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Make headphone jack non-muting?

B

belzebass

Feb 21, 2012
305
78
#1
Hi!

I wonder if there's a way to make a headphone jack non-muting.
A have an small amp with nice sound, but no line-out :-)

If the headphone jack didn't mute the speaker, I could use it as additional monitor, or send the sound to PA or recorder.

Has anyone already done it?

Thanks!
 
#3
It's a Roland Micro Cube Bass RX.
Nice little fella if you ask me. Sometimes I jam with a guitarist and a drum machine at bedroom volume, all three going through the amp.Would be nice to send all output to recorder.
 
#4
I don't see the schematic for that one, although I suspect it's like the Cube 15 and Cube 20. These use a switching jack to break the output to the speaker. It appears possible to go into the amp and put a jumper across the switched contacts, if I had the amp in front of me it might be relatively easy (or not, depending how the amp is constructed!)

Before doing anything like that though it might be worthwhile to try making a recording using that headphone out, just to see if it drives your recorder OK. Note that the headphone output will change when you adjust the volume or EQ on the Roland which makes it a poor "line out".
 
#5
Headphone output drives my recordes just fine (I've tested it already). In any case it has gain knobs :-) And it seem to have impedance of 10 kOhms (in mic/line mode), so I don't think it change the volume much.
And I don't use it with headphones anyways (prefer a headphone amp :-) )

Is it a DIY operation? Basic soldering skillz, I has it!
 
#6
When you change the volume or EQ on the Roland: Turn the Roland down, the signal going into your recorder will go down. Put more bass on the Roland, the signal to the recorder will get more bass. (The headphone out on the Roland merely takes the signal to the speaker and puts a dropping resistor or two inline.) It's quite possible to record this way but you just have to be aware of it and not make any changes mid-song.

If you had a good schematic, it could easily be DIY. I don't have the schematic to your amp so I can't tell you which pins on the output jack to jumper. Don't be tempted to experiment without knowing for sure, as you could burn up the amp's output very easily.
 
#7
Well, took a little testing yesterday with an advanced probing technique (wiggling a chopstick in the jack socket :-) )
It seems to be a simple switch jack socket with the switch on the sleeve of the jack. So I think I'll try this mod on my amp this weekend: [Invalid or Expired Link Removed]
 
#8
It's a simple enough mod to perform. Be careful to not use too much heat when soldering. If you do, it can damage the circuit board traces.

I would test it out before drilling a hole to install the switch. One potential problem is impedance loading. Whatever you connect to the line out might load the signal that is being fed to the amp. If splitting the signal is an issue you will notice a volume drop in the amp's output level. How well this mod will work depends on the design of the amp. Best you can do is try it and see.
 
#9
Hey I forgot to ask: is this a stereo amp? If so, there are two sets of contacts that need to be jumpered, and a DPDT switch instead of a SPST.

In other words, the instructions for the Cube 30 are not *quite* correct! Do not follow them literally, the same principle applies but it will be a tad more complex for you, since the Cube 30 is a mono amp and yours has 2 channel output.
 
#12
My thinking was to check and note the impendances between the ground of the amp and each contact coming out of the headphone jack and the ground, than plug in a headphone jack et re-note them. That would indicate me which ones act as muting switch. And than disable muting.

Does it make sense to you?

beans-on-toast said:
Have you seen this Roland Cube Club: Invalid Link Removed
Click to expand...

Nope, I'll take a look.
 
#13
belzebass said:
My thinking was to check and note the impendances between the ground of the amp and each contact coming out of the headphone jack and the ground, than plug in a headphone jack et re-note them. That would indicate me which ones act as muting switch. And than disable muting.

Does it make sense to you?
Click to expand...

That might work, depending on the accuracy of your meter, and how good you are at interpreting the results. In addition, I would recommend looking carefully at the output jack, see if you can identify a manufacturer and part number (Roland didn't make the jack, they buy it from somebody). If you can find out the jack part number, you can probably find a data sheet and identify which pins are switched. Also, trace back from the speaker leads to the switching jack. That will give you which contacts are switched out.

There's other ways--using a signal generator and a signal tracer of some sort-- which could be faster, but you would need special equipment.
 
#14
Aaaaaand it's done! :-)

The hard part was opening the amp. Boy, this thing is built sturdy and solid. Deep screwsfrom every side, and the unit is very tightly made. Even when I un-screwed all the necessairy screws (and many unneccessary ones :-) ) the unit stil stayed together and I had hard time taking it apart. There was a 7-pin 6.35 headphone jack socket. I identified the switch pin (there was only one pin that changed its relationship to the other pins when a jack was plugged) and short-circuited it permanently. It's a very small and modern amp, so it's all integrated circuit, very hard to tinker around and solder (especially with a normal house soldering iron). No way I could add a switch without proper equipment. So I put just a drop of metal between 2 contacts and it was all. Works fine. Didn't notice a serious drop in volume between headphones plugged or not. Didn't test throughly neither. I'll do it this today.

Nice mod to have, IMO. Not too complicated, the hardest part is to gain access to headphone jack contacts. I don't use headphones with it anyways. There's headphones amps for that.

A crappy cellphone pic of the insides of the amp :-)
2014-08-01 09.21.49.jpg
 

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