Lil' Bumble-B - 'micro' Bassman with OD channel

[Lynxtrap]

I would love to hear some soundclips if that's convenient and possible! I've got a friend that has expressed wanting a low watt overdriven amp sometime in early 2023.

With respect, 10thtx

I will absolutely do some recording as soon as I get the new pots and final tweaks done!

[Lynxtrap]

I am considering a slight overhaul of the OD channel. I'm not 100% happy with the tone control, and having some problems voicing the OD channel to sound good both with the tone control engaged and bypassed.

I suddenly realized that a James can be done on a dual pot. Alternatively I could put the bypass on a physically smaller switch, and use two smaller pots for the James. Or even skip the bypass switch.

I don't want to leave this at "good enough"

[Bergheim]

I don't want to leave this at "good enough"

I've learned that what is "finally perfect" today almost always turns into "good enough" tomorrow.
The amp I'm most pleased with so far is the one I've let sit for a year without touching it, after tweaking it continously for two years without getting it just right for _everything_.

Sounds like you got a pretty versatile setup already

[Lynxtrap]

Other projects, life and that kind of stuff tends to happen, so half a year later I'm back to working on this.

Still having problems with the overdrive channel. Most recent changes are efforts to remedy excessive gain and fizzy/fuzzy top end.
That got better, but at the moment it suffers from grainy overdrive and a lack of low mids, and I'm getting kind of lost trying to figure out what to try next.

(That is, with the OD level set so low that the only overdrive comes from the actual overdrive channel. Turning up the OD level to add overdrive from V3 is not what I'm tweaking the circuit for).

As can be seen, I've taken ideas from an ODS type circuit. I don't expect it to sound like an ODS, but I want the overdrive sound to be as smooth and mid-focused as possible, while still maintaining some string separation at least on lower gain setting with the treble turned up in the James TS. But that is not what I'm getting now.

Any kind of input and thoughts are more than welcome!

Lil Bumble-B_Rev 11.png

[10thTx]

My best guess is you have way too much bass and way too much gain??

If I were trying to mod your amp to something I would like ................ this would be my starting point to consider.

1) lower gain
2) lower some values of caps
3) add smoothing caps

The amp in this soundclip has a 5751 with a cathode follower as the switchable OD gain stage. However, it came after the clean stage similar to a Dumblish design. I do think the amp sounds reasonably smooth.

Considering the changes I'm suggesting might possibly get you closer to that sound of OD??

https://soundclick.com/share.cfm?id=10391428

With respect, 10thtx

[Lynxtrap]

My best guess is you have way too much bass and way too much gain??

If I were trying to mod your amp to something I would like ................ this would be my starting point to consider.

1) lower gain
2) lower some values of caps
3) add smoothing caps

The amp in this soundclip has a 5751 with a cathode follower as the switchable OD gain stage. However, it came after the clean stage similar to a Dumblish design. I do think the amp sounds reasonably smooth.

Considering the changes I'm suggesting might possibly get you closer to that sound of OD??

https://soundclick.com/share.cfm?id=10391428

With respect, 10thtx

Thanks for the suggestions and effort! I'm sorry if this comes across as a "yes, but..." answer.
I don't think I have too much gain. The amount of overdrive approaches what I'd call "hard rock" at about 1-2 o'clock on the gain knob.
Regarding the bass, I guess I could try a smaller coupling cap between V2A and V2B.

I should have explained my reasoning more clearly. The clean channel is a Tweed Bassman, it sounds great and I'm hesitant to make any changes to it.

My thought was that the circuit around V2A would be a "self contained" OD-channel in the same fashion as the 3rd and 4th gain stage in an ODS. That was a big mistake, as the OD channel in an ODS is not self contained in any way, as the sound is like 80% dependent on the circuitry before it. And I don't have that circuitry, just a gain stage and and a gain pot.

I may have to rethink the OD channel once again and will take your suggestions into account. But I will do it one small step a time to see if I can get it to sound the way I want without tearing it all out and starting over.

[10thTx]

Still having problems with the overdrive channel. Most recent changes are efforts to remedy excessive gain and fizzy/fuzzy top end.

I don't think I have too much gain.

Which is it? I'm confused .............. I thought you said you had excessive gain??

My opinion is the fizzy/fuzzy top with excessive gain is because some of the cap values are too large to have smooth overdrive. Simply offering an opinion that may or may not be of help or of value. When I've experimented with amps with overdrive that was too fizzy/buzzy etc..... I found some value in reducing some of the cap values to help in smoothing the overdrive. Maybe that will not work for you?

If you note on the 2nd page of the thread when I discussed the D'Mars Overdrive amp, that the overdrive section was suggested to be after the clean instead of between the first and second gain stage. I still believe that is likely an issue.

So, some more thoughts to ponder for you. Not saying you should follow any of these ideas. I think you should have your amp topology and component values however suits you. These thoughts may be of no value or help to your goals.

Respectfully, 10thtx

[Lynxtrap]

@10thTx : Thanks, and sorry for the confusion. I wrote "most recent changes are efforts to remedy excessive gain and fizzy/fuzzy top end. That got better, but...". So I meant that the excessive gain had already been taken care of. English is not my first language...

[Lynxtrap]

I've been doing a lot of component swapping, testing and thinking.

During the process I came to the conclusion that one of the main problems was that V2B alone generated most of the overdrive. As such it was also pretty much center biased.

I think these two factors were the main contributors to a sound that I would compare to the overdrive channels in the red knob Fenders back in the day.

Turned out it wasn't too hard to remedy. To distribute overdrive duties more evenly between the gain stages, I tried sending a stronger signal into V2A, biased that stage cool without any cathode bypass, and then biased V2B hot also without a bypass cap.

Leaving out all the details of the process, I ended up with the circuit below. I'm quite happy with it (at least for the moment...) It totally transformed the overdrive sound, and it is now much closer to what I had in mind when I started this project.

[10thTx]

Hooray! I love success stories. Thanks for sharing the results. Glad this worked out well for you.

With respect, 10thtx

[Lynxtrap]

Hooray! I love success stories. Thanks for sharing the results. Glad this worked out well for you.

With respect, 10thtx

Thanks, but hold your horses
I tested it some more, and...it's about 85% there so I guess there will be a few more updates coming.
I'm trying it through a bunch of different speakers and with different guitars, and that tends to reveal weak spots.

It's still on the bright side, and there's a little bit of the "ripping cardboard" sound to the overdrive = it could be a bit smoother.
The best way to describe the OD sound right now is a Marshall Bluesbreaker pedal into a Fender amp.

Two things seem kind of unexpected. One is that there is no overdrive to speak of until the gain knob is at noon. The other thing is that I have to turn up the bass knob almost all the way in the James to match the amount of low end of the clean channel. So too much low end does not seem to be a problem with the OD channel.

[WhopperPlate]

During the process I came to the conclusion that one of the main problems was that V2B alone generated most of the overdrive.

I always find the typical Marshall cathode follower to be a double edged sword when it comes to stacking for high gain . The midrange character accenting the fuzzy fizz sizzle can overwhelm if you don’t have some careful considerations. I prefer plate driven stacks overall for such , a bit more forgiving imo , but that’s generally speaking . Compare a ripper to an ODs . For lower gain non master volume amp though I almost always prefer having one . Marshall super lead . Nothing punches and cuts through a mix better imo.

I think of the rockphonix as a good example of what it takes to smooth out that sound for high gain . Many other high gain amps used a cold clipper stage to help compress and tame all that. Jcm800 of course . Soldano even colder. Dual rectifier ripped off soldano. Friedman s have their tricks . Then there’s Jose Arredondo lol slap another 200k/2k7/.68uf gain stage in front and call it all gold

[Lynxtrap]

I always find the typical Marshall cathode follower to be a double edged sword when it comes to stacking for high gain . The midrange character accenting the fuzzy fizz sizzle can overwhelm if you don’t have some careful considerations. I prefer plate driven stacks overall for such , a bit more forgiving imo , but that’s generally speaking . Compare a ripper to an ODs . For lower gain non master volume amp though I almost always prefer having one . Marshall super lead . Nothing punches and cuts through a mix better imo.

Yes cathode followers are not always that straightforward when it comes to overdrive.

In this amp, the CF is not intended to be overdriven. The clean channel is basically Bassman all the way before the power amp, while the OD channel has its own master volume before the CF.

Cranking up the OD Level pot is certainly an option and that could slam the CF pretty hard, but I try to tweak the OD channel so that it sounds good on its own with all stages downstreams running clean.

[WhopperPlate]

If you don’t want clipping maybe take a note from Merlin Blencowe and increase the cathode load resistor for more headroom , or switch to ecc82 .

http://www.valvewizard.co.uk/dccf.html

[TUBEDUDE]

If you have the real estate for another tube, using a 12AX7 bracketing a 5879 for the distortion channel might be more pleasing.
Pentode good!