# The MacGuffin - A Dumble ODS preamp with submini tubes



## jubal81 (Feb 28, 2021)

Wife working from home started me on a silent rig quest that led me this and now I'm in headphone heaven.

It's a full Dumble ODS preamp with Russian 6n17b submini tubes in a 1590XX enclosure. I used grill cloth to cover the heat vent ports for the tubes.

Well-worn 555 SMPS with about 140V at the plates.

I added a high-voltage mosfet buffer on the output (Dumbleator style) and it even works really well as a boost/OD pedal into another tube amp. Mostly I run it into a delay > diy Surfy Bear reverb > Two Notes Cab M+.


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## giovanni (Feb 28, 2021)

Wow! Did you design the circuit?


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## denfox (Feb 28, 2021)

Really nice build


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## jubal81 (Feb 28, 2021)

giovanni said:


> Wow! Did you design the circuit?


Not really. Just the PCB. It's 1-to-1 a low-plate ODS. I used a trim pot for the master volume to adjust the max output level, then it goes to a mosfet "Dumbleator" buffer with the volume after.


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## giovanni (Feb 28, 2021)

Still very impressive!


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## Chuck D. Bones (Mar 2, 2021)

SWEET!!!


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## cooder (Mar 2, 2021)

Most excellent boxing up of Unicorns there!


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## jubal81 (Aug 26, 2021)

Sometimes you just get lucky - very lucky.
6+ months later and this thing is still going strong. I've even accidentally left it powered for more than 24 hours straight more than once and had no issues whatsoever.
I'd probably like to do another one or two preamps like this down the road - maybe the Hot Rubber Monkey version or an SLO. Two tubes seems like the sweet spot, though, and I'd probably run the heaters in series with a 12V power supply and get rid of the 6v regulators. No thermal shutdowns so far, but there's no point in using current to make more heat.


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## Paradox916 (Aug 26, 2021)

jubal81 said:


> Sometimes you just get lucky - very lucky.
> 6+ months later and this thing is still going strong. I've even accidentally left it powered for more than 24 hours straight more than once and had no issues whatsoever.
> I'd probably like to do another one or two preamps like this down the road - maybe the Hot Rubber Monkey version or an SLO. Two tubes seems like the sweet spot, though, and I'd probably run the heaters in series with a 12V power supply and get rid of the 6v regulators. No thermal shutdowns so far, but there's no point in using current to make more heat.


The SLO! you gotta do the SLO! I’m so jelly.. I want to pick your brain one of these days when I get a little better and designing circuits. All I do is play through headphones these days. And been trying to work up to something like this!


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## fig (Aug 26, 2021)

jubal81 said:


> Sometimes you just get lucky - very lucky.
> 6+ months later and this thing is still going strong. I've even accidentally left it powered for more than 24 hours straight more than once and had no issues whatsoever.
> I'd probably like to do another one or two preamps like this down the road - maybe the Hot Rubber Monkey version or an SLO. Two tubes seems like the sweet spot, though, and I'd probably run the heaters in series with a 12V power supply and get rid of the 6v regulators. No thermal shutdowns so far, but there's no point in using current to make more heat.


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## Harry Klippton (Aug 26, 2021)

Paradox916 said:


> All I do is play through headphones these days.


Me too for the most part, but I just got infant hearing protection for my daughter in hopes that my wife and I can resume playing together in the not too distant future


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## perfboarder (Aug 26, 2021)

Sweet build!

Jubal, Chuck, Bugg and everybody. Talk about headphone heaven. Did you have a simple headphone amp circuit, not a cmoy based with aux in?

Want build some for my friend who just became Daddy as gift. I know they have multi fx for that. But, give a gift always make me excited and happy.


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## Paradox916 (Aug 26, 2021)

Harry Klippton said:


> Me too for the most part, but I just got infant hearing protection for my daughter in hopes that my wife and I can resume playing together in the not too distant future


It’s tough when they are little, I feel ya man.


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## Chuck D. Bones (Aug 26, 2021)

fig said:


> View attachment 15259



"Spock...


Let's jam!"

"Yes, Captain, that would be logical."


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## jubal81 (Aug 26, 2021)

perfboarder said:


> Sweet build!
> 
> Jubal, Chuck, Bugg and everybody. Talk about headphone heaven. Did you have a simple headphone amp circuit, not a cmoy based with aux in?
> 
> Want build some for my friend who just became Daddy as gift. I know they have multi fx for that. But, give a gift always make me excited and happy.


I'm still using the Two Notes Cab M+ and highly recommend it. There's no DIYing something like that, though. They have some very sophisticated reverbs built in and it's pretty easy to tweak them to get a lot closer to the sound of being in a room with an amp. The sound quality is better than a Simplifier I had, and that thing is all analog.

Basically, I treat the Cab M like the effects loop return on a tube amp. Pedals into tube preamp, then pedals that would be in the 'loop' like delay and reverb, then into the Cab M, which takes the place of the power amp, speakers and mics.

EDIT: Forgot to add that it has a really good aux in for playing with tracks and a DI out for recording. Very handy.


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## Chuck D. Bones (Aug 26, 2021)

perfboarder said:


> Sweet build!
> 
> Jubal, Chuck, Bugg and everybody. Talk about headphone heaven. Did you have a simple headphone amp circuit, not a cmoy based with aux in?
> 
> Want build some for my friend who just became Daddy as gift. I know they have multi fx for that. But, give a gift always make me excited and happy.


I have been working on it.  Breadboarded a MOSFET push-pull using the 42TM013 transformer, but that transformer lacks bandwidth and killed the treble.  Tried another MOSFET design (transformerless) but had hum problems.  We could always go with an LM386.  What it lacks in elegance, it more than makes up for in simplicity.


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## SillyOctpuss (Aug 26, 2021)

Harry Klippton said:


> Me too for the most part, but I just got infant hearing protection for my daughter in hopes that my wife and I can resume playing together in the not too distant future


Yup me too most of the time.  Our Little Dude turned 3 this month and most of my playing is done after he goes to bed with a hx stomp and either studio monitors or headphones.  Thankfully pedals sound excellent in it's loops. 

Playing through my amps is reserved for playing during the day now and when I get together with friends for a jam every few weeks.

@jubal81 your Macguffin looks fantastic.  Have you thought about doing a run of pcbs for it?


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## Edge59 (Sep 26, 2021)

Hi, where does one get the PCB, I do not see it available on pedalpcb.com website, Also the parts, is there  a good source for parts or is this a one-off build? I am very curious 

Thanks
Ed


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## Preverb (Sep 28, 2021)

Very cool.  I had an Ethos clean a few years back.  Then had Ceriatone ODS 50 and 20 back to back.  Neither of the ceriatones captured the OD tone I was looking for but I have seen a few expensive preamp pedals with clean/OD channels that sounded great.  I've got a ton of preamp tubes but no mini ones.  I would be interested in tackling this one day but it looks way beyond my current ability (currently just getting into pedal building).


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## jubal81 (Sep 28, 2021)

Edge59 said:


> Hi, where does one get the PCB, I do not see it available on pedalpcb.com website, Also the parts, is there  a good source for parts or is this a one-off build? I am very curious
> 
> Thanks
> Ed


It's just a personal project with a lot of SMD parts and pretty uncommon tubes - not at all suited for a DIY project.


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