Ross "Compressor" or Optical Compressor?

[Jorge_S]

I am planning my first compressor build, and I have trouble deciding to go with a Ross Compressor or a DOD 280A.

Both plans/schematics I'd be using will be the ones from General Guitar Gadgets.

The Ross would also have the mods described in:
http://fuzzcentral.ssguitar.com/ross.php
http://www.lynx.bc.ca/~jc/pedalsDynacomp.html

Which one do you recommend me to go with? the Ross (which I've acts more as a "limiter" than a "true" compressor) or the optical one? It'll be used to feed a Brown Sound in a Box and mostly used for heavy metal leads.

thanks!

[PRR]

> I've acts more as a "limiter" than a "true" compressor

There is no core difference. A limiter is a "hard" compressor.

Ross and DOD use nearly similar sidechains (where comp/limit "hardness" is designed-in). The DOD makes its threshold rectifiers work harder, and also allows them to bias-down, which is perhaps why it seems "soft".

Beyond that.... Ross et all use an OTA chip which is somewhat fragile and hard to get (Aron or Bear has 'em). DOD uses a Vactrol which is somewhat easier to get(?) and far more robust, in a much simpler (EZ-build) circuit. I used to build opto-limiters an hour before the show. I've worked with OTAs and often gone back to optos.

Here's a hasty-hack with Ross's hard sidechain adapted to the DOD opto.

Softening the sidechain is perhaps easier: remove base diodes, put about 100 ohms in each threshold transistor's emitter.

[roseblood11]

There are many more compressor projects:

- Mictesters "Really Cheap Compressor" and "Compression Sustainer"
- Bajamans version of the Demeter Compulator and his Optical Limiter, that is based on the Demeter as well...

[Le québécois]

I build the dynacomp (identical to the Ross or almost) and the DOD. The DOD is still around........

PRO dod : the sustain is longer (more possibility of inducing feedback while playing with distortion pedal (in a good way I mean)).
CON : maybe a little noisier but It may be due to  some tweaking that I did with the opamp gain resistor against the LDR to maximize the sustain (you need to find a compromise between more sustain and more noise or smaller sustain and less noise).

I also implement an attack knob. or maybe it is on the schematic? I don't remember. easy and effective over the full knob range. I can share how, if i dig a little in my files. 

The sound of the dynacomp is very bright and clear while the dod have more bass in it. This increase amount of bass emphasis the compression. At least that is what I feel.

[Jorge_S]

Thanks to all for your answers!

I think I'll end up building both, and then decided about how they sound and all. Luckily I was able to find both IC's on ebay for fair prices, and I've already bought them.

As stated in my previous post, Ross model will have some mods to give it more headroom, are there any mods you will suggest for the optical compressor besides the ones given by PRR?

I'm also considering building Mictesters compressor shown http://www.freestompboxes.org/download/file.php?id=6250&mode=view (thread here http://www.freestompboxes.org/viewtopic.php?f=13&t=8513). Any suggestions/opinions on this?

thanks again!

[Jorge_S]

I also implement an attack knob. or maybe it is on the schematic? I don't remember. easy and effective over the full knob range. I can share how, if i dig a little in my files. 

Attack knob for the DOD? that sounds nice, can you share the schematics?

The sound of the dynacomp is very bright and clear while the dod have more bass in it. This increase amount of bass emphasis the compression. At least that is what I feel.

That's why I'm doing the mods I mentioned in my first post, they supposedly give more bass to the sound. GGG schematic already had one of the mods I planned.

thanks!

[Le québécois]

Attack knob for the DOD? that sounds nice, can you share the schematics?

It's based on Tonepad schematic. Basically, the attack knob (some may say that ''attack'' is not the proper term) replace the 4.7k between the LED and the transistors. The pot was wired as a variable resistor and I certainly add a fix resistor to avoid a situation with 0k. I will have to open the unit to confirm the value (I will... given more time....a day or two). Another Mod that I did was to add a capacitor (50Pf or close) in parallel with the 1M resistor connected to Pin 1 and 2 of the Op amp. This gave some sparkle to the sound.  The 22k to ground connected through 0.05 µf and the 500k pot was decrease to 18k and maybe more (will confirm). This increase the max gain = sustain.  I use a homemade LED/LDR.
Finally, for the attack knob to work better it is possible that I've changed the 47µf capacitor to something bigger or smaller. This will interact with the attack knob since the resistance from this knob will control the charging time of the cap and the time require for the led to dime and hence for the gain to increase which kick in the sustain/compression.
It's a long time, I hope I have not made any mistake in my explanation.

Charles

[Jorge_S]

It's based on Tonepad schematic. Basically, the attack knob (some may say that ''attack'' is not the proper term) replace the 4.7k between the LED and the transistors. The pot was wired as a variable resistor and I certainly add a fix resistor to avoid a situation with 0k.
Charles
[/quote]

I was planning on using an attack switch instead of a knob, as referenced here in red:
http://fuzzcentral.ssguitar.com/ross.php

They state that the intermediate values will make not much of a difference, so using 3 pre-defined attack values is good enough. Any reason you think the knob will be a better option?

thanks!

[Le québécois]

Ok, I have no time.... here is it in fast speed....

The cap in parralel on my unit is 100 pf see previous post
The 4,7K was replace by a 10 k pot plus 470 ohm see previous post
it was 18 k instead of 22k. see previous post
The 47 µF cap was change to 10 µF (this give faster response)

I agree that the switch is also good but for me a dpdt switch or a 10k pot is the same price and take the same amount of space in the box so I rather use a pot. I use it normally at around 3/4 or 0/4.

will come on this if you have question tomorrow.
good luck