[BUILD] 1176LN Rev D DIY

[audiophreak]

Hello  ;D

  I've done a couple searches but haven't found exactly what I'm looking for ...

  My power ON switch has an LED indicator and I have LEDS for meter illumination , I have add them to the -10vdc rail and have made some current draw tests with my DMM.

  With out and LEDs , just the two Rev.D circuits I'm reading 140mA on the +30vdc side and 15mA on the -10vdc side - I am using an older mnats (+/-) psu with a mnats 30VA dual 25vac PT.

  I added all three LEDs to the -10vdc side and measured 50mA draw.

I read in one of the searches that you shouldn't run the LEDs from the -10vdc rail

although it seems to have worked, is it advisable to keep it this way ?

and do those current draw figures without the LEDS look correct ?

and if I shouldn't run the LEDS from the -10vdc rail , should I run them from the +30vdc rail ? or make a separate PSU.


  any and all suggestions appreciated , Thanks !! 

 

[Chryst]

Hey! I've build several HB 1176's without any problems, but I can't seem to be able to solve this one. Everything seems to work fine, however when I come to the last calibration step I can only get about 5 db of compression. The other calibration steps went without any problems.

To be sure I rematched a new set of FETS with higher HFE's, but the response seems to be the same. What I did notice however that it was extremely hard to get the right output voltage as the output pot seemed extremely sensitive. I've tried to measured its resistance and I only get 125 ohm instead of 250. However it was already connected, so it's possible that the lower resistance is caused by that. Output voltage can be as high as 20V though with everything cranked up.

I also remeasured all voltages and they seem to be fine.

It looks a bit like I'm lacking some throw on the input pot. However all the voltages on that side (entering the board) seem fine.

Does anybody have any suggestions how to tackle this one? Thanks for your help! It's greatly appreciated!

Lots going on here.

Measuring resistance in circuit rarely gives the correct reading as there is usually some parallel resistance.

Checking against the schematic w/ voltages works out?  Nothing weird?

The output pot could be slightly sensitive coma red to the original.  It's no really sensitivity but rather a steeper log curve.

In by pass is the signal clean and sound ok?

You could try a 5K rather than 2K pot in the GR section.  HFE measurements on a DMM can be hit or miss.

Thanks!
I've replaced all the suspect FETS, but there isn't any significant change. The signal sounds fine and I it compresses as well, but way to little. I can only get about 5 db's of compression with the meter tracking adjustment.
I did put in the 5k pots from the start on the 'Q Bias', the 'Null adj' and the 'tracking adj' pots. Could replacing them with 2k pots make any difference?

Really appreciate your help!

 

[Echo North]

Hey! I've build several HB 1176's without any problems, but I can't seem to be able to solve this one. Everything seems to work fine, however when I come to the last calibration step I can only get about 5 db of compression. The other calibration steps went without any problems.

To be sure I rematched a new set of FETS with higher HFE's, but the response seems to be the same. What I did notice however that it was extremely hard to get the right output voltage as the output pot seemed extremely sensitive. I've tried to measured its resistance and I only get 125 ohm instead of 250. However it was already connected, so it's possible that the lower resistance is caused by that. Output voltage can be as high as 20V though with everything cranked up.

I also remeasured all voltages and they seem to be fine.

It looks a bit like I'm lacking some throw on the input pot. However all the voltages on that side (entering the board) seem fine.

Does anybody have any suggestions how to tackle this one? Thanks for your help! It's greatly appreciated!

Lots going on here.

Measuring resistance in circuit rarely gives the correct reading as there is usually some parallel resistance.

Checking against the schematic w/ voltages works out?  Nothing weird?

The output pot could be slightly sensitive coma red to the original.  It's no really sensitivity but rather a steeper log curve.

In by pass is the signal clean and sound ok?

You could try a 5K rather than 2K pot in the GR section.  HFE measurements on a DMM can be hit or miss.

Thanks!
I've replaced all the suspect FETS, but there isn't any significant change. The signal sounds fine and I it compresses as well, but way to little. I can only get about 5 db's of compression with the meter tracking adjustment.
I did put in the 5k pots from the start on the 'Q Bias', the 'Null adj' and the 'tracking adj' pots. Could replacing them with 2k pots make any difference?

Really appreciate your help!

Are you only compressing 5dB (measured at the output) or are you compressing lots and it's a meter issue?

 

[Echo North]

So I am all business now, +4, +8 and GR shows OK, compression switch works just fine and I am getting visible (on scope at least) compression. However with 0.775VAC on input I am getting audible distortion on every compression rate when GR meter shows -1 to -2dB compression. When off (attack fully CCW) the audio out is good and without distortion, when attack on it doesn't matter if I am fully CW or 12 o'clock, distortion is there. Any idea what is wrong?

Did you check your voltages against the schematic with voltages?

 

[musicalsl]

Hello. After Reading and re-reading this thread. i feel i still dont have a definitive answer to how to either raise the threshold or to lower the preamp level. Ultimately to make it so i can drive the input harder with less compression or compression happening later. having the Input and output pots higher than 9 o'clock. I keep seeing the issue mentioned but no actual definitive way to manage the issue.

One person say "100k resistor in series with the link between (22) on the pcb and the 'GR off' switch" and others say put a 100k trimpot in series with the sidechain input: one side to the top leg of the output pot, the wiper to the 56k(r26) at input and the other side of the trimpot to ground.

I found the 100K resistor only lifted the threshold a small amount 3-4db and didnt translate to what i wanted.

I have the same desire with my REV and 2 REV J to get more scope out of my input and output with a higher threshold.

Cheers.
Sam

 

[musicalsl]

Using a 180k resistor lifted the threshold up by around 8db which is great but I think I want the output from the preamp lowered aswell.
Thoughts?

 

[Chryst]

Hey! I've build several HB 1176's without any problems, but I can't seem to be able to solve this one. Everything seems to work fine, however when I come to the last calibration step I can only get about 5 db of compression. The other calibration steps went without any problems.

To be sure I rematched a new set of FETS with higher HFE's, but the response seems to be the same. What I did notice however that it was extremely hard to get the right output voltage as the output pot seemed extremely sensitive. I've tried to measured its resistance and I only get 125 ohm instead of 250. However it was already connected, so it's possible that the lower resistance is caused by that. Output voltage can be as high as 20V though with everything cranked up.

I also remeasured all voltages and they seem to be fine.

It looks a bit like I'm lacking some throw on the input pot. However all the voltages on that side (entering the board) seem fine.

Does anybody have any suggestions how to tackle this one? Thanks for your help! It's greatly appreciated!

Lots going on here.

Measuring resistance in circuit rarely gives the correct reading as there is usually some parallel resistance.

Checking against the schematic w/ voltages works out?  Nothing weird?

The output pot could be slightly sensitive coma red to the original.  It's no really sensitivity but rather a steeper log curve.

In by pass is the signal clean and sound ok?

You could try a 5K rather than 2K pot in the GR section.  HFE measurements on a DMM can be hit or miss.

Thanks!
I've replaced all the suspect FETS, but there isn't any significant change. The signal sounds fine and I it compresses as well, but way to little. I can only get about 5 db's of compression with the meter tracking adjustment.
I did put in the 5k pots from the start on the 'Q Bias', the 'Null adj' and the 'tracking adj' pots. Could replacing them with 2k pots make any difference?

Really appreciate your help!

Are you only compressing 5dB (measured at the output) or are you compressing lots and it's a meter issue?

It's even hard to really measure because of the very steep response of the output pot. It passes audio fine and it also seems to compress a bit, but not a workable amount. I'm now getting another unit to the studio to physically compare them and see if any mistake on the board is made. Could swapping out the pots make any difference? Thanks!

Edit: To clarify, swapping back the 5k pots with 2k pots.

 

[dmnieto]

Using a 180k resistor lifted the threshold up by around 8db which is great but I think I want the output from the preamp lowered aswell.
Thoughts?

Are you sure you did not wire the input transformer reversed? What appears to be is that your input is too hot. What is the output level of your interface?

 

[musicalsl]

Sorry, I'll explain myself better. Everything work as it should.  Im just chasing a modification of the compressor the lower the level going to the gain reduction circut so I can push the input up higher before compression and push the output higher than 9 0'clock.
Cheers
Sam.

 

[Echo North]

Hey! I've build several HB 1176's without any problems, but I can't seem to be able to solve this one. Everything seems to work fine, however when I come to the last calibration step I can only get about 5 db of compression. The other calibration steps went without any problems.

To be sure I rematched a new set of FETS with higher HFE's, but the response seems to be the same. What I did notice however that it was extremely hard to get the right output voltage as the output pot seemed extremely sensitive. I've tried to measured its resistance and I only get 125 ohm instead of 250. However it was already connected, so it's possible that the lower resistance is caused by that. Output voltage can be as high as 20V though with everything cranked up.

I also remeasured all voltages and they seem to be fine.

It looks a bit like I'm lacking some throw on the input pot. However all the voltages on that side (entering the board) seem fine.

Does anybody have any suggestions how to tackle this one? Thanks for your help! It's greatly appreciated!

Lots going on here.

Measuring resistance in circuit rarely gives the correct reading as there is usually some parallel resistance.

Checking against the schematic w/ voltages works out?  Nothing weird?

The output pot could be slightly sensitive coma red to the original.  It's no really sensitivity but rather a steeper log curve.

In by pass is the signal clean and sound ok?

You could try a 5K rather than 2K pot in the GR section.  HFE measurements on a DMM can be hit or miss.

Thanks!
I've replaced all the suspect FETS, but there isn't any significant change. The signal sounds fine and I it compresses as well, but way to little. I can only get about 5 db's of compression with the meter tracking adjustment.
I did put in the 5k pots from the start on the 'Q Bias', the 'Null adj' and the 'tracking adj' pots. Could replacing them with 2k pots make any difference?

Really appreciate your help!

Are you only compressing 5dB (measured at the output) or are you compressing lots and it's a meter issue?

It's even hard to really measure because of the very steep response of the output pot. It passes audio fine and it also seems to compress a bit, but not a workable amount. I'm now getting another unit to the studio to physically compare them and see if any mistake on the board is made. Could swapping out the pots make any difference? Thanks!

Edit: To clarify, swapping back the 5k pots with 2k pots.

You don't touch the output.

Just set the input and output to 12 o'clock with the attack full CW.  Measure the AC at the output xor between 2 and 3.  Use this to convert the AC reading to DB:

http://www.sowter.co.uk/decibels.php

Now switch the attack to "off".  Measure again and convert.  How many DBs are you reducing by?  What does the meter say?

 

[Chryst]

Hey! I've build several HB 1176's without any problems, but I can't seem to be able to solve this one. Everything seems to work fine, however when I come to the last calibration step I can only get about 5 db of compression. The other calibration steps went without any problems.

To be sure I rematched a new set of FETS with higher HFE's, but the response seems to be the same. What I did notice however that it was extremely hard to get the right output voltage as the output pot seemed extremely sensitive. I've tried to measured its resistance and I only get 125 ohm instead of 250. However it was already connected, so it's possible that the lower resistance is caused by that. Output voltage can be as high as 20V though with everything cranked up.

I also remeasured all voltages and they seem to be fine.

It looks a bit like I'm lacking some throw on the input pot. However all the voltages on that side (entering the board) seem fine.

Does anybody have any suggestions how to tackle this one? Thanks for your help! It's greatly appreciated!

Lots going on here.

Measuring resistance in circuit rarely gives the correct reading as there is usually some parallel resistance.

Checking against the schematic w/ voltages works out?  Nothing weird?

The output pot could be slightly sensitive coma red to the original.  It's no really sensitivity but rather a steeper log curve.

In by pass is the signal clean and sound ok?

You could try a 5K rather than 2K pot in the GR section.  HFE measurements on a DMM can be hit or miss.

Thanks!
I've replaced all the suspect FETS, but there isn't any significant change. The signal sounds fine and I it compresses as well, but way to little. I can only get about 5 db's of compression with the meter tracking adjustment.
I did put in the 5k pots from the start on the 'Q Bias', the 'Null adj' and the 'tracking adj' pots. Could replacing them with 2k pots make any difference?

Really appreciate your help!

Are you only compressing 5dB (measured at the output) or are you compressing lots and it's a meter issue?

It's even hard to really measure because of the very steep response of the output pot. It passes audio fine and it also seems to compress a bit, but not a workable amount. I'm now getting another unit to the studio to physically compare them and see if any mistake on the board is made. Could swapping out the pots make any difference? Thanks!

Edit: To clarify, swapping back the 5k pots with 2k pots.

You don't touch the output.

Just set the input and output to 12 o'clock with the attack full CW.  Measure the AC at the output xor between 2 and 3.  Use this to convert the AC reading to DB:

http://www.sowter.co.uk/decibels.php

Now switch the attack to "off".  Measure again and convert.  How many DBs are you reducing by?  What does the meter say?

Thanks a lot for your help!

If I connect a oscillator with a 1V 1000KHz tone (0.775V) I get an output of 10,25V with the settings you described. If I turn of the compression I get 15,51 on the output. The meter stays in the red all the way the whole time. With the Sowter table I understand that this is almost 16 dB's of compression (right?).

I really appreciate your effort. Thanks!

 

[StudioJakubka]

So I am all business now, +4, +8 and GR shows OK, compression switch works just fine and I am getting visible (on scope at least) compression. However with 0.775VAC on input I am getting audible distortion on every compression rate when GR meter shows -1 to -2dB compression. When off (attack fully CCW) the audio out is good and without distortion, when attack on it doesn't matter if I am fully CW or 12 o'clock, distortion is there. Any idea what is wrong?

Did you check your voltages against the schematic with voltages?

Yes I did, and all seems OK apart from Q8, down about 0.5V (14.31V, 29.9V, 14.95V) and the main problem is, I think, Q14, where I can not get the right voltage (10.91V, 29.9V, 11.52V) which is 1V bellow. Should I try to put resistor/ trimmer parallel to  R14 and try to set voltage up to match 12.58V there?

I am not sure if my idea is doable. Is 1V bellow on Q14 the cause of distortion? When I  bypass (Attack fully CCW - off position) there is no distortion and level is OK.

 

[audiophreak]

Hello All ,
            Just wanted to report that I finished my Dual mnats Rev.D's   Very Happy with them , they sound awesome and am experimenting with different sources and such.

            I had a problem ( I reported and posted starting on page 187 and painfully going to page 197 )  The problem I was having seemed to be a common symptom but could not find any one particular fix, tried the fixes / checks posted and all was good, problem persisted which was the " I cant get the -10db meter drop in step 3 of the calibration "

  In my particular case ( pun intended ) I used these input PCBs - http://mnats.net/files/1176_rev_d_xformer_board.pdf  with LL1540 - well ... it turns out the LL1540 needs a different LOADING RESISTOR  ( R4 )  listed in the BOM  and PCB  as a 270R which is for the Altran C-3837-1  ,  the LL1540 however needs 15k which I didn't find mentioned anywhere ( or I missed it )  except on the LL1540 data sheet  ;D  which Mike at HairBall Audio ultimately discovered and after replacing R4 with the proper 15k resistor for the LL1540 everything was good - also had to replace the 2k trimmers with 5k as originally suggested to me by member Bobby Baird , but I dismissed his suggestion ...well ... it "turns" out ( pun intended )  that as I was on the third step of calibration when I was sooooo close to the -10db  ( OCD )    I heard the "click" as the trimmer was at the end of its travel - removed and measured and it was at its max at 1k9 ( tolerances )  replaced with a 5k trimmer and did a Happy Dance  ;D

  so that's my story Thanks to Mnats , Bobby Baird and all , especially Mike at HairBall Audio for his incredible patience and persistence.

here are some pix - just need to fabricate a more permanent way to secure the meter LEDs

EDIT :    I also ended up running the power ON and meter LEDs from the positive side of the PSU - not that I ran in to any problems or anything ... it just seems that's what everyone else has done  :

https://picasaweb.google.com/audiophreeek/1176RevD?authuser=0&authkey=Gv1sRgCKXM5JuEluHqNg&feat=directlink
 

 

[Chryst]

Does the numbers I gave represent a normal compression ratio and do I thus have a meter problem? Thank you, thank you!

 

[Mr.Franky]

Hey,

I built a rev d kit quite a while ago, and it sounds very good. But I have a little question. I wonder what a 'normal' setting is for the rev d output pot. When I my rev d unit inserted on a channel on the console.. my output pot is only around 30. With the output setting on 30 I'm already comming back pretty hot on channel. Is this normal?

I've used several Universal Audio 1176 reissues before (in other studios though), and I really had to cranck up the output pot on those units to get unity level between the bypassed signal and the compressed signal. I wonder if the Hairball reissues are way hotter on the output than the UA reissues. I haven't used any other Hairball reissues so I couldn't compare, therefore this question.


Regards,

EDIT: I must add I'm on 4:1 and the input pot is around 24 getting pretty hard compression. The attack pot is not in bypass either.

 

[dmnieto]

maybe is the law of the pots?

 

[Chryst]

Can somebody please confirm the compression I posted? If there is really 16 dB's of compression and the meter is maxed out, what would be a good strategy? Shall I replace the output pot because it's running so hot that I can't meter anything? My rationale is this: since I can't get a normal reading with a reasonable throw on the output pot, could my problems come from the pot simply being not stable enough to pass in the lowest portion. Or is a component fault in the meter circuit a more likely candidate? I already replaced almost all the FETS.

Thank you very much for your help guys. I really want to tackle this one  ;D

 

[Harpo]

If I connect a oscillator with a 1V 1000KHz tone (0.775V)

Connect your oscillator to XLR input pins 2/3 (XLR-pin1 is connected to cable shield and not involved in your measurement),
set oscillator for 1kHz=1000Hz (not 1000KHz=1MHz) sine frequency
and adjust oscillator level until input level measures 0.775VAC between XLR input-pins2/3.
(setting the oscillator for 0.775VAC output level  and connecting it hereafter to the input of the device under test might give you a different readout, depending on drive ability of your oscillator).

..I get an output of 10,25V with the settings you described.

LOG(10.25VAC)*20=20.214dBV or
LOG(10.25VAC/0.7746)*20=22.433dBu.

If I turn of the compression I get 15,51 on the output.

LOG(15.51VAC)*20=23.812dBV or
LOG(15.51VAC/0.7746)*20=26.031dBu.

With the Sowter table I understand that this is almost 16 dB's of compression (right?).

no, you must be looking at a different table then.
23.812dBV-20.214dBV=3.598dB reduction or
26.031dBu-22.433dBu=3.598dB reduction or
LOG(15.51VAC/10.25VAC)*20=3.598dB reduction.

 

[Chryst]

If I connect a oscillator with a 1V 1000KHz tone (0.775V)

Connect your oscillator to XLR input pins 2/3 (XLR-pin1 is connected to cable shield and not involved in your measurement),
set oscillator for 1kHz=1000Hz (not 1000KHz=1MHz) sine frequency
and adjust oscillator level until input level measures 0.775VAC between XLR input-pins2/3.
(setting the oscillator for 0.775VAC output level  and connecting it hereafter to the input of the device under test might give you a different readout, depending on drive ability of your oscillator).

..I get an output of 10,25V with the settings you described.

LOG(10.25VAC)*20=20.214dBV or
LOG(10.25VAC/0.7746)*20=22.433dBu.

If I turn of the compression I get 15,51 on the output.

LOG(15.51VAC)*20=23.812dBV or
LOG(15.51VAC/0.7746)*20=26.031dBu.

With the Sowter table I understand that this is almost 16 dB's of compression (right?).

no, you must be looking at a different table then.
23.812dBV-20.214dBV=3.598dB reduction or
26.031dBu-22.433dBu=3.598dB reduction or
LOG(15.51VAC/10.25VAC)*20=3.598dB reduction.

Wow Harpo, thanks for your detailed response. I clearly made the mistake of looking up the difference in voltage while compressing in the table, which is a stupid mistake as it's logarithmic. Thanks for pointing this out!

This is too little compression right? Which would make sense as I can't get enough compression with the input fully cranked to do the meter tracking adjustment. I've tested the input pot, which seems to be fine and the unit also passes audio. Where should I be looking?

Thanks guys!

 

[Harpo]

maybe start with double checking component values when you say ...

What I did notice however that it was extremely hard to get the right output voltage as the output pot seemed extremely sensitive. I've tried to measured its resistance and I only get 125 ohm instead of 250.

If your output level pot R23 is 250 ohms for real (249750R difference on paper from the suppost to be fitted value 250K with a log taper) this alone would explain a lot. There might be other, or just be more exact with your numbers, dimensions or multipliers.