Low Gain, neutral dist/OD

[Fancy Lime]

...
What's a CMOS gate drive? Do you mean like the red llama?

Yes, the Red Llama (and the likes) can be considered a "CMOS gate drive", although "CMOS inverter drive" or something of the kind are more common terms.

BTW, you can also add a couple of diodes to ground (like in the DOD-250, Electra...) to the end of the Red Llama and see how that sounds. Make it switchable with a on/off/on switch to get "both diodes" / "no diodes" / "one of the diodes" and you'll have yourself quite a versatile drive pedal.

Andy

[Killthepopular]

I've had a bash at trimming down the tube screamer. What I think I've done is remove the input and output buffer, the bypass, the hpf in the clipping section, the lpf in the tone section and the tone control itself. Does it still make sense as a circuit?

EDIT: On second thought, it makes more sense for me to just use the ROG Tube Reamer and go from there. Those guys know what they're doing.

[Fancy Lime]

I've had a bash at trimming down the tube screamer. What I think I've done is remove the input and output buffer, the bypass, the hpf in the clipping section, the lpf in the tone section and the tone control itself. Does it still make sense as a circuit?

EDIT: On second thought, it makes more sense for me to just use the ROG Tube Reamer and go from there. Those guys know what they're doing.

Yes, your own schematic is missing a few caps and has some connections not quite right. Most importantly, the negative input of the opamps needs to be connected to ground via a DC-decoupling cap if you have a single sided power supply (as is the case for the vast majority of pedals including the Tube Screamer). You also need a resistor in there, else you get extremely high gain (so called open loop gain, meaning the maximum gain that the opamp is capable of) and unstable operation.
You are right, just build the Tube Reamer instead. That is almost the same as yours would be with the errors fixed.

Andy

[bluebunny]

build the Tube Reamer instead

+1 

[Rob Strand]

A better example of a stripped down Tube-Screamer is Jack Orman's Son of Screamer,
http://www.muzique.com/tech/scream.htm

One way to remove some of the mid sound is to add a bit more of the lows back like the bass control in Timmy, see reply # 15,
https://www.diystompboxes.com/smfforum/index.php?topic=121481.0

This trick is used on many "Transparent" pedals eg.  Clark Gainster,  Menatone Red Snapper.   One method is to put a pot in series with the gain resistor (R2 on Son of Screamer).  Another method was the Tube-Screamer "Fat Switch" which increases the low-cut cap (C2 on Son of Screamer).   IIRC, Fulltone Fulldrive pedals are hard-wired with the Fat cap in place.

The Marshall Blues-Breaker adds an extra low-pass filter to get rid of the fizz, which is sometimes a good idea when your amp is set-up for clean.  It also cuts the lows more for high gain than low gain.

The problem with this stuff is there's no perfect solution.   Every few years a new golden transparent pedal comes out and it often turns out to be some sort of older circuit, many times a tube screamer variant (eg the Xotic stuff).

[cab42]

build the Tube Reamer instead

+1 from me too!

Try version 1, the one with a single opamp (741). I preferred this to version two. I'm not sure that the v. 1 schematic can be found on ROG anymore, but I think I have it somewhere.

Another suggestion. Earlier in the thread, Mark Hammer's AEFEA Drive was mentioned. I added a switch to mine, that removes the diodes from the feedback loop, and adds a diode pair to ground before the tone control.  It sounds great on lower gain settings!

[Killthepopular]

I'm leaning away from the TS circuit. I'm getting the impression that it really is geared towards the mid focussed sound which I don't want and that it's not really straightforward to get a neutral tone from it (like with the red llama). Also I already have a modded SD1 and I'm not a huge fan of the TS sound anyway so it's probably a less worthwhile circuit for me to tinker with compared to some of these other circuits.

I appreciate the advice you guys have given thus far but I have to limit my options or I'm gonna be snowed under with circuit tinkering (instead of actually playing my guitar). Currently I'm leaning towards the following circuits. In no order:

1. Electra (Fancy Lime). ~ 9 components. It's really simple and sounds awesome.
2. Vox 1901 (roseblood11) 18 components. I love the Dod 250 and this sounds similar but warmer and smoother.
3. Red LLama (Fancy Lime, ElectricDruid) 14/15 components. This seems like it's the closest to my original conception of what I want from this project. It's pretty simple, it sounds kinda tubey and generally sounds nice. Also lots of you guys seem to think highly of this type of circuit.
4. Crowther Hotcake. 29 components. This is a bit of a curveball because it seems like a bit of a quirky circuit which doesn't really produce a "natural" crunch but it is well balanced overall and something about it has kind of captured my imagination. Scott Kannberg, guitarist in pavement (my favourite band) has pretty much just used this one dirt pedal for his whole career, so the Pavement affiliation adds to my interest.

I'll order the parts soon. I should probably get another breadboard while I'm at it. My current one (10X30 + power rails) is probably a bit cramped for a circuit like the hotcake.

[Steben]

Natural transparent does not need to mean soft clipping typology. A low gain plexi can sound very natural, while it is rather hard clipping. Minibooster/mu amp circuits do not lip that soft either.
https://www.youtube.com/watch?v=GLE9Bo9B8F4

[Killthepopular]

Natural transparent does not need to mean soft clipping typology. A low gain plexi can sound very natural, while it is rather hard clipping.

Good to know. I think the gritty, marshally, mesa boogie type sound is what i tend to like.

[Killthepopular]

How capable is the electra of going from clean to dirty? Is it one of these LPB1 style transistor based circuits that is almost always a little dirty unless you roll your guitar volume right back? If I use a low gain transistor is it reasonably easy to get clean tones? Here's the boost part:

[Mark Hammer]

The transistor does not have gain by itself.  It has the capability of higher gain (or not), depending on the biasing components around it.  In the case of the Electra circuit, the 2M2 resistor between collector and base helps to boost the gain, such that the signal has a high-enough amplitude to be clipped by the diodes.  I suppose if a person wished to, they could use a toggle to simultaneously lift the diode pair and change the effective value of R5.  Would reducing the gain of the transistor create significant level drop?  Not at the output, likely.  Keep in mind that the diodes remove peaks,  So by eliminating that diode action and reducing the gain, you may well end up with the same final output level.

[Rob Strand]

4. Crowther Hotcake. 29 components.

Along the lines of the The Hotcake and the perhaps the FullDrives with feedback you should perhaps check out the "One Control" Honey Bee; BTW it has three controls.    That one is one of the later incarnations of that type of circuit.  There's schematics and layouts on-line - the cap across pins 1 and 8 should be 100p.   You probably don't want the Honey Beest as that has an extra gain stage.  I have *not* build either of these. You can find clips on youtube.   To me it's just a tad muddy on some clips but not on others.

You could even try removing the last gain stage.

It uses a CMOS CA3130 opamp.

[garcho]

Clean to distorted without a frog leap or "fizzle" can be done perfectly by blending in a little  dry signal with overdrive signal made from diodes in the feedback path of an op amp. Combine the two in a summing amplifier configuration. Along with either your picking velocity or volume knob stuff, it sounds linear, from clean to velcro. Add a treble-cut knob and call it a day. Perfect for chords, 3rds/6ths sound clean, but then riffs and licks can still sound nice and fuzzy with a little more knuckle grease.

[Killthepopular]

I'm going ahead with the four circuits mentioned above. Electra. Vox distortion. Red Llama. Hotcake.

Just writing up a list of all the parts I need.

Just checking, 50k-RA is the same as C50k right?

[Mark Hammer]

No.  They have the reverse taper.  That said, if you flip which wires go to the outside lugs, and are willing to have clockwise = "less", rather than "more", a C and A taper will work identically with respect to dialability.

[Rob Strand]

Just checking, 50k-RA is the same as C50k right?

No.  They have the reverse taper.  That said, if you flip which wires go to the outside lugs, and are willing to have clockwise = "less", rather than "more", a C and A taper will work identically with respect to dialability.

Normall "-RA" = Reverse Audio which is the same as C.   Whereas  50kA or A50k are just normal Audio ("A")  taper which are different but can be used in reversed with some inconvenience.

Clean to distorted without a frog leap or "fizzle" can be done perfectly by blending in a little  dry signal with overdrive signal made from diodes in the feedback path of an op amp. Combine the two in a summing amplifier configuration. Along with either your picking velocity or volume knob stuff, it sounds linear, from clean to velcro.

Interestingly the feedback diode configuration naturally adds some clean *provided* the opamp with the feedback diodes doesn't clip.   However the clean in this case get filtered by the tone control.

Add a treble-cut knob and call it a day. Perfect for chords, 3rds/6ths sound clean, but then riffs and licks can still sound nice and fuzzy with a little more knuckle grease.

Actually adding a lot-pass filter, or treble control to the Vox/MXR/DOD circuit goes a long way to take the sizzle out.    The 10k resistor and the 100k volume pot make it more difficult to get the filter to work.   Reducing the 10k to 1k or 2k can help but it does change the sound a little bit.  The volume control loads the tone control filter so it's best to add a buffer.  I guess the way the Rat does the tone control is the best example of that; you don't need a JFET for the buffer you can use an opamp.  The other way to do it is to put the tone control after the volume pot but then the filter frequency moves about a bit with different volume control settings and with the cable capacitance.

If I was putting a fixed filter in there I'd probably go for about 6kHz or so.   IMHO a good balance between removing sizzle and not losing 'air' from the clean tone.  If you look at the fixed filters in the tube-reamers the fixed filters are 4.8kHz on the old and 7.2kHz on the new.  This is right in the the zone.  4.8kHz can be a little dark and 7.2kHz will start to bring back the natural air but also has more sizzle.

Back in 2001/2003 I put up simple example circuit of a diode clipper with a RAT type control together with a clean blend.  I chopped and changed between output clipping and feedback clipping.   Each have their own sound.

[Rob Strand]

FWIW, here's a way to add a control to the DOD 250.
(For the tone control: The C taper isn't going to be fairly ineffective for the half the rotation so maybe the B taper is better here ).

[Steben]

https://www.youtube.com/watch?v=lH4xD8W-7Io

Check this out, the axis face. A silicon fuzz face that cleans up very well with single coils.
This is greatly there due to the 100k pot in front. This flattens the input impedance by adding resistance. Since the silicon fuzz has bigger gain, this results in a smooth result at gains comparable to germanium but with less farty wool.

[Killthepopular]

I've set up the electra circuit and am trying different diodes. Red LED, 1n34a, 1n914. So far I've done:

LED
LED - Something warm and classy about LED but it sounds very un-amplike. The big test seems to be how well a diode combo can handle droning fingerpicked arpeggios. This technique creates a wall of sound which you want to be very slightly fuzzy all the time. LEDs seem to throw in farty sounding clipping at random intervals. Sounds awful. Seems like LEDs are good for a hard crunch but not good for smooth valvey tones.

Si
Si - A bit shrill and nasty sounding though maybe more solid than germanium. The clipping is a bit nicer than LED but seems to make the tone a bit harsh.

Ge
Ge - The best so far, sounds very smooth and natural and amp-like.

gonna try the following five combinations:

Ge Ge
Ge

Ge Ge
Si

Ge Si
Si

Ge Ge
LED

Ge Si
LED

[Rob Strand]

I've set up the electra circuit and am trying different diodes.

What collector voltage are you operating at?  I can affect the sound quite a bit.
A good starting point would be 4.5V but should try tweaking the bias point up and down from that a see if the sound is more appealing to you.