ODS pre with Subminis (complete)

[10thTx]

That's really quite an impressive project! Thank you for sharing it.

With respect, 10thtx

[dorrisant]

Yes, very nice! Thanks for posting>

[didit]

Hello --

More clean interesting work Alexander. Fine example to inspire.

Suggest another possible inspiration would be pictures floating about of Kingsley pedals. Those are fairly compact, similar in spirit. Also there's Seymour Duncan's "twin tube" design actually using US mil-surplus sub-miniatures.

Fully agree with Andy Fuchs regarding difference of various sub-miniatures versus 12AX7. Can still get interesting results, but don't expect a perfect sub-mini clone.

Best .. Ian

[norburybrook]

does it need to use the mini tubes?


Here's a full tube pre amp using 2x 12X7's built into a nice pedal factor.

lov-pepper-01.png

lov-pepper-04.jpg

pepper-layout-schematic.pdf

seems like you could change some component values here to make an ODS type pre amp.


M

[didit]

Hello -

The T-T Pepper construction looks well thought out. Relatively low operating point for 12AX7, given their power supply outputs 60V. Quite likely tweakable.

Here is gutshot of a Kingsley Jester scraped/scrapped off TGP. It's presumably a recent one as the power supply is a 555-based pump. Similar in spirit. Bolted on sockets via standoffs connected to the chassis seems a good choice.

Kingsley pedal.jpg

To be clear, I was not disparaging subminiatures but they do behave a bit differently than our overly familiar 12AX7. The durability and low microphonics very much recommend them for use in pedals.

Best .. Ian

[jubal81]

Hello -

The T-T Pepper construction looks well thought out. Relatively low operating point for 12AX7, given their power supply outputs 60V. Quite likely tweakable.

Here is gutshot of a Kingsley Jester scrapped from TGP. It's presumably a recent one as the power supply is a 555-based pump. Similar in spirit. Bolted on sockets via standoffs connected to the chassis seems a good choice.

Kingsley pedal.jpg



To be clear, I was not disparaging subminiatures but they do behave a bit differently than our overly familiar 12AX7. The durability and low microphonics very much recommend them for use in pedals.

Best .. Ian

The lower voltage from the SMPS is definitely another factor in trying the 6N17Bs. I should be able to get to upper 200s (fingers crossed). Also found some 450V rated 8mm diameter caps on Mouser.
Working on the layout now. I've got the SMPS isolated on an island and plan to have separate ground planes for each section that all run back to a star point. Also going to be cautious to avoid any capacitive relationships between traces with careful routing, which should help stave off oscillations.

I've thought that if I were to transition this project to 12AX7s, I'd probably mount them similarly to Kingsley, but on the footswitch side with breakout PCBs to keep the heat away from the other components. I'd really prefer a solution that keeps the tubes inside. I did a JTM800 preamp in a box like this with the tubes on top and it worked fine, but I never felt like it was as secure as it should be.

[jubal81]

Got a first draft for the PCB layout. The SMPS is together on the tab between the footswitches.

[jubal81]

Ordered some PCBs today. Fingers crossed.

[xtian]

Looking slick, man.

[norburybrook]

really interested to hear/see how this turns out.

Great project.


M

[dorrisant]

Cool beans!

[jubal81]

Just waiting for Pots now. Everything else is mounted.
Got some heat reflective tape to put between the tubes and PCB. Hope that helps a bit. Also added some pads so I could run bus wire to tie down the tubes to secure them mechanically.

[alkuz1961]

I am a little surprised by the size of the capacitors. What is their voltage range?

[jubal81]

I am a little surprised by the size of the capacitors. What is their voltage range?

The HV electrolytics are 400V. HV film caps are 250V. The others are at least 50V.

[jubal81]

There are signs of life. Still waiting for pots, but tubes are working and I'm able to get 170V on plates with 9V one-spot.