Visual Check before I turn it on - Mnats 1176 Rev D

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canidoit

Well-known member
Joined
Apr 6, 2009
Messages
1,168
Location
Australia
Anyone notice anything that I have done wrong with this build?

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Light blue wires going parrallel to Meter boards from IEC socket live. Out Meter board light blue wires in parallel to Hairball Power Transformer blue wire.

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Light Blue wires in parallel from IEC live socket to go to Meter board.

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Drips ground lift system implemented.

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I grounded "G" from Main board directly to chassis (refer to green wire in pic) which is right below it. I'm not sure whether that would be good though, I read somewhere that ALL ground should be at 1 point only as in the star ground.

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Swiss cheese down the bottom.  ;)

Close up of the board

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canidoit said:
Anyone notice anything that I have done wrong with this build?

Apart from sticking a Urei logo in a unit that is blatantly NOT Urei?

You have a case of what I would call chassis grounding paranoia. I don't know what you expect from those MASSIVE rfi removal caps, but they are very likely completely unnecessary, but with a switch also?

You should do this kind of stuff after you have tested the unit, when you find out if you actually need it. You probably don't. You only really need one chassis ground wire in the beginning: the IEC. Then ground input pin1, or first PSU filter cap to chassis. That is probably enough. You have 5 other star ground points in a simple unit like this... You're only asking for more ground loops.

But don't worry. those are easy to remove.

One other thing that strikes my eye is those twisted (or braided???) output wires. You seem to have some sleek grey 1 pair shielded cable available. That is much better suited here.
 
Kingston said:
Apart from sticking a Urei logo in a unit that is blatantly NOT Urei?
I got that from Purusha. I paid good money for that case.  :)

Kingston said:
You have a case of what I would call chassis grounding paranoia. I don't know what you expect from those MASSIVE rfi removal caps, but they are very likely completely unnecessary, but with a switch also?
The switch is my ground lift switch to turn ground lift on or off. I don't know, but I may as well implement it incase, it's Drips ground lift system.

Kingston said:
You should do this kind of stuff after you have tested the unit, when you find out if you actually need it. You probably don't. You only really need one chassis ground wire in the beginning: the IEC. Then ground input pin1, or first PSU filter cap to chassis. That is probably enough. You have 5 other star ground points in a simple unit like this... You're only asking for more ground loops.

But don't worry. those are easy to remove.
The star ground contains
- the IEC ground

Ground lift switch system, only one ground pathway will work, depending on the switch whether ground lift is active or not.
- the ground from input pin 1 XLR out
- the ground from input pin 1 XLR out using Drips ground lift system
- the ground from input pin 1 XLR in
- the ground from input pin 1 XLR in using Drips ground lift system

- the ground shield wire from Hairballs output Transformer (is it meant to be connected to the star ground? it's an option, so I thought I would implement it)

Kingston said:
One other thing that strikes my eye is those twisted (or braided???) output wires. You seem to have some sleek grey 1 pair shielded cable available. That is much better suited here.
On Skylars diagram, it shows seperate wires for the output transformer, so I did not use grey shielded cables here.

Do you think my unit is good to go?

Should I do anything else?
 
canidoit said:
Do you think my unit is good to go?

Should I do anything else?

Seems like it's ready for a smoke test.

I don't know if you did that already, but it's a good idea to socket the FETs (at least Q1). Probably the most common error is to fry them on first try if you get the pins wrong. And it's also good if in the future you want to improve FET matching.

This way you could also easily have them removed on the initial test and measure some basic PSU voltages.
 
Kingston said:
canidoit said:
Do you think my unit is good to go?

Should I do anything else?

Seems like it's ready for a smoke test.

I don't know if you did that already, but it's a good idea to socket the FETs (at least Q1). Probably the most common error is to fry them on first try if you get the pins wrong. And it's also good if in the future you want to improve FET matching.

This way you could also easily have them removed on the initial test and measure some basic PSU voltages.
Socket the fets? I am not familiar with that procedure?

I have installed the fets Q1-11 etc to match the transistor outline picture on the Mnats Rev D board and I am using 2N3708 transistors. How come? Aren't the pictures on the board correct to suit the 2n3708?
 
something like that, available in any standard electronics store:

http://www.banzaieffects.com/SIL-64-pins-pr-14556.html

cut three pins from the strip and solder that instead of the FET. now you have a socket.

But this is just an additional precautionary measure for very a common troubleshooting case. Not absolutely necessary.
 
canidoit said:
I have installed the fets Q1-11 etc to match the transistor outline picture on the Mnats Rev D board and I am using 2N3708 transistors. How come? Aren't the pictures on the board correct to suit the 2n3708?

There are only two FETs on the board: Q1 and Q10. the rest are common BJTs.

Do not EVER install a transistor on anything without checking the pinout first. And then double check it. This is the absolutely the most common case where people make mistakes with any transistor. Never trust the images on PCB boards! Check the traces yourself.
 
Looks like an okay build.

I would avoid having "loose" components. for example, the caps on the xlr's, or the resistor hanging from the pcb (meter lamp series R ?? - depending on the power going through, it can become pretty hot, so watch the cables that are touching it)

and watch out for those screws on the bottom! they will definitely scratch the unit (or a nice wooden 19") rack underneath it. You could use countersunk screw.

Try it! Turn it on, see that nothing catches smoke, measure power rails, etc
 
rodabod said:
Have you got a mains fuse on that?
I did this calculation thing and ended up with 250 volts and 250mA fuse installed at my IEC power socket for this build.

Here is the post from it:
Quote from: Biasrocks on Today at 09:54:35 am
Quote from: canidoit on Today at 08:17:16 am
What fuse for the IEC socket? On the UA 1176 re-issue, they use I think a 250 volts 1/16 amp fuse Slo Blo. What is it for the Mnats 1176 Rev D using Hairball Power Transformer for 240 volts?

http://www.groupdiy.com/index.php?topic=47.msg420494#msg420494

Mark
Looking at that link:
Assuming, you use a 6VA transformer, divide this VA by your mains voltage, giving 6VA/110V=0.055A. This transformer is maybe only 70% efficient, so multiply the 0.055A by (1/0.7), giving 0.078A. Nearest larger fuse rating will be 100mA. For the larger inrush current of a toroid you want this with slow blow/time lag characteristic. Fuse voltage rating is at least your mains voltage to prevent arcing when this fuse blows, so a 250V/100mA T (=slow blow) might fit for this example. Your transformer may/will be different, so do the math with your values.


Hairball's power transformer specs:
TRANSFORMER, 30VA, 2 X 25V
Voltages, primary:0-115, 0-115
Voltages, secondary:0-25, 0-25
Power, per secondary winding:15VA
Approval Bodies:EN60950, EN60742, UL Recognised
Current rating:0.6A
Diameter, bolt hole:5mm
Diameter, RoHS Compliant: Yes

That would mean Hairballs power transformer is 30VA. So using that method, 30va/240v = 0.125.
0.125 X 1/0.7 = 0.178A

That would mean the closest larger fuse rating would be 200ma fuse at 250 volts that I should install? Have I done this right?
 
Arno said:
I would avoid having "loose" components. for example, the caps on the xlr's, or the resistor hanging from the pcb (meter lamp series R ?? - depending on the power going through, it can become pretty hot, so watch the cables that are touching it)
Yeah, I was concerned about that as well. I saw it in one of the 1176 pictures that they placed that fat resistor there. I was thinking of putting it up near the VU lamp, but it is huge!

That fat resistor is sourcing power from the Hairball power transformer on the Main board. I think its about 35 volts and it's being downgraded to 12 volts abouts, using that fat 5 watt resistor.

Will heatshrinking the resistor make it safer for the other cables?
 
No need to overthink your fuse. You should really double that value (it will still be perfectly safe). But no point in having a fuse that is so close in spec to breaking that you'll end up constantly changing it. I have a commercial mixer with these exact symptoms (easy to fix, just put a bigger one in).

A slowblow fuse and transformer in-rush current for example, is a fuzzy area (and difficult to measure or calculate), so it's best just to over rate your fuse and not worry about it.
 
Kingston said:
No need to overthink your fuse. You should really double that value (it will still be perfectly safe). But no point in having a fuse that is so close in spec to breaking that you'll end up constantly changing it. I have a commercial mixer with these exact symptoms (easy to fix, just put a bigger one in).

A slowblow fuse and transformer in-rush current for example, is a fussy area (and difficult to measure or calculate), so it's best just to over rate your fuse and not worry about it.
O.K., Il bump it up to 500mA then.

Anyone use that fat resistor in their build to downgrade the voltage to 12 volts for the VU lamp? Where did you guys put the resistor? Where I have mine or up near the VU lamp? Does this resistor get hot? I think Hairball was using two small resistors in parallel.
 
I put the fuse in and turned it on, no smoke within the 30 seconds I left it on. Has that new smell about it. No sparks on the meter switch when I turn it on and off thru the front meter switch.

This is pretty exciting  ;D

When I press the GR on the meter board, the VU goes hard right. Time to calibrate this mother I think and plug something in to hear how it sounds.  :)

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Obviously, you're good to go. Congratulations on a beautiful build!

...time to start calibrating...

PS: I wouldnt' heatshrink that resistor. The heat has to be allowed to escape somehow.
 
canidoit said:
I put the fuse in and turned it on, no smoke within the 30 seconds I left it on. Has that new smell about it. No sparks on the meter switch when I turn it on and off thru the front meter switch.

This is pretty exciting  ;D

When I press the GR on the meter board, the VU goes hard right. Time to calibrate this mother I think and plug something in to hear how it sounds.  :)

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I also have the R44 headers not shorted.
 
I have calibrated Q-Bias and Discreet Meter circuit. What problems I encountered on the way that you can avoid doing.

Qbias points:
- When you turn the Q-bias trimmer pot, you may think it is not working because the VU meter is not moving. Keep turning it and eventually the VU meter will move and latch on depending on how far out of calibration the Qbias trimmers are. Check to see if you are turning it the right way as well, you may be going further away from getting the VU meters to move.

Discreet Meter circuit:
- If your VU meters are not moving when you turn the zero trimmer, check to see if your VU meter cabling is the right way around. My VU meters were not moving and I notice it was moving backwards so I swapped the VU cabling and it fixed the problem.
- Also if your null trimmers are so out of calibration, turning the zero trimmers will not move the VU meters. Try turning the Null trimmers CW till it is sort of at the end of its turns(it feels a little harder to turn), then CCW about 5-7 turns so that it is center of the total amount of turns it can do. Something like that. After this, turn the zero trimmers and the VU meters should start moving. Play around with that concept.
 
canidoit said:
I have calibrated Q-Bias and Discreet Meter circuit. What problems I encountered.

Qbias points:
- When you turn the Q-bias trimmer pot, you may think it is not working because the VU meter is not moving. Keep turning it and eventually the VU meter will move and latch on depending on how far out of calibration the Qbias trimmers are. Check to see if you are turning it the right way as well, you may be going further away from getting the VU meters to move.

Discreet Meter circuit:
- If your VU meters are not moving when you turn the zero trimmer, check to see if your VU meter cabling is the right way around. My VU meters were not moving and I notice it was moving backwards so I swapped the VU cabling and it fixed the problem.
- Also if your null trimmers are so out of calibration, turning the zero trimmers will not move the VU meters. Try turning the Null trimmers CW till it is sort of at the end of its turns(it feels a little harder to turn), then CCW about 5-7 turns so that it is center of the total amount of turns it can do. Something like that. After this, turn the zero trimmers and the VU meters should start moving. Play around with that concept.

Are you saying that your meter is pegged and not responding to the adjustment?

If that's the case, I had a similar problem that was solved by moving the meter lead to the alternate place provided on the PCB. It should be right next to where you have it installed now.

Mark
 

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