[BUILD] Hairball Audio "Lola" Mic Pre - On Sale Now

[Echo North]

Please help:

I build a lola and it smoked out on me during a session.  Worked for 2h and then stopped.  The DOAs were very hot.  R37, R32, R31 look fried.  Is it the DOAs?  Have I fried the whole thing?

Yikes!

What DOA's do you have? JH-990C's or the Hairball kind?  If you have the Hairball kind were the pre-built or DIY?

Those R's you refer to are 10Ω current limiting resistors that sit at the DOA supply pins.  They protect your DOA in case of a short or failure.  Likely there is an issue with the DOA's.  A misplaced part, short, or some type of failure.

Let me know what type they are and if you built them, and we can move from there.  Once we get the DOA's fixed, you should be able to replace the 4 supply pin R's and be back in business.

Mike

 

[solarplexus]

The DOAs are DIY from your kit.  Have I fried some parts on the DOA with the heat?

 

[Echo North]

The DOAs are DIY from your kit.  Have I fried some parts on the DOA with the heat?

Not necessarily.  Do you have the diodes properly mounted to the output transistors with clips?  Check for shorts on the DOA.  Are C3-6 oriented correctly?

Somethings causing the DOA's to pull a lot of current and fry those resistors.  Is there are chance you mixed up some resistors when building the DOAs?  Like mixing up the 3.9Ω and 33KΩ resistors?

 

[dmp]

The DOAs are DIY from your kit.

Did you use the right value resistors for 24v? Two resistors in the 990 kit are for 16v

 

[solarplexus]

Which resistors are they and what are their value for 24v?

 

[Echo North]

Which resistors are they and what are their value for 24v?

You're using your Lola in a lunch box right?  So it'll be running on 16V rails.  In this case R10 and R11 should be 33K.  These are the ones supplied with the kits.  For 24V they should be 62K.  Even if you mixed this up, it really shouldn't cause that issue (I don't think).

I've had this issue in the past and it was a short on the DOA causing it.

 

[Echo North]

Make sure there isn't a short at your input TX for the K1/K2 relays.

It's weird that they are BOTH getting hot and both had supply reistors fry.

Where are you located?

 

[solarplexus]

I also find it weird that it worked for 2h before smoking.  I am in Canada.  I saw that maybe the leads on the DOA's L2 might have touched.  Could it be the problem?

 

[solarplexus]

Ok I think I know what I did wrong.  The output transistors....

JE181G and JE171G... they are not at the same place on each board.  Could this be it?  Probably is.  Do you think I fried the DOA with this error?

 

[Echo North]

I also find it weird that it worked for 2h before smoking.  I am in Canada.  I saw that maybe the leads on the DOA's L2 might have touched.  Could it be the problem?

A little weird but not necessarily.  The op-amps are pretty tough, they'll last a bit at high current until something breaks down or thermally runs off.  I'm thinking it might just be one opamp.

I don't think shorting L2 would cause that issue but it's possible.  You could fix that and replace the 10Ω resistors, fire it up again and monitor.  Send me an email at the "info (at) hairballaudio (dot) com address if you like and I can give you a few options to get it working for you.

Mike

 

[Echo North]

Ok I think I know what I did wrong.  The output transistors....

JE181G and JE171G... they are not at the same place on each board.  Could this be it?  Probably is.  Do you think I fried the DOA with this error?

Ya that would do it.  You probably fried a one or both.  Little bugger probably held on for a bit before breaking down. 

Shoot me an email, I'll send you new ones if you pay for shipping.

 

[3nity]

Hi Mike one question here, you using a gapped transformer here. however im wondering if theres a chance to uses a non gapped transformer??

 

[solarplexus]

How can I test to see if the transistors are fried?  I have unsoldered them and I have a multimeter.

 

[Echo North]

Hi Mike one question here, you using a gapped transformer here. however im wondering if theres a chance to uses a non gapped transformer??

I don't think it would be an issue.  There shouldn't be significant DC at the output.

 

[Echo North]

How can I test to see if the transistors are fried?  I have unsoldered them and I have a multimeter.

There are a number of articles out there like this one:
http://www.learnabout-electronics.org/transistor_faults_06.php

Basically test junctions, I'm pretty sure they would be fried but it's worth a look.  Here is the pinout info for the 171(PNP) and 181(NPN).

http://www.onsemi.com/pub_link/Collateral/MJE171-D.PDF

Mike

 

[solarplexus]

I checked both, and they have a hfe of 1400.  I think they are still good?

 

[Echo North]

I checked both, and they have a hfe of 1400.  I think they are still good?

No shorts beween the junctions like in the link?

You could always pop them in.  The worst case is that the 10Ω R's burn-up again.  You need to replace those.

Something had to have broke down.  Maybe it was just the R's.

Mike

 

[solarplexus]

I tried them.  Works!  I'll let it sit there ON for a while, see if something else goes wrong.  Thanks for all the help guys!

 

[Echo North]

Cool!  Ya there was surely excess current which eventually burnt out the 10Ω R's.  Which is exactly why they are there, to sacrifice themselves to prevent further damage.

I think you'll be ok now.  8)

Mike

 

[Pliplo]

I finished my unit and have been using it for some weeks now... I noticed the meter lights flicker when i turn the PPM/VU switch up and down, but it doesnt give me readings when im tracking... Does it only work in line mode or i made a mistake somewhere?