Flatline attack speed?

[BAARON]

Would changing the value of the 100ųF cap in the middle of the diode bridge affect the attack speed of John Hollis's Flatline compressor?  I finished building one today and it works properly, but I wish the attack was a wee bit faster to smooth it out more: the attack is a bit harsh at some settings, as is.  Any thoughts?

I'll post my (verified) layout soon, for those who are interested.  It's for the 15x15 small perfboard sold at SmallBear, for the sake of convenience.

[davepedals]

a 2 year old thread but i would like to know this myself so here goes.....

bump!

[Mark Hammer]

Yeah....ummmm.....about that cap.

Many people are likely working from the original Hollis hand-drawing, where the visual difference between a 'mu' and a 'n' is negligible.  That same drawing also uses a schematic symbol for the cap which is clearly indicative of an electrolytic/polarized type and different from the 1nf (.001uf) cap in the input.

RG's PCB layout lists that particular cap as 100nf not 100uf.  So, depending on whom or what you wish to believe, consider use of a 100nf (i.e., 0.1uf) cap in that position, and see if that makes the difference you want.

I've not built the unit myself, so I have no empirical confirmation.  And as close to saintliness as Brother Keen has been throughout his association with this forum, he HAS been known to make errors in drawings.  Indeed, I seem to recall a spate of hasty drawings during that historical period when young Mr. Keen was contemplating a career change in the midst of boring corporate meetings.   So an error is not entirely out of the question.

That being said, confirmation from those who have a functioning Flatline on their pedalboards would be useful here, to settle the actual value of that component.

[CynicalMan]

The Hollis drawing definitely shows 100uF. He just drew the proper lines on each side that a lot of us don't bother with. I've played around with this circuit, and if you use a cap lower than 47uF you get a growly distortion on the decays of notes. Switching it to 47uF gives a slight improvement, but the attack is really set by the LED-LDR. If you use a pre-made optocoupler like a CLM6000 or a VTL5C*, the attack is often faster than if you make your own.

[Mark Hammer]

Thanks for the info.  Makes perfect sense.  When we think of some other types of envelope-controlled devices, like filters, having a little bit of attack lag can sometimes provide a desirable character and feel.  In the case of compressors and limiters, though, the sort of lag time that might lend character to a filter sweep comes way too late in the game to constrain the pick attack and keep the piercing bits under control.  As Alex notes, you tend to rely on the dynamic characteristics of the LDR itself to do all of that for you.

[davepedals]

Many thanks for the info!

[Earthscum]

... and if you use a cap lower than 47uF you get a growly distortion on the decays of notes. Switching it to 47uF gives a slight improvement, but the attack is really set by the LED-LDR. If you use a pre-made optocoupler like a CLM6000 or a VTL5C*, the attack is often faster than if you make your own.

Thanks a bunch for that info. I now understand what was wrong with every one I've breadboarded. I was getting overshoots on the attacks on the first one I tried, along with the distortion as the notes decayed. I found an LDR that worked too fast in an envelope filter, so I set it aside and tried a comp with it. I had no more overshoot, but I still couldn't get rid of the decay distortion.

One time I remember trying different caps, up to a 220u. I either had distortion again, or I could hardly get any effect. I got frustrated and pulled that one. That may have been the last time I tried the Flatline, but now I think I'm gonna try it again.I have renewed hope that I can get it working.