[BUILD] 1176LN Rev D DIY

[joe-electro]

Sounds like a problem wiring the switch on the back of the attack pot.  Make sure the wire referred to as #22 is being switched to ground when the switch is in the "off" position.

--Joe

hello,
I have just powered my unit up.
I got the BEAUTIFUL KIT from hairball audio: Trafos, ratio switches Input PAD.
the attack pot is the suggest one from moused with DPDT.
I have wired my unit according to SKYLAR instructions (apart from output trafo which the color coding doesn not match what I have here) and used hairball instructions on how to wire the attack pot up.
i get (even before line up) 46dB of gain before it peaks, i am monitoring using a Neutrik A1 meter (nice piece of kit)
everything seems to be working fine BUT...
I get gain reduction even when the attack pot is on "OFF"
I have checked the usual suspects : wiring, loose connections, dry joints... even if I have left the kattle on....(sorry kinda english humor)

what else am I missing?

any tips will be much appreciated.


Best,
Mattia.

 

[mata_haze]

Sounds like a problem wiring the switch on the back of the attack pot.  Make sure the wire referred to as #22 is being switched to ground when the switch is in the "off" position.

--Joe


Quote from: mata_haze on Today at 06:46:01 pm
hello,
I have just powered my unit up.
I got the BEAUTIFUL KIT from hairball audio: Trafos, ratio switches Input PAD.
the attack pot is the suggest one from moused with DPDT.
I have wired my unit according to SKYLAR instructions (apart from output trafo which the color coding doesn not match what I have here) and used hairball instructions on how to wire the attack pot up.
i get (even before line up) 46dB of gain before it peaks, i am monitoring using a Neutrik A1 meter (nice piece of kit)
everything seems to be working fine BUT...
I get gain reduction even when the attack pot is on "OFF"
I have checked the usual suspects : wiring, loose connections, dry joints... even if I have left the kattle on....(sorry kinda english humor)

what else am I missing?

any tips will be much appreciated.


Best,
Mattia.

If i do a continuity test between the common of the switch and ground when in OFF position it's an open circuit hence it's not shorting pin 22 to ground...
where is this missing ground then....???

 

[mata_haze]

Again...
is "Shield from 22 (BLK)" on the ratio board (provided by Hairball) meant to be connected to ground at all?

tha seems to cure it but i am not sure if it is meant to be like that..


Best,
Mattia.

 

[joe-electro]

Yes, that's where they got the grounding point in the original.  Weird but true.

Joe

Again...
is "Shield from 22 (BLK)" on the ratio board (provided by Hairball) meant to be connected to ground at all?

tha seems to cure it but i am not sure if it is meant to be like that..


Best,
Mattia.

 

[Stagefright13]

Yeah if you look at Skylars diagram it has grn and blk on the ratio board. The hairball audio boards also say blk and grn. (In parenthesis) Same thing

John

 

[Echo North]

There is a step by step guide for this about 2/3 down Mako's J page:
http://www.geocities.com/m_natsume/1176-wiring-pushbutton.html

The only difference is to remember when he says "solder 22/Grn/Blk to the meter board" it will be the attack pot switch for you.

Mike

 

[mata_haze]

YOU GUYS ROCK!

Thank you very much!

Mattia.

 

[Stagefright13]

Cool ya got it working? Congrats! I'm working on making a 2-rev D right now. They sound great on everything.

John

 

[mata_haze]

I have used it on female vocals last night in during mix session.
I am speechless..it does have a very unique sound (compared to G1176 or New UAs) and it's very very pleasant.

Very impressed.
I will post pictures soon ( I have used it with no cover on nor meter so it does not look good as yet).

Best,
Mattia.

 

[RedNoise]

Hi , actualy finalizing my revD and A , I would like to power 4 (2 x RevD and 2 x revA) with the same psu.
I know this is a dumb question , but :
Do you think I have to change components in Mnats external PSU to power my four 1176?
Maybe T versions of the LM3xx , or 1A versions of the 1N4007?
By advance , thanks.
T.

 

[mata_haze]

Hi everybody just finishing my first unit,
I did the full calibration procedure today (although I have tested it in the studio the other day without calibrating it...I was too curious!) and althought everything went fine I have a problem:

there is a self oscillation at the output stage which shows up when the output pot is either between -infinite and 40 and when is between 6 and 0 (IE the two extreme parts of the run).
this happens regardless of the input attenuator pot, but it happens when there is no signal going through it. IE = no sinewave or music.

the scenario is the following:
if you turn the comp on and leave the input pot to zero and the output pot to zero there is a self oscillation (which shows up on the meter even when in gain reduction mode).
as soon as you rise the output pot the oscillation disappears and it comes back on the last 1/4 of the pot ride: between 6 and 0.

I have conducted some tests and apparently the oscillation appears in the signal line amp section and it goes away if I touch collector of Q4, the base of Q5 or the collector of Q6.

shorting the input doesn't do anything, nor the oscillation disappears if I touch any other component on any other part of the board.
I have tried to move the board around in the chassis but it not make any difference.
the oscillation (if seen on a scope) looks like (and sounds like) a quick burst of dc which goes form -100 to + 10 dBu every 250 mS (ish).

mmm puzzled.bad transistor? bad earth?

any hint will be much appreciated.

Bet,
Mattia.

what could cause that section to self oscillate?

 

[joe-electro]

Look for solder jumpers across adjacent traces.

Joe

Hi everybody just finishing my first unit,
I did the full calibration procedure today (although I have tested it in the studio the other day without calibrating it...I was too curious!) and althought everything went fine I have a problem:

there is a self oscillation at the output stage which shows up when the output pot is either between -infinite and 40 and when is between 6 and 0 (IE the two extreme parts of the run).
this happens regardless of the input attenuator pot, but it happens when there is no signal going through it. IE = no sinewave or music.

the scenario is the following:
if you turn the comp on and leave the input pot to zero and the output pot to zero there is a self oscillation (which shows up on the meter even when in gain reduction mode).
as soon as you rise the output pot the oscillation disappears and it comes back on the last 1/4 of the pot ride: between 6 and 0.

I have conducted some tests and apparently the oscillation appears in the signal line amp section and it goes away if I touch collector of Q4, the base of Q5 or the collector of Q6.

shorting the input doesn't do anything, nor the oscillation disappears if I touch any other component on any other part of the board.
I have tried to move the board around in the chassis but it not make any difference.
the oscillation (if seen on a scope) looks like (and sounds like) a quick burst of dc which goes form -100 to + 10 dBu every 250 mS (ish).

mmm puzzled.bad transistor? bad earth?

any hint will be much appreciated.

Bet,
Mattia.

what could cause that section to self oscillate?

 

[rodabod]

Mattia, I know you said it is occuring in the line amp section, but have you also 'scoped the preamp section for low level oscillation and also the power supply rails? Just thought I'd ask.

As always I'd double-check wiring and consult Skylar's wiring drawing too.

Cheers,

Roddy

 

[mata_haze]

Look for solder jumpers across adjacent traces.

Joe

thank you will do so first thing tomorrow morning!

Mattia, I know you said it is occuring in the line amp section, but have you also 'scoped the preamp section for low level oscillation and also the power supply rails? Just thought I'd ask.

As always I'd double-check wiring and consult Skylar's wiring drawing too.

Cheers,

Roddy

I'll check the preamp section tomorrow and make sure it actually comes from the line amp.weird it seems like it just appeard now...
I'll also double check the wiring too, although I have done that already.


thank you guys for your suggestions!

Rock and Roll!

Best,
Mattia

 

[mata_haze]

Still regarding the output oscillation:

no solder jumpers across adjacent tracks the wiring looks ok too.

I cannot track the oscllation down because as soon as I put my scope probe on any part of the circuit the oscillation disappears.
(is it called capacitive reactance?)

I also have noticed that it does it with:
my headpphones preamp (custom build) and as insert return.it behaves normally when nothing is connected to it or when I plug my neutrik A1 at the output.

this is interesting.
I wonder if the output transformer might be loaded (or loading) or If I have connected it wrongly to the mother board.

-Can anyone confirm the MNats color coding on the pcb is correct when using hairball 5002 output trafo, please?

-also, when I first powered the unit up the resistor across the primary output trafo went up in smoke.
rewired the trafo, replaced resistor and replaced the 3053 transistor.
does anyone think I should also replace the other transistors in the line amp section?


mmm I am curious to see where the problem lies.

PS Happy Easter everybody!

Best,
Mattia.

 

[Echo North]

-also, when I first powered the unit up the resistor across the primary output trafo went up in smoke.
rewired the trafo

That's the thing about using Skylar's wiring guide.  His is based off the V1 PCB...the output wiring is different for the V2.

Go to Mnats site and download the V2 pdf guide (on the left).  Check the PCB layout in the V2 PDF and make sure you have the colors right.  It's the same for the 5002.

Make sure you connect the remaining orange and yellow wires together (off the board), connect the blue to + (hot) and red to - (cold).

Mike

Edit: Oh I see in your earlier post you may have already done this.

 

[mata_haze]

Make sure you connect the remaining orange and yellow wires together (off the board), connect the blue to + (hot) and red to - (cold).

Mike

is this a must? I have connected red as hot (+) and blue as cold (-)...would this be the problem?

Best,
Mattia.

 

[mata_haze]

AH!

I have built 3 units so far an believe or not they all behave the same.

Then today I tried to swap pin 2 and 3 at the output transformer (IE= pin 2 is Blue and pin 3 is red) and at the input (for phase consistency).
guess what?

oscillation is gone.
now questions:

-how many people in EUROPE have built this unit, I mean how many have used the "standard european configuration" pin 2 being hot and pin 3 being cold using hairball 5002 trafo? Am I the only one?

-why did it mis-behave like that?If I understand correctly there is a form of negative feedback going back into (or from) the transformer in the output stage, what could happend if the output polarity is reversed?Would that become POSITIVE feedback and therefore generate instability?


I will conduct more tests tomorrow just to make sure I haven't foreseen anything but the baby seemed stable.


Best,
Mattia.

 

[rodabod]

If I understand correctly there is a form of negative feedback going back into (or from) the transformer in the output stage, what could happend if the output polarity is reversed?Would that become POSITIVE feedback and therefore generate instability?

Sounds like you have hit the nail on the head. Well done. I wouldn't have thought of that...

 

[mata_haze]

ehm silly question...
the absolute phase ot my 1176 is now reversed compared to the rest my kit (PIN2 hot).
is my assumption correct?

Best,
Mattia.