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

[psgretsch]

Hello from Nashville. I finished my first build of the Hairball revA Blue Stripe 1176. It sounds great but we are having to really crank the output. And it's compressing with low input. Any ideas what I may have done wrong? I have calibrated as well. Thanks!

 

[Echo North]

Getting any weird voltages?

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

 

[mnats]

The only major deviation is the Q4 voltage as mentioned above.

I'm curious if you actually measured the gate voltage of Q4 (not shown on the schematic)? That should be around 2ish VDC.

I recalibrated my Q-Bias successfully but despite all of this there is still no compression and there is an apparent loss of gain.
Am I missing something obvious perhaps?

What does a signal trace show? In which stage does the level drop?

 

[psgretsch]

Getting any weird voltages?

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

I'll test the unit to the best of my ability as soon as our bass player get's it back to me. Hopefully this evening. Thanks very much.
Sep 22-I'm still waiting. He likes the sound too much! But we do want it to be right.

 

[frazzman]

The only major deviation is the Q4 voltage as mentioned above.

I'm curious if you actually measured the gate voltage of Q4 (not shown on the schematic)? That should be around 2ish VDC.

I recalibrated my Q-Bias successfully but despite all of this there is still no compression and there is an apparent loss of gain.
Am I missing something obvious perhaps?

What does a signal trace show? In which stage does the level drop?

Hi mnats,

The gate voltage of Q4 measures at 2.29vdc, so its inline with what you stated. At Drain we have 14.79vdc and at source we have -4.43vdc

I don't have a scope unfortunately so I can't trace the signal to work out where the level drop is. I was hoping that any wonky measurements when referencing the schematic expected voltages should point me in the right direction, which so far suggests an issue in the signal line amp but I am not certain and I can't find any shorts or incorrect components.

As is often the case in DIY, I must persevere! Thank you for your help.

 

[mnats]

I don't have a scope unfortunately so I can't trace the signal to work out where the level drop is. I was hoping that any wonky measurements when referencing the schematic expected voltages should point me in the right direction, which so far suggests an issue in the signal line amp but I am not certain and I can't find any shorts or incorrect components.

As mentioned previously there are two ways to attack the problem. Re-read the FAQ. The signal tracer is linked from there.

 

[frazzman]

I don't have a scope unfortunately so I can't trace the signal to work out where the level drop is. I was hoping that any wonky measurements when referencing the schematic expected voltages should point me in the right direction, which so far suggests an issue in the signal line amp but I am not certain and I can't find any shorts or incorrect components.

As mentioned previously there are two ways to attack the problem. Re-read the FAQ. The signal tracer is linked from there.

Hi mnats,
Thanks - as per your advice i've built the signal tracer so I will give it a go tonight and see how we go. Any wisdom you can impart on how to navigate the rev A circuit with the signal tracer?

I'll try and follow the signal path as referenced through the schematic

 

[psgretsch]

Getting any weird voltages?

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

here's what I measured. Not far off except for Q4 is a bit strange. Thanks very much for the help.

voltages
r9  2.084
r11  4.29
r13  6.09
r14  14.00
r15  5.51
r26  15.99  (Q4) a bit hi ?
r27  5.04    (Q4) a bit low ?
r30  3.2
r35  24.30
q5 to q6  2.68
wht/blk  2.1
q6  26.75
r80  -9.79
r36  5.13
r38  16.66
r39  4.61
r40  16.03
r43  3.65 (this had a bad solder joint)
r47  14.52
r48  3.03
r49  13.93
r79  10.49
q11 to q12  -0.82
tp10  9.63
tp11 9.68
r68  1.40
r69 1.44
r75  -0.874
I recalibrated and still don't have any head room. The unit sounds great. Any ideas how I can get more output?

 

[psgretsch]

Getting any weird voltages?

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

here's what I measured. Not far off except for Q4 is a bit strange. Thanks very much for the help.

voltages
r9  2.084
r11  4.29
r13  6.09
r14  14.00
r15  5.51
r26  15.99  (Q4) a bit hi ?
r27  5.04    (Q4) a bit low ?
r30  3.2
r35  24.30
q5 to q6  2.68
wht/blk  2.1
q6  26.75
r80  -9.79
r36  5.13
r38  16.66
r39  4.61
r40  16.03
r43  3.65 (this had a bad solder joint)
r47  14.52
r48  3.03
r49  13.93
r79  10.49
q11 to q12  -0.82
tp10  9.63
tp11 9.68
r68  1.40
r69 1.44
r75  -0.874
I recalibrated and still don't have any head room. The unit sounds great. Any ideas how I can get more output?

Okay, I found the problem. This is the perfect example of one small part causing trouble. R28 calls for a 560 resistor. I mistakenly used a 560k from my parts. One reason this happened is I ordered parts for a RevA and a RevD in the same Mouser order. Next time I will make sure each cart is separate just to make things less confusing. Even testing the resistor I still used the wrong value. Now my RevA is kicking ass!!!

 

[Siegfried Meier]

Hey guys,

After many years of sitting on these I finally decided to finish them up.

Got it all wired in today, and before connecting the trafo I tested to make sure I was getting proper voltage - I was.

I have it connected to the PCB in the following manner

Primary
Brn, Gry = 115v
Vio, Blu = 0VCT

Secondary
Red, Yel = 25V
Org, Blk =0VCT

So, on the board, that should mean (since there's only 3 pads) that my red and yellow go to AC, and my orange and black go to CT, correct?

Why then when I fired it up, the trafo made a crazy humming noise and I saw smoke...??  :-(

I've wired up quite a few power transformers to boards in the last 10+ years, and I'm no understanding what's different here now...I saw the proper voltage before I connected, so it should be fine?  Unless the boards are labelled wrong...

Now I have to attempt to figure out what's burned out on the PCB...ugh.

Any help much appreciated.
Sig

 

[Echo North]

Hey guys,

After many years of sitting on these I finally decided to finish them up.

Got it all wired in today, and before connecting the trafo I tested to make sure I was getting proper voltage - I was.

I have it connected to the PCB in the following manner

Primary
Brn, Gry = 115v
Vio, Blu = 0VCT

Secondary
Red, Yel = 25V
Org, Blk =0VCT

So, on the board, that should mean (since there's only 3 pads) that my red and yellow go to AC, and my orange and black go to CT, correct?

Why then when I fired it up, the trafo made a crazy humming noise and I saw smoke...??  :-(

I've wired up quite a few power transformers to boards in the last 10+ years, and I'm no understanding what's different here now...I saw the proper voltage before I connected, so it should be fine?  Unless the boards are labelled wrong...

Now I have to attempt to figure out what's burned out on the PCB...ugh.

Any help much appreciated.
Sig

It's wired incorrectly.  The labeling on the tx is deceiving.

Checkout the full explanation here:
http://www.hairballaudio.com/blog/d_assembly/revd/building-the-power-supply/

Mike

 

[germoju]

Hi !
Because I cant find anymore Orange Sprague 0,15uF, do you think think cap is good in replacement ? -> http://www.banzaimusic.com/Nichicon-YX-0-15uF-50V.html

 

[Siegfried Meier]

Hi !
Because I cant find anymore Orange Sprague 0,15uF, do you think think cap is good in replacement ? -> http://www.banzaimusic.com/Nichicon-YX-0-15uF-50V.html

Lesson learned...always read the trafo diagram, and CORRECTLY!  Don't listen to others.

Thanks Mike, you rock!

 

[germoju]

Hi !
Because I cant find anymore Orange Sprague 0,15uF, do you think think cap is good in replacement ? -> http://www.banzaimusic.com/Nichicon-YX-0-15uF-50V.html

Lesson learned...always read the trafo diagram, and CORRECTLY!  Don't listen to others.

Thanks Mike, you rock!

???

 

[Studio Mollan]

Hi all!
I tried searching the forum but i couldn't find any threads about adding a sidechain HP-filter to the MNATS 1176. Anyone knows how to?
/
Emil

 

[evilcat]

I assume you could put a simple RC filter on the sidechain input (pad 21 or 22, I'm not sure). I have never thought about it but it could be a good idea, food for thoughts!

 

[Studio Mollan]

I assume you could put a simple RC filter on the sidechain input (pad 21 or 22, I'm not sure). I have never thought about it but it could be a good idea, food for thoughts!

I imagine it is a pretty easy mod. Just a matter of finding the input to the sidechain and find the value for the components for the filter. Just a series cap? Adding that to a front panel switch should be real easy. A sidechain filter is really handy for drum bus and other bass heavy stuff. Would def add to the design.
/
Emil

 

[rjd2rjd2]

Can someone help me read the signal path on the schematic for the rev D by chance? my rev D's have proper PSU voltage, but just BARELY pass signal at 10/10. i knocked up a signal tracer, and had a look, but it's still not totally clear to me, after the input tranny, where it heads from there. would it go R5>C1>R8 etc? I have never traced signal on a schem, so i'm green here. thanks for the help.

EDIT: oops, put this in the rev A post accidentally, but the question still stands...

 

[Echo North]

Can someone help me read the signal path on the schematic for the rev D by chance? my rev D's have proper PSU voltage, but just BARELY pass signal at 10/10. i knocked up a signal tracer, and had a look, but it's still not totally clear to me, after the input tranny, where it heads from there. would it go R5>C1>R8 etc? I have never traced signal on a schem, so i'm green here. thanks for the help.

EDIT: oops, put this in the rev A post accidentally, but the question still stands...

Best thing to do is turn off GR and trace through the amp sections.

Check it at R5 (should be a lot lower than you're input), then at C7, then your output.  This helps to isolate it to the signal or line amp.

Mike

 

[rjd2rjd2]

Thanks. Here's where I'm at:

I built a signal tracer. I printed out the schems and have the exact signal path. with the power off, i traced the circuit. my problem is that the signal stops at the input transformer on BOTH of my units. (building a pair). i get a sort of loud hum with no signal from there on out.

i have quadruple or quintuple checked my wiring against the instructions. it all appears to be EXACTLY per the hairball site instructions. input xlr pin 1 is tied to chassis pin on xlr, ground continuity follows thru to the shielding on the cable between input tranny OUT and PCB IN.

here's the part that is stumping me: i unscrewed the input tranny from the chassis, and for one 5 minute stretch, the signal passed thru the input tranny. i traced it all the way thru the circuit to the output xlr, and it was all continuous. when i reassembled, it went back to no signal.

i can't tell, but it SEEMS as though there is maybe a short from ground to the signal outputs at the input tranny? since both units behave the exact same way, i have to assume there is some user error going on here. but for the life of me, i can't figure out what it could be.

with power not running to the unit, should i be able to trace signal past the input transformer? thanks for the help, really want to wrap this project up, it's kicking my ass!