Ross Compressor mods!

[ZtaRDuZT]

Has anyone tried a pot to alter attack instead of the hammer mod?


What value pot? 250k? 100k?
Add a resistor in series before the pot? 10k? more? less?
What was the result? good? bad?

Trying to figure out wich way to go with my ross clone.
Any ideas out there are most welcome.

[Mark Hammer]

The so-called "Hammer mod" is really a response to how little obvious change there is as a result of using a pot.  I'm not saying the pot is absolutely useless, but I'm a guy who can never get enough controls to twiddle and I found myself basically using one extreme of the pot rotation or the other.  So why even have a pot when you're probably not going to do more than that?  The 3-way thing probably meets the needs of 95% of all players...seriously.  If you are in the other 5%, use a pot with my blessings.  A 150k pot will be next to impossible to find, so the next best thing is to use a 250k pot and a fixed resistor in parallel to achieve a maximum 150k resistance.  There is probably some utility in experimentaing with different positions for the parallel resistors to get different tapers.  See "Secret Life of Pots" over at Geofex for some ideas.

[ZtaRDuZT]

What could be better than an answer from the man himself


Struck me kinda odd to choose a 3-position switch when a pot would give you the same thing.......
and everything in between.
Now I understand better, thx.
So I guess the choice of 150k is proven good and there is no need to stray far from that. Nothing
much will come out of it. Or?
I guess I'm gonna use a pot because I'm using a 1590BB, couldn't get it to fit a 1590B with my setup.
I got plenty of room left for another pot in a 1590BB, so I might as well. (Already drilled and ready as well )
Who knows, I could fall in love with the attack at 65,7k

It seems like you've had the chance to try different settings and come to the conclusion that the really intresting settings
lie around 10 to 50 to 160, is that about right?
Since getting a 150k pot would prove difficult I guess I could aim for a 250k if that assumption holds true.

Really appreciate the input!

[1978]

Just to add my 2 cents -- I did the "Hammer Mods" last night to my Dynacomp clone.  My biggest problem was loss of treble, but while I was at it I did the attack/release/decay/what-have-you mod.  I was thinking of using a pot--but I tend to turn all the knobs all the way to the right, and so the SPDT seemed like it would force me to actually try the other settings.  It sounds great in the apt., and I can't wait to gig with it Tuesday.  Thanks Mark!

[Mark Hammer]

If cost and space aren't an issue (and I understand that for some people the difference between a $2 pot plus $1 knob and a $1.50 switch can be meaningful), by all means go for the continuously variable control.  Your reasoning that the setting you like may be something *other* than the suggested presets is absolutely sound.

The suggested values for the preset are based on the following logic process:

• the Dynacomp and Ross adopt a set resistance of 150k, and people like that
• all other commercial compressors that have adopted a variable resistance use a minimum resistance of 10k and a maximum resistance of 160k (150k pot plus resistor)
• the middle setting of a 3-position switch becomes useful when the degree of change between positions 1 and 2 is the same as between 2 and 3
• I tried the suggested resistances and they achieve noticeable changes
• presets that reliably reproduce a given sound are frequently preferable to continuously variable settings that may sound terrific but be next to impossible to nail every single time out.

I don't think it's a particularly brilliant idea, but it gets the job done with minimum fuss and space and is the sort of thing gigging musicians like because it gets the job done.  Naturally, those priorities don't have to be your own.  You may also find that smaller and larger values of that critical resistance do useful things for you too.  Several other companies that used the identical sidechain circuit (and I mean *identical*) have had the option to explore other resistance values and never diverged from the 10k/160k range.  That maybe their unwillingness to explore, or sheer laziness, but my guess is that it struck the right balance between avoiding envelope ripple and maintaining some degree of responsiveness.

In terms of equal proportional change, the ideal is to have the medium setting provide the same ratio change from fast as from medium to slow.  The charge-up time of the 10uf cap will be a function of the resistance and cap value.  If your medium setting gets a resistance of around 40k that makes the cap charge up 4x slower than if the resistance is 10k and if the resistance is 160k it charges up 4x slower than that, so equal changes in charge-up time.

Of course no one is *required* to use a 3-position switch.  A 2-position switch may do all you need if it gives you fast and slow.  Personally, though, I find that 3 positions strikes a nice balance between what a continuous control yields and the simplicity but inflexibility of one setting.  I also like it because it takes up much less space than a 4 or 5 position rotary switch.

Getting 10k/40k and 160k with a switch is easy to do.

• Run a 10k and 150k resistor in series between V+ and the 10uf cap
• where the 2 resistors join, run a wire from there to the centre lug of the toggle
• one outside lug is going to run directly to the other end of the 150k resistor
• the other lug is going to run to a 39k resistor and then to the other end of the 150k resistor

When the toggle is in the middle position, there is no connection to the side lugs so the resistance is 160k (10k + 150k).  When the toggle is in one of the side positions, the direct connection to the other end of the 150k shunts that resistor so the effective resistance is 10k.  When the toggle goes to the other position, a 29k resistor is placed in parallel with the 150k, giving a combined resistance of 30.95k, which gives about 41k when in series with the 10k.  So, you go from 10k to 41k to 160k, which is close to equal proportional change.

[stumper1]

I use Mark's 3 position switch and it works great.  Perfect blend of useful and predictable.  If you really want to try the pot I believe Keeley has 150k pots made for his compressors and will sell them to DIYers.

[ZtaRDuZT]

If going outside the range 10-160k could cause problems I guess I'd want to keep
myself within that range. So a 150k pot and a 10k resistor in combination is the
way to go, if you want to use a pot.
If Keeley has a 150k pot it will still cost me way more than a switch since I gotta
ship it to Sweden. Ordering a 150k pot + shipment might not be the best solution
here, in terms of money anyway.

I think the hole I drilled will fit a switch as well, I can still go with a switch, or at least I
hope so.
If I'm not mistaken the "Secret life of pots" article describes how to make a custom value pot.
Gotta look in to this some more before I decide.

Thx very much for sharing!.

[dubs]

So you would use a 380k resistor in parallel with 250k pot to get approx 150k?

I find i get overdrive in the last quarter turn of the attack pot  just using 250k

[mojotron]

I traced out a Fender COM-1 - which is a ROSS compressor with a great attack mod. The thread is:

http://www.elixant.com/~stompbox/smfforum/index.php?topic=40575.0

If interested I can draw it up. I have not modded a ROSS compressor with this mod yet, but I plan to.

[MR COFFEE]

Hi mojotron,
I read your description of the differences from the Ross, but I would be interested in seeing the schematic if\when you draw it up, even if it is a partial.

It's SO much clearer than verbal descriptions!

Thanks for sharing!!

[nelson]

I traced out a Fender COM-1 - which is a ROSS compressor with a great attack mod. The thread is:

http://www.elixant.com/~stompbox/smfforum/index.php?topic=40575.0

If interested I can draw it up. I have not modded a ROSS compressor with this mod yet, but I plan to.

I would be interested in that too.

[mojotron]

I traced out a Fender COM-1 - which is a ROSS compressor with a great attack mod. The thread is:

http://www.elixant.com/~stompbox/smfforum/index.php?topic=40575.0

If interested I can draw it up. I have not modded a ROSS compressor with this mod yet, but I plan to.

I would be interested in that too.

Cool, I will draw this up - I would really like to get one built as this is my favorite compressor - but extremely noisy and I think I can fix that with some redesign. I also thought I would make a daughter board with a discrete component implementation of a CA3080 that just wired into the ROSS - I'll get to all this Friday night.

[gaussmarkov]

me, too!  yes, please mojotron. 

[ZtaRDuZT]

Count me in as well mojotron. it'd be interesting to see what you come up with.
Hopefully before I get mine done
I got the last of the parts I was waiting for the other day and the box is about to be painted.
My primer actually broke down today so I gotta get me another one. The bottle is basically
full but nothing comes out of it.
I'm working on 4 pedals at the same time now so I could easily spend some time on the
others for a while.