John Hollis - Flatline Compressor (Layout + Transfer)

floris · Post by **floris** » 26 Aug 2008, 19:39

ManCas wrote: My V readings on the TL072 are:
1: 4.03, 2: 4.03, 3: 4.01 (coming from the 1/2V output) 4: 0.00 (To ground)
5: 1.01 (coming from Input), 6: 4.03, 7: 4,04 and 8: 8.08 (coming from V+)

Referering to the components on MarkM's layout:
Pin 5 should be Vbias = 4V. You measure 1.01V which is wrong. Vbias should be the "regulated" halve of the power supply voltage that needs to be a stable DC which is critical to the circuit. The Vbias voltage is determined by the voltage divider: R3 (10k) and R4 (10k). It is "regulated" into a stable DC voltage by C2 (10uF) that is parallel over R4. This Vbias is then connected to all kinds of points in the circuit as you ca see in the schematic:
http://www.hollis.co.uk/john/flatline.jpg
as well as in the layout by MarkM.
You can see the trace connecting: R3 R4 C2 Pin5 R2 Sustain-pot-1-2. On all these points, the voltage should be Vbias which should be 4V if your power supply is 8V.

floris · Post by **floris** » 26 Aug 2008, 19:45

ManCas wrote: Basically the LED isn't working, I think it's compressing (it sounds almost like an od when Sustain is maxed) but since the LED is not working it's useless.

How do you know the LED is not working, didn't you put shrinkwrap or some kind of light-blocking enclosure around your homebuild LED-LDR optocoupler?
You can try to use a little flashlight or something to shine on the LDR while being in a dark environment. This should lead to a change of signal volume in correlation with the light-intensity: The more light, the lower the volume.
This way you can test if the LDR-gain-reduction element of the compressor works.
But first, focus on fixing the Vbias as I mentioned in my previous post.

msnl · Post by **msnl** » 27 Aug 2008, 21:15

earthtonesaudio wrote:I think you could also drive an LED with an emitter follower connected to the output of the envelope section, at the junction of the existing LED and the op-amp. That could save you a few solder connections.

Thanks, but I don't have that much knowledge about electronics.
Is it possible to make a small drawing of this

Thanks

MSNL

ManCas · Post by **ManCas** » 30 Aug 2008, 18:24

floris wrote:
ManCas wrote: Basically the LED isn't working, I think it's compressing (it sounds almost like an od when Sustain is maxed) but since the LED is not working it's useless.
How do you know the LED is not working, didn't you put shrinkwrap or some kind of light-blocking enclosure around your homebuild LED-LDR optocoupler?
You can try to use a little flashlight or something to shine on the LDR while being in a dark environment. This should lead to a change of signal volume in correlation with the light-intensity: The more light, the lower the volume.
This way you can test if the LDR-gain-reduction element of the compressor works.
But first, focus on fixing the Vbias as I mentioned in my previous post.

Thanks a lot for your help man, I was testing the LDR like you said and it's working fine. I'll try to see what's going on with the Vbias, maybe a wrong resistor value or something. Thanks again!.

devastator · Post by **devastator** » 11 Oct 2008, 11:10

It's possible to put a pot. instead of a Resistors to have an attack control ?

We must use an other IC to create a fashing led ?

(i ask 'cause I've an empty box with 3holes, and i don't know what I can do with)

thx.

marshmellow · Post by **marshmellow** » 11 Oct 2008, 12:27

Refer to this for some more ideas.

stelm · Post by **stelm** » 23 Nov 2008, 13:47

Hi guys. First post and first project here. I tried to make this compressor using the MarkM layout (thanks) but it didnt work. The volume pot seems working but the sustainer pot doesn't work. I have double checked all of the component and it was all in working order. I realised that the LED did not light up.
While i checked volt on IC with multimeter the reading was around 4.4 on pin 1,2,5,6,7 ; 0.2 on pin 3(which is from the input) ; 0 on pin 4 and 8.8 on pin 8.
The strange thing while i touch the input line which go through pin 3 on IC, the LED will light up.
Is the LED supposed to be light up or not? Please help guys.

And also any idea where to buy optocoupler in australia? cheers.

floris · Post by **floris** » 23 Nov 2008, 14:29

Pin 3 should also be 4.5V: R2 (10M) should put the bias voltage (4.5V) from voltage divider R3 (10k) and R4 (10k) onto pin 3.
The voltage divider seems to work because pin5 is 4.5V so R3 and R4 seem to be ok. Probably the fault is around R2/pin3/C1. Perhaps pin3 shorts to pin4?

stelm · Post by **stelm** » 23 Nov 2008, 15:44

Thanks for your quick response floris. I checked and it is all in the right value R1,R2 (10M) and C1(102). And it is not short between pin 3 and 4. I am so confused.

Is it because cold solder joint?

Anyway thanks for your input.

floris · Post by **floris** » 23 Nov 2008, 16:33

Remove the opamp from the socket.
Check for bad solder points and shorts. Resolder them if needed or do that anyway just in case.
Measure resistance between traces and pins that should not be connected to check for shorts.
Connect power and measure the Vbias voltage on R3/R4. Then post the voltages on the socket pins (opamp chip still removed from circuit).

stelm · Post by **stelm** » 24 Nov 2008, 14:06

it is worked now.

It wasn't working because of short.

Thanks floris for your tips.

It is a transparent compressor but a bit noisy while sustain in full, well that's what all compressors do. Nice project btw.

floris · Post by **floris** » 25 Nov 2008, 23:10

Great that you got it to work!

davejones101 · Post by **davejones101** » 30 Jun 2010, 11:02

sorry to bump such an old thread, but i just wanted to ask for your opinions..

should i build a flatline compressor or an orange squeezer compressor?

in terms of difficulty, they're both pretty easy, but as ive never had the opportunity to play either of these, the big question is TONE: which one is better. i guess they both excel at different things, but which would you guys recommend?

mictester · Post by **mictester** » 30 Jun 2010, 20:55

davejones101 wrote:sorry to bump such an old thread, but i just wanted to ask for your opinions..

should i build a flatline compressor or an orange squeezer compressor?

in terms of difficulty, they're both pretty easy, but as ive never had the opportunity to play either of these, the big question is TONE: which one is better. i guess they both excel at different things, but which would you guys recommend?

They sound quite different. The Orange Squeezer has some distortion because of the crude FET attenuator, and has to be used as the first effect in the chain for it to work properly, as it needs a high source impedance (like a guitar output). The original version plugged straight into the guitar!

Hollis' Flatline is OK, but can be noisy, and has a slower attack, because of the response time of the LDR.

You should consider my compressors: https://www.freestompboxes.org/viewtopic.php?f=13&t=8581 https://www.freestompboxes.org/viewtopic.php?f=13&t=8513 https://www.freestompboxes.org/viewtopic.php?f=13&t=5504 https://www.freestompboxes.org/viewtopic.php?f=28&t=7854 https://www.freestompboxes.org/viewtopic.php?f=28&t=8248 https://www.freestompboxes.org/viewtopic.php?f=13&t=7751 https://www.freestompboxes.org/viewtopic.php?f=10&t=6126

davejones101 · Post by **davejones101** » 01 Jul 2010, 14:00

thanx mictester, you're a ledge

ansil · Post by **ansil** » 28 Jul 2011, 09:20

i know its an old thread but was looking for some help on this one. i built this little critter on perfboard, i used 1n4148 instead of germaniums and a .1uf input cap because mouser sent me the wrong stuff. oh yeah a vactrol and a slew of opamps tlo72 jrc4558 tlc2262 all the same results sustain pot is crackling like crazy and it have clips the audio wave form sounding like a bad fuzz factory.

votlages
input 9.5
vbias 4.75
pin 3 3.2
pin 2 4.75

pin 5 4.75
pin 8 9.5
pin4 ground

i have double and triple checked the diode layouts they all check correctly with rg keens board layout at geofex. plugged it into the oscilloscope and you can watch the sine wave go from normal to slightly squared to total positive square wave with sine bottom and almost sunk in at extremes on the square wave side.

each bias point was inspected for continuity as well as each ground point. all good shiny connections parts make good continuity through top of board as well as bottom.

any takers??????????

also i realized i used a 270k instead of 220k resistor but i used a resistor box and checked for difference and got nothing.
and the vactrol is about 6M dark resistance and verified that across the 270k i had 268.3k. all one percent milspec parts. and the resistance dropped while the pedal was under test. so now i am thoroughly confused and i am also going to bed. feel free to hit me up with some ideas someone please

floris · Post by **floris** » 28 Jul 2011, 10:05

Please also post the voltages on opamp pins 1,6,7.

If the sustain pot is "crackling" (I guess you hear that when moving it?) there must be a DC voltage difference between pins 1 and 3 of the pot. Can you measure that?

ansil wrote:... plugged it into the oscilloscope and you can watch the sine wave go from normal to slightly squared to total positive square wave with sine bottom and almost sunk in at extremes on the square wave side.

Is this the waveform you see after the diode rectification or are you describing the resulting output of the compressor?

Check the signal that's going into the opamps, how does that look?

Disconnect the LDR:

How is the signal now the LDR is disconnected?
Clean, no distortions?
Nicely amplified when using the Sustain pot?
So the LDR resistance drops when signal is applied? How low does it get?
Measure the resistance between the -input of the first opamp and Vbias.
Measure the resistance between the -input of the first opamp and its output without signal applied.
Measure the resistance between the -input of the first opamp and its output with signal applied.

snk · Post by **snk** » 19 Oct 2018, 23:25

Hello,

I successfully built the Flatline using the (and a ready-made vactrol, as advised on the Madbean Afterline instructions).
I added a sensitivity (which is really great imho), and an attack knob.
Overall, it is a nice compressor, quite transparent and versatile, great for invisible compression.

I would have 3 questions :

1- Is there any component/value to change to get a HPF sidechain in the compressor path ?
I would like to remove the bass (say around 100-150Hz) from triggering the compressor circuit, without removing them from the "audible sound". I am thinking about a switch with the stock value (which is great) on one side, and a "HPF sidechain" on the other side of the switch... but i don't know which component value i should change to reach this effect :icon_confused:

2- I have also tried adding an indicator led by plugging it into A3 and C3 (from the Guitar FX Layout veroboard) : the led blinks when the compression is stronger, so it gives a rough estimation of the compression occuring, but i noticed that it also some very nasty crackles as soon as i don't have the sustain set up to the maximum position.
Is there any way to keep an indicator led, but not having it modifying the processed sound ?