Key Board stereo headphones to mono input

D

Dinosaur_Rocks

New member
Key Board stereo headphone output to mono input. What's the best way besides buying a Mixer?
I want to run my Yamaha NP11 Key Board from the stereo head phone out to a Guitar AMP (MONO)
 
If it is stereo out 2-plug left and right, left is generally mono. If it is stereo single plug and for whatever reason you are not receiving the full mono signal on the other end, try a stereo to mono adapter jack (they are like two bucks) or any number of Y adapters (without seeing exactly what you are describing it's hard to say which).
 
It is generally bad practice to simply connect LINE left and right outputs together to mono them since the very low impedance "shorts" each output into the other. This can cause distortion and in rare cases, mostly with very old equipment, damage.

However, headphone outs are different. They must be able to drive all sorts of headphone loads right down to the incredibly stupid eight Ohms. It is therefore quite safe to simply connect together left and right, either in a made up lead or using a Y adaptor.

http://www.ebay.co.uk/itm/6-35mm-MO...ion_Audio_Cables_Adapters&hash=item53ebcf9651


OOPS! No, that won't work, you will be coming out of a stereo 1/4" jack? So you need a stereo (TRS) cable and a TRS to TS combiner. I shall have another look!

Well, THIS..
http://www.amazon.co.uk/Stereo-Plug-Mono-Jack-Adapter/dp/B000UX7JR4
Is what you need (and a guitar cable) but unavailable! And this found only after MUCH searching. Better I think to buy a stereo, TRS cable and get someone to link the left an right tags or fit a mono jack plug.
Dave.
 
Last edited:
The headphone out is a TRS stereo but single 1/4 inch TRS plug, which carries left and right signal. This is not a problem, but the guitar amp might be.

1) NO MIXER NO ADAPTOR, Even with adaptor, it is just shorting it in the sleeve of the adaptor, Just short it at the insert, meaning, You just plug in a mono TS cable 1/4 and it will short the stereo and send it mono. I did it regularly when my wife was using a very lightweight 88 key Korg SP series, forget the exact model. Anyways, no 1/4 outs only 1/8 inch headphone out. We used a stereo 1/8 adaptor to 1/4 mono, which was basically doing the same thing shorting the stereo to mono. Yours is easier, just plug in TS mono cable and rock on. Some might suggest it could damage the HP circuitry on the keyboard, never had an issue and KORG was fully aware of this when they made the stereo HP out as the only output.

2) Here is the issue, putting that vey hot HP signal into your guitar amp will work, but the HP out is not an instrument level signal, as mentioned it has ability to drive relatively low impedance loads and some higher impedance HPs, but instruments are even higher impedance, hence the guitar amp was not made to handle this hot signal. Another however, it will work. I use a GK 2x10 Bass amp for my wife''s NORD Stage 2 when she plays the role of bass with her left hand on keyboard with a Latin group. However, one more time, these are line level outputs, but again, lower impedance than pure instrument plug in. Sounds great and bass lines from keyboard with bass samples split with Fender Rhodes, but I can tell the amp circuit is not thrilled about it. Just seems a bit staticy, and unstable. However, last time, been 4 years of using it several times a week for the first few years and lately not so often. We do use it now as a Bass amp go figure, works fine, sounds great.

Good luck, no adaptor needed, even an adaptor as far as I know will not solve the fact that there is no output for the ground for the TRS on the mono end. Just shorting it is most common way.
 
Hi Bob.
I bow of course to your hands on experience but if I may?

Inserting a TS (mono) plug into a stereo headphone jack will pick up the tip, left signal but it will also short the right channel to earth/common and therefore you will get nothing from the right channel. This may not matter of course in many situations.

Shorting the RH channel will almost certainly do the headphone amplifier no harm at all.

Impedance: Hardly ever is the problem Level is. It is standard audio practice to feed from very low Z <100 Ohms to highish Z, >10 kOhms but it makes no difference at all to go from VLZ to very high Z, 1 M Ohm even a G Ohm! Because the low Z shunts the high. This is NOT to say that some guitar amplifiers will be happy being fed from a keyboard, ***t 'appen but there must be some other mechanism going on for there to be a problem, ground loop perhaps?
The level issue is of course easily fixed with an attenuator. Headphone outputs tend to be in the neg ten region, about 300mV and guitar amps are happier at about -40dBV, around 10mV so a 30dB attenuator would be indicated but 20dB is more commonly available and should be fine in practice. Best solution IMHO is my fave DIY noob project, a 10k log pot in a tin!

Not sure what and where the losss of "common/earth/ground" comes about Bob? Even if the keyboard were "floating" the amp should be earthed?

Note to OP. Many headphone cable products, extensions etc, are NOT shielded cable. You must use shielded cable twixt keys and amp.


Dave.
 
I disagree with Bop, and agree with Dave - you can't just use a 1/4" TS guitar cable.

Here's 1/8" TRS to 1/4" TS 10' cable: AMAZON

If you have 1/4" stereo headphone jack (you didn't say), use this adapter, too: AMAZON
 
Ah! Those loverly Rane people !

Yes Arc' that is indeed the proper way to do it.

If anyone is going to build such a box, I would suggest a couple of changes?

Instead of a 20k fixed R use a pot, 10k or so and take the output from the wiper.

The 475 summing Rs are rather low for "prosumer" kit which likely uses the otherwise very useful TL072 op amp. These show increased distortion* if loaded below a few k Ohms and so I would make the resistors 2k2. This will cause an earlier HF rolloff but only for very long cables, way beyond anything likely in a home studio.

Lastly, fit a ground lift switch in the output earth path and shunt it with ~ 1nF. You now have a passing useful re- amp box!

*But then we ARE talking synths so who really cares?


Dave.
 
Wow! You Guys are incredible!
I have done a lot of Searches and one that I found was to do the same as arcaxis said but using 2-100 ohm and 1-33k...so they were on the same page as you. Yes I am very DIY inclined and it seems like a I have a giant box of 1/4 watt Metal film resistors here some where. I would be inclined to try the 475 Ohm/20k first. I want run this keyboard to my guitar amp to see if I can get a Jon Lord type of sound.

ECC83 >>how about putting a 20k Linear Potentiometer in place of the 20k Fixed resistor? is that what you were saying?
 
Last edited:
I say try it with a guitar cable first and see if there's a problem.

If the keyboard puts out actual stereo sound - a piano with the lower notes further left, for example - then you'll definitely lose something when you throw away the right side. You will notice immediately and then move on to the passive mixer.

If, on the other hand, it fakes the stereo by way of some effect process or other, I would guess you'd probably be okay with throwing away the right hand channel. You will lose somewhere between a little and a lot of the full impact of the sound. When you hear it, you'll know whether or not it will work for you.

On the third hand, if the thing uses some phase fuckery to create a fake stereo sound, it will almost definitely sound stupid with the two channels mixed together, and the TS>TS will be completely necessary.

The mixer above presents just about 1K to either of the outputs. That's plenty for most things meant to drive headphones. Maybe a little low for TL07x. 2K2 starts to get a bit big for going to something like a 10K line input, but if you're just going to attenuate anyway... It's plenty fine going to a guitar amp. The 20K resistor is in fact not at all necessary, but replacing it with a pot will give you a volume control for the thing. It occurs to me that the keyboard itself probably has a V control, but the pot makes this mixer more versatile.
 
A lot of keyboard fake stereo by using some sort of chorus effect. If you sum the left and right together, some of the patches will sound thin and weak due to the phase cancellation. Since the guitar amp isnt stereo, just running a mono signal out of the keyboard is the safest bet. (without some experimenting/knowing what keyboard you have)
 
JLondon said:
This is why I didn't get to college in the 70's.
Click to expand...
Fine, then. Post a question without anywhere near enough information and wait three days while a bunch of strangers make guesses about what might and might not work. Maybe go out and spend a bunch of money on some crap that you might not need and might actually make things worse. A couple weeks down the road maybe you'll actually get around to making some music.

I went on to give good reasons why my suggestion is likely to work just fine...
 
Here is what I Came up with and so far It works super great!
Had a 2" piece of aluminum Angle>
2-5k 1/4 watt metal film resistors>
1-25k linear potentiometer
1-1/4" mono jack
1-1/4" stereo jack
Wired the tip of the stereo jack to the Pot with 5k 1/4 watt metal film resistor
Wired the ring of the stereo jack to the Pot with 5k 1/4 watt metal film resistor
(Calibrate pot before wiring)
Thanx to all

100_1542.JPG
100_1543.JPG
 
Last edited:
Ash... my reply was a poor reference to drugs of the 70's... ( I tried them without asking questions never got to college etc...) Bad joke, wasn't bagging on your answer.

Good job Dinosaur Rocks, you need a summing circuit to do it right.
 
Yes, sooooper job Dino!
I use ally angle all the time for lashups.

Can I just mention? I would have used plastic jacks so as to give myself the option of an earth lift but if that works for you? Bazinga!

Dave.
 
I still say summing a keyboards outputs to mono generally ends in tears because of the way they stereo-ize the patches.
 
I have an older YDP with only midi and headphones. Tried using a straight 1/4 guitar cable, but you get way too much bass end and way to soft treble. What you did here is pretty much what I did, without the pot...no 70's drug ref intended, but I didn't...no really! No potentiometer and no drugs either.

Dude sounds paranoid!

We are NOT schizophrenic!!! And we ar...I am not paranoid! :D
 
You must log in or register to reply here.
Back
Top