• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

flexy -a multirole driver/preamp-

Folks

I am about to start a new project and as I need to experiment with many configurations I ended up with an idea for a flexible PCB that allows to switch among them by means of jumpers. So in a matter of minutes the PCB will allow to build a very different preamp or driver. The project will use noval dual triodes and can be set up as

1) SE+SE (two channels)
[IMGDEAD]http://img690.imageshack.us/img690/1028/sesem.jpg[/IMGDEAD]

2) SE+CF (one channel ... ie two PCBs)
[IMGDEAD]http://img340.imageshack.us/img340/7982/secfu.jpg[/IMGDEAD]

3) SE+splitter (one channel ... ie two PCBs)
[IMGDEAD]http://img19.imageshack.us/img19/5800/sespltr.jpg[/IMGDEAD]

4) SRPP (with active load ... one channel per PCB)
[IMGDEAD]http://img804.imageshack.us/img804/4124/srrp.jpg[/IMGDEAD]

5) LTP (one channel per PCB)
[IMGDEAD]http://img404.imageshack.us/img404/7082/ltp0.jpg[/IMGDEAD]

CCSs and LEDs are used to bias the tube. I drafted also a PCB for the CCS, the now classical supertex cascoded DN2540s, that can be installed directly onto the main PCB or used for other projects

[IMGDEAD]http://img528.imageshack.us/img528/2162/ccs01.jpg[/IMGDEAD]

[IMGDEAD]http://img88.imageshack.us/img88/7528/flexy.jpg[/IMGDEAD]

If there is enough interest I can try to run a batch of PCBs. Target costs for bare PCBs might be

20$ for the main PCB
5$ for the CCS


I am also working on a ladder stereo attenuator as I could find none online (well ... there is a superexpensive 41 steps made in Japan ... and a supercheap 24 steps made in china). I spotted a nice switch made by palazzo that seams to fit perfectly onto the idea. Link to the switch

And here it is the prototype I am assembling that should not look much different from the final one.
[IMGDEAD]http://img713.imageshack.us/img713/7694/11292010104.jpg[/IMGDEAD]

I drafted a PCB for the ladder attenuator and Palazzo switch with 1206 SMD resistors: they fit perfectly between the switches' pins. I am waiting for a quote for the assembled PCBs but I believe it should be in the 80$ ballpark: the switch itself costs 40$. Now, 80$ is much more than a pot but much less than big brands switched attenuators and this is a ladder attenuator not a shunt attenuator so I am using 2x resistors.
[IMGDEAD]http://img232.imageshack.us/img232/8514/laddero.jpg[/IMGDEAD]

The switch is not-shorting but I contacted Palazzo and they are ready to make it shorting if there is a "big enough order".

All that being said, having a proto board made just for me or a small batch will not be very different pricewise but I believe the idea might be useful. What I really need is the ladder attenuator but they are not assembling the shorting switch just for a couple of pieces ...

Let me know. I have very small free time for this hobby but hopefully I can finalize the idea during the XMas holidays ... sob :eek:

Gianluca