[BUILD] 1176 Rev A - Back to the beginning...

[Echo North]

Did more searching on the boards.

Issue: Tracking wont let me adjust the meter in a propper way.

Voltages on Q11,12,13 are looking all good. Switch is also working good. Solder-points are also checked.

The meter I also checked. It is exaclty working like the other one. (DUAL)

But tracking-adj  lets me only adjust -3dB, where the other board I can go up to -10dB (what I need)

Anybody got some hints for me where I am doing something wrong?  ???  ???

And what is about the Toroidal, is that normal that they got a little buzz when connected to AC?

Thanks.

PS: and yes, the trim is working and the GR is working 

Have you pulled the trimmer to confirm it's wiring correctly?

 

[sl4zhz]

Update in my case. VU meter still does not respond with 0dB signal directly.
Is VU meter broken?

Sounds like it.  Is it a Hairball meter?

If so email me:  info at hairballaudio dot com

Mike

Sorry for late respond in this forum. I was sent email to you about VU meter, many thanks to hairball audio for fast respond.

Back to my problem. While waiting new VU meter, I borrow VU meter from my friend (buy from hairball too).  I get 0dB in the VU meter from directly input signal. But I still can't do Q bias. Meter not reaction when input potentio turn CW.

I have exact same problems.. get 0db in the vu meter, but still can't do Q Bias. the meter seems not reacting when the input pots turn CW.. anyone can help please?

thanks

 

[Echo North]

Update in my case. VU meter still does not respond with 0dB signal directly.
Is VU meter broken?

Sounds like it.  Is it a Hairball meter?

If so email me:  info at hairballaudio dot com

Mike

Sorry for late respond in this forum. I was sent email to you about VU meter, many thanks to hairball audio for fast respond.

Back to my problem. While waiting new VU meter, I borrow VU meter from my friend (buy from hairball too).  I get 0dB in the VU meter from directly input signal. But I still can't do Q bias. Meter not reaction when input potentio turn CW.

I have exact same problems.. get 0db in the vu meter, but still can't do Q Bias. the meter seems not reacting when the input pots turn CW.. anyone can help please?

thanks

When you turn your Qbias trimmer, does the Qbias change?  The Qbias is at the gate of Q1 and is measured in DC.  You should see a negative voltage there that moves from near 0 VDC to -2VDC or more as you rotate the trimmer.

 

[mikerl]

So,

i had been sending the "wrong" level to the compressor for calibration.. and Echo North schooled me on my mistakes.  Thanks for that.  Now my question is...

i am using the compressor as an insert in pro tools, for mixing.. with pro tools set to prefader metering.. my track is RMS around -18... if i then add the 1176 to the insert.. in order to get acceptable gain reduction and output levels (as to not clip pro tools on the way back in) i have to have my input and output set very low... each around 7 and 8 oclock...

is this normal?  most of my experience with "real" 1176's is tracking.. not mixing (as an insert) but generally when tracking i would find acceptable levels around 9 oclock.. and output around 3 oclock... so it seems that i am having to really attenuate my compressor to make it act right...

thoughts?


Mike

 

[mnats]

most of my experience with "real" 1176's is tracking.. not mixing (as an insert) but generally when tracking i would find acceptable levels around 9 oclock.. and output around 3 oclock... so it seems that i am having to really attenuate my compressor to make it act right...

thoughts?


Mike

Correct me if I'm wrong, but it seems to me that further attenuation of the input signal isn't what you're after but rather raising the threshold by attenuating the signal to the Gain Reduction Control Amp. See the recent discussion ca. page 163 of the Rev D thread for a possible solution - otherwise you could try the trim pot option proposed by Jakob and added as an option on my rotary switch boards.

 

[mikerl]

Correct me if I'm wrong, but it seems to me that further attenuation of the input signal isn't what you're after but rather raising the threshold by attenuating the signal to the Gain Reduction Control Amp. See the recent discussion ca. page 163 of the Rev D thread for a possible solution - otherwise you could try the trim pot option proposed by Jakob and added as an option on my rotary switch boards.
[/quote]

right, i didn't mean to imply that i would want to further attenuate the signal.. just that it seems that in order to get acceptable levels, i have too... but perhaps that does mean attenuating to the GR control amp... i am a total newbie who's only level of expertise is plugging in a soldering iron.. it sounds like what your mentioning is a mod of sorts.. im not sure thats what im looking for... my goal is to have a functioning unit much like a typical 1176, and im just not sure that, at this point, i am. 

does anyone else have this issue with having to run your input and output very low?  im feeling like there is something wrong with my compressor, despite the fact that it passes signal and sounds clean.

I guess part of my confusion is... if i have the same PCB, same components (from the hairball BOM) and same transformers as the rest of you.. it would seem to me that something is wrong with my build.. maybe thats the newb in me talking, but im not sure i understand how - altho otherwise i have a functioning unit - mine is doing this, and others are not.

Mike

 

[sage]

IMPORTANT TO ALL CINEMAG USERS:

I finally put my units (REV A and REV D) in the rack in the studio and we checked the PHASE and realized the units were both outputting out of phase...

Obviuosly we checked the XLRs and the Patchbay and it's all good... so we had to swap the polarity on the INPUT trafos - so now the Yellow and Orange are reversed AND THIS FIXED THE ISSUE !

So if you used the CINEMAG TRAFO you MUST WIRE THE WAY SHOWN IN THE PICTURE:

NOW IT SOUNDS AND GREAT AND IN PHASE 

sage

 

[Che_Guitarra]

Sage, is there a marked difference in noise levels between the two revisions?

Are you able to give a brief account of what you're hearing A vs D?

 

[mnats]

Sage, is there a marked difference in noise levels between the two revisions?

Have you read the first post of this thread? I took a measurement there which is IMO more useful than a subjective opinion.

 

[Che_Guitarra]

G'day Mnats - yes I read your account.  It's a fail at my end - while I have a ballpark idea of your measurements, I don't really have a reference point to understand noise floor quantification.  The only time I ever see a dB measurement is usually in reference to speaker efficiency.  But, it's all a learning curve, and i'm wanting to learn

I've since read through this whole thread, and think I have a fair idea of what kind of mojo to expect from a Revision A unit.  Nonetheless I think i'm best off building a Rev D first.

 

[DJArtery]

Love what has transpired through the efforts of those involved - Looking forward to building atleast one Rev A  .  Perhaps joining the purely carbon based resistor 'crew'.

I have a favour to ask of someone - In aid of myself understanding the schemtaics a little better  ::

Would someone be so kind as to draw on one of the Rev A schematics the signal flow?  I understand that electrons are free to run around in any and all directions (unless diodes are involved)? 

I am specifically trying to follow the flow of the audio signal so I can segregate the compression, line amp (and so) on sections from one another.

This is all very new to me and something I can't wait to dig into, and later, draw up my own schematics for my own custom dynamics processor.

Yesterday I learned why there is a feedback out of the/an IC and into the negative input of the IC...  I also learned that the capacitor takes time to charge, and a resitor (running in parallel to this) will increase this time (respective to attack and release times).  Slowly my understanding is increasing but I still don't quite follow the signal flow.

When I have conducted searches, short and concise keywords are often convoluted into irrelevant topics.  I apologise in advance, with premeditated concern that someone will vehemently exclaim 'look it up'.  That said it is specific to this build  .

All the best.  ;D

 

[Echo North]

Congrats on taking a step toward some deeper understanding.

Electrons are not really free to roam around.  Electrons flow (actually passed between atoms) between two voltage potentials, towards the more positive.

I don't have time to draw it up right now but let me try to attempt some basics of the circuit and provide a link.  For reference, I'm looking at: http://mnats.net/files/1176REVD_VOLTS.pdf

Focus on the top 1/2 of the schematic.  The signal amp and the signal line amp.  Ignore the ratio switch S4A and S4B for now.  That top 1/2 of the schematic is the only place the audio signal that you hear at the output travels.  The input is attenuated at the input and fed into the circuit.  It moves through R5 and CI across the top of Q1 which is the GR FET.  Think of the GR FET as a "trap door" and it's closed now so all of the signal passes.  It moves to Q2, Q3 and Q14 as the first gain block.  Next it hits the output pot where the final output gain is set via final signal line amp which also includes a feedback winding at the output transformer.

What you have here is really a low gain (45dB) mic pre.

The magic happens after C7 when you take some of your audio signal and dump it down into the gain control amp.  The amount is actually controlled by the attenuator.  Attenuate less and the signal is louder at C7 increasing the level at the Gain control amp input.  The signal travels through S4A where the it is decreased via that resistor ladder that depends on ratio selected and feeds into C17 where it goes through the gain control amp where the NEG swing inverted so the AC is all positive.  The threshold is set by S4B which sends a negative DC voltage down to the control amp.  The play between these two voltage and the CR2/CR3 diode create a DC voltage that is sent back to the gate of Q1.  The DC voltage which is representative of the AC signal created to movement of the "trap door" that created the signal reduction/compression.

That is a REALLY bad description but start with that

For in-depth reading of the magic of the ratio switch, read SSLTech/Keith's here:
http://prorecordingworkshop.lefora.com/2011/02/01/all-buttons-in-1176/

That'll blow your mind.

Mike

 

[DJArtery]

Congrats on taking a step toward some deeper understanding.

Electrons are not really free to roam around.  Electrons flow (actually passed between atoms) between two voltage potentials, towards the more positive.

I don't have time to draw it up right now but let me try to attempt some basics of the circuit and provide a link.  For reference, I'm looking at: http://mnats.net/files/1176REVD_VOLTS.pdf

Thank you! - No problem mate, any info is great   Did believe they travelled to the positive and then somehow 'convinced myself' they followed the inverse...  Last time I did electronics was well over a decade ago    Time flies.

Think of the GR FET as a "trap door" and it's closed now so all of the signal passes

  Yes I've grown to understand the purpose of BJT's, MOSFET's and the like - Found a very intersteing article on this forum regarding VCR FET's and incorporating feedback to realise linearity   Still learning, though - Need to revise these NPN BJT's. 

That top 1/2 of the schematic is the only place the audio signal that you hear at the output travels.

  Yes, now that you say this, I can make sense of it.  What goes on elsewhere is added to the the signal - to attenuate or otherwise.

The signal travels through S4A where the it is decreased via that resistor ladder that depends on ratio selected and feeds into C17 where it goes through the gain control amp where the NEG swing inverted so the AC is all positive.

  Aha!  Yes, I missed this inversion - begining to make more sense.  Just to make sure - S4A and B are actually connected (red line indicative of this I believe?), what you do to one is refelcted by the other to realise/impose this 'negative DC voltage down to the control amp'.

sends a negative DC voltage down to the control amp.  The play between these two voltage and the CR2/CR3 diode create a DC voltage that is sent back to the gate of Q1

Feeling greater understanding - The output is all on it's own, nothing more than a gain stage to output.  Everything happens at/after the input, and fed back to Q1 to compensate.

Out of curiousty, and with the Capacitors in mind these take time to charge - Is it agreeable that this time coefficient is negligable on the resulting 'signal'?  Noticed C27 (running parallel to R54 with the variable resistor to make up the attack parameter) is 0.022uF.  Others like C1 are significantly greater.  I am going to have to read up more on these.

With C7 in mind, this inversion (from what I can make out) into signal line amp (output) doesn't seem to flip back to positive  ??? Does C8 adhere to this?

If I have grossly misunderstood somewhere - Deepest apologies!  This is something that in the last two weeks has fascinated me - Realising it is proving easier with each new learnings acquired.  Who on this planet, original or not, would reject an 1176?  Going to revise this all further, and in the coming days begin a seperate thread, with all purposes to pose my understanding of this units function,.. And pose further questions - I'm taking up too much space on this thread :

If any one with further learning resources would like to forward - Fire away  [email protected]

Best regards, and thank you for the other readings - most appreciated!  ;D

 

[Majestic12]

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.

 

[mnats]

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.

Bingo. Though it's likely that the input capacitor rather than the transistor is the sensitive node.

I was finally able to duplicate this problem by moving my VU meter wires close to the input circuit on the main board. Notice that on my wiring pages I've routed some very long VU meter wires near the case well clear of the main PCB, which explains why I never had this problem. I'll add some notes to my wiring pages.

Thanks for your input (so to speak).

 

[Majestic12]

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.

Bingo. Though it's likely that the input capacitor rather than the transistor is the sensitive node.

I was finally able to duplicate this problem by moving my VU meter wires close to the input circuit on the main board. Notice that on my wiring pages I've routed some very long VU meter wires near the case well clear of the main PCB, which explains why I never had this problem. I'll add some notes to my wiring pages.

Thanks for your input (so to speak).

In my case it's definately Q2 where the oscillation is most present, it's getting weaker when moving the cable to the input cap.
I run the cable over the pcb because I didn't want to come close to the power transformer.

 

[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]

Even though I have a Rev D in the works, i'm still very interested in building a blue stripe.

I've tried to search for this, but two days of looking i've come up empty - how does the Rev A sound/react when slammed, compared to a rev D or later 1176?  Are the sonics still in the same ball park or a completely different animal?  I'm mainly interested in employing a blue for vocal and bass duties, with a view to recording rock, roots, reggae and rockabilly.

 

[evilcat]

I don't know for the comparaison thing w/ slam mode, I "only" have blue stripes ones, but it's a killer comp, especially for vocals and bass!!! Good choice man.
In terms of comparaisons, the changes are audible of course, but it's still an 1176 so it will be in the same ball park. I heard a modern UA 1176 which had a deeper and cleaner sound, more transparent compression but they was the same kind of compressor.

Best,

Ben

 

[KSeaton]

Built my first 1176 Rev A. Thought I had it calibrated correctly and it passes audio fine but I'm having these issues:

Input is EXTREMELY sensitive. With barely any signal coming in it starts to clip
It sounds as if there is a dramatic high pass filter on the signal.
When switching between metering modes the output signal changes level a little bit
Turning the release control clockwise seems to raise the overall signal level
Don't get expected result with all buttons in (no VU pinning)

Ok, so i guess it doesn't pass audio "fine," but it passes audio. Not really sure where to start troubleshooting on this one and with time being at a premium currently, any help or suggestions on where to start would be much appreciated. Could this largely be a grounding issue?

- Kevin

Updated: Added a photo. Also, if there is anyone in the LA area who has experience with these and might be able to help troubleshoot, I would happily compensate you for your time