Help with analog VU meters

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Externet
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Re: Help with analog VU meters

Post by Externet » Sun Nov 10, 2013 8:53 am

Thanks.
That is what is expected on professional equipment. Then, there alone is a 6 decibel loss.
Being 600 Ohm, there you may have more signal drop if your particular CD player wants a higher impedance load for its output.
Measure CD output amplitude unloaded with oscilloscope and compare when plugged to your load.
Miguel
- Abolish the deciBel ! -

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ModRob
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Re: Help with analog VU meters

Post by ModRob » Sun Nov 10, 2013 11:50 pm

Again, many thanks guys...I don't have tech stuff like scopes and such (hmmm...wish I did though), other than a DMM, and again, at my age, my learning of ohms and impedances is troubling. I've always been fairly lucky at "fixing" or modifying things with my "jack-of-all-trades-master-of-none" skills. When it comes to electronics, the folks on this site have helped me with success for a few years now, as well as teaching me new things....so...

Jerry...can you explain a little about the 600 ohm balanced inputs? I know the physical properties of a physical balanced line, but when I see all of the inputs on the input boards connected by two pin (black, red) pairs, I just figured unbalanced (hmmm...now reflecting, thinking that the cable connecting IS balanced, because a ground is connected to one of the two conductors, which is still only total of two physical conductors connected to the input?) If so, is there a simple explanation on the degradation of signal strength with my current cable of two conductors as opposed to a balanced cable?

Next...In its original state (a bit different from that now) there were transformers in many places, and I could see in the schematics that these were 600:600, 150:600, 600:150, and I think another odd one or two. Again, I can't seem to grasp the impedance thing, instead again relying on old "trial and error" to see what works and what don't. I figured that keeping these in-line would probably be detrimental in what I wanted to do (since they were there for purpose in the original state). After several weeks of fruitless searching for parts and also trying to repair, rebuild, etc. boosters, amps, I grew frustrated and decided to just "rip out everything" in the monitor/amp circuits, and just use the front end of the console, adapting it to feed outboard amps. [please understand that while I know a fairly cheap, modern piece of equipment would have prevented all of this, I am heartset and waxing nostalgia on using a similar board that I worked on in the late seventies, for the "feel" of the old days...I'm sure most of you guys too miss the days of old :smile: ]

My plan was/is to bring my audio into the console, run through a pot, and eventually to the existing speaker outs, to then feed my outboard amps. What I found was this: audio comes in from the CD Deck and solders to the input boards (TT4 pot currently). Cabling then runs to front panel to a "master select switch" for routing, then feeds through a small transformer, (I bypassed this by wiring around it) directly into the "key switch" (AUD-off-PRG), then into the big Shallco pot. Comes off the pot and feeds back to the "master select" which I believe then runs over to each side "bus rods" (group of rods that many cables are soldered to). Then feeds to the Master Volume Pot, and back to the input/output cards, where I made one feed to go to the outboard monitor amp (Sony stereo/receiver). I've then been working on getting another feed to supply the actual "program" that wouldn't be affected by the console master volume knob. (which I think I found success earlier yesterday).

You see, my thinking was that if I eliminated transformers and pretty-much just "straight wired" everything together in that little string, then maybe impedances and such wouldn't be that big an issue. However, that big Shallco pot has always made me think it would cause problems because of some "crazy to me" specs on it. At one point I had considered ripping ALL of it out, and going back with basically a hand-made small mixer in a large frame! hahaha...like with a single on-off switch to turn on each channel, maybe keeping the key switch, using a modern stereo pot (hopefully that would have been able to be modded to attach the big knobs to)...I think you get my drift. But I've already taken a lot of the guts out of it, and just didn't feel right getting rid of anymore (more of that nostalgia kicking in). I still feel like this will work, it's just giving me some speedbumps along the way, that with help like yours, can get me around them...

So with that, I apologize for such long-windedness, but wanted you to "feel" what I'm trying to accomplish. When this is done and up and running, I believe you will find it very interesting and entertaining. (don't want to let too much out of the bag too soon-will elaborate more later)

Again, many thanks for the help and ideas.

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Re: Help with analog VU meters

Post by CeaSaR » Mon Nov 11, 2013 3:26 am

Okay, you've just confirmed what I was thinking you did - bypassed all the active components and
went with a completely passive setup.

Without the active boards in the signal path, there is no amplification for the VU meters. That is why
they didn't work the way you want or expect them to, so the CMoy is a step in the right direction.
Now all you need to do is make sure that the readings shown correspond to what Miguel (Externet) said -
and add amplification or attenuation accordingly to achieve those results.

At this point, the input impedance is moot. You've removed the reason(s) to adhere to them. BTW, your
CD player should expect to see about 10,000 ohms (IIRC) from it's output to the input of the "board".
This may not be an issue if there is no real degradation in audio quality or clipping / distortion.

This is what I can give for now - work calls...

CeaSaR
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Re: Help with analog VU meters

Post by Externet » Mon Nov 11, 2013 6:29 am

ModRob wrote:s...I don't have tech stuff like scopes and such (hmmm...wish I did though), other than a DMM, and again, at my age, my learning of ohms and impedances is troubling.
- Any modern DMM has high enough impedance and bandwidth to accurately measure audio amplitude. Just read the audio level with your DMM in AC low scale if you have no oscilloscope. Apply a sinewave 1KHz or play a standard CD with the tone, or record your own CD with several minutes of standard tones.
Audio readings will be in Volts RMS as should, instead of f%#[email protected]&* decibels. An oscilloscope would show peak and peak-to-peak amplitudes in Volts as should, instead of f%#[email protected]&* decibels.

- About impedance matching :

Form a cotton ball; throw it as far as you can; it will land about 4 feet away.
Make a paper ball; throw it as far as you can; it will land about 25 feet away.
Throw a tennis ball as far as you can; it will land about 100 feet away.
Throw a golf ball as far as you can; it will land about 150 feet away.
Throw a baseball as far as you can; it will land about 200 feet away.
Throw a football as far as you can; it will land about 120 feet away
Throw a basketball as far as you can; it will land about 80 feet away.
Throw a bowlingball as far as you can, it will land about 15 feet away.
Throw a lead demolition ball as far as you can, watch your feet.

Now, have the same test done with a seven year old kid:
Distances reached will diminish accordingly to the strenght of the kid.-

What is going on ?

It is not the lightest nor the heaviest the one that got the farthest away.
It is not the lightest nor the heaviest the one that used up the full strenght
CAPABILITY of the arm muscles.

It is the one that MATCHES the arm strenght. There is one object
that flew the farthest for each person... you ; the kid.

When an audio amplifier drives a speaker or a
subsequent load, there will be an optimum FORCE -TO- LOAD ratio
=(ARM -TO- BALL) that will deliver the most POWER.
That load will not be a tiny nor a huge one.

A rated output is the capability of a certain device AT a given
impedance load.

Unmatched driver-to-driven does NOT mean that there will be no action.
Your 400 watt stereo will burn yours ears off at full volume knob through
headphones but will be delivering only a couple of watts power, not
the 400 rated watts... because your headphones impedance is 600 ohms
instead of the at-rated 4 ohms... it is like the grown up throwing the paper ball.

As mismatch extremes, it is possible to push a ship by swimming,
or use a bulldozer to tow a bicycle.

Miguel
- Abolish the deciBel ! -

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Re: Help with analog VU meters

Post by JerryR » Tue Nov 12, 2013 6:09 am

[quote="ModRob"]Again, many thanks guys...I don't have tech stuff like scopes and such (hmmm...wish I did though), other than a DMM, and again, at my age, my learning of ohms and impedances is troubling. I've always been fairly lucky at "fixing" or modifying things with my "jack-of-all-trades-master-of-none" skills. When it comes to electronics, the folks on this site have helped me with success for a few years now, as well as teaching me new things....so...

Jerry...can you explain a little about the 600 ohm balanced inputs? I know the physical properties of a physical balanced line, but when I see all of the inputs on the input boards connected by two pin (black, red) pairs, I just figured unbalanced (hmmm...now reflecting, thinking that the cable connecting IS balanced, because a ground is connected to one of the two conductors, which is still only total of two physical conductors connected to the input?) If so, is there a simple explanation on the degradation of signal strength with my current cable of two conductors as opposed to a balanced cable?

600 ohm is the input impedance of your console(Established by the input xfmrs), , to get max *power* transfer between the signal source(in your case the CD player) to the load(the console)the source and load impedances should be the same. (for the theory and math involved, Google Impedance matching). currently, I think most audio mixers present a very high input impedance(bridging input) so that they don't load down the source signal and provide max *voltage* transfer.
As far as balanced Vs. Unbalanced, the red and black wires provide a balanced line, but if I understood you correctly the ground(Shield)is tied to one of the wires thereby Unbalancing the line.
HTH
JerryR
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Re: Help with analog VU meters

Post by ModRob » Wed Nov 13, 2013 7:37 pm

Wow! Thanks guys...lot to absorb there, and I'll have to find me a quiet spot sometime and juggle it around in my head. I'm sure I'll need it soon, BUT...for now SUCCESS has been achieved! I have my audio running in two separate feeds, even built in my CMOY headphone amp, AND now computer is running the audio input to it. I did have what I thought was big problem when first trying to get the computer to play the audio, it would play about a minute or so, then shut off audio. I tried all kinds of things, then, I uninstalled the Realtek audio stuff, found the newest and installed it, and voila! Now audio is constantly running....
So, a hearty thanks to you guys for bearing with me, trying to teach me new things. I can't wait for you guys to check out my station when I get it fully functional....

Now, only lacking a couple of things to make it totally right...
1. still want to drive the meters, but I think I have a better grip on that with your tips;
2. still have to install some kind of mic pre, connecting it directly to channel 3;
3. need to build some kind of mute circuit that will kill the control room speakers when the mic is engaged.


Ideas still welcomed... :grin:

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Re: Help with analog VU meters

Post by CeaSaR » Thu Nov 14, 2013 9:56 am

ModRob wrote:Now, only lacking a couple of things to make it totally right...
1. still want to drive the meters, but I think I have a better grip on that with your tips;
2. still have to install some kind of mic pre, connecting it directly to channel 3;
3. need to build some kind of mute circuit that will kill the control room speakers when the mic is engaged.


Ideas still welcomed... :grin:
Glad to hear it is functional.

Let's take these 1 at a time...

1. From your description, you still need more "drive" for the meters. Not sure if they are milli or micro ammeters
or if they are set up for voltage - probably voltage. Since they don't need to be in line, a class B or AB amp
could be used to drive them directly - which is what you are doing with the CMoy amp. Once you get something
that could actually peg the meters, you'll have to attenuate them enough to be useable (on scale). Empirically,
you could feed a signal into the panel and turn it up until it just starts to distort, then back it off a tad (distortion
starts before we humans can discern). This is the point where you want the meters to just touch the red. Set them
and forget them (darn that Ron Popeil!). You should be good to go from there.

2. Mic Preamp can be either chip based or discrete built. For chips, look at the TL06x, TL07x or TL08x series. With
these chips you can quickly throw something together and be sure it works. For discrete, search this forum for the
Mic preamp that the guys here helped design for/with me. Mine is seriously quiet and can easily overdrive either a
consumer stereo or a computer Line-In. It is designed for standard moving coil mics, but could easily be adapted to
use electret mics with a few additional components.

3. The mute circuit can be either purely mechanical (single switch), all electronic or a combo thereof. Depends on
what you'd like to do. I won't even speculate on that until you have an inkling which way you want to go on that.

Got to get going, so I'll catch you later.
CeaSaR
Hey, what do I know?

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ModRob
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Re: Help with analog VU meters

Post by ModRob » Sat Nov 16, 2013 5:38 pm

Let's see where we are at now in last couple of days:

I've learned that I am real good at tearing something apart, and going back with something that can easily be looked upon as "why in the h-e-double-ell would he do something like that for?" (hehe)...

Bought myself a four-channel headphone amplifier and fed my Program signal into it. Then outputs to:
*one channel now feeds the added headphone jack and associated pot with it;
*two channels feed left-right VU meters;
*still have one left over...

I did have my DIY CMOY headphone amp running the headphone jack, but this little unit has a bit more gain. I'll move the CMOY to my CUE bus on the pots to bring back that function.

Yep, very odd setup I'm sure you're thinking...haha...but that's my thought process for you...(hehe)

Next issue? The mic setup. I also bought a little cheap ART mic preamp. I go into it with LO Z mic (right now Shure 58)
XLR, then come out the TRS jack with TS(I believe I lose 6db this way) with two conductor cable and feed to the left and right two-post connections on each input board. At this point, yes, mic works, but with the channel pot wide open and input/output gain controls on preamp nearly wide open, I get low volume and a bit of distortion. Again, after coming onto the input boards, signal just goes through wiring (no active components), into the KEY/PROG switch, into the channel pot, then right to the stereo bus. I even tried removing all wiring from adjacent pot, and went directly into it with signal, listening through headphones attached to the pot's output terminals...still no difference in level. I did remove a couple of resistors that were inline on the outputs from the pot, and that gave me a little boost in level...but no where near enough to compete with the music program.
At this point, I'm thinking I've got to amplify the mic signal even more...does that make sense?

IF/WHEN I get that resolved, then my plan is to use a little electronic relay from Radio Shack (I have on hand a DPDT miniature PC relay, 12vdc coil, rated 5A, at 240VAC/24VDC). My early thinking is to trigger off the mic key switch so when engaged, it will disconnect the (-) side of the outputs that feed my outboard stereo amplifier. Never tried it before, so I'm guessing at this point...

All-in-all, getting closer and closer to having all working, and soon to get on "air" with programming...
Thanks again, for bearing with my "jackleg" thinking and tactics.

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Re: Help with analog VU meters

Post by Lenp » Wed Jan 15, 2014 6:12 am

Modrob
I've been listening in to LOVradio and it sounds like your work has paid off! I know of another station in the Midwest that uses Silverlight and it is bad, and won't work on many mobile devices. The players you use work well and I would like to pass the info to the station owner. Could you share the details of your setup? I'm sure others would be interested...
Len

“To invent, you need a good imagination and a big pile of junk.” (T. Edison)
"I must be on the way to success since I already have the junk". (Me)

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Re: Help with analog VU meters

Post by CeaSaR » Thu Sep 03, 2020 10:30 am

Been trying to listen to LOVRadio for the past month or 3 and I do believe they are "off the air". Bummer, since they played a lot of good music that you don't hear all that often. (Oh, and the commercials were a treat!)

ModRob, if you are still on here, would you comment? I can't find the contact # or email that used to be on the site.
Hey, what do I know?

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Re: Help with analog VU meters

Post by Lenp » Thu Sep 03, 2020 11:11 am

Yup, I have also missed lovradio.com. The site is up, but no stream, and, I could not find an email.link there. Hopefully all is well
and it retutns.
Len

“To invent, you need a good imagination and a big pile of junk.” (T. Edison)
"I must be on the way to success since I already have the junk". (Me)

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