Structo wrote:Forgive me if this is redundant but what exactly defines a BM PI?
I was looking at a D'Lite BM schematic and it shows 100k/110k plate resistors with 47pf caps in parallel.
That was the only difference that jumped out at me.
IIRC, there are four resistors that change, along with two caps. The presence control changes, too. Take a closer look.
I've attached a diagram that I *think* represents the differences in the PI's between the standard and Bluesmaster. Stronger experts than I can correct me if I'm wrong. Bluesmaster values are in blue.
One thing I don't understand is why my plate voltage would be different between the PI's, unless I had a leaky cap. But the caps test fine on a cap meter...
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Like heisthl said, the bias is different. The regular one uses the 820ohm cathode resistor and the BM uses the 511ohm...so more current...more current through the plate load resistors creates a bigger voltage drop across them.
Also, FWIW the BM PI is very similar to a Marshall PI (with the 'later' presence circuit)...the values are just a little different (like 511ohm instead of 470ohm).
The type of cleans I am looking for are the cleans that have a little hair on them. They sound clean with volume rolled back/lighter touch, but get a little dirty when playing with a heavier touch.
Change V1a to 100k plate(Rp) 1k5 cathode (Rk) with a 10uF to 25uF bypass cap (I like 25uF) , put in a .047 (or.05) mid cap and leave everything else the same. Run the preamp volume above 4.
Heisthl,
Curious what effect changing V1 to a 100k/150k values has on the OD channel? I went to 150k/120k pair on V1, and while it does sound somewhat fuller than the high plate pairs, I still don't get any appreciable grind unless the volume is past 3:00.
Last edited by greiswig on Sat Apr 19, 2008 12:30 am, edited 1 time in total.
The 100k plate has less headroom but you need the larger bypass cap to keep the tone full. With the larger bypass cap/100k combination(V1A only) in a non-HRM you may have to adjust the entrance trimmer but really nothing else is needed. greiswig - I thought you tried the 100k plates in a previous thread.
heisthl wrote:The 100k plate has less headroom but you need the larger bypass cap to keep the tone full. With the larger bypass cap/100k combination(V1A only) in a non-HRM you may have to adjust the entrance trimmer but really nothing else is needed. greiswig - I thought you tried the 100k plates in a previous thread.
Negative. Closest I've gotten is the 150k/120k pair I have now. Are you saying 100k V1a with the stock 150k V1b values, or are you suggesting the 100k/100k values like #124 had? Gil had tried that latter pairing and seemed to not care for it much...
I know, it's easy enough to try, and I probably will...but I'm very curious as to what your findings were.
I think Gil says his favorite amp is the dual 100k plates on V1. Using both at 100k does affect the overdrive but if you just do it to V1a it doesn't affect the OD nearly as much. Heck, even changing where you set the preamp volume affects the OD.
TimS wrote:How close to the dual 100k clean sound does the "100k on V1a only" setup get? Are the cleans more Fendery or Voxy?
Yes More Fendery and more Voxy. Just kidding, A description that might have meaning is to say It puts a (non master volume) Fender on 5 edge to the clean tone. Especially if you use a 25uF bypass and also have a 10uF bypass on V1b (150k plate/2k2 Rk) side.
If you really must have more of the Fender "scoop" in your clean tone you can also reduce the treble cap for a 250pf net capacitance. (if using the mid boost seriesed .002 a 300pf will get you in the ballpark)
I did a gig this weekend after changing V1 from a 150k/120k Kr pair to 100k/120k pair, with a 15uF cap on the V1a cathode. Standard PI, with a Skyliner tone stack.
Boy, even with my PRS and Harmonic Designs humbuckers, I can't get the clean side to start breaking up. It just gets really loud. Basically, it seems the same as before, but with a more "velvety" clean channel. I do like the cleans better, but I can't get the breakup that heisthl described out of it.
Heisthl:
Thank you for a great recommendation. I made the change you suggested (as close as my parts would allow), and now I am getting exactly the clean tone I was seeking.
I will admit that I was shocked at the significance this change made to the overall feel of the amp.
I am gonna post my findings in another thread to avoid hijacking this one.
More Fendery and more Voxy. Just kidding, A description that might have meaning is to say It puts a (non master volume) Fender on 5 edge to the clean tone. Especially if you use a 25uF bypass and also have a 10uF bypass on V1b (150k plate/2k2 Rk) side.