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Speaker to Line out circuit

prprog

Member
I have a Casio electronic piano that does not have Line Out connection. I used the headphone connection for a while but it is noisy and have a low frequency hum which is not acceptable. I peruse the web and found the attach circuit. I used a DI Box , to convert the headphone signal to line signal, but decided I want a permanent solution. Since the keyboard have two speakers I disconnect one , built the circuit and attach the speaker output to it, It sounds good and the the hum noise is not present.
The questions is do I have to add a resistor (6 ohms) to compensate for the load (speaker)? The speaker is rated 7w , 6 ohms.

The site I found the circuit is www.epanorama.net

Thanks,
PRPROG
 

Attachments

Nigel Goodwin

Super Moderator
Most Helpful Member
I have a Casio electronic piano that does not have Line Out connection. I used the headphone connection for a while but it is noisy and have a low frequency hum which is not acceptable. I peruse the web and found the attach circuit. I used a DI Box , to convert the headphone signal to line signal, but decided I want a permanent solution. Since the keyboard have two speakers I disconnect one , built the circuit and attach the speaker output to it, It sounds good and the the hum noise is not present.
The questions is do I have to add a resistor (6 ohms) to compensate for the load (speaker)? The speaker is rated 7w , 6 ohms.
No, the entire load resistor thing dates back 75 odd years to valve amplifiers, which can destroy the output transformer or output valve if used without a load - 'modern' (50-60 years old and newer) semiconductor amplifiers have no such issues, and are even happier without the load as they will run cooler.
 

AnalogKid

Well-Known Member
Most Helpful Member
As above, the amplifier will work fine without the low impedance load. but - you do not have to disconnect the speaker for the output being used. You can connect your line out circuit across the speaker. The amp circuit will not care.

ak
 

rjenkinsgb

Well-Known Member
Most Helpful Member
Another suggestion, if it is a stereo keyboard rather than mono (the two speakers come from different points in the electronics):

If one side of each speaker is connected to the internal amp ground, use a resistor from the driven side of each speaker to combine the two channels - that way you do not lose anything if there are differences between channels with some sounds.

eg. In your circuit, add another 10K from the other speaker driven terminal to the line out junction.
 

prprog

Member
Thanks a LOT !!! to Nigel , AnalogKid and rjenkinsgb . I will implement the circuit right away. It have two speakers but I don't really think they make a difference (stereo) . If they do, I can considered rjenkinsgb suggestion.


Thanks,
PRPROG
 

Pommie

Well-Known Member
Most Helpful Member
If one side of each speaker is connected to the internal amp ground, use a resistor from the driven side of each speaker to combine the two channels
I've heard this method can be used on some modern recordings to cancel out the lyrics as they're the only thing on both channels. Would this cancel out anything that is in the middle of the separation range?

Mike.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
I've heard this method can be used on some modern recordings to cancel out the lyrics as they're the only thing on both channels. Would this cancel out anything that is in the middle of the separation range?

Mike.
No, because they are in-phase - you need to invert one to do that - and it's a fairly poor way of trying to do it. My PA mixer/amp has a 'karaoke' button, for the tape/CD input, which attempts to cancel out the vocals - essentially the same method, but at line level.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
I've heard this method can be used on some modern recordings to cancel out the lyrics as they're the only thing on both channels. Would this cancel out anything that is in the middle of the separation range?
As Nigel says, not that configuration.

You can either invert one channel and add, or take the output directly between the two channel outputs via some form of isolation if appropriate.


It's a fairly common complaint with portable audio, if the ground connection breaks in either the headphones or device socket.
The two earpieces are then connected in series across the two outputs and the centre of the stereo image is cancelled out.
The usual complaints are the vocals have gone, or it just sounds faint and wrong.

You can also use the same effect deliberately on a stereo amp that has single-ended (one side grounded) speaker connections; connect an extra two spare speakers, positive to the speaker driven outputs on the amp and negatives connected together but not to the amp...
Position them as rear speakers and you get a pseudo-surround effect, with the stereo image expanded.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
It's a fairly common complaint with portable audio, if the ground connection breaks in either the headphones or device socket.
The two earpieces are then connected in series across the two outputs and the centre of the stereo image is cancelled out.
The usual complaints are the vocals have gone, or it just sounds faint and wrong.
A fair few years back now, on a TV service course, I was talking to a guy who worked for Dixons/Currys and did their repairs.

Now he was expected to repair cheap own-brand Walkmans under warranty, and as they are so cheap he got paid absolutely sod all for the work - so if he had a complaint of one channel not working, he'd just put a blob of solder across L+R on the headphone socket - both headphones now work, job done! :D

On a similar theme, we were expected to repair Sharp Walkmans under warranty, and again they paid sod all for doing so - so all we did was give the customer a new one, and put a claim in for new headphones - with the usual complete rip-off spares prices the headphones were more than the retail price of the complete unit, and the profit made on the job paid for doing the paperwork :D
 

audioguru

Well-Known Member
Most Helpful Member
Bass is also frequently done in mono like the lyrics so when you mix out-of-phase stereo channels then the bass and the lyrics are both cancelled. You hear only the difference between the channels which might be only background noise.
Background hiss on an FM stereo receiver with a weak signal is usually cancelled by "blending" the stereo so that the separation and hiss are both reduced.
 

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