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

Discussion in 'Shock Brother's DIY Amps' started by kleydejong, Dec 1, 2020.

  1. jmp81sc

    jmp81sc Tele-Meister

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    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.

     
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  2. sds1

    sds1 Tele-Afflicted

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    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.
     
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  3. kleydejong

    kleydejong Tele-Holic

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    This is great! I have a letter & number punch set that I use for stamping golf clubs that I thought would be great for use on a faceplate. My first attempt didn't go so great, but I grabbed another piece of aluminum and am borrowing my friend's anvil as I wasn't getting good clean punches on my work bench. I think the wood is too soft and kinda springy almost. Just this morning I went to the hardware store and picked up a fresh sheet of aluminum. I like that it can be worked with woodworking tools and dig the look quite a lot. Thanks for posting. I picked up some nice pointers from the video.
     
  4. Larry F

    Larry F Doctor of Teleocity Vendor Member

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    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.
     
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  5. dogmeat

    dogmeat Friend of Leo's

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    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
     
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  6. dogmeat

    dogmeat Friend of Leo's

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    what the heck. heres a silkscreen I did a while back. done a couple amp faces & getting ready to do another P1100963.JPG P1100978.JPG
     

    Attached Files:

    Last edited: Dec 2, 2020
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  7. David Barnett

    David Barnett Doctor of Teleocity

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

    ThermionicScott Poster Extraordinaire

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    I must be living under a rock. What are "haunting mids"? :D
     
  9. jmp81sc

    jmp81sc Tele-Meister

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

    Larry F Doctor of Teleocity Vendor Member

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    Can't reveal this here.
     
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  11. kleydejong

    kleydejong Tele-Holic

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    I'm using it as a tongue in cheek jab at some of the Dumble discussions that take part on the internet where people get a bit over the top in describing and debating the minutiae of tone.
     
  12. kleydejong

    kleydejong Tele-Holic

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    Relay Switching from a NOOB

    I have ran into a bit of a mental roadblock on the relays thing. I contemplated skipping relays altogether. I thought about adding an additional 12AX7 and simply having two parallel inputs that join at the phase inverter. One for the clean channel using two triodes. The second for the drive channel using four triodes. Two totally separate preamp signals. Then I could use an A/B switcher between my pedalboard and the amp. It would be nice to have ability to dial in the tones of each channel totally distinct. But I scrapped this idea out of space concern. I think the build would get tight quickly.

    I also chewed on the idea of just ditching the clean channel and making a single channel ODS with just the drive signal path. I already have several 'cleaner' amps, and to me - the primary appeal of an ODS is the drive channel. I also wonder if you put enough volume controls in the signal path that you could get a good clean tone from the drive channel. But it seems a bit goofy.

    So I committed to doing relays, perhaps for the channel switching only. No LED's or funny business. I spent much of this past week banging my head against various internet articles and threads trying to figure it out. After enough brute force I think I found my light bulb moment:

    https://el34world.com/projects/relay_switch.htm

    https://el34world.com/Forum/index.php?topic=14348.msg135594#msg135594

    Hoffman is nice because he sells all these components in his store too.

    https://el34world.com/projects/images/Hookup1_small.png

    [​IMG]

    So let's say I were to do channel switching. My signal exiting the second gain stage would be 'Signal In A'. Then for the clean channel mode it would go from Signal Out 1 directly to the Phase Inverter. Signal Out 2 would go to the drive channel gain stages.

    Side B means I could implement a second SPDT type switch, or change the above and use some kind of DPDT switch instead? But any which way, you only get to use one switch to control one / both? THat would be the blue SPDT switch in the picture. I couldn't use Side A for channel switching with one footswitch, and a second for the PAB or some other preamp switch?

    I could choose to replace the SPDT switch with an external footswitch. I could use a 1/4" jack and a one button footswitch that needs to be isolated from the chassis.

    Questions

    I believe I could use the unused 5vac winding on my PT instead of the 6.3vac heater tap?

    Using 5vac instead of 6.3vac - https://ampgarage.com/forum/viewtopic.php?t=11487

    https://ampgarage.com/forum/viewtopic.php?t=11371

    I found this layout which appears to use the two yellow 5vac leads from the PT to power the two relays. That seems ideal for my purpose. But I don't see a voltage regulator. Is that optional?

    [​IMG]
     
  13. sds1

    sds1 Tele-Afflicted

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    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.
     
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  14. papa32203

    papa32203 Tele-Afflicted

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    The scary kind. You now.
     
  15. jmp81sc

    jmp81sc Tele-Meister

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    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.

    Relay1a_small.png
     
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  16. sds1

    sds1 Tele-Afflicted

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    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.
     
    Last edited: Dec 12, 2020
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  17. sds1

    sds1 Tele-Afflicted

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

    dogmeat Friend of Leo's

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    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...
     
    Last edited: Dec 13, 2020
  19. kleydejong

    kleydejong Tele-Holic

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    Honing my schematic a bit. Definitely not a final draft. I'm taking a lot of inspiration from the Brown Note D'Lite. It is a bit of a simplified D style circuit that used to offer as a DIY kit, so there is a good bit of info that I find helpful for my stage of building.

    [​IMG]

    In the preamp I want the mid boost and rock / jazz switches. I have the bright switch, but I may elect to do the deep switch instead. I typically dislike bright switches / caps. I'm intrigued by the local NFB loop on V1B. One and only relay footswitching for the drive channel. Having the trimpot on the inside kind of breaks my soul. I have never understood trimpots... Snubbing caps, bypass caps, and coupling cap values trim treble and bass frequencies to keep the drive in check. No HRM tone stack at the end.
     
  20. jmp81sc

    jmp81sc Tele-Meister

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    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
     
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