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

[keevhren]

Nope.  Read through a bunch of the pages in here to no avail, have pulled our the main PCB to check over my work and everything looks good as far as I can tell... still stumped.  Suggestions?  Thanks in advance!

What are the transistor voltages compared to the ones on the Rev A schematic linked from the troubleshooting FAQ? If no issues there, try signal tracing using Mark Burnley's signal tracer also linked from the FAQ.

Been super busy since I last posted.  Just went through all the transistor voltages on the schematic and everything checks out... they're all super close to what's in the schematic so I don't think the problem lies there.  Just bought the parts I was missing to make the signal tracer... now to wait for them to show up so I can hopefully fix this issue!  Thanks for the help thus far!

 

[thomasdf]

Hi all!
Just finished wiring my 1176 Rev A from Hairball, and I am having troubles achieving the 1st step of the calibration... I have a very weak and distorted signal, so I get approx 0,4VAC at the ouput when maxed out... What should I begin with? Can it be linked with transistor matching / choice?

 

[Echo North]

Hi all!
Just finished wiring my 1176 Rev A from Hairball, and I am having troubles achieving the 1st step of the calibration... I have a very weak and distorted signal, so I get approx 0,4VAC at the ouput when maxed out... What should I begin with? Can it be linked with transistor matching / choice?

Where to begin:

-Make sure your QBias pot is rotated for max gain to start.
-Check your signal preamp and signal line amps agains schematic w/ voltages (http://mnats.net/files/1176REVA_125_VOLTAGES.pdf)
-Make sure you're actually in bypass be confirming pad 22 is shorted to ground
-double check all wringing
-double check all component values and placements

Mike

 

[thomasdf]

Ok, it finally decided to work.. Everything was wired and placed correctly, I simply zero-ed the meter and tweaked some trimpots and then it decided that it was time to be working properly... Anyway, I did the calibration and man, I love the sound of it... Really cool! I noticed that it was a bit noisy at high gain settings, so I did some testing and I have that frying bacon noise in the background that can be quite loud if it is pushed... I never head that kind of noise before, sound like white noise a bit... So I started poking around, moving the wires and I noticed than when I touch C2 (0,15uF orange drop in mine) I get a loud electric buzz that replaces that white noise / frying noise...
Anybody experienced  that? I am wondering if I should change this one or if it is a common thing... I hope my noise problem is related.. but can't tell yet.
Cheers and thanks in advance

 

[Echo North]

Ok, it finally decided to work.. Everything was wired and placed correctly, I simply zero-ed the meter and tweaked some trimpots and then it decided that it was time to be working properly... Anyway, I did the calibration and man, I love the sound of it... Really cool! I noticed that it was a bit noisy at high gain settings, so I did some testing and I have that frying bacon noise in the background that can be quite loud if it is pushed... I never head that kind of noise before, sound like white noise a bit... So I started poking around, moving the wires and I noticed than when I touch C2 (0,15uF orange drop in mine) I get a loud electric buzz that replaces that white noise / frying noise...
Anybody experienced  that? I am wondering if I should change this one or if it is a common thing... I hope my noise problem is related.. but can't tell yet.
Cheers and thanks in advance

Are you running your output wires under the PCB?

 

[thomasdf]

Yes I am... Maybe I should change that? You def are a 1176 magician

 

[Echo North]

Yes I am... Maybe I should change that? You def are a 1176 magician

Some areas of the PCB are sensitive to noise, especially where impedances are high.  You generally want to run your wires around the case edges.

Mike

 

[thomasdf]

I will do that and report back! I hope that will solve my radio capacitor problem too... Will keep you guys posted, thanks a lot Mike, you rock!

Edit: it's working perfectly now... I wired the output following the enclosure as you said!! Thanks!
My caps stills hums when I place my finger near or on it, but otherwise it's fine. Not dead silent, but really quiet.

 

[Echo North]

I will do that and report back! I hope that will solve my radio capacitor problem too... Will keep you guys posted, thanks a lot Mike, you rock!

Edit: it's working perfectly now... I wired the output following the enclosure as you said!! Thanks!
My caps stills hums when I place my finger near or on it, but otherwise it's fine. Not dead silent, but really quiet.

Cool!

Ya you're touching a high impedance area and inducing noise.  As long as it's good with the enclosure fully attached and continuity through the enclosure parts your golden!

Mike

 

[eqp1a]

Having issues with step 2 of calibration with my latest build. Can't get the meter to move from the far left in GR mode.  VU modes working fine.

Also having an issue with a different build, getting a jump in gain and additional noise when moving the output pot past 9 or so.

Anyone have any ideas of most likely issues?

 

[mnats]

Also having an issue with a different build, getting a jump in gain and additional noise when moving the output pot past 9 or so.

Anyone have any ideas of most likely issues?

Have a look at the FAQ linked from the first post of this thread.

 

[eqp1a]

Also having an issue with a different build, getting a jump in gain and additional noise when moving the output pot past 9 or so.

Anyone have any ideas of most likely issues?

Have a look at the FAQ linked from the first post of this thread.

Duh. Thanks MNATS. I feel a right knob as I swear I've read through that FAQ a thousand times. Any thoughts on the calibration issue?

 

[alexgg]

i just finished wiring up my rev a and find that sound is passing through the unit + sounds 100% fine, no distortion, no noise problems or anything like that.
the input + output knobs seem wired up fine, raising + lowering volume as expected.

came to Qbias calibration + unfortunately changing the Qbias pot appears to do nothing to change the units output level ??

I checked pad 22 to ground as in similar issue above + its definitely in bypass.

what else should I try looking at ?

 

[Echo North]

i just finished wiring up my rev a and find that sound is passing through the unit + sounds 100% fine, no distortion, no noise problems or anything like that.
the input + output knobs seem wired up fine, raising + lowering volume as expected.

came to Qbias calibration + unfortunately changing the Qbias pot appears to do nothing to change the units output level ??

I checked pad 22 to ground as in similar issue above + its definitely in bypass.

what else should I try looking at ?

Measure you DC V @ pad 18.  Does that change as you rotate Qbias?

Mike

 

[alexgg]

i just finished wiring up my rev a and find that sound is passing through the unit + sounds 100% fine, no distortion, no noise problems or anything like that.
the input + output knobs seem wired up fine, raising + lowering volume as expected.

came to Qbias calibration + unfortunately changing the Qbias pot appears to do nothing to change the units output level ??

I checked pad 22 to ground as in similar issue above + its definitely in bypass.

what else should I try looking at ?

Measure you DC V @ pad 18.  Does that change as you rotate Qbias?

Mike

yes it does, from 0v at full cw to -2.8v dc fully ccw.

 

[Echo North]

i just finished wiring up my rev a and find that sound is passing through the unit + sounds 100% fine, no distortion, no noise problems or anything like that.
the input + output knobs seem wired up fine, raising + lowering volume as expected.

came to Qbias calibration + unfortunately changing the Qbias pot appears to do nothing to change the units output level ??

I checked pad 22 to ground as in similar issue above + its definitely in bypass.

what else should I try looking at ?

Measure you DC V @ pad 18.  Does that change as you rotate Qbias?

Mike

yes it does, from 0v at full cw to -2.8v dc fully ccw.

That's good.

Try same at PAD 7.

 

[alexgg]

i just finished wiring up my rev a and find that sound is passing through the unit + sounds 100% fine, no distortion, no noise problems or anything like that.
the input + output knobs seem wired up fine, raising + lowering volume as expected.

came to Qbias calibration + unfortunately changing the Qbias pot appears to do nothing to change the units output level ??

I checked pad 22 to ground as in similar issue above + its definitely in bypass.

what else should I try looking at ?

Measure you DC V @ pad 18.  Does that change as you rotate Qbias?

Mike

yes it does, from 0v at full cw to -2.8v dc fully ccw.

That's good.

Try same at PAD 7.

aha went to look at this pa with reference to wiring guide + I realized my mistake!

shield + signal wires reversed in wrong pads. ooops.

I switched these round and went back to make Qbias calibration without any difficulty

thanks a lot for guiding me there mnats + the speedy response appreciated

 

[rolphrico]

Hey Everyone,

I just finished my second Hairball build for a Rev F 500 and have been comparing it to my Rev A. I am finding that the output stage of the A is very strong compared to the F. So much so that if I set a 1k tone for 1db of reduction and the same output level on both limiters, the Rev F output is around the 2PM position whereas the Rev A is around 9-10. I have double checked all connections and resistors, and measured the voltage of the transistors and all of them check out except Q4 where I'm getting the following numbers (Measured 12V at collector, Should be 13.72, Measured 4V at emitter, Should be 6.6). Everything else is very close to dead on.

I know these are different circuits with different output transformers (AB on the F) but its a pretty dramatic difference so I am just wondering if anyone has experienced this and if there are any remedies. I really like the sound of cranking the output transformer and find that the Rev A sounds thin because I have to keep the output so low. Any guidance is appreciated!

 

[Echo North]

Hey Everyone,

I just finished my second Hairball build for a Rev F 500 and have been comparing it to my Rev A. I am finding that the output stage of the A is very strong compared to the F. So much so that if I set a 1k tone for 1db of reduction and the same output level on both limiters, the Rev F output is around the 2PM position whereas the Rev A is around 9-10. I have double checked all connections and resistors, and measured the voltage of the transistors and all of them check out except Q4 where I'm getting the following numbers (Measured 12V at collector, Should be 13.72, Measured 4V at emitter, Should be 6.6). Everything else is very close to dead on.

I know these are different circuits with different output transformers (AB on the F) but its a pretty dramatic difference so I am just wondering if anyone has experienced this and if there are any remedies. I really like the sound of cranking the output transformer and find that the Rev A sounds thin because I have to keep the output so low. Any guidance is appreciated!

Hard to say without handling the units but keep in mind:

- The A has about 5dB more gain than the D or F.  That's almost 2X the voltage output.
- The output pots are completely different values and will have different curves.

I would check the over all gain.  Feed the unit a -40dB signal and but it in GR off.  Crank the input and output and you should see about +5 on the output for +45dB of gain.

Mike

 

[rolphrico]

Alright I just ran that test. I used a 40dbu signal (measuring 0.007745V at input), cranked the input all the way, then put the multimeter on the output as I cranked the output pot. The voltage climbed to a peak of 2.1 before going to 16 with the last little turn. I'm going to assume the peak of the pot was around 2.1 which works out to about 8 DB. That's pretty close to what you are saying so although its a little more hot then 5, I might just be hearing the difference between the revisions.

Thanks!