PhAbb Cruize Control

[phatt]

The Aim,
Build a circuit that captures the magic dynamic response of old Valve amps.
I'll save you the chatter of a novice trying to explain the endless detail with a very good example of this dynamic compression effect;



Notice how Joe B only used the on-board controls of a stock guitar with passive electronics with stunning results. Sadly Joe fails to tell the viewers that this
only works with specific types of Valve amplifiers like ye old 5E3 fenders. Few SS power amplifiers can do this trick, including some Valve rigs.
Even clever dirt boxes lack the dynamic spread because they can't reproduce the broad compression range of old saggy cathode biased Valve rigs.

For those that may not know, the type of amplifier demonstrated in the video has a major design flaw (no clean headroom) which is the main reason for the effect. So with the amplifier volume up past mid point and a low incoming signal the Amplifier sounds clean but the moment you dial up the guitar volume the amp blooms into a fat O-drive sound while the actual sound level (SPL) does not jump by a huge amount.
Bingo, a very natural compression allowing you to use the guitar volume to great effect.

I knew I needed some kind of compressor but I'm yet to find a compressor that works well with distortion, they tend to kill off any chance of dynamic Odrive.
Go up market for the studio units and it gets even worse, Of course they have a place there but too clinical for El guitar.
So what if I build a really Bad compressor that distorts like crazy while also compressing. Anyway after a lot of head scratching and false starts I have a test circuit up and running.

To my ears at least, there is No Attack to Comp-phut the signal while the Release is evident after a long held power chord but you will be hard pressed to notice it.

Worth note;
Joe's rig only works at one volume setting on the Amp and that will likely be quite loud. This circuit overcomes that limitation as your master SPL is now set via the main poweramp so you can still have endless Odrive at low Volumes.

Circuit notes;
The big breakthough was when I realized the diode section needs a fair bit of grunt to make it sing so U3&4 double the current. I was then able to open the bottle of scotch.

You can delete VR1 but you may wish to hear how well the effect works. Backing off VR1 backs away from full effect but you will start to loose the
magic of the circuit and loud becomes a lot louder which defeats the purpose. I tried other Diodes 1N34 but it then squashes too much and no longer sounds convincing. Play around with input values to suit your setup, this works fine with my setup.

If any interest I'll try to get a sound sample up but at this time of year it's hard to find a quite moment to record.
Merry Xmas to all, Phil.

[smackoj]

very nice work Phil. what op amps are you using for U1 thru 5? Can you post a picture of the board please?

[The G]

Thanks, Phil!
What's the reason for U2 and U4 repeaters? AFAIK, it could use just U3.
Also, the R1-R2 divider lets only ~9.1% of the signal to pass (side info: U1 will clip when the input signal goes higher than ~2.8Vpp, depending on the op amp). Why do you divide the input signal (R1-R2), only to amplify it in the next stage (U1)? Wouldn't it be simpler (and quieter) to just make U1 a x11 amplifier and not use a input divider?

[bajaman]

Thanks Phil
I was going to ask the same question as ggedamed.
I also cannot understand U2 - is it a buffer or a wrongly drawn inverting gain stage ?
Why use a 10k input resistor and a 100k resistor in the feedback loop, but no resistor to reference the negative supply rail ?
cheers
bajaman

[phatt]

Wow thanks for the interest. and corrections.
Opps, thanks *bajaman & ggedamed* , I did indeed draw U2 wrong.
Wrong time of the year to make breakthroughs. lol.

I know the input is not right but it's working after my preamp. This is a work in progress and I'm still trying to keep the noise down while keeping the gain up.
@ *ggedamed* The reason for the odd input is that if you make R2 large and with guitar on half volume the sound is bright and clean with a little hair on the note BUT when you dial up full the fatness becomes overpowering so much so it renders it useless. Rather odd as normally when you dial back you loose treble but I'm having the opposite issue here, weird stuff? I've had many tries at this with several different circuits all joined together but today I've scrapped a whole lot and setup a much simpler sequence.

Because I still don't fully understand the compressor section I'm just throwing values at this. All I know is that this is delivering what I've always wanted and that is a dynamic interface where one only uses the guitar to control the dynamics of the sound. I have little doubt that better minds will see what I missed, I believe the circuit holds great potential.

Tone shaping is obviously going to need some refinement but this is all on a test breadboard at the moment so it's going to be a work in progress for a while yet. What I've found so far is that the compressor section needs a lot of boost to drive it hence u2,3,4. It does not spit or splutter like some circuits it is just a very rich smooth OD reminiscent of some classic Valve gear.
@ *smackoj*
U5 is a ua741 hence the 2k ground reference is needed, the others are what was laying around, (LF353). The final build will likely be LM833's and U3&4 will be NE5534's. Sorry no board yet, The intention is not a pedal more like a complete preamp with the bare minimum of knobs , hopefully.

Anyway bear with me as I've made a lot more discoveries in the last few days and I'll post that but obviously I need to check my drawings before I post them.
Give me a couple of days and hope to have an updated circuit and a small sound clip.
Phil. ps I'll fix the mistake latter,, got to sleep.

[phatt]

Oh bum just realized I can't alter the mistake on the first drawing.
No matter as I have done some more mods and this time I've drawn up the complete circuit I'm using.

I was going to post a quick and dirty recording but no go for a short mp3.
Guess I'll have to finally bite the bullet and work out how those sound cloud type places work.
Bugga more stuff for an old bloke to work out.

Meantime here is the full circuit, You could remove U5 and U6 section but then you
will need to tweak the eq. One thing I wanted to avoid was having a huge change in
tone when the circuit is engaged. A lot of pedal circuits tend to jump the tone around
a lot and that can be a problem to balance out.
VR1 was only half wound so there is a lot more drive on tap but hey I have neighbors that work odd hours.
Not quite the Valve rig emulation yet but It's closer than a lot of gear I've used.

BTW this is working more like a limiter so if you want it to work as a compressor lower
the 680uF caps to say 50 ~ 100uF. You can remove R32 & R33 for more but it gets crazy fast.
Obviously there is a balance between the 2 levels so other PU's will mean some tweaking
of the circuit to find the sweet spot.
The setup now is such that it acts more like a limiter which is what I wanted so I'm happy.

Phil

[WarrenPease]

Phil, have you abandoned the triode stage of your preamp or is this just a test circuit? I also noticed that you altered some of the values of your tone stack. Permanent changes to the Phabbtone or just tailoring it to this circuit?

[phatt]

Hey I'm impressed Warren, very astute of you to note the alterations.

The Big pedal build (PhAbbZone, Valve frontend ) has seen some alterations and running fine, still in use every few weeks I gig at the local open mic sessions. As I carry far too much gear I'm always trying to cut down if possible. The reality of the big Valve front end Phabbzone is simply that I tried to do too much in one unit.
The CC circuit is very responsive in that the transition from clean to OD is progressive not on/off like pedals which tend to do two completely different sound /tone /dynamics.

I've put aside The CC for the moment but it shows great promise and if I take my time it maybe all I need as it gives the rattle as well as the OD with no need of Valves. I'm just putting together some modules so I can swap the sequence of circuits in real time then I can get back to testing.

Even after redesigning the Distortion section of the Pzone 4 times it still can't do the progressive OD trick like this CC circuit.
Yes You are on the button ,, The PhAbbTone circuit alterations are to accommodate the different circuit. Is it better? Well maybe just different??

I did find that the mid pot had a bit too much control so with the values given it allows for a bit more treble control when mid is up high.
You loose a bit of the very deep notch but as with most of these tone stacks, you gain one thing and loose another.
The Hiwatt tone setup is unique in that it is the only passive tone stack that can pull a deep mid notch. All the others are just a round dip when mid is dialed back.
The only other way to get a deep mid notch is to use a dedicated parametric EQ setup.

Just as with most circuits the sequence of stages can deliver quite different outcomes not just tone wise but also the way distortion happens.
The original Ptone has the ability to do a very clean rattle even with a basic TS9 circuit, dial the mid up high and you go back to the more obvious dirt sound. Also in front of dirt and after delivers quite different results.
Which is what I'm experimenting with the CC idea. filter before and after diodes, gain before and after tone. I will just keep experimenting.
I know it in there somewhere,, but experimentation does take a fair bit ot time and patience.
I just keep chippin away at it .
Phil.

[phatt]

As you can see this is an ongoing pursuit which keeps tormenting me and maybe I'll never get perfection but hey I learn a lot in the process.

Here is my latest effort.

This time back to basic ideas, although this may look complex most of the mojo comes from using a small LM1875 power chip driving a 12Volt/120mA lilliput bulb. Incandescent lamps resistance when cold is quite low but the moment they start to glow the resistance across the element rises x10~15 times.
Even with that in place there was still not quite enough limiting which had me stumped for quite while.

I won't bore you with the many ideas I tried but lets just say that I've never liked compressors and have an aversion to them but thought I'd try out that clever little compressor that member *Mictester* dreamed up.

The 2 pedal compressors I have here just slam shut as the signal is likely too big at this point in the signal path but Mictester's circuit does a very
good job here. Yoo Hoo so a big thanks 2 Mic.

The little transformer might look clumsy and not needed but without that in place it does not seem to sound as good.
Remember I'm trying to capture the sound of one of the most basic designed valve amps, which from a technical point were crap low teck with pathetic
headroom which is why they are so different.

The switched cap changes the tone (likely an L/C quirk going on) but it makes it sound like an old boxy amp from years back.
Disengage the cap and it has a more hard rock sound. The next part is the LM1875 chip which is powered from only 18 volt supply rails.
This only lights the bulb at higher volumes, lower volume settings are close to clean. Keep in mind the actual SPL from speaker remains fairly constant so you don't get the massive jump in volume when you turn up the guitar volume just a graceful progression into OD. Suweeet stuff

Now of course at bedroom levels you won't need the compressor at the end but once you turn up the main amplifier to gig levels there is still not enough
limiting to keep it in the narrow SPL range I need.

So Mictesters Compressor comes into play then. Full up it does start to loose some dynamics and sound processed but about halfway on the compress dial
gives me a a very close approximation of the 5E3 effect.

Although I may never quite replicate the sonic magic of those old amps, there is one big advantage,,, The ability to get the same/similar feel at very
low levels.

After many weeks of testing I'm etching pcbs for this so in the next few weeks it should be in a box. There are likely many other circuits that may work in a similar manner and I'll keep hunting but for now I like this one. Hope it helps anyone chasing that elusive dynamic effect of older valve amps.
Phil.

[smackoj]

Mr. Phil. Hi. Are you going to put all 3 parts into one box, pcb or ? This is such a cool idea you have produced. Very impressive. Please notify if you make any 'extra' pcb's cuz I doubt my ability to make all three circuits and have them all work. However, I have built several of MicT's optical compressors and they work very good. So, I guess I have one outta three ready to go.

[phatt]

Hi smackoj,
Yes all into a mid size metal case which will just sit on top of main Amplifier which is actually not even a guitar Amp, just a crappy old SS laney Keyboard amp of around 40~50Watts.
Bear in mind IF you are going into a hot rod guitar rig some tweaking will likely be needed. I strongly advice you to build with that in mind, maybe one section at a time.
As you have Mic's compressor sorted already then build maybe the LM1875 part with lamp and then look at preamp ideas for the front end.

You can replace the glass frontend with sand if you wish as the limit/sag/sustain will still function much the same. The Valve front end makes it much easier to get a big signal into the tone section where there can be up to 70% signal loss and I wanted the extra bit of half wave clip that comes from large value series resistors and I have a Valve preamp sitting around doing nothing so may as well use it.
But likely many SS frontends will also work.

Re PCB's
No I don't do PCB's for folks this is all strictly a low budget hobby building thing for me. You can do small PCB's with Free Eagle CAd and boards like mine are all doable on Eagle.
Are you aware? If you have access to a laser printer you can print and iron directly onto blank copper board which is how I do this all on the cheap.
For small boards this by far the easiest way to go and you don't need fancy paper to do it. I found magazine pages are the best, as long as they have that semi glossy finish on the surface of pages. Don't use photo paper as you will be there all day trying to remove the paper.
Print, iron onto board,, then into hot water,, soak for 10min then slowly roll off the paper,, then Etch, Drill and done like in the picture.

Adding pics for reference in a few days I should have more done and it will then make more sense.
Phil.