Echo North
Well-known member
Ataraxia said:
Hi,
I just walked JingleDjango through this above. You need to track the negative bias voltage. Read the stuff about testing pad 18 and 7 and report pack.
Mike
[BUILD] 1176LN Rev D DIY
- Thread starter mnats
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Help Support GroupDIY Audio Forum:
Hi,
I just walked JingleDjango through this above. You need to track the negative bias voltage. Read the stuff about testing pad 18 and 7 and report pack.
Mike
Echo North
Well-known member
Starts here:
http://groupdiy.com/index.php?topic=20058.msg765656#msg765656
http://groupdiy.com/index.php?topic=20058.msg765656#msg765656
JingleDjango
Well-known member
My last post got deleted when the server was rolled back, so I just want to reiterate that a new output pot did solve my issue with this unit. I'm happy with the sound and calibration was smooth.
One thing I wondered about was, despite doing the final meter tracking adjustment with no problems, several hours later I powered on the compressor to the GR meter mode and saw that the tracking needle was no longer zeroed. It sat at +0.5 in the red of the meter. It was easy to zero the meter again with R71 but I wonder if someone can give me an idea why the needle would be off, even if during calibration I had consistent, repeatable readings.
One thing I wondered about was, despite doing the final meter tracking adjustment with no problems, several hours later I powered on the compressor to the GR meter mode and saw that the tracking needle was no longer zeroed. It sat at +0.5 in the red of the meter. It was easy to zero the meter again with R71 but I wonder if someone can give me an idea why the needle would be off, even if during calibration I had consistent, repeatable readings.
Echo North
Well-known member
JingleDjango said:
Normal.
The discrete meter circuit drifts, that's why there is an adjustment pot on the panel. You should do calibration after it's been on for an hour. When you power it back up wait an hour and it should mostly get back to 0.
Mike
JingleDjango
Well-known member
That's reassuring, thanks.
JingleDjango
Well-known member
Could someone please tell me what healthy voltages are for the source and drain legs on Q1 with no input? Ideally I would check on the unit I just finished but he's already with his adoptive parent. :-\
Echo North
Well-known member
JingleDjango said:
Should be no DC there. Only on the gate.
JingleDjango
Well-known member
Thanks again. I'm curious: does using a foiled shield like the one provided with the kit confer any serious advantage over copper shields, braided or otherwise?
Edit: referring to the shielded two conductor cable...
Edit: referring to the shielded two conductor cable...
useme2305
Well-known member
good morning everyone!
just finished assembling my revD yesterday and it powers up nicely. voltages in the psu section are fine, too.
Q12 and Q13 are both 335.
now my problem:
when doing the 0.00V across R74 while nulling the meter untill both conditions are met procedure i can't get the voltage across R74 to go lower than 0.35V before the 2k Null Adj trimmer ends.
is this are common problem which has numerous known causes?
just finished assembling my revD yesterday and it powers up nicely. voltages in the psu section are fine, too.
Q12 and Q13 are both 335.
now my problem:
when doing the 0.00V across R74 while nulling the meter untill both conditions are met procedure i can't get the voltage across R74 to go lower than 0.35V before the 2k Null Adj trimmer ends.
is this are common problem which has numerous known causes?
useme2305
Well-known member
ok, this is embarrassing. Q11 was installed the wrong way around by me and i didn't notice untill now.
in other words: fixed!
in other words: fixed!
Just finishing up my Hairball 1176 Rev. D. I've got a couple of questions before I move to calibration.
1. I didn't see where I was supposed to terminate the ground on the output transformer. This is the bare wire that is soldered to the outside of the output transformer.
2. What AWG cable should I use when wiring the lamp of the meter?
Thanks!
1. I didn't see where I was supposed to terminate the ground on the output transformer. This is the bare wire that is soldered to the outside of the output transformer.
2. What AWG cable should I use when wiring the lamp of the meter?
Thanks!
Echo North
Well-known member
bdunard said:
1. If you removed some powder from one of the transformer mounting holes, then you transformer is already terminated there, you can just trim of the ground wire.
2. 22 AWG is fine.
Mike
Ok got everything wired and plugged in to start my first calibration test...Q Bias. I got a 1khz sine wave going and is .775 VAC coming out of my DAW, checked my output xlr pins and adjusted the output control knob to get to 2.75 VAC on the DMM between pins 2 and 3. The problem is that when I push the GR button my needle goes all the way to the right and no amount of CCW turns on the Q Bias adjust seems to make it move. What else can I check?
Echo North
Well-known member
bdunard said:
Monitor the output with your meter. The QBias trimmer is a 20 turn trimmer. When it's at the end it'll give a slight "click".
If that doesn't work there could literally be any of a 100 things wrong. Start by measuring your DC at PAD 18 and see if it changes when you rotate the trimmer.
Mike
Echo North
Well-known member
Sorry should have said "Monitor the output with your MULTI-meter"
Echo North
Well-known member
bdunard said:
No, that's only for Null Adjust.
Are you reading here?
http://www.hairballaudio.com/blog/resources/post/calibration
Just follow the text.
Yes I am using the build guide calibration steps.
My input and output knobs do influence the VAC at the output xlr.
I checked VDC on pad 18 to ground and it does change when i turn the Q Bias resistor. It shows -3.001VDC at full CCW. Not sure if I should be getting a negative reading.
GR meter is still fully right.
My input and output knobs do influence the VAC at the output xlr.
I checked VDC on pad 18 to ground and it does change when i turn the Q Bias resistor. It shows -3.001VDC at full CCW. Not sure if I should be getting a negative reading.
GR meter is still fully right.
Echo North
Well-known member
bdunard said:
That is all normal, the negative voltage is perfect.
Don't worry about the GR meter. Don't even look at it.
You're setting the qbias right? Follow written steps. At no point to they mention the GR meter:
"Apply a 1 KHz O dBu signal to the input and confirm with your DMM between pin 2 and 3 of the input XLR. Now move your DMM to the output XLR and measure AC between pin 2 and 3. Adjust the output control to read +11dBu (2.75 VAC) on your DMM at the output. Slowly turn the Q-bias adjust (R59) CW until a drop of 1 dB occurs, and your DMM reads +10 dBu (2.44 VAC). This places your gain reduction FET Q1 slightly into conduction. "
See if you can set you trimmer so that ACV on the DMM on the output is as high as possible, then set as described above and see if you can get that drop on the DMM.
Mike
Sorry at some point last night I watched a video on this and for some reason I was reading the text but I was looking for a 1db difference on the GR meter basically subtracting +11 to +10 and somehow I couldn't get it out of my mind. My apologies.
I did get the VAC to drop to 2.44 on output pins 2 and 3 after many turns CW on the Q Bias resistor.
One thing I am confused by is that the build guide says put the header onto the two pins that are closest to Q13. According to the PCB label that suggests it is shorting it...is that correct? Is this where the header will go for normal operation?
Thanks for your help Mike.
I did get the VAC to drop to 2.44 on output pins 2 and 3 after many turns CW on the Q Bias resistor.
One thing I am confused by is that the build guide says put the header onto the two pins that are closest to Q13. According to the PCB label that suggests it is shorting it...is that correct? Is this where the header will go for normal operation?
Thanks for your help Mike.
