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

[mrtomcat]

It is done!

Going to calibrate tomorrow.

In case there are any obvious visible issues please let me know

 

[mrtomcat]

I am having trouble calibrating:

First off, the unit turned on great, I measured the power rail again, the meter came on and everything looks fine, so I proceeded to calibrating.
Step 1 (based of the mnats videos) worked like a charm
Step 2 not so much...
      I set the jumper as requested, I turned the R71 knob until it reached 0, the test point reading was 0.71 volts, I then set the the zero adjust to go to 0.00 but when I tried to compensate with R71 it had reached it's max. The knob won't let me turn any further clockwise.

So what am I doing wrong? What can I check on? Should that knob (R71 poti) have a max value?

Please help

thanks

 

[Echo North]

I am having trouble calibrating:

First off, the unit turned on great, I measured the power rail again, the meter came on and everything looks fine, so I proceeded to calibrating.
Step 1 (based of the mnats videos) worked like a charm
Step 2 not so much...
      I set the jumper as requested, I turned the R71 knob until it reached 0, the test point reading was 0.71 volts, I then set the the zero adjust to go to 0.00 but when I tried to compensate with R71 it had reached it's max. The knob won't let me turn any further clockwise.

So what am I doing wrong? What can I check on? Should that knob (R71 poti) have a max value?

Please help

thanks

Are you using TP10 and 11 for your DC measurement?  IIRC the video's use a rev D which is measured across a resistor.

Like from my build guide:

"Note on calibration for Revision A builders: Measure accross TP10 and TP11 when setting the null adjust as opposed to accross R74 as shown on the Revision D."

If you're doing that are you measuring DC?

Mike

 

[mrtomcat]

I am having trouble calibrating:

First off, the unit turned on great, I measured the power rail again, the meter came on and everything looks fine, so I proceeded to calibrating.
Step 1 (based of the mnats videos) worked like a charm
Step 2 not so much...
      I set the jumper as requested, I turned the R71 knob until it reached 0, the test point reading was 0.71 volts, I then set the the zero adjust to go to 0.00 but when I tried to compensate with R71 it had reached it's max. The knob won't let me turn any further clockwise.

So what am I doing wrong? What can I check on? Should that knob (R71 poti) have a max value?

Please help

thanks

Are you using TP10 and 11 for your DC measurement?  IIRC the video's use a rev D which is measured across a resistor.

Like from my build guide:

"Note on calibration for Revision A builders: Measure accross TP10 and TP11 when setting the null adjust as opposed to accross R74 as shown on the Revision D."

If you're doing that are you measuring DC?

Mike

Yes on both.

I have the Multimeter set to V DC 20, that is giving me 2 decimals. Is that correct?

 

[Echo North]

This one can be a bit tricky.

It takes a bit of finesse.  Start with the 0 adjust trimmer in the center and set the null trimer to 0.  Try to anticipate how one will effect the other to avoid maxing out the zero pot.

If you can't do it, it's possible something is out. 

Did you match Q12 and Q13 for HFE?

If those are poorly matched that will cause an issue.

If you can get it below 0.1 that should be fine.

Mike

 

[mrtomcat]

I did match all eight of those, their values were between 320 and 324.

I tried again, and no matter what if I want a 0 reading I have to have the null adjust at .72 DC.
Step 1 works like a charm each time and I played around this some by increasing/decreasing the input signal, no dice on step 2.

at least it's consistent.

I checked the wiring between the poti and the pcb for R71 vs the manual and they look right on...Could that have been reversed by any chance and cause this effect?

Should I remove Q12 and Q13 and recheck them? Or is there a way to check them while on the board?

This one can be a bit tricky.

It takes a bit of finesse.  Start with the 0 adjust trimmer in the center and set the null trimer to 0.  Try to anticipate how one will effect the other to avoid maxing out the zero pot.

If you can't do it, it's possible something is out. 

Did you match Q12 and Q13 for HFE?

If those are poorly matched that will cause an issue.

If you can get it below 0.1 that should be fine.

Mike

 

[mrtomcat]

Still no luck. I removed the null adjust and q bios trimmer and remounted them based on a recent picture here...they were reversed but in the correct slots.
I replaced Q13, this one was dead when I tried to measure it. I was hoping the replacement would do it but nada.
still the only way to get 0 is by having the null adjust at .72 vdc

I was told by another user with a similar problem that he had a defective ratio board...could that be my problem?

Other than trying to measure every component is there anything else I can do? The wiring looks right, I went over the videos and manuals again a few times. Everything looks like it should be right... so frustrating.

Anyone?

 

[Echo North]

Still no luck. I removed the null adjust and q bios trimmer and remounted them based on a recent picture here...they were reversed but in the correct slots.
I replaced Q13, this one was dead when I tried to measure it. I was hoping the replacement would do it but nada.
still the only way to get 0 is by having the null adjust at .72 vdc

I was told by another user with a similar problem that he had a defective ratio board...could that be my problem?

Other than trying to measure every component is there anything else I can do? The wiring looks right, I went over the videos and manuals again a few times. Everything looks like it should be right... so frustrating.

Anyone?

Did you check your voltages against the MNATS schematic with voltages on the Rev A site?  Which ones are off by more than 10%?

Mike

 

[mrtomcat]

I will do that tonight.

Complete rookie question: What is the correct way to check these?
Looking at the schematic for Q11 which should read 10.52 Volts...Where are the test points for that? The two outside pins on the transformer? And on and on Q12 which has 3 different readings 9.5, -0.81 and -1.41? Is that red lead on B and Black Lead on C for the 9.5, red lead on E and Black on C for the -1.41? And if so how to read the middle voltage -0.81?
Is that correct or am I completely off here?

Once I know how to do that I should be able to finally trouble shoot this.

Your help is much appreciated!

thanks

Still no luck. I removed the null adjust and q bios trimmer and remounted them based on a recent picture here...they were reversed but in the correct slots.
I replaced Q13, this one was dead when I tried to measure it. I was hoping the replacement would do it but nada.
still the only way to get 0 is by having the null adjust at .72 vdc

I was told by another user with a similar problem that he had a defective ratio board...could that be my problem?

Other than trying to measure every component is there anything else I can do? The wiring looks right, I went over the videos and manuals again a few times. Everything looks like it should be right... so frustrating.

Anyone?

Did you check your voltages against the MNATS schematic with voltages on the Rev A site?  Which ones are off by more than 10%?

Mike

 

[hymentoptera]

I will do that tonight.

Complete rookie question: What is the correct way to check these?...Is that red lead on B and Black Lead on C for the...

Black lead (plugged into COM) on ground, which is the middle pin on the power supply side of the PCB where your AC comes in from the power transformer (gator clip is nice for this). Red lead to appropriate junction in the circuit to be tested. Each point to be tested will be between two or more componants (voltage should be the same anywhere at this part of the circuit), and any of the two or more exposed leads or solder joints at this junction will work for the test, just be sure to not short anything with your test lead (mini-pincers are great for grabbing a resistor leg, etc, and use regular probes for anything else).

 

[All Ears]

A question about tantalum caps...

How critical is the value of C19 and C20 in this circuit ?  (the two 6,8uF tants)

Reason I ask is that I have a pile of 50v tantalums that are "marked" as 6.8uF but all of them seem to be testing at 8uF - 8.3uF on both my meters.

Is this a measurement error (ie something to do with measurrment freq) or is it normal for tantalums to read higher than their marked value, or is it a bad batch ?

Would I be better going ahead with the "8uF" tants or just punting for nice modern tight tolerance electrolytics for C19 and C20 ? (maybe a Panasonic or Philips or Nichicon)

cheers - all ears

 

[mrtomcat]

Black lead (plugged into COM) on ground, which is the middle pin on the power supply side of the PCB where your AC comes in from the power transformer (gator clip is nice for this). Red lead to appropriate junction in the circuit to be tested. Each point to be tested will be between two or more componants (voltage should be the same anywhere at this part of the circuit), and any of the two or more exposed leads or solder joints at this junction will work for the test, just be sure to not short anything with your test lead (mini-pincers are great for grabbing a resistor leg, etc, and use regular probes for anything else).

Thanks! Will report back once I get some readings

 

[mrtomcat]

So I measured across the PCB and except for the following everything was within 10% or better.

here's where I am way off:

Q11 -> should be 10.52 but is 4.1
TP 10 -> should be 9.5 but is 4.1
TP 11-> should be 9.76 but is -1.3

What's my next step?

 

[mrtomcat]

Problem solved!

after doing the readings I found that the trouble started right after R79. Input is 30v but after the 15k r79 resistor the voltage was only 4.0 instead of the 10.52, so I removed the resistor and checked it, but it was ok at 15k, then I traced the board and noticed that my green and orange wire from the meter board were reversed...I thought that was it but no go.
Next stop R67 coming in was 4.0 coming out was 4.0...no resistance...so I removed this sucker but he checked out ok as well...so I noticed that Q12 had a tiny solder bridge...shorting itself out. I removed that, cleaned up the area and put a new transistor in (THANK YOU MIKE FOR ADDING ADDITIONAL TRANSISTORS IN THE MOUSER CART!!!). I soldered it back in, plucked it back in and voila, everything worked!

I was able to easily finally complete step 2 of the calibration...

I dared to start working on Step 3 but ran into some issues there and did some more measurements, but all the voltage readings are in synch with mnats schema now, so I might be just too tired and decided I do it tomorrow when I'm fresh.

Anyway, I am incredibly happy right now and I learned a dramatic amount about electronics this week.

 

[hymentoptera]

A question about tantalum caps...

How critical is the value of C19 and C20 in this circuit ?  (the two 6,8uF tants)

Reason I ask is that I have a pile of 50v tantalums that are "marked" as 6.8uF but all of them seem to be testing at 8uF - 8.3uF on both my meters.

Is this a measurement error (ie something to do with measurrment freq) or is it normal for tantalums to read higher than their marked value, or is it a bad batch ?

Would I be better going ahead with the "8uF" tants or just punting for nice modern tight tolerance electrolytics for C19 and C20 ? (maybe a Panasonic or Philips or Nichicon)

cheers - all ears

I can't really answer the question except to mention that the Mouser cart includes 6.8uF 10% tantalums, while 8.3uF doesn't even fall within 20%. The purpose of C19 and C20 seems to be to block DC while passing gain control amp signal through the rectifiers and on to the attack/release pots and ultimately to the GR FETs. I wouldn't mess with the cutoff frequency of this circuit. Maybe someone more knowledgable than me can tell you the cutoff freq. I THINK they're making high pass filters at 0.5Hz with those 47k resistors, so maybe there's some wiggle room here, and if I'm right here then 8.3uF would drop the cutoff to just 0.41Hz, but again, I'm not one to say. I'm still pretty new to this stuff.

I would try to stick with 10% 6.8uF tantalums for C19 and C20.

 

[mrtomcat]

More problems...

I can't get Step 3 to work, and I have noise in my output.

Step 1 and 2 now work perfectly.

Step 3...well I can't get any gain reduction, when I set the VU to 0 via output and then turn on the GR via the attack know the meter drops  maybe half a DB. and if I turn it back off nothing changes.
On top of it I have a very noisy output.

I replaced all my audio wire (I was not happy with the wire I used to begin with and replaced it with high quality wire now), when over every connection and did find I had the attack know wired wrong also one of the wires on the little harness had gone lose...I fixed all that and double and then double checked once more that everything is now fine but absolutely no difference.

Any thoughts? The PCB voltages are all checking out

Also what could cause the noise? it's not a ground hum, it's a bit more high pitched

I was so hoping to be done with this by now and to actually use it but I guess not.

I'm digging through the archives but if anyone knows what I should check on please let me know

thanks

 

[Echo North]

More problems...

I can't get Step 3 to work, and I have noise in my output.

Step 1 and 2 now work perfectly.

Step 3...well I can't get any gain reduction, when I set the VU to 0 via output and then turn on the GR via the attack know the meter drops  maybe half a DB. and if I turn it back off nothing changes.
On top of it I have a very noisy output.

I replaced all my audio wire (I was not happy with the wire I used to begin with and replaced it with high quality wire now), when over every connection and did find I had the attack know wired wrong also one of the wires on the little harness had gone lose...I fixed all that and double and then double checked once more that everything is now fine but absolutely no difference.

Any thoughts? The PCB voltages are all checking out

Also what could cause the noise? it's not a ground hum, it's a bit more high pitched

I was so hoping to be done with this by now and to actually use it but I guess not.

I'm digging through the archives but if anyone knows what I should check on please let me know

thanks

The noise is most likely some type of oscillation.  Sometimes this can be caused by audio wires being too close to certain PCB components.  Keep you audio wires away from the PCB and towards the edge of the case.

The oscillation issue is probably causing the lack of GR.  Seems like a wiring error of some type to me. 

Is the oscillation only there in GR mode? Is it always there regardless of input/output position?  Was it these prior to the re-wire?

Do you have the R44 jumper in the right position?

 

[mrtomcat]

We got compression!!! ;D

I bow my head in shame because the noise didn't come from the unit it came from my Converter because I forgot to change the sample rate...in my defense I just recently switched to the SSL Alphalink where you have to set this manually, I'm still used to my old RME where the host controlled everything but I digress.

Of course I didn't find this out until AFTER I took everything apart again... but I guess I deserved this one...

In any case it took a bit of trial and error but I got this baby calibrated and it sounds amazing!!!

Thank you all so much for your patience with me on this my first DYI project!!

Going to do a rev D in a few weeks as my next project

 

[Curran]

OK- I am still getting distortion on my compressor. it is clean when the comp is switched out, but the headroom is lower than my other rev A. when I have it switched in. should I just go through the voltages on the back side of this beast or does anyone have a "this happened to me hear is what you do to fix" type of comment. I would believe that this distortion is just coming in on the gain reduction part of the comp.

 

[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