Fulltone - OCD  [traced]

General documentation, gut shot, schematic links, ongoing circuit tracing, deep thoughts ... all about boutique stompboxes.

Postby Lovepedal Detective » 05 Jan 2008, 23:39

So does Fuller stop gooping a pedal after a certain amount of time? That OCD doesn't look like it was ever gooped.

LPD
Lovepedal Detective
Breadboard Brother
 
Posts: 121
Joined: 08 Nov 2007, 21:01
Has thanked: 0 time
Have thanks: 4 times

Postby madbean » 06 Jan 2008, 00:04

Yeah, they stopped gooping a while ago. What's the point after someone degoops and traces it (which will happen to every gooped pedal eventually :D)?
madbean
 

Postby vanessa » 06 Jan 2008, 02:05

madbean wrote:Yeah, they stopped gooping a while ago. What's the point after someone degoops and traces it (which will happen to every gooped pedal eventually :D)?


On top of that I'm sure it costs money to goop. When the cat's out of the bag why would Plexiplayer, I mean Fuller spend the extra money? The stupid part about it is why would you goop anything in the first place if you know that someone is going to RE it anyway? :roll:
vanessa
Cap Cooler
 
Posts: 468
Joined: 08 Jul 2007, 18:51
Has thanked: 0 time
Have thanks: 10 times

Postby vanessa » 06 Jan 2008, 02:27

What's better, OCD or the original Voodoo Labs?

For this message the author vanessa has received thanks:
BaklavaMetal (27 Nov 2012, 10:02)
vanessa
Cap Cooler
 
Posts: 468
Joined: 08 Jul 2007, 18:51
Has thanked: 0 time
Have thanks: 10 times

Postby bajaman » 06 Jan 2008, 02:57

What's better, OCD or the original Voodoo Labs?


they are both completely different pedals :roll: :roll: :roll:
PlexiPlayer would not rip anyone off :lol: :lol: :lol:
bajaman
User avatar
bajaman
Old Solderhand
 
Posts: 4345
Joined: 26 Jun 2007, 22:18
Location: New Brighton, Christchurch, NZ
Has thanked: 455 times
Have thanks: 1556 times

Postby briggs » 06 Jan 2008, 11:15

vanessa wrote:What's better, OCD or the original Voodoo Labs?


The diodes used to clip make the biggest difference. I prefer the mosfets, they sound a little less fizzy than the standard 1N4148 used in the original voodoo labs.
Image

I am Klon.
User avatar
briggs
Tube Twister
 
Posts: 1997
Joined: 12 Jul 2007, 11:02
Location: Breaking into Heaven.
Has thanked: 30 times
Have thanks: 124 times

Postby orogeny » 06 Jan 2008, 18:20

Earlier in this thread there were a couple posts from people who had breadboarded both circuits and found the OCD to be a big improvement over the VLOD. I'm no expert but I don't think the circuits are identical. It's obviously based on the VL but he's tweaked it quite a bit , no? And he continues to refine the circuit based on user feedback which is nice. Boss never revises their circuits even though the web is filled with comment like "this Boss pedal would be great if it had less treble, more bass, more gain,..." etc. The whole after market mod industry sprung up because Boss and other major manuf. refuse to change a few component values to make their pedals better.

Anyway, the OCD didn't quite do it for me through my fender amps. It was a bit harsh in the high end, too boomy in the low, not enough mids and the volume was unity @ 8:30. I did like the texture of the distortion and how well it cleaned up from the volume knob so I think the circuit has potential enough to try the newest revision and see if its an improvement.
orogeny
 
Posts: 30
Joined: 15 Dec 2007, 23:18
Has thanked: 0 time
Have thanks: 0 time

Postby MKB » 07 Jan 2008, 14:01

I first built the VLOD on perfboard, it sounded like a standardish MXR Distortion type pedal, it didn't do anything for me; kind of useless. I then modded it to the OCD configuration, being careful to use the proper cap dielectric types and the TL082 op amp. HUGE difference. All the tone characteristics and clarity in the OCD clips was there. I've used it as the main distortion on my pedalboard for months now, it has worked fine and completely killed my desire to find the perfect distortion box to add grit to a clean amp. I use it with the HP switch activated, and all controls at 12 o'clock. The real secret for heavy overdrive is to boost it with another pedal; the circuit sounds bad if the gain goes above 12 o'clock or so. If it has any problems it would be that it is a bit "marshally" sounding for some applications, but it apparently was designed to do that.
MKB
Breadboard Brother
 
Posts: 92
Joined: 06 Sep 2007, 13:03
Location: USA
Has thanked: 0 time
Have thanks: 0 time

Postby gaussmarkov » 09 Jan 2008, 19:12

The VLOD is not an op-amp clipper. In this sense the DOD OD 250 and the OCD clone (that I have seen: markm's schem) are much more similar. In the VLOD, the amplitude of the signal never gets over 1.1V for a 100mV guitar signal. I suppose this keeps the diodes from being super hard clippers.

At the gain stage, one of the biggest differences between the OCD clone and the DOD OD 250 is the lower corner frequency. The 2.2K resistor narrows the passband significantly so that the bottom of the range is 723Hz if I have done my calculations correctly. That is quite high.

This corner frequency is so high that it actually cuts the maximum gain of the op-amp to less than the usual 1 + R1/R2, where R1 is the resistor in the feedback loop. But that still doesn't prevent op-amp clipping over much of the range of the gain pot.

I bet that this attentuation of the low frequencies is responsible for a lot of the tonal differences. Remove the lows and you are going to get a less muddy distortion. This happens automatically in the DOD OD 250 because the gain pot is placed in R2 position of the voltage divider, so that as gain is increased the lower corner frequency rises. But it never rises to the level of the OCD clone.

By coincidence, I just happened to be working out some of this stuff (not for the OCD specifically). For more on my attempt to understand the theory, see Op-Amps 4: Divided Negative Feedback. There's also a math appendix: Divided Negative Feedback and Capacitors.

All the best, gm
User avatar
gaussmarkov
 
Posts: 18
Joined: 13 Jul 2007, 04:24
Location: Bay Area, California
Has thanked: 0 time
Have thanks: 0 time

Postby soulsonic » 09 Jan 2008, 19:24

Very nice, GM!
User avatar
soulsonic
Old Solderhand
 
Posts: 3531
Joined: 27 Jun 2007, 04:38
Location: Buffalo, NY
Has thanked: 56 times
Have thanks: 280 times

Postby gaussmarkov » 09 Jan 2008, 19:36

soulsonic wrote:Very nice, GM!


thanks! :D much appreciated. 8)
User avatar
gaussmarkov
 
Posts: 18
Joined: 13 Jul 2007, 04:24
Location: Bay Area, California
Has thanked: 0 time
Have thanks: 0 time

Postby gaussmarkov » 09 Jan 2008, 20:49

after i go through learning something, i often start to make connections with things that i have read before. so i just realized that R.G. Keen made a similar observation about the lower corner frequency in his classic "The Technology of the Tube Screamer" where he notes

With the stock 4.7K resistor and 0.047uF capacitor, this frequency is 720Hz. Only notes and harmonics above this point get the full gain of the distortion stage, and everything below it gets pregressively less gain - and distortion. This fact probably accounts for the lack of "muddiness" of the distortion in the TS series as bass notes are clipped least.


i think i mentioned in an earlier post that markm's schem shows values that are similar to the tubescreamer for this part of the circuit. the reason that the frequencies mentioned are so similar (723Hz and 720Hz) is that the "time constant" (the product of the resistance and the capacitance) is almost the same: 4.7 x 47 = 220.9 and 2.2 x 100 = 220. see, for example, the wikipedia entry for "RC time constant."
User avatar
gaussmarkov
 
Posts: 18
Joined: 13 Jul 2007, 04:24
Location: Bay Area, California
Has thanked: 0 time
Have thanks: 0 time

Postby gaussmarkov » 12 Jan 2008, 01:23

i put together a voodoo lab overdrive layout that appears on gaussmarkov.net. the principle differences with the OCD are well-discussed here and similar changes have been applied by folks here and diystompboxes to many other circuits, so i will leave the details to other posts.

i kind of like leaving the gain pot where it is in the voodoo version. it makes the high pass corner frequency of the first gain stage go up and down with the gain so that when there is relatively little distortion and less need for attenuating lows they are there.

given all the info here that inspired this effort, the VLO seemed like a good one to repost here. as usual, you can pull the Eagle CAD files down from gaussmarkov.net and change my layout as you please. if you come up with something you like, please share. 8)

all the best, gm :D
User avatar
gaussmarkov
 
Posts: 18
Joined: 13 Jul 2007, 04:24
Location: Bay Area, California
Has thanked: 0 time
Have thanks: 0 time

Postby briggs » 12 Jan 2008, 14:08

Great work Gauss. Looks like a nice project you've put together there. I noticed on you scheme the first op amp stage only has a gain of 11, is this to avoid op amp clipping?
Image

I am Klon.
User avatar
briggs
Tube Twister
 
Posts: 1997
Joined: 12 Jul 2007, 11:02
Location: Breaking into Heaven.
Has thanked: 30 times
Have thanks: 124 times

Postby gaussmarkov » 12 Jan 2008, 14:27

briggs wrote:Great work Gauss. Looks like a nice project you've put together there. I noticed on you scheme the first op amp stage only has a gain of 11, is this to avoid op amp clipping?


thanks. :D that's the voodoo lab overdrive spec and i suppose that is what they had in mind. it certainly makes it different from the dod od 250 and fulltone ocd. :wink:
User avatar
gaussmarkov
 
Posts: 18
Joined: 13 Jul 2007, 04:24
Location: Bay Area, California
Has thanked: 0 time
Have thanks: 0 time

Postby s.r.v. » 12 Jan 2008, 19:33

i didnt really want to read the whole thread, but i have made an OCD clone. if you search OVD in the layouts gallery over at diystompboxes it will come up. I also have a real version 3 OCD. they sound pretty similar, but the clone lacks in the harmonic and rich sound quality the real one has. could be the parts, but if you make it make sure to ground the lug on the tone pot not in use! the tone section will not work if you dont
User avatar
s.r.v.
 
Posts: 34
Joined: 12 Jan 2008, 19:17
Has thanked: 0 time
Have thanks: 0 time

Postby JHS » 13 Jan 2008, 11:34

There's no need to ground the 3rd lug on the tone pot. It's a simple treble-cut control and it works w/o grounding the 3rd lug.

No guitar has a grounded 3rd. lug on the tone pot and they all work as they should.

All OCDs differ, due to the tolerances of the IC and other parts, a bit in terms of harmonics, dynamics and sound.

IMHO the IC is a crucial parts, for best results use a 082 from the same manufacturer as Fulltone.

JHS
JHS
Cap Cooler
 
Posts: 484
Joined: 14 Jul 2007, 12:20
Has thanked: 0 time
Have thanks: 3 times

OVD

Postby alman » 13 Jan 2008, 13:38

I think what S.R.V. is saying by "ground the third lug not in use" is if you are using the layout in diystompboxes the 2nd and third lugs are shorted together so the first lug needs to be grounded to complete the circuit.

In a guitar the tone pot doesn't short two lugs and only uses the middle and whichever other lug to make it variable.
alman
 
Posts: 2
Joined: 23 Nov 2007, 01:26
Has thanked: 0 time
Have thanks: 0 time

Postby s.r.v. » 13 Jan 2008, 16:39

what i meant was if you build from this:
http://www.aronnelson.com/gallery/v/Mar ... 1.png.html
then you need to ground tone lug #1, or else the tone section won't affect the sound.

I've heard that the components do make a big difference, so I might try swapping some in and out. still a great build
User avatar
s.r.v.
 
Posts: 34
Joined: 12 Jan 2008, 19:17
Has thanked: 0 time
Have thanks: 0 time


PreviousNext

Return to Boutique Stompboxes dissected...

Who is online

Users browsing this forum: Agent86 and 17 guests