All of the HRM schematics I've seen have a lower gain network at the OD entrance (sounds good with PAB). And it seems that the 'default' for HRM amps is PAB ON when in OD.
But non-HRM amps sound good with PAB or without (correct?...Gil's amp for sale sure seemed to). So I guess I'm curious why use the low gain network when it would appear that it diminishes the non-PAB OD tone? Were/are there any HRMs with the 'regular' OD entrance?
My Skyliner/HRM seems to sound better with a more 'regular' OD entrance but of course it has quite a bit of gain that way...but that just seems to be what suits this amp/person better. It seems like it even sounds better when I back off the gain than it did before at similar gain levels. I'm probably converting my ODS to be closer to a late Boogie but whatever.
FWIW - what I'm using now is a compromise because I don't have any 100K trimmers but it's: .002u-330k-50K trimmer-22K-ground. Wiper of trimmer to 68k grid stopper.
NOTE: my PAB is also different...bass wiper stays connected and other (now unused) half of PAB relay places a 560pF cap in parallel with the existing treble cap.
Can you elaborte on your PAB circuit - not sure I fully understand what you've done, but regardless, it strikes me that it isn't fair to compare the pre-OD networks (HRM versus non-HRM style) if you're no longer using a tradiational PAB circuit. It's become apples and oranges... no?
"Let's face it, the non HRMs are easier to play, there, I've said it." - Gil Ayan... AND HE"S IN GOOD COMPANY!
Yea, I suppose it is getting apples vs. oranges. My PAB is fatter than standard...more gain and more lows.
We talked about this in your 'fatter PAB' thread...here is a cut 'n paste from that thread (I'm still using this same boost...never tried the suggestions that followed):
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.
My Clean is fairly standard Skyliner with 5uF Rk's and a .047uF CL2 output.
Got it! So you are effectively engaging a 'custom' mid-boost when you engage the PAB. That's what I've done to fatten up my PAB, albeit, in a slightly different way (I used a fixed resistor in series with the cap and attached to the 'bottom' of the treble pot rather than the top).
"Let's face it, the non HRMs are easier to play, there, I've said it." - Gil Ayan... AND HE"S IN GOOD COMPANY!
