[BUILD] 1176LN Rev D DIY

[SonicWeaver]

Appreciate the reply about the release pot!  This is another “is this normal” question…

With nothing physically connected to the input  (input pot all the way down, GR can be on or off it makes no diff)  I start to hear hiss when the output pot reaches the 9:00 position, at 12:00 it’s louder than any of my other gear at full output and at 3:00 it sounds like a waterfall.  There is a usable range from around 8:00 to 11:00 that works fine with low noise, but most of my equipment is dead quite until pushed into gain which is usually about 80% of the output pot’s range.  Is seems like the output stage is too hot which limits the usable rage of the output pot.

Could this be caused by using the higher gain 2n3708 as Q5 (mine is 470 hfe) as was suggested rather than using the lower gain 3707 in the original or is this just the nature of the beast?  Is there a mod that will provide a more “normal” output pot throw range?

Thanks again!
Gary

 

[Zackster]

no resistor could cause this

It can. Wrong value transistor will throw the voltage divider off and you will have weird resulting voltages.
I always check them before putting them in with a ohm-meter

Thanks for the response. I did check all resistors with a multimeter before populating the board. I also checked colour codes after the problem had surfaced.

Zack

 

[Zackster]

You've got a QBias issue.  The issue is it's not set correctly.  The voltages provided on the MNATS schem are for a FULLY calibrated unit.  If your QBias is not
set those voltage will be off.  The voltage at the gate of Q11 changes everything down the line.

You need to get your qbias working.  It's a very simple circuit (the qbias).

Have a look at pad 18 on the schematic.  It's the wiper of the QBias pot.  One of the outside pins on this trimmer goes to ground and the other is tied between to R's that make a voltage divider off the -10 rail.  So basically that wiper is pulling a neg DC from the divider plus some DC from pad 18 off the ratio PCB.  This neg qbias voltage then travels by wire through the attack/release network (see schem) and to pad then to pad 7.  Do you have a neg voltage at the wiper of the pot that changes?  If not something is wrong with R59, R35, R60.  If there is, but nothing at the Q1/Q11 gate, your ratio/attack wiring is bad.

Thank you very much! This was some grand advice! I knew there was something wrong with the q-bias, but was looking for the problem on the main PCB. Turns out, I had earlier soldered one leg of the rotary ratio switch in the wrong pad, desoldered it and soldered it in the right pad. Now when inspecting the ratio board I noticed this pad (looked OK) was broken and did not provide connection between two adjacent pads. Seems that a jumper fixed this problem. The voltages are now in the ballpark and don't reset when repowering. I don't have the tools to calibrate it at home, but I am confident it will work.

Thanks again!

Zack

 

[mnats]

Hi Folks

Just finished my first rev D build.  It fired right up with no problems and was calibrated per the vids. It sounds great and is compressing.

However when the unit's GR is on (makes no difference where the attack is set) and there is no signal at the input I can change the reading on the VU meter by a full db by turning the release pot.  So turning release from full CW to full CCW takes the meter from 0 to +1

Can someone tell me if this is normal or do I have a problem?

Thanks!
Gary

Normal(ish).  Mine is more of a 0.5dB swing.

When this symptom came up on the Rev A thread I checked both my A and D units. I wasn't able to duplicate this effect with either of them.

Each unit was connected only to AC power with the GR switch activated. After waiting for the meter to settle and with Gain Reduction "ON", I chose each of the ratio buttons and turned the release knob from fully CCW to fully CW. The meter wouldn't budge.

Maybe someone could describe the conditions under which this change on the VU meter is seen in more detail.

 

[jplebre]

My rev D and my original LN's, 1178 (which are a different beast) don't do it either.

Although, I have massive fluctuations in my mains at home. I had proper 1dB drift around the "kettle effect" times or when the washing machine went into a cycle

At the studio with power conditioner, the meters behave spot on (after you zero'd it)

 

[Echo North]

I was thinking it may be related to the issue experienced by a few users, including myself, who get HF oscillation in the circuit/meter with the output near max.  Something MNATs mentioned previously that he does not experience.  I've never been overly concerned about it since I would never have the output that high, however this was just posted in the A thread:

I've got a massive 66kHz sine wave HF oscillation at the output when turning up the output pot. The voltage is high enough to drive the meter to full right when in one of the VU modes. Strange....

PROBLEM SOLVED: The oscillation starts when running the VU meter wires to the XLR socket over the main pcb and coming close to Q2. I routed the wire somewhere else and everything's fine now.

This is something I'll check next time I have my build open.

Mike

 

[Dvaughn]

Hello all,

I had my rev. D opened up to replace my input T-pad to see if it was the culprit of some scratchy noise.  While in the midst of replacing, i was gandering around and noticed that the red/white wire from the 5002 output transformer looked a little cooked where it connects to my terminal blocks.  The insulation (plastic) looks a bit melted and is brown and burned looking right where it was stripped.  I was wondering if this is a problem, or how I might go about checking things out in that area.  I've checked all my voltages against the mnats schem and they are all good.  Everything works but i was wodering if this might be an issue in the long run.  The heat sink for Q6 is right in the area, could that be heating up enough to affect the output transformer wires at the terminal block?  I really only see this on the red/white wire the others look fine.

Thanks

Dylan

 

[SonicWeaver]

Hello all,

I had my rev. D opened up to replace my input T-pad to see if it was the culprit of some scratchy noise.  While in the midst of replacing, i was gandering around and noticed that the red/white wire from the 5002 output transformer looked a little cooked where it connects to my terminal blocks.  The insulation (plastic) looks a bit melted and is brown and burned looking right where it was stripped.  I was wondering if this is a problem, or how I might go about checking things out in that area.  I've checked all my voltages against the mnats schem and they are all good.  Everything works but i was wodering if this might be an issue in the long run.  The heat sink for Q6 is right in the area, could that be heating up enough to affect the output transformer wires at the terminal block?  I really only see this on the red/white wire the others look fine.

Thanks

Dylan

Dylan my input is also scratchy when my input is unbalanced (1/4 headphone out on my Presonus Firetube) but is has no noise at all when the input comes from by mixer's balanced monitor outs.

 

[sage]

Finally me and Marson put up in the studio the gear built in the past few months and here is a FB page with pictures, thanks to all on this Forum that have helped with these great projects:

http://www.facebook.com/marsonaudio

sage

 

[Che_Guitarra]

I just want to post this up to get the nod of approval and also some clarification.

My main board is largely done.  I'm guessing the spare heatsink I have in my kit goes over this little guy in the green circle?

Also, correct me if i'm wrong here - the Rev D bill of materials designates 3x 2K trimmers, but I seemingly require 4?  I also want clarification what gets installed in the position above R69 - the loaded PCB pics I have seen seem to indicate something goes here, but I can't get a clear enough zoom to ID the component.

 

[Echo North]

That "0" trimmer is the front panel mounted pot (see the wiring pages).  You need to move that over to the null adj.

The area above R69 is where the three pin header goes. 

Mike

 

[SonicWeaver]

Hi Folks

Just finished my first rev D build.  It fired right up with no problems and was calibrated per the vids. It sounds great and is compressing.

However when the unit's GR is on (makes no difference where the attack is set) and there is no signal at the input I can change the reading on the VU meter by a full db by turning the release pot.  So turning release from full CW to full CCW takes the meter from 0 to +1

Can someone tell me if this is normal or do I have a problem?

Thanks!
Gary

Normal(ish).  Mine is more of a 0.5dB swing.

When this symptom came up on the Rev A thread I checked both my A and D units. I wasn't able to duplicate this effect with either of them.

Each unit was connected only to AC power with the GR switch activated. After waiting for the meter to settle and with Gain Reduction "ON", I chose each of the ratio buttons and turned the release knob from fully CCW to fully CW. The meter wouldn't budge.

Maybe someone could describe the conditions under which this change on the VU meter is seen in more detail.

FOUND THE PROBLEM AND YOU'LL NEVER GUESS WHAT IT WAS!!!

I decided to move the unit into my control room where I could run it through my Mackie 824s and put it under a brighter light to see things better.  After letting it warm up for a 1/2 hour the meter now moves from 0 to +3 (it makes no diff if the GR is on or off) when turning the release from full CW to full CCW. Now it's 3x worse than yesterday but I haven't changed anything...WTF!!!

I spend the next 6 hours double & triple checking component orientation, placement & values, wiring, validating voltages, googling and reading dozens of forum threads. The only things that were off were a couple of voltages around the GR meter circuit transistors that changed when the release knob was turned.

By now it’s 3:00 am and I decide to call it a night.  So I put the top lid on and that’s when the world became unglued!  As I go to shut down my mains in the control room I look one more time at the meter and notice that it’s right on 0 db.  So I give the release knob one more turn just for grins and I’ll be damned…the meter only moves about a needle’s width when turning the release a full twist back and forth.  What it fixed itself?  Nooooooooooo…I hate when that happens!

I can’t go to bed now because I have to see if the problem GR voltages are now normal, time to lift the lid and take some measurements.  As I slide the lid forward the meter starts moving when the lid is about ¾ of the way off.  Luckily the release was fully CCW or it wouldn't have moved at all and I wouldn't have discovered this symptom.  I take the lid completely off and it’s back to a 3db swing again!  I can reproduce it…YES!

The electronics part of my brain is thinking the metal lid must be shielding some stray EMF.  Could I have wired something wrong or is my wire routing coupling something?  I start to move the wire harness around the output transformer and notice that the meter moves from +3 back to almost zero and then back to +3 when I remove my hand.  Relief, I finally found it!  I must be inducing something when I touch the wires, right?

But then I move my 150 watt incandescent lamp around to get a better look and notice that the meter moves.  Pull the lamp away and the GR meter goes to zero.  Move it back in place and it goes back to +3!!! You've got to be kidding me…did I build the LA2A with the photo cell detection circuit and just didn't realize it? LOL

Long story long is that the CR2 and CR3 diodes (like all glass diodes) are photosensitive.  They act as low output solar cells and inject a few millivolts into the GR circuit.  The closer the lamp is to the diodes the bigger the effect is on the meter.  This only occurs with certain types of lamps, which explains why I didn't see the problem when I built & calibrated under my fluorescents.  The bright incandescent creates a huge swing and pegs my meter if moved close enough.  But there’s no effect whatsoever with my high output compact fluorescents or my super bright LED headlamp, even when placed right on top of the diodes.  My guess is that the diodes are sensitive to the greater output of incandescents in the red portion of the spectrum.  The reason that my hand changed the meter isn't due to induction it's because it was casting a shadow over the diodes. The lid is on now and it's solid as a rock.

So it turns out that my baby never really had an issue. She’s just shy and doesn't want anyone to examine her private parts under bright incandescent light!

I hope this post is illuminating (rim-shot please) for those that have experienced this issue!

Gary

P.S. – Me thinks that there is a product opportunity here.  What do you think folks, I can see the marketing copy now...”The new 1176PP (Photon Powered) edition thickens the mix to the perfect consistency and injects just the right amount of photonic warmth to turn that mediocre song you’re working on into a million seller!”  Don’t get any ideas Mike & Mako I’m patenting the circuit! LOL

 

[Che_Guitarra]

That "0" trimmer is the front panel mounted pot (see the wiring pages).  You need to move that over to the null adj.

It's all becoming clearer now.  Thanks Mike 

 

[jplebre]

And yes the heathsink goes over the big bad silver guy

 

[mnats]

Long story long is that the CR2 and CR3 diodes (like all glass diodes) are photosensitive.  They act as low output solar cells and inject a few millivolts into the GR circuit. 

Nice work. So everyone else who had this issue had the cover off and a bright light shining into the unit?

 

[mnats]

It's all becoming clearer now.  Thanks Mike 

You can link to my wiring pages if you like but please don't post my images without permission or attribution.

 

[Che_Guitarra]

It's all becoming clearer now.  Thanks Mike 

You can link to my wiring pages if you like but please don't post my images without permission or attribution.

Photo has been removed.

 

[Che_Guitarra]

So the Hairball kit arrived today ;D

All I can say it WOW!  I didn't really know what to expect for $360, but the quality of the enclosure and components has exceeded all my expectations by tenfold - super impressed  8)  Of all the kits/projects i've built before this certainly sets the benchmark.


Anyway, time to get this bad boy rockin'.  I've never dealt with a non-240V transformer before so i'm double guessing myself a little here - I want another set of eyes to double check my actions before I commit.

To get to 230V I need to run the primary windings in series (ie - jump from grey to violet)?  Or am I having a brain fade and actually need to run these windings in parallel?

 

[Echo North]

Did you see this link on the MNATs wiring pages (1st page):
http://web.archive.org/web/20090914070140/http://www.diyfactory.com/data/transformer_connections.gif

 

[Che_Guitarra]

So i'm on the 'go slow' for a while - I never got any molex connectors in the Mouser kit (for the meter/ratio boards), i'm not sure if I was supposed to, but no matter - a local hobby shop has some on order for me.

I also want to ask about those bi-polar transistors (N3708 x 20) in the kit.  I went a bit gung-ho and just installed the first ones I picked from the packet and now realise this isn't the smart way to do it.  I'm unfamiliar with these components - how do you check for a match between pieces with a a DMM?