Do I have an impedance mismatch?

[CECAA850]

Nope.

 

I keep one handy as I build sub boxes from time to time.  Most home gear won't drive a pro amp without one.

[juniper]

 

20*Log(V1-V2) if I recall correctly where V1 and V2 are the respective input sensativities of your amps. That will tell you by how much you want to attenuate the more sensitive amp. Once done, they will be in unison to each other.

 

Wouldn't it be 20*Log(V1/V2) ?

 

V1=1.6V for the Yamaha and V2=.2V for the Panasonic   1.6/.2=8       The Panasonic is 8 times more sensitive vs. the Yamaha.

 

(Log8)20 = 18db   

 

You will want to attenuate the Panasonic 18db through the DX. Also what speakers do you have hooked up to the Yamaha? You will want to set the correct load for them.

Wow.... thanks again!!! I had an engineer set my system up,  I  don't  think he had these parameters in his mind.... As far as speakers, I am just using jub clones, made out of 13ply BB with a doubled front face, and K402's with K69's in a 2 way system.

[Coytee]

That explains it.  You evidently didn't get the memo that horns are honky.

[mikebse2a3]

This isn't making sense to me.... What  model of CD player are you using?

 

Do you have the specifications for the CD player's output's Impedance/Voltage also?  I believe I read that you said it had an output impedance of 10 ohm which should drive the EV DX38 OK if it also puts out the standard line level voltage of 2 volts.

 

Do you have anything else to try as a source to drive the EV DX38?

 

 

By the way if you are using an unbalanced (RCA) to balanced (XLR) interconnect between the CD Player and the EV DX38 and pin 1 & 3 of the (XLR) are connected together (ie: measure like a short-circuit) then you do not loose 6db. If this leads to interference noise then connection 1 & 3 should not be tied together but you will loose 6db in that case. Be aware the same is true for the Outputs to Amplifiers interconnects also.

 

 

 

As a test experiment have you tried driving the Jub LF amps directly (ie: not through the EV) to see how much power/loudness you can achieve...?

 (Of course don't do this with the K402/K69)

 

 

miketn

Edited December 1, 2015 by mikebse2a3

[juniper]

This isn't making sense to me.... What  model of CD player are you using?

 

Do you have the specifications for the CD player's output's Impedance/Voltage also?  I believe I read that you said it had an output impedance of 10 ohm which should drive the EV DX38 OK if it also puts out the standard line level voltage of 2 volts.

 

Do you have anything else to try as a source to drive the EV DX38?

 

 

By the way if you are using an unbalanced (RCA) to balanced (XLR) interconnect between the CD Player and the EV DX38 and pin 1 & 3 of the (XLR) are connected together (ie: measure like a short-circuit) then you do not loose 6db. If this leads to interference noise then connection 1 & 3 should not be tied together but you will loose 6db in that case. Be aware the same is true for the Outputs to Amplifiers interconnects also.

 

 

 

As a test experiment have you tried driving the Jub LF amps directly (ie: not through the EV) to see how much power/loudness you can achieve...?

 (Of course don't do this with the K402/K69)

 

 

miketn

Thanks Mike, I haven't tried LF amps directly bypassing the EV, the player I am using is a HK HD7600mkll, which is one of my all time favorites, its connected to the IN 1 mono and the IN 2 right, in the back of the DX 38. I don't have the output impedance/voltage, but will search for it....

Edited December 1, 2015 by juniper

[juniper]

Found it, its 2 volts at 10 ohms....

[Chris A]

Here is a short blurb from Tom Danley on the subject of active crossovers that may help to clarify the issue:

 

The “down side” of operating pro / commercial gear in the home is that these units operate at pro-sound signal levels (hifi level is -14dB relative to 0 dB) however many of the units like the Xilica’s I use have an input and output gainstages which one can buy that back.

The up side if your amps are compatible is that the outputs are +14 dB hotter and can be run balanced which eliminates any chance of ground loop hum etc.

 

I think that you simply need more preamp gain.  Since I've always had plenty of gain out of my preamp (an AVP) and I use balanced connections in general (except to the First Watt F3), I've never run into an issue. 

 

But I see setups that are using passive preamp controls and direct from disc players to amplifiers--that run into trouble with not enough gain to fully drive the active crossover input section.

 

Chris

Edited December 2, 2015 by Chris A

[juniper]

Thanks Chris!!!!!

[xxJPMxx]

That Cd player is more than plenty to drive both amps to full power, period.

 

Maybe you have the Panasonic model where the sensitivity is 26mV and you need to attenuate more? Mike makes a great point, quit the guessing and either measure the CD player output voltage and or just plug the thing directly into the Yamaha and see how loud it gets.

[Chris A]

Okay, if the issue is the inability to control gain within your LF amplifier, I'd recommend taking the Dx38 out of the loop as suggested above, to see if the problem goes away. 

 

I believe what I'd look for after that is the grounding of the XLR-RCA cables from the Dx38 to your current LF amplifier.  I believe that you're going find your answer there.  I'd try the two different grounding configurations and look to see if your amplifier gain control issue changes.

 

Chris

[juniper]

Okay, if the issue is the inability to control gain within your LF amplifier, I'd recommend taking the Dx38 out of the loop as suggested above, to see if the problem goes away. 

 

I believe what I'd look for after that is the grounding of the XLR-RCA cables from the Dx38 to your current LF amplifier.  I believe that you're going find your answer there.  I'd try the two different grounding configurations and look to see if your amplifier gain control issue changes.

 

Chris

Thanks grounding helped!!!!  I got my bass amps controls back......Thanks once again!!!!!!

[babadono]

 Juniper,

So are you getting more LEDs on the input bargraph meter coming on now? I think before you said only up to -24.

Edited December 3, 2015 by babadono

[Coytee]

That Cd player is more than plenty to drive both amps to full power, period.

 

I'm guessing that you have a technical background....  (I don't) so don't let me offend you if this doesn't type well...

 

The CD player might have enough volts to drive his amps, but, does it have enough volts to drive his active crossover?

 

(honest questions since I'm a dummy on this stuff)

[xxJPMxx]

The CD player might have enough volts to drive his amps, but, does it have enough volts to drive his active crossover?

 

 

If the active crossover you speak of is the DX-38 then yes, it has an input impedance of 20k. Think of the thevenin equivalent for the circuit. The output impedance of the CD player is <10 ohms, lets say 10. His CD player puts out 2Vrms I believe he said so plug the numbers into the voltage divider equation;

 

2(20000/20010)=1.99Vrms

 

That's the benefit of an active crossover, they are much easier to drive     So clearly there is no impedance mismatch. Also in the DX38 manual it states that with a nominal input voltage of 1.55V it will put out a nominal 1.55V, it has unity gain up until you drive it with more than 8.7V then it will attenuate and keep the output voltage at a max 8.7V.

[babadono]

 

The CD player might have enough volts to drive his amps, but, does it have enough volts to drive his active crossover?

 

 

If the active crossover you speak of is the DX-38 then yes, it has an input impedance of 20k. Think of the thevenin equivalent for the circuit. The output impedance of the CD player is <10 ohms, lets say 10. His CD player puts out 2Vrms I believe he said so plug the numbers into the voltage divider equation;

 

2(20000/20010)=1.99Vrms

 

That's the benefit of an active crossover, they are much easier to drive     So clearly there is no impedance mismatch. Also in the DX38 manual it states that with a nominal input voltage of 1.55V it will put out a nominal 1.55V, it has unity gain up until you drive it with more than 8.7V then it will attenuate and keep the output voltage at a max 8.7V.

 

A 10 ohm output impedance driving a 20k ohm input impedance is not an impedance mismatch? It most certainly is. This is exactly how all line level audio equipment operates. A relatively low output impedance drives a relatively high input impedance allowing almost the entire output signal VOLTAGE to be delivered to the input as your equation demonstrates.

[xxJPMxx]

A 10 ohm output impedance driving a 20k ohm input impedance is not an impedance mismatch? It most certainly is.

 

I can't tell if you are agreeing with me that there is not an impedance mismatch or if you are trying to say there is?

 

Chris asked if the CD player has enough volts to drive the active crossover. My answer was yes it does provide enough voltage and I demonstrated why mathematically.

 

I think we agree, but you may or may not have misread my answer.

Edited December 3, 2015 by xxJPMxx

[jacksonbart]

^{could be}

[Coytee]

 

 

Like I said...  totally lost on that conversation.  

 

 

That's the benefit of an active crossover, they are much easier to drive     

 

That is more my language!  "yes stupid (you talking to me) it is much easier to drive"

 

 

 

 

 

Is "thevenin" a typo or is that actually a thing/concept?

[Coytee]

Never mind.  Just googled it.  New word of the day.

[babadono]

 

A 10 ohm output impedance driving a 20k ohm input impedance is not an impedance mismatch? It most certainly is.

 

I can't tell if you are agreeing with me that there is not an impedance mismatch or if you are trying to say there is?

 

Chris asked if the CD player has enough volts to drive the active crossover. My answer was yes it does provide enough voltage and I demonstrated why mathematically.

 

I think we agree, but you may or may not have misread my answer.

 

Yes we agree this should work. In fact I stated this is how all line level audio equipment works. We are striving to get 100% efficient signal VOLTAGE transfer from an output to the next input. This is done by having a low output impedance driving a high input impedance. But by definition this is an impedance mismatch.