C-100 LED meters & WATTAGE or VU meters & what do they connect to?

[Cpl-Chronic]

Heyya, all

I got these cool LED meters from Vintage man, complete with driver boards & case covers but want to use them for another blaster, which is secret for now unitl the MOD is complete. the 2 meters & boards have a single 4 pin connector & I have never seen a C-100 in person, let alone the guts of 1 inside so I have no clue how to hook them up to an audio circuit.

I'm guessing they display the wattage output from the amp stage but I could totally be wrong in my un-educated assumption. Instead of causing mis-understandings from inaccurate information I'll start by saying I don't know squat about this & need the help of experienced techs who know the C-100 & how these meters work.

Can I hook up the wires from the 4-pin connector in parallel with the speakers circuits &if so what wires do I hook up & what polarity are what color of wire etc.

Please help me out if you know how they work. Here's a pic of what I got from Vintage Man:

Thanx,
Cpl

 

[caution]

I'm working on my C100 right now, I haven't taken a detailed look at that board yet since I'm still carefully documenting as I tear down, but I'm also curious what it uses seeing I just built my own circuit to do just this. I'm actually interested in converting my C100 LED meters to be independent of volume level. The board shows a Sanyo LB1407, which is a seven-segment driver chip, which is cool, I've only seen five and ten segment chips. It's similar in setup to the LM3916 I used on the M70 in that it's scaled semi-logarithmically for audio.

 

[Cpl-Chronic]

Well, I know from high school electricity class that watt meters use a combination of volage(parallel to load) & current(series with load) to provide a reading & was thinking this might work similarly but how does it hook up & to where. I know the VU's on the C-100 are for source input voltage 1-2v normally & the LEDs are for power out, no?

Anyways, if you find out, I would love to know....

Cpl

 

[caution]

The four wires running to the connector are ground/power and left/right audio. I can tell for sure that the red wire is left or right, because it only runs to the second board. Orange is the other channel since it stops at the first board. That would leave yellow and brown as power, take a closer look at the marking on the board and see if they say which one is positive or negative. I see a little "C" there by the brown wire going off to the second board, that may be ground (common). According to the datasheet the chip is designed to run between 5-16V, so it may be tied a voltage regulator circuit elsewhere within this range.

I'll have to get in there and look at the circuit and measure things to know for sure what's going on (I don't have a schematic) but as with any LED meter using an IC the audio signal is connected to a series of comparators that all have one of their inputs strung together with higher and higher value resistors. The other input on them are all tied to some reference, like ground or a steady voltage. So as the audio level climbs, more and more comparators will activate, since the difference between the reference input and the audio signal input is increasing. As the signal climbs it overcomes higher and higher value resistors tied to the audio input of the comparators. If you think it might help better understand, I can post some images showing this in more detail.

All of these driver ICs have a slightly different method of configuring, this one allows you to use an external resistor to set the LED current. It also has a built-in input amplifier so you can easily adjust the meter sensitivity. Conion seems to have calibrated it so that the meters represent line-level at what, maybe around 15 or so for full-strength FM stations? The meter also has some form of peak detection/decay so those may be what one or more of those capacitors are used for.

If you want to wire it so that they bounce the same regardless of volume you'll have to rewire them to the line out signal instead, but that may involve changing one or more parts on the meter board so that they work correctly with the different signal level and impedance.

What I don't know is if the signal the C100 uses to feed the meters has been adjusted for high impedance inputs or if it's tapping directly off the speaker outputs, in which case the meter circuit may need a higher value input resistor to work with line out if that's something you want to do.

 

[Cpl-Chronic]

Yeah, I'm pretty sure you're right, 'C' is common or ground which would be the negative, so Brown(-) yellow(+) for powering the modules, while Red(R) & Orange(L) audio connections & also guessing that the positive leads from each amp channel would connect to these L/R audio wires.

@ Caution: waiting for your input to verify what's what. I don't want to damage anything by hooking it up wrong so if you can let me know, that would be awesome.

Thanx,
Cpl

 

[caution]

Traced out the boards tonight. Still need to figure out the formula on the datasheet to modify for line level vs. speakers.

 

[Cpl-Chronic]

Thank you so much Caution.

This is great info for me. I want to use them as watt meters anyway, just didn't want to hook up the power leads wrong & fry the IC's so this should help me out tons.....

I have 2 more questions & then I will stop badgering you about it.

1. So, the 2 audio input wires, I could hook up to the positive leads of each speaker for audio input since I'm guessing negative & ground are the same?

2. Can I tap the DC voltage at the mainboard input without blowing the IC, as long as it's within that 5-16v range?

Thanx again,

Cpl

 

[caution]

Yeah, I had the power backwards, C definitely doesn't mean common. It's for the wire color (the yellow is marked with Y) so it must be for some other color like cyan, and ran out of that and used brown instead.

I'm going to partially reassemble the box this weekend so I can figure out the voltage level going to the modules, since the resistor values on there may only work (or work best) when you feed it the same voltage the C100 does.

 

[Cpl-Chronic]

hey Caution!

Thanx again for your help & your skills are off the chart . I'm guessing the power into the IC's isn't that regulated & depending on AC or battery source, it could vary as widely as 10-16v from the blaster's power block but definitely could be very wrong on that so waiting for your input again.

Thanx again for the help & if there is anything I can do in return for this giant favor, let me know...have a great week,

Cpl

 

[caution]

No sweat! Glad I help I didn't get a chance to test the box but you should be fine hooking it up to main power, the datasheet for the IC says that it can run safely anywhere between 5.5V and 16V. The audio section doesn't seem to rely on this to be a specific level to function properly.

 

[Cpl-Chronic]

Cool...I'll try it & if you can, would you be able to measure main DC into the mainboard vs voltage in for the moduels? That would tell us for sure if there is some sort of regulation before supplying the moduels...

Thanx again Caution. I'm still in awe that you could whip up that schematic so quickly & accurately.....just amazing!

Cheers & have a great week brother!

Cpl

 

[caution]

Aww it's nothin, I do it for a living
Yeah, there is some sort of control circuit upstream, it's getting over 17 volts from a half-watt power transistor. I noticed I made a mistake on the wire colors, power comes into the first board on orange and then it's brown when it goes to the second board. Also I found that there are some mainboard resistors on the audio lines, they go to a very big connector so it might be the main speaker outputs.

 

[Cpl-Chronic]

Yeah, I noticed that orange in & brown to the 2nd board were connected when looking at the traces on the back of the first board & thought that was weird so didn't know if I had that right or not. That was partly why I was badgering you with all of these questions since, really this is quite beyond my skills to sort it all out. From what I gather on the forum, the C-100 is a bit strange, like a mix between an M90 & a cheap lasonic as far as build quality. It doesn't surprise me that it throws a couple of curve-balls at you when backwards engineering the details...

I do know the VU's in the corner of the C-100 are for line/rec levels(1-2v max?) & the LED meters are for AMP power as sort of a watt output meter on each channel. Am I correct in thinking that more LEDs light up as you increase volume? Does that fit with what you are looking at & do I have to pad the audio inputs with resistors, like the diagram above, to avoid saturation & blowing the IC's for the LED meters?

Basically, I want to adapt the meters to another blaster & have it do the same watt meter job for another project...not a VU meter or source line level application but for displaying output levels to the speakers....

Thanx again Caution & sorry for the saga of questions from a noob like me...

Cpl

 

[caution]

Yeah, the build quality on the box is decent, it's just got more of where it's harder to get at areas without assembling more than you'd like to.
You're exactly right the LEDs are showing the amp output, not like the analog VUs... so you'll have to add some padding resistors of similar value, it seems that the modules are meant to be driven by something closer to a line level signal by themselves.