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

[Echo North]

Im not sure this is a "problem" because the compressor sounds great. But I have noticed a lot of drift on the zero adjust. It doesnt seem to be related to anything specific either, If I leave the unit on for two days it still drifts around anywhere from -3 to +2. My rev J units are really stable after they've been on for a while. When I performed the null adjust I was able to get it down to 0.00V so Im not sure why it fluctuates so much. But, like I said, it sounds terrific. With a Rode NTV and 1290 pre it sounds great on vocals.

Drift is normal.  It's a discrete meter circuit.  The "J" has a more modern IC circuit.

+/- 3 dB is pretty eccessive though.  In my experience +/- 1dB is more notmal, but I don't use them everyday in an actual recording setting.

 

[sl4zhz]

Update in my case. VU meter still does not respond with 0dB signal directly.
Is VU meter broken?

Sounds like it.  Is it a Hairball meter?

If so email me:  info at hairballaudio dot com

Mike

Sorry for late respond in this forum. I was sent email to you about VU meter, many thanks to hairball audio for fast respond.

Back to my problem. While waiting new VU meter, I borrow VU meter from my friend (buy from hairball too).  I get 0dB in the VU meter from directly input signal. But I still can't do Q bias. Meter not reaction when input potentio turn CW.

I'm friends of this user "Lukidewa"
I still can't do Q bias. Meter not reaction when input potentio turn CW.
and also have a weird noise/buzz when I crank the output above 9 o'clock
also here's the short video of the unit I test it through an audio loops.
I don't know where to start, to troubleshoot this unit problems

http://www.youtube.com/watch?feature=player_embedded&v=LyrXJjTclbo

thanks

 

[Echo North]

Start by turning off gain reduction.

With the meter turned on and your DMM set to DC volts, place the common probe on the transformer CT PCB lug and the test probe on pad 18.  What is your reading here?  Now place you test probe on the gate of Q1 and what is your reading here?

Let's start by fixing the Qbias.  Them move on from there one step at a time.

Mike

 

[K.March]

Hey Guys,

This is my second build, but my first without help. Everything went great but I've think I've run into a spot of trouble while calibrating. I'm hearing a very high pitched hum.... so I figured I'd ask for help instead of continuing calibrating before I really break something. I've done a fair amount searching the forum for similar problems and it seems that it may be helpful to have measured voltages to help diagnose the problem.

        So I'm generating a 1khz tone of .775 V ac from my DAW (measured across xlr pins 2 & 3) and sending it to the 1176's input

        I next adjusted my q bias until it passed maximum voltage by turning CCW, measured off the 1176's output's 2 & 3 pin (specific V AC varies with input and output)

        I raise input until my 1176's meter reads +1Vu (I only have to raise it by the skin of my teeth to do this)

        I then drop my qbias 1 db (by turning my trimmer CW), so my 1176's Vu now reads 0.

This all progresses very well, except that right when I raised my input that tiny bit I begin to hear a very high-pitched hum/squeal/whistle/whine... raising the input raises the volume of this high pitched sound.

So checking the power rails at R87 I get 32.36 V DC and at R6 I get -9.75. This seems correct within tolerances.

Voltage in the GR Control Amp and GR Meter Driver sections are: at R 49 is 15.39V, R 47 is 15.97, R48 is 3.4 V, R 43 is 3.97 V, R 40 is 17.65, R38 is 18.27, R39 is 5.12, R37 is 5.64. R68 -1.39, R79 is 12.6

Voltage in the Signal Preamp section is: at R8 is 2.53 (when I check this voltage my 1176's Vu meter maxes out too) at R13 is 7.68, at R 11 is 4.56, at R14 is 14.8, R15 is 7.1

Voltages in the Signal Line section is: at R27 is 4.44, R26 is 15.61, R 30 is 3.56, R 33 is 29. R35 to output is 32.7 V

So I was really hoping this build would go without a hitch and I wouldn't need to ask for help, but I'm just not sure how to proceed with identifying and rectifying the problem. I double checked all resistor values and I've triple checked my wiring... perhaps someone with more experience than me can see what's going on here. This is my first post here, I apologize if I've formatted something wrong, thanks in advance for any consideration and help!

 

[Echo North]

Start by turning GR off and and measuring the pre and line amp voltages against the MNATS schematic (top 1/2).  No signal.  DC voltages.

http://mnats.net/files/1176REVA_125_VOLTAGES.pdf

 

[mnats]

        I raise input until my 1176's meter reads +1Vu (I only have to raise it by the skin of my teeth to do this)

You didn't mention where your output pot is set to which is relevant since the meter in +4 or +8 mode is showing the output.

This all progresses very well, except that right when I raised my input that tiny bit I begin to hear a very high-pitched hum/squeal/whistle/whine... raising the input raises the volume of this high pitched sound.

Sounds like feedback. Did you use my wiring guide? If so, did you read it carefully?

Voltage in the GR Control Amp and GR Meter Driver sections are: at R 49 is 15.39V, R 47 is 15.97, R48 is 3.4 V, R 43 is 3.97 V, R 40 is 17.65, R38 is 18.27, R39 is 5.12, R37 is 5.64. R68 -1.39, R79 is 12.6
...I apologize if I've formatted something wrong, thanks in advance for any consideration and help!

You have - voltages are measured at the transistors, not in relation to the resistors. Base, Collector, Emitter.

No need to quote them all if they agree with the schematic (no one will bother to read them anyway...well...almost no one). Just quote the one(s) that are really wacky. Or better yet, start probing around where they don't agree and use my troubleshooting FAQ. You have your work cut out for you.

 

[K.March]

Start by turning GR off and and measuring the pre and line amp voltages against the MNATS schematic (top 1/2).  No signal.  DC voltages.

OK, I was wrongly measuring them at the resistors, with a signal coming in. Novice mistake, I'm learning thank you for your patience! So measuring DC voltages at the transistors with no input gives me,

Signal Preamp:
Q2= 2.59 (g), 4.62 (s), 7.9 (d)
Q3= 7.89 (b), 15 (c) 7.29 (e)

Signal Line Amp:
Q4=2.54 (g) 4.53 (s)16.17 (d)
Q5=3.65 (b), 28.1 (c), 3.1 (e)
Q6 oriented center pin closer to me as I take readings (-_-)= 2.6(right)3.13 (center) 30.5(left)

I mights be writing this wrong, I was able to look up  the NPN 2N3708s Base collector and emitter terminal assignments, but I'm not 100% sure which is the collector voltage and emitter voltage on the schematic, my understanding is the base is the single path vs the C & E being the 2 paths. I do believe the J309's are not written with base, collector & emitter rather Gate Source & Drain, I was also able to look up their assignments, but I'm similarly not sure which is the Source and Drain on the schematic. Thanks for the speedy reply, and all your help through this, this has been incredibly fun, and wicked educational!

 

[Echo North]

Double check your transformer output transformer wiring.  If you have the color codes covered with terminal blocks on the PCB download the MNATS doc for your Revision and look at the overlay to confirm it's wired correctly.  make sure orange and yellow are connected to each other and not anything else.

Tripple check wring agains the MNATS guide.

J209's and 2N5457's are JFETS.  They have a Gate, Drain, and Source. 

 

[K.March]

Double check your transformer output transformer wiring.  If you have the color codes covered with terminal blocks on the PCB download the MNATS doc for your Revision and look at the overlay to confirm it's wired correctly.  make sure orange and yellow are connected to each other and not anything else.

Tripple check wring agains the MNATS guide.

J209's and 2N5457's are JFETS.  They have a Gate, Drain, and Source.

Double checked transformer output wiring, all good- yellow and orange together and no else, then connected to terminals correctly. Another check on the MNATS wiring guide revealed two problems, ONE: it looks like I had wired my output xlr with reversed polarity to input, which I fixed. TWO: My Output Pot had reversed ground and positive wires (although the negative was correct). Having fixed both of the issues, it still creates this hum/squeal when calibrating. Do you think I could have damaged something?

 

[K.March]

        I raise input until my 1176's meter reads +1Vu (I only have to raise it by the skin of my teeth to do this)

You didn't mention where your output pot is set to which is relevant since the meter in +4 or +8 mode is showing the output.

My mistake Sir! Output pot was set per the first q bias calibration video at about 3/4 the way up, and the meter was +4 was engaged.

This all progresses very well, except that right when I raised my input that tiny bit I begin to hear a very high-pitched hum/squeal/whistle/whine... raising the input raises the volume of this high pitched sound.

Sounds like feedback. Did you use my wiring guide? If so, did you read it carefully?

I did indeed use your wiring guide, an unbelievable resource, I checked it awful careful but... I just spent the last several hours going over it again, and it revealed two errors on my part, ONE I have the output xlr's polarity reversed and TWO: On my Output Pot I had the the ground and positive wires reversed. I've fixed both of these, and following the same procedure as before, the feedbackish sound returns the same. I hope I haven't damaged something. I wonder what could be feeding back? That's very interesting, sound is vibrating air right? I wonder what could be vibrating the air? I was concerned that one of my capacitors was about to blow.

Voltage in the GR Control Amp and GR Meter Driver sections are: at R 49 is 15.39V, R 47 is 15.97, R48 is 3.4 V, R 43 is 3.97 V, R 40 is 17.65, R38 is 18.27, R39 is 5.12, R37 is 5.64. R68 -1.39, R79 is 12.6
...I apologize if I've formatted something wrong, thanks in advance for any consideration and help!

You have - voltages are measured at the transistors, not in relation to the resistors. Base, Collector, Emitter.

No need to quote them all if they agree with the schematic (no one will bother to read them anyway...well...almost no one). Just quote the one(s) that are really wacky. Or better yet, start probing around where they don't agree and use my troubleshooting FAQ. You have your work cut out for you.

Boom! I have learned so much doing this project, thanks for your help! I'm sure the problem is right in-front of me, and I'm having trouble understanding what I'm seeing. As I use voltage to hone in on my problem, How far a variance is acceptable for my voltages? Is it a % thing, like the power rails? or perhaps a more linear thing, like +or- a certain voltage? Thank you so much!!

 

[Curran]

I have been stuffing my Rev A board for the last day or so , and I am missing a couple of 6.8uf caps. I have three electrolyticis's  and two Tantalum's. I put the electrolytics in the silkscreen spots calling for 100v caps, then I popped the tantalums in two spot. reviewing the boards physical layout I am MISSING two 6.8uf caps. they are polorized BUT there is no info on what kind they should be! the gaps I have are C19, and C20. Hell does it even matter what I throw in there? I can grap some tanta's or electro's. Just want it to come out awesome!!!

love and Metal Curran

 

[Echo North]

I have been stuffing my Rev A board for the last day or so , and I am missing a couple of 6.8uf caps. I have three electrolyticis's  and two Tantalum's. I put the electrolytics in the silkscreen spots calling for 100v caps, then I popped the tantalums in two spot. reviewing the boards physical layout I am MISSING two 6.8uf caps. they are polorized BUT there is no info on what kind they should be! the gaps I have are C19, and C20. Hell does it even matter what I throw in there? I can grap some tanta's or electro's. Just want it to come out awesome!!!

love and Metal Curran

When in doubt reference the MNATS Doc.

http://mnats.net/files/1176REVA_125_DOCUMENTATION.pdf

You have 3 x 6.8 electrolytic - C3, C23, C9
and 2 x tant = C19, C20

Mike

 

[Curran]

I thought i had done that BUT I clearly missed this info?!?!!? what a goon

 

[K.March]

Double check your transformer output transformer wiring.  If you have the color codes covered with terminal blocks on the PCB download the MNATS doc for your Revision and look at the overlay to confirm it's wired correctly.  make sure orange and yellow are connected to each other and not anything else.

Tripple check wring agains the MNATS guide.

J209's and 2N5457's are JFETS.  They have a Gate, Drain, and Source.

I have identified that the sound is coming from the VU meter! ...And only when there is an input, and, only when the meter registers in red and beyond. Hmmm...

 

[AntonSwe]

Hi everybody!

I have a quick question. A month ago I finished two Rev A compressors. I really like them and they sound great, however I started to notice that they sounded a litte weak in the bottom end so I did a frequency measurement with Fuzzmeasure.

I sent a 10 second frequency sweep from 1Hz to 22kHz and got the frequency response in the picture. This was with the compression bypassed (attack knob in off position), I set the input to 42 and calibrated for unity gain with the output pot which ended up at about 30. The signal was -10 dBFS out of my RME fireface 800 (not sure what the exact voltage of that signal was but I can look that up).

It looks like the signal starts to drop at about 500Hz and at 75Hz it is at -3dB.

I just wanted to know if this is normal for this compressor? Both compressors show the exact same response. I really love the sound of it but because of this I don´t use it on bass and kick drum.

Thanks!
/Anton

 

[Echo North]

Hi everybody!

I have a quick question. A month ago I finished two Rev A compressors. I really like them and they sound great, however I started to notice that they sounded a litte weak in the bottom end so I did a frequency measurement with Fuzzmeasure.

I sent a 10 second frequency sweep from 1Hz to 22kHz and got the frequency response in the picture. This was with the compression bypassed (attack knob in off position), I set the input to 42 and calibrated for unity gain with the output pot which ended up at about 30. The signal was -10 dBFS out of my RME fireface 800 (not sure what the exact voltage of that signal was but I can look that up).

It looks like the signal starts to drop at about 500Hz and at 75Hz it is at -3dB.

I just wanted to know if this is normal for this compressor? Both compressors show the exact same response. I really love the sound of it but because of this I don´t use it on bass and kick drum.

Thanks!
/Anton

That's not normal at all.  Should be +/- 1dB 20Hz-2KHz.

 

[AntonSwe]

Thanks for your quick answer Mike!

Hmm that was what I was afraid of. Strange thing is that everything else seems fine, no hum or strange noises and it compresses the way it should (I think at least. I read a few earlier posts with people having problems their compressors acted like 400Hz hipass-filters but they had more problems with noise, hiss and distortion which I haven´t noticed.

I guess I better start troubleshooting then. Any ideas where I should/could start?

 

[Echo North]

Thanks for your quick answer Mike!

Hmm that was what I was afraid of. Strange thing is that everything else seems fine, no hum or strange noises and it compresses the way it should (I think at least. I read a few earlier posts with people having problems their compressors acted like 400Hz hipass-filters but they had more problems with noise, hiss and distortion which I haven´t noticed.

I guess I better start troubleshooting then. Any ideas where I should/could start?

What I would do is start by injecting a 1K signal into the compressor at 1dBu then setting the output to get 1dBu on the output (GR off).  Then check the signal level in AC voltage at the input XLR, + in of the PCB, at C7 -, then at output XLR.  Note the levels.  Then do the same thing with 50Hz signal.  The level should be the same, see where it drops. 

Maybe a bad cap/cap value.

 

[AntonSwe]

Ok, so now I have done som testing. It turned out the voltage levels started to differ almost immediately. I sent +1 dBu to the compressor and at the input XLR the voltages were the same for 50 Hz and 1kHz. But on the output of the bournes 600 Ohm T-pad that changed. For example, when I got 390 mV out of it at 1kHz it only gave me 190mV at 50 Hz! Strange right?

The only time it gave me about the same values was when I had it fully open (at 0 on the front panel), otherwise the 50Hz signal was always considerably lover.

When I did this measurement I  had disconnected the input transformer from the PCB.

I don´t know what to think. Both of my 1176 compressors show the exact same frequency response, I measured my newly built SA-3A right after using the same outputs, levels and cables and it measured fine. It seems very unlikely that BOTH of my input T-pads are broken, but I have gone through the MNATS input wiring page over and over and I can´t se that I have done anything wrong.

Are the T-pads very sensitive to heat? Was thinking maybe I overheated them when I soldered them, although I believe I was careful.

 

[Echo North]

Ok, so now I have done som testing. It turned out the voltage levels started to differ almost immediately. I sent +1 dBu to the compressor and at the input XLR the voltages were the same for 50 Hz and 1kHz. But on the output of the bournes 600 Ohm T-pad that changed. For example, when I got 390 mV out of it at 1kHz it only gave me 190mV at 50 Hz! Strange right?

The only time it gave me about the same values was when I had it fully open (at 0 on the front panel), otherwise the 50Hz signal was always considerably lover.

When I did this measurement I  had disconnected the input transformer from the PCB.

I don´t know what to think. Both of my 1176 compressors show the exact same frequency response, I measured my newly built SA-3A right after using the same outputs, levels and cables and it measured fine. It seems very unlikely that BOTH of my input T-pads are broken, but I have gone through the MNATS input wiring page over and over and I can´t se that I have done anything wrong.

Are the T-pads very sensitive to heat? Was thinking maybe I overheated them when I soldered them, although I believe I was careful.

I can't imagine how the t-pad would cut frequency.  It's just resistance.

This was without the the PCB attached?  You should keep it attached to the PCB to keep the input transformer properly loaded.

Check all of the input cap/r values near the input.

Mike