Getting the 1176 hotter & 11 db vs VU calibration

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atticmike

Well-known member
Joined
Oct 28, 2011
Messages
502
As you all may know, the 1176's in and outputs are affected by both the in and output transformer.

Especially the output transformer has an offset between hot and cold. If for the calibration, you take wire that connects both sides of the magnet
and ground it against the case, you'll get an even waveform. Now, if you start doing the calibration at this kind of output level, the compression
will be way hotter (positively) than with just the peak measuring between hot & cold without grounding the transformer.

Give it a try and let me know what you're thinking.
 
gyraf said:
Could you explain a bit further?

~confused~

Jakob E.

I mean it is obvious that the more signal you have by an equal waveform, the fewer you're gonna lower the q-bias to -1db from 11 (at least that way it makes sense to me).

Also, I should've posted I did the non-vu calibration (2.75 & 2.45).

Somehow, for what I can say, with my first calibration, where I grounded the output transformer (just for the calibration), I had a lot more juice in the input segment = more compression.
Already a tad more than half way in, at 4, it was doing serious pumping. Now with the input all the way in and at a ratio of 4, i don't even get it distorted.
 
Since I've started a new thread, I'll be also using this one to ask an often asked question:

1. What is the best calibration approach for this particular unit, either 11 to 10 dB or going by the VU?
 
Grounding one side of the output transformer should not affect output level. ???

What do you mean by "offset"?
There shouldn't be any DC on the OT secondary windings.
What are you using to measure/monitor the output level?

The output amplifier does not affect the compression threshold.
And setting the fet bias is relative. No need for absolute measurements, just make sure it's attenuating 1dB when "idle"
 
Arno said:
Grounding one side of the output transformer should not affect output level. ???

What do you mean by "offset"?
There shouldn't be any DC on the OT secondary windings.
What are you using to measure/monitor the output level?

The output amplifier does not affect the compression threshold.
And setting the fet bias is relative. No need for absolute measurements, just make sure it's attenuating 1dB when "idle"

Arno it does not affect the output level relatively because the signal is ac: In alternating current (AC, also ac), the movement of electric charge periodically reverses direction.

But still, with grounding the output transformer you stabilize both sin-waves equally. Giving you a more accurate readout on your meter.

Concerning your question about what was I using to measure / monitor the output: At first a regular dmm but that had not been accurate enough so I used an oscilloscope.

Also, the bias may be relative but I think loosing input level by turning the input knob does affect the quality of the calibration. That's why you should position it from the very beginning and leave it there until the calibration is done, solely turning the ouput knob afterwards.
 
I see you are using a scope. So did you just connect the hot lead from the 1176 to the scope probe? Without connecting the scope ground to the cold lead? If so, think about it. The 1176 has a floating output. Floating means no connection to ground. So in order to get signal transfer, you MUST connect both sides of the output winding to your receiving device.
Because the scope is a high impedance device, if you connect only the scope probe to one side of the output of the 1176, then stray capacitance to ground in the output transformer will mean that the scope will display some waveform. But this is not the way to do it.

Always connect both sides of a circuit, especially one featuring transformers!

Regarding the Q bias, as mentioned previously the Q bias has nothing to do with the level read at the output. It is just a way to ensure that the fet is just turned on. Hence you feed signal to the limiter well under its limit threshold, and adjust for 1 dB of gain reduction.

There is a lot of bad advice on forums, and it is not helpfull if someone who is not knowledgable adds to the confusion. Think about posting only if you really know what you are talking about!
 
atticmike said:
But still, with grounding the output transformer you stabilize both sin-waves equally. Giving you a more accurate readout on your meter.

Concerning your question about what was I using to measure / monitor the output: At first a regular dmm but that had not been accurate enough so I used an oscilloscope.

Please elaborate on this?
What is "stabilize" in this context
"both sine waves"?
The last time i checked, the 1176 has only one output:
A transformer secondary winding consisting of two wires.
Connect both wires to load in order to let current flow. The transformer doesn't care whether one side is connected to ground or a pile of dogpoop.

Don't know which scope you have but my fluke digital storage scope wouldn't be my first choice for level calibration.
You should be able to measure fairly acurately with any half decent dmm
 
Arno said:
atticmike said:
But still, with grounding the output transformer you stabilize both sin-waves equally. Giving you a more accurate readout on your meter.

Concerning your question about what was I using to measure / monitor the output: At first a regular dmm but that had not been accurate enough so I used an oscilloscope.

Please elaborate on this?
What is "stabilize" in this context
"both sine waves"?
The last time i checked, the 1176 has only one output:
A transformer secondary winding consisting of two wires.
Connect both wires to load in order to let current flow. The transformer doesn't care whether one side is connected to ground or a pile of dogpoop.

Don't know which scope you have but my fluke digital storage scope wouldn't be my first choice for level calibration.
You should be able to measure fairly acurately with any half decent dmm

Sorry, I stand corrected, the primary and secondary winding. I said two transformers because I've built a stereo unit :D

If you compare together the sin wave of both hot and cold, they will have an offset between each other (at of one em being at 2.45, the other one rests at 1.65 V).
Grounding the cable which connects the primary and secondary winding, it'll give you equal levels.

Most dmms are not built to correctly readout at such high hz rates.
 
radardoug said:
I see you are using a scope. So did you just connect the hot lead from the 1176 to the scope probe? Without connecting the scope ground to the cold lead? If so, think about it. The 1176 has a floating output. Floating means no connection to ground. So in order to get signal transfer, you MUST connect both sides of the output winding to your receiving device.
Because the scope is a high impedance device, if you connect only the scope probe to one side of the output of the 1176, then stray capacitance to ground in the output transformer will mean that the scope will display some waveform. But this is not the way to do it.

Always connect both sides of a circuit, especially one featuring transformers!

Regarding the Q bias, as mentioned previously the Q bias has nothing to do with the level read at the output. It is just a way to ensure that the fet is just turned on. Hence you feed signal to the limiter well under its limit threshold, and adjust for 1 dB of gain reduction.

There is a lot of bad advice on forums, and it is not helpfull if someone who is not knowledgable adds to the confusion. Think about posting only if you really know what you are talking about!

I didn't refer to putting your transformer to ground as your go to operation approach, just for calibration.

And regard the q bias and the output reading, if you're calibrating the unit via vu, it'll not cause you any trouble but as soon as you take measurements from the xlr out, you'll be having an indifference between hot and cold.
 
atticmike said:
Sorry, I stand corrected, the primary and secondary winding. I said two transformers because I've built a stereo unit :D

Your terminology of primary/secondary looks wrong.
In a schematic symbol, the primary winding is the one on the left side of the 'core', the secondary is the winding on the right side.
Forget the primary winding, it's not important here.

atticmike said:
If you compare together the sin wave of both hot and cold, they will have an offset between each other (at of one em being at 2.45, the other one rests at 1.65 V).

Do I understand your question correctly:

When you measure Volts from one side of the secondary to ground you read 2,45Vrms.
The other side of the secondary to ground is only 1,65Vrms.
When you connect one side of the transformer to ground you're getting a "stable", higher reading between ground and the other side of the secondary, effectively measuring between hot and cold.

is this correct?

atticmike said:
And regard the q bias and the output reading, if you're calibrating the unit via vu, it'll not cause you any trouble but as soon as you take measurements from the xlr out, you'll be having an indifference between hot and cold.

A voltage is measured between to points.
Hot and Cold are the two points you should be measuring.
How could you say there's a difference between these two.

atticmike said:
Most dmms are not built to correctly readout at such high hz rates.

"hz rates" as in Frequency?

What frequency are you using to calibrate this unit?
 
I understand what he means about dmm being inaccurate at higher frequencies.  My fluke will give me one rms reading at 120 hz and another reading at 1khz. (Same amplitude measured on a scope) . I'm still thoroughly confused about what he is actually trying to say in the op. The output tx will provide the same level whether it's floating or referenced to ground (I'm assuming you meant via center tap vs single ended)
 
Yellow & orange, according to the schematic are to be soldered together. I'll be taking the uncovered soldering point and hold it against the case to ground it, which then fixes the lower rated connection (either hot or cold) to an equal output. Maybe it is nitpicking but I expected a little more concern from people properly building such a unit instead of just settling with what has been posted so far.

Lots of people prolly don't even understand what it means to put GR slightly into conduction and therefore solely follow the steps mentioned in the tutorial.

Also, I haven't seen anyone yet comparing the 11 db vs VU calibration approach.
 
Aha the transformer has two secondary windings in series.
I assume you're referring to this transformer?
http://hairballaudio.com/docs/5002/5002.pdf

And you're measuring a different level between blue-yellow and orange-red
I don't see how that would affect performance.
The fact that you get a different reading when one side is grounded still sounds suspicious.

As far as calibration is concerned, the only thing that truly affects the compression is the Fet bias.
The others are all GR meter zero-ing and tracking.
I'm not sure what you mean with "11dB calibration"

btw, "putting GR in conduction" is a strange way to say it. Either the Fet is conducting, or gain is reduced but you can't conduct gain reduction...
Try not to sound too offensive. People do care about their builds. We try to focus on what we individually think is important.
 
Arno said:
Aha the transformer has two secondary windings in series.
I assume you're referring to this transformer?
http://hairballaudio.com/docs/5002/5002.pdf

And you're measuring a different level between blue-yellow and orange-red
I don't see how that would affect performance.
The fact that you get a different reading when one side is grounded still sounds suspicious.

As far as calibration is concerned, the only thing that truly affects the compression is the Fet bias.
The others are all GR meter zero-ing and tracking.
I'm not sure what you mean with "11dB calibration"

btw, "putting GR in conduction" is a strange way to say it. Either the Fet is conducting, or gain is reduced but you can't conduct gain reduction...
Try not to sound too offensive. People do care about their builds. We try to focus on what we individually think is important.

Well i think that's just done by the output transformer and nothing unusual, just my guess. Especially because I've built two units (stereo) and they're sort of having the same "issue".

With 10 dB calibration I mean instead of reading the vu, measuring 2.75 at the output for +1 and then lowering it to 2.45 (10dB).

For me, it is important that the unit sounds as hot as it gets without burning it down to the ground ;P

PS: I didn't mean to offen anybody around here about I try to dig in in what I do as much as possible. Otherwise I can't really appreciate what I'm using.
 
So this is my first post and i've looked pretty hard but this is the closest and most relevant place I can think to post this problem with my Hairball Audio 1176 rev A. EVERYTHING WORKS- by everything i mean, everything except my meter isn't metering- oops.. I'm getting 29v at the power supply, audio is passing in and out, all ratio switches work, attack + release, and INPUT & OUTPUT work great. Where is the most likey place I dropped the ball here? Ive spent all day (literally) with a probe trying to find the cold solder joint or crossed wire and i'm stumped. Help please? aka be gentle lol ?

Travis
 
gemini86 said:
Pop into the 1176 revA build thread to get help with this.
http://www.groupdiy.com/index.php?topic=29981.0
that way its easy for others to find. Good luck!

Not for nothing I've clearly given this thread a different title. But just follow the trace of breadcrums my fellow player has laid out :)

And by what do you mean your meter is not working? Not showing any vital signs at all? Perhaps, you've failed to connect the cables, supplying the meter with juice?

Please answer on behalf of my response in the respective thread.

Mike
 

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