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

[Biasrocks]

In the document, The ratio board is noted as Y X 28 29 VU VU, but from atticmike's picture (I haven't checked my own ratio boards) his ratio boards are silk'd X Y 28 29 VU VU.[/u]

@atticmike

I will generally defer to the PCB silkscreen.

In this case it doesn't matter because as Mike pointed out, X & Y can be reversed and not have any effect on the meter.

I respect the fact that no one wants to make an error. But it's important that you develop some basic skills like reading a schematic and using your meter to trace circuits in order to build these things.  If there is any doubt, the schematic and your meter will answer just about any question.

I was once the guy who stared at a schematic and went huh? Looked inside a piece of gear and had no idea where to start, but my skills improved with time, effort and necessity.

Posting a question here should be your very last option.

Regards,
Mark

 

[atticmike]

I appreciate your concern at my premature nitpicking and inexperienced posting on this thread but what I did was simply going by the schematic and if I hadn't put any trust in mnat's wiring pages (which are pretty much a straight deviation from your "professional approach), I would've prolly connected it the wrong way

And the more people do troubleshooting when building the unit, the better any follower can handle their very build.

I hugely appreciate all the help I've gotten so far from all the members of this community and by the same token, I'd pass my knowledge to anybody else in the need of it.

And whenever you were stuck, I don't think you were solely on your own? Plus the quicker you get out of a mess, the faster you learn and the better you become in a shorter amount of time.

Sorry for a little OT.

In the document, The ratio board is noted as Y X 28 29 VU VU, but from atticmike's picture (I haven't checked my own ratio boards) his ratio boards are silk'd X Y 28 29 VU VU.[/u]

@atticmike

I will generally defer to the PCB silkscreen.

In this case it doesn't matter because as Mike pointed out, X & Y can be reversed and not have any effect on the meter.

I respect the fact that no one wants to make an error. But it's important that you develop some basic skills like reading a schematic and using your meter to trace circuits in order to build these things.  If there is any doubt, the schematic and your meter will answer just about any question.

I was once the guy who stared at a schematic and went huh? Looked inside a piece of gear and had no idea where to start, but my skills improved with time, effort and necessity.

Posting a question here should be your very last option.

Regards,
Mark

 

[Biasrocks]

if I hadn't put any trust in mnat's wiring pages (which are pretty much a straight deviation from your "professional approach), I would've prolly connected it the wrong way

In this case, there was no 'wrong way'.

Which probably explains why the documentation doesn't match the PCB exactly.

I've used similar pages and this build thread to construct my REV A. If I had a question, I studied all the materials including the schematic to make sure I hadn't overlooked something. I've run into many cases where I had to question what was written in a 'guide' or a BOM. In most cases I'm able to resolve the problem on my own.

And whenever you were stuck, I don't think you were solely on your own? Plus the quicker you get out of a mess, the faster you learn and the better you become in a shorter amount of time.

No I read until my eyes hurt,  I made sure I exhausted all my options and only then did I post a question.

In fact, if you look around you'll see evidence that I went beyond the 'build docs' and investigated alternate component values and approaches for this build along with a few other valuable members of this forum. Which Mako incorporated into the latest version of the PCB.

http://www.groupdiy.com/index.php?topic=34502.msg456556#msg456556

Sorry for a little OT.

No need to apologize, it's not off topic.

Hookup your meter and start compressing!

Regards,
Mark

 

[ChrioN]

Feeding a signal through the whole PCB, from the input transformer secondary to the output transformer primary shows a perfectly fine unit.
But as soon as I'm going through either of the transformers, things gets strange.
As seen from recent photos, the output transformer is correctly wired.
As seen from a drawing I posted some time ago, the input circuit (pad & transformer) is correctly wired.
what gives..
When going through the output transformer, I get a 400hz high pass filter. And only signal present on -. No signal at all on +.

 

[Harpo]

When going through the output transformer, I get a 400hz high pass filter. And only signal present on -. No signal at all on +.

You measured across the transformer secondary +/- ends ? Transformer secondary is floating, not ground referenced.

 

[ChrioN]

Didn't think of that when I was tracing! ...but the signal gets even wierder when looking at it correctly, between + and -. Very low level as well.

When going through the output transformer, I get a 400hz high pass filter. And only signal present on -. No signal at all on +.

You measured across the transformer secondary +/- ends ? Transformer secondary is floating, not ground referenced.

 

[Biasrocks]

Didn't think of that when I was tracing! ...but the signal gets even wierder when looking at it correctly, between + and -. Very low level as well.

Have you listened to the output pre-transformer?

Does it track with the OUTPUT control?

Is it distorted, bandwidth limited?

Regards,
Mark

 

[ChrioN]

Didn't think of that when I was tracing! ...but the signal gets even wierder when looking at it correctly, between + and -. Very low level as well.

Have you listened to the output pre-transformer?

Does it track with the OUTPUT control?

Is it distorted, bandwidth limited?

Regards,
Mark

pre-output transformer its clean, and freq response is perfect. It reacts with the OUTPUT control. Just like a working 1176 in every way except the transformer issues.

 

[Biasrocks]

pre-output transformer its clean, and freq response is perfect. It reacts with the OUTPUT control. Just like a working 1176 in every way except the transformer issues.

Have you verified that the center tap on the secondary side is joined for a 600 ohm output?

If so, then perhaps, you have a defective transformer or a bad output transistor.

Do you have another transformer and a replacement for Q6 you could try?

Regards,
Mark

 

[atticmike]

I have a general question about the power transformer (toroid).

Since I'll be doing a dual unit and am little worried having two units run at the hairball transformer's max capacity, what else could I set up behind the steering wheel?

Though I got a transformer for my neve project, I could use it for my dual 1176 couldn't I (Just worried whether the 50Vac are too much or not):

http://search.digikey.com/scripts/DkSearch/dksus.dll?x=19&y=12&lang=en&site=us&KeyWords=TE62085-ND+

Are there some other alternatives you favor?

 

[Echo North]

That is a 22V transformer which is not enough.  You need a 25V dual secondary.

The VA (Volt Amps) rating is the total sec voltage X the current it can supply.  For the one I sell it's a dual 25V (50V total) that can supply 0.6A.  Multiply those and you get 30VA.  If you know a transformers sec voltage and VA, you can divide to get the current rating.  0.6A should be plenty of current.  The 1176 runs at less than 0.2A per channel.  The LED meters and link board are not drawing much.

If you are really concerned get a 50VA but make sure it has dual 25V secondaries.  Your circuit will only use the current it requires so 50VA will not be too much.  It just means the size of the transformer will be larger.

Mike

Edit: Avel does a 50VA version of the one I sell and the have no MOQ.

 

[atticmike]

That is a 22V transformer which is not enough.  You need a 25V dual secondary.

The VA (Volt Amps) rating is the total sec voltage X the current it can supply.  For the one I sell it's a dual 25V (50V total) that can supply 0.6A.  Multiply those and you get 30VA.  If you know a transformers sec voltage and VA, you can divide to get the current rating.  0.6A should be plenty of current.  The 1176 runs at less than 0.2A per channel.  The LED meters and link board are not drawing much.

If you are really concerned get a 50VA but make sure it has dual 25V secondaries.  Your circuit will only use the current it requires so 50VA will not be too much.  It just means the size of the transformer will be larger.

Mike

Edit: Avel does a 50VA version of the one I sell and the have no MOQ.

Weird because I got this transformer from the neve 1073 bom and this will surely not provide enough juicy to run 48v+ then... trash.

But now that you've brought the ugly truth home to me, it is starting to make sense.

Is there a go to power transformer with a lot of juice, still fitting in a 1RU and fringing closely at 100 bucks for all my future projects?

 

[Biasrocks]

Weird because I got this transformer from the neve 1073 bom and this will surely not provide enough juicy to run 48v+ then... trash.

Not true, many 48v phantom supplies use a voltage doubler/tripler to get the voltages up. So chances are you're fine.

Regards,
Mark

 

[atticmike]

I got two questions on my mind:

1. The gray wire on either output transformers has no connection to any of the other wires, how come?

2. This one is about the zero adjustment control. As far as I know, this lets you turn off the unit's compression but why does it connect to a continuous trimmer potentiometer? Wouldn't be a rotary switch such as this one more appropriate to either put it to 100 or zero value: http://mnats.net/1176_slam_mode_rotary.html (two settings)

 

[Echo North]

I got two questions on my mind:

1. The gray wire on either output transformers has no connection to any of the other wires, how come?

2. This one is about the zero adjustment control. As far as I know, this lets you turn off the unit's compression but why does it connect to a continuous trimmer potentiometer? Wouldn't be a rotary switch such as this one more appropriate to either put it to 100 or zero value: http://mnats.net/1176_slam_mode_rotary.html (two settings)

1. Look at the schematic.  Grey is on the secondary of the feedback winding.  It's connected to the circuit.
2. The zero adj pot?  It does not disable compression.  It just allows you to set the needle at zero in case of drift.

 

[atticmike]

I got two questions on my mind:

1. The gray wire on either output transformers has no connection to any of the other wires, how come?

2. This one is about the zero adjustment control. As far as I know, this lets you turn off the unit's compression but why does it connect to a continuous trimmer potentiometer? Wouldn't be a rotary switch such as this one more appropriate to either put it to 100 or zero value: http://mnats.net/1176_slam_mode_rotary.html (two settings)

1. Look at the schematic.  Grey is on the secondary of the feedback winding.  It's connected to the circuit.
2. The zero adj pot?  It does not disable compression.  It just allows you to set the needle at zero in case of drift.

Thanks.

Ah so for number 2 just fine adjustment in case the needle is drifting off?

And about calibrating the q-bias, I got a question about adjusting the attack knob and vu meter.

He says that I shall put the attack knob counter clock wise as much as possible and refers to the older revisions, being able to to this with the attack knob and therewith advises to take the gain reduction circuit out of action since this is based on the rotary version. I'm using the classic knobs, meaning I don't have to take anything out of circuit and just flip the attack knob off until it clicks?

 

[Echo North]

Yes and yes.

 

[ChrioN]

I was once the guy who stared at a schematic and went huh? Looked inside a piece of gear and had no idea where to start, but my skills improved with time, effort and necessity.

Posting a question here should be your very last option.

Regards,
Mark

Anyone can get stuck at times. No matter the basic skills.
When I built my newest ones, which I'm still having problems with, I have a couple of (four or six, lost track) 1176s finished "in my backpack". I can't remember anyone of them working at first power up. The first time I had problems I think I went straight to the forum and asked for help. I even got a phonecall form a member later in the evening But while I were waiting for someone to reply, I started studying the schematic and the pcb. And thats the way I've been solving all my problems until. The first times you fix a broken circuit is the moment you feel like you've mastered the whole art of electronics. (which of course you haven't, and probably never will to the fullest extent ;D) But you understood what was wrong, and you fixed it. Thats a nice clap on the back.

 

[atticmike]

Yes and yes.

thanks marc, the compression works but I'm still in hot water with the meter calibration.

Somehow, R74 doesn't respond to any of the turns i do at R75, remaining at -0.46 constantly which kind of foils my plan to do a proper calibration. However, if I turn R75 to a certain degree, it moves the meter's needle a bit but doesn't change anything of the voltage.

Also, I did the calibration using the original ddm values such as 11dBu (2.7484 vAC ) and 1 db lower: http://www.gearslutz.com/board/6814614-post30.html

Purportedly, seems to be more accurate than doing the not calibrated vu meter q-bias adjustment. What's your statement on that approach?

Also, the output xlr has a hefty dissonance from pin 2 (blue) = higher value to pin 3 (red & brown from the output transformer) = lower value (prolly because of the old kind of replica transformer?). Using the 1176 and listening to the output signal, considering the output xlr's dissonance, doesn't seem to be an issue at all but just the measuring kind of leaves me puzzled.

By the way, both issues are caused by either side. So this is prolly not something caused by misallocated parts.

Stereo link also seems to be working properly, boosts the units's volume a little bit when activated on both sides (prolly to an equal level but I can't say for sure, I'd have to measure it.

-

By the way, do you guys have a secret to calibrate the unit the best way possible apart from using the values instead of the vu meter? Like maybe trying to get the targeted value with the knobs (input & output), being at the same angle? <-- Talking about Q-Bias.

 

[atticmike]

Here is a little soundtest I did: http://soundcloud.com/atticmike/sets/1176-rev-a-self-built-testrun

For converting the signal either D/A or A/D, I've used a Lynx Aurora 16.

And please, don't forget to check on the issues I've posted (Vu meter calibration & XLR out dissonance), anybody

*Update*

Alright, got the info about calibrating the VU (TP10/TP11 instead of R74) luckily from MicDaddy, many thanks mate

However, I haven't solved the issue with the dissonance at both xlr outputs yet. I would like to know whether the obvious smaller value of the third (red pin) is a regular anomaly of the unit ?

*Update 2*

Having started to wreck my brains on the q-bias again, I'm wondering whether I'm supposed to look at the waveform not clipping and therefore stopping cranking R59 just before it distorts and clips or should I get there and use the the actual lower 1db to go away from that? I'd like to know that because that'd probably give me even more performance.

And as I said before, I'd be interested in mnat's and Mark's opinion on the value 2.7 V = 11 db adjustment instead of watching the VU Meter (saw that's the calibration they've used on UA units at 4 db).

Then it'd be also quite useful to know whether it is better for me to measure with the DMM (at the xlr out) or look it up through my aurora 8 via signal scope pro? Sorry for being so fussy on the details but I really want the unit to perform at it's best.