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PhAbb Cruize Control

Started by phatt, October 29, 2014, 03:04:16 AM

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Hi all,
       I Finally built my limiter circuit into a working unit. yoo hoo
It's Called the "Cruize Control".
Think power amp sag control or an Overdrive limiter, might help explain what it does.

Works like a charm with no pumping and produces the effect reminicant of old cathode biased Valve amps which tend to sag/limit/compress the sound at high volume while adding a fair amount distortion.

So just by using the on-board volume control on most electric guitars you can go from clean to scream without the need for a dashboard of fancy pedals.

For those who missed my other thread,
A very good example of the effect I'm talking about is here;

Sadly Joe Bonna does not explain to the masses that this only happens with certain types of valve amplifiers (look at Fender 5E3 and similar schematics for clues)

As a lot of Valve amps use fixed bias and stiff psu the power stage does NOT sag much and most of the fancy dirt distortion is done inside the preamp sections. In my experience this is not as convincing as a saggy old valve amp from a forgotten era.
Most SS power amps are even more clinical, staying clean all the way up with very little sag and rely even more on preamp tricks to get the distortion to work.

So rather that trying to re-invent power amplifiers with no idea of how to find the square root of the universe  :duh I thought I would try something simple and to my surprise it works far better than I expected. <3)

with my "Cruize Control" The difference between half volume and full volume is not a huge jump, the sound level remains between a fixed range so you don't get a massive jump in volume level, it just sags and distorts a lot more while raising the volume just enough to play over the top of clean rhythm parts.

If you are using this after a pedal just change R2= 1Meg and R5= 1k.

Trim 1 sets the gain for the limiter section and can be a front panel control but I've got enough knobs to Ef up the sound so one less knob on the panel means less to go wrong. I've set mine around 30~50k.
VR2 is the main knob and turns down (Clamps/Limits) the output level as you turn it up so set for what ever works for you.

If you read the other thread I've dropped the transformer as it's not needed. I also realized the extra parts on the limiter drive circuit were not needed. so this makes it dead simple to build. :tu:

It runs from a 9Volt AC plug pak and with a trick little rectifier circuit delivers 15/0/15VDC split rails. (If there is any interest I'll post the supply I used.)

I've used 3 different LDR's on the test circuit and it seems these can make a bit of difference as they can have slightly different response times.

For those in Australia, the Jaycar part for the LDR is RD3480, cost $3.
The torch is likely overkill with 9 LED's but the torch was cheaper that buying just one white Led and came with an alloy housing to mount the LDR. to easy :)
The Torches I found in the "Reject shop" cost $4
If you go with a led torch be aware that some of those torch leds won't work, my guess is the type with a single Hi intensity led are a no go, usually a tiny yellowish led, Obviously not all leds are equal.

While testing I removed my dedicated PhAbbZone preamp and raised the gain (as mentioned above) and played direct and it works fine. I then inserted a Boss OS2 dirt pedal (unaltered) and got some very long sustain to happen so it's no slouch if asked to do big distortion. :dbtu:
The circuit is noise free and dead quite.
Have fun.

J M Fahey

VERY cool and THANKS for posting.  :dbtu:   <3)


Thanks Phil, he said with a shake of his head... 8|
Just when my world is going through major upheaval, other half retiring in 6 weeks, trying to get ready for a move of a couple hundred miles back to where we tied the knot thirty mumble years ago, getting the workbench stuff packed up for moving as well as a household that has accumulated an incredible amount of "stuff" over the last couple of decades here in the great state of Taxes, and now you come up with something that begs to be built.

Looks very nice, just don't know when I will be able to get to it. I just can't let a certain bass playing friend see this or I won't get any peace until he has one tailored to his needs.


Not to worry Bob ,, I'm sure it will still be here when you get settled. :)
Meantime you have time to ponder and may come up with an even better idea.

I'd be interested to hear the experience of others who build this.
The test circuit is still setup so when time permits I might try a few more modifications, maybe adding a tone knob much like the TS9 circuit.
Then again, experience tells me the more you add the worse it often becomes but being the eternal tinker type I can't help to explore possibilities.

You can probably use a Vactrol if you have those but I live on a limited budget so I use whatever is at hand, often scrounged from junk.
D3&D4 diodes are Germanium and I'm told germanium transistors can work the same.
If you read the other thread (hybrid preamp idea) you will note I started out trying to get a SS powerstage to soft clip or sag with no real plan in sight, I just felt there must be some way it could be done.
After some help from better minds I could see there was little hope of a novice perfecting such a task so back to some kind of preamp trick.

I got a bit carried away with all sorts of ideas but once I used the LDR on the Feedback diodes I realized I was getting closer.

It's just another distortion box except the 2nd pair of diodes are controlled by the LDR resistance.
Nearly every dist circuit I've ever seen has a fixed clip point and that is not what happens in a valve poweramp stage hence nearly all the dirt boxes I've tried including many of my own builds most have little or no dynamic window to work with.

One thing that always bothered me with distortion pedals is every time you
turn up the gain you also have to back off the level and vv.
Wouldn't it be nice IF that could be done with one knob?

And for the benefit of those that may not realize;
The average TS9 pedal or similar will do kind things to a well tweaked Valve Amp but not so with a lot of SS rigs where the power stage has little or no sag to soften the output level. They tend to sound very hard edged at loud volumes.

I do have a couple Of Valve Amps which would make life easy but as I play keys as well as guitar (and only have a sedan car) I'm forced to use a 112 SS amplifier as an all round rig so I miss the dynamics of an electric guitar rattling old power valves.

Most distortion circuits come on too strong through SS poweramps and hence you are either too loud or too soft when you hint the pedal.
This has greatly improved touch response over the basic dirt pedal concept while also keeping absolute level under control.

The big bonus was the fatness that happens as you turn the guitar volume to full creating an effect much like the Video link. Watch out for the low freq as it can get very flabby which ironically was what I found happens when building some classic Valve circuits if built as per the original values of inter stage caps.

The fatness thing intrigues me as even some very old transistor radios have a distinct sonic quirk when turned up full volume the sound is heavily compressed and distorted but it's still musical and you can still make out the lyrics. This just does not happen with (Clinical Correct) SS poweramps built since those old days of transistor radios. Now even a 10 watt chip amp stays clean and then breaks up in a not pleasing manner. Harsh.
Enough ramble, Phil.


Quote from: phattThe fatness thing intrigues me as even some very old transistor radios have a distinct sonic quirk when turned up full volume the sound is heavily compressed and distorted but it's still musical and you can still make out the lyrics.

First generation transistor radios (and a few later ones) simply adapted valve Class-B2 topology, a small Class-A power driver, through a driver tranny, into a couple of "power" transistors (in starvation bias), into an output matching transformer.  Only later did "OTL" - output transformer-less become a feature.

Suprisingly most of the usual suspects still carry these tiny trannies today (and I have difficulty imagining what they are being used for).
If you say theory and practice don't agree you haven't applied enough theory.


Quote from: Roly on November 10, 2014, 11:58:00 PM
Quote from: phattThe fatness thing intrigues me as even some very old transistor radios have a distinct sonic quirk when turned up full volume the sound is heavily compressed and distorted but it's still musical and you can still make out the lyrics.

Suprisingly most of the usual suspects still carry these tiny trannies today (and I have difficulty imagining what they are being used for).

Why Yes some years back I did find a few tranny radio schematics once I got on the web but found that none gave info on the transformers used. At that time I was not confident to take on a 100 watt version of an old idea which may or may not work and having already melted a few poweramp circuits I figured I'd leave that one for the experts. xP

As for finding a use for those tiny Transformers You can always make reverb drivers with some of them  8)
I recently contacted Rod at ESP and mentioned the transformer drive idea which I found worked wonders and He has obviously tested the idea and found merit in my crazy experiment. lol.
The ESP Reverb page has been updated with a tranz drive circuit for those that wish to improve the drive section for Rev Tanks with High Z transducers. :tu:
Page Here; http://sound.westhost.com/articles/reverb.htm
(under Transformer Drive , halfway down)


Updating this with another hair-brain idea which is a combination of a snippet
I found after a long search trying to get my head around Logs ???,, Erh log
transfer that is. Compressors do my head in  xP

Rather than try to explain stuff I've never actually learned I'll just let the pictures tell the story.
Same master plan as before but far less complex and works even better,
hey no Led torches this time. ;)

Note the 2 screen shots, one with 100mV input. (Output is slightly larger than input)
The other has a 1Volt input but the output is very squashed.

The sonic result, Guitar Volume at half the signal is very clean but the moment you dial up full it crunch's But the SPL only rises by a small amount,
Yay I finally have a compressor that sounds like a real old Valve amp. <3) <3) <3)

Those with Sterile SS rigs might like to try inserting this in the efx loop or after a preamp might be useful.

I'll do another recording if there is enough interest but leave it a while as I've annoyed the locals for quite a few weeks already so I need to give them a break. :-X

J M Fahey

I'm still wrapping my head around this  :o

Not sure it's a "diode compressor" , a variable threshold (just to call it a name) clipper, "all of the above",  but certainly it looks interesting.

Please, we deserve a recording or two.

Won't complain about the howling dingoes in the background  :lmao:

It definitely looks good.

What does the Vr2 100k pot do at different settings?


Hi Jaun,

I found this while searching for log compressor schematics
The circuit came with a label saying "Passive Dynamic Audio Compressor" and
I've learned not to under estimate passive circuits so it got my attention straight up.


It claims to keep the output around 70mV while the input can be anywhere from 100mV up to 10V. Now that's a 100 times window which is a big claim, Of course if one just built every circuit on the net you could waste a lifetime building crap so you have to have some idea of the validity of these circuits.
Anyway within a few hours I had a working compressor circuit using much the same layout as I've shown. All I've done is raise the value of the 2 Caps which I think alters the clamp time.
The pot you asked about gives some adjustment to the release time.
Of course the pot is now likely redundant as the time is so long it never releases. I've always disliked compressors as they tend to suck the life out of the sound and they move further away from the dynamic feel of a real valve amp. Sure if all you ever do is play funk chops then they deliver but for most other forms of music they are of no value.

22uF will deliver the familiar compressor effect, even 100uF it still releases over time. 680Uf is all I could find but I'd guess ~ 470uF would be high enough.
R1 at 220R seems rather odd and kills the signal so I deleted that. The 2 extra 10k resistors were a mistake on my test circuit but I noticed that when I corrected the mistake it was not as good so I put it back.

I found you do need some series resistance in front otherwise you will hear the dreaded diode hash, it's not shown on my simulation but 10k after c3 seems to keep that at bay. The buffer stage may not be needed but it was already on the board so still work in progress at the moment.
You will have to wait a few days for another sound clip but meantime my observations are thus,
No hint of the awful attack com-phf effect of compressors while any release (if there) is not heard.
Just a smooth progression into the classic overdrive which is reminiscent of Valve era equipment. <3) <3) <3)

Meantime life gets in the way of hobbies so I'll get back to it all in a few days, might find something I missed. I should mention for those that might think this would make a good pedal,,,  as a stand alone pedal type circuit it may not sound great on it's own but used in conjunction with a good preamp will
find it may add that missing dynamic effect which is often missing, especially from modeling amps like Yamaha THR5 10-Watt. They might have all the tone shaping worked out but they lack the feel. Which sadly is not much improved since units like my Digiteck RP80 toy, (horrible thing) :grr.


Have made some big inroads now after trying many different ideas.

Adding the schematic below

With my preamp setup driving this circuit into a crappy old Laney Keyboard amp I can get clean from ~3 on the guitar volume and full crunch at full dial. :dbtu:
This makes for a very responsive guitar amp interface capable of many different styles from articulate finger picking to fat crunch chords.

In spite of many interruptions that happen at this end of the year I've finally come to a seriously useable circuit.
The sustain at full crunch is easy lasting 5 seconds and even longer with my stock Boss OS2 in front, though I doubt I'd ever need the extra but hey pretty wild if that is what you require.

So looks like I've designed and built my best Christmas present ever.
It's a huge buzz for me after all these years I've come close to emulating what has always eluded me.

Any decent preamp in front of this should work but if it's lacking in bass raise the values of C1 and C2. Lower values for C7 will pass more treble response but watch out for the dreaded diode hash with too much treble. :trouble

U3&4 was the magic breakthrough as it doubles the current which is needed to drive the compressor section. (that was my stumbling block) :grr :grr
Delete R13&15 if you want even more but you will loose some of the leveling ability between low volume and high volume,, try it both ways.
VR1 can also be deleted but you may like a little control over the effect even if only to hear how well it works.

This sounds nothing like a compressor though if you hold a chord for long enough you can just hear a tiny bit of release but just like a real valve rig it's almost impossible to hear any attack or release like most of the typical compressor circuits that are used for guitar. (Yuk I hate those things) xP

Be patient ,, I will get a sound clip up here next year,,, and that is only a week away.  ;)

J M Fahey

CON CON CON CON CONGRATULATIONS !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Just a single one didn't seem to be enough  :dbtu:   :dbtu:


Quote from: J M Fahey on December 24, 2014, 12:18:39 AM
CON CON CON CON CONGRATULATIONS !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Just a single one didn't seem to be enough  :dbtu:   :dbtu:

Thanks Jaun,
I just keep chipping away at ideas and every no and then I have a win. 8)

Well as luck would have it,, I found some free time so another quick and dirty test direct to laptop.
Same test as before, first part with Cruize Control bypassed then same again with circuit engaged.
At 1 minute you maybe able to hear just a hint of release from the compression.
Only using the onboard guitar volume to control the sound, guitar volume starts on 4 then turned up full for both tests.

This time I've decided to see how cheap I can go so I'm using the little Casino 12 amp
I fixed up long time back. One of those generic little cheap chip amplifiers found everywhere with many different brand names.

So signal path is $199 Casino strat with cheap pickups > PhAbbtone (of course) > Casino Amp (signal taken from line out) > Cruise Control > Laney Keyboard Amp. Laptop is about 3 feet away from speaker.

Oops forgot to turn off the spring Rev in the Laney but what the heck it still gives a basic idea of the effect. no post editing just converted to mp3.

For those that might not see the point of the test.
Of course the loud bypassed bit is quite loud and the last bit is heavily compressed and some might think that is a weak but it makes the A/B test fair.

In use, the Cruise control is engaged all the time, set the volume on guitar to 3~4 and then set main Amp volume high then it's as loud as the clean section you hear on the clip. Then you turn up the guitar to get the crunch and it's a good balance.
The clean (Guit Vol on 4) has got just a little hair on the edge of each note,, which actually adds some quite nice sparkle to clean finger picked notes. Crank up and it roars but not deafening.
Should be obvious that really hot pickups will alter where you set dials.

Interesting to note;
If I swap the sequence of Ptone and Casino it becomes too bright. Hum? I'd guess the filter I added to that Casino does need to be right before the Cruize Control.


J M Fahey

Loved it.   <3)

Very responsive.   :dbtu:


First, Thanks Mr Fahey for the support, shame we live so far apart. :(

Well after a few side tracks,, finally a built and working unit. :cheesy:
The Aim is still the same, finding a SPL balance between clean and drive using only passive onboard guitar controls, not as simple as it seems as I've found out.

After some live gig testing I found at high volume levels the full up level was still too strong (loud)
but I refuse to be totally defeated.  :grr
As luck would have it a friend had a compressor pedal he did not use so I borrowed that to see if it might help. Now I normally hate these things and if used in front of my circuit it does the classic comp muffing sound and robs the dynamics (which I Hate) But when inserted After my CC circuit it does indeed help to balance the clean/OD levels without sounding too compressed.
Now I could spend another month trying to perfect a compressor circuit and build a new PCB xP

Narh ,, I'd rather just learn some new songs so for now I'm just going to use a separate compressor.
So think of this as a front end for a compressor, I'm sure many others will work in this way with similar

Take note here if the level entering the compressor is high it will effect the clean which will sound just
like any other compressor (everything gets chocked) But if you back off the Cruise Control output level  knob the clean goes through uneffected. The sweet spot of the CC is wide enough to give good results so it's only the OD that gets the extra comp treatment. (The compressor led only flicking here and there)
Yay I now have another bottle of scotch to open. 8)

The sound clip;
Guitar is my Real Cheap Strat copy > Cruize Control > Ulite Comp > Laney keyboard amp > laptop. (Laney reverb is the only effect)
As per usual straight into laptop and converted to low res mp3. All knobs are at ~ noon except the
midrange of CC which is 9 o'clock.
So plenty of room for more grunt/OD if needed but this is all I really use when playing at gigs giving
just enough rattle and crunch to cover a fair amount of rock era songs and sweet enough to do ballads with a nice edge for cleaner el Guitar sound which makes for a fuller clean sound.
Guitar volume is the only control used, starting at halfway.
(Oh yeah, the clicking in the background is the laptop mic picking up the hard drive)

Watch the layout as the input of IC3 is high Z so keep it short as possible from centre treble wiper to
input of IC3. R9 is 2 meg but 1 meg will work fine, below 500k you start to loose the tone effect.
Of course if you don't want the tone control the input can start at C9 but you will need to re-tweak the circuit to suit your sound. The dreaded hiss was an issue but with the aid of a breadborad I eventually worked out where most of the noise came from.

If someone wants the pcb layout I'll post it for reference and layout options.

The compressor in use here is an odd ball unit I've never heard before, the brand is "Ulite" which is
obviously an analog optical device. I will eventually try out others in time but this will have to do until I find another.
The Ulite is very quite and only introduces noise when dialed full but that's to be expected as this is a
hot preamp anyway.

With all knobs at 12 O'clock and bedroom level output the circuit noise is so low you don't know it's on but at high levels there is still some hiss but still way better than some brand name gear I've serviced over the years.
cheers, Phil. 


I thought your recorded example sounded good, and I like that you mentioned the unit's interaction with other things in the signal path and which order of items worked best...that's important and overlooked in enough equipment reviews as to make them pretty much meaningless.

The clean-to-"hair around the notes dirty" transition is nice, and the hair around the notes tone has a nice texture while retaining some clarity. Cool!