I am intrigued by the possibilities! That is a good idea you have Razzorick.
Question/comment for you and SimonB: That idea inspires me to want to build a ''tubed'' version, but as you say we need to get some decent peak to peak signals. So how about for the ''preamp/tube distortion effect'' we go for it? preamp stage v1/v2 in a 12AX7 or something, then the EB 91 (with a variable signal bias to adjust +/- clipping). I know there are a lot of tube based distortion pedals but a lot just run with low plate voltage. But a proper preamp, tone stack with tube diode clippers..well that is getting real interesting.
Who wants to start a new thread??
Question/comment for you and SimonB: That idea inspires me to want to build a ''tubed'' version, but as you say we need to get some decent peak to peak signals. So how about for the ''preamp/tube distortion effect'' we go for it? preamp stage v1/v2 in a 12AX7 or something, then the EB 91 (with a variable signal bias to adjust +/- clipping). I know there are a lot of tube based distortion pedals but a lot just run with low plate voltage. But a proper preamp, tone stack with tube diode clippers..well that is getting real interesting.
Who wants to start a new thread??
Mmm, the valve distortion pedal - got to be better right? Maybe so, maybe not, depends what you want. When I've thought about this, the place I end up is a small but fully featured push-pull valve amplifier, with a dummy load, a line out and an optional speaker socket. You can have a stomp switch if you want, but traditionally it's a pair of toggles, marked off, on and standby. The foot switches can always be put in an A/B stompbox.
For distortion purposes, there are almost unlimited options for non-linear elements and combinations of elements to put in either across the signal, or in a feedback loop. Add to that the importance of pre and post distortion EQ and there's easily more than a lifetime's worth of possible experimentation. As I said, the infinitely expandable world of...
Of course, there's no denying the 'Real Thing' appeal of tubes in a pedal, so I'm not expecting my reasoning to dissuade you from going there...though you can get some of the vibe, aesthetically, by using small incandescents as indicators, run well below max rating you get a similar glow from them, you can glue the little wire ended ones into led bezels, colour he glass with red flet pen and they look very old school.
Anyway, the EB91, as far as I can see, reading the datasheets
View attachment 6d2_EB91 - duncanamps.com.pdf
looks pretty linear to me - great for its original purpose of demodulating radio signals undistorted, perhaps not what you want here?
I'll get my coat........
For distortion purposes, there are almost unlimited options for non-linear elements and combinations of elements to put in either across the signal, or in a feedback loop. Add to that the importance of pre and post distortion EQ and there's easily more than a lifetime's worth of possible experimentation. As I said, the infinitely expandable world of...
Of course, there's no denying the 'Real Thing' appeal of tubes in a pedal, so I'm not expecting my reasoning to dissuade you from going there...though you can get some of the vibe, aesthetically, by using small incandescents as indicators, run well below max rating you get a similar glow from them, you can glue the little wire ended ones into led bezels, colour he glass with red flet pen and they look very old school.
Anyway, the EB91, as far as I can see, reading the datasheets
View attachment 6d2_EB91 - duncanamps.com.pdf
looks pretty linear to me - great for its original purpose of demodulating radio signals undistorted, perhaps not what you want here?
I'll get my coat........
Hi Simon, I had to quote you on this from the fuzzface thread, as it is the essence of a good distortion. A preamp/tube clipper distortion should do this nicely. You mention the odds only part on the second stage, and also that circuit has NFB. It is kicking back some of the odds only frequencies to the 1st stage with even/odd..you get emphasis and reinforcement of the ''evens'' that way.
I am definitely getting into that region with this soft-clip stage running out to the postclip. Interesting when run together. With the gain, bias, tone and postclip options there is potential to make very bad sounds with it (!) but if setup carefully it sounds sweet. Not to much clip (asymetical) at the op amp, reasonable gain, then play with the postclip settings. Tune out any edginess with the tone control.
Even harmonic distortion of 3d harmonic gets you 6th, 12th, 18th etc, of the 5th gets you 10th, 20th, 30th etc - you very quickly end up above audio frequencies, and even more quickly over what will actually get out of an average guitar speaker. As I recall, your circuit is doing distortion in the feedback loop, as well as outside it. The fuzzface feedback network is quite linear - it's a resistor.
If the fuzz face sound interests you, my advice is this:
Build one, in silicon, getting the bias right. Understand the issue of its low impedance loading the guitar heavily and thus cutting highs, prior to the distortion creating a lot of new ones. If the sound you end up with is too toppy, which with silicon it probably will be, experiment with small value caps across the base & collector terminals of the transistors. I usually end up with just one on Q2.
It's a great, distinctive, distortion, very different from the norm.
Whatever you do, don't try to follow in the footsteps of an approved MSc thesis I've read, on a digital simulation of a fuzzface, that contained some serious errors of basic circuit analysis, including ignoring the effect of Q1's very low base to emitter resistance on total input impedance.
When you've explored the fuzzface, let me know. As I said, distortion pedals are an infinitely expandable area. I have a lot of schematics....
Hi Turbon,
For the second build I replaced the single switch above the test diode with a DIP switch, and I have 6 clipping elements (that I tried on my first build) to choose from. I soldered them in place except for the mosfets which are in sockets. You can try any combination of diodes, LED, or Mosfets that you like (or have on hand). On the gain/drive potentiometer circuit I added a switch to drop some resistance, because my friend wanted the ability to give a mild boost to the sound.
Like SimonB said there are endless possibilities for distortion, but I tried to keep it as simple as possible while keeping some flexibility.
For the second build I replaced the single switch above the test diode with a DIP switch, and I have 6 clipping elements (that I tried on my first build) to choose from. I soldered them in place except for the mosfets which are in sockets. You can try any combination of diodes, LED, or Mosfets that you like (or have on hand). On the gain/drive potentiometer circuit I added a switch to drop some resistance, because my friend wanted the ability to give a mild boost to the sound.
Like SimonB said there are endless possibilities for distortion, but I tried to keep it as simple as possible while keeping some flexibility.
A new thread about a new pedal sounds great! im going to guess using a 12vac wall wart and a 12 to 230v/110v transformer to get some more usuable HT for the 12ax7. the EB91s could be used as clipping in feedback aswell which could be interesting with a valve. also, a heater voltage control will allow you to change the forward voltage of the diode. (say between 6 and 2v) this way you should only need 1 12ax7, but itl depend on what kind of output impedance you want, and the type of tonestack.
Simon, I agree with your last comment to the level of how I understand it. (!)
When playing with this circuit, I was impressed with the fact that people can very well detect the sequence and type of distortion that that is going on in the signal path. Some clipping combinations sounded wonky to my ears, but others were spot on. So I guess this could lead to a few other variations to the basic layout. I might try a few tweaks and/or incorporate some of those principles into a completely different design. As for the tube preamp-diode distortion thing: yes it might as well be a full on amplifier.Razzorick was looking at dropping one in a stock amp..so if anyone gets a hold of the tube and tries it let me know please.
When playing with this circuit, I was impressed with the fact that people can very well detect the sequence and type of distortion that that is going on in the signal path. Some clipping combinations sounded wonky to my ears, but others were spot on. So I guess this could lead to a few other variations to the basic layout. I might try a few tweaks and/or incorporate some of those principles into a completely different design. As for the tube preamp-diode distortion thing: yes it might as well be a full on amplifier.Razzorick was looking at dropping one in a stock amp..so if anyone gets a hold of the tube and tries it let me know please.
think i may be able to get hold on a few of these quite easily and cheap, i have got a spare 12AU7 PP amp i could build this in, but i need a new output transformer for it, its getting old and considering it just appeared one day its done a good job, though my other thinking was using an EL84 or 12k5 as a preamp tube, ive done some thinking and looking but ive just never got around to it, 12k5 is specifically designed as a 12v tube, and people have said it distorts like an EL84. Im swamped in school work at the moment though so if anyone has the ability to do this then il mroe than happily share some ideas.
Hi Razorrick! Yes a new thread is in order for that. If we don't call it a ''pedal''..
calling it a preamp or micro tube amp head it is possibly more interesting for all! As Simon mentioned, might as well add the power output with that amount of work. Can make it small enough to fit in a Hammond 1590DD size case even better! 2 to 4 W maybe? Could even have a Mosfet as power output, or use a pre-reverb transformer..Just kicking some ideas around.
calling it a preamp or micro tube amp head it is possibly more interesting for all! As Simon mentioned, might as well add the power output with that amount of work. Can make it small enough to fit in a Hammond 1590DD size case even better! 2 to 4 W maybe? Could even have a Mosfet as power output, or use a pre-reverb transformer..Just kicking some ideas around.
I had an Alembic preamp, and with both channels in series it would make any 'fenderish' distortion tone I wanted, but twiddling the knobs was never convenient. I totally seperated the 2 channel outputs, turning it into two complete fender preamp channels, all single-ended. In the first stage, I modified the input resistor network so the guitar pickup went pretty directly to the first 12AX7 grid. Next it burned off the gain in "tone controls" then recovered the gain...with the volume knob very low the "bright" switch is just a cap across the volume so it ends up with a lot of extreme treble boost (and I added a switch to vary the "bright" cap value). Then this treble-boosted signal overdrives the first stage of the 2nd channel, creating most of the distortion. Then the 2nd stage's tone controls roll off that extreme treble.
One intent is of a 'tone curve' around your distortion...kind of like the RIAA tone curve is arond the record and playback process. When the objective is to control the tone of the distortion independently of the main signal, attempts to run the distortion thru a seperate EQ and then mix in a percentage just doesn't work if the distortion really modifies the main signal. But if you want seperate control of the tone of the distortion, you can achieve that by putting the main signal thru pre-emphasis before the distortion is added, then the distortion and main go thru the final de-emphasis filtering. The main goes thru both, but the distortion only goe thru the final filtering. The result is what we used to call a creamy smooth distortion that has its irritating treble and extreme-order harmonics de-emphasized while retaining plenty of treble for main signal intelligibility. Boost treble, add distortion, cut treble = mian guitar tone is boosted & cut and sounds natural, distortion only had its treble cut.
Then I started listening more to some good blues players, Roy Buchanan, that sort of thing. These guys are often playing major against minor in question/answer suspense/resolution and also often playing clean against dirty. When they pick hard (and I mean extreme attack with a HARD pick) it doesn't get louder, it gets BITE. Like a saxophone or a vocal tract distorts when over-driven. Like a tube does pretty naturally, and compressed some like when a tube supply sags.
So I'm running this Alembic preamp like 2 fender channels in series, and a 2nd volume control on the output of each channel. So I have 5 volume controls in this gain line (including one on the guitar). I always run the guitar full-volume into the first tube stage, so that volume control on the guitar is only for 'swell' effects when I turn it while picking. I pretty much always have the first channel's volume control low and the bright switch on because that makes the treble boost. I always run with extreme treble boost at the start, because I can always reduce the treble later. For a really nice clean bright sound, I just run the 2nd channel more flat, all tubes running in their linear range. Turn up the later volume controls and maybe turn down the last one, and get some intense tube distortion.
So...too late to make a long story short...I got a dual-pot Ernie Ball footpedal, and replaced the dual-audio taper pot with a dual-linear and added resistors to make the taper more like an audio-taper, except I made one pot 'reverse taper'. The idea was to make a footpedal that, when pushed forward, reduces the volume of a later stage (think master volume) but increases the volume of an earlier stage. Plenty of intial trim, range, and taper pots to adjust the pedal operation. Then I had a second more normal volume pedal at the output (actually later after the power amp buffer). So the first "distortion" pedal didn't change volume much, it changed how hard you have to pick to get the tone to 'cross the line' from smooth to dirty. This is for highly emotive playing with exceptional 'feel'...and instant ability to match to any guitar, strings, pickups, and pick.
Of course, this is all far divorced from stomp-box distortion devices, which are kind of the opposite. They tend to use a lot more compression with a different intent. Here their objective is a little like a computer's 'spell-check' but more like "pick check"...it makes each note the same volume and same amount of distortion, regardless of whether it's a trill, hammer-on, pull-down, fingerboard tap, etc. It corrects every attack, making them all the same. Less emotive perhaps, but easier to play those Van Halen or metal tricks, and incredibly easy to get weird harmonics if you use 2 pickups out of phase (emphasizing what's different between the two pickups).
Now I have two small tube stomp-boxes, each of which is fundamentally a Fender channel, and I'm in the process of wiring them in series and installing similar pedals. They originally came with a small output transformer and speaker as an inductive dummy load!
I use the Ernie Ball string-type pedals.
I guess my point is that it takes 4 tube stages to make a nice preamp IMHO; what usually makes 2 channels in parallel works much better in series. Then it will do nice clean or dirty.
Just my opinion. Oh, BTW, know what Jerry Garcia used? Alembic preamp with both channels in series...
One intent is of a 'tone curve' around your distortion...kind of like the RIAA tone curve is arond the record and playback process. When the objective is to control the tone of the distortion independently of the main signal, attempts to run the distortion thru a seperate EQ and then mix in a percentage just doesn't work if the distortion really modifies the main signal. But if you want seperate control of the tone of the distortion, you can achieve that by putting the main signal thru pre-emphasis before the distortion is added, then the distortion and main go thru the final de-emphasis filtering. The main goes thru both, but the distortion only goe thru the final filtering. The result is what we used to call a creamy smooth distortion that has its irritating treble and extreme-order harmonics de-emphasized while retaining plenty of treble for main signal intelligibility. Boost treble, add distortion, cut treble = mian guitar tone is boosted & cut and sounds natural, distortion only had its treble cut.
Then I started listening more to some good blues players, Roy Buchanan, that sort of thing. These guys are often playing major against minor in question/answer suspense/resolution and also often playing clean against dirty. When they pick hard (and I mean extreme attack with a HARD pick) it doesn't get louder, it gets BITE. Like a saxophone or a vocal tract distorts when over-driven. Like a tube does pretty naturally, and compressed some like when a tube supply sags.
So I'm running this Alembic preamp like 2 fender channels in series, and a 2nd volume control on the output of each channel. So I have 5 volume controls in this gain line (including one on the guitar). I always run the guitar full-volume into the first tube stage, so that volume control on the guitar is only for 'swell' effects when I turn it while picking. I pretty much always have the first channel's volume control low and the bright switch on because that makes the treble boost. I always run with extreme treble boost at the start, because I can always reduce the treble later. For a really nice clean bright sound, I just run the 2nd channel more flat, all tubes running in their linear range. Turn up the later volume controls and maybe turn down the last one, and get some intense tube distortion.
So...too late to make a long story short...I got a dual-pot Ernie Ball footpedal, and replaced the dual-audio taper pot with a dual-linear and added resistors to make the taper more like an audio-taper, except I made one pot 'reverse taper'. The idea was to make a footpedal that, when pushed forward, reduces the volume of a later stage (think master volume) but increases the volume of an earlier stage. Plenty of intial trim, range, and taper pots to adjust the pedal operation. Then I had a second more normal volume pedal at the output (actually later after the power amp buffer). So the first "distortion" pedal didn't change volume much, it changed how hard you have to pick to get the tone to 'cross the line' from smooth to dirty. This is for highly emotive playing with exceptional 'feel'...and instant ability to match to any guitar, strings, pickups, and pick.
Of course, this is all far divorced from stomp-box distortion devices, which are kind of the opposite. They tend to use a lot more compression with a different intent. Here their objective is a little like a computer's 'spell-check' but more like "pick check"...it makes each note the same volume and same amount of distortion, regardless of whether it's a trill, hammer-on, pull-down, fingerboard tap, etc. It corrects every attack, making them all the same. Less emotive perhaps, but easier to play those Van Halen or metal tricks, and incredibly easy to get weird harmonics if you use 2 pickups out of phase (emphasizing what's different between the two pickups).
Now I have two small tube stomp-boxes, each of which is fundamentally a Fender channel, and I'm in the process of wiring them in series and installing similar pedals. They originally came with a small output transformer and speaker as an inductive dummy load!
I use the Ernie Ball string-type pedals.
I guess my point is that it takes 4 tube stages to make a nice preamp IMHO; what usually makes 2 channels in parallel works much better in series. Then it will do nice clean or dirty.
Just my opinion. Oh, BTW, know what Jerry Garcia used? Alembic preamp with both channels in series...
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Cyclecamper, that is a cool solution to the setup. That is about what I experienced when playing with these circuits controls. The bias control in this soft clip changes the '' crossing line'', and interacts very closely with the gain drive. At mid point on the bias there is practically no distortion from that section. As you move the bias away you can hit mild distortion, but you have to play the notes harder to get it..it only bites when you play hard..if you soften up the playing it cleans up. But then you can add more gain and you don't have to play it as hard to get that same bite.
Hi Cyclecamper, I guess this starts to become a question of personal taste as to where and how much clipping happens. The reason I built up this soft clipping pedal with a few options was to experiment a bit with the sequence and type of overdrive that could be created. The asymetric clipping is adjustable on the op-amp NFB, and plugged into the input of my tube amp I just give a little bit of either positive or negative clipping and tend to dial up the gain. That setting sounds IMHO more natural with the tube amp,and keeps a lot of headroom. For a solid state amp (on the clean channel) I could bring in more of that soft clip, and/or post clip to get some more drive.
Tube version softclip
Hi Razorrick, I think that through our discussions and your idea about doing this in a dual diode tube version is brewing up some ideas , or is it the beer(?!) talking..
So I have been pondering the setup of a dual triode,2 stage with the dual tube diode in between. There could be a control to bias the diode clipping points to vary asymetry, adjustable filter, gain/drive on first stage, and adjustable output volume. That would follow the same layout as the original SS version of the soft clip.
You were thinking about using a low voltage triode version, so I may try this with a 12AX7/7025, run off a regulated external 12VDC or perhaps AC supply. I will probably build up in a slightly bigger enclosure at least for ease of prototyping. This setup could be run as a <<hot channel preamp>> for a single channel tube amp or driving an SS amp.
It would be interesting to compare how setups sound:the low voltage triode, pentode and higher voltage triodes.
So let me know if/when you want to start the new thread..will get some preliminary ideas sketched out
Hi Razorrick, I think that through our discussions and your idea about doing this in a dual diode tube version is brewing up some ideas , or is it the beer(?!) talking..
So I have been pondering the setup of a dual triode,2 stage with the dual tube diode in between. There could be a control to bias the diode clipping points to vary asymetry, adjustable filter, gain/drive on first stage, and adjustable output volume. That would follow the same layout as the original SS version of the soft clip.
You were thinking about using a low voltage triode version, so I may try this with a 12AX7/7025, run off a regulated external 12VDC or perhaps AC supply. I will probably build up in a slightly bigger enclosure at least for ease of prototyping. This setup could be run as a <<hot channel preamp>> for a single channel tube amp or driving an SS amp.
It would be interesting to compare how setups sound:the low voltage triode, pentode and higher voltage triodes.
So let me know if/when you want to start the new thread..will get some preliminary ideas sketched out
i think a 12au7, or better yet a 12u7 would be better for 12 volts. if the diodes were used in a typical shunt to ground configuration, a 10k pot with each side on anode of one, cathode of the other and wiper from a 470k "headroom" pot. might be quite good, with NFB gain control on the second stage using a 2.2M log pot. a starting point maybe?
Yes for a 12 volt supply I would go with those tube options. Good starting point definitely.
There are a few things I was thinking of, too. Diode anode on grid, cathode tied to variable pot to cathode bypass network of triode stage, then other diode shunting off of output of that stage/grid of second stage..well lots of different things to try anyways!
There are a few things I was thinking of, too. Diode anode on grid, cathode tied to variable pot to cathode bypass network of triode stage, then other diode shunting off of output of that stage/grid of second stage..well lots of different things to try anyways!
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