Solid State Guitar Amp Forum | DIY Guitar Amplifiers

Solid State Amplifiers => Schematics and Layouts => Topic started by: phatt on October 29, 2014, 03:04:16 AM

Title: PhAbb Cruize Control
Post by: phatt on October 29, 2014, 03:04:16 AM
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.
Title: Re: PhAbb Cruize Control
Post by: J M Fahey on October 29, 2014, 10:30:10 AM
VERY cool and THANKS for posting.  :dbtu:   <3)
Title: Re: PhAbb Cruize Control
Post by: bobhill on November 08, 2014, 08:57:44 AM
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.
Title: Re: PhAbb Cruize Control
Post by: phatt on November 10, 2014, 08:39:35 PM
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.
Title: Re: PhAbb Cruize Control
Post by: Roly on November 10, 2014, 11:58:00 PM
Quote from: phatt
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.

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).
Title: Re: PhAbb Cruize Control
Post by: phatt on December 18, 2014, 05:38:39 AM
Quote from: phatt
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.

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;
(under Transformer Drive , halfway down)
Title: Re: PhAbb Cruize Control
Post by: phatt on December 18, 2014, 05:48:27 AM
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
Title: Re: PhAbb Cruize Control
Post by: J M Fahey on December 18, 2014, 07:45:27 AM
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?
Title: Re: PhAbb Cruize Control
Post by: phatt on December 18, 2014, 09:11:11 PM
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.
Title: Re: PhAbb Cruize Control
Post by: phatt on December 23, 2014, 07:31:53 AM
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.  ;)
Title: Re: PhAbb Cruize Control
Post by: 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:
Title: Re: PhAbb Cruize Control
Post by: phatt on December 26, 2014, 01:38:47 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.

Title: Re: PhAbb Cruize Control
Post by: J M Fahey on December 26, 2014, 07:06:31 PM
Loved it.   <3)

Very responsive.   :dbtu:
Title: Re: PhAbb Cruize Control
Post by: phatt on January 19, 2015, 05:16:23 AM
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. 
Title: Re: PhAbb Cruize Control
Post by: mexicanyella on January 27, 2015, 11:59:25 PM
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!
Title: Re: PhAbb Cruize Control
Post by: nipperiodic on January 28, 2015, 07:15:07 PM
I always wondered how some guitarists were getting so much use out of their volume and tone knobs. Thanks for explaining the power stage sag.

I went back and compared your clip to the Bonamassa video, and I gotta say, I think you nailed the effect/sound/magic. Very, very cool. I want to build one but I think it's out of my league for now.

For what it's worth, I'm throwing in a vote for you to design some type of compressor circuit so everything is always dialed in just right.

Again, awesome job.
Title: Re: PhAbb Cruize Control
Post by: phatt on January 29, 2015, 05:49:38 AM
@ "mexicanyella"
Hi Mex thanks for the feedback, :tu: good to know what others think
as we all hear things a bit different.
Full bore OD/Dist is fairly easy to get but it's all those subtle
in between sounds that are hard to reproduce, and more so with SS clinically clean amplifiers.
In my experience most SS rigs I've encountered have 2 or more channels where Clean is so glass clean you can use it as a hi fi amp and the other channels are just way over the top distortion, the later the model the more fizz/grunge they have which is obviously aimed at the market.
No offense to those that want metal, just not for me. :-X

Thanks for dropping by and adding comment.
Well tiss ironic that you mention Compressor  ;)
Have I got news for you!!! I've made some interesting inroads with compressor circuits which I'll post next. I did think of buying other compressors but you can waste a lot of money buying gear only to find it's no better than the other stuff you already own.

Re building your own;
The beauty of making your own gear is that over time you learn heaps and you get to know how everything effects the sound. Knowing your circuit and signal path inside out can be a big asset when things go wrong on stage. Just start small and read as much as you can absorb, at first it is a little slow
but you will soon build you knowledge base.

Title: Re: PhAbb Cruize Control
Post by: phatt on January 29, 2015, 06:11:19 AM
OK here is my findings after ~ 30ish years trying to get my head around the age old question of Valve verses Transistor stuff and  overcoming the limitations of SS guitar systems which are often less than impressive.

There are many systems that do this trick but often expensive. Maybe no holy grail here but I think I've found (stumbled upon) an inexpensive way to avoid the negative effects compressors impart to the sound.
In my circuit just adding that extra magic to polish the sonic experience.

I've found a simple way to remove the horribul "Umph" compressors produce when dialed up hard. xP

Just so we are all on the same page;
Using a compressor (at least the pedal types guitar players use) is much like when you open
your mouth to speak and the split second you utter a word somebody slams you in the back and it takes your breath away and hello becomes, H-u - -low.

By the time a compressor starts to sound good the trade off is the Umph on every attack
which makes the instrument sound breathless and robs it of any dynamic feel while a saggy old valve amp which also compresses actually adds some mojo.

Why Why Why??? I keep asking myself. There must be a way to make a SS compressor work just like a Valve rig. :'(

Story so far; OK my "Ulite Compressor" is working but maybe the limits of LDR circuit are showing, not fast enough to react to completely remove the attack.
So thinking that the problem might be speed related I whipped up Rod Elliot's
ESP super Fast Limiter circuit on my test bed which has been running for the last 2 days.
OK it's very fast and with some tweaks might be better than the Umile unit.
ESP circuit here;

Now recall My Cruize control plus Umile idea works at low volume ok but at high volume
there is still an issue with volume difference between clean and distortion.
To test this I have no choice but to have my amplifier at a loud level otherwise you get a false sense of SPL levels.

Sadly I live in the burbs and have to respect my neighbors so I dragged out my cheap set of head phones and run the signal through my old ghetto blaster.
So with Hphones on and tweaking some values on Rods Fast limiter circuit I did 90% eliminate
the umph comp effect. oh goody :)

Now headphones can give you a false representation so for a short time I run through the Guitar amp
again at live loud volume just to be sure.

Damm it!!!  :grr :grr The umph was now worse than before.   :grr Arrh hair pulling  rage,,,Why, What 'n How? What the hell is going on??
After a stiff coffee and a few hours pulling weeds from the garden trying to escape my utter frustration a little ray of insight run through my mind. (insert light bulb here)
Hang on,,,Those el cheapo headphones I use have shocking low frequency response. Ding!!!!!!!!!!!! (Even more light bulbs)

Sure enough,, Rip off everything below 100hZ and indeed the horrible "umph" magically disappears
from the sound and you are left with a very realistic guitar sound.
Ok now it sounds a bit hollow but simply but running my old hifi Graphic EQ After the compressor solves that.
Sigh,, enough time spent on this for now just wanted to share what for me has been a big revelation.
This is getting long so I'll explain why i think it happens next time.
You will have to wait for sound clips as the over grown garden awaits me.
Title: Re: PhAbb Cruize Control
Post by: phatt on March 02, 2015, 06:50:37 AM
I know I know,, I do get a bit carried away just because something works,, but over time and lots of a/b testing one realizes it's maybe not so good.
Tiss all part of the journey of experimentation.  ;)

Circuit update,
After much testing I've come up with another hair brain idea. "Cruize Control ver3"
I've reverted back to a triode front end much like the PhAbbzone which was very good but lacked the compression/sag effect.

A quick run through,
The preamp is just a 2 stage triode > into a HiWatt styled tone stack then buffered and boosted via an opamp stage which then drives a small 1k/8-Ohm line transformer the signal is then amplified via an LM1875 power chip.

The LM1875 output drives a small incandescent lamp which soaks up a fair bit of power as the signal becomes large, this creates the sag/limiting effect. Although the lamp idea works very well it's still not enough to keep the overall SPL in the range I needed for this to work.
The Ulite pedal compressor I have can't handle the bigger signals and hence it pops hard on too fast and destroys the effect. :(

Meantime a wonderful chap "mictester" over at FSB has a clever little optical compressor circuit and I thought I should at least try it out. Yoohoo it works and does not pop or muff the signal.

So the end result is a 3 stage unit which does what I want and only has 7 knobs. :dbtu:
After many hours of tweaking each part I've decided to build this,, damn now I've run out of sheet metal. :(

BTW the overdriven effect is likely some triode rattle and then at full volume maybe opamps hitting the rails but without a scope you don't know for sure but simulation gives a fair idea. Either way it sounds more convincing than using Diodes for clipping.
I'm getting spanky clean and loud with guitar volume at 4~5 and sweet OD past 7 but not the massive jump in volume.

Power supply is a 2 part setup;
12VDC 1 Amp for the DC/DC converter to give ~250VDC Ht for triode as well as the 12VDC heaters then a second dual supply delivering 18/0/18VDC for the LM1875 and then into 7812/7912 reg chips for dual 12Volt rails to drive the opamps.

2 points worth note;
The switch at the small transformer "Rock/Woody" was a mistake but it works so well I've decided to keep it.  (Likely some L/C quirk going on there?)
It sounds a lot like an old boxy amp from 50 years back with loose bass,, nice for those JJcale type riffs. In rock mode it's brighter and the bass is tighter. I like both. :)

The small lamp maybe an issue long term but it does not glow white hot,, time will tell. 
The test circuit has been running now for many hours each day in the last few weeks and I have plenty of spare bulbs anyway. (these bulbs are only 90cents at the local electronics store)

As I'm only running the LM1875 from 18volt rails it likely won't reach full output, it only needs to put out enough energy to light the bulb and increase the resistance across the filament.
The signal has to pass through the element and the resistance rises in sympathy with larger signals causing the Sag  effect as well as lighting the bulb, giving a visual indication of sag.

Thanks to Roly,s recent scale on light bulb limiters for amp servicing it seems the resistance in general rises about 10~15 times when hot so my lilliput bulb is about 10 Ohms cold So I'd say that would rise to ~100 Ohms or more when hot.
Which means the LM1875 chip is driving a Cold load of 10~12 Ohms (counting the 2R7 resistor) and ~100R when hot.

Though this bulb idea may look very backyard basic the limit/sag effect is very useable. No pumping or wonky release just a very smooth transition into a bigger fatter sound. <3)

My only concern is the noise creeps in (mainly hiss) at higher levels but no worse than many of the big name gear that is around.
Single coil noise is evident but with HBuckers it's not a problem.
Of course with wires running all over the bench most of my noise/hum/buzz/hiss will be resolved when it's all boxed up.

Give me a few weeks while I make some PCB's and mount the maze of wire on the bench into a case and I'll get some demos recorded then.

Title: Re: PhAbb Cruize Control
Post by: J M Fahey on March 03, 2015, 09:29:14 AM
Hi Phatt, how ya doin' ?
You're being well spoken about at MEF, just check:

Title: Re: PhAbb Cruize Control
Post by: phatt on March 04, 2015, 07:04:42 AM
Thanks for the plug :tu:
Yes I certainly can attest to the idea that many of the problems that face the modern player can be traced back to too much bandwidth.

As to my project,, put aside for a few days as a dead amp awaits me on the bench looks like a dead power amp section. I might take a few pictures of this old Jade LB120 Amp (Aussie rig from way back)
Interesting build, all the parts mounted on the copper side of PCB.
Title: Re: PhAbb Cruize Control
Post by: phatt on May 13, 2015, 02:51:05 AM
Well in spite of many setbacks I did end up building this idea into a working preamp.
I have no doubt the clever tecks here will shake their heads and wonder what the hell I was thinking,, :duh
But hey it does work. :tu:
There may well be better ways to do the same thing but this is almost devoid of any compressor effect even though the signal passes through two compressor stages.

The gain is very high and hiss with single coils is present at higher levels but then I've played pro gear with bad hiss at lower gains.  :-X
With HB's the hiss is almost non existent even at full bore.

Adding a short clip so you can make your own judgement.

The only knob used here is the volume control on the guitar, Starting out at halfway then turn up full.
Of course the strat has low power pickups and HB's make for a bigger distortion. (so another day for that, the wife is complaining)  ::)

Signal path, Cheap Strat > Cruize Control > Laney > into a mic at 18' off axis. No effects and no editing, just converted to MP3.
I've let it ring out so you can hear the sustain of the last chord,, I can't hear any compressor pumping or pops. I've made a few small changes so adding updated schematics.
Title: Re: PhAbb Cruize Control
Post by: phatt on May 13, 2015, 07:52:23 AM
Oh I forgot, I did take some pictures while the sun was out.

Bare with me I'm trying to get my head around linking stuff,,,Hopefully this is the right way :-\

( (
image hoster (

Title: Re: PhAbb Cruize Control
Post by: phatt on May 13, 2015, 08:52:21 AM
Now that I seem to have some idea as to upload/link pictures I thought I'd put it all on one page with a pic of front panel as well. These are up to date as of may 2015 and reflect the unit shown.

Front Panel;
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screen shot on pc (

Preamp Circuit 1/3

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free adult image hosting (

Sag Control Circuit 2/3

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upload a picture (

Mictester Comp Circuit 3/3

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free image hosting (

The supply is not shown to keep it simple but it's a 3 part setup the Valve section is powered via a redundant 15VDC laptop supply hidden on back panel. This is then used to power an oddball Valve kit I purchased some years back and was sitting idle. looks ugly but why build another circuit ;)

The rest should be obvious, a small transformer delivering ~ 17/0/17 VDC which drives the LM1875 power chip (Lamp Sag Compressor) then regulated 12V rails for the opamps.

Feel free to disect my brain storming ideas lol.
Now if I can squeeze all this into a small pedal that would be great.
I did have a go at using an LM383 (Car Audio) power chip but it would not light up the lamp enough to make it viable to run at 12Volts. Likely hard to find lamps small enough to make it work.

Title: Re: PhAbb Cruize Control
Post by: J M Fahey on May 24, 2015, 02:52:15 PM
EX-CEL-LENT  :dbtu: :dbtu: :dbtu:
Title: Re: PhAbb Cruize Control
Post by: phatt on May 29, 2015, 08:46:23 AM
Thanks for the vote Juan.

I'll Update soon as I've re drawn the schematic mods. I used this a few times at gigs and found some issues which have now been rectified.

It's always a slow ongoing process when building oddball ideas like this. :duh

Basic problem was gain in the wrong place, not enough drive for AX7 to get into the sweet spot and too much gain after that. Sounded great but noise was then a big issue especially with single coils.
EMF on stage can be a nightmare with stage lights and such. :grr :grr :grr

Hiss and hum is now much better and the sweet zone of the triode rattle is much more progressive.