Taming the Bass

[Structo]

I was wondering if you guys had a favorite method of dropping some bass from the ODS style amp.
As in, lowering the bypass cap, lowering coupler value, etc?
Combination of the two?

I can't have my bass pot up above 9:00 before it is too much.
The mid is just about as bad.

I guess I would like to have more range in the control rather than all of it in the first quarter or half rotation.
Mainly in OD mode, the bass seems to lose definition down low.
I set the OD trimmer at 26K to ground with amp on.

I also need to filter just a bit of fizzie content off of the top in OD.

I tried larger snubber caps on V2 and didn't like that when they got too big at 500pf.

I backed those down to 390pf.
Then I tried a .02uf cap at V1b. That seemed to almost disable the bass pot so that went back to .047uf.
Then I tried a 1uF bypass cap on CL2, that seemed pretty good and is where it's at right now.

I also have a Ayan treble bleeder on the OD volume but it is set where it isn't doing much at all right now.

I was just curious if you guys had a standard approach to this?

Like, too much bass, lower bypass cap.
Or, too much bass lower coupling cap.

Or am I simplifying it too much?

Would it be as simple as installing a 250K bass pot?

[David Root]

Tom, from what value would you be dropping to a 250K pot? What's the mid pot?

And what slope resistor?

One way for sure is to change out those RCA blackplates for Sylvanias. I tried that recently in my '70s ODS 50W, which is not bass heavy to begin with, and it was TOO lean, at least with my 2x15 JBL E130s.

Maybe in my Bloozman (Bluesmaster HRM) which has plenty good bass, or my #124 with both PAB and MB on, it would work OK, haven't got around to trying that yet.

On the fizzies, try taking the snubber off V2A. I had two 500pFs on V2 in my #124 and like you say it was too much, I just took V2A off and left V2B at 500pF and it cleaned up.

[Structo]

THanks David.

The bass pot is 500K and the slope resistor is 150K.

Not sure what you mean by the tubes but currently this amp has TAD 6L6 STR's in it with three vintage long plate Raytheon 12ax7's.

Someone suggested I have a wiring mistake while not impossible I don't think I do.
I have compared my wiring to the layout several times to be sure.


How about the 10K tail and .001uf cap on the bass pot.
Do those increase bass?

[greiswig]

What are your cathode bypass caps on V2? Is your clean tone where you want it bass-wise?

I ended up playing with both the cathode bypass caps on V2 (creates a low shelf filter, IIRC) and the couplers (not a shelf...drops off at 6db per octave or something like that) to get to where my OD channel had beef but not too much, and my clean channel still has lots of body. The more obvious effect on the tone came from the couplers, definitely, but playing with the cathode bypass caps let me not lower the couplers as much while still getting some low end there.

Hope you'll make it to the Portland D-fest this weekend, Tom!

[Structo]

Right now I have a 1uf bypass cap on V1b, 4.7uf everywhere else.
390pf snubbers on V2.

[tubedogsmith]

Tom, do a search on Ayan. He has a great pre OD filter for cutting bass and leaving pretty much everything else as is.

[Structo]

Yeah, I forgot about that.
I used that on my D'lite for a while.

It was a .05uf cap on the OD entrance if I recall.

[greiswig]

Yeah, I forgot about that.
I used that on my D'lite for a while.

It was a .05uf cap on the OD entrance if I recall.

I think that's right, or maybe .02uF. I have been amazed at how low the series capacitance can be taken, and still have quite a bit of bass in there.

[tubedogsmith]

Gil used a .0047 usually which cuts a lot of bass and a 4.7meg to ground at the input of the OD stage. I've used the .05 before and is about all I needed.

[tubedogsmith]

Tom, .05's for PI caps is nice too, as is a .01 or smaller PI input cap instead of the .02. Getting away from the model but still they work.

[Structo]

You know, I went down that road with my D'lite amp and I seemed to come full circle on that amp because after a while it stopped sounding like a Dumble and more like a high gain amp.

I know from that experience you can start tweaking a lot of components and sort of lose sight of the tone that makes these amps great.

I just figured that there seemed to be quite a few guys that said their ODS amps had too much bass that there might be a simple adjustment to bring it down a bit.
I think I like the 1uF bypass cap on CL2, there still seems to be plenty of bass in clean mode and it tightened up the bass a bit in OD.

I find when I mess with the coupling caps that it sort of changes the character more than I want.

With my amp, it also may be from having the EVM 12L's and having the amp and cab sort of in a corner.
There is other stuff behind the cab but the rear still faces a corner so that may be adding to the problem.

I'd say the hardest problem with the ODS amps is to make both the clean and OD balanced since there is the single tone stack so you have to sort of compromise between the two modes.

I'll just have to devote a day or two and set the amp up so I can make a change then hear it immediately. Right now I don't have the room to do that.

[dogears]

I find the opposite actually. I don't like the character of the smaller bypass at all. I much prefer the slightly smaller coupler. Btw, the 1uf cuts more bass than moving to a .02 should. At least on paper.

I find when I mess with the coupling caps that it sort of changes the character more than I want.

[jaysg]

I reverted to the 'Classic' tonestack. ymmv

[butwhatif]

I like the classic stack (.047 mid) also, but have the skyliner (.01) on a pull pot for the rooms i play where i think i need it. If u can get rid of the bass when you turn off the bass pot you're ok. I run mine on 3-5 usually, except for the odd situation. I have 15uf byp on v1a, and 22uf on v1b, which gets a full clean sound for use w/pedals, 4.7 uf on v1+2. .047 coupler. i like 100k pots for both drive and od level,

[Deric]

I played with smaller bypass caps and agree with Scott - smaller couplers seemed to retain more of the vibe...

If u can get rid of the bass when you turn off the bass pot you're ok.

I agree with this 100% (at least it seems like a good idea ). Not sure if I've tried it on my main amp (started as a scratch built D Lite 112 combo - now basically a 101 Non HRM with a (very) small V2a coupler and an iron sounds loop. I like it a lot but it really loses it balls in PAB.

I plan on rebuilding it soon with a couple of changes. I'm going to go back to a stock V2a coupler to start. I think Tony suggested using Sprague TVA bypass caps all around to help tighten up the bass so I will try that. I'm also going to try to cram a tube loop in it.....there's room but I want to try to make it fit with the holes I already have in the chassis. I've been thinking about the "Bass at zero (off)" thing for a while and it occurred to me I may have never tried it that way..... I kept thinking about the Carlton thread bashing Brandon because Carlton turned the bass on his Bludo to zero (or close). Last weekend I was giving a sound system seminar at a small upstart church. One of the "sound guys" kept trying to tell me the gain knob on the mixer was supposed to be set in a certain spot (regardless of input/instrument). He said that one of the guitar players had a "defective pickup" because the signal was "too hot". I asked him if he turned the gain down. He said "Yes". I asked if the knob was at Zero.. he said "No, you can't have the knob at zero...."

Funny.....I was thinking about my amp on the way to the church....