Hairball/Mnats 1176 rev D calibration/meter issue

jeffinaustin · Nov 23, 2012

Been using the comp for a couple of weeks now, but it never has responded correctly (though it sounds great!). My buddy and I went through the calibration steps again tonight and all is well until we get to the final step. What we notice is that:
- 4:1, 8:1, 12:1 seem to respond ok, but when pressing 20:1 it indicates no gain reduction
- when selecting 4:1 in VU mode the meter pings up to +1-+2 before slowly resetting itself back to 0

After all is said and done do you think the meter is just not 100% or do you think we've missed something else?

One more thing: on the final calibration step we never could get it to go to the -10db drop without increasing the input up almost all the way and the output almost all the way down.

Any help GREATLY appreciated!

Echo North · Nov 24, 2012

jeffinaustin said:
Been using the comp for a couple of weeks now, but it never has responded correctly (though it sounds great!). My buddy and I went through the calibration steps again tonight and all is well until we get to the final step. What we notice is that:
- 4:1, 8:1, 12:1 seem to respond ok, but when pressing 20:1 it indicates no gain reduction
- when selecting 4:1 in VU mode the meter pings up to +1-+2 before slowly resetting itself back to 0

After all is said and done do you think the meter is just not 100% or do you think we've missed something else?

One more thing: on the final calibration step we never could get it to go to the -10db drop without increasing the input up almost all the way and the output almost all the way down.

Any help GREATLY appreciated!

Might be an issue with R61 or R58 on the ratio board. Wrong value or maybe a short around there?

jeffinaustin · Nov 25, 2012

Checked the values of both and they are correct. Soldering looks clean. No bridges or gaps anywhere. Any more thoughts?

MoakJones · Feb 24, 2013

Hello All,

Saw this thread and have been having the same issue.

"on the final calibration step we never could get it to go to the -10db drop without increasing the input up almost all the way and the output almost all the way down."

jeffinaustin, have you had any luck since you posted? I've built 12 of these kits and for some reason this same problem has existed with every single one I had built, so I think that there must be a fundamental issue that I am doing and not a problem with solder/components.

Any help would be much appreciated, thanks!

Bobby Baird · Jun 20, 2013

I had the same problem during calibration after building my first 1176 clone. I could only get 7db of gain reduction with the recommended 2k bias pot. All you have to do is replace it with a 5k pot which will effectively give you more input gain as well as lowering the threshold of gain reduction enabling you to get the recommended 10db of gain reduction for the calibration. You may want to replace the meter tracking pot with a 5k pot as well. These modifications allowed me to get the proper calibration on my 1176 clone. Squish. 8)

Echo North · Jun 21, 2013

Bobby Baird said:
I had the same problem during calibration after building my first 1176 clone. I could only get 7db of gain reduction with the recommended 2k bias pot. All you have to do is replace it with a 5k pot which will effectively give you more input gain as well as lowering the threshold of gain reduction enabling you to get the recommended 10db of gain reduction for the calibration. You may want to replace the meter tracking pot with a 5k pot as well. These modifications allowed me to get the proper calibration on my 1176 clone. Squish. 8)

Did you HFE math the two transistors in the meter section. Q12 and 13 I think? That could cause that issue.

Bobby Baird · Jun 21, 2013

Yep HFE 330 & 334 on my meter. I used 2n3707. I bought 20 transistors and matched all of them. I measured HFE on a $40.00 meter kit that I built, so I can't guarantee how accurate the reading is.

Steventje123456789 · Oct 7, 2013

Hello, I recently finished my Rev D from mnats and I have a small issue. When calibration the meter for the 3e step, i only can get -4db of gaan reduction. Also when the video said to adjust your input if the drop isn't 10 db my problem is that when I turn the input up as said in the video the GR Goes back to zero instead of dropping to -10db anybody had this problem and know how to fix this?

I matches Q12and Q13 so that isn't the problem.

Kind regards and thanks for any help.

Steven

heffree · Nov 20, 2013

Hello, I just finished a rev D kit from mnats/hairball and seem to be having this same issue. Everything looks good till I get to the last calibration step. I go back and forth trying to get a -10db drop but even with the input all the way up i can only get about -7 db in gain reduction. Does anyone have any updates on this issue? I have double checked all the components such and R61 and R58 and the problem persists. I guess I'll attempt switching out the bias pot for a 5k one next?

Echo North · Nov 21, 2013

heffree said:
Hello, I just finished a rev D kit from mnats/hairball and seem to be having this same issue. Everything looks good till I get to the last calibration step. I go back and forth trying to get a -10db drop but even with the input all the way up i can only get about -7 db in gain reduction. Does anyone have any updates on this issue? I have double checked all the components such and R61 and R58 and the problem persists. I guess I'll attempt switching out the bias pot for a 5k one next?

If anyone wants to try a 5K trimmer let me know and I can send you one. Send and email to "info at hairballaudio dot com".

If that works than it's an issue with HFE most likely. The issue is probably how the individual meter is testing HFE. If the supply for the meters HFE tester is not getting into the transistors Q point and hanging out in the lower or upper part of the curve, the van look matched when they really are not.

Mike

heffree · Nov 21, 2013

Hairball Audio said:
If that works than it's an issue with HFE most likely. The issue is probably how the individual meter is testing HFE. If the supply for the meters HFE tester is not getting into the transistors Q point and hanging out in the lower or upper part of the curve, the van look matched when they really are not.

Mike

Maybe I'll go get another meter and check my HFE again on it. Just to double check, I'm supposed to be matching Q12 and Q13 right?

Countrymetalguy · Nov 21, 2013

Hairball Audio said:
heffree said:

Hello, I just finished a rev D kit from mnats/hairball and seem to be having this same issue. Everything looks good till I get to the last calibration step. I go back and forth trying to get a -10db drop but even with the input all the way up i can only get about -7 db in gain reduction. Does anyone have any updates on this issue? I have double checked all the components such and R61 and R58 and the problem persists. I guess I'll attempt switching out the bias pot for a 5k one next?

Click to expand...

If anyone wants to try a 5K trimmer let me know and I can send you one. Send and email to "info at hairballaudio dot com".

If that works than it's an issue with HFE most likely. The issue is probably how the individual meter is testing HFE. If the supply for the meters HFE tester is not getting into the transistors Q point and hanging out in the lower or upper part of the curve, the van look matched when they really are not.

Mike

Hi Mike, I just finished two REV D kits and am having the same problems on the last calibration step as well. The kits i got were the complete ones and I used the "matched transistors" you have packaged seperately in the correct spots to I wonder if its is the HFE. I am going to try the 5k trimmer trick and see if that fixes it.
Love my 1176 kits by the way... Thanks for making them available for all us DIYers. Your efforts are greatly appreciated!
Mark

Countrymetalguy · Nov 22, 2013

Countrymetalguy said:
Hairball Audio said:

heffree said:

Hello, I just finished a rev D kit from mnats/hairball and seem to be having this same issue. Everything looks good till I get to the last calibration step. I go back and forth trying to get a -10db drop but even with the input all the way up i can only get about -7 db in gain reduction. Does anyone have any updates on this issue? I have double checked all the components such and R61 and R58 and the problem persists. I guess I'll attempt switching out the bias pot for a 5k one next?

Click to expand...

If anyone wants to try a 5K trimmer let me know and I can send you one. Send and email to "info at hairballaudio dot com".

If that works than it's an issue with HFE most likely. The issue is probably how the individual meter is testing HFE. If the supply for the meters HFE tester is not getting into the transistors Q point and hanging out in the lower or upper part of the curve, the van look matched when they really are not.

Mike

Click to expand...

Hi Mike, I just finished two REV D kits and am having the same problems on the last calibration step as well. The kits i got were the complete ones and I used the "matched transistors" you have packaged seperately in the correct spots to I wonder if its is the HFE. I am going to try the 5k trimmer trick and see if that fixes it.
Love my 1176 kits by the way... Thanks for making them available for all us DIYers. Your efforts are greatly appreciated!
Mark

Did the 5k pot thing to both of mine today and it fixed em right up!
Thanks for the tip!

veve · Jan 20, 2014

I've the same problem with my revD... I will try this asap..

Cool; I wondering how I can find the solution!!!

;D

Chryst · Apr 29, 2014

I have the same problem. Too little compression when doing the meter tracking adjustment. I already have the 5k pots installed. Can somebody confirm that it is likely that this problem is caused by unmatched (3708) FET's? I'm about to order a meter to sort this out, but I never had this problem before.

Thanks!!

ericfergus · Jun 25, 2014

Hello, this is my first post so my apologies in advance if I have done something wrong.

I seem to have a similar issue. The unit passes audio but does not compress. The Q bias and Discrete Meter Circuit/Null Adjust seem to calibrate fine, but I get no compression, let alone -10dB, when following the "Gain Reduction Meter Tracking Adjustment" steps. Turing on/off the attack does nothing.

If done my best to check everything. Connections look fine. I double checked all resistor codes and cap value stencils. I couldn't find a short. I also checked the voltage values of all transistors to the MNATS troubleshooting schematic. Although not perfectly the same, all were close and were proportional between pins.

I did check the HFE on a pile of 708s when stuffing the board and they are closely matched. Although I purchased a complete kit, I failed to check the HFEs when first stuffing the board, so I purchased a bunch of 708s after the fact and made a matched pair. If I recall, they measured around 320.

Could this problem be solved by swapping out for 5k trimmer pots or does anybody else have a suggestion?

Thanks for your help in advance!

Eric

bdunard · Sep 22, 2015

Ericfergus,

I am having the same problem that you are having. Steps 1 and 2 are fine but I am getting no gain reduction when rotating my attack in step 3. I know that I matched the transistors in Q12 and Q13. Any insight is appreciated. Thanks!

Dr. Lessley · Mar 4, 2016

hello, I'm having trouble with step 1 of the calibration...i've turned the q bias adjust all the way in both directions and nothing happens to either the voltage reading or the vu meter. i,ve checked all of the wiring and solder joints and everything looks good. any hints or advice would be much appreciated.

thanks in advance

Echo North · Mar 4, 2016

Dr. Lessley said:
hello, I'm having trouble with step 1 of the calibration...i've turned the q bias adjust all the way in both directions and nothing happens to either the voltage reading or the vu meter. i,ve checked all of the wiring and solder joints and everything looks good. any hints or advice would be much appreciated.

thanks in advance

I'm going to copy this over to the D thread. Let's work on it there

http://groupdiy.com/index.php?topic=20058.5180

Mike

Hairball/Mnats 1176 rev D calibration/meter issue

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