The Nobel/Noble Tube Screamer

[Mark Hammer]

A thread on another forum prompted me to try out something on a Tube Screamer circuit that I'm amazed I hadn't tried before.

The Nobels ODR-1 has a number of things about it that are quite different from a TS/derivative.  One of them is that, instead of rolling off bass, it uses the same dual-ground-leg strategy used in the Proco Rat,to provide flat boost down to the low end and additional boost for the upper mids and treble.  I thought I'd try it out, just to see what difference it made.  It made a very NICE difference.  Nice thick sound with more bottom and plenty of bite.  Max gain is greater than a stock TS, so you get a louder output for any given drive/volume setting.

This is all it involves changing. (Thanks for use of the drawing, R.G.)  Max gain for low end is 167x, and max gain for content above 2.3khz is 307x.  This is in contrast to a max gain of 118x in a standard TS.  Obviously, this is but one of the differences between an ODR-1 and TS, but it changes the character of a TS in a desirable way.

Try it, you'll like it!

[Mark Hammer]

Here's the result:  https://www.youtube.com/watch?v=FG5aiJaNKo8

[Matthew Sanford]

That sounds really good, opens up it's sound!

That three thing pedal... is the TS always through the BMP, or do you get to choose your routing?

[Mark Hammer]

Order is fixed.  I picked up the enclosure when visiting Diamond pedals several years ago, pre-pandemic.  There was a box of discarded drilled enclosures they had used for experiments and prototypes, and I snagged a few.  With most of the holes already machined, I installed what I thought might go nicely in there.  There's some holes in the back that I thought I might use for an external loop that could be repositioned, but the pots for the circuits simply didn't allow room for jacks in the back; at least not where those holes are

I'm not hurting, though.  I have duplicates and triplicates of each of those drives, so if I want to experiment with order, I don't need to do it with that pedal.


Again, the small mod does not instantly turn a TS into an ODR-1, but it does replicate at least one of the elements that people like about the ODR-1.  And it's small enough that you can do it to most commercial pedals, with the exception of SMD-based units.

[Matthew Sanford]

Too bad about the jacks, I'd suppose you could glue board mount to the back if you could just get the pins in the hole...but tacky I suppose. That mod is a nice change, I feel if well placed may do many a fuzz some good.

[Fancy Lime]

Nice! The Blues Breaker also comes to mind.

Andy

[Mark Hammer]

Good call.  Yeah, the dual ground-leg strategy is a useful one.  The bass rolloff used in the original Maxon design was a reasonable first approximation at achieving relatively equivalent clipping across the fingerboard, but at the cost of eliminating the "guts" of the resulting tone.  Instead of handicapping the low-end, the dual ground-leg approach simply gives the unwound strings an advantage at any given drive-control setting, without forfeiting low end.

[Rob Strand]

Nice! The Blues Breaker also comes to mind.

Andy

What people don't realize is the Blue Breaker/KOT RC networks can be transformed in the two parallel RC networks used on the RAT and the ODR1.   The transformation is *exact*, not an approximation.

Here's a comparison of the responses of the various pedals.

Schematic:


Responses:


The idea is to scale the RC networks for equal volume, which isn't as straightforward as you would think.    I've normalized to 900Hz.

You can see my ODR1 network has less gain than Mark's, although the frequencies are obviously the same.  The diode clipping helps level things out a bit.   I haven't compared Mark's or my ODR1 network with the TS9 to see which is closer.

The actual ODR1 has some low-end roll-off before the gain stage, say around 100Hz to 125Hz.  So in reality not as much LF boost as shown here.  If you try to move that roll-off to the feedback network it's not the thing because the pre-filter affects the clean blend signal inherent in the non-inverting stage.  Of course you can make an approximation.

100nF input cap:


68nF input cap: (low end now a lot like TS9 with FAT mod.)

[Fancy Lime]

What people don't realize...

Don't they? It's rather obvious, isn't it? Just a slightly unusual way of writing a Y-Δ-transform.

[Rob Strand]

What people don't realize...

Don't they? It's rather obvious, isn't it? Just a slightly unusual way of writing a Y-Δ-transform.

No.  Y-Δ-transform isn't that common for hobbyists.   

Besides, if you start with an RC network the Y-delta transformation doesn't guarantee the resulting network will be an RC network.   A good example is the Bridge T network.  If you take the bridge-T network with the capacitor in the bridge and ground leg, the T to Y gives an inductor in series with a resistor for the delta-equivalent bridge impedance.  That inductor resonates with bridge cap which is why you get a notch in a bridge-T network.

The form I taling about is in the bottom panel and bridge-T network at the bottom left,
http://www.geofex.com/article_folders/eqs/paramet.htm#bridged_t

In the case of the Blues Breaker feedback network you do get an RC equivalent after the Y-delta transformation, provided you can see the pattern in the equations, but my point is it's not obvious up front an RC network will result.

[antonis]

Y-Δ-transform isn't that common for hobbyists.

True & Correct..!!

Never dealt with that $%^%$# transformation till I tried to understand Baxandall Treble boost at high frequencies..

[Fancy Lime]

Alright, fair enough. I did not mean to drail the thread. Anyway, my point about the BB was that it also uses a double ground leg, albeit in a slightly less obvious but, as Rob pointed out, perfectly equivalent, configuration. And it seems to me that the sonic goal of doing so might have been that same as Marks two-legged Screamer endeavor. Might I suggest calling it the Two Screamer

Andy

[Mark Hammer]

[matopotato]

Wish I had seen this about two weeks ago before completing a TS clone build (Cirrus by Aion FX). Sound like it would have been a very nice mod.

[ElectricDruid]

That's a picture of me when someone mentioned the Y-Δ-transform!

[Mark Hammer]

Wish I had seen this about two weeks ago before completing a TS clone build (Cirrus by Aion FX). Sound like it would have been a very nice mod.

You can still do it.  Doesn't take up much space, if you have room for a toggle.

[matopotato]

Wish I had seen this about two weeks ago before completing a TS clone build (Cirrus by Aion FX). Sound like it would have been a very nice mod.

You can still do it.  Doesn't take up much space, if you have room for a toggle.

Could be tight



Trying to think of why I would like to toggle back to stock. Although I love to keep all options available (it is a bit of a curse), I still thought this mod was better enough to be a keeper.

[stallik]

I whipped up a mini TS today with this mod on a toggle. May be just a little too much bass through my setup if I start whacking the strings but really nice when I'm not. For that reason, the toggle stays on mine.

And I might BB some of Robs suggestions....

[Rob Strand]

I whipped up a mini TS today with this mod on a toggle. May be just a little too much bass through my setup if I start whacking the strings but really nice when I'm not. For that reason, the toggle stays on mine.

And I might BB some of Robs suggestions....

The input HPF will help tame the lows.   

It is possible to use the simple 2xRC network with different values to approximate the effect of the input HPF present on the ODR1 circuit.   That greatly simplifies the switching.

I've matched the case where the input cap is 68n, like aion's, instead of the original 100nF.
https://aionfx.com/app/files/docs/andromeda_legacy_documentation.pdf

Schematic: ckt 7 = original without input HPF, ckt 8 = original (w/HPF), ckt 9 = HPF effect with 2xRC circuit.


Response: ckt 7 = grey, ckt 8 = dark green, ckt 9 = gold


For more low cut the next step would be to use the RAT or circuit, except with the scale values to preserve the gain.

There's plenty of scope to play with the values yourself and make "in between" responses.   It can be a bit fiddly.
If you look at the simplified HPF version it's pretty much tuning the C91 value.

If look at the value of the leftmost resistor (eg. R31, R61, R91)  then the values follow BB1 > RAT > ODR1 (modded).   The value of that resistor sets how much low-end comes through, which can be seen on the frequency response.  The corresponding cap (C31, C61, C91) sets what frequency the low-end roll-off occurs.

I've got some notes on gain matching but it's all packed away and under a different cad package.  I think the 900Hz normalization point is reasonable.  If you need to increase the gain then decrease the resistors by some factor like 1.2 and decrease the caps by the same factor.

[Rob Strand]

Something that triggered in the back of my mind regarding the ODR-1. 

Last year there was a thread on the schematic of the ODR-1 and some variants.  The later ODR-1 is the ODR-1 BC "bass cut" version which has an internal switch to cut some of the bass.   As far as I am aware this version has the pre-opamp high-pass filter (not sure if the cap is 100nF or 68nF, I'm guessing 100nF).  The switch changes the values of the left-most RC network "R71" and "C71"  on my schematic; these are the 1k5 and 2u2 on the original unit.   The cut is quite noticeable.