Roland Cube 20xl

[dssr]

I need a schematic for a Roland Cube 20xl


( before I get pointed to this link The Free Information Society - Roland Cube 20 Electronic Circuit Schematic its not for the 20xl )

[dssr]

boing

[Jazz P Bass]

Did you try calling Roland?
I know they charge, but hey, if you gotta you gotta.

[dssr]

I did and they said not unless I was an approved Roland repair center ( thats the UK for you ).

[doctor]

I did and they said not unless I was an approved Roland repair center ( thats the UK for you ).

Please take into account that electronic components for this device are
not supplied by Roland as a service parts.
Only main board or panel board may be supplied for replacement.

In any case, what is the problem?

[dssr]

In any case, what is the problem?

I cant get the volume past 12 O’clock without a harsh clipping through the headphones using the clean JC channel. Its ok through the speaker and ok(ish) into a desk.

A friend has the same issue on a 20xl he bought a few weeks before me at another store. So before I return out I want to see if its part of the amps ‘character’.

Seeing as there should only be a couple of passive resistors on the end of the TDA2050 IC ( the ic used in the 20xl ) to feed the headphones, I cant see how they can get it wrong ? Either by trying to squeeze Line Level and Headphone level out of the same jack, Roland have inbuilt headphone distortion or its a fault.

If I use Sennheiser PX100 headphones, the JC Clean sounds like it’s digitally clipped, but if I use those cheap JVC gummy earphones, it doesn’t start to clip until higher volumes. Impedance of the phones dont appear to make any differance. In fact one pair of new JVC 16 Ohm phones sound ok(ish ) and another pair of new JVC 16 ohm phone sound terrible

[doctor]

I cant get the volume past 12 O’clock without a harsh clipping through the headphones using the clean JC channel. Its ok through the speaker and ok(ish) into a desk.

A friend has the same issue on a 20xl he bought a few weeks before me at another store. So before I return out I want to see if its part of the amps ‘character’.

Seeing as there should only be a couple of passive resistors on the end of the TDA2050 IC ( the ic used in the 20xl ) to feed the headphones, I cant see how they can get it wrong ? Either by trying to squeeze Line Level and Headphone level out of the same jack, Roland have inbuilt headphone distortion or its a fault.

If I use Sennheiser PX100 headphones, the JC Clean sounds like it’s digitally clipped, but if I use those cheap JVC gummy earphones, it doesn’t start to clip until higher volumes. Impedance of the phones dont appear to make any differance. In fact one pair of new JVC 16 Ohm phones sound ok(ish ) and another pair of new JVC 16 ohm phone sound terrible

Both left and right headphones are connected to power amp’s
output through 820 Ohm resistors.
Thereby related output impedance is very high and for this reason
voltage applied to headphones depends on headphones impedance.
Obviously that it is bad-quality design (I have an additional occasions
conducting to idea that this device was designed in China).

The only way to obtain quality sound for any headphones from this amp
is to use impedance converter connected to the amp’s headphone output.

The following options are suitable for this purpose:

1. Professional headphones amplifier.

2. Self-made 2-channel impedance converter.

It is possible to use:

a) Standard dual OpAmp having high output current (either NJM4556A
or M5216 commonly used for this purpose) connected as voltage
followers.
b) Standard stereo headphone amp: TDA1308, NJM2769A/B,
AP4809 and so on.

Good luck.

[dssr]

Both left and right headphones are connected to power amp’s
output through 820 Ohm resistors.
Thereby related output impedance is very high and for this reason
voltage applied to headphones depends on headphones impedance.
Obviously that it is bad-quality design (I have an additional occasions
conducting to idea that this device was designed in China).


.

I've not looked inside the amp at this stage has its only a week old ( hence why I was asking for a diagram on another thread ). I'm interested in the 820 ohm resistors they've used. I've seen a rough pic inside a 20xl and they look to be 920 ohm's . Have you got a schematic or have you looked inside a cube to get the info ?

I know the main board on the cube 20xl is also used for the 20x and 30x as well.

A dealer checked out one of their Cube 20xl's in the store and it exhibits the same problem, so I've no doubt it's a bit of a cheap design solution. What I can't understand is the amount of these amps in circulation, yet I appear to be the only person highlighting the problem !


I dont use the Record out function anyway, so if I decided to keep the amp and was prepared to lose its warranty, I was thinking of modding the headphone output using a pot divider. eg:

TDA out -> 270R 1W -> 47R -> Phones : with a 120R .5 watt to ground inbetween the 270 and 47.

[doctor]

I've not looked inside the amp at this stage has its only a week old ( hence why I was asking for a diagram on another thread ). I'm interested in the 820 ohm resistors they've used. I've seen a rough pic inside a 20xl and they look to be 920 ohm's . Have you got a schematic or have you looked inside a cube to get the info ?

I know the main board on the cube 20xl is also used for the 20x and 30x as well.

A dealer checked out one of their Cube 20xl's in the store and it exhibits the same problem, so I've no doubt it's a bit of a cheap design solution. What I can't understand is the amount of these amps in circulation, yet I appear to be the only person highlighting the problem !


I dont use the Record out function anyway, so if I decided to keep the amp and was prepared to lose its warranty, I was thinking of modding the headphone output using a pot divider. eg:

TDA out -> 270R 1W -> 47R -> Phones : with a 120R .5 watt to ground inbetween the 270 and 47.

The measure you recommend will not solve your problem;
on the contrary output impedance will increase (820+270 Ohm).

The same effect you can achieve by decreasing amplifier’s GAIN/VOLUME
and sound quality will be better that after your “improvement”.

Unfortunately it is impossible to solve design bags by primitive ways.

[dssr]

The measure you recommend will not solve your problem;
on the contrary output impedance will increase (820+270 Ohm).

.

I would replace the current 820 ohm resistors with the above pot circuit. ( TDA out -> 270R 1W -> 47R -> Phones : with a 120R .5 watt to ground inbetween the 270 and 47. )

I have another TDA2050 based amp with the above pot divider and it works fine.

Although I believe they're 920 ohm not 820.

[paleeman]

Hi.
I have the schematics for CUBE15XL.

[Jazz P Bass]

Can you please post it?

[paleeman]

Hi.

I hope you can find it useful....


Laslo

[johnjohnjohn]

Hello do you know if it would be possible to modify this amp and get speaker and headphone sound at the same time?

[J M Fahey]

Hello do you know if it would be possible to modify this amp and get speaker and headphone sound at the same time?

Aren't you asking the same on another post?