A Transparent Overdrive Voicing (alternative to TS-9 mid hump)

[Rob Strand]

This continues on from the following recent threads.   

"The Nobel/Noble Tube Screamer"
Mark Hammer
https://www.diystompboxes.com/smfforum/index.php?topic=130948.0

GGBB circuit
"RAT bass mod?"
(more bass as opposed to being for bass)
https://www.diystompboxes.com/smfforum/index.php?topic=130988.0

The motivation is entirely the same as Mark Hammer's thread.

The additions to Mark's thread are:
- Make the level of the alternative network closer to the TS-9 level (4k7 + 47n)
  so when you switch between the two networks the level is more or less the same.
- The target response isn't the ODR1 but is more an average of a number of pedals.

I plotted the frequency response of a number of pedals.  For pedals with bass controls
I allowed the bass pot to vary 11 O'clock, 12 O'clock and 1' O clock.

I then reduced the pool of pedals and settings to ones which were similar and
ideally had about +6dB bass boost relative to the TS-9 *when* the overall level
is perceived to be the same as the TS-9.   Kind of bundling the knowledge of the
masses.

The reduced pool of responses consisted of:
- ODR-1 including the input 100nF high-pass filter ; this is another difference to Mark Hammer's
- Timmy with the bass set to 1'O clock; old pedals where that is bass cut.
- J Rockett 45 Calibre set to 12 O'clock and 1 O'clock (boost)
- GGBB's RAT bass boost mod,  high boost setting.

FWIW, when scaled to the same output level/gain all these networks sounds quite close.
OD-1+HPF slightly more bass boost then GGBB's bass-boosted RAT.

I then averaged the responses and fitted an average network.   In reality there
was a second step where I fine-tuned the level and used standard E12 values
for the resistors and capacitors.

When you use standard E12 values the perceived level can only be set in finite increments.
When the amount of bass boost is set to a low level it becomes difficult to compare the tone
vs the level.   For this reason I created a second option which was easy to adjust the amount
of bass boost.   The lower bass-boost settings drop the level a small amount, but in a natural way.

Circuit A is intended for switching between it and the TS-9 circuit.

Circuit B can be used as a bass control or you can increase resistor R91 for less bass to suit you taste without changing the level too much.   (Yes circuit A can be used for less bass but needs more playing around to keep the level the same.)

Schematic of all circuit:


Frequency Response:
You can see a general trend in the responses.  Also you can see VR1 and VRav sit in the middle.


Response relative to a TS-9: 
You can see bass-boost and mid-cut which knocks back the mid-hump.


Here's the response and relative response of the final networks for circuit A and circuit B.


I set this up with quite a low amount of drive.   You might get slightly different conclusions for higher amounts of drive.
I consider these results a starting point more than an end point.   You can tweak the caps values.   I found varying the values produced quite small changes in the results.   I find I back-off the amount of bass-boost over time, the extra bass sounds good at first but then turns out to be too much - maybe not such a big deal if you have a switch option.

If your base circuit doesn't have the standard TS-9 values of 4k7 and 47n, for example 2k2 and 100n then take the values in circuits A or B and reduce the values of the resistors by a factor (2k2/4k7) and increase the values of the capacitors by (4k7/2k2).   That way you will get roughly the same level as 2k2 + 100n when you switch between the networks.

Compared to the TS-9: more bass, less nasal/mid hump.

EDIT: corrected general plot

[m_charles]

This continues on from the following recent threads.   

"The Nobel/Noble Tube Screamer"
Mark Hammer
https://www.diystompboxes.com/smfforum/index.php?topic=130948.0

GGBB circuit
"RAT bass mod?"
(more bass as opposed to being for bass)
https://www.diystompboxes.com/smfforum/index.php?topic=130988.0

The motivation is entirely the same as Mark Hammer's thread.

The additions to Mark's thread are:
- Make the level of the alternative network closer to the TS-9 level (4k7 + 47n)
  so when you switch between the two networks the level is more or less the same.
- The target response isn't the ODR1 but is more an average of a number of pedals.

I plotted the frequency response of a number of pedals.  For pedals with bass controls
I allowed the bass pot to vary 11 O'clock, 12 O'clock and 1' O clock.

I then reduced the pool of pedals and settings to ones which were similar and
ideally had about +6dB bass boost relative to the TS-9 *when* the overall level
is perceived to be the same as the TS-9.   Kind of bundling the knowledge of the
masses.

The reduced pool of responses consisted of:
- ODR-1 including the input 100nF high-pass filter ; this is another difference to Mark Hammer's
- Timmy with the bass set to 1'O clock; old pedals where that is bass cut.
- J Rockett 45 Calibre set to 12 O'clock and 1 O'clock (boost)
- GGBB's RAT bass boost mod,  high boost setting.

FWIW, when scaled to the same output level/gain all these networks sounds quite close.
OD-1+HPF slightly more bass boost then GGBB's bass-boosted RAT.

I then averaged the responses and fitted an average network.   In reality there
was a second step where I fine-tuned the level and used standard E12 values
for the resistors and capacitors.

When you use standard E12 values the perceived level can only be set in finite increments.
When the amount of bass boost is set to a low level it becomes difficult to compare the tone
vs the level.   For this reason I created a second option which was easy to adjust the amount
of bass boost.   The lower bass-boost settings drop the level a small amount, but in a natural way.

Circuit A is intended for switching between it and the TS-9 circuit.

Circuit B can be used as a bass control or you can increase resistor R91 for less bass to suit you taste without changing the level too much.   (Yes circuit A can be used for less bass but needs more playing around to keep the level the same.)

Schematic of all circuit:


Frequency Response:
You can see a general trend in the responses.  Also you can see VR1 and VRav sit in the middle.


Response relative to a TS-9: 
You can see bass-boost and mid-cut which takes knocks back the mid-hump.


Here's the response and relative response of the final networks for circuit A and circuit B.


I set this up with quite a low amount of drive.   You might get slightly different conclusions for higher amounts of drive.
I consider these results a starting point more than an end point.   You can tweak the caps values.   I found varying the values produced quite small changes in the results.   I find I back the amount of bass-boost over time, the extra bass sounds good at first but then turns out to be a bit much - maybe not such a big deal if you have a switch option.

If your base circuit doesn't have the standard TS-9 values of 4k7 and 47n, for example 2k2 and 100n then take the values in circuits A or B and reduce the values of the resistors by a factor (2k2/4k7) and increase the values of the capacitors by (4k7/2k2).   That way you will get roughly the same level as 2k2 + 100n when you switch between the networks.

Compared to the TS-9: more bass, less nasal/mid hump.

I really wish I knew enough to truly appreciate this info

[Rob Strand]

I really wish I knew enough to truly appreciate this info

You can always ask.

At the end of the day it's a try it, like it, hate it, tweak it kind of thing.    The idea is it starts somewhere in the right region.

FYI: One of the plots got screwed up - now fixed.

[GibsonGM]

I really wish I knew enough to truly appreciate this info


Hang around long enough, and you probably will (at least most or a large chunk of it)!

[Mark Hammer]

I salute your diligence, Rob.  Much to chew over, there.

[Steben]

What about this as sound trimming?

[m_charles]

I really wish I knew enough to truly appreciate this info


Hang around long enough, and you probably will (at least most or a large chunk of it)!

Well, I've been here since 2007, so.... haha. I'm also being a little facetious. I understand the basics of it, but not nearly to the depth of the author.

[Rob Strand]

What about this as sound trimming?

If the left cap is the bass cap and the right cap is the treble cap that configuration has very little scope to vary the response - you are only changing a small resistance in series with a larger one.

If the left cap is the treble cap and the right cap is the bass cap the configuration will change the treble a lot and the bass little.

[Steben]

What about this as sound trimming?

If the left cap is the bass cap and the right cap is the treble cap that configuration has very little scope to vary the response - you are only changing a small resistance in series with a larger one.

If the left cap is the treble cap and the right cap is the bass cap the configuration will change the treble a lot and the bass little.

The latter would be a sort of presence control

[GibsonGM]

I really wish I knew enough to truly appreciate this info


Hang around long enough, and you probably will (at least most or a large chunk of it)!

Well, I've been here since 2007, so.... haha. I'm also being a little facetious. I understand the basics of it, but not nearly to the depth of the author.

Yeah, I DO understand that   There's a 'whole other world' inside these devices and networks. 

I'm sure you know enough to truly appreciate the thorough 'breakdown' that we're fortunate to be able to get 'round here!

[POTL]

put in my 5 pennies. Having tried almost every known overdrive, I think the best starting point would be the good old Marshall Bluesbreaker.
1) Analogman prince of tone, with all mods
2) For those who like a brighter and thinner sound, you can set the switch between AM and stock / JHS
3) Definitely worth a look at Wampler Pantheon and using volume boost mods and post EQ.
4) You should definitely avoid Timmy-style bass control. EQ before distortion is not as effective as after (hello Mesa Boogie Mark series).
5) If you make an equalizer for several frequencies, then in the style of Friedman or gyrator avoiding James / Baxandall. Blues Breaker based pedals are the most natural, transparent and harmonic overdrives.
6) if you make a modern transparent pedal, a great feature in addition to the post EQ, adjust tight, in the style of Friedman, last resort Timmy, but with smaller frequency ranges to switch from the full range of frequencies (until our overdrive looks like fuzz like a rat). Until the low-frequency cut, as in modern amplifiers designed for chug.

[Rob Strand]

put in my 5 pennies. Having tried almost every known overdrive, I think the best starting point would be the good old Marshall Bluesbreaker.
1) Analogman prince of tone, with all mods
2) For those who like a brighter and thinner sound, you can set the switch between AM and stock / JHS

The Bluesbreaker stretches the top end, like most of the other transparent pedals and the ones in this thread, but doesn't really boost the bass.  So it's like a large bass resistor (R91 in circuit B).


Mark's thread which I linked in the first post shows the parallel RC equivalent circuit of the Bluesbreaker and you can see the high valued bass resistor for the circuit A form.

[POTL]

put in my 5 pennies. Having tried almost every known overdrive, I think the best starting point would be the good old Marshall Bluesbreaker.
1) Analogman prince of tone, with all mods
2) For those who like a brighter and thinner sound, you can set the switch between AM and stock / JHS

The Bluesbreaker stretches the top end, like most of the other transparent pedals and the ones in this thread, but doesn't really boost the bass.  So it's like a large bass resistor (R91 in circuit B).


Mark's thread which I linked in the first post shows the parallel RC equivalent circuit of the Bluesbreaker and you can see the high valued bass resistor for the circuit A form.

that's right, a transparent sound, not really a flat equalizer value, it's the prevailing high and mid frequencies and reduced low frequencies. Less low frequencies, more transparent sound, notes are better read in chords. The Analogman POT has a flatter frequency response. The problem with the original Blues Breaker or JHS MG is that it's a very bright sound, increasing the distortion requires lowering the high frequencies, which is why the JHS has a Hi cut control. But in any case, cutting low frequencies at the stage of distortion is the way to a transparent overdrive.

[Rob Strand]

Less low frequencies, more transparent sound, notes are better read in chords. The Analogman POT has a flatter frequency response. The problem with the original Blues Breaker or JHS MG is that it's a very bright sound, increasing the distortion requires lowering the high frequencies, which is why the JHS has a Hi cut control. But in any case, cutting low frequencies at the stage of distortion is the way to a transparent overdrive.

That's what the tone control is for.

Both the TS9 and the Bluesbreaker are cutting the lows.   All the pedals do the same thing.   The TS-9 rolls off below 720Hz and the Bluebreaker roll-off below 1340Hz.   The ODR-1 sets that point at 2370Hz.  You can see the f2 frequency in the previous thread. 

https://www.diystompboxes.com/smfforum/index.php?topic=130948.msg1271365#msg1271365

Where to stop rolling off is just a trade-off:
- The TS-9 makes the distortion sound even for the lower notes/harmonics but the result is the nasal sound.
- The more transparent pedal makes the distortion sound even for the higher notes/harmonics but the result is a brighter sound.
- All have a perceived loss of bass.

The thing about pushing the cut-off frequency up is it maintains some transparency even after post EQ, it's kind of fixable by post EQ.   Whereas with the TS-9 post EQ doesn't work as well.   The "damage" is already done once the signal is distorted by the diode clipper.

[Ben N]

4) You should definitely avoid Timmy-style bass control. EQ before distortion is not as effective as after (hello Mesa Boogie Mark series).

But in any case, cutting low frequencies at the stage of distortion is the way to a transparent overdrive.

These two statements seem to be contradictory to me, and also to be missing the point of pre-distortion eq, which is to shape the quality of the distortion, and not EQ in the conventional sense. Apples & elephants. Correct me if I'm wrong, but this seems to me to be what Rob is saying: If you don't cut lows before distortion, you can't fix the sound with eq after.
[Edit: Or is your point that the pre-gain bass cut should not be variable? My recollection of Paul C's comments way back is that he felt the amount of bass cut required varies with the gain level, which is why he set it up this way. Maybe better/different results can be had by adjusting either the roll-off frequency or the Q of the LPF to compensate for different gain levels.]

[abc1234]

These two statements seem to be contradictory to me, and also to be missing the point of pre-distortion eq, which is to shape the quality of the distortion, and not EQ in the conventional sense. Apples & elephants.

Yeah, I was about to point out the wrongness before I saw your post.

Anyone who has used a flubby overdrive/distortion/fuzz with terrible chord clarity knows the value of pre-distortion bass cuts.

I have a Timmy clone, and for me it's an OK circuit (it's a bit bland), but the pre-distortion EQ is definitely an essential part of its "transparency". (I'm using quotation marks because that word means different things to different people—in this instance it means being able to go from clean to warm to overdriven without feeling like the low end and high end are experiencing significant changes.)

[Steben]

It's all a form of what is called presence on amps.

[POTL]

4) You should definitely avoid Timmy-style bass control. EQ before distortion is not as effective as after (hello Mesa Boogie Mark series).

But in any case, cutting low frequencies at the stage of distortion is the way to a transparent overdrive.

These two statements seem to be contradictory to me, and also to be missing the point of pre-distortion eq, which is to shape the quality of the distortion, and not EQ in the conventional sense. Apples & elephants. Correct me if I'm wrong, but this seems to me to be what Rob is saying: If you don't cut lows before distortion, you can't fix the sound with eq after.
[Edit: Or is your point that the pre-gain bass cut should not be variable? My recollection of Paul C's comments way back is that he felt the amount of bass cut required varies with the gain level, which is why he set it up this way. Maybe better/different results can be had by adjusting either the roll-off frequency or the Q of the LPF to compensate for different gain levels.]

Hello. I am not a native English speaker and I try to express things as simply as possible so that the translator is accurate, otherwise it may lead to ridiculous expressions. I remember the case when the word "power" was translated as feeding, because in my language this word has several meanings. My thought is the following. Bass control is most useful at the end of a circuit, whether it's a Tonestack or an active EQ. At the end of the scheme, we will receive from it the result that we plan. The Timmy-style adjustment is not very useful, as it affects the overdrive structure and is more for fine tuning.

I didn't just cite Mesa Mark amplifiers as an example, where the main 5-band EQ is located at the end of the preamp circuit, who used them is aware of how the tone stack behaves, which is located at the beginning of the circuit. Low frequencies correct the bass response between Chug and Sag. The mid frequencies do not change over the entire range of adjustments and rather resemble a volume knob with a small range of operation. The treble functions as a gain control. I talked about the differences between pre and post EQ. yes, I think Timmy's bass tuning should be at the end of the circuit, not where it is.

[POTL]

yes, I think it's enough to have one switch at the beginning of the circuit, between normal and tight sounds. possibly 3 position with saggy sound. I agree with Paul C that correcting low frequencies before distortion is important, the more distortion, the less low frequencies should be at the beginning of the circuit if we want to maintain transparency. but I don't consider this to be a bass tuning, as in my understanding the bass tuning sounds and works correctly/as we would expect, only at the end of the circuit.

[Rob Strand]

I talked about the differences between pre and post EQ. yes, I think Timmy's bass tuning should be at the end of the circuit, not where it is.

I agree with Paul C that correcting low frequencies before distortion is important, the more distortion, the less low frequencies should be at the beginning of the circuit if we want to maintain transparency. but I don't consider this to be a bass tuning, as in my understanding the bass tuning sounds and works correctly/as we would expect, only at the end of the circuit.

Neither are perfect.
- Timmy has perhaps too much bass before (in my pool of pedals I had the bass at off the 12 O'Clock position with a slight cut).
- ODR-1 has perhaps too much after.

The high-end point is often ignored in these discussions. When you have the TS-9 with a 720Hz or a Fat tube screamer with the 100nF cap at 340Hz, it's easy to think of this roll-off as being a bass roll-off.  However, when that point is extended into the 1kHz to 2.4kHz region we still have the filtering at low frequencies but we are now affecting much higher frequencies.  The OCD sets that point at 1060Hz.  The Bluesbreaker sets it at 1340Hz.  I call the frequency f2 frequency in my plots.  As with the bass frequencies post EQ of the high frequencies does not produce the same results.


This type of set-up: