Anyone built the "Really Cheap Compressor"? How is it doing?

[nguitar12]

Anyone built this "Really Cheap Compressor"? Looking very simple.
Just wonder how well  is it doing. How to add a threshold/attack/release if necessary?

[induction]

I built it and I'm very happy with it. I leave it on almost all the time. Lots of squish available at high settings if you want it, very subtle at low settings if you prefer that. I found it a bit dark, stock, so I added a bright mode on a switch. I also increased the coupling caps a bit so I could use it on bass as well.

I got some distortion at high settings at first. I pulled out the ldr I had scavenged from some home appliance and replaced it one from the Radio Shack assortment pack, and the distortion went away.

[nguitar12]

I built it and I'm very happy with it. I leave it on almost all the time. Lots of squish available at high settings if you want it, very subtle at low settings if you prefer that. I found it a bit dark, stock, so I added a bright mode on a switch. I also increased the coupling caps a bit so I could use it on bass as well.

I got some distortion at high settings at first. I pulled out the ldr I had scavenged from some home appliance and replaced it one from the Radio Shack assortment pack, and the distortion went away.

Thanks for your info. How do you add the bright switch and do the mod for bass? I am surprised that it is doing well when it is such simple.

[samhay]

I built one, but found it had to many parts, so build this, which has been on my board ever since: http://www.diystompboxes.com/smfforum/index.php?topic=101118.0

In either case, be prepared to audion different LDRs until you find one that works satisfactorily. If they generally have too high resistance, you will get op-amp clipping, and if they have too low resistance, you will get little compression and output. The LDR response time, which can be quite variable, also sets the attack and decay times.

[nguitar12]

I built one, but found it had to many parts, so build this, which has been on my board ever since: http://www.diystompboxes.com/smfforum/index.php?topic=101118.0

In either case, be prepared to audion different LDRs until you find one that works satisfactorily. If they generally have too high resistance, you will get op-amp clipping, and if they have too low resistance, you will get little compression and output. The LDR response time, which can be quite variable, also sets the attack and decay times.

WOW This one have even fewer parts. So what will be the major different  on the performance between two?

[midwayfair]

I think the Flatline is the superior design: Less likely to distort (dry is not fixed gain), higher input impedance and uses the non-inverting input, more stable LED driver, and you can easily add the threshold control like in the RCC. Still fits in a 1590A easily.

[Cozybuilder]

I built it- love it. 3 circuit mods: 470pF paralleling 220k input R, 10nF across the vol pot, and 2K2 output R on vol-2.

I tried various LED-photoresistor combinations, different colors, single LED etc, and wound up using 3mm diffused green with a GL5537 (Tayda). I filed a flat on each side of the LEDs, superglued together, and used heat shrink tubing to make a nice compact package.  Ends are sealed with black RTV.



And it fits in a small box 

[induction]

How do you add the bright switch and do the mod for bass? I am surprised that it is doing well when it is such simple.

Bass mod:
I used a 2.2uF cap for coupling to the leds (instead of 1uF), so it would work well for bass. Doubling the 15nF input and 100nF coupling caps didn't seem to have any effect, so I left them alone.

Bright mod:
470pF and 10nF caps in parallel with the 220k input resistor and the level pot, respectively. Those are controlled by a switch. I added a 2k2 resistor before the output permanently. This mod was suggested by mictester, the designer of the circuit.

[samhay]

>WOW This one have even fewer parts. So what will be the major different  on the performance between two?

The design is somewhere in-between the 'Really Cheap' and 'Flateline' compressors. A major advantage over the former is that if you turn the compression down, you turn the gain down and thus turn the noise-floor down. The Flatline has a more complete envelope detector than the other designs and is a good choice too.

They are all fairly simple circuits, so I suggest you breadboard all 3 and see if you have a preference.

[nguitar12]

I built it- love it. 3 circuit mods: 470pF paralleling 220k input R, 10nF across the vol pot, and 2K2 output R on vol-2.

I tried various LED-photoresistor combinations, different colors, single LED etc, and wound up using 3mm diffused green with a GL5537 (Tayda). I filed a flat on each side of the LEDs, superglued together, and used heat shrink tubing to make a nice compact package.  Ends are sealed with black RTV.



And it fits in a small box  

Nice job. Very Clean build  

[nguitar12]

How do you add the bright switch and do the mod for bass? I am surprised that it is doing well when it is such simple.

Bass mod:
I used a 2.2uF cap for coupling to the leds (instead of 1uF), so it would work well for bass. Doubling the 15nF input and 100nF coupling caps didn't seem to have any effect, so I left them alone.

Bright mod:
470pF and 10nF caps in parallel with the 220k input resistor and the level pot, respectively. Those are controlled by a switch. I added a 2k2 resistor before the output permanently. This mod was suggested by mictester, the designer of the circuit.

Thanks. I will definitely apply these mods if I built mine.

[nguitar12]

>WOW This one have even fewer parts. So what will be the major different  on the performance between two?

The design is somewhere in-between the 'Really Cheap' and 'Flateline' compressors. A major advantage over the former is that if you turn the compression down, you turn the gain down and thus turn the noise-floor down. The Flatline has a more complete envelope detector than the other designs and is a good choice too.

They are all fairly simple circuits, so I suggest you breadboard all 3 and see if you have a preference.

That's is good idea. So bad that I don't know how to use the bread board. Every times I test out a circuit I have to layout in eagle and make the board. It is a time consuming job for me.

[samhay]

If you can learn how to use Eagle, you can learn how to use a breadboard.
If you need a push, you might find these helpful:
http://diy.smallbearelec.com/HowTos/Breadboarding/BreadboardIntro.htm
http://diy.smallbearelec.com/HowTos/BreadboardSiFF/BreadboardSiFF.htm

[GGBB]

If you can learn how to use Eagle, you can learn how to use a breadboard.

+10

Breadboarding is way easier to learn than Eagle.

[~arph]

Built it twice for a multifx. It's ok, it really needs the bright mod though. Stock it sounded muffled.

[Ben Lyman]

I wanna build this but I'm confused. There is no mention of a VB or VR or whatever, the junction of the 47uF and 33k even says +9v.
Do I need to make a voltage divider circuit for this? And if so, should I tie the 47u/33k to VB?
Or should I just build Sam Hay "Another Optical" but then with that one, also green LEDs or different color?
Thanks!

[induction]

Both op-amps have a half-rail voltage applied to the non-inverting inputs. Follow the path from the +9V you mentioned. It goes through two 33k resistors before it reaches ground. The non-inverting inputs are connected to the junction between those resistors: that's Vref. It's not necessary to label it if the schematic shows those connections explicitly.

The color of the led's is chosen to match the optimum frequency that the ldr responds to. You can test your ldr specifically if you like, or just use green or yellow. In my experience the color isn't crucial in this circuit, but let your ears be the judge.

[Ben Lyman]

Thanks induction, I see now. So I will build as it looks in the schematic with the exception of adding my standard +9v input like this:

[Groovenut]

I've built many of the RCC, it's a great simple circuit. It does need the bright mod. I personally use a 5-10p in the feedback loop and 100p in parallel with the 220k. also to avoid any LED consuction noise I strap a 10n across the LEDs. I roll my own LDRs and measure the light and dark parameters and sort accordingly. It's a wonderfully simple design that works very well.

[Ben Lyman]

Thanks Groovenut, I was planning on using the aforementioned mods but I will try yours as well. I rolled a diffused green vactrol w/LDR from Tayda and it's on the BB now, sounding really good in the stock form, so now to tinker with the mods and see if it gets even better. Thanks!