Very 5 yr old question

[Karsoncookie]

After reading that above article, my head feels like it went through a Ninja blender.    Lars

[WMcD]

Summarized question at this point -     Will feeding an amplifier-  from my receivers headphone jack-  allow my receiver to properly function as a pre amp?

 

May be posting while being answered.

Lars

Yes it will. You are just taking a signal off the speaker output.

You can look at the schematic in the manual for which a link was posted above. The headphones are fed from the speaker terminals though 4 ohm (hard to see) resistors.

There is a potential problem with too strong a signal getting fed to you new power amp. "Line level" like at RCA jacks is probably only going up to 2 volts or so. The power amp at the speaker terminals can get much higher. Therefore some sort of attenuation is warranted. The adaptors mentioned should handle that.

If you want to home brew, you should look to the PWK mini-box. https://community.klipsch.com/index.php?/topic/161253-how-to-set-up-klipschs-3-channels-stereo/?hl=%2Bdope+%2Bfrom+%2Bhope+%2Bcenter#entry1964460

In the first version we see that he uses 25K pots to allow adjustment of line level signals. But this can be used for speaker level too. I'll bet the adaptors do the same.

The schematic for your unit is a bit low resolution but also shows what is going on with the "front end" of the unit. "Front end" is actually from radio receivers, it is where the antenna is connected. Below I go though a tour of the circuit. Actually, only one channel of the left and right is shown, which is typical. There is a lot of information there about the topology of the unit.

There is a phonograph pre-amp (that delta is generally the symbol for an amplifier and often an IC chip amp) from the phono input feeding the input selector switch.*

Note that tape in, CD in, and aux in, (all bridged together) and the output of the radio tuner (generally at the top of the schematic) are fed to the selector switch. This is just like you had an external radio tuner. (In the nomenclature, a combination radio tuner and pre-amp is called a receiver.)

The output of the selector switch (I'm squinting and relying a bit on experience) goes to the record out RCA. This means that if you're using that to drive a tape recorder input, you are actually feeding what came from the tape in, CD in, aux in, and radio. The receiver's volume (gain) and tone controls are farther down the line to the right and have no effect here. This is good for tape recording because you adjust the input level on the tape machine. You could feed a power amp but the volume control will not affect this either.

* The output of the selector switch also goes to the accessory bridge. That is the set of jumpers mentioned.

So what is that for? A: we can insert some signal processing right there if we want to.

The manual shows that you can remove the jumpers and insert there a graphic equalizer. A buddy had a nice Yammy combination equalizer and real time graphic display. It is fed by whatever comes out of the selector switch. (Watch the glowing bars bounce up and down. Cool.) The equalizer unit has a line level output which of course goes back into the other side of what would be bridged. Essentially, we've inserted the equalizer into the circuit before these line level signals are sent deeper into the guts of the receiver going to the right on the schematic.

Going farther we see a lot of devices: one is probably a motorized volume control pot and then an amplifier (the delta) with the tone controls adjusting feedback, tone defeat switch, and a stereo-mono switch. Then the signal goes to another delta which is the power amp.

d

The power amp feeds the speaker selection switch and headphones though the aforementioned 4 ohm ? resistors.

Also, down below seems to be a feed to a system which senses the current to the speaker block and goes to a protection circuit which shuts down the power supply. It may not like low impedance speakers like Klipsch.

Maybe more than you want to know but maybe inquiring minds will benefit.

WMcD

Edited May 12, 2016 by WMcD

[Karsoncookie]

WMcD -  Thank you so much for taking the interest and time to write the above.

 

Wery well written.

 

I definitely followed through it , and all makes sense.

 

I see again now, I cannot take "out" by the jumpers, at least,   sorry ,may be more reasons but mainly because I lose my tone controls.

 

So let me go back to outputting from headphone jack - Please tell me again if that "signal level" layman term)  will work feeding the Crown K2 or similar optimally as it comes out, or need a decreaser/ or increaser (as above in a few posts) (sloppy layman terms) in between??   Lars 

[Karsoncookie]

I'm studying manual for ART cleanbox, and trying to see if a basic "Pro" mixer is better or not. 

 

Lars

[CECAA850]

So let me go back to outputting from headphone jack - Please tell me again if that "signal level" layman term) will work feeding the Crown K2 or similar optimally as it comes out, or need a decreaser/ or increaser (as above in a few posts) (sloppy layman terms) in between?? Lars

 

The cleanbox has attenuation knobs to decrease output  if needed.  It will also increase the signal as that's what it's supposed to do.  Hook up the Crown and see if you actually need anything.  The K2 has gain knobs as well.  I'd only put a cleanbox in the signal path if you need a hotter signal.  You may not.

[WMcD]

Thank you for the kind words. I didn't see the request for clarification. Let me turn to that. I see I got long winded but I do that to be accurate and understandable. Click and Clack moaned about how when speaking to a layman, a short answer is technically incorrect and a long answer is incomprehensible.

Again, if you use the headphones out you are essentially using the power amplifier's voltage output to the speakers. That can get dangerously high and must be attenuated to feed a line-in RCA type to a piece of equipment. How high is described below.

This is a nice article which gives some salient information on a lot of things and we have to mine it for the important stuff.

https://en.wikipedia.org/wiki/Line_level

You'll note it describes RCA and mini plugs TRS. The latter is just the 1/8 inch diameter stereo connector with three connections or tip, ring, and sleeve (TRS) for stereo. Also used on modern earphones. There is some equivalent in millimeters (3.5 mm?).

When these types of connectors are used we are dealing with consumer "line level" signal. Per the article, the "nominal" level is about 0.300 volts or 300 millivolt (mV). (We just about always deal with "rms" volts, and this is another story.)

I'll say that 0.300 volts is the average program level coming out of a CD player. (Music of course varies wildly in equivalent level as we see watching the meters bounce. We usually use a pure sine wave in testing.)

But the article goes on, in the subject of computer cards, that it can go up to 2.00 volts. That makes sense because there are peaks, etc. well above average. And in quiet passages of music the voltage is far less.

It is also true that the line-level input to an outboard power amp is designed to take this range of voltages of sound levels. Line level out is line level in, because their connected by the feed wire.

Further, when we are using a pre-amp, we use the volume control to vary the level of the line level pre-amp output. You can turn the volume down to zero with a volume control knob.

Now, you say, I understand that the line level input of my power amp is wanting to get a signal of zero to up to 2.00 volts (and not more) but what about the headphone out, which is the speaker output of the power amp. How much voltage is there?

We have to mention what the article says about line-level. In short, there is no power being transferred, to speak of. This is because the input impedance (say resistance) of whatever we're sending the line-level signal to is about 10,000 ohms. I will not do the math but it would take a heck of lot of voltage to get 1 watt into 10,000 ohms.

But, to get an idea of the voltage output of a power amp we have to look at something we know about the power we can get and figure backwards.

You've seen that speakers are rated at such and such acoustic output in dB (like 104 dB for a K-Horn) while being fed with 2.82 volts frm the power amp. This 2.82 volts is essentially 1 watt of electrical power being fed into an 8 ohm speaker. We know that no speaker acts like an 8 ohm resistance, but we have to pick something to work with.

So, the power calculation.

Suppose we want to calculate power the amp is putting out. We know it is volts times amps. P = Volts x Amps.

By Mr. Ohms law: Current in amps = volts / resistance. So, in the power equation we substitute V/R for I and we get power = volt x volts / R. Therefore, we don't need a measurement of amps.

Suppose we say, how many volts will put 1 watt Power into an 8 ohm resistor? (Yeah- hold on, We're doing this calculation to get voltage.)

Our equation is 1 watt = V x V /8. This may lead to some math head scratching. The answer is that V must equal the square root of 8 and that is 2.82. 1 watt = 2.82 x 2.82 /8. You see, 2.82 x 2.82 = 8 and 8/8 = 1 watt.

What is WMcD getting at?

It means that if the volume control on you amp is set so that the speakers are getting 1 watt(this assumes a pure sine wave) , the voltage at the output to speaker terminals is 2.82 volts. That is in excess of the 2.00 volts the line level input which our power amp is expecting as max from the RCA line level as described above.

How bad can it get? Let's assume we turn up the volume control so the amp is putting out 10 watts into 8 ohms. Then 10 = V x V /8. V x V must equal 80. Without going to calculator we know 9 x 9 is 81 so we're just a smidge under 9 volts which is way above our 2.00 volt limit.

The bottom line here is that you must be very, very careful if you substitute a headphone out for a line level out. The safe solution is to use an attenuator. Really a "must" to avoid damage.

- - - - -

Also in the article. The professional equipment is indeed using a higher nominal level.

You should not tie two line level outputs together with a Y connector or the output amps are fighting each other -- left wants to be high level, right wants to be low. They don't average. If you have to, use a large value of resistance in series, then they average, which is to say "add". While not stated in the article, this is PWK's mixing box.

- - -

Comment: Headphone outs on Walkmen, smartphones are not very powerful because they are only driving little headphones, not speakers. Mine would not drive a power amp. They should be able to be used as a line-level input to a pre-amp though.

WMcD

[Karsoncookie]

WMcD - Again, thank you.

 

Your first long post, written by you, was totally orderly and understandable.

 

Post #66, was confusing.

 

And I have studied the Wiki "line Level" page and links from DEANG.

 

Have learned alot.

 

Anyway, my receiver specs state - Headphone jack - . 75 V (point 75)  270 Ohms.

 

The "Rec out" is even lower, 150 mV, 470 Ohms.

 

 

I invested  about 10 hours study since I posted last, And I'm a very fast reader.

 

 

So, I'm ordering an ART cleanbox and feeding it from my headphone jack, the only out I have retaining Volume and tone controls.

 

Unless anyone has a better way tonight.

 

Thank you, and all for help.       Lars

[Karsoncookie]

Click and Clack were great.   Lars

[Karsoncookie]

bump

[djk]

"Click and Clack were great."

 

I always loved it when they were stalling for time and would ask (a woman) 'what color the car was' (and she would always politely answer).

[WMcD]

I'll have to look at these matters over the weekend and determine how I went from hero to zero in one post.

 

Car Talk was fabulous. 

 

https://en.wikipedia.org/wiki/Car_Talk

 

It seems that other reporters for NPR sought to be top dog in listenership for their very serious, insightful reporting on world-wide affairs and mellow radio announcer voices.  But the two mechanics with acute Boston accents took top prize for years.  Granted, they were MIT grads with brains and humor.

 

I had a mention on "The Puzzler."   The question was what is so special about the word "facetious."  Of course, all vowel in order.  But I wrote them  that there was a word with vowels in reverse order, based on WordPerfect wild card letters and spelling check.  They described my post card on the air and suggestion, "He wrote a computer program to show . . . ."  But Ray then shut up Tom and said it would be a good puzzler.

 

It never happened and I didn't get any fuzzy dice.  Rats.

 

WMcD

 

.

[Karsoncookie]

WMcD - Hero in my book, VERY helpful.

 

Cleanbox and cables not ordered yet, need to wait few weeks.

 

But pretty much all figured out, pretty sure anyway

 

Lars

[Karsoncookie]

DEANG, et al   - -  Every word you wrote, after much study, I now have at least a basic understanding of.

 

I now see you are spot on.

 

Shoulda known.

 

The Gentleman I got the K2 from, messaged me saying he used the K2  in his "consumer" ( VERY nice - My words) system with no problem.

 

I wrote the following to him -  

 

 

           

 "Well, the necessity of the "box" (OR a "Pro" output Pre of some sort) is not really to get to the balanced thing.

 

That's just a side result, 

 

 

The main purpose is to "boost" the "Consumer audio" typical signal level voltage  to the "Pro" level typical voltage.

 

To feed the "pro" amp enough energy to be able to work to it's fullest potential output.

 

It will "work" without the boost, but the output will be limited by this.

 

Highly possibly unbeknownst to the owner of the system.

 

 

I recall who says what in posts pretty good, and know you're a pretty smart guy.

 

So you probably already know about this.

 

Anyway - Three links, ordered in increasing depth and length of info -  

 

http://www.crownaudi...?showtopic=3839

 

This one - Notice especially - "Overview" and Sine wave graph portions-  https://en.wikipedia...wiki/Line_level

 

Lastly - (link given by DEANG)  http://www.hometheat...our-system.html

 

This is just the tip of the iceberg of my readings.

 

I am now pretty sure most folks with "Pro" amps in a otherwise "consumer" system, are underfeeding their amps, and falling far short ( debatedly very ballpark, like 40% short) of the Pro amps output potential.

 

No matter how "high end" their pre amps are, cause they still output a consumer level signal voltage .

 

If interested, get back to me with your thoughts, 

 

Possibly this was your case??

 

Anyway, I'm happy I got your K2, just need to figure out these issues".   

 

I'm getting on track Folks thanks to Y'all  !!!       Lars

Edited June 1, 2016 by Karsoncookie

[Karsoncookie]

The above applies of course, only to those that have not made any provision for like boosting the signal to that Pro amp proper input level.

 

  Lars