0Vu = 1.625v

guze · Aug 29, 2020

Hi,
I always tought my master out was too hot, so i measured with the multimeter and it outputs around 1.625v at my master output.

The mixer is a Stancoil Alice 2008 and the schematic is only from the master card.

Where or how can i make it the standard +4dbu?

thanks

RuudNL · Aug 29, 2020

Lower the value of R22 (22K), IC3c.
And R10 (22K), IC3d.

16K.ohm should be about right.

Bo Deadly · Aug 29, 2020

RuudNL said:
Lower the value of R22 (22K), IC3c.
And R10 (22K), IC3d.

16K.ohm should be about right.

Yep. Sounds about right.

analogguru · Aug 29, 2020

guze said:
...I measured with the multimeter .....

Which multimeter ? At which frequency ? Output loaded or unloaded ?

BTW, a TL08x driving an output transformer.... phuhh, a little daring ....

guze · Aug 29, 2020

A standard multimeter with the tone generator from the mixer but around 300hz not 1khz
It has an opa4132, the original opamps where the harris4741.
I was thinking of trying 2xne5532 instead of opa4132

In dbfs its -12dbfs and it can handle +18dbu

abbey road d enfer · Aug 30, 2020

guze said:
Hi,
I always tought my master out was too hot, so i measured with the multimeter and it outputs around 1.625v at my master output.

The mixer is a Stancoil Alice 2008 and the schematic is only from the master card.

Where or how can i make it the standard +4dbu?

thanks

I don't really understand your question.
If the level is too hot, just turn down the gain somewhere...
Is it against some meter? I can't see any on your schemo.

RuudNL · Aug 30, 2020

analogguru said:
BTW, a TL08x driving an output transformer.... phuhh, a little daring ....

Yes, maybe not the best choice for driving an output...
But if it works, it works.

guze · Aug 30, 2020

abbey road d enfer said:
I don't really understand your question.

So, i set the tone generator at 1khz from the mixer at 0VU and it reads around 1.6v in the multimeter and -12dbfs on a +18dbu converters

I think it was calibrated at +6dbu/0vu , i want to make it +4db/0vu

The schematic was user timshel! that had/have a similar one and kindly made it for me (thanks), i wrote the summing,inverting,non-inverting and buffer in the schematic (not sure if it's correct)

In mine the original opamps where harris 4741 , i tried opa4132, tl074, mc33079, lme49740(unstable), and i settled for the opa4132
I have some dual to quad opamp adapter and i want to try 2xNe5532 or do you recomend any other or maybe even 2 different dual opamps. It will never take "great" opamps, i just want something with low noise and able to drive the transformer

MagnetoSound · Aug 30, 2020

Yeah, sounds like your VUs need calibrating.

abbey road d enfer · Aug 30, 2020

guze said:
So, i set the tone generator at 1khz from the mixer at 0VU and it reads around 1.6v in the multimeter and -12dbfs on a +18dbu converters

I think it was calibrated at +6dbu/0vu , i want to make it +4db/0vu

Where are the VU-meters connected? Is there VU buffer? Are they "real" VU-meters or just some kind of GP meter?

abbey road d enfer · Aug 30, 2020

MagnetoSound said:
Yeah, sounds like your VUs need calibrating.

+1

zamproject · Aug 30, 2020

Hi

Yes... meter schemo as balistic can help
Are you sure it's a Vu meter and not a PPM ?
+6PPM is more or less a "standard"

If it's a "real" Vu, for sure 0Vu at -12dbfs is little short...
If your converter is +18dBu<=> 0dBfs, calibrating the 0Vu at +4 is hot too :

Best
Zam

guze · Aug 30, 2020

The meters are sifam and i don't know if they are driven from a buffer, the signal comes from the monitor card (don't have schematic).

But for 0vu they should read 1.22v and -14dbfs

from left to right, power supply, monitor, talkback, aux, master, channels

guze · Aug 30, 2020

MagnetoSound · Aug 30, 2020

Ted Fletcher was the Alice guy, he might be able to help you.

https://tfpro.com/

[silent:arts] · Aug 30, 2020

+6 dBm = 0VU (= -9dBfs) is broadcast standard in Germany

analogguru · Aug 30, 2020

[silent:arts] said:
+6 dBm = 0VU (= -9dBfs) is broadcast standard in Germany

+6dBm is neither 1,23V nor 1.625V, it is 1,55V.

And it should be mentioned that in german broadcast they don't use old, lazy and inaccurate british telephone-meters - they use instead faster peak-meters according to DIN 45406:

The VU meter, originally intended for signals sent via telephone lines, has shortcomings when used in high fidelity systems. Due to its slow response time, a VU meter will not accurately display transients that can saturate a magnetic tape or drive an amplifier into clipping. The fast-attack peak program meter (PPM) does not have this problem.

While several European organizations have specifications for peak program meters, the German DIN specification 45406 is a de facto standard. Rather than respond instantaneously to peak, however, PPM specifications require a finite “integration time” so that only peaks wide enough to be audible are displayed. DIN 45406 calls for a response of 1 dB down from steady-state for a 10 ms tone burst and 4 dB down for a 3 ms tone burst. These requirements are consistent with the other frequently encountered spec of 2 dB down for a 5 ms burst and are met by an attack time constant of 1.7 ms.

The specified return time of 1.5s to −20 dB requires a 650 ms decay time constant.

So it doesn't really matter to which level an old and lazy VU-meter is calibrated because it is not an measurement instrument it is more an "estimation-iron" as we say to it in german.

MagnetoSound · Aug 30, 2020

analogguru said:
So it doesn't really matter to which level an old and lazy VU-meter is calibrated because it is not an measurement instrument it is more an "estimation-iron" as we say to it in german.

It may not matter to you.

There's a reason we use line-up tones.

user 37518 · Aug 30, 2020

analogguru said:
BTW, a TL08x driving an output transformer.... phuhh, a little daring ....

Thats why they are using 2 opamps to drive the transformer, the output of the non-inverting amp is connected to the output of the following buffer, thus doubling the current drive. Still, I agree, a TL08x is not the best choice.

ruffrecords · Aug 30, 2020

guze said:
The meters are sifam and i don't know if they are driven from a buffer, the signal comes from the monitor card (don't have schematic).

But for 0vu they should read 1.22v and -14dbfs

Like all good VU meters, the SIfams will read 0VU for for 1.22V rms when fitted with the recommended external series resistor.

It is not clear to me right now whether or not the VU calibration is correct.

Cheers

Ian

0Vu = 1.625v

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