Hi all, I'm new to this forum. After being a lurker for a couple of days :roll:  I've decided to register.

My first question , I have a Keeley SEM which I don't use that much. I'd like to try the Ultra upgrade just to see what the difference is. As far as I know, other than the cool knobs, there are just a few capacitor / resistor changes, but I have no idea which they are. Can anybody tell me?

Also, I have a Boss OD1 which kills the bass frequencies too much, though I like its basic tone. Can anybody suggest any changes in the circuit.

I have the schematic, but I don't know how to post it. It's a .pdf file

Thanks in advance

In the DS-Ultra mod we change C11 to a 0.047uF metal film or better and lower R13 to 2.4Kohm. As well as changing C3 and C13 to 0.1Uf metal film or better.

D5 change to 3mm red led (the power LED that we take out!) In the D-Ultra mod we switch in another LED in series with D4.

I got this in the Keeley site some time ago.

Here are the two schematics that you can compare for differences.  The components highlighted in red are the ones that he change:

Seeing Eye Mod:
http://axiseffects.home.att.net/misc/DS1_Seeingeye.gif

DS-1 Ultra Mod:
http://axiseffects.home.att.net/misc/DS1_Ultra.gif

Phillip

Do the extra cap and resistor changes in the Ultra mod make much of an audible difference?  Or is it mainly the extra clipping LED?

Yes, the extra caps and resistors in the Ultra mod do help improve the sound quality even more.  

As an extra mod, I would replace the 250pF capacitor across the base-collector of Q2 with a 470pF Silver Mica.

Phillip

Robert Keeley's website says the Ultra has a "Larger Silver Mica Cap installed to further smooth the overall sound" -is that the 47nF that replaces C11?  Would a monolithic or plain old greencap suffice?

Your schems are great btw Phillip.  Really easy to follow!  Keeley did a good job coming up with this mod too.

I suspect that the caps that he replaces with a "large Silver Mica" is C4, the 250pF ceramic capacitor that's across the base-emitter of Q2.  In the pictures of the guts of one of the pedals he modified for Steve Vai, there's a large Silver Mica capacitor in that position...and I've read an article that he wrote for a magazine mentioning that replacing that one with a 470pF Silver Mica helps smooth out the sound some.

Phillip

Hey phillip!  I added extra Ultra mods (sans LED) and it does make a real improvement.  I also added the 470pF cap as you suggested -and it's a real winner.  Unfortunately I couldn't find a silver mica, so I just used a regular Ceramic (it looks like a dinner plate compared to the rest of the components).

I wonder what it would sound like if all the Ceramic caps and Carbon resistors were replaced with Metal films too?  You'd have to be really bored to try...but hey, why not go all the way!  

p.s. thanks for the tips phillip.  my ds-1 sounds awesome now.

Hey thanks all for the answers !!!!!!!! I'll take the pedal to one of the techs at my company to do the changes (I'm really terrible at soldering :lol: )

2 more questions:

When you say "replace C2" or whatever, how do you know actually what capacitor is C2? because normally I don't see the numbering in the schematics...

Is it the values of the caps what makes the difference, or the material (carbon / metal film / silver mica ?

C2 is marked in the board of your DS-1. Some schematics have this marks too.

Quote from: phillip

As an extra mod, I would replace the 250pF capacitor across the base-collector of Q2 with a 470pF Silver Mica.

Phillip

Well, I'm finished with the mod, and I have to say that I like it better than the SEM !!!

My 2 cents on the mod:

This cap replacement removes a big part of the available gain. In fact i went through a panic stage when I re-assembled it , it was like "WTF has happened to the gain?". So after examining the pedal, I put the original 250pF and the gain was back. I even went beyond and lowered it to 200pF. Much more gain on tap.......

I also used a 3 way switch (on-off-on) as I had not any 2 way available. The effect in the "off" position is very nice. As you actually eliminate one of the diodes (there's only one left in the circuit), you have a volume bump and somewhat less gain and more punch.