and soldering is solid as a rock ...

That's grounding issues.  You need to ground properly using the MNATS guide and definitely do the power supply filter cap or you'll get exactly what you're describing.

It will also never compress properly with out the qbias set.

Thanks Mike... you are a legend. The proper grounding (particularly from the filter cap) has made a huge difference. The unit is now stable and appears to be working as expected. Now to calibrate... I've built a number of rev Fs in the past , had no issue not grounding them for the "pre enclosure test"... this unit though was clearly not happy without being properly grounded. Thanks again I feel like a dumbass having wrecked my brain over what seemed to be a pretty obvious thing....

I only know because I went down this same road not long ago

Good work coming up with the solution! This is my first Rev A build, I certainly didn't have the same issue on the rev F build. I usually test all my units on the bench before racking them.

This was really odd though, without that grounding it was an absolute mess. I'd checked and rechecked every component, wiring, quality of solder joints... all to no avail.... I thought I was going insane....

You're a wealth of knowledge.... now to the calibration stage

 

[frazzman]

Hey Mike,

I'm a bit stuck on the gain reduction meter tracking step. I had the same problem on my rev F's and you held my hand and explained the step to me in way that made sense. I'm following your steps as you advised me in the rev F thread.

1) Start with input and output half way, attack in GR off position - full CCW, release full CW, Ratio 20, meter mode: GR
2) I send a 0dbU 1khz sin wav into the input - I get my DMM and measure AC voltage across input pins 2 and 3 - I read 0dbU (.775VAC)
3) I then move my DMM prongs to the output XLR pins 2 and 3 and start raising the input whilst monitoring the voltage reading - aiming for +10dbU (2.45vac)

Thats where I hit a snag... even with input maxed out I never seem to get to 2.45VAC. Am I doing this step correctly???

I completed q-bias and null adjust calibrations without issue. The unit is passing nice clean audio in both metering and GR modes but it does not sound like it is compressing at all.

The meter is not very responsive but it does move a little in metering modes and in GR when the ratios are changed (I guess the lack of meter responsiveness is due to the fact I haven't completed the GR meter tracking calibration??)

Also the signal through the compressor is lower than the original source, not hugely but enough to notice when you take the compressor out of the chain

Thoughts??

 

[frazzman]

So I've made a little bit of progress on my build and got a handle of where some issues might still be.

I put a larger heatsink on the 7824 regulator and Q6 which has stabilized the unit. Grounding has been completed and all other wiring as per mnats wiring guide.

I was able to complete the q-bias and null adjustments.

However, I have no gain reduction and it has become very apparent that I actually am loosing a fair bit of gain somewhere in the unit. I've attached two samples of a snare drum, one going through the 1176 and one with it out of the chain. The wav forms are identical (there's no compression) but the audio out of the 1176 is considerably lower - even with the input and outpot pots maxed.

I have checked and rechecked all components and wiring and I can't account for the loss of gain, I am suspecting that this issue in itself might be the reason why gain reduction is not working. Also in metering modes, the meter is not overly responsive - for example it only gets tickled on the peaks, where as my other units the needle is usually flying left and right on the peaks in VU mode.

Could this loss of gain help explain why I have no GR?

I hope that the sound clips might help explain

Soundclip without 1176: https://dl.dropboxusercontent.com/u/108741277/snare-no1176.mp3
Soundclip with 1176: https://dl.dropboxusercontent.com/u/108741277/snare-1176.mp3

Appreciate any guidance....

 

[mnats]

Appreciate any guidance....

Have a look at the troubleshooting FAQ linked from the first post of this thread. There are at least two ways to narrow down your problem and both are described in the FAQ.

 

[frazzman]

Appreciate any guidance....

Have a look at the troubleshooting FAQ linked from the first post of this thread. There are at least two ways to narrow down your problem and both are described in the FAQ.

Hi mnats, Thanks your response. I will review that again, I guess most of what is in point 1 of the FAQ applies to me, I have explored some of that already but I just noticed the schematic with typical voltages denoted so I will use that as my reference and hopefully see where I am falling short.

 

[frazzman]

Ok so I have measured all the transistors to compare typical voltages as per mnats schematic.
I have attached an annotated copy. My values are in green.

Just about everything was ok except there were 2 very apparent deviations.

Referring to the schematic :

In the signal line amp, on Q4 I am supposed to see 6.6V on Pin 3 but I am only seeing 2.08V.
My reading on Pin 1 Q4 is inline with schematic:  schematic: 13.72V, mine - 13.44V

The other short fall is in the GR Meter driver section.
I am supposed to see 9.76V as per the schematic but I am only seeing 1.53V (due to incorrect setting on null adjust trimmer?)

All other transistors check out relatively closely to the schematic.

Any thoughts on what could cause my low voltage? Particularly in the signal line amp?

I have checked for all the usual suspects but so far I can't find anything that looks incorrect, component or connection wise...

 

[frazzman]

Anybody out there? I've been rechecking my build over the last couple of days. The only major deviation is the Q4 voltage as mentioned above. I've lifted all resistor legs to confirm correct designations. The only thing I haven't been able to do is replace J309 FET to see if this is the issue. I recalibrated my Q-Bias successfully but despite all of this there is still no compression and there is an apparent loss of gain.
I have tested to see that GR is being enabled by the attack switch. GND is shorted to Pad 22 in bypass and when GR is enabled I  have continuity to GRN on the ratio PCB.
Am I missing something obvious perhaps? Thank you all