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Old 13th May 2021, 5:23 am   #21
Diabolical Artificer
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Default Re: Suitable panel meters for use as a "VU" style meter on amplifier

If you have one level your fine, then the meter is only showing peaks but if you take a signal that is amplified from 0v to whatever RMS then fitting this range onto the meter face can be problematic.My amps had a gain of over 26dB when on full whack the meter needles were slap up against the stops. That said how many folk play music at full whack? Most amps run at about 1w for normal listening.

If your intended ampis high gain a series resistor can be put before the meter with a little SW to shunt it out if the amp is ever used in party mode.

Andy.
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Old 13th May 2021, 8:56 am   #22
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Default Re: Suitable panel meters for use as a "VU" style meter on amplifier

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Originally Posted by retailer View Post
Back when I built an optical audio compressor for my nephew I purchased a Vu meter from Ebay a quick look shows there is still plenty to choose from, along with driver boards etc should you need one.

https://www.ebay.com.au/itm/36336677...YAAOSwZqtgfr-L
Yeah ive seen plenty of those around. I was hoping to make use of something a bit more old school, as ive got a few of these old panel meters floating around.

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Originally Posted by Diabolical Artificer View Post
If you have one level your fine, then the meter is only showing peaks but if you take a signal that is amplified from 0v to whatever RMS then fitting this range onto the meter face can be problematic.My amps had a gain of over 26dB when on full whack the meter needles were slap up against the stops. That said how many folk play music at full whack? Most amps run at about 1w for normal listening.

If your intended ampis high gain a series resistor can be put before the meter with a little SW to shunt it out if the amp is ever used in party mode.

Andy.
Is there any way to have the meter respond in a logrithmic fashion?
I think someone mentioned this earlier, but if there was a way that it could be calibrated to max out only if the volume is turned up, but with low levels it could still move the needle 20-50% on average it would be fine with me.
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Old 13th May 2021, 10:26 am   #23
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Default Re: Suitable panel meters for use as a "VU" style meter on amplifier

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Is there any way to have the meter respond in a logrithmic fashion?
The answer is yes or at least something non-linear if not exactly logarithmic. If you are happy for the meter to be on the amplifier output (and you're not worried about accuracy) then this will do the job.

I've used this circuit successfully in an amateur theater environment where there were multiple speakers (not all of them within my hearing) and I wanted to monitor that signals were being sent to the right ones.

Hugh
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Old 13th May 2021, 4:54 pm   #24
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Default Re: Suitable panel meters for use as a "VU" style meter on amplifier

With a simple mod, the circuit in the link in post 23 does not need anything special for D1.

The mod is to swap the positions of D1 and R1, then connect a diode (lets call it D5) between the junction of R1-D1 and ground, anode to ground so that D5 conducts with negative inputs.

For positive input swings, the circuit behaves exactly like the original, the added diode is reverse biassed, and current passes througn R1 and D1 to the meter.

For negative input swings, current passes through R1 and D5, D1 is reverse biassed to block current to the meter, but only by the forward drop of D5, (0.7V for a small silicon diode). Thus D1 can be any small signal germanium diode, it doesn't have to withstand significant reverse voltages.

Stuart
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Old 13th May 2021, 5:06 pm   #25
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Default Re: Suitable panel meters for use as a "VU" style meter on amplifier

How about a stereo pot on the input of each channel of an amp, one as a standard volume control and the other to decrease the sensitivity of the meter circuit as the volume is increased.
Stuart.
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Old 14th May 2021, 2:59 am   #26
nzoomed
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Default Re: Suitable panel meters for use as a "VU" style meter on amplifier

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Originally Posted by stuarth View Post
With a simple mod, the circuit in the link in post 23 does not need anything special for D1.

The mod is to swap the positions of D1 and R1, then connect a diode (lets call it D5) between the junction of R1-D1 and ground, anode to ground so that D5 conducts with negative inputs.

For positive input swings, the circuit behaves exactly like the original, the added diode is reverse biassed, and current passes througn R1 and D1 to the meter.

For negative input swings, current passes through R1 and D5, D1 is reverse biassed to block current to the meter, but only by the forward drop of D5, (0.7V for a small silicon diode). Thus D1 can be any small signal germanium diode, it doesn't have to withstand significant reverse voltages.

Stuart
Im tempted to implement this, but will need to modify it if im using a milliamp meter, the schematic in that link specifys a microamp meter.
I guess its just a matter of shunting the meter to suit?
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Old 14th May 2021, 7:07 am   #27
Stockden
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Default Re: Suitable panel meters for use as a "VU" style meter on amplifier

Er no, shunting your milliamp meter will make itís sensitivity worse (full scale will be more milliamps rather than less).

The combination of the meter and R4 (the series pot) forms a voltmeter that reads the voltage across C1 and the diodes. Setting R4 to a lower resistance should allow you to use a milliammeter rather than a microammeter but will probably make the whole circuit less sensitive as well as altering itís response to changing volume levels.

My advice would be to breadboard the circuit and test it so you can see whether the meters you want to use will be ok before you cut any metal.

Hugh
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Old 16th May 2021, 3:43 am   #28
nzoomed
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Default Re: Suitable panel meters for use as a "VU" style meter on amplifier

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Originally Posted by Stockden View Post
Er no, shunting your milliamp meter will make itís sensitivity worse (full scale will be more milliamps rather than less).

The combination of the meter and R4 (the series pot) forms a voltmeter that reads the voltage across C1 and the diodes. Setting R4 to a lower resistance should allow you to use a milliammeter rather than a microammeter but will probably make the whole circuit less sensitive as well as altering itís response to changing volume levels.

My advice would be to breadboard the circuit and test it so you can see whether the meters you want to use will be ok before you cut any metal.

Hugh
OK, well looking at that link it appears its designed to connect across the speaker output?

Anyway, ive found a pair of voltmeters yesterday, i bought them both since they were identical and only cost $1.

Can they easily be converted to operate as ammeters?
From what I understand, ammeters essentially are an internally shunted volt meter (or the other way round, i cant remember)
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Old 16th May 2021, 7:48 am   #29
Andrew2
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Default Re: Suitable panel meters for use as a "VU" style meter on amplifier

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Originally Posted by John M0GLN View Post
There's this company which lists Sifam Audio Level Meters,
https://www.canford.co.uk/Sifam/SIFA...O-LEVEL-METERS

John
Sifam meters give me a nice warm glow and I've got a few in my drawers if you'll excuse the expression. I see they've realised there's a nice little earner in the 'mug's eyeful' vintage style!
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Old 16th May 2021, 10:24 am   #30
Stockden
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Default Re: Suitable panel meters for use as a "VU" style meter on amplifier

Quote:
Originally Posted by nzoomed View Post

OK, well looking at that link it appears its designed to connect across the speaker output?

Anyway, ive found a pair of voltmeters yesterday, i bought them both since they were identical and only cost $1.

Can they easily be converted to operate as ammeters?
From what I understand, ammeters essentially are an internally shunted volt meter (or the other way round, i cant remember)
Yes, that circuit connects across the speaker output of the amplifier.

Although those meters look great I'm afraid that whether or not they can be converted for use in this application rather depends on what's inside them. As voltmeters they should have an in internal series resistor (not a shunt - that's a parallel resistor). In addition, as the scale states that they're "AC DC" instruments, they've probably also got an internal rectifier.

So to use them somebody is going to have to open the case, carefully withdraw the meter movement, identify and remove the unwanted components, connect the movement to the terminals on the back of the case and put it all back together. This is well within the bounds of possibility (and there are people on this forum who will have done it many times) but it isn't trivial and it needs great care, a steady hand and a workspace free of magnetic particles if you're to avoid ruining the meter. If you haven't done it before it'd be worth getting hold of another cheap meter of similar design and practicing on that first.

On the other hand, at a cost of only $1 you're not going to lose much if it all goes horribly wrong.

Good luck whatever you choose to do1

Hugh
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Old 16th May 2021, 11:18 am   #31
nzoomed
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Default Re: Suitable panel meters for use as a "VU" style meter on amplifier

Quote:
Originally Posted by Stockden View Post
Quote:
Originally Posted by nzoomed View Post

OK, well looking at that link it appears its designed to connect across the speaker output?

Anyway, ive found a pair of voltmeters yesterday, i bought them both since they were identical and only cost $1.

Can they easily be converted to operate as ammeters?
From what I understand, ammeters essentially are an internally shunted volt meter (or the other way round, i cant remember)
Yes, that circuit connects across the speaker output of the amplifier.

Although those meters look great I'm afraid that whether or not they can be converted for use in this application rather depends on what's inside them. As voltmeters they should have an in internal series resistor (not a shunt - that's a parallel resistor). In addition, as the scale states that they're "AC DC" instruments, they've probably also got an internal rectifier.

So to use them somebody is going to have to open the case, carefully withdraw the meter movement, identify and remove the unwanted components, connect the movement to the terminals on the back of the case and put it all back together. This is well within the bounds of possibility (and there are people on this forum who will have done it many times) but it isn't trivial and it needs great care, a steady hand and a workspace free of magnetic particles if you're to avoid ruining the meter. If you haven't done it before it'd be worth getting hold of another cheap meter of similar design and practicing on that first.

On the other hand, at a cost of only $1 you're not going to lose much if it all goes horribly wrong.

Good luck whatever you choose to do1

Hugh
OK, ive taken these things apart in the past, they are usually quite simple, just take care to not to disturb the movement.

I saw someone in another thread somewhere who modified his meters and disconnected the shunt resistor by snipping one end and simply putting it back together.

Speaking of rectifiers, these are probably good to keep as spare ones for the meter in my valve tester.
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Old 16th May 2021, 1:24 pm   #32
Stockden
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Default Re: Suitable panel meters for use as a "VU" style meter on amplifier

Well if you've been inside a panel meter before then you shouldn't have a problem.

One thing though. As these are voltmeters, there are no shunts. Instead they have multipliers.

A shunt is a low-value resistance connected in parallel with a current meter, to enable it to read a higher FSD range of current than the basic meter does alone.

A multiplier is a high-value resistance connected in series with a current meter, to enable it to read and be calibrated in terms of voltage.

So you can indeed snip one end of the shunt in an ammeter and end up with a more sensitive ammeter but if you snip one end of the resistor in a voltmeter you will simply end up with a non-working voltmeter.
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Old 17th May 2021, 1:19 am   #33
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Default Re: Suitable panel meters for use as a "VU" style meter on amplifier

Quote:
Originally Posted by Stockden View Post
Well if you've been inside a panel meter before then you shouldn't have a problem.

One thing though. As these are voltmeters, there are no shunts. Instead they have multipliers.

A shunt is a low-value resistance connected in parallel with a current meter, to enable it to read a higher FSD range of current than the basic meter does alone.

A multiplier is a high-value resistance connected in series with a current meter, to enable it to read and be calibrated in terms of voltage.

So you can indeed snip one end of the shunt in an ammeter and end up with a more sensitive ammeter but if you snip one end of the resistor in a voltmeter you will simply end up with a non-working voltmeter.
Yes I think he had converted an current meter to a voltmeter in that instance.
Doesnt look like that would work in my case, if anything, I need to add a shunt across these to convert them into a current meter?
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