Here's something incorporating a couple of circuit snippets I have been meaning to build for a while:
It uses a bootstrapped BJT buffer (think 'Cornish buffer' or some of Gus' designs), but I have made the input impedance adjustable by playing with the bootstrapping. The Zin control might be useful to some, but is quite subtle in many cases and could be set with an internal trimmer, or the pot replaced with a 10k resistor and C2 taken from Q1 emitter.
There is a fair bit of hype surrounding the Cornish buffer. I can't say that it has changed my world, but it works nicely, has high enough impedance for our needs (perhaps excluding a piezo) and is fairly bulletproof.
The active 'tilt' control is similar to that used in some '70s Quad preamps and the Diamond compressors. The version I started with came from Rod Elliot's (ESP) page here (Fig 20):
http://sound.westhost.com/articles/eq.htm
I added 2 additional caps to roll off extreme bass and treble (C9 and C12, respectively) - compare top and bottom frequency response below. The treble roll-off is definitely recommended, as it gets quite hissy otherwise when turned all the way up (as one would expect with a 20 dB treble boost). For less roll-off, reduce C12 to 1n5 or 1n.
I am not sure if this control would be very useful for subtle Hi-Fi EQ'ing, but I like the tilt control as a guitar and bass effect. The crossing (0 dB) frequency makes more of a difference than I was anticipating, so is worth experimenting with and/or making switchable, as is the case in the bass version of the Diamond compressor.
I will try and get sound clips up this week and will be building one of these as a bass preamp with switchable bass cut (C5) and crossing frequency - probably 3 options each via on-off-on switches.
(https://dl.dropboxusercontent.com/u/11996927/Tilt_Preamp.png)
'view' for larger version
Simulated frequency response with Cx = 10, 15, 22, 33, 47, 68n.
Top: Tilt section with C9 and C12 removed.
Bottom: Circuit with C5 = 1u.
(https://dl.dropboxusercontent.com/u/11996927/tilt.jpg)
'view' for larger version
Very nice Sam.
Reminds me of the fa1 without the F.
I'll try this as I really like the fa1.
I like the tilt too.
What's the reason for the bias 22k 27k.? Guess its running at about 6v
Why the 5523 and not tl072?
Thanks for sharing
QuoteI like the tilt control as a guitar and bass effect.
me three
Quotein some '70s Quad preamps
those Quad amps sound sweet!
Thanks Rich.
Had to look up the FA1, and yes the same general arrangement - 2 inverting op-amp stages with a transistor buffer up front for sensible input impedance.
Putting the level control before (rather than after) an active EQ makes sense as you can turn the gain down to prevent the EQ stage from clipping.
If you don't want a level control that can go below unity gain, and you don't mind an effect that inverts the signal polarity, then you could replace Q1 and IC2A with a non-inverting op-amp with variable gain.
>What's the reason for the bias 22k 27k.? Guess its running at about 6v
Gives Q1 a bit more headroom - collector should sit somewhere near half supply this way. IIRC, it might help with the op-amp headroom too, as some of the usual suspects can swing closer to the + rail than the - rail.
>Why the 5523 and not tl072?
TL072 is a fine choice too, but I like the NE5532 and the tilt control can work the op-amps pretty hard, so the extra grunt from the 5532 won't hurt.
>me three
Cool. Am not too sure how well know this control is, so good to hear that I am not alone.
>those Quad amps sound sweet!
Never heard one in the flesh, but they are certainly a very nice piece of kit.
another cool samhay project...looking forward to hearing clips.. 8)
I have used that circuit in a flatline type compressor (vactrol based) and put the tilt control after the compressor part. Pretty happy with how it works.
I got the idea from a commercial compressor (diamond ) - a quick google search shows they use it in a EQ pedal too
Andrew
Found this/your 'tilt'-circuit last week on the interwebs (somewhere) and breadboarded it for a Tone-knob on a lm386 amp.
Fiddeled with C10 and C11 to chang the 'tilt'-point from 1Khz to 640 Hz.
These changes were very very subtle for guitar. It didn't alter the frequencyresponse as much as I had hoped (or not as dramatically as I had anticipated). Opamp was a 4558.
Thought it would have a better use in a TS-circuit ;).
But it is an interesting and simple one-knob tonecontrol without 'gain-loss' like you would have with a Big Muff toneknob.
Seems like a good idea to use this tonecontrol Samhay.
Quotethose Quad amps sound sweet!
And they last a lifetime if you take care of them.
I still use a 303 , 405 and a Quad 33 preamp. In the poweramp I put new powersupply caps.
Had to make some adjustments fot the smaller size of those electrolytics nowadays.
Alf
Andrew - It was the various internet chatter about the Diamond compressor's EQ control that got me interested in this design again.
I thought I had forgotten about their EQ pedal, but did think about adding a mid range boost/cut, so it was probably lurking somewhere in my subconscious.
diydave - it have been playing with setting the crossover frequency / pivot (just looked at the Diamond Boost-EQ demo) frequency quite low - 200-300 Hz - for bass. I found that this makes some difference, but it may be in conjunction with the bass and treble roll-off filtering I have added.
One reason I would like to build this is to get to know it better - if switching the crossover frequency doesn't make much useful difference, then I will know for next time - and post my thoughts.
Also, the version of the tilt control I am using is slightly different to the version that pops up in most searches - it same generally topology and principle, but different implementation and component values - and I have only seen it on the ESP site. Which version did you try?
Alf - thanks.
Not quite sure (since I'm at work for now), but I think the filtercomponents were 2k2 and 22n. The other resistors and pot were the same. Where I got it from... no clue at all. It wasn't from ESP, and I can't seem to find the site.
I just copied the image to my harddrive.
To change the pivotfrequency, I switched between 22n and 33n filtercaps. Before breadboarding, I simulated it in LTspice (which I saved, so I can look this up).
Circuit was simpel: a non-inverting buffer/boost followed by the tilt going into the lm386.
I found this while searching for tilt eq
http://www.edn.com/Pdf/ViewPdf?contentItemId=4368935
im half way through my build straight to perf just got the tilt to do.
wow - you don't muck about Rich.
I have seen the linked article - it's a nice read.
Have you decided which crossing frequency to use for the tilt? If not, you could socket the caps and play...
The plan is to socket some caps it's an experiment build I want to know what it sounds like. 😃
If imagine you could mess with component values a but to get something like a Big Muff's mid scoop in the center position. Could probably get a bit if mid boost there if you prefer. I'm sure there's also a way to get more (or less) overal gain from it, but it makes me dizzy looking at the schematic so I couldn't tell you how. :(
I had a stupid idea a while back for a nasty distortion thing based on the tilt control. I never saw this in my "research", but I did find that a single pole filter like this wasn't quite steep enough to get what I was shooting for.
Hey Sam. Cool project, as always :)
I did something similar a couple of years ago, but without the input buffer.
http://www.parasitstudio.se/uploads/2/4/4/9/2449159/active_tilt_eq_pcb.pdf (http://www.parasitstudio.se/uploads/2/4/4/9/2449159/active_tilt_eq_pcb.pdf)
I found the most use of the tilt EQ with the center frequency as low as 125hz.
I have about 50 fabbed PCB's for mine laying around. Was going to sell them in the webshop but I never bothered.. :P
ashcat - You can certainly unbalance the tilt control so that it is not flat at mid position, but I'm sure that it would be amenable to adding a mid scoop - will have a play.
Conceptually, the tilt circuit is not so hard to understand if you think about how it works at each extreme of the tilt pot and either side of the crossing frequency - i.e. when 2 of the 4 'legs' of the filter have much higher impedance than the other two.
Freppo - cool circuit, but isn't yours a mid boost/cut? It looks like the mid band from the old TL082 data sheet 3 band active tone control example.
> isn't yours a mid boost/cut?
Yes, but "mid" may be defined by capacitor choice to be 64Hz to 4KHz. For guitar, that is "anywhere". A 64Hz choice is clearly a deep bass bump; 4KHz will boost-cut the string-zing and ice-pick.
All done and it sounds good too. Thanks Sam
I dont have any C10k in stock so i used a B10 for Zin. might just be me but i cant see that it adds anything to the circuit when turning it. Maybe I'm not listening to what i need to listen to, hence why i cant see why its there. Unless its for active/ passive pups?
Next time i'm thinking just make a voltage divider with 2x 4k7s
I prefered the bigger caps sizes for C10,C11
I tried 82nf range to 10nf.
my favorites are the 68nf or 47nf
having said that all testing done at low volume (its the middle of the night right now) with a small noisy cricket amp. Not ideal but needs must.
And my test measuring stick (ears) are not what they used to be.
This is a really effective tone stack. I really like it. One knob, keeps it simple. less box drilling.
i will bread it with a TL072 and see how it fairs. for future use in other circuits.
Brilliant thanks Sam
I think Dead Astro will like this stack.
> i used a B10 for Zin. might just be me but i cant see that it adds anything to the circuit
Sam Hay's plan combines *two* features:
1) variable Z buffer
2) tilt EQ
Either could be used alone.
There may be some musical synergy, with Tilt to shift highs/lows balance and Zin to zing-up/down the topmost half-octave of naked guitar pickup, giving two actions and many more overall shapes.
It is possible that even right off a guitar, the lowest input Z (100K) has hardly any effect.
Just for jollies, tack 5K across R3. Now Zin goes from ~~500K to 5K. 5K should suck all the zing and half the mids/lows out of a naked guitar. (May do "nothing" if there's already a buffer or other active stage before; may just suck signal with a hi-Z source such as many pedals' output volume pot.)
I love jollies. I'll try that thanks.
> isn't yours a mid boost/cut?
>>Yes, but "mid" may be defined by capacitor choice to be 64Hz to 4KHz. For guitar, that is "anywhere". A 64Hz choice is clearly a deep bass bump; 4KHz will boost-cut the string-zing and ice-pick.
Quite right - I should have known better than to use loose English - I guess it is better to call it a band pass/cut filter?
In any case, it is quite different to a tilt EQ unless you put it at either extreme of the audio band where you can't hear one side of the mid-band frequency.
>There may be some musical synergy, with Tilt to shift highs/lows balance and Zin to zing-up/down the topmost half-octave of naked guitar pickup, giving two actions and many more overall shapes.
That's the idea.
>Just for jollies, tack 5K across R3. Now Zin goes from ~~500K to 5K....
That will certainly give you more milage, at the expense of less maximum input impedance. If you do this, you may want to increase C1 as it will start to roll off signifcant bass at higer Zin settings.
PRR - I have always used roughly equal value resistors for bootstrapping. I guess this is not as important as I thought?
> roughly equal value resistors for bootstrapping. I guess this is not as important
It's complicated.
In this case, if it works with 100K+100K, it will work with one reduced to 5K (and re-considering that coupling cap as you say!). That's a hasty-hack to show it DOES give variable input impedance-- get the low limit so low that it is sure to suck. I doubt anybody would ever want 5K input in a guitar-chain, but Kipper is smart enough to realize that if 100K does little, and 5K is too much, some in-between value may be interesting.
> roughly equal value resistors for bootstrapping. I guess this is not as important
It's complicated.
OK. First you figure the maximum base resistor you can tolerate.
In this case you aim for nearly 4V across the 10K emitter resistor, being nearly half the total 9V supply. (You actually want emitter near 4.5V if no load, and near 6V since R5 10K is similar to emitter resistor 10K... but that demands another bias voltage and our signal levels don't require all that headroom.)
{EDIT} I just noticed the 22K:27K Vref divider. So Vref is close to 5V and all else sits half-Volt higher than I ass-umed.
If you make base resistor hFE higher (say hFE=100 then Rb=1Meg), base resistor drops as much voltage as emitter resistor, 2V on each. We'd rather lose less in Rb. 200K is less than 1Meg. Also hFE is likely to be >100. With 200K we will have about 3.3V at emitter(?), 1.6V peak neg swing, fine. {EDIT: 4V at emitter, 1.8V peak swing}
Now we want to drive the base resistor with emitter (or emitter-pot) signal. If we don't know the external source impedance, we must assume it may be very low. What place on Rb makes the easiest load on the emitter network? 10% makes 18K. 50% makes 100K. 90% makes 18K (to external source). As 18K is not-small compared to the ~~10K emitter network, and 100K is larger and pretty large, we DO see that "roughly equal value resistors" is an optimum when the follower does not have huge current gain.
What difference does the current gain make? Replace Q1 with a unity-voltage-gain '5532. The input bias current may be similar, in the general area of a microAmp. But <1uA input to a '5532 can make >10mA output, "hFE" above 10,000! More to a point, Q1 with 10K under it should not be asked to drive another 10K, while a '5532 can easily drive <1K with 0.999 gain and 0.01% THD. So with '5532 you may still want total input DC resistance in the 100K-200K range, but R4 can now be reduced even to 1K (C2 needs to be larger for full effect to bass) and R3 can be 199K. That only cuts your input offset in half, and throws a heavy load on the buffer, but it will work. You may decide it works just as good with R4=10K and R3=190K (now C2=10uFd is fine, and pennies cheaper than a 100uFd).
I do wonder (personal taste) if it is "too clever". 1980 was long ago. We have "better" buffers than a single NPN. In fact if there were triple-opamps you probably wouldn't consider Q1? Throw a TL07x in Q1's spot, bias with 10Meg, then just put a dumb 1Meg audio pot at R1 to set an input impedance. The intended action is "obvious" to techs who come after you (or you, when you forget what this is supposed to do). Keeping it stupidly simple is never a bad idea.
One extra-minor issue with the bootstrap and pot: as you turn "Z(in)" there's a DC shift which couples into the audio path. Thump. At guitar-level, perhaps THUMP; though Kipper didn't complain. And it isn't meant to be a mid-song adjustment. There's no DC in the wiper so it should not zap the pot track. The e-cap polarity is consistent and correct.
"but Kipper is smart enough to realize that if 100K does little, and 5K is too much, some in-between value may be interesting."
I'll take that as a compliment.
I might not be the smartest cookie in the jar when it comes to EE but I'm having fun and learning bits as the need arises.
I'll take that.
There IS some kind of cross over point on the Zin pot that is doing something funky. Even If i didnt report hearing it, it's there.
Havent had time to experiment with the 5k yet.
Thanks Paul
> but that demands another bias voltage and our signal levels don't require all that headroom.
I did/am considering that - it only costs an extra R and C after all.
> With 200K we will have about 3.3V at emitter(?), 1.6V peak neg swing, fine. {EDIT: 4V at emitter, 1.8V peak swing}
Not bad - SPICE says 4.2 V at emitter when R3 = R4 = 100k. With load R5 = 10k, bottom of waveform clips at about 2.1V, giving 2.1V peak.
> What place on Rb makes the easiest load on the emitter network?
Ah, the light bulb moment - thanks.
> What difference does the current gain make?
Q1 has a fairly heavy load via R5 (which I am loath to increase, as this would bump up the volume pot resistance), so the current gain is quite a long way from where we could get with an op-amp.
and
> I do wonder (personal taste) if it is "too clever". 1980 was long ago...
You're quite right (although how long ago 1980 was is probably relative) - if I had a spare op-amp, I would have used it.
Alternatively, I could have used a FET at Q1 and used the same trick with variable pull-down or gate resistor.
Edit:
> One extra-minor issue with the bootstrap and pot: as you turn "Z(in)" there's a DC shift which couples into the audio path.
The DC on the pot wiper? Yes this will shift, but the next stage is not DC coupled, so I would imagine you would have to turn pretty fast to cause a thump - I will give it a try. I figured this was the lesser evil of most other options - varying the pull-down resistance aside - as it does not change the Q1 bias.
> There IS some kind of cross over point on the Zin pot
It works much better with a reverse log taper pot. If you don't have one, try a log pot and remember that it works backwards.
> One extra-minor issue with the bootstrap and pot: as you turn "Z(in)" there's a DC shift which couples into the audio path.
The DC on the pot wiper? Yes this will shift, but the next stage is not DC coupled, so I would imagine you would have to turn pretty fast to cause a thump - I will give it a try. I figured this was the lesser evil of most other options - varying the pull-down resistance aside - as it does not change the Q1 bias.
OK - turning the Zin knob does cause a thump. It is not loud, and is low frequency, but I have a PIC VU(ish) meter hooked up to the output of the circuit and you can definitely see something, especially if you quickly pan from min to max.
Not a game changer, but if you don't find the control to be very useful, one more reason to leave it out and/or make it an internal trimmer.
Finally got round to building this and here's the vero layout it used.
It's not boxed yet, but I got it to work, so it is somewhat verified.
(https://dl.dropboxusercontent.com/u/11996927/Tilt_Preamp_vero.png)
(click for larger version)
If anybody is interested in building it without the Z(in) control, I have a layout I can post for this too. It is largely the same, so should work ok. Edit - see next post
The white wires show the points you can add off-board switching of the tilt crossover and/or bass cut frequency. I have used on-of-on DPDTs to switch both. Edit - layout updated to show how I did this with a daughter board. It probably needs further explanation, so ask if interested.
And here's the (not entirely verified) layout for a version without a Z(in) control - it is set to max impedance.
(https://dl.dropboxusercontent.com/u/11996927/Tilt_Preamp_vero_no_Zin.png)
(click for larger version)
I have a verified Pad per hole layout too.
Love this one Its right up my street. Thanks Sam
Excellent - glad like you like it Rich.
Do you find the Z(in) control useful and did you make the bass cut and/or crossover frequency switchable?
Its been a while since I built it, I'll revisit it. I did include the Zin pot and tilt and level pots.
i didnt make the x over freqauncy switchable. I'll send you the layout for approval.
> didnt make the x over freqauncy switchable.
Probably a good choice - the wiring was not much fun on my build.
Hope this works.
edit 2
(http://i.imgur.com/AYJwl0f.jpg?1)
Of a fashion.
Can you edit the picture to remove the white space? Edit - apparently yes. Thanks Rich, looks good.
And finally, here's my finished product:
(https://dl.dropboxusercontent.com/u/11996927/Tilt_Preamp_face_photo.jpg) (https://dl.dropboxusercontent.com/u/11996927/Tilt_Preamp_guts_photo.jpg)
Don't look too close or the wonky drilling and the wee mistake in the labelling of the crossover frequencies will make me blush.
The obvious mission creep added a pic-based VU meter. I'm still tweaking the code, but it does a pretty decent job of full-rectifying the output and doing a cheap RMS or peak detection calculation, running at about 20 kHz.
As for the preamp, there is a lot of wiring and the jury is still out on whether the switchable crossover frequency and variable input impedance is worth the effort. The bass cut control (switch) works nicely and is a keeper. The actual tilt control is quite lovely and worth a try.
Quote from: samhay on April 19, 2016, 01:31:42 PM
Don't look too close or the wonky drilling and the wee mistake in the labelling of the crossover frequencies will make me blush.
Looks OK from over here, Sam. Only now I can't reach the computer keyboard... ;)
Yep - generally once you are standing over the pedal it doesn't matter too much. Except, I have 10 bright LEDs to remind me that I can't drill 10 holes in straight line.
That said, I only just looked at the photo properly and realised that the skewed perspective from the way I took the photo makes some of the mistakes look better, and others worse. The LEDs are at least roughly parallel with the bottom of the box, albeit a wee bit scattered about that line.
Marc - this works quite nicely with my fretless bass....
It's a passive 4 string, but the bass cutoff frequencies were designed with 5 string bass in mind. The 580 Hz crossover frequency is probably most useful when you turn the bass up quite high.
Wow
Is that a 125B stuffed to the gills?
Nice work Sam. :)
1590B stuffed to the gills.
The LEDs and associated resistors are on a daughter board under the main one and the extra caps and pull-down resistors for the bass cut and crossover frequency switching are on another (vertical) daughter board connected to the 3 pots.
I have decided to keep the next few projects simpler.
Quote from: samhay on April 20, 2016, 03:28:33 AM
Marc - this works quite nicely with my fretless bass....
Useful to know - thanks Sam. Perhaps another one for the backlog! :D
Nice tight build Sam! Happy to see the jacks on the back of the box, the anti-turn holes for the pots & switches, and those LED holes aren't bad looking. Is that etched or a waterslide or some fancy calligraphy? It looks good 8)
Thanks Russ.
If it's worth building, it's worth building something that will last.
The labelling is a toner transfer.
looks great sam...very nice :icon_cool:
ive been using toner transfers a bit lately....being lazy and not etching
but when its just for me toner transfer/clearcoat is more than adequate.. 8)
nice quick way of labelling.. ;)
Thanks Rob.
Necropost to re-post pictures that disappeared thanks to Dropbox's purge.
Apologies as some of these are quite large files (~1M). You should be able to see larger versions by clicking on them/'viewing' image in a new page/tab.
(https://i0.wp.com/samdump.files.wordpress.com/2018/04/tilt_preamp_schematic.jpg)
(https://i1.wp.com/samdump.files.wordpress.com/2018/04/tilt_preamp_face_photo.jpg)
(https://i2.wp.com/samdump.files.wordpress.com/2018/04/tilt_preamp_guts_photo.jpg)
(https://i2.wp.com/samdump.files.wordpress.com/2018/04/tilt_preamp_vero.jpg)
(https://i0.wp.com/samdump.files.wordpress.com/2018/04/tilt_preamp_vero_no_zin.jpg)
(https://i2.wp.com/samdump.files.wordpress.com/2018/04/tilt.jpg)
QuoteNecropost to re-post pictures that disappeared thanks to Dropbox's purge.
Apologies as some of these are quite large files (~1M). You should be able to see larger versions by clicking on them/'viewing' image in a new page/tab.
It's funny how thing like this get lost and found.
Good thing we have got lots for heads on the forum to fill in the cracks.
These pictures were never lost, just hiding.
Where I've put the pedal is another matter - it might be hiding too. Nice to be reminded to pull it out and have a play.
Another necropost here.
I am about to build this circuit , has anyone built it ? So far I have spotted a mistake in the layout (apparently). According to the schematic it's input to R1 (10M).
As per the layout, Input goes to R2 (1K) and then into R1, so I stopped there....
Yes, I've built several using the posted layouts.
While placing the input resistor before or after the pulldown resistor is not entirely equivalent, it makes very little difference, so I moved to to make the layout cleaner.
As with any filter, I suggest you breadboard it to tweak frequencies to taste. I also wouldn't suggest you build the fully featured version as this is overkill.
I would stick with a single tilt centre frequency, keep the switchable bass cut, and set Zin to max (i.e. you don't need the pot). This way it's 2 pots and a switch. Without a few tweaks to the layout you could fit it in a 1590A if you were so disposed.
Hi Samhay, thanks a lot for the answer, and for posting this circuit !
I will build the simple version. I will use it in front of a Marshall JVM410HJS to clean some of the bass frequiencies before the distortion, to make it palm-mute friendly. It will be my "tight" pedal.
No problem.
Good luck, and let us know how you get on.
I think I found a couple more issues, since I've been trying to debug for a while.
According to the schematic, center lug of the Tilt pot goes to pin 6 of the opamp. In the layout it goes to pin 2 of the opamp
Also, Level 1 and 3 should go to opamp pins 2 and 1 respectively. In the layout, Level 1 and 3 go to opamp pins 6 and 7 respectively.
Tilt 1 should also be connected to R7, but it isn't in the schematic....
I will try to redo the layout since I am very interested to finalize it..........
I guess I switched IC1A and 1B in the layout as pins 2 and 6 are both inverting inputs and pins 1 and 7 are outputs. As long as pins 3 and 5 are also switched (or in this case connected to the same point) then it's not a problem as the 2 op-amps are equivalent.
Tilt 1 goes to Cx + R8 (1k) and C9 + R7. I've switched the order of C9 and R7 in the layout* - R7 is the 10k top right in the layout (I assume you can see R7 in the schematic above "TILT CROSSING"?).
*the order of components in series can be switched as long as nothing is connected between them.
Similar to a DOD FX-10.
Broadly, but the filter topology is different, which is the centre piece of this design.
Sam, I like that input stage with the impedance control. I may steal that from you to use in some future project! :icon_mrgreen:
regards, Jack
The variable Input Z is really cool. Would somebody of you more experienced folks here mind explaining to me how it works? I don't really get it yet. It would be great to have a simple multi-purpose preamp with adjustable input Z for use with guitars, mics etc.
Thanks heaps!
Jack, I'm sure I've borrowed a few ideas from you over the years, so please be my guest.
Iefes. The input impedance is 'bootstrapped'. I'm sure Rod Elliot can explain it better than I can:
http://sound.whsites.net/articles/high-z.html