[BUILD] New FET/RACK Official Help Thread - Please read first post!

Help Support GroupDIY:

mnats

Well-known member
Joined
Jun 3, 2004
Messages
984
Location
Australia


You can see more about it at Hairball Audio. Build guide is at Hairball's blog site. Some background information and documentation can be found on my FET/RACK page.

Problems with this build? Read the 1176 FAQ.

Please post any questions not answered by the FAQ above or the extensive information at Hairball Audio's site to this thread. Please do not start new threads just for your particular issue with the FET/RACK as these will not be monitored by Mike or myself. Please keep any commercial discussion confined to the White Market Thread

 

Hxcplayer

Member
Joined
Jul 5, 2016
Messages
23
Thanks Mike & Mnats for helping us out to get our hands on some great sounding gear!

I just have a small quick question which I am a bit worried about.

I'm kind of a noob in electronics and I'm trying to nail down everything properly on the first go for my build.

I just finished building my power supply and was checking the ground resistance.
Mike states on his blog that you need to have a ground reference close to 0.2 Ω and anything above 1 Ω is danger.
I'm getting a reading of 0.8 to 0.9 Ω. I'm not sure why it is that high. Is this an alright ground to start plugging in my 1176?
What can I do to decrease the resistance?

EDIT (NEW QUESTION):
I turned on my unit to test out the readings as stated in the build guide.
After about 5 sec from power up a quick tiny line of smoke passed by.
I didn't catch from which component it came from as I was a bit worried about the capacitor blowing up as mentioned in the guide.

I proceeded to do the readings of the -10V diode and +30V zener diode and they were reading correctly.
I then turned off the unit and tested the two 1k resistors. they were ranging around 900 and 950 ohms.
The 75 resistor was ranging properly at almost exactly 75 ohms.

Should I be worried even if everything is reading correctly?

I would also like to mention that when I first turned on the power supply, there was a small weird noise at the IEC that lasted like 3 sec before the smoke.

Thanks!
 

Echo North

Well-known member
Joined
Jan 21, 2006
Messages
4,433
Location
Seattle, WA
Hxcplayer said:
I just finished building my power supply and was checking the ground resistance.
Mike states on his blog that you need to have a ground reference close to 0.2 Ω and anything above 1 Ω is danger.
I'm getting a reading of 0.8 to 0.9 Ω. I'm not sure why it is that high. Is this an alright ground to start plugging in my 1176?
What can I do to decrease the resistance?

Hard to say, but there is a chance that resistance is from you meter probes. You could touch your probes together (not touching your build) and see what the resistance reading is in just the probes.  Subtract that number from the number your getting when you measure the FET rack ground.

Hxcplayer said:
EDIT (NEW QUESTION):
I turned on my unit to test out the readings as stated in the build guide.
After about 5 sec from power up a quick tiny line of smoke passed by.
I didn't catch from which component it came from as I was a bit worried about the capacitor blowing up as mentioned in the guide.

That's not a cap failing.  That would be huge event that would stink up your room.

Hxcplayer said:
I proceeded to do the readings of the -10V diode and +30V zener diode and they were reading correctly.
I then turned off the unit and tested the two 1k resistors. they were ranging around 900 and 950 ohms.
The 75 resistor was ranging properly at almost exactly 75 ohms.

Should I be worried even if everything is reading correctly?

I would also like to mention that when I first turned on the power supply, there was a small weird noise at the IEC that lasted like 3 sec before the smoke.

Thanks!

Readings were good, that's good.

You can't really test resistors on the board without considering what's around them.  Those resistors are in series so they shouldn't be interacting with one another however there may be other considerations like the caps and diodes around them. If you're worried about those resistors you can de-solder and lift one leg and then measure.  I suspect they'll read fine.

Make sure your voltage select switch is set correctly.

Not sure about the smoke but it sounds like you're working ok. I little high pitched noise on power-up is normal if I recall correctly. Probably the power transformer. If you had anything really wrong the fuse would blow.

Mike
 

Hxcplayer

Member
Joined
Jul 5, 2016
Messages
23
Hairball Audio said:
Hxcplayer said:
I just finished building my power supply and was checking the ground resistance.
Mike states on his blog that you need to have a ground reference close to 0.2 Ω and anything above 1 Ω is danger.
I'm getting a reading of 0.8 to 0.9 Ω. I'm not sure why it is that high. Is this an alright ground to start plugging in my 1176?
What can I do to decrease the resistance?

Hard to say, but there is a chance that resistance is from you meter probes. You could touch your probes together (not touching your build) and see what the resistance reading is in just the probes.  Subtract that number from the number your getting when you measure the FET rack ground.

Hxcplayer said:
EDIT (NEW QUESTION):
I turned on my unit to test out the readings as stated in the build guide.
After about 5 sec from power up a quick tiny line of smoke passed by.
I didn't catch from which component it came from as I was a bit worried about the capacitor blowing up as mentioned in the guide.

That's not a cap failing.  That would be huge event that would stink up your room.

Hxcplayer said:
I proceeded to do the readings of the -10V diode and +30V zener diode and they were reading correctly.
I then turned off the unit and tested the two 1k resistors. they were ranging around 900 and 950 ohms.
The 75 resistor was ranging properly at almost exactly 75 ohms.

Should I be worried even if everything is reading correctly?

I would also like to mention that when I first turned on the power supply, there was a small weird noise at the IEC that lasted like 3 sec before the smoke.

Thanks!

Readings were good, that's good.

You can't really test resistors on the board without considering what's around them.  Those resistors are in series so they shouldn't be interacting with one another however there may be other considerations like the caps and diodes around them. If you're worried about those resistors you can de-solder and lift one leg and then measure.  I suspect they'll read fine.

Make sure your voltage select switch is set correctly.

Not sure about the smoke but it sounds like you're working ok. I little high pitched noise on power-up is normal if I recall correctly. Probably the power transformer. If you had anything really wrong the fuse would blow.

Mike

Thanks a lot for the great detailed and fast replies Mike!

I will proceed with the soldering of the signal pre-amp section.

Cheers!
 

Harpo

Well-known member
Joined
Oct 29, 2005
Messages
2,399
Location
Rahden, Germany
Hxcplayer said:
I proceeded to do the readings of the -10V diode and +30V zener diode...
Both are zeners  ;) (the 1N4740 for the -10VDC rail obviously with wrong symbol for CR9 in the schematic), but if you placed the correct part with correct orientation, all should be fine.
 

mnats

Well-known member
Joined
Jun 3, 2004
Messages
984
Location
Australia
Harpo said:
(the 1N4740 for the -10VDC rail obviously with wrong symbol for CR9 in the schematic)
Thanks for pointing this out. I will fix the documentation. *edit - zener symbol fixed as well as some resistor quantity errors on the Rev D doc.*
 

Hxcplayer

Member
Joined
Jul 5, 2016
Messages
23
Quick question about Q12 & Q13 transistors.

Is it necessary for them to touch on their flat surface?

If so, can anybody explain why? I am quite curious.

I'm having a hard time getting them to touch perfectly!

Thanks.

EDIT: Nevermind...  Answer: "THERMAL COUPLING"

But if someone has some tips on how to get them flat touching on each other, that would be great!

*Picture Below*
 

Attachments

  • 21312312321.jpg
    21312312321.jpg
    416.2 KB · Views: 69

Hxcplayer

Member
Joined
Jul 5, 2016
Messages
23
This is as close as I could get them...

Any help or recommendation would be much appreciated.

FRONT SIDE
Transistor_Side_1.jpg


BACK SIDE
Transistor_Side_2.jpg
 

mnats

Well-known member
Joined
Jun 3, 2004
Messages
984
Location
Australia
Hxcplayer said:
This is as close as I could get them...

Any help or recommendation would be much appreciated.
If I'm understanding correctly you want to know how to get two transistors to contact each other after they are soldered in place. In my experience it is best to bind them together - either temporarily or permanently - before soldering them. Otherwise the three leads create a stable tripod that inhibits their movement.

However there is no compelling reason why they need to touch in this application. It just helps the stability of the circuit if they are near, otherwise thermal variations cause the needle to drift in GR mode.
 

Potato Cakes

Well-known member
Joined
Jul 1, 2014
Messages
1,886
Location
Nashville, TN
Dang it!

How am I ever supposed to finish remodeling my house with all this cool stuff to build?!

Also, the stereo linking option looks more solid than the original red versions. How well do the two compression circuits track with the new linking version? I may have to replace the ones in my stereo Rev D that I build some time ago.

Thanks!

Paul
 

Hxcplayer

Member
Joined
Jul 5, 2016
Messages
23
mnats said:
Hxcplayer said:
This is as close as I could get them...

Any help or recommendation would be much appreciated.
If I'm understanding correctly you want to know how to get two transistors to contact each other after they are soldered in place. In my experience it is best to bind them together - either temporarily or permanently - before soldering them. Otherwise the three leads create a stable tripod that inhibits their movement.

However there is no compelling reason why they need to touch in this application. It just helps the stability of the circuit if they are near, otherwise thermal variations cause the needle to drift in GR mode.

Hey Mnats, Thanks for the reply.

Yea I want them to stay in contact to prevent any mishaps in the latter stages.

Would you say using duct tape to couple them together is a safe way to do this?
If not, what material would you recommend to couple them properly together?

But from what I understand, the way I have them placed will do just fine I suppose, correct?
 

Potato Cakes

Well-known member
Joined
Jul 1, 2014
Messages
1,886
Location
Nashville, TN
You could do how the the transistors on Hairball's 990. They use shrink tubing to keep them right next to each other. or you could just apply some thermal paste.

Thanks!

Paul
 

Echo North

Well-known member
Joined
Jan 21, 2006
Messages
4,433
Location
Seattle, WA
Potato Cakes said:
Dang it!

How am I ever supposed to finish remodeling my house with all this cool stuff to build?!

Also, the stereo linking option looks more solid than the original red versions. How well do the two compression circuits track with the new linking version? I may have to replace the ones in my stereo Rev D that I build some time ago.

Thanks!

Paul

Hi Paul,

It's the same linking, adapted from the MC77. It's just set up to be integrated easier.

It tracks well however, since the linking is preformed before the side chain, all of the side chain component tolerences are brought into play. So you need to tweak the att/rel and output on each unit a little once your stereo material is set up.

The kits come with the traditional UREI RCA link which is post side chain and tracks well. However, it does slow your attack time and you'll need stereo FETs or a UA link box.

Both have pros and cons.

Mike
 

Potato Cakes

Well-known member
Joined
Jul 1, 2014
Messages
1,886
Location
Nashville, TN
Mike,

Thanks for the info.

I think that if it's pretty close, it will be more than sufficient for the material that this was designed for, or at least how I use mine.

Thanks!

Paul
 

Hxcplayer

Member
Joined
Jul 5, 2016
Messages
23
Is this ruined?

I suppose there is no way to fix this right?  :'(

 

Attachments

  • 231321312312.jpg
    231321312312.jpg
    729.7 KB · Views: 138

Hxcplayer

Member
Joined
Jul 5, 2016
Messages
23
I checked continuity from the RED point to both GREEN points using the Diode function on my DMM.

It was reading 1V when not touching, and 0V when touching either points.

Does this mean the scratched trace is not damaged and will function properly?

How can I cover it up/fix the scratched part?

Thanks.
 

Attachments

  • Continuity Points.jpg
    Continuity Points.jpg
    847 KB · Views: 74

Echo North

Well-known member
Joined
Jan 21, 2006
Messages
4,433
Location
Seattle, WA
I don't really see anything too bad.

Check the continuity with the Ω setting.  When you touch each end of the trace, is the reading less than 1Ω?

Mike
 

Hxcplayer

Member
Joined
Jul 5, 2016
Messages
23
Hairball Audio said:
I don't really see anything too bad.

Check the continuity with the Ω setting.  When you touch each end of the trace, is the reading less than 1Ω?

Mike

Hey Mike,

I'm getting a reading between 0.7 to 0.8 Ω, that's a good thing I suppose?
 

Echo North

Well-known member
Joined
Jan 21, 2006
Messages
4,433
Location
Seattle, WA
Hxcplayer said:
Hairball Audio said:
I don't really see anything too bad.

Check the continuity with the Ω setting.  When you touch each end of the trace, is the reading less than 1Ω?

Mike

Hey Mike,

I'm getting a reading between 0.7 to 0.8 Ω, that's a good thing I suppose?

Yup...most of that resistance is probably in your leads.  You should be good.
 

Latest posts

Top