Hi folks,
I have had a few threads here recently pestering you all for advice on "amp-like" distortion, "noise-less" preamps and such. Finally, these discussions have borne fruit. May I present to you: the 74W preamp for guitar and bass. In case you're wondering, that is the element symbol for Tungsten, not a wattage.
(https://i.postimg.cc/0rYpK6yG/74W.png) (https://postimg.cc/0rYpK6yG)
Design objectives
I was trying to emulate the typical "low gain amp at full volume" sound popular in stoner rock and doom metal. Notorious amp popular in that genre include the Orange OR120, Matamp GT120, Sunn Model-T, and Ampeg V4 or SVT, preferably from the 70's. All of these have a few things in common that set them apart from the Marshall/Fender crowd. Most obviously, they all have James Tonestacks, which means they do not duffer the permanent mid cut of Marshalls and Fenders. They also seem to all have rather more generously sized power supplies, giving them lots of dynamic and less sag. Lastly their preamps are not particularly gainy. If you want to get them to distort properly, you have to play them way open. That, in turn, means that a significant part of the distortion happens after the tone stack, in the phase splitter or poweramp (in some of these the tone stack is even before the first clipping stage in the preamp). It also means that it is popular to hit the front with a treble booster, lest it gets too gloomy. So these were the things I tried to emulate while keeping the design reasonably simple. More importantly than design complexity, I did not want the resultant device to have more controls than necessary and wanted the controls to be intuitive, which I often find tricky to balance with keeping the total number of controls low because it means that controls cannot be too interactive. I also wanted the thing to work from 9V to 18V single supplies, and not be excessively noisy.
Design rationale
Input buffer
Not strictly necessary but I wanted to have the option to add a buffered dry out when necessary. This also provides a convenient place to add channel switching, if one were to build this as part of a multi-channel preamp.
Main gain stage
Fairly standard stuff here, basically a gain stage with built-in treble booster. The Presence and Gain controls are interactive. Presence does nothing when Gain is at minimum, at higher Gain settings, it boosts highs with a corner frequency of around 3kHz. When gain is set higher than noon, the opamp slowly starts to clip and C5 starts cutting the highs at 7kHz. When gain is at max, the high cut starts at 700Hz, which can be partially counteracted with the Presence. If Presence is wide open at max Gain, you get quite some clipping from the opamp, which is rather mid-boosted. Opamp choice makes a difference here. I used the NJM2068 (aka JRC2068) because it gave me a bit more clean headroom and nicer clipping than a NE5532. A TLC2262 will probably sound nice too but will be more noisy. I would not bother to try a TL072, as it clips early and real nasty. I find the two controls work nicely together and are fairly intuitive despite the (on paper) complex frequency shaping.
Bass control
Essentially half a Baxandall tone stack. The bass control is placed before the main clipping stages, so that the sound can be tightened or boomified (that's not a word but you know what I mean) pre clipping. I find this an important aspect of tone shaping for the sound I was looking for. At the highest gains, bass boosting looses some efficiency but not as much as I feared originally. And how often do I want an extremely distorted sound to be very bassy? Exactly. For clean and slightly dirty sounds, bass boost effectiveness is not really influenced by the placement. Implementing this stage with a CMOS inverter makes it sound nice even when the stage itself clips. Yeah!
Clipping stages
I love the sound of CMOS-clipping in the morning. The first of the two stages has a Boost switch to go from gain=1 (well, -1 actually but here we only care about the absolute value) to open loop gain. I experimented with a second gain control pot here, but found a switch together with the existing Gain control in the gain stage completely sufficient. With Boost engaged, the distortion with Gain at about 9 o'clock picks up around the same point where it left off with Boost disengaged and gain at 3 o'clock. Wehn building this (currently it is still on the bread board), I will make the Gain pot push-pull and activate the boost with the Gain pulled. The second clipping stage has gain=1. I like having a "gainless" CMOS stage behind the gainy clipping stage because it rounds off the clipping some more due to the non-linearity of the inverters. At a gain=0, the second stage is driven into non-linearity exactly when the first one is as well, which essentially just doubles the effect. That makes for a nice smooth transition from clean to distorted. I experimented with more stages but for anything above 2 total stages I cannot hear any more difference.
Treble control
Now this one was tricky. This is the second half of the Baxandall. I definitely wanted to have the Treble after the clipping stage, else it would loose too much efficiency for high cuts on highly distorted sounds. But this stage also needed to bring the overall level down by about 6dB so itself and the following stages would not clip. I could not find a good design tool for this (as most people seem to want their baxandall to have a out-of-band gain=1), so I wrote one myself. Here is the simulated response, x-axis in Hz, y-axis in dB (labeling of the pot setting is reversed and the simulation ignores C19, sorry):
(https://i.postimg.cc/D86B9TB1/Treble74-W.png) (https://postimg.cc/D86B9TB1)
Speaker sim / output buffer
Just a 2nd order Sallen-Key bandpass with near-Butterworth characteristic implemented with the leftover half of the NJM2068. Not strictly necessary as all preceding stages already limit the bandwidth to ~20Hz-7kHz. But having this here allows easy later changes to tighten the bass or make it resonant (to simulate an open or a vented cab) by changing the ratio of R22 to R23, or make it more or less present by changing C22/C23.
The rest should be self explanatory, I hope. If not, please ask. I must say, I am really happy with how this turned out. Really nice overall sound when played straight into a neutral headphone amp as well as when fed into a bass amp. Very nice break up at the verge of clipping with guitar as well as bass. Great overdrive sound, again with bass as well as guitar. And it definitely captures the stoner/doom/sludge sound I was after. Hurray! It also sounds very good for bluesy and hard-rocky stuff. I'll try to make some sound samples but I don't have a working recording interface at the moment and I'll be super busy for the next weeks, so this may be a while. Maybe I can manage to draw up a perf or vero schematic but I cannot promise that that will be any time soon either. If anyone else wants to build this thing and add some sound samples here, I'll promise my eternal gratitude :)
EDIT: A few words on the name: I wanted to keep the unofficial naming conventions for amps, namely 1-3 letters and some numbers. A chemical symbol seemed to fit the bill. And since this was supposed to be aimed at the heavy / stoner rock crowd, the symbol for tungsten seemed most appropriate. "Tung sten" is Swedish for "heavy stone" or "heavy rock". So the name of the preamp should be written "74W" but spoken "tungsten".
Cheers and keep on rockin',
Andy
QuoteEDIT: A few words on the name: I wanted to keep the unofficial naming conventions for amps, namely 1-3 letters and some numbers. A chemical symbol seemed to fit the bill. And since this was supposed to be aimed at the heavy / stoner rock crowd, the symbol for tungsten seemed most appropriate. "Tung sten" is Swedish for "heavy stone" or "heavy rock". So the name of the preamp should be written "74W" but spoken "tungsten".
Nice work, nice schematic, nice plot, and nice post, well done. But seriously, calling it "74W" and expecting anyone to think anything but 74 Watts is a Quixotic, uphill battle. Just my 2 öre ;)
Quote...is a Quixotic, uphill battle.
But I like those. 8)
Andy
Quote from: garchoBut seriously, calling it "74W" and expecting anyone to think anything but 74 Watts is a Quixotic, uphill battle. Just my 2 öre ;)
I worried that I might have reflexively punched him in the face if I were in the same room as him during that name reveal. I would've felt terrible and would have probably apologized non-stop for several days, of course--I'm really a very nice person, honestly! :icon_razz:
I do like the name now, though. :icon_wink:
Anyway, Andy, I'm glad you designed this, I'm glad it sounds good, and I'm glad no one got hurt, but just to be safe, please promise me that you'll never label a power jack
23V. :icon_lol:
Hey, I have been dealing with enough students trying to solve equations by confusing units with variable names. But I am open to renaming it the "Tung Sten". Or maybe "Tongue Stan"?
BTW, is "Quixotic" taken as a name for a booster? Or is that a bit too on the nose?
Andy
EDIT: There, see what you made me do? I changed the title of the original post... ;)
No, don't rename it. Like I said, I actually do like the name.
Apropos of nothing:
Dibs on the "42Mo Fullrange Booster", the "77Ir Treble Booster", the "2He Octave" (unless that one already exists. I have a hunch it might), and the "SF6 Suboctaver".
Pedal name dibs is a thing, right? No? Damn!
Andy
Quote from: EBK on July 06, 2019, 04:12:29 PM
No, don't rename it. Like I said, I actually do like the name.
No worries, it's just a second name. The "74W" stays.
I'd like to see you make a germanium fuzz and call it 23Es for экасилицій (ekasilitsiy)/ekasilicon.
Need to add one more comment here:
I really like your schematic style. :icon_cool:
This looks pretty neat, and if it gets into the sounds of stoner doom I'm there with you!
I'm not getting the purpose of the two LEDs on the input, what"s going on here? From my amateur perspective if the input is more than the 2v drop of the diodes it clips the input. If I'm correct in this assumption is that useful?
Is there another effect somewhere that uses this? I'd like to hear it.
Quote from: EBK on July 06, 2019, 06:07:15 PM
Need to add one more comment here:
I really like your schematic style. :icon_cool:
Thanks! I was not aware my schematics had a distinct style. In case someone is interested, I use the "gEDA Schematic Editor". That takes care of most of the look. Then there is just a bit of prettying up in Inkscape.
Andy
Quote from: soggybag on July 06, 2019, 06:16:29 PM
This looks pretty neat, and if it gets into the sounds of stoner doom I'm there with you!
I'm not getting the purpose of the two LEDs on the input, what"s going on here? From my amateur perspective if the input is more than the 2v drop of the diodes it clips the input. If I'm correct in this assumption is that useful?
Is there another effect somewhere that uses this? I'd like to hear it.
Hi Mitchell,
thanks! Yeah, these diodes are not strictly necessary. All they do most of the time is protect the JFET from excessive voltage spikes that should not occur at the input under normal circumstances anyway. The only situation, where they actually do matter, is if you hit the front end of the preamp with a booster that delivers more than +- 1.7V or so. In that case, you get additional clipping from the diodes and still get a fairly predictable results from the Gain and Presence pots without excessive clipping from the opamp. If the preamp is run at 18V, one might want to change these diodes to blue LEDs, or a pair of back-to-back Zeners with about 5V.
Andy
Quote from: Fancy Lime on July 06, 2019, 06:17:45 PM
Quote from: EBK on July 06, 2019, 06:07:15 PM
Need to add one more comment here:
I really like your schematic style. :icon_cool:
Thanks! I was not aware my schematics had a distinct style. In case someone is interested, I use the "gEDA Schematic Editor". That takes care of most of the look. Then there is just a bit of prettying up in Inkscape.
Andy
It's mostly the neatly labeled boxes and the overall flow/width, but the font choice is cool too.
So... can we hear it? ;D
Very nice! I love the approach, the modular schematic, the use of CMOS, and the split eq. I also suspect that this might be a an effective tool outside of the intended sonic territory.
Wrong name.
You should rename it to "74W Tung Stone" preamp.
Spelled "Tung", not "Dung", he he he...
Quote from: Fancy Lime on July 06, 2019, 01:30:25 PM
Quote...is a Quixotic, uphill battle.
But I like those. 8)
Andy
the Quix-exotic would have a tilt tone control? been dibs'ed yet?
Quote from: EBK on July 06, 2019, 04:28:41 PM
I'd like to see you make a germanium fuzz and call it 23Es for экасилицій (ekasilitsiy)/ekasilicon.
I have never bothered with Ge, so far. But with that name, it is, admittedly tempting. Especially because a fuzz is exactly what should go in front of the 74W.
Cheers,
Andy
Quote from: EBK on July 06, 2019, 07:24:10 PM
Quote from: Fancy Lime on July 06, 2019, 06:17:45 PM
Quote from: EBK on July 06, 2019, 06:07:15 PM
Need to add one more comment here:
I really like your schematic style. :icon_cool:
Thanks! I was not aware my schematics had a distinct style. In case someone is interested, I use the "gEDA Schematic Editor". That takes care of most of the look. Then there is just a bit of prettying up in Inkscape.
Andy
It's mostly the neatly labeled boxes and the overall flow/width, but the font choice is cool too.
The organization in boxes is something I stole from Electrosmash. I always found that extremely useful for discussions about what does what. The "overall flow", as you call it, is also something I like in the Electrosmash schematics, so I guess mine resemble that a bit as well. I want to explain as clearly as I can to anyone who is interested what part does what and why it is designed like that and not some other way. Other people doing the same thing is what taught primarily me this whole business, and still does. I would like to contribute to educating the next generation with the same method that worked well for my own learning and Electrosmash makes a damn good job of that for many classic circuits. So I just shamelessly copy their method. :icon_wink:
The font is called Gismonda FG. It is free and can be downloaded here:
https://www.dafont.com/gismonda-fg.font
Cheers,
Andy
Quote from: Fancy Lime on July 06, 2019, 06:26:42 PM
If the preamp is run at 18V, one might want to change these diodes to blue LEDs, or a pair of back-to-back Zeners with about 5V.
Pardon me, Andy, but a pair of back-to-back Zeners clips at a level similar to Si diodes (despite their nominal voltage rating).. :icon_wink:
Quote from: antonis on July 09, 2019, 05:21:35 AM
Quote from: Fancy Lime on July 06, 2019, 06:26:42 PM
If the preamp is run at 18V, one might want to change these diodes to blue LEDs, or a pair of back-to-back Zeners with about 5V.
Pardon me, Andy, but a pair of back-to-back Zeners clips at a level similar to Si diodes (despite their nominal voltage rating).. :icon_wink:
By back-to-back I mean this:
https://upload.wikimedia.org/wikipedia/commons/1/17/Zener_Diode.svg
not this:
https://upload.wikimedia.org/wikipedia/commons/d/d7/Antiparallelschaltung_Dioden.svg
The latter, which is called anti-parallel, not back-to-back, if I am not mistaken, would indeed be the same for Zeners as for normal silicon diodes. But the former would clip at Zener-voltage + silicon diode forward drop. So about Zener-voltage + 0.7V.
Andy
My bad (english language skills), Andy.. :icon_redface:
Cheers.. :beer: :beer: :beer:
Have you tried this preamp design with your ONKOtherium overdrive pedal? I m trying to make a stripboard out of this one but thought that maybe these two free inverters could be used somewhere and looking at the ONKO it seems like a chance to have it all together. Disto+Preamp in a little pedal maybe 125n size, but maybe these 2 effects together, or are redundant or does it make it sound like mudd or boomy? Thank you for sharing your work and ideas.
back-to-back = zener+1junction drop
Quote from: sergiomr706 on July 11, 2019, 05:04:05 AM
Have you tried this preamp design with your ONKOtherium overdrive pedal? I m trying to make a stripboard out of this one but thought that maybe these two free inverters could be used somewhere and looking at the ONKO it seems like a chance to have it all together. Disto+Preamp in a little pedal maybe 125n size, but maybe these 2 effects together, or are redundant or does it make it sound like mudd or boomy? Thank you for sharing your work and ideas.
The 74W and the Onkotherium are quite similar, so I would say having both in one enclosure may be a bit redundant. The Onkotherium has a higher gain range though. So what I would do, if I wanted to use those extra inverters and get more different sounds out of the thing, is add two more stages of the same design as the first clipping stage between the main gain stage and the bass control stage. You could use two footswitches for the boost switches of those stages and get footswitchable extra gain. I haven't tried this but the result should be fairly similar to a Red Llama with one switch engaged and a Red Llama on steroids with both engaged. Lots. Of. Steroids. If you try it, let us know how it went.
Cheers,
Andy
The Zener voltage (+ a diode drop) clipper would be "inverse-series" while normal back-to-back clipping diodes are "inverse-parallel". I prefer to call inverse-series "nose-to-nose".
Stripboard, I know there are people much better skilled than me, so all suggestions are welcomed. after looking a this a couple times more I think this should work. Layout is following exactly the schematic, if it works, I ll see if space allows me and I can make something more out of the 2 spare inverters. Instead of using the spare to make it sound more distorted, could these be used as a Clean blend from Q1/ R4 junction , then use an inverter as a Highs roll off at 400-800 Hz and then make a lo fi mixer out of the other inverter and make r21/c20 the dirty output, and both signals being thrown to the speaker sim, does it make sense?
(https://i.postimg.cc/5jVZNgW9/Tungsten-74-W.jpg) (https://postimg.cc/5jVZNgW9)
Awesome! Thanks, Sergio! I hope I can find the time to trace the schematic back from the layout, one of these days. Always a good way to check for errors.
Cheers,
Andy
Very interesting. Stoner metal distortion is pretty nice to my ears. Any soundclips?
Hi there,
finally got my $#!+ together and made a sucky little demo. I am no guitar player, so no judgement, please. In fact the main reason I recently bought one and started learning to play is, so I can test pedals and make demos (that's not what I told the wife though, so: shhh!). Signal chain: Yamaha Pacifica 311, neck PU solo (P90, tone and vol full) --> Digitech JamMan solo XT --> (modified Jordan Bosstone clone, true bypass) --> 74W Tung Sten preamp still on the breadboard --> Focusrite Scarlett 2i4 --> Audacity.
https://www.aronnelson.com/DIYFiles/up/74Wdemo.mp3
I start with Gain and Presence at 0, Bass and Treb at noon, Boost off. Then I first increase Gain, then Presence, then start fiddling with Bass and finally Treble. Around 2:30, Boost is switched on, then same procedure as before. Because a regular use case for a stoner rock amp seems to be hitting it with a big ol' fuzz, I switched on the Jordan Bosstone clone just after 4:20 (by happy coincidence). Some knob-fiddling ensues (only of the 74W, the Bosstone stays the same all the time), first with the Boost engaged, then, at 5:09, the Boost is disengaged.
Cheers,
Andy