A Unicorn with Haunting Mids - Dumble ODS Analysis & Build Adventure

On my last two builds I used water slide decals then used a satin clear coat. I just printed them at home on an ink printer and sealed the paper with the same clear coat so the ink doesn't run when you put them in the water.

I just lined them up by eye and some are a little crooked but not too bad.

You can still see the edges of the decal if you look closely.

On my last build I used some really thin aluminum as a face plate. I used contact spray glue to attach it to a board then cut it to size on a table saw, marked and drilled the holes, then sanded it for a brushed look. I got the idea from this video.

 

You're welcome. IMO this is the opposite project for going no-choke, not just because of noise but also the response. A responsive and more linear power supply is one of the D-takeaways IMO. That includes: solid state rectifier, choke input filter, and 220uF at the res node.

Just a reminder the relays are not just about footswitching, they also physically separate the user switch and the switching mechanism. So even in the context of a panel switch, now you can put a simple SPDT switch anywhere and your signal wires stay put, only a little 2-wire bundle of 5VDC wire and return. In a high gain amp this arrangement becomes less negotiable.

So, you're going to need to embrace the relays footswitch or not, I reckon.

It's like @FenderLover points out, you can take as little or as much from Dumble's work and still come out with a great amp. I don't think "dud" is a possible outcome.

But, I think you are here to see what all the "fuss" is about, to wit, what was Dumble's intent on the ODS and what circuit features did he employ to achieve his design goals? In which case while there are some negotiable aspects of the circuit -- tone stack, bright cap values mostly, and also a few feature exclusions like the FET jack -- I think that the proper D-experience doesn't exclude very much at all. Which, yeah, it's unfortunate because it's not a simple build.

Also, regarding the use of EL84's I think it's fine. The trick will be to keep them out of overdrive, or heavy overdrive, if you can, if you find that unpleasant. That is a luxury you have with this amp, if you set it up to work with a clean output section then the power tubes conveniently matter less. I'm optimistic with fixed bias you should be able to do that with plenty of clean headroom for home/bedroom use.

 

Great thread! I usually avoid Dumble discussions in this forum. Too many people with little experience with amps like these are critiquing the amp based on what other people say about it. It takes a fair amount of work for a guitarist to learn to control the sound in a musical way, and having achieved that kind of control, learn what ticks under the hood.

Honestly, though, I sort of like having amps that generate as much controversy as Ds do.

 

yeah, nice wood work that guy did in the vid.. and the to crap it up with that ugly lettering job. ish. so, when you punch letters, you want the work surface to be hard. a steel welding bench... something substantial. if you only have a small work solid surface you'll have to move the piece and the guide. the softer the work surface, the more the metal stretches when you hit it. and a bunch of letters will pull it into an arc. if you want the letters to all be in an even line, fasten the piece down and use a sturdy guide bar. the punches are square on the sides and a good guide will keep the letters all in the same plane, not wandering up & down. it will also help keep the letters from tipping out of plumb. I learned all that from a job I had once long ago punching information plates

 

what the heck. heres a silkscreen I did a while back. done a couple amp faces & getting ready to do another

 

Word is if HAD has to service something under the goop, he just cuts off the whole mess with a Dremel and rebuilds it.

 

I must be living under a rock. What are "haunting mids"?

 

I tried the letter punch on some scrap and I didn't like the results, so I went with water slide decals.

 

Can't reveal this here.

 

I realize "appeal" is subjective, and the O is for "overdrive" ...

But overdrive is easy. The real interesting achievements in that amp are in the cleans.

 

The scary kind. You now.

 

Hey Kley,
I am working on an amp with the hoffman channel switching relay kit. Not sure about the 5V winding for power, I used the 6.3 v heater supply to power mine with hoffman power supply.

It took me some time to figure out the wiring of the relay. I think of the Signal in A and B as the common poles (center poles) on a DPDT switch.

I'm not sure if this is the right term but I think of it as a "ground lift" to close the relay. There is no connection to chassis ground, thus the need for an isolated input jack for the foot switch.

I got lucky and mine worked first time.

Here is a picture of the wiring for the foot switch.

 

The 7805 is optional, apparently, but I've only used it with.

The layout you posted is using 5V secondaries to a voltage doubler rectifier configuration, no regulator. This would give over 11VDC to the relay coils

The Omron G5V-1 series relays can handle 200% of rated VDC on their coil.
https://www.mouser.com/datasheet/2/307/en-g5v_1-1097070.pdf

The layout doesn't specify the relays used but as you can see, there is a rating consideration there. A 5V relay would be under-rated for this circuit.

If you build the Hoffman solution, you can simply swap out the bridge for the voltage doubler on 5V secondary. The LED footswitch is available off the shelf from AES for < $30, if you follow the Hoffman solution the LED's don't come with any additional challenge.

 

The relays pictured are DPDT relays, both sides switch together.

 

I've used Hoffman's 5v relays (Omron brand). I tested them on my variable power supply. they pull in at under 3VDC. I don't remember exactly, but a way lower voltage. they stay latched until under 1 volt or so. I'd bet the 5 VAC would work fine. I'd put a 7805 on it and a cap. I don't remember the current draw but it's not much... a couple mA, maybe 3 or 4

be aware that they are polarity sensitive. the picture on top of the chip is the layout when you flip it over. read that last bit again...

 

Hi Kley,
For your foot switch for the relay you need to use an isolated switched jack. The relay power supply ground goes to one pole of the switch and the ground lug of the jack. The other pole of the panel switch goes to the switch lug on the jack. The tip of the jack is connected to the ground of the relay board.

There is no connection to the chassis ground.

With the switches open the ground connection is interrupted and the relay is in it's normal open position. Close the switches, and the power is applied to the relay and it switches just like a DPDT switch.

The diagram I posted is a little confusing because it doesn't show the negative symbol on the relay connection.

As far as the rest of the schematic, that is above my pay grade ha ha. Looks like a difficult build.

John