Marcus
Sorry the original layout was not updated and what you expected.
Tony
Tony,
That's an old post resurrection
Funnily enough I've got a box here with a dumbleator in it ready to be made so you must have some sort of voodoo powers of intuition going on!
M
Yeah I know it's an old one but you know me never pass up a good jab!.
No real Voodoo powers here my friend.Just being my usual smart ass self..
Good luck with the Dumbleator and watch the polarity on those caps.
T
Tony,
thanks. Actually I've not been using the Dumbleator at all recently. Got into using wet/dry. I'm liking the simplicity of adding FX to a separate amp/speaker and keeping the dumble dry and 100% as is
Also means i can record dry as i just record the dry amp and leave the wet amp for my own vibe. It's working nicely like this with the 2nd gen amp. you were right about that amp, I had to stick with it
Some recent discussion on the send buffer and cable loss (https://ampgarage.com/forum/viewtopic.php?f=4&t=32162) got me looking into the frequency response. It's true that the buffer is not very well equipped to handle long cables with its 250k send pot, and that will be a problem if the buffer's output is run out to a pedal board. Attached below is a tweaked schematic that addresses that, and includes an alternate power supply using a current production Hammond transformer that will fit in a 1u rack box.
The lower value send pot is accommodated by raising the cathode resistor and tweaking the bias point. If that is all you are after, you can just change the pot, Rk, and Rbias, and leave everything else alone.
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Mark wrote: ↑Tue Jun 23, 2020 5:15 am
Great work Martin, thanks for sharing the improved circuit with us. Who knows we might see it in a Dumbleator in the future.
I've a ceriatone kit sat in a box here. Since I made the last one they've now made it as PCB so even easier. I'll see if I can build it like this and report back.
I've had it a year now but have gone wet/dry with my Dumbles so have had no need of a Dumbleator.
[quote="martin manning" post_id=413673 time=1592844229 user_id=4984]
Some recent discussion on the send buffer and cable loss (https://ampgarage.com/forum/viewtopic.php?f=4&t=32162) got me looking into the frequency response. It's true that the buffer is not very well equipped to handle long cables with its 250k send pot, and that will be a problem if the buffer's output is run out to a pedal board. Attached below is a tweaked schematic that addresses that, and includes an alternate power supply using a current production Hammond transformer that will fit in a 1u rack box.
The lower value send pot is accommodated by raising the cathode resistor and tweaking the bias point. If that is all you are after, you can just change the pot, Rk, and Rbias, and leave everything else alone.
Martin, I don't understand the heater schematic. Would you mind explaining the hookup the heater wires to pins 4 and 5 and the 9 pin ground? How that's physically layed out? thanks!
tubedogsmith wrote: ↑Mon Jul 13, 2020 2:15 pmI don't understand the heater schematic. Would you mind explaining the hookup the heater wires to pins 4 and 5 and the 9 pin ground? How that's physically layed out?
Since the small PT listed is only available with a 12V heater winding you have to take the 12V option for powering the 12AX7 heaters. That means putting 12V across both 6V filaments by connecting to pins 4 and 5. You need a ground reference, so it’s convenient to just ground pin 9, which is connected to the junction of the the two filaments.
Thank you for that, so basically do it just the way it's drawn. One heater wire to pin 5, the other to pin 4, connect them with a wire to pin 9 and then on to ground? do I have that right? thanks again
tubedogsmith wrote: ↑Mon Jul 13, 2020 3:21 pm
Thank you for that, so basically do it just the way it's drawn. One heater wire to pin 5, the other to pin 4, connect them with a wire to pin 9 and then on to ground? do I have that right? thanks again
Almost. The two heaters are connected internally at pin 9 so you don't need to do anything but ground pin 9.
M Fowler wrote: ↑Mon Jul 13, 2020 4:37 pmI was looking at the power supply and need a lesson on why the HT is wired to the diodes that way I'm confused.
It's just a full-wave doubler, same as HAD used for the relay supply on the ODS layouts.
I made a layout in DIYLC based on Martins schematic (to the best of my ability) and borrowing from the .jpg layout provided at the beginning of this thread. I tweaked the power board to use radial caps since I couldn't easily find axials in those values and I did my best to dimension the boards, traces and eyelets so the trace mask could be exported as a PDF, printed and then transferred onto copper clad board for anyone who might like to build it that way.
I'm still waiting on some parts, but once I get measurements, I'll tweak any pad locations that need tweaking and will post a PDF of just the boards here if anyone would find it to be useful. The same goes for the .diy file...if you want it, just ask and I'll get it to you.
If I could get a set of eyes on the layout, I'll be sure to correct any mistakes and replace this file.
First question - should the shield of the coax cable be attached to ground? I thought it should, but couldn't make it out on the other layout.
edit: I deleted the file since it had errors. will replace shortly
Last edited by Vertigo on Fri Aug 28, 2020 3:04 pm, edited 2 times in total.
Looks like your tube base is not oriented correctly, it needs to be rotated 180 degrees so the filament supply leads connect to pins 4 and 5, and you need to remove the short between those pins. Then you will need a ground for pin 9, which is the junction of the two filaments. That should go to the power supply ground.
The safety ground (earth lug on the IEC inlet) should go to a dedicated chassis ground lug, separate from the power supply ground.
