PeterC's 4 LED meter question

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Aharon

Well-known member
Joined
Jul 20, 2004
Messages
121
Location
Ontario Canada
I just made a PCB for the meter hoping to connect it to my Green Pre.
Can I feed + - 15V to this circuit instead of building another PS for 12V?.
Thanks
Aharon

http://1176neve.tripod.com/id12.html
 
The plight of the newbie....
There's a 4K resistor in the schem that is shown as another value(1K?) on the layout,any problems there?.
Also,can I sub TL082 for the 72?.
Thanks
Aharon
 
I?ve often wondered if the fluctuating LEDs might cause some slight ripple on the supply voltage? I?ve never tested this theory, though. Anyone know for sure?

Of course if that were true and the LED driving voltages were the same as the op-amp supply voltages, it could affect the audio.

I?ve noticed that some pre builders regulate the LED/meter voltages down from the main supply, but I don?t know that this is the reason. I suppose using more filter caps could do the trick.
 
Aharon

Not sure which resistor you are referring to?
TL 082 will work fine.

Flatpicker

on the Green pre I used a pair of RC filters on each supply line to provide some isolation. I could not hear the effect of the LED's turning on or off.

Peter
 
Aharon

Not sure which resistor you are referring to?
TL 082 will work fine.
peterc


Hi peterc,if you look at the schem you have there's a row of resistors that connect to the LM339,from top to bottom 10K/16K/4K/1K/470R.
I don't see a 4K on the layout and I was wondering if there were changes made.
As always TIA.
Aharon
 
There is a way to semplify the 4 led meter to use only 2 leds or a bi-colour ? like in the original ssl mic preamps ?
 
[quote author="Neeno"]There is a way to semplify the 4 led meter to use only 2 leds or a bi-colour ? like in the original ssl mic preamps ?[/quote]Yep. Pick the two levels that you want to monitor and wire them to a bi-colored LED. Not trying to be a smart @ss, but it's really that simple. You might want to wire the unused inputs to ground, but I'm not sure if it matters.
 
If you look to the right of the LM 339, there is a 2k2 in series with a 1k8 giving 4k total. They are between pin 9 & pin 11 of the 339.

Peter


Thank you for all the help.
Aharon
 
might be a stupid question, but i want to know, does this meter affect the audio quality in any way?

if not, why? its on the signal path, correct?

I'm keen on implementing it into my G9 project.

Thanks
 
Smoke,

Metering the G9 makes little or no sense. It's not behaving like solid-state devices, where you need to keep close to a relatively low headroom, and where overload is clearly defined.

I have spent a lot of time experimenting with level indication for the G9, and haven't found any that are better than the current - no meter.

There is a reason why you don't have metering on classic mic pres.

Jakob E.
 
from Jakob:
I have spent a lot of time experimenting with level indication for the G9, and haven't found any that are better than the current - no meter.

There is a reason why you don't have metering on classic mic pres.
I have a few EM4 magic eyes.
Since the HT-supply is present anyway in a G9 I'm tempted to add one/two, just for coolness. I should check them though, I'm not sure they're still OK. So I'll be testing them first (simple cap, some R & an Ge-diode will do the trick I figure) and have to be sure I have a few spares before I make a front-panel hole for them.

They're not that accurate I understood, so precise level-meting is still not obtained - so that's in line with the idea that level-indication here is not really in place.

The 'band-types' (like EM84 ? Or was it EM80) would be more accurate I think, but these are visually not as nice as the EM4 imho.

Bye,

Peter
 
from Jakob:
They'd surely look nice

- but just don't expect them to be useable..
Sure, no, it'll be definitely a gimmick (of a retro kind), even when adjusting them.

I thought the EM4 or one of its close brothers had a two range field, should read the datasheet again. So when one section has filled up 'with beam' the other section still can go on a little - until it's full as well.

If I were you I'd add a restriction to your G9-design: "not allowed to be used with any kind of metering or other irrelevant gimmickry" :wink: :thumb:

Bye,

Peter
 
does this meter affect the audio quality in any way?

The input of the meter is well buffered, so there should be no loading on the pre-amp circuit.

Some designs have a constant current source suppling juice to the LED string. This is to prevent clicks on the audio when the LED's light up & switch off.

I have to say I never heard this on any of the pre's that I hung this meter on (more than 10). It's pretty quick & easy to put together & check out.

Peter
 
> I have a few EM4 magic eyes. ... I'll be testing them first (simple cap, some R & an Ge-diode will do the trick I figure)

Diode? CAP? Why are you building a peak-detector?

Just dump audio on the control electrode. It is actually a very useful, though imprecise, indication. The density and size of the blur is a clue to average power, and in a dark room the extreme edge of the glow is a clue to peak level.

Technically this ignores half the audio, but music tends to be pretty symmetrical.
 
from PRR:
> I have a few EM4 magic eyes. ... I'll be testing them first (simple cap, some R & an Ge-diode will do the trick I figure)

Diode? CAP? Why are you building a peak-detector?

Thanks, you're right, I forgot it could be done directly as well.

Just dump audio on the control electrode. It is actually a very useful, though imprecise, indication. The density and size of the blur is a clue to average power, and in a dark room the extreme edge of the glow is a clue to peak level.

Technically this ignores half the audio, but music tends to be pretty symmetrical.

Let's tell Jukka Tolonen that it could be done much simpler :wink:
(you know the article:
http://koti.mbnet.fi/siliconf/JukkaTolonen/ga/peakmtr/peakmtr.html)
OK, he's not using the EM4 there.

fig2.gif


Directly connecting even simpler indeed - and no worries about an eventual clamping of the diode.

Thanks,

Peter
 

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