VU BUFFER & PEAK LED KIT BUILD THREAD

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Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Postby Joe Malone » Mon Nov 26, 2018 6:34 pm

jrowell wrote:
Joe Malone wrote:
api wrote:Hi.

I just ordered a large quantity of the these pcb´s which are going into a vintage Neve that i built a custom VU bridge for.
There will be 16 small Simpson VU´s and 5 larger ones.

My question is if i can omit the parts on the pcb that relates to the peak LED?
I will most likely not use this feature and wanted to save a few bucks on parts and also save time when building them all.


Yes you can leave off D4 BAT85, C3 1uF, R9 1Meg, R10 47k, RV2 5k trimpot, RED LED.

So spare opamp half doesn't now oscillate solder opamp pin 4 & 5 together and 6 & 7 together.


Hi,

To avoid unused op amp section being driven to negative rail connect Pins 6 and 7. Pin 5 must go to 1/2V source for single ended PSU topology. Re:
https://www.maximintegrated.com/en/app- ... vp/id/1957

James Rowell


While I agree with the link in normal precision audio path setups. Not in this case as with TL072 in VU buffer sharing the 1/2v with another input just makes opamp lock up more common at high gain setting. If you want to do this you must down size the 2 x 47k half rail resistors down to 2 x 10k and increase the half rail cap to 100uF to stop large turn on thumps pinning the VU meter to Full Scale and not have lockup problems. This mod uses more current than driving the spare opamp to 0v.

Or easier just do as I said originally as the extra current is tiny in TL072 and noise floor change is minimal and not seen due to the diode bridge feeding the meter.
Joe :-)
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mrclunk
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Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Postby mrclunk » Sat Aug 17, 2019 10:01 pm

If i want to sum a balanced stereo signal to mono for inputing to the one of these boards, what's the best way?
This would hang off the mix bus so wouldn't want it to affect signal.
Do i need to add a buffer?

Is the circuit attached overkill?
balmix.jpg

thanks
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Merlot
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Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Postby Merlot » Wed Aug 21, 2019 10:33 pm

Hey Joe,

I plan on building a tube mic preamp and would like to add a vintage Telefunken VU meter. I wanted to ask, what the best way would be to power the buffer from the power rails I have.
The power transformer has 250V 20mA, 6,3V 700mA and 6,3V 500mA.
I wanted to test AC heaters plus de-hummer pot first and if it's too noisy connect the two 6,3V lines and rectify it.
Can you tell me how much current the buffer without peak LED consumes?
Thought about using the B+ rail with a series resistor. But I'm not sure if the trafo has enough juice for that as the B+ needs about 8mA (x1,6 for DC rectification so around 13mA)...
If I use DC heaters I could just use that as it would have around 18VDC right after rectification. Or does the buffer rail have to be well filtered?

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Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Postby Joe Malone » Sat Aug 24, 2019 9:17 pm

mrclunk wrote:If i want to sum a balanced stereo signal to mono for inputing to the one of these boards, what's the best way?
This would hang off the mix bus so wouldn't want it to affect signal.
Do i need to add a buffer?

Is the circuit attached overkill?balmix.jpg
thanks

That circuit will unbalance the balanced summing a bit so is not a good idea
Joe :-)

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Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Postby Joe Malone » Sat Aug 24, 2019 9:17 pm

Merlot wrote:Hey Joe,

I plan on building a tube mic preamp and would like to add a vintage Telefunken VU meter. I wanted to ask, what the best way would be to power the buffer from the power rails I have.
The power transformer has 250V 20mA, 6,3V 700mA and 6,3V 500mA.
I wanted to test AC heaters plus de-hummer pot first and if it's too noisy connect the two 6,3V lines and rectify it.
Can you tell me how much current the buffer without peak LED consumes?
Thought about using the B+ rail with a series resistor. But I'm not sure if the trafo has enough juice for that as the B+ needs about 8mA (x1,6 for DC rectification so around 13mA)...
If I use DC heaters I could just use that as it would have around 18VDC right after rectification. Or does the buffer rail have to be well filtered?

I need to see the exact power supply circuit to advice the best way to do this.
Joe :-)

JLM Audio

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Merlot
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Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Postby Merlot » Mon Aug 26, 2019 2:34 am

It will be this one but instead of the rectifier tube I will use diodes.
I plan on using AC heaters but when that's too noisy I'll go with CR filtered DC heater.
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Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Postby Joe Malone » Mon Sep 02, 2019 10:04 pm

Merlot wrote:It will be this one but instead of the rectifier tube I will use diodes.
I plan on using AC heaters but when that's too noisy I'll go with CR filtered DC heater.


Due to the 6.3vac being centre ground 0v it will not work to drive the buffer.

The CR filter DC heater will work if you ground 0v one side so you have at least 9vdc
Joe :-)

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Merlot
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Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Postby Merlot » Wed Sep 04, 2019 4:34 am

Hey Joe,

thanks for the reply.
I did not mean to use the 6.3vac to drive the buffer. I thougth about using the B+ with a dropping resistor.
And as a last resort I could use DC heaters and then thought about using this for the buffer. Thats why I ask if the supply voltage has to be well filtered for the buffer.
Can you tell me, how much current the buffer needs without the LED?

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Re: VU BUFFER & PEAK LED KIT BUILD THREAD

Postby Joe Malone » Wed Sep 04, 2019 9:32 am

Merlot wrote:Hey Joe,

thanks for the reply.
I did not mean to use the 6.3vac to drive the buffer. I thougth about using the B+ with a dropping resistor.
And as a last resort I could use DC heaters and then thought about using this for the buffer. Thats why I ask if the supply voltage has to be well filtered for the buffer.
Can you tell me, how much current the buffer needs without the LED?


Buffer needs 10 to 20mA depending on meter type it is driving so drop resistor would need to 10W type and be wasting 3 to 6w of heat so not a good idea but could be done with 33v 5w zener across the buffer power input.
Joe :-)

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