I'm back to working on this, but I have a couple of questions about previous posts in this thread. I really like what adding a .001u cap in parallel with the treble cap does to fatten the tone with the PAB engaged, particularly if it has 470k in front of the cap. But the overall boost is still pretty high.
mdroberts1243 wrote:After reviewing the thread again, it seems like a lot of the phat effect you're after might come just from adjusting the PAB lift resistor... most of the BM builders seemed to have gone for a pretty low one with the fender-ish stack (I ended up at 72k). Maybe 4.7M is sufficient for the skyliner stack. You might not have to go as far as modifying the PAB switching and adding in the additional treble cap.
I'm not sure what resistor is being spoken about here. Where is this typically placed?
bcook wrote:Try soldering a 1M pot between the low treble pot lug and the high bass pot lug, and see if you can dial in your PAB.
-Bob
Huh? Can you describe this in a bit more detail? First of all, are you talking about the same resistor as mdroberts? And I'm not sure which lugs you're referring to with the terms high and low...
I'm not sure what resistor is being spoken about here. Where is this typically placed?
Their talking about replacing the 22M resistor.
Huh? Can you describe this in a bit more detail? First of all, are you talking about the same resistor as mdroberts? And I'm not sure which lugs you're referring to with the terms high and low...
High means 'top' and low means 'bottom' when looking at the schematic. The PAB breaks the connection between the bottom lug on the treble pot and the top lug on the bass pot and places the 22M resistor there...you're putting a much smaller resistance in there to get some fat 'bleeding' back into the signal. So just put a 1M pot in there and dial it in.
I'm not sure what resistor is being spoken about here. Where is this typically placed?
Their talking about replacing the 22M resistor.
Huh? Can you describe this in a bit more detail? First of all, are you talking about the same resistor as mdroberts? And I'm not sure which lugs you're referring to with the terms high and low...
High means 'top' and low means 'bottom' when looking at the schematic. The PAB breaks the connection between the bottom lug on the treble pot and the top lug on the bass pot and places the 22M resistor there...you're putting a much smaller resistance in there to get some fat 'bleeding' back into the signal. So just put a 1M pot in there and dial it in.
Okay, that explains my confusion: on the D'Lite, the PAB simply breaks a connection between the low side of the treble pot (thanks for the terminology!) and the tied wiper/top lug of the bass pot, with no resistor there.
Are people using a pad resistor with this setup, too?
I'm interested in this as well as my PAB boost is way too much.
I removed the bass mod and was thinking about inserting a large valued resistor ( <1M> ) between the bass pot and treble pot on the legs that connect to the relay switch.
The D'Lite simply breaks the connection between the bass and treble pot for it's PAB.
I just tried an idea for a fatter PAB on my Skyliner/HRM/BM PI amp.
Basically I disconnected the bass pot wiper from the PAB relay and jumpered it to the 'top' lug at the pot (so the bass wiper is perma-connected to the top lug just like 'non-PAB' mode). This freed up half the PAB relay to use for the mod (you also disconnect the two lugs on the PAB relay that were connected together). Then I ran a wire from the PAB relay to the middle lug of the Mid-boost switch (aka the 4M7/.002uF junction) and another wire from the PAB relay to the 'bottom' lug of the Mid-boost switch (aka 'top' lug of treble pot). One of these new wires has a series 560pF cap on it. That's it. I used some of that 2-conductor+shield cable since it's sort of a 'send-return' thing. I also kept the 22M resistors on both sides of the PAB relay (except in my amp they are 10M).
This mod makes it such that the 560pF cap is placed in parallel with the 390pF cap in PAB...and the resultant capacitance is in series with the .002uF cap...I think the total net equivalent capacitance is like 644pF or something. You can size the added cap to taste and to be honest I haven't experimented too much here. The Mid-boost, clean tone, and non-PAB-boosted tones are unaffected.
With the bass pot wiper disconnected from the PAB and jumpered at the bass pot you can hear the CL Bass/Mid pots affect the tone when in PAB but it's not a huge effect and I usually keep my CL Bass and Mid pots somewhere near the middle or upper-middle of the range...and those knobs have very little affect on the PAB-boosted OD tone when kept within that range. So for me that is a total non-issue.
The setup that I've been happiest with in my D'Lite has been a .001uF cap in series with a 470k resistor that gets switched in in parallel to the treble cap when PAB is engaged. It also has a 470k to ground to tame it a bit, and I could easily see that a trimmer there that is externally accessible would be very useful.
greiswig wrote:The setup that I've been happiest with in my D'Lite has been a .001uF cap in series with a 470k resistor that gets switched in in parallel to the treble cap when PAB is engaged. It also has a 470k to ground to tame it a bit, and I could easily see that a trimmer there that is externally accessible would be very useful.
Ditto - I'm using something very similar to that with good results. (Credit to yeahyeah for posting the the suggestion and simulation pics that got me thinking along these lines).
"Let's face it, the non HRMs are easier to play, there, I've said it." - Gil Ayan... AND HE"S IN GOOD COMPANY!
The setup that I've been happiest with in my D'Lite has been a .001uF cap in series with a 470k resistor that gets switched in in parallel to the treble cap when PAB is engaged. It also has a 470k to ground to tame it a bit, and I could easily see that a trimmer there that is externally accessible would be very useful.
Is that extra 470k to ground to tame the gain? I have gain to spare (it occurred to me last night that my amp sounds/plays more like a late Boogie Mark series amp than what I imagine an ODS does ).
What other things did you try in parallel with the treble cap? I intentionally tried to keep it extra simple because I wasn't sure if I would be introducing strange phase shifts by having any extra resistors in there.
The setup that I've been happiest with in my D'Lite has been a .001uF cap in series with a 470k resistor that gets switched in in parallel to the treble cap when PAB is engaged. It also has a 470k to ground to tame it a bit, and I could easily see that a trimmer there that is externally accessible would be very useful.
Is that extra 470k to ground to tame the gain? I have gain to spare (it occurred to me last night that my amp sounds/plays more like a late Boogie Mark series amp than what I imagine an ODS does ).
What other things did you try in parallel with the treble cap? I intentionally tried to keep it extra simple because I wasn't sure if I would be introducing strange phase shifts by having any extra resistors in there.
Yes, the R is there to get rid of some of the gain. Other things I tried were just different cap values and resistor values, but this is what I settled on as liking. Part of what I was after was a tone that was good enough to use in clean mode as well. With this R/C value, there is plenty of body there in clean, but it doesn't swamp the lows in overdrive.
).