Getting a smoother OD

[philbard]

First post on the forum, hello everyone. Impressed with the breadth of knowledge and experience here.

Been playing for years, but only on the side as I was running a small business not music related. Since retiring from that I've turned my attention back to guitars and just recently amps. I had never heard of Dumbles until about 6 months ago a friend mentioned them to me. After becoming better acquainted with various models online and watching a ton of YouTube vids, I stumbled onto this forum and spent some time reading up. A little lost in all of the different flavors of Dumbes that are out there, but have a general sense. I decided to build one and since my high school electronics classes are in the distant past chose a kit build thinking it would get my feet wet and help me determine if I wanted to go further. After checking out some options I landed on the Ceriatone OTS Special 50. I know there are a lot of bad vibes here about what Nik is doing, but I'm not here for troubleshooting help, the amp worked fine the first time I fired it up.

My question has more to do with where in the Dumble world the OTS's design falls. I love the clean sounds, beats hell out of my Fender Custom Deluxe and rivals a Mesa Boogie 50 Cal+ I have had for years, but the OD seems a bit harsh for my liking at bedroom volumes. If I lower the brightness and treble settings and boost the mids and it is more in the realm of what I'm hearing in others' builds, but those settings kill off the brilliance when I go back to clean. In retrospect I'm wondering if I should have chosen an HRM style schematic, I understand that those builds allow separate tone controls for clean and OD.

So is that the limit of this particular configuration or is there a mod that can be applied to the build I have to smooth out the OD? Beyond that I think I'm hooked enough to pursue building from the ground up and am contemplating where to go next design wise.

Thanks in advance for any suggestions.

[norburybrook]

Phil

Welcome to the forum.

I think you've basically just found out the main balancing act needed by everyone who plays these kind of amps. As the clean channel setting affect the OD as they're cascaded it is just a case of balancing/compromise.

Also I don't think these amps are designed to work best at bedroom levels, they need to move some air IMHO. Also it's hard to judge an amp solo. In that, I mean the sort of sound that works in isolation is rarely one that works when you're sat in a band soundscape so bear that in mind too.



M

[martin manning]

...the OD seems a bit harsh for my liking at bedroom volumes. If I lower the brightness and treble settings and boost the mids and it is more in the realm of what I'm hearing in others' builds, but those settings kill off the brilliance when I go back to clean. In retrospect I'm wondering if I should have chosen an HRM style schematic, I understand that those builds allow separate tone controls for clean and OD.

Search "OD treble bleed." There are several options, but all are basically dumping some HF to an AC ground on the OD only.

My question has more to do with where in the Dumble world the OTS's design falls.

That depends on which model you have. I gather it's not an HRM, or a Bluesmaster (which is a HRM variant). Most non-HRM OTS seem to be the high-plate type, like the 102 and 183 documented here.

[ijedouglas]

Hey Phil,

Welcome and congrats on the build.

Unfortunately there is a bit of a balancing act with regards to the non-HRM amps. Here are some of the things I have done with varying levels of success:

- Roll tubes through V1 and V2
- Add a Dumbleator via the loop (affects both clean and OD)
- Adjust OD trimmer
- Swap out resistors
- Set for OD tone and ride volume to clean up

I'm sure others with far more experience than I will chime in. Can you post some gut shots? Always helpful for members to help troubleshoot or provide recommendations.

Regards

Ian

[xtian]

And you can add an HRM tone stack after the fact, by adding a little PCB that sits above the existing circuit. But I would tinker with the treble bleed mods suggested above.

[Charlie Wilson]

Hello, after tweeking and retweeking and rebuilding the same amp for about 5 years(and learned a lot), I have come to the conclusion that there is bright and then there is harsh. An amp(OD Special) can sound bright but still be musical. I don't think Dumble used the HF taper to make an amp less harsh. If your circuit is a low plate, you may want to try a high plate. A bit darker and more compressed sounding at bedroom volumes. Also, for the lower volumes, as the other guys have said, the Dumbleator is kind of a must. I would first make the clean side of your amp as nice sounding as you can get it by playing around with component choices, lead dress, and outer foil orientation of your coupling caps. Also experiment with the 10m resistors on your LNFB. Those things can make or break your top end. Then move on to your OD. Try to get a nice musical sound out of your amp from top to bottom and then try to balance the brightness between your OD and Clean with the HF taper(if it needs it). My .02 cents.
CW

[dorrisant]

Philbard, welcome!

Charlie, if you don't mind, I'd like to ask...

Which circuit did you start with? and where did you end up? Just curious about your preferences and why. I think it relates back to smoothing the OD, not to derail.

Thanks for the tuning info as well.

[philbard]

Phil

Welcome to the forum.

I think you've basically just found out the main balancing act needed by everyone who plays these kind of amps. As the clean channel setting affect the OD as they're cascaded it is just a case of balancing/compromise.

Also I don't think these amps are designed to work best at bedroom levels, they need to move some air IMHO. Also it's hard to judge an amp solo. In that, I mean the sort of sound that works in isolation is rarely one that works when you're sat in a band soundscape so bear that in mind too.



M

Yeah I get the comment about bedroom levels. Maybe I should be saying loud bedroom levels, or small clubs, which is where this amp will be used. And mixed with a band it will of course need some highs. But no performing until quarantine is over so I don't have the opportunity to compare in that setting. Thanks...

[philbard]

Search "OD treble bleed." There are several options, but all are basically dumping some HF to an AC ground on the OD only.

My question has more to do with where in the Dumble world the OTS's design falls.

That depends on which model you have. I gather it's not an HRM, or a Bluesmaster (which is a HRM variant). Most non-HRM OTS seem to be the high-plate type, like the 102 and 183 documented here.

Nik calls it the OTS Special, and I was wondering which of HAD's circuits it was based on so I could use the information on this forum to get a sense of where it lies along the spectrum.

[philbard]

Hey Phil,

Welcome and congrats on the build.

Unfortunately there is a bit of a balancing act with regards to the non-HRM amps. Here are some of the things I have done with varying levels of success:

- Roll tubes through V1 and V2
- Add a Dumbleator via the loop (affects both clean and OD)
- Adjust OD trimmer
- Swap out resistors
- Set for OD tone and ride volume to clean up

I'm sure others with far more experience than I will chime in. Can you post some gut shots? Always helpful for members to help troubleshoot or provide recommendations.

Regards

Ian

Thanks Ian, I'm happy to have gotten success on my first amp build. I've tried adjusting the OD trimmer, will do some more fiddling there. I've seen a lot of recommendations for Dumbleator and may go that route. As far as rolling the tubes that isn't something I understand at this level of experience, and swapping resistors would also require some advice. I'm just not able to make those calls yet.

[philbard]

Here is a build shot...

Final Top view.jpg

[norburybrook]

just had a look and that's a #102 high plate skyliner. Lovely amp




M

[PicknStrum]

Of all the people who have responded, I'm the last one you should listen to, but:

Having just finished one of these builds myself - a #102 - I found the same issue as you. To get a nice clean, it seemed like it was at the expense of making the OD a bit too trebly. After tinkering for a while I realized there is a ton of power in that little OD trimmer. It took me a long time but I found that even a mm change on that trimmer could be the difference of an OD that was too harsh vs. just right. With that said, it also seems to depend on the level of gain you want. I've got mine set somewhere around low/medium to medium gain and the OD is perfect while retaining a nice sparkly clean. That's just been my experience since finishing the amp.

Curious what speaker you're using. Seems like most recommend the EVM12 but I'm loving the Texas Heat I have it paired with.

[ijedouglas]

Phil,

Very nice build! I agree with everything Charlie has to say. I would also add, amp break in and speaker break in. Both can have a pretty big impact on your amp.
Amp break in - I like to get around 100 hours of play on the amp before I throw the baby out with the bathwater. A dummy load resister and looper or CD player get you there if you are impatient
Speaker break in - if your speaker/s are new they may also be contributing to the harshness. Hell, speaker selection in general has a HUGE impact. What speaker/s are you using?

Regards

Ian

[philbard]

Ian and Picknstrum,

Yeah I think break in is likely contributing, I've run across that mentioned a lot on this forum. I initially played it by setting the chassis on top of my Fender Deluxe Reverb and using that speaker, which has fair mileage on it, a Celestion. I purchased a Warehouse to put in the cab I just finished building, no experience with that speaker so will have to see. I'll take the advice and noodle the OD trimmer some more, there was no mention of its function in the Ceriatone manual so I didn't have a lot to go on initially. Only about 3 hours of playing on it so far so pretty early on.