trimpot in ross compressor

[blanik]

i'm about to box my tonepad Ross compressor and i don't know what is the trimpot for... 
i did the orsange sqeezer and was able to adjust the trimpot until the decay sounded natural but they don't say on TP what's the Ross comp trimpot is for.... same as OS or attack adj.?

how should i adjust it?

thanks

R.

[blanik]

i tried the search and couldn't find a clear awnser, some said the trim was an attack/release (linked in one trimpot) adjusment other said it was for bias?

?

R.

[stumper1]

From Tonepad

Q. How to set the trimpot?

A. Set the trimpot in the middle, slowly turn it to both sides while letting single notes ring. Leave it in a position where the decay doesn't sound gated.

-*-

[blanik]

dooh... i checked the PDF document but not the web page...

thanks.

R.

[Jay Doyle]

To be honest, the easiest way to set the trim is to crank up both knobs, turn up the volume on your guitar and adjust the trim to where you hear the MOST noise.

[R.G.]

Frankly, the simplest thing to do is to replace it with two fixed resistors of half the pot value.

That is a BALANCE control, not a bias control, not an attack or decay control. It is intended to provide the best balance of the inputs so that there is least feedthrough of the control signal in the Iabc pin to the output. In most cases, you can either set the pot to middle and forget it or replace it with two equal value resistors and forget it.

ICs were worse back when the Dyna/Ross compressors were first designed and it might have been needed. I've seen very few instances with today's ICs where it's really needed.

[blanik]

thanks for the precision!

R.

[R.G.]

By the way, Jay actually had his finger on it. The "most noise" position is also the "best balanced" position as a side effect, since when both sides are balanced, they both contribute noise equally.

[blanik]

sooo counter-intuitive 

R.

[blanik]

small question about compressors, (mine isn't boxed yet and i nerver had one before)...

when you roll down your guitar volume to get a clean sound, how does the comp reacts? does it keep the volume high so it's hard to control with your guitar volume??

R.

[R.G.]

when you roll down your guitar volume to get a clean sound, how does the comp reacts? does it keep the volume high so it's hard to control with your guitar volume??

A compressor takes a wide variation in loudness and compresses that range into a small variation in loudness. What comes out has much less variation in loudness than what went in.

There are limits, of course. There are signals too large to be contained by the compressor, and these are either passed through at a larger level or distorted depending on the compressor circuit. There are signals below the compressor's threshold, and these have their original variation in loudness; however, being quite small, they are less noticeable.

So if you roll down your guitar volume, you feed the compressor a smaller and smaller signal. It reacts by boosting the signal more and more to try and keep it the same. Within a wide range, the output of the compressor does not vary much. Each note sounds about the same level until it decays below the compressor threshold. Reducing your guitar volume reduces the input signal, but doesn't change the output much. The compressor is doing what it should - keeping its output the same.

What does change is any noise. All amplifiers produce hiss, and the higher the gain, the more noticeable the hiss is on the output. With a compressor, the gain varies inversely with the input signal. So a loud signal causes low gain, and low noise. As the signal gets smaller, the compressor gain goes up to keep the output level the same, and so noise increases. With some compressors you can actually hear a rising tide of hiss behind the note as the gain rises. So reducing your guitar level may cause more hiss but the same loudness.

[markm]

I agree with RG.
Sometimes however, rolling the Vol back a bit can open up some real nice tones from a comp and you won't be hitting
the comp as hard either so, less squish.

[R.G.]

What can happen if you get down in the low end of the compression range is that only the loudest notes get compressed.

[chieljan]

Hey! Nice coincidence, this post on the Ross trimpot: I was thinking about taking a Ross compressor as my next build, but I can't find a 2k trimpot at banzai. Can I replace it by a 2,5k, or something else? Or, Blanik, did the 2 1k resistors suggestion by RG work for you?

Thanks! Chieljan

[markm]

I think the 2.5 would be okay.
I must confess though, about the resistors, I have had Dyna/Ross builds where the trim did not fall in the middle for the ideal setting.

[blanik]

sorry Chieljan, i used the 2k trimpot, i just didn't know how to adjust it... but i guess 2k5 wouldn't be that far off...


R.