doing a new "flatline" vero - need recommendations on LDR/LEDS/VACTROLS

[ulysses]

hey guys

ive just completed a new build of the john hollis flatline compressor on vero 21x10 to fit in a hammond 1590b.

im going to build it tomorrow and need some advice from people with experience building this one with ldr's/leds.

jaycar have 2 LDR's listed which i can purchase
1. 2.8k-8.4k resistance
2. 48k-140k resistance

can anyone tell me the light/dark resistance of the ldr's they used in this circuit - and had success with?

or should i just take marks advice, buy them both and various leds and go for the "crap shootout"

would like to make a proper recommendation on my vero layout for everybody though..

maybe you can tell me of success you had with certain vactrols also so i can mention them also.

cheers
ulysses

[markm]

Hey Ulysses!!
I used a VTL5C2 for mine and it worked well.
Don't know if you have access to those in your area but, I had tremendous success with it.

[MartyMart]

I made one up from a smallbear Clairex CL7P5HL and a red 3mm LED wrapped in
heat shrink, that's 28k-14meg !!
Seemed to work well, I dont think those Jacar values look right !! 2.8k to 8.4 meg perhaps ?

MM

[ulysses]

hey guys,

thanks for the replies.

i should have mentioned the dark resistance of the ldr's.
1. light resistance: 2.8k-8.4k - dark desistance: 500k
2. light resistance: 48k-140k - dark resistance: 10M

i will look up the data sheets of the ldr's and vactrols you guys mentioned and make an informed choice. prob #2.

cheers
ulysses

[ulysses]

Hey guys

I checked the data sheets of the products you mentioned.

The VTL5C2 has the following specs:
LED Power: 0mA Reststance: 1M
LED Power: 1mA Resistance: 5.5K
LED Power: 10mA Resistance: 800R
LED Power: 40mA Resistance: 200R

I couldn't find as detailed information on the CL7P5HL
At complete darkness it provided 14M. At at max light it would prob provide 28k, at min light - prob 10k..

Surely there has to be a point of resistance on the feedback loop that will give us
A. the start of the minimum resistance for no compression
B. the end of the maximum resistance for full compression

if we knew these two points of resistance then we could tailor the 220k resistor to the starting point of (A) and buy an LDR with the right ammount of swing to reach (B) from (A).

This would give us the capability to use the sustain knob to its full potential. I read many posts looking for this information and couldnt find it. I did find a lot of people saying "sustain knob didnt do anything past half way" - and im sure this is the reason.

Is anyone out there able to calulate the resistance points of A or B?

Cheers
Ulysses

[ulysses]

ok. i built it and from what it sounds like i am getting a flat response compression. this is, instead of an adjusted compression curve based on input level.

im sure that the LDR is the primary adjustor for the compression curve and that with my current LDR im not achieving this compression curve correctly.

as i strum the led does light up.. but i dont sense the compression ratio increasing.. just a flat response.

as i increase the the volume of my guitar (strumming harder) the compression curve should increase, and i dont believe it is.

as i increase the sustain knob the volume goes up significantly.. this indicates to me that the compressor is increasing the volume but not compressing it correctly in the second stage.. i know that compression does increase the volume, but not with this much boost.

i checked johns site and it has no additional information on this circuit. just the schem.

i think that the only way i am capable of determining the correct min/max compression points is by wiring in a test pot in place of the ldr, sticking it in an osciliscope, running a sine wave through it and adjusting the test pot, marking the min/max compression points and then externally measuring the resistance of the pot at those points.

anyone else got any good ideas?

cheers
ulysses

[MartyMart]

OK, first question is ... have you done a new layout ? and are you SURE that it's
correct ? ...... and checked the build for errors ?
The Flatline that I built is from a vero posted last year and works perfectly, NOT at all
how you're describing it .
MM

[markm]

OK, first question is ... have you done a new layout ? and are you SURE that it's
correct ? ...... and checked the build for errors ?
The Flatline that I built is from a vero posted last year and works perfectly, NOT at all
how you're describing it .
MM

Same with mine, no issues, functions well and sounds very good.

[ulysses]

yeah, double checked it.. should be good. fairly simple circuit, im pretty confident with the vero layout and build.

ill check a couple of things with you.

when you strum the led lights up.

when you turn the sustain level up, the volume increases

are these correct?

cheers marty & mark
ulysses

[ulysses]

i checked my ldr on the multimeter - it measures 50k in the dark, 0k0 in the light

so.. the maximum compression point should be when the ldr is measuring 0k0 (the led is lit up brightest)

the minimum compression point will be when the ldr is at its highest resistance (no led light) (50k)

so.. my maximum compression point is ok. (it measures 0k0 when the led is lit) looks like my minimum compression point is wrong. which means, my ldr is delivering to much resistance when the led is not lit up..

anone else agree with my hypothisis?

cheers
ulysses

[markm]

Well,
I can't rightly say as I am not near my Flatline at the moment however, I would think you need more resistance from the LDR when dark.
I could be wrong, I've been wrong before (just ask my wife!  ) but that's my thought.

[ulysses]

i just stuck in a 100k pot in place of the ldr.

i noticed that when i turn the pot up to 100k resistance the led gets brighter, and when i turn the pot down to 0 k resistance the pot led gets darker - even when playing the same volume - which makes me think its self biasing the led to match the resistance of the ldr..

hmm very interesting.. will play with it some more.

cheers
ulysses

[markm]

That is interesting.
I never went this far into this circuit.

[ulysses]

ok..

seems i had differernt expectations from this circuit than what it actually does..

here i am used to all fancy compressors that have adjustable curves.. expecting this circuit to actually compress the volume as it got higher..

what this circuit actually does is raise the volume when it gets low. which is why its called the flatline i guess hehe

i was expecting the led/ldr combo to adjust the compression ratio when i played hard.. when in actual fact, if you play hard, its almost like playing it in bypass..

thanks to mark and marty for the replies..

i can confirm that my build is in fact working correctly.

oh, and the reason it was boosting when not playing? it was boosting the feedback of my single coils into a hum..

cheers
ulyssess

[MartyMart]

Hmmm, still not convinced that you have this working correctly.
I used the Clairex LDR mentioned above and a "regular" 3mm Red status LED, as used in
Boss pedals.
I never got to see it "lighting up" as it's glued to the LDR and totally wrapped in heat shrink !
If you can see the LED, then it's not going to work correctly, you're letting light in !!!
Compression goes from off->light->heavier->very heavy with the "comp" pot and volume
is used to match the bypassed sound OR to have a bit of boost.
The range is from quite subtle to fairly "clamped down" and is VERY obvious past 12 o'clock
on the comp pot.
It makes for a GREAT compressor, I like it better than my OS and Dyna.
Do you have this level of performance ?
If not, I repeat that "something" 'aint right with your build OR choice of LED/LDR

Marty.

[markm]

I have to chime in here to add that mine functions similar to yours Marty.
Ulysses.....did you not shrink the LED/LDR? I thought you were using a Vactrol.....maybe I mis-read you?

[ulysses]

Hmmm, still not convinced that you have this working correctly.
I used the Clairex LDR mentioned above and a "regular" 3mm Red status LED, as used in
Boss pedals.
I never got to see it "lighting up" as it's glued to the LDR and totally wrapped in heat shrink !
If you can see the LED, then it's not going to work correctly, you're letting light in !!!
Compression goes from off->light->heavier->very heavy with the "comp" pot and volume
is used to match the bypassed sound OR to have a bit of boost.
The range is from quite subtle to fairly "clamped down" and is VERY obvious past 12 o'clock
on the comp pot.
It makes for a GREAT compressor, I like it better than my OS and Dyna.
Do you have this level of performance ?
If not, I repeat that "something" 'aint right with your build OR choice of LED/LDR

Marty.

i turn the lights off when testing - this way i can see the effect of the led on the circuit when i play.

with the lights on, when i move my hand over the circuit to block the light i can hear the input boost rising.

did both of you guys build this one from the same vero layout? im sure mine is right, maybe i'll check the one you guys built.

im sure this circuit is a compressor/sustainer. not a compressor in the traditional sense (boost and squish). it works by altering the output volume in accordance with the input volume.

an example of this hypothisis follows:
turn the sustain knob right up.
play nothing and you will hear the "SSSS"  (this is the circuit boosting the input volume) then play a high e string. the input boost will drop back and the e string will play at a perceived flat level (the "SSSS" will disappear becasue the boost has dropped back), when the string starts to ring out the input boost will start to raise again giving a perceived "sustain" and the "SSSS" will make its way back in.

now try this: repeat the above, but when the high e string starts to ring out (and the input boost starts to raise), play the d string, the input boost will immediatly drop back, and take with it the e string that it was "sustaining".

this is typical of a compressor/sustainer - a traditional compressor will not drop that original high e - it will squish the d string instead.

im rushed atm and i have to go out. will try and explain further tonight.

btw mark, i had a look at the datasheet for your vactrol yesterday, am i remembering correctly that it had a response time of 500ms? you would prob find the sustain to be a lot smoother with a faster LDR/vactrol. maybe im wrong. im using one with a response time of 35ms. i think martys has a response time of 10ms - so his is prob smoother than both of ours.

cheers
ulysses

EDIT: another example you can try is this:
play a simple chord progression and take note of the volume. then play it again but this time mute the strings after each chord and trill the muted strings as you change between chords. the "chicka chicka" of the string trilling will be raised to the same volume level of the chord playing.

in a traditional compressor the "chicka chicka" of the trilling will not be raised in volume - but the chords compressed.

[markm]

Strange. 
My Flatline doesn't seem to be overly slow......it recovers FAST to me.

[ulysses]

Strange. 
My Flatline doesn't seem to be overly slow......it recovers FAST to me.

hey mark,

if you have a VTL5C3 (30k, 35ms) or VTL5C1 (20k, 35ms) lying around give 'em a go and let us know if it sounds any smoother.

cheers
ulysses

[markm]

Strange. 
My Flatline doesn't seem to be overly slow......it recovers FAST to me.

hey mark,

if you have a VTL5C3 (30k, 35ms) or VTL5C1 (20k, 35ms) lying around give 'em a go and let us know if it sounds any smoother.

cheers
ulysses

I'll have to look around and see what I have for Vactrol types.
Man, I have LOADS of projects going right now it's not even funny!