DiSCO - Dirty compressor and overdrive

[samhay]

First, I should stress that if you like the sound of it now with the gain turned up, then it might not be worth trying to 'fix' it.

The problem with the way I had drawn it is that D1 shouldn't be connected to the junction of D2 and D3 but rather between the 2k2 resistor and the op-amp output. Changing your wiring won't fix this, you need to move the D1 anode to lug 1 of the gain pot / op-amp output by breaking the connection to the D2-D3 junction.

[Freppo]

Freppo, in your layout, you will need to shift the anode of D7 (your labelling) down to the op-amp output - it will fit if you move it left 2 rows.
Russ, not sure how you wired your switch, but it will probably work better if you do it as now drawn.

Okidoki. I will fix it and update the layout
cheers / Freppo

[Cozybuilder]

I see my description was badly worded, that would short out D3. I meant move the anode of D1 to SW1-2 (the junction of op-amp out and gain). The D2-D3 junction remains intact at SW1-3. Perf usually isn't a whole lot of fun to modify, however on this build D1 is at the bottom of the row of 3 diodes with an empty hole next to it, making the change straight forward. (well, after disassembly  )

Do you still have this on breadboard? Can you test out the way mine is currently wired to see if there is much difference in the sound? If you think its significant, I'll do it.
Thank you,
Russ

[samhay]

Yes - perf's shortcomings become significant when you have to make mods. Sounds like it should be about as easy as it ever is with your layout, but I will still feel bad about it if you decide to open it up.

I still have it on breadboard and will make a clip of the 2 options. Might not be for a couple of days though.

[Cozybuilder]

I'll probably open it anyway. Thanks for a great circuit, growing pains are part of the game.

[samhay]

Here is a quick clip recorded direct with gain at max and a fairly quick attack and slow recovery. SW2B is open, so the second stage (clipping to the moving ground) is symmetrical.

https://dl.dropboxusercontent.com/u/11996927/DiSCO_audio2.mp3

There are four SW2A settings recorded first with depth at minimum, then again at maximum:
1. SW2A closed - symmetrical clipping
2. SW2B open - asymmetrical clipping (latest / updated schematic)
3. SW2B open  - old / incorrect schematic with D1 anode connected to the junction of D2 and D3 - i.e. 2 diodes in one direction and none in the other.
4. same as 1.

setting 3 - the wrong one - is cleanest / has the most headroom with the depth at minimum (although if you turn the gain down, the other settings can sound like this).  However, with the depth at max, the clipping from the 2nd stage is pretty extreme in this 'setting ' and there is all sorts of compressor fluttering, etc.

In summary - Russ, it is probably worth opening her up. Sorry.

[Cozybuilder]

Sam-
Thanks for all- while I don't have the #3 condition, I'm going to change it anyway.

[jtn191]

Hey Samhay, any idea how this might sound as an outboard compressor on drums? I've been playing around with the Engineer's Thumb and it's usable!

[samhay]

I have no experience with drum compression.
The Engineer's thumb is a better compressor than the DiSCO, which is primarily an overdrive. That said, the DiSCO can have a fairly quick attack and both attack and release are adjustable over a wide range, which I imagine is quite useful when compressing drums. However, the gain stage is not flat and is voiced for guitar, so it will probably need to be tweaked to play nice with drums - to do this, I would remove R2 and C2, and make C1 somewhat bigger. You may also want to get rid of the symmetry switch and replace the 1N4148s in the first gain stage with LEDs to increase the headroom.

I have a few 'proper' compressor designs in the works. What is it about the ET that isn't ideal for compressing drums?

[jtn191]

My particular Engineer's Thumb has the "attack glitch" you hear some people talking about, only really noticeable on guitar. I mean it sounds pretty good...I would change the tapers/values of the attack/release pots. Most of the useful attack range happens in the first 25% of the turn. I don't hear much of a difference with release, though I have measured to ensure it works. I almost bought an Earthquaker Warden to try out as an outboard compressor. A "dirty" compressor would be very interesting to me in this context. Something like a Distressor or 1176. The 1176 has been cloned a lot...may as well go that route eventually.

[samhay]

Looked up the Warden - it's optical so might be fast enough for your needs (but then I am only wildy guessing).

I always suggest you try something on a breadboard before building it. Shouldn't take long to give the DiSCO a try, and I would be interested to hear way you think of it as a drum compressor - I like the idea of a drum overdrive too.
It also occured to me that you can run the DiSCO on higher voltage if you need more headroom - again you may have to tweak the filtering and diode choices though.

[samhay]

I finally got round to building this using my vero layout (below).
The combination of a switch and top mounted jacks makes for a snug fit, but the board fixes to the base happily enough.
Only changes are to the compression indicator / Millenium bypass, which I built as a daughter board. The trim pot parallel to the LED allows a nice adjustment of the LED range.




layout - now somewhat verified; save/view for a larger version:

[sajy_ho]

Nice work man, I tried to design a pcb layout for this pedal a month ago but somehow I found this circuit way more complex than I thought it would be! So I ended up with an unfinished work.
But your vero layout is awesome and I probably go with it.
Thanks for your sweet sounding circuit man.

[samhay]

Thanks.
The vero layout was a bit more difficult than I was expecting too - it's a bigger circuit than it looks.
It's a credit to Freppo that he could knock up a vero layout so quickly, and the only reason I didn't use his was that I wanted to try to tidy the wiring up as much as possible by putting wires as close to pots, etc. as I could.

[Cozybuilder]

Great looking pedal Sam 

I'm very happy with mine, its a superb circuit design.

[samhay]

Thanks Russ. Thought I was going to need your cut-offs at one point when I was trying to get the back on, but it all seems to fit ok with a bit or re-arrangement.

I hadn't played with the circuit for a while and I still like it post-build, which must be a good sign.
The symmetry switch seems to work better than expected too, and I'm glad I went to the trouble of including it. The 3 settings all have quite different character, with the asymmetric clipping being somewhat brighter, which makes for a strange sort of tone control. The volume drop when R5 is shorted is only marginally noticeable, which is a relief too.

[samhay]

Got around to re-posting images, etc...
https://samdump.wordpress.com/welcome/projects/disco-disco-2/  [edit - link fixed]





audio: https://www.dropbox.com/s/iyfklmfyr2v6auc/DiSCO_audio1.mp3?dl=0

[287m]

https://wordpress.com/page/samdump.wordpress.com/130

That blank Sam 
https://samdump.wordpress.com/welcome/projects/disco-disco-2/

[samhay]

https://wordpress.com/page/samdump.wordpress.com/130

That blank Sam 
https://samdump.wordpress.com/welcome/projects/disco-disco-2/

Thanks - link fixed.
In any case, there isn't anything there that isn't in the above posts.