Sunday, February 28, 2016
Recently bought this cute retro-looking amp, Ibanez TSA5TVR. It is a 5Watt, all valve, class A amp, ideal for home use. I am not good at describing tone, for me it is the same as it happens with the wines: if the wine is good I usually like it and if its bad I normally don't. So this amp I like, so I suppose it is good... that is all I will say about it... check other places for good reviews. I will discuss here about some "non intrusive" modifications that I did.
The amp has a headphone output, but somehow the amp does not switch off the speaker when you plug the headphone and you are not supposed to unplug the speaker when the amp is working or you could damage the transformer (or so I have read). So what is the solution? my first thought was to replace the speaker with an 8 ohm dummy load. Doing some more research I found about L-Pad attenuators. This is kind of like a rotary potentiometer that lets you change the output level on the speaker with the peculiarity that the amp always "sees" the same 8 ohm loads no matter the configured level. This basically allows me to reduce the output level of the amp to 0, so that the speaker is muted, but still get audio in the headphone output. Some people also use it as a way to be able to crank the power amp but still not annoy the neighbors. I have not tried this yet. There is more info on L-Pads and also a calculator here. I added a bypass switch (to quickly switch between attenuator and normal) and some people also adds a switch to get more brightness, see here. I would have liked to add this to the amp instead of making it a external box, but I don't want to void the warranty, so it will stay in a box for 2 years, I suppose.
The other thing I did was a footswitch with LED to turn on/off the included overdrive. I tried the Marshall schematic that I found on the internet... did not work. This is the circuit:
I looked for other circuits and found this other one which worked OK:
Not having the schematic of the ibanez IFS1G original footswitch from Ibanez, I can not tell if this is the exact same circuit, but this does indeed work. I used a 1K resistor for R1, but I suppose you can adjust that depending on the desired brightness of the LED.
And that is all for now... further work on the amp will most likely happen when the warranty is over, until then I will have to hold myself from getting my dirty soldering iron inside it.