New Project

[martin manning]

This project has been on the back burner for a while, but now making progress in the last couple of days stuffing the boards. The main board was made by Tony D from my drawing, FET board is my KiCad design, fabricated by PCBWay. Second photo is test-as-you-go in the extreme; HV power supply no-load check.

[ElectronAvalanche]

Nice!

What is this? Intrigued.

Best,

Electron

[fred.violleau]

Very interesting Martin.
Are you working on a racked version of the ODS preamp?

Fred.

[rogb]

This project has been on the back burner for a while, but now making progress in the last couple of days stuffing the boards. The main board was made by Tony D from my drawing, FET board is my KiCad design, fabricated by PCBWay. Second photo is test-as-you-go in the extreme; HV power supply no-load check.

Now that's a thing of beauty right there!
If only we could get a decent 2 channel power amp into a rack space like Mesa 20 20... From my research it's just too costly, especially here in the UK.

[martin manning]

Are you working on a racked version of the ODS preamp?

Sorry for making you guess, but that's close ;^) There's more iron there than a preamp would need, but the power supply on this board could easily be modified to do that. Maybe I should draw one up!
Next step: chassis drilling.

[martin manning]

This project has been on the back burner for a while, but now making progress in the last couple of days stuffing the boards. The main board was made by Tony D from my drawing, FET board is my KiCad design, fabricated by PCBWay. Second photo is test-as-you-go in the extreme; HV power supply no-load check.

Now that's a thing of beauty right there!
If only we could get a decent 2 channel power amp into a rack space like Mesa 20 20... From my research it's just too costly, especially here in the UK.

Thanks, Rog. Seems like a tube pre and a SS power amp would work. IDK how much power you are thinking, but a 100W Class D power amp would fit, not sure if there would be noise issues, but you can buy boards pretty cheap; $100 or so.

[pullshocks]

Single ended amp?

[martin manning]

Single ended amp?

Yes! With built-in resistive load and pseudo-balanced line out.

[pullshocks]

Cool. Will be watching with interest as I cycle through preamps in my ever-evolving SE platform.

[dbharris]

Very cool project Martin! I'm looking forward to watching this build.

-Dan

[rogb]

This project has been on the back burner for a while, but now making progress in the last couple of days stuffing the boards. The main board was made by Tony D from my drawing, FET board is my KiCad design, fabricated by PCBWay. Second photo is test-as-you-go in the extreme; HV power supply no-load check.

Now that's a thing of beauty right there!
If only we could get a decent 2 channel power amp into a rack space like Mesa 20 20... From my research it's just too costly, especially here in the UK.

Thanks, Rog. Seems like a tube pre and a SS power amp would work. IDK how much power you are thinking, but a 100W Class D power amp would fit, not sure if there would be noise issues, but you can buy boards pretty cheap; $100 or so.

I've been down the Class D road and bought a Palmer Macht 402 power amp. Unbelievable amount of power and very well made for £289.
But it was lacking that Dumble PI interaction that flavours the sound we love.
I got a Mesa 20/20 power amp that sounds really good.
It seemed there was no way to recreate 2 x tube power amps in a 1U space without spending a crazy amount of time and money.
Better to find a Mesa and tweak that. I added bias adjustment and fat switching, it's very good and there are PIs to hit with preamp signal!
But please keep feeding us more about your project. Looking at the transformer, you could be running a pair of 6V6 or 6L6?

[martin manning]

The 20/20 must be pretty crowded inside, maybe a bit hard to work on?

My project is a single ended amp, so no PI. I don't know if I'll miss it since the Dumble power amp is pretty much a clean Hi-Fi type. It's a bit of an experiment, so I'll just have to see how it turns out. The preamp is a copy of my 100W low-plate, so it will be interesting to see how much different it sounds with the low-watt power section.

[rogb]

The 20/20 must be pretty crowded inside, maybe a bit hard to work on?

My project is a single ended amp, so no PI. I don't know if I'll miss it since the Dumble power amp is pretty much a clean Hi-Fi type. It's a bit of an experiment, so I'll just have to see how it turns out. The preamp is a copy of my 100W low-plate, so it will be interesting to see how much different it sounds with the low-watt power section.

Very much looking forward to seeing it!
I've got a little SE EL34 I built into a rescued combo cab, great sounding and full of character. I guess you'll be paralleling a pair of tubes?
The Mesa is not too bad to work on actually. Well laid out for its size.

[didit]

Hello --

My project is a single ended amp, so no PI. I don't know if I'll miss it since the Dumble power amp is pretty much a clean Hi-Fi type. It's a bit of an experiment, so I'll just have to see how it turns out. The preamp is a copy of my 100W low-plate, so it will be interesting to see how much different it sounds with the low-watt power section.

Look forward to learning what you do discover. Somewhat skeptical foregoing the PI. A dummy load on the input triode and then pulling output drive from second maybe? This is something I recall seeing when someone was designing to couple into a class D power brick.

Could you start by assembling the SE power stage and feeding it with your existing low-plate loop to verify?

..

[pullshocks]

Years ago Mat in Finland posted a SE ODS with no "phase inverter." By all accounts it sounded great https://ampgarage.com/forum/viewtopic.p ... rm&start=0

There have been a number of others since then, search the forum on "mini hrm".

In my own (limited) experience, I found running my "Hybrid Rev A" preamp into a SE power amp sounds just fine, at least at the bedroom volumes I use.