All things G1176 - the new "repost" thread.

[gyraf]

..does your meter fluctuation follow your -8.8 to -9.4 variation? In this case the varying voltage is the reason for your meter error..

 

[gabik23]

Yes it does. What could be the cause of the problem? Kind regards, Gabriel

 

[gabik23]

Yes it does. What could be the cause of the problem? Kind regards, Gabriel

I mean what could be the cause of this varying voltage? Could the LM7824 be the problem? Thank you!

 

[sodastereo]

Is your meter battery okay? Place an alligator clip on the ground with the negative tip, and only take measurements with the positive tip.
You could remove the ICs from their sockets to see if they affect that fluctuation.
If at the output of the 7824 it has more than 24v it is probably fried

 

[gabik23]

Is your meter battery okay? Place an alligator clip on the ground with the negative tip, and only take measurements with the positive tip.
You could remove the ICs from their sockets to see if they affect that fluctuation.
If at the output of the 7824 it has more than 24v it is probably fried

My meter is Ok. I changed the LM7824 and the TL071CP and still don t have stable -10. When I take out the TL071CP the voltage stabilizes at -9.8V.

The FETS I am using are J113 and are paired(matched) with TC1 wich I guess is not the best tool for matching transistors but the FETS are from the same batch.

Should i check resistors and caps around TL071CP? What else should i check?

The compressor works fine with audio, it compresses, the only issue is with the meter for not being stable because of the voltage fluctuation on -10V.

Kind regards, Gabriel

 

[sodastereo]

Yes, it is best to check that area, also everything that surrounds those -10v. such as the rotary knob and welds/components in that sector. Did you make the PCB? or buy a kit, I could check for undesirable tin bridges.
My advice is: if you can place a flashlight or strong light that you can backlight the tracks and have the image of the pcb ready to make at hand, then you can follow the route and compare if there is a cut track or an undesirable bridge, if The pcb is ok, you should check component values associated with those -10v and that the wiring is correct, if you cannot find the fault, good quality photos help.

 

[spoontex]

Hello,

how can I check if the ratio board works properly with a DM?

thanks.

 

[spoontex]

Hi,

I use a DC meter in my build. So I need to mount a bridge rectifier and add a resistor in series. What value I need for the resistor?

https://groupdiy.com/threads/all-things-g1176-the-new-repost-thread.646/page-3

 

[Olegarich]

Din't know if I can write it here or should find anohter topic.

I Biuld 1176 Revision D, Mnats pcb. Everything is cool and it sounds great. I decided to move it to the new box and change the meter.

Everything is working exept one thing. The meter is not showing 10db compression when i compress 10db.

I did "Q bias" calibration with no problme. did "Null" calibration (When it's null and meter shows null or 0v betwen R74.
Now i have to do -10db calibration, needle is just moving 1db, Tracking pot basically doing nothing. It trims max 1db.

I took and old meter and made this calibration with no problem.

I'm not sure if this new VU meter is bad, is it possible that some resistor might need to be changed so it can work with this one.
Any thought about that?

The old meter is from the Trident desk, small one. New meter is TN-73 model.

 

[gyraf]

perhaps meter jfet is defective?

 

[Olegarich]

thanks Jacob, I'll try that.

I Thought about that, but as i said with other meter it works fine, plus when play some loud drums and there is more then -10db compression hapening, i see on new meter that needle is moving with a rythm, not showing -20db but moving around -5.

Is it possible that I need to change some resistor value, for this meter sensetivity? If so maybe you can point me which part to play with.
Wonder if it should be R44, or R74.

Specs of new meter are:
Specification:
Item Type: VU Meter
Material: ABS
Color: As shown in the picture
Overall Size: Approx.62x56x84mm/2.44x2.2x3.31in
Model: TN-73-9213
Internal DC Impedance: 500Ω±10%
Insulation Resistance: 50MΩ±10%
Maximum current sensitivity: 650uA±10%
Backlight Board: DC 12V 1.2W
Friction: ±1mm/0.04in
Pointer Length: 30mm/1.18in±1mm/0.04in from the pointer tip to the axes
Pointer Width: 0.45mm/0.02in±0.05 mm/0.002in
Working Direction: Vertical

Is it possible that I need to change some resistor value, for this meter sensetivity? If so maybe you can point me which part to play with.

 

[Olegarich]

I Found the problem. Want to share how I solved it. It was in the thread, but now thread is so big that you might missed it.
Vu meters are different. Some of them like Sifam or from HAirball Audio, they have built in diode bridge rectifier and 3.6K resistor.
Others, like mine for example it just a vu meter with no components inside. For 1176 you need one with rectifier and resistor. If you have one without rectifier you can add it and still use it with 1176. How it's done?
From meter pcb, vu pad, it goes to the resistor (3.6K) and then to 4 Germanium diodes (1N34A) which makes bridge rectifier and then it goes to the meter+
That helped me and i could make -10db drop calibration.
If you need scheamtics, just check in google "Vu meter bridge rectifier" you will find info.

Diodes must be germanium like 1N34A, don't know why but i could not make calibration just with simple recifier.

 

[gyraf]

Very good - thanks for reporting back!

The confusion comes from above : "Item Type: VU Meter" - if there is no internal rectifier, then it's a simple DC current meter, not a VU-meter (dosen't matter what the scale says)

 

[gswan]

I Found the problem. Want to share how I solved it. It was in the thread, but now thread is so big that you might missed it.
Vu meters are different. Some of them like Sifam or from HAirball Audio, they have built in diode bridge rectifier and 3.6K resistor.
Others, like mine for example it just a vu meter with no components inside. For 1176 you need one with rectifier and resistor. If you have one without rectifier you can add it and still use it with 1176. How it's done?
From meter pcb, vu pad, it goes to the resistor (3.6K) and then to 4 Germanium diodes (1N34A) which makes bridge rectifier and then it goes to the meter+
That helped me and i could make -10db drop calibration.
If you need scheamtics, just check in google "Vu meter bridge rectifier" you will find info.

Diodes must be germanium like 1N34A, don't know why but i could not make calibration just with simple recifier.

Must be germanium (or schottky) because Vf is lower. For silicon, Vf is about 0.7V, which is going to obscure most signals up to 700mV (ie 0dBu). Germanium diodes have about half this Vf.
However, as rectifiers, their current waveform will cause distortion of whatever it is measuring, particularly if you just hang it off the audio source. It's mostly small (depending on source impedance), but be aware of it. Hence the modern use of a buffer circuit to isolate the meter/rectifier from the direct signal.