Dumbleator inspired FXLoop & Mixer

[rob@tele]

So this is my first serious build. It is my take on a dumbleator II. It has two inputs which can be muted and which are mixed together into one balanced FX Send. It has a balanced stereo return, a balance control and a master volume. The send and return are galvanically isolated by means of transformers (rather expensive solution, I know). I have included a schematic and two pictures. More hi res pictures to follow...

The idea is to have a stereo setup with two amps and then to be able to switch between the two pre-amps or even use both at the same time (like e.g. Joe Bonamassa).

The chassis and faceplates are stainless steel and cut with laser. The chassis is CNC bended and it has pressed nuts and bolts which result in a perfectly flat bottom plate. The bolt for the transformer is welded to the bottom plate. The face plates are laser engraved.
It works really nice, no hum and no hiss. I have tested it with a USB scope (picoscope 2203) and I will be doing a full Frequency Response Function measurement, but I have to interface the scope with Matlab first before I can carry out the measurement.

This is actually one of two units I'm building. The second one still needs to be wired. Wire is mostly teflon insulated.

Next build will be an overdrive special inspired amp with some twists such as MIDI control. But I'm still working on the design...

*** Edit: Added hi-res pics

[NickC]

Stunningly beautiful build!

[erwin_ve]

That's a great built Rob!
Excellent quality built I would say...

As long as grounding points are good there is no hum in the original design so that brings me at this question: Why did you choose for galvanically isolated outputs for the cathode followers and DC filament?

Edit: Galvanically isolated: Using 2 amps! Clever move...

[Structo]

Wow!
That is cool!

I would love to see some higher resolution pictures of the interior.

I like how the power supply is segregated from the amp side but that dividing piece.
It looks like it should work well.

What is your background?
Because if that is your first build, I can't wait to see the Overdrive amplifier.

Does Joe B. use something like this?
[/list]

[boldaslove6789]

Very cool! Looks super Versatile!

[rob@tele]

That's a great built Rob!
Excellent quality built I would say...

Thank you.

As long as grounding points are good there is no hum in the original design so that brings me at this question: Why did you choose for galvanically isolated outputs for the cathode followers and DC filament?

Edit: Galvanically isolated: Using 2 amps! Clever move...

The reason behind the galvanic isolation is to have at least the FX Unit isolated as there will be two amps already. The output to the amp is not isolated as the possible voltage swing to drive a poweramp may even be 20V and a transformer that can handle that much signal would be way to expensive. Furthermore, I needed a solution to mix the two inputs and also have a cathode follower to drive the FX Unit. The two transformers do this nicely and give you balanced and galvanic isolated outputs at the same time.
I am still looking for a good solution to combine a common cathode (or anode?) mixer and the cathode follower to do the same without the transformers.

The DC filament supply is a result of the transformer secondaries (14V) and the relay supply combined.

[rob@tele]

Wow!
That is cool!

I would love to see some higher resolution pictures of the interior.

Hi Res pics will be made soon, my wife is a photographer and see will make some pics

I like how the power supply is segregated from the amp side but that dividing piece.
It looks like it should work well.

What is your background?
Because if that is your first build, I can't wait to see the Overdrive amplifier.

Does Joe B. use something like this?

The bracket that is dividing the box holds the tube sockets as well and it gives more strength to the box. There is one extra space for a socket as I have a few more boxes to build e.g. a preamp in the future.

My background is in mechanical engineering (BSc,MSc) and I have a PhD in robotics. I am working as a mechatronic designer at ASML and my speciality is in multibody dynamics and advanced servo control. So it was not a big step to engineer the FX Loop. I have some experience in building (made a champ like combo once and refurbished a '66 bassman head which I bought in a modified (=messed up) state.

Joe B. uses an Lehle amp input switcher and he has always two amps on at the same time. The one that is on all the time is a Silver Marshall and he combines it with a CAT5 or Van Weelden (dutch D-clone) or a Two Rock or a Carol Ann. The exact config changes from time to time

[martin manning]

Very nice unit! Looks like a commercial product. Can you tell me what is the purpose of the 10n // ?R networks at the inputs, where SW3 and SW8 are?

[rob@tele]

The R-C networks at the inputs with the switches are intended as ground lifts. These will (hopefully) break any ground current (50/60Hz) so that hum by a ground loop wil be eliminated. The C will act as ground for RF noise. In the same way I can lift the complete circuit from the housing and mains-ground.
At the balanced FX send and FX return the ground lift is just by means of a switch without the RC networks.

The unit is more or less designed as a commercial product, but then for the niche market as it is quite expensive with the signal transformers and the non-standard housing (I still need to compute the costs... ).

It would be nice if I could sell some units and also some amps in the future, but it wil most likely stay a non-commercial activity (I have a good income with ASML ).

[ElectronAvalanche]

Looks fantastic!

Excellent work. Can't wait to see more pics.

Will you do a YT demo?

Cheers,

Electron

[rob@tele]

As promised: more pictures

[rob@tele]

and more...

[rob@tele]

And more...

[67plexi]

Rob, What a work of art.


Thank you. Steve.

[Structo]

Nice pics!:D

I notice you don't have the earth ground on the IEC connector connected to chassis ground.
Are you planning on leaving that as so and doesn't that create a shock hazard in the event of a short to chassis ground?