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Laurie
Double Platinum Member
Canada
4854 Posts |
 Posted - 05/31/2008 : 03:48:01
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Please note that all this is still a bit experimental, so if you try it and it doesn't work, please post in here and we can take another look at it. Zentropa made this all possible by trying all the ideas on his SD-1.
Looking at the circuit for the stock SD-1, it seemed to me that the only way the input could bleed to the output or the tone could bleed away was through R2 into the +4.5V rail. The mod is simply one to "beef up" the +4.5V rail so it is unaffected by any input signal, and can't pass the input signal to the output.
Essentially, R18 and R19 and C11 form a voltage divider and low pass filter. Lowering R18 and R19 and increasing C11 will give more stability to the +4.5V rail than the standard values (it lowers the filter cut-off frequency to make it closer to being completely stable or "pure DC").
Lower resistors = more current to keep the filter capacitors charged.
Higher value filter capacitor = better able to keep the rail at a constant voltage when the rail is loaded down (e.g. by a signal applied through R2). C11 at 100�F electrolytic provides stability to the +4.5V rail for slowly changing rail load.
The additional 1�F ceramic is to provide transient filtering for the +4.5V rail - it responds to fast transient loads on the rail better than the electrolytic capacitor (different physical properties).
So, the mod is dead easy - replace R18 and R19 with 10k resistors, replace C11 with a 100�F capacitor. Add a 1�F ceramic capacitor across C11.
Standard circuit:
Laurie mod circuit:
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Edited by - Laurie on 05/31/2008 15:50:57 |
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zentropa
Gold Member
USA
837 Posts |
Posted - 05/31/2008 : 07:02:30
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hehe.
this almost drove me insane.
my gear is currently in storage following my apartment being flooded by an upstairs neighbor who broke their toilet and rained butt water down through the walls/ceilings for 15 hours.
have 1 guitar at my disposal and a craptastic solid state amp.
soooooo much easier to trace the bleed on a tube amp since the tone change is more significant... couple that the one guitar i have is a single humbucker w/ a dimarzio super distortion didn't help on that for the solid state amp.
almost drove my gf nuts with my going into the pedal... then going straight to the amp... then going into the pedal into another pedal etc. nightmare. so happy it's done :) |
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Dr. Bob
Moderator
Australia
6593 Posts |
Posted - 05/31/2008 : 07:31:42
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Hi Laurie
Well thought out Laurie.
Have you tried this with an unmodified (bleed Fix) SD-1?
I have noticed that over the years the resistors,
in the Boss split rail voltage divider, have changed values many times.
In the later pedals, they use a transistor, or a transistor/zener to buffer & isolate the split rails.
Good work Laurie
Regards Dr. Bob |
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zentropa
Gold Member
USA
837 Posts |
Posted - 05/31/2008 : 07:38:32
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haven't tried it on a stock SD-1.
i think i'm getting one in a trade tomorrow and may give it a whirl.
the pedal i did it on was built in 2006.
i still plan to do the normal J201 fix on MIJ SD-1/OD-1's but will do this on the taiwan SD-1's i get. |
Edited by - zentropa on 05/31/2008 07:39:54 |
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Dingus
Silver Member
USA
472 Posts |
Posted - 06/03/2008 : 20:17:45
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| interesting guys.... have either of you seen the SD-1 Bleed Fix mod that Brian Wampler (Indyguitarist) put out via his newsletter a while back? I think yours requires fewer component changes, but I'll have to see if I can't find his e-mail. |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 06/03/2008 : 20:25:56
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quote:
Originally posted by Dingus
interesting guys.... have either of you seen the SD-1 Bleed Fix mod that Brian Wampler (Indyguitarist) put out via his newsletter a while back? I think yours requires fewer component changes, but I'll have to see if I can't find his e-mail.
Is that the one with the J201 FET? |
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zentropa
Gold Member
USA
837 Posts |
Posted - 06/03/2008 : 23:33:31
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if it's the JFET one, this one was developed because the JFET one wasn't hacking it with modded pedals (especially those with "clarity" type mods) since it eats a ton of high end.
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MoonWatcher
Bronze Member
USA
98 Posts |
Posted - 06/22/2008 : 22:30:31
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quote:
Originally posted by Laurie
Please note that all this is still a bit experimental, so if you try it and it doesn't work, please post in here and we can take another look at it.
Hey folks -
First post, probably of many. Please excuse my rambling. I think I've gone off the deep end with this one much like Zentropa has.
Most of my tweaked SD-1's are still bleeding even with this rail stiffening mod (currently have 3 in the works).
I do have a few observations, for what they're worth -
1. The bleed is most clearly heard through little solid state amps, IME. I simply can't hear it through my '71 Vibrolux Reverb, which is my main amp.
2. Park another buffered pedal in front of an SD-1, and the bleed disappears, IME. Possibly the easiest fix of all.
3. A-man and a fella named Claus Holm Jensen have come up with a solution that only involves moving one component and one wire. Since they charge $10 for the tweak, I don't think they'll be divulging the particulars any time soon.
4. The older full size metal Dano pedals use a 4.7k/4.7k setup for the rail splitter. They also use a 560K resistor for the equivalent of R2. Lastly, the stabilizer cap in the rail splitter is a big 'un - ~500 uF. These pedals may sound overdamped to some, but zero bleed.
My biggest "bleeder" right now is an SD-1 that's kinda in the OCD vein - I have a pair of mosfets as clippers where C4 used to reside. I've bypassed the gain pot with a 330K resistor to convert it to a quasi 250K log pot, as there's drive to spare.
If I had to venture a guess as to what A-man is doing, I'd think it would have to do with relocating where C3 dumps into the rail. R2 is no doubt letting signal through, but what's the most sensitive area where it's being picked up?
I was also comparing the original TS PCB, as well as clone boards that still utilize the buffer trannies. I noticed that The input and output transistors' buffer resistors are on opposite sides of the board.
I used to do a lot of work on tube amps. One of the biggest noise culprits is AC filament noise. The easiest way to fix it is by floating the filament ground above zero by using DC offset - typically by forming a voltage divider on a cathode or something similar. It got me to thinking - R2 is 470K, whilst R12 and R13 are at 1 meg...This means that the signal can skate under everything else in the 4.5V line and surface where it likes to...
The answer has to lie in the layout of the TS board - where everything is parked on the 4.5V rail, along with the fact that both buffer trannies and both switchers get the same impedance on the input, of 510K.
Does it sound like any of this nonsense makes sense? |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 06/23/2008 : 01:20:48
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Here's a couple more things to try...
1) Make R2 1M and attach it to +9V instead of +4.5V
2) Put the non-R6 side of C3 to ground instead of the 4.5V rail
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zentropa
Gold Member
USA
837 Posts |
Posted - 06/23/2008 : 03:26:14
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moon:
i don't want to add to your neurosis here but here's what i found...
i did notice a tone difference after the mod when running through the pedal, but it was on par with the tone difference of running through any other boss pedal inline between the guitar an amp (e.g. going through my TU-2 before the amp had about the same tonal change as going through the SD-1). what i was using as a benchmark was making sure other distortion pedals sounded the same when running before and after the SD-1.
i tried R2 with both 620k and 1M... and didn't like it.
when i raised R2 above 470k it seemed to f with the high end (in the same way the J201 bleed fix does). granted, when i was testing this it was on a FD2 modded SD-1 w/ hifi mods and i'm guessing this would be less noticeable on a stock pedal.
1M gave a definite cap on the high end (~5500hz) and 620k had a bit more headroom on the high end but definitely had an artificial ceiling on it (~6500hz). the 470k didn't seem to steal treble when you switched the pedal to bypass (seemed to have a peak frequency in the 8000-9000hz range).
the tests i did with this mod did have a tone color change (seems like there was a slight scoop in the 1000-1500hz range) but it didn't cause any added gain through the tube amp. a bypassed stock SD-1/OD-1 with the drive set high behaves like an increase in 4 on the gain knob of a high gain tube amp.
hehe, i just upgraded my gf's amp to a better solid state amp than i was testing on before and this one shows all the bleed better than the other one did.
i believe the next place to experiment is probably on the R18 and R19 values. if you do any tweaking on those please share the results.
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Dr. Bob
Moderator
Australia
6593 Posts |
Posted - 06/23/2008 : 10:18:28
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Hi MoonWatcher
Welcome to the forum from Australia.
It's great to see more Tech. guys coming on board.
Regards Dr. Bob.
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MoonWatcher
Bronze Member
USA
98 Posts |
Posted - 06/23/2008 : 21:10:15
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quote:
Originally posted by zentropa
i believe the next place to experiment is probably on the R18 and R19 values. if you do any tweaking on those please share the results.
First - thanks for the welcomes!
Second - regarding R18 & R19, I have dropped them down to 4.7K on one ped. No audible difference that I can detect (with R2 kept at 470K). There's probably a negligible improvement in DC stability, but probably not overt without going to a HUGE cap for C11.
I've currently got myself convinced that C3 is the sensitive spot, more precisely the interaction between C3 and R4.
I'm also intrigued that Q1 and Q2 are segregated by a pair of 22K resistors, whilst the TS has none, and the TS feeds both with a dedicated 510K resistor.
I know that it's all the rage to run peds at 12V or higher these days, and I wouldn't be surprised if that added enough buoyancy to stop the bleed, but I simply don't like the tonal changes when things go much above 10V, personally...
I've got 3 very different SD-1's on my board right now, so I'll try to keep everyone up to date on anything relevant that I found out. |
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zentropa
Gold Member
USA
837 Posts |
Posted - 06/23/2008 : 23:06:53
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hrm. on most of my mods we've swapped out C3 for a 0.1uf.
if i was better at soldering i'd probably do more tweaking.
how huge of a cap is needed for C11 do you think?
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MoonWatcher
Bronze Member
USA
98 Posts |
Posted - 06/24/2008 : 02:24:37
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quote:
Originally posted by zentropa
how huge of a cap is needed for C11 do you think?
In my Dano Daddy-O and FabTone, the rail is 4.7K/4.7K with a massive 470 uF cap! |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 06/24/2008 : 03:19:52
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Hi Moonwatcher! Sorry I forgot to say...  WELCOME!!
I still think it's worth trying to take the 4.5V rail out of the picture a little. R2 is simply the DC bias resistor, so attaching it to +9V instead of the +4.5V should be OK (with commensurate increase in value). C3 to ground instead of the 4.5V rail should also work... (and it may turn out to be the most effective thing) - I think it just needs a solid rail to connect to. Anyway, worth trying.
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Edited by - Laurie on 06/24/2008 03:20:41 |
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MoonWatcher
Bronze Member
USA
98 Posts |
Posted - 06/25/2008 : 04:53:45
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I'll try R2 to +9 and C3 to ground next.
I just got my hands on an early Polytone Mini Brute - this could be the best solid state amp that I've heard pedals through. I know it was designed for jazz, but it really works for pedals of all kinds.
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Topic |
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SD-1 "Laurie & Zentropa" bleed mod
