Replacing amplifier on Digital Piano

[Brian2001]

Hello everyone. I am new to this. I have a very nice digital piano (Technics SXPR602) that is over 20 years old. The internal amp went bad in it and there are no replacment parts available for it. It is a proprietary amp that is on a board with a lot of other "stuff". The original power output is 120w (2x60) It has 4 speakers, a 16cm 4ohm and a 6.5cm 8ohm speaker on the left and then the same exact speakers on the right. I have found a small amp on amazon (Dayton Audio DTA-120 Class T Digital Mini Amplifier) that says it is 120w (50 WPC continuous into an 8 ohm load or 60 WPC continuous into a 4 ohm load).

My question is how can I wire the exisiting speakers to work since they are different ohms and the way they are situated in the cabinet of the piano will be an 8ohm speaker and a 4 ohm speaker on left channel and same on the right? If someone could steer me on how I should wire these up so they'll work (if that is even possible) or even give me and idea I haven't thought of yet. Is there a different or better amp suited for this i should look at?

I had even thought about just purchasing a good set of powered bookshelf speakers and sitting them on top of the piano and hooking them to the headphone jack. A lot less trouble but I'd kinda like to try using the existing internal speakers.

Thanks for any help!!

 

[TLS Guy]

Hello everyone. I am new to this. I have a very nice digital piano (Technics SXPR602) that is over 20 years old. The internal amp went bad in it and there are no replacment parts available for it. It is a proprietary amp that is on a board with a lot of other "stuff". The original power output is 120w (2x60) It has 4 speakers, a 16cm 4ohm and a 6.5cm 8ohm speaker on the left and then the same exact speakers on the right. I have found a small amp on amazon (Dayton Audio DTA-120 Class T Digital Mini Amplifier) that says it is 120w (50 WPC continuous into an 8 ohm load or 60 WPC continuous into a 4 ohm load).

My question is how can I wire the exisiting speakers to work since they are different ohms and the way they are situated in the cabinet of the piano will be an 8ohm speaker and a 4 ohm speaker on left channel and same on the right? If someone could steer me on how I should wire these up so they'll work (if that is even possible) or even give me and idea I haven't thought of yet. Is there a different or better amp suited for this i should look at?

I had even thought about just purchasing a good set of powered bookshelf speakers and sitting them on top of the piano and hooking them to the headphone jack. A lot less trouble but I'd kinda like to try using the existing internal speakers.

Thanks for any help!!

I have no idea what you are dealing with. Without a circuit you have no idea of the design. Also you don't know where to get the take off the the power amp from the synth/preamp section.

Only a very experienced technician with a circuit could attempt this. In addition it sounds as if you have no experience and so this would be very dangerous.

Your best bet is to send that unit to the recycling center and buy a new digital piano.

 

[Brian2001]

I am hardly going to "recycle" a $6,000 plus piano when it plays perfectly well through the line out and headphone jacks. I am simply wanting to feed an external (small) amplifer from the piano's existing headphone jack and hook the existing speakers to it. The problem is that 2 of the speakers are 8 ohm and 2 are 4 ohm. The question I had was in what sequence could I possibly hook these up to have them work with the amp I described or recommend a different amp. A schematic is not required because I am not changing any of the exisiting wiring of the piano, just basically building my own "keyboard amp" using the existing speakers and feeding that amp from the headphone jack of the keyboard. I need advice from someone who knows about adding ohms and matching impedance. that is not my strong suit. lol

 

[BoredSysAdmin]

TLS is right (in a way) you idea of ghetto repair with dayton amp is non-starter.
I think since you know/feel that this item holds large value, your best bet is to find electronics repairs shop and send the faulty circuit board to them for repair.
I found one shop in UK here:
http://www.mikebarden.com/sending-technics-pcbs-for-repair-from-uk-eu-and-worldwide/

I could also tell you than I used these guys for my recent TV board repair. Obviously piano amps are not their forte - I recommend getting in touch with them first.
http://www.coppelltvrepair.com

You should seek for more info on a specialty forums like this one:
http://technicskeyboards.com/technics-keyboards-forum/

 

[Darenwh]

Another option would be to use the headphone output with a small amp and a set of bookshelf speakers placed on the keyboard. You could even get away with a set of computer speakers, that have a built in amp, plugged into the headphones output. For either of these, start with the volume on the piano all the way down and adjust up slowly as the headphones jack out, if turned up too loud, could damage the speakers or amp.

Doing this would replace both the AMP and the speakers in the digital piano. The replacement speakers could even be better than the ones built in.

You should also look to see if your keyboard has a line level output as that is the idea way to connect to an external amplifier. This may be in the form of RCA outputs or a 3.5MM jack that looks just like the headphone jack but should be labelled differently.

 

[TLS Guy]

I am hardly going to "recycle" a $6,000 plus piano when it plays perfectly well through the line out and headphone jacks. I am simply wanting to feed an external (small) amplifer from the piano's existing headphone jack and hook the existing speakers to it. The problem is that 2 of the speakers are 8 ohm and 2 are 4 ohm. The question I had was in what sequence could I possibly hook these up to have them work with the amp I described or recommend a different amp. A schematic is not required because I am not changing any of the exisiting wiring of the piano, just basically building my own "keyboard amp" using the existing speakers and feeding that amp from the headphone jack of the keyboard. I need advice from someone who knows about adding ohms and matching impedance. that is not my strong suit. lol

Your question is not a simple as you think. I strongly suspect that with the varying impedance of the speakers that there is at least a crossover on that piano. More likely I suspect that there is actually more than one amp and that the amplification is in fact active.

Again without a circuit for the unit it is impossible to advise you and in fact dangerous.

Can you take the unit apart and see how the speakers are connected to the board, and whether there is any series or parallel connections?

I think in view of the value of the unit using the headphone jack is the best bet. You could either buy an amp with a volume control and use passive speakers, or you could drive powered or active speakers from the headphone jack. Active speakers would be best.

Be advised however that the instrument may not sound the same. Instrument and H-Fi speakers are very different animals. Instrument speakers often having a purposely skewed response.

And yes, you do need a schematic as I can be certain those internal speakers are not fed the same frequency band.

What is the model number of the unit. We can see if a schematic is available on line. They quite often are.

Your question is not a simple one at all.

 

[slipperybidness]

I am hardly going to "recycle" a $6,000 plus piano when it plays perfectly well through the line out and headphone jacks. I am simply wanting to feed an external (small) amplifer from the piano's existing headphone jack and hook the existing speakers to it. The problem is that 2 of the speakers are 8 ohm and 2 are 4 ohm. The question I had was in what sequence could I possibly hook these up to have them work with the amp I described or recommend a different amp. A schematic is not required because I am not changing any of the exisiting wiring of the piano, just basically building my own "keyboard amp" using the existing speakers and feeding that amp from the headphone jack of the keyboard. I need advice from someone who knows about adding ohms and matching impedance. that is not my strong suit. lol

Trust TLS advice, he is the most knowledgeable electronics guru that you will find, period. He may be a bit quick to pass judgment, but his technical knowledge is second to none.

If it were my equipment, I would likely just go the headphone->>powered speakers route. Or, I would at least try that first, especially if you have some computer speakers laying around, it would be free to try that.

And, yeah, if this thing is worth $6000 then either REPAIR IT RIGHT or don't bother. A shoddy repair will make it worth $0.

 

[BoredSysAdmin]

Trust TLS advice, he is the most knowledgeable electronics guru that you will find, period. He may be a bit quick to pass judgment, but his technical knowledge is second to none.

Understatement of the year , but yeah Mark aka TLSGuy knows his stuff (unless it's about audio and audio electronics)

I still think that best way to go is not headphone/line-out (which are fine as a temporary solution) but in long term, letting a pro to repair it is the best way. Shipping whole piano (just like whole TV) is not practical nor cheap, so if you are certain about which circuit failed and can disassemble and ship it yourself, it will save you LOTS of money.

 

[slipperybidness]

Understatement of the year , but yeah Mark aka TLSGuy knows his stuff (unless it's about audio and audio electronics)

I still think that best way to go is not headphone/line-out (which are fine as a temporary solution) but in long term, letting a pro to repair it is the best way. Shipping whole piano (just like whole TV) is not practical nor cheap, so if you are certain about which circuit failed and can disassemble and ship it yourself, it will save you LOTS of money.

Have you ever met an engineer that is a good people-person?

Just be glad that he wasn't YOUR doctor

I agree here, if there is any value in this thing, get a pro to repair it. If you just want to use it now and then, try the powered speakers as a workaround.

 

[BoredSysAdmin]

Have you ever met an engineer that is a good people-person?

Just be glad that he wasn't YOUR doctor

I agree here, if there is any value in this thing, get a pro to repair it. If you just want to use it now and then, try the powered speakers as a workaround.

10 of 10 times I rather have somewhat rude but knowledgeable Doc *cough*House*cough*, rather than the opposite. Pretty much same goes for engineers, but the problem is not everyone agrees with me
(they are wrong )

 

[TLS Guy]

Brian2000.
I'm sorry I missed that you did state the model number.

I was able to download the 79 page service manual. I have to say that it was unusually informative. I have had a good chance to study it.

The service manual is unusually complete and informative on this extremely complex unit.

As to the point at issue. The power amp stage is two amps in Bridge mode. The 16 cm drivers are connected in parallel. These are 8 ohm making a four ohm load The 13 x 6 cm drivers each have a cap in series creating a first order crossover. These units are connected in parallel on the amp side of the capacitor. These 13 x 6 cm drivers in the manual are stated to be 6 ohm. Unfortunately they forgot to number these caps. So the impedance would be 3 ohm in the pass band of these drivers.

By the way there is a line out on the unit which could be used to power an amp.

So what you want to do is possible. You need to look at the power supply amp board and find the value of those caps.

You will need a 4 ohm stable amp. Connect the 16 cm drivers in parallel. Now place the caps ahead of the 13 x 6 cm drivers and connect the other ends in parallel and place these in parallel with the 16 cm drivers. This should do the trick for you.

You were luck there was a manual available.

There is a discrepancy in the manual. In the circuits, the 16 cm speakers are listed as 8 ohm. However in the parts manual it states they are four ohm.

Have you looked at the drivers, and what is stamped on them? If they are 4 ohm you will need a 2 ohm stable amp, which will be hard to find. The amps are MOSFET by the way.

I made another careful search for the value of those caps. They appear in the circuit without a number but do not show up in the parts list. I suspect the caps may be soldered directly to the speakers. This is quite usual and may have caused the over sight.

 

[TLS Guy]

Brian2000.
I'm sorry I missed that you did state the model number.

I was able to download the 79 page service manual. I have to say that it was unusually informative. I have had a good chance to study it.

The service manual is unusually complete and informative on this extremely complex unit.

As to the point at issue. The power amp stage is two amps in Bridge mode. The 16 cm drivers are connected in parallel. These are 8 ohm making a four ohm load The 13 x 6 cm drivers each have a cap in series creating a first order crossover. These units are connected in parallel on the amp side of the capacitor. These 13 x 6 cm drivers in the manual are stated to be 6 ohm. Unfortunately they forgot to number these caps. So the impedance would be 3 ohm in the pass band of these drivers.

By the way there is a line out on the unit which could be used to power an amp.

So what you want to do is possible. You need to look at the power supply amp board and find the value of those caps.

You will need a 4 ohm stable amp. Connect the 16 cm drivers in parallel. Now place the caps ahead of the 13 x 6 cm drivers and connect the other ends in parallel and place these in parallel with the 16 cm drivers. This should do the trick for you.

You were luck there was a manual available.

There is a discrepancy in the manual. In the circuits, the 16 cm speakers are listed as 8 ohm. However in the parts manual it states they are four ohm.

Have you looked at the drivers, and what is stamped on them? If they are 4 ohm you will need a 2 ohm stable amp, which will be hard to find. The amps are MOSFET by the way.

I made another careful search for the value of those caps. They appear in the circuit without a number but do not show up in the parts list. I suspect the caps may be soldered directly to the speakers. This is quite usual and may have caused the over sight.

Those 16 cm speakers will be four ohm. I have worked it backwards from the power supply voltages. Those speakers have to be 4 ohm and present a 2 ohm load in parallel.

The reason is there is one power supply with two regulators. Back over 20 years ago regulators were limited in how much they could down regulate. It would have been better if the power amps or one amp actually could have had a dedicated higher voltage supply. So at that time using one power supply then they had to use a low output impedance amp. The downside is that the output driver current is 7.5 amps.

I'm actually surprised this amp survived over 20years. I bet a lot did not, especially if driven hard.

This amp if you use one channel will give you 150 watts into 2 ohm, and would do what you want.

There is another option, to use a 60 watt or higher 4 ohm stable stereo amp, and couple the channels together at the input.

Then you would connect one 16 cm driver in parallel with one 13 x 6 cm driver with the cap in series with that. You would connect that to one channel and then do the same with the other pair and connect that to the other channel.

 

[Wynnmontana]

Elk

Hello everyone. I am new to this. I have a very nice digital piano (Technics SXPR602) that is over 20 years old. The internal amp went bad in it and there are no replacment parts available for it. It is a proprietary amp that is on a board with a lot of other "stuff". The original power output is 120w (2x60) It has 4 speakers, a 16cm 4ohm and a 6.5cm 8ohm speaker on the left and then the same exact speakers on the right. I have found a small amp on amazon (Dayton Audio DTA-120 Class T Digital Mini Amplifier) that says it is 120w (50 WPC continuous into an 8 ohm load or 60 WPC continuous into a 4 ohm load).

My question is how can I wire the exisiting speakers to work since they are different ohms and the way they are situated in the cabinet of the piano will be an 8ohm speaker and a 4 ohm speaker on left channel and same on the right? If someone could steer me on how I should wire these up so they'll work (if that is even possible) or even give me and idea I haven't thought of yet. Is there a different or better amp suited for this i should look at?

I had even thought about just purchasing a good set of powered bookshelf speakers and sitting them on top of the piano and hooking them to the headphone jack. A lot less trouble but I'd kinda like to try using the existing internal speakers.

Thanks for any help!

I have exactly the same digital piano as this with the same exact problem. These “techs” on here have nothing but egos standing in the way of what you’re asking. My son (not a tech or an engineer, just a highly intelligent kid) did exactly what you’re wanting to do.I have an external amp connected through my headphone jack and I still use the internal speakers of the piano because they are “total “kick-ass speakers. People with technical knowledge like to make everyone feel stupid, and they’re the ones who look like idiots.
I will ask him what he did and try to get back to you. Email me if you’d like to go that route.
Lisa at:
luvnote0430@gmail.com

 

[Wynnmontana]

Hello everyone. I am new to this. I have a very nice digital piano (Technics SXPR602) that is over 20 years old. The internal amp went bad in it and there are no replacment parts available for it. It is a proprietary amp that is on a board with a lot of other "stuff". The original power output is 120w (2x60) It has 4 speakers, a 16cm 4ohm and a 6.5cm 8ohm speaker on the left and then the same exact speakers on the right. I have found a small amp on amazon (Dayton Audio DTA-120 Class T Digital Mini Amplifier) that says it is 120w (50 WPC continuous into an 8 ohm load or 60 WPC continuous into a 4 ohm load).

My question is how can I wire the exisiting speakers to work since they are different ohms and the way they are situated in the cabinet of the piano will be an 8ohm speaker and a 4 ohm speaker on left channel and same on the right? If someone could steer me on how I should wire these up so they'll work (if that is even possible) or even give me and idea I haven't thought of yet. Is there a different or better amp suited for this i should look at?

I had even thought about just purchasing a good set of powered bookshelf speakers and sitting them on top of the piano and hooking them to the headphone jack. A lot less trouble but I'd kinda like to try using the existing internal speakers.

Thanks for any help!!

There is only 1 person in the world that I know that repairs these and he’s in the UK. Too expensive to ship back and forth.

 

[lovinthehd]

Well hopefully in the four years since he's figured something out....

 

[Wynnmontana]

Well hopefully in the four years since he's figured something out....

Yes, hopefully. I just found the forum but would like to know what his solution ended up being.

 

[lovinthehd]

Yes, hopefully. I just found the forum but would like to know what his solution ended up being.

He last visited the day after he posted this thread....

 

[TLS Guy]

Yes, hopefully. I just found the forum but would like to know what his solution ended up being.

There is no easy solution, without at least some electronic experience, but I did suggest one. However that is very old for modern electronics. So that means bypassing the internal amp. To use the instrument speakers in the keyboard is somewhat complex, because of unusual impedance issues. The easiest solution is powered speakers from the phone jack.

I have no idea of your level of expertise. So unless you have some experience this is not the point of departure for you. If you do have some experience then it is doable.