So I went to guitar center today and picked up an RCA to TRS plug to I could connect my home theater receiver to the headphone jack of my px-130. The first thing that really suprised me was that the 100x2 watt stereo channel on the receiver was barely louder than the 8x2 watt internal system of the px-130.

Secondly, the sound SUCKED. Ill chalk this up to the KLH 12" floorstanding speakers I used. I know they arent that great and color the sound, but it just didnt have much oomph. Tons of bass (too much actually), but not the right kind. Lacked in the mids. But I still expected more. I really hope that if I get some smaller, higher quality speakers it will sound better...

Just cant get over the lack of volume... does it have to do with the fact that the "line out" is actually a headphone jack and doesnt have the gain a real line out would??

Yes, I think so. I run my P90 through my stereo and it sounds great, and my speakers are about like yours. I take it the px-130 doesn't have a line out or you'd be using it. I know they make little preamps, you might need something like that.

Do you mean something like this?? Gemini Preamp

*sigh* more money to spend... Its not necessary though as the receiver WAS loud enough, just not as loud as I expected.

Do you think an equalizer unit would work by just upping all the frequencies to make it louder? I have an EQ, so I may try that. Hope it doesnt add any distortion/noise!

Strange. When people hook a piano headphone output to a line-level input, they usually get WAY too much volume ... and they need to pad down the levels.

If the receiver has a headphone output, plug the headphone there and compare the sound with the sound directly from the piano outlet.

This should be very much the same. If this is not the case then something is wrong with the connection. Maybe the stereo channels are shorted or something else.

It is also possible that the headphone output needs a mininimum load. (I dont believe it, but it is possible) In this case an Y cable would help. Then the headphone can be plugged in parallel to provide the necessary load.

Peter

Head phone out to line in creates an impedance mismatch. It won't damage anyting, but you lose some signal power due to the mismatch.

Now the PX 330 has a specified line-out impedance of about 2kOhm and the voltage is 1.8V eff.

The PX130 has a specified headphone output impedance of 3 Ohm and the voltage is 1.5V eff.

A typical line input should match to both. The impedance is typically 10kOhm ... 100 kOhm.

Impedance match means that the load must be within the recommended limits. It does not mean that the impedances are equal.
Therefore the impedances (and voltage levels) are pretty good "matched" here.

There are 3 types of impedance matching in signal transmission systems:

1) Match for accurate voltage transmission: Source imp. << Sink imp.
Line length is small to medium, resistance, inductivity and capacitance have to be small.
Used e.g. for audio line level lines.
2) Match for optimal energy utilization. Source == Sink.
Used for Antennnas, Microfones and so on.
Distance must be as short as possible.
3) Match for accurate current transmission: Source >> Sink.
Used e.g. for currentloop transmission lines in analog precision measuring systems.
Line length of several km, inductivity, capacitance and resistance of the line can be very high.

So, in this case (1) , impedances are matched.

(I wrote this because there is commonly much confusion and false information propagated about this. This is valid for DC and NF systems only. RF sytems are not covered here, you have to study if you want to understand RF technology)

There are, however cheap headphone and speaker amplifiers that produce more distortion without load. But I dont think that is the case here, because modern designs typically dont have this problems.

There are also devices that have too much RF noise on the Headphone outputs. While this is not audible it can overdrive the input stage of an amplifier and can make distortions or in the worst case destroy amplifiers and speakers.
This should not be the case for the headphone output of branded wellknown quality pianos ;-)

There are also PA's where the inputs are poorly filtered, and these might malfunction or might be destroyed by low impedance headphone outputs. Now that's not a problem, that is the law of evolution ;-)


Peter.

Thanks for all the info. Ill mess around with the setup and see what I come up with.

About the headphone jack needing a minimum load... wouldnt a high power receiver be a hefty load??

No. the high power comes out of the mains outlet.
At the line input there is no high power.

Peter

Thank you Peter!

I remember impedance matching being covered in some detail in my intro to circuits class, I believe because it is one of those fundamental behavior things you can prove with a bit of math, it is a bit counter-intuitive, and it gets the students thinking - and not because it is all that desirable in all scenarios (unless the meaning of the word "match" is situational).

To add another to your first category, certainly you don't want the output impedance of your amp to match that of your speakers. That would lead to poor damping factor, poor frequency response, poor bass, and a lot of wasted power.

If you look at line level circuits, particularly those found in consumer grade electronics, on the TX end they are driven by an op-amp output through a small resistor (100 Ohms or so) in series with an electrolytic cap. The resistor is there to suppress oscillation and to protect the op-amp output, and not for impedance matching. On the RX end the input impedance is generally on the order of 10k Ohms, and this is mainly to reduce noise pickup by unconnected inputs, not for impedance matching.

Im hoping the speakers were the cause of the poor sound quality. Sounded nothing like my sony mdr-v6 headphones!! I have a stereo EQ, so Ill try that next time to see if I can give the sound a more realistic frequency response. Im also going to pick up these sony book shelf speakers (120W) to see if it helps the sound. Theyve received good reviews everywhere I look so we'll see. I checked my local FRY's online and they seem to have them in stock.

Ive heard bad things about using stereo speakers with DPs though, and that you need a hefty system to avoid the chance of blowing the stereo/speakers. Though this may only be when using the line out.

Yes exactly...

Just for the non technical trained readers here:
The combination headphone output + line level input /can/ work and in most cases this /should/ work.

When it doesnt work then some of the components in use have this or those design flaws.
And of course all problems that can occur with line output plugs can occur with headphone outputs too....

Finally there is a risk when there is a shortage. When the headphone amplifier is not shortcircuit proof, it can fail.
However, because most TRS type plugs cam make shortages too, the headphopne amp /should/ be protected at least for some 10 seconds against this case.

So it is low risk to try it,and a very good chance for success, but if there is strange noise like buzzing, cirping or total silence, immediately interrupt the connection ;-)

Peter

You can easily check this. Plug the headphone into the headphone outlet of the amplifier. This must sound exactly the same as if the headphone where plugged into the PX130.

If not, then there is a compatibility problem.

Peter

Gotcha, I will. Too bad I have 6.5 hours left at work!! I want to try NOW!

There is something going one here. Typical home theater systems are not good for music reproduction but this is extreme. The first thing I'd do is change out the source. Do you have an iPod or portable CD Player? Connect that in place of the piano. Is the sound OK? Be sure and play some solo piano recordings and listen. Don't skip this step. You need to verify the input jack on the receiver is not broken. Test the same input that the piano would be connected to. Would be good to include the new cables in this test as well.

Next, A/V receivers have some fancy DSP inside. Verify that this is turned OFF. Maybe there is some digital artifact in the signal from the piano that the receiver sees and is put into a non-stereo mode like Dolby decode or whatever. There should be some kind of display that systems the mode that is being used. Make sure it is plain old "stereo".

What kind of test equipment do you have. I meter would be good. You could measure the AC voltage with and without the receiver connected.

When I say the sound sucked, I think that was me being overly picky. It didnt sound like something in the setup was malfunctioning in some way, it just lacked the character and correct frequency response needed to make the piano sound like a piano. It sounded like a synthesizer stage amp, pretty artificial.

Im using the same input I had my tv hooked up to not too long ago, so I know it works fine. I really think its just the speakers and not using an EQ. Ill do some testing tonight and post my results. Ill try the ipod as well.

Oh, and when only 2 speakers are hooked up its forced to stereo mode, no DSP available in stereo mode. Im hoping those 5 1/8" bookshelf speakers I linked to will sound better, less boomy and more true frequency response. I really think the EQ will make a big difference though. I hope FRYs has a return policy, if I dont like the speakers I dont wanna be stuck with them!!

Thanks for clearing this up. It's elementary stuff for an electrical engineer, but it lies outside the knowledge base of most people (including those who claim to know what they're talking about, but don't).

As for the OP's poor frequency response (excessive bass) ... long distance diagnosis is very difficult. It could be the speakers, or perhaps not. But the OP is thinking of getting an equalizer. I think this is a very good idea. They're extremely cheap.

Fry's has a great return policy. Save the boxes and you can bring them back within 30 days. I have returned un-opened items after 6 months. Qith pianos the midrange is key. Middle C is about 400 Hz (give or take) and the two octaves above and below is what most of us play most of the time. This is 100Hz to 1,600Hz. But some music has some powerful chords down low and you need flat response down to 40Hz to hear it. Read the specs on the speakers to check they are flat (to 3 dB) from about 40Hz up. (be careful as some companies will use 10 dB or nothing at all)

Also, you say you were unhappy with the volume. The amount of sound you here is the product of the power in the amp times the speaker sensitivity. Adding watts is the expensive way to make it louder. Yougain very little if you double the watts, only about 3dB in percieved loudness but the difference between a speaker rated at 86 dB/W and 96 dB/W is 10 dB. So read the sensitivity spec. before you buy the speaker. Go for "high 90s".

How much power does the amp have? Many are rated in watts of "Music power" or "peak" which is just BS marketing. You want to know the watts in RMS over the full frequency range in each channel.

If you are shopping at Frys wait for a sale on the Polk speakers I linked to in another thread. Sometimes the R50 or R300 get marked down to $50 or $100. "bookshelf" size speakers are always a compromise and tend to have lower sensitivity.

Ive already got one! (Earlier) "I have a stereo EQ, so Ill try that next time to see if I can give the sound a more realistic frequency response."

Ill be trying tonight most likely!

About the excessive bass, Ive noticed that almost all of the sounds on the px-130, even through the built in speakers, are bass heavy, but the boomy, upper frequency bass. For example, the electric piano and FM piano are very, very muddy sounding due to the bass response. Its better though headphones, but I can still detect a hint of it. I guess its just the processing in the piano itself. This is where the EQ will come in handy, probably drop the 400hz and up the 1kz areas (my eq has 60-100-400-1k-.....-16k) some and see how that sounds. Just throwing ideas out here, Im bored at work.

Hm, well maybe the boomyness would be closer to the 100hz range after reading this. Shame it doesnt have a 200hz slider.

I just dont have alot of money to spend now, so Im willing to compromise with those bookshelf speakers. There is a pair of 3-way 8" speakers in that same line, if I can get those at a good price Ill try them too.

EDIT: Just looked into those Polks, Ill definitely check them out if FRY's has them.

$100 speakers are lame. You get what you pay for.

Now, for the price of a pair of new speakers you could instead get MUCH MUCH better used speakers.

You might want to try craigs list. It's not uncommon to see speakers that cost $500 (when new) sell for $100 used.

How were your speakers positioned? I originally had a pair of high quality stereo speakers set up next to my keyboard for playing. After a year or two I finally invested in some near field studio monitors. I noticed a real improvement in the sound clarity. Home audio speakers are not designed for listening in the near field. Is there a chance that what you are noticing is the change in speaker position and more importantly the listening position the speakers are designed for?

I paid $49 each for these at Frys but even at normal street price they are not expensive
Polk R50 $120
Fry's normal price of $199 is a joke. No one else sels them for that price. NewEgg.com always has them for a better price except if you are lucky to get them on one of Fry's loss-leader sales but they sell out in hours at the $49 price.

About the "bass boom". these is a very good chance it is casued by the room and not so much the speakers. if you say it happens at 100Hz I'd think it's the room even more.

You description of the sound seem like the explaination below might apply. You can test it before spending money on more equipment. . Test with just your ears or for $50 buy a sound level meter from radio shack be be more analytic and make plots. (Yes the cheap 'rat shack" meter is very popular and well regarded.)

http://en.wikipedia.org/wiki/Resonant_room_modes

The above might be a little hard to understand at first but basically it says an empty room with six reflective flat surfaces is going to sound horrible and don't blame the speakers, good speakers will sound horrible too.

I actually found some Polk R50s on craigslist... 4 of them for $200. Im going to try to get 2 for $70 if I can cantact the seller. Though as was said earlier, maybe home theater speakers arent good for near field listening??

And when I tried my speakers they were relatively far away, about normal couch listening distance. Its not the room, I genuinely think its just the signal from the piano.

This is fairly frustrating (speaker choice). I dont want large speakers, Id like 4 bookshelf sized speakers so that I can hide them under/behind the piano and not take up any extra room, but everyone is saying for my price range they are $#!+.

Good news!! I tried me EQ and it worked WONDERS for the sound. Its still not exactly where I want it, but its MUCH better. Im thinking its actually the receiver that is really lacking in midrange output. We'll see if thr receiver that my girlfriend is giving me helps.

I went to Frys and bought some of the 5 1/8" sony bookshelf speakers and they are surprisingly good for $25 EACH. They have good mids and highs to give the piano a clear voice. I have them hooked up to the B channel of my receiver, and the large floor speakers are on channel A. I have them both running at the same time with no problems. Im not pushing the amp hard by any means so I have no worries that it will overheat. The sound is so much better than with the internal speakers, Im really happy.

I contacted the craigslist seller who has the Polk R50s, and he would take no less than $100 for 2 of them. So Im going to go try them out and see if they sound better than my KLH speakers. I tried them in the store and they seemed to have alot more mids than the other speakers, but it could have been the receiver or the room. Bass wasnt too impressive though... again could have just been the room. Regardless, they are better quality than my KLHs so Im sure they will sound great.

Indeed. An EQ works wonders. As for the receiver lacking in the midrange ... not likely. Amplifiers these days are as flat as flat gets. Generally you'd suspect the speakers, especially since you're using two very different speakers for each channel.
The speakers on keyboards (and on most consoles up to about the $4000+ range) are lame. A little help from a modest external sound system works wonders.
ChrisA reports that you can get the Polks BRAND NEW for around $100. So if that seller wants $100 for a used pair, he must be smoking some funny weed.

Whats interesting is both of the speakers sounded "scooped" without the EQ. Ive noticed it with this amplifier ever since I bought it years ago, never sounded quite right to me. Ive even got the entire range from 400hz to 2.5khz pegged to the max on my EQ and the rest about normal. It doesnt seem like I have enough EQ range to play with as it still lacks some punch in the mids (only talking about piano here, not music at this point). Something just doesnt sound "right" you know? This (and the fact that without the EQ the amp has NO midrange detail regardless of the speaker used) is what leads me to believe the receiver is at fault.



I thought ChrisA mentioned something like $65 each, but even so FRYs has them for $100 each right now. Even online I cant find them for much less. For what they are, $100 for a pair is amazing!

Does your receiver have a "Loudness" button? If so, enabling this feature applies a crude inverse Fletcher-Munson EQ curve to the output. Basically it boosts the bass and treble at lower volumes to make up for the human ear's response falling response here.

Nope. This is my receiver: Technics SA-AX730

Oh I forgot to mention an interesting point. I had to turn the bass eq on the receiver (it only has bass and treble) all the way down to 0 and the treble to 50% for it to sound decent. The curve on my separate EQ looks something like this. I still cant get a totally natural midrange sound, something sounds artificial. Ill keep working on it!

I know that this was mentioned earlier, but BE SURE that the receiver is set to the 2-channel mode - no surround.
The speakers can make all the difference - I use a pair (or occasionally 2 pair) of vintage Klipsch KG-4's. They are plenty loud and sound much more accurate than any PA speaker or "standard" home speaker that I have tried. And I've tried a few. I use no tone or eq adjustments on the amplifier, but I have tweaked the piano sound a bit.

Wow, I think I'd work that thing into the trash.

I think you are on the right track! I really wish I had a few different receivers to compare this one to, Ill have to wait for sunday to be able to compare my girlfriends old ass receiver (it was her fathers).

ChrisA reports that you can get the Polks BRAND NEW for around $100. So if that seller wants $100 for a used pair, he must be smoking some funny weed. [/quote]

Normal street price is about $110 EACH. I was able to get them for $49 each but I doubt we will ever see that price again. Frys has them on sale right now at $99 EACH. So if you see them used in good condition for $100 a PAIR that is about right, 50% of retail for current model in-production gear is about right for used.

So I just went to see the man who was selling the polk speakers... he gave me the deal of the year!!! He initially wanted $200 for 4 R50s, but I told him I only needed 2 and I offered $80. He declined and said hed take $100 for 2. So I agreed to come look. When I got there he said "man I really need to get rid of all four of these speakers cause I just got a new system. How about $150 for all four." I grinned and said "hmm... I really just dont need 4, but thats a good deal... I really hadnt wanted to spend more than $100..." So we talked some more (this late 40's ex marine was at least 6'6" and 275 lbs... HUGE freaking guy) and he was playing some mind games jokingly and kept trying to get me to buy them. After some more talking we discovered we were both engineers from Georgia Tech and he seemed to like that alot so he said "aw hell just take them all for $100! Pass the good deal on to someone else in the future!" The dude scared the hell out of me, he seemed like he could be in the mafia or something, had a real odd devious air about him. So I accepted, gave him the money, grabbed the speakers and got the hell out of there! Thoughts of his sledgehammer sized hands (no exaggeration) punching a hole through my solar plexus and taking his speakers back crept into my head as I was packing up, but he turned out to just be drunk, not a killer.

So, Im the proud owner of 4 cherry colored, like new, Polk R50s! FOR $100!!!!

Joey, Your comment about turning the bassEQ all the way down, leads me to add my own observations. When I take the line out from a CD player to my CambridgeSoundwords 2.1 system, I add about 30% of the bass boast to listen to a piano CD. But when I connect my DP, I have to turn the bass all the way back, and it is still too much. I have observed this with my NP-30, and a couple of previous keyboards. My guess is that the small amps in these very portable instruments are EQ'd to give more bass (the illusion of bass that is) thru the very small, $2 built-in speakers, and that the headphone jack, which is used for a TSR out, is not adjusted back to flat. So "mud" is what you hear trying to go into a stereo receiver. And who knows what the "curve" of this output looks like in other ways? So I'm not surprised that you're getting closer with your 7-band EQ.

My Korg SP-170 headphone out seems to be flatter--I add a little boast to the bass of the same 2.1 system to make it sound good to my ear.

You folks with the electronics/engineering minds, does this make any sense?

I think you may be right, that does make sense. Although when I use my studio monitor headphones the EQ seems to be perfect. Either way, I just hooked up my R50s and ss-b1000s through the other receiver I just brought home and man, even without the EQ it sounds great. Again I turned the bass all the way down, but it hits the sweet spot there and sounds great. Im going to add an EQ just to play around with it, but MAN Im happy now! The R50s sound AMAZING. Thanks to ChrisA for pointing them out to me.

Great find! There are lots of great speaker deals out there, ripe for the grabbing at low, low prices.

I went that route, too, and I got a great deal. But I can't match your story about Mr. Big Guy.

I added the EQ and it does sound better. Pretty close to right where I had hoped it would be sound wise. Theres still a little unpleasant "ringing" in the upper-bass/lower-mid range, but I think that has to do with the fact that Im sitting SO close to the speakers and am practically inbetween them. They are made to be at home theater distance, so Ill just deal with it. I tried turning them sideways facing left/right and also directly backwards, and both positions produced different sounds. Better in some ways, worse in others. So Im leaving them facing forward but slightly turned in for now.

Its definitely good overall though. Cant wait for my wooden stand and pedal bar to arrive monday, Ill post pics in the pic/setup thread once its all finished.

EDIT: I have some of that polyfill stuff that people use to stuff in their speakers cabinets. Its supposed to improve the bass response of speakers and remove "boomy" bass. Im thinking of trying this to see if it gets rid of that ringing bass I mentioned. Has anyone here ever tried this??

Polyfill changes the behaviour of the airspring in the enclosure go from "adiabatic" to "isothermal". Basically it makes the enclosure seem bigger than it really is. If the enclosure is too small for the woofer (common) then polyfill could help. The best way to tell is by plugging the woofer TS parameters into a calculator and measuring the internal volume of the enclosure.

If this is a ported enclosure than a different tuning might help.

Often the woofer and enclosure are both POS, and it's easier to do it right from scratch.

It is ported, and they arent POS speakers, but definitely not top end. Its a pretty big enclosure and has 2x6.5" woofers each + tweeter. Dont feel like messing with all that TS stuff, Ill just use the 1/2 lb per sq ft rule with polyfill and see what it does. I think Ill definitely do it with the small bookshelf speakers as I would probably notice the biggest change there.