well had a bit of a tweaking session this morning and this is what I've changed from the stock #102
V1 plate resistors all 100k
cathode resistors 1.5k
V1 input 22k
0.5uF mid cap
250k bass pot with 1.8k resistor
100k mid pot.
First thing I noticed is was quieter as there's less mid's and bass now.
However it actually sounds like a fender amp now in clean mode with my tele I tried it with the ported 1x 12 EVM cab which is very clean and then tried with the dumble oval cut out 1x 12 with a celestion g12 80 and that gave it a slight crunch when pushed, much like a fender combo.
Overdrive still sounds great so all in all I'd say it's a winner.
so low plate V1, high plate V2 with all cathode caps 4.7uF with non skyline EQ and a 47pf master bright cap.
Very cool Marcus! I should have mentioned that I have a single-coil point of view (no HB guitars in the house!).
You must mean 0.05uF mid cap, no?
Checking my notes I have the same tone stack values as the 124 schematic with the exception of a 370p vs. 300p mid-boost cap. The pots are 500kA Bass, 250kA mid.
BTW, what are we going to call this hybrid amp? A Lojai?
Martin I did indeed mean 0.05. the original is a 0.01 so I just tagged on a 0.04
There are 2 #124 layouts , and you did them I believe the one I got everything from was the 'original form' version which had the pot/resistor values I used.
can you remind me what the boost switch does on the #102 , it's not a tone stack lift is it? I wonder whether a tone stack lift might work better now as a boost, is that possible?
Well, I made some pieces (individual boards) from the 124 post-update photos, and then Tony Albany assembled them into a complete 124 post-update layout. Some of those boards were recycled into the other layouts Tony did as well.
There are two 124 schematics, done by ic-racer: a 124 post-update, and his guess at the original circuit.
The Mid Boost switch is a treble cap bump, whereas the PAB (Preamp Boost), controlled by a relay, is a tone stack lift. You already have both functions, I believe.
norburybrook wrote:Martin I did indeed mean 0.05. the original is a 0.01 so I just tagged on a 0.04
There are 2 #124 layouts , and you did them I believe the one I got everything from was the 'original form' version which had the pot/resistor values I used.
can you remind me what the boost switch does on the #102 , it's not a tone stack lift is it? I wonder whether a tone stack lift might work better now as a boost, is that possible?
Marcus
Marcus, the PAB boost does defeat the function of the tone controls but what it really does is force most of your signal through the treble cap. I think a straight tone stack lift would sound like a wall of mud with humbucker guitars in OD mode so adding a boost in the upper frequencies makes sense with a Les Paul but with a strat it sounds kind of bright and boxy. If you study some of the past posts there are tons of variations on the PAB. I am curious about your master bright cap, 47pf? You must like a bright amp.
CW
norburybrook wrote:Martin I did indeed mean 0.05. the original is a 0.01 so I just tagged on a 0.04
There are 2 #124 layouts , and you did them I believe the one I got everything from was the 'original form' version which had the pot/resistor values I used.
can you remind me what the boost switch does on the #102 , it's not a tone stack lift is it? I wonder whether a tone stack lift might work better now as a boost, is that possible?
Marcus
Marcus, the PAB boost does defeat the function of the tone controls but what it really does is force most of your signal through the treble cap. I think a straight tone stack lift would sound like a wall of mud with humbucker guitars in OD mode so adding a boost in the upper frequencies makes sense with a Les Paul but with a strat it sounds kind of bright and boxy. If you study some of the past posts there are tons of variations on the PAB. I am curious about your master bright cap, 47pf? You must like a bright amp.
CW
Charlie, that makes complete sense, that's exactly what I'm hearing. Regarding the master bright cap, 68pf is the normal on this amp so 47 is less bright than that
Marcus
p.s interesting point; changing the 33k NOS Piher rresistor for a new Xircon 33k made a noticeable difference in amp noise, in a good way
norburybrook wrote: I wonder whether a tone stack lift might work better now as a boost, is that possible
You might try lifting the bass pots 10k tail resistor and the mid pots ground simultaneously for a tonestack lift. I put a 250k trimmer in place of a 22M Resistor to get a variable tonestack lift. It's a a simple mod to have 2 boost options without straying from the path too much. The full tonestack lift is too overbearing.
Last edited by Duble on Sun Nov 01, 2015 9:15 pm, edited 1 time in total.
Charlie Wilson wrote:Marcus, the PAB boost does defeat the function of the tone controls but what it really does is force most of your signal through the treble cap. I think a straight tone stack lift would sound like a wall of mud with humbucker guitars in OD mode so adding a boost in the upper frequencies makes sense with a Les Paul but with a strat it sounds kind of bright and boxy. If you study some of the past posts there are tons of variations on the PAB. I am curious about your master bright cap, 47pf? You must like a bright amp. :D
CW
Comparing a full lift to the Skyliner PAB, I see about 2dB increase across the board, i.e. no significant change in the frequency response (looks like a typical first-order high-pass filter).
Martin I am confused by that. Looking at the schematic I see a 22m as the bass frequencies only pathway to the lower terminal of the treble pot when the PAB is engaged. I also hear a considerable loss of lower frequencies when the PAB is engaged.
CW
I've been having a browse around about this and found a thread where they added a 900p ( in place of the 500p)cap to give a 'fat boost' on the schematic enclosed. Is that 900/500pF regular film cap?
Where is that actually placed physically?
Also would that work on my now classic tone stack?
If not what would be the best way to get a fatter PAB?
Marcus
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Marcus, I think it would be hard to find a polyester cap that small. It would have to be a mica or ceramic disc (rated at least 500v). One side of the cap would go at the junction of your treble cap and slope resistor and the other end would probably have to go to a wire(shielded?) and then to your relay. Also note that the 22m resistors become 4.7M. You may want to first try simply changing the 22m to 4.7m. The boost is less but a bit more of the lower frequencies remain.
CW
Charlie Wilson wrote:Martin I am confused by that. Looking at the schematic I see a 22m as the bass frequencies only pathway to the lower terminal of the treble pot when the PAB is engaged. I also hear a considerable loss of lower frequencies when the PAB is engaged.
CW
PAB puts 22M between the top of the bass pot and the bottom of the treble pot, and 22M between the wiper and the top of the bass pot. That makes the bass pot a 1M resistor with a 1n cap across it. The remaining path to ground is then through the 150k slope resistor, then split between the 0-250k mid pot (depends on its setting) and the 1M bass pot. Either way (PAB or full lift) you are pretty much left with 260p of treble cap over the 1M volume pot, which has a corner frequency of ~600Hz ... so yes there is a significant bass roll-off in PAB, but a full lift doesn't change that. If the mid boost is on, however, then you have 1n and 1M, or 80Hz.
Thanks Martin. Sometimes I only see the series pathways and forget about the parallel stuff when I am studying the schematics. Still gives me a bit of a headache.
CW
Ha, headache is my permanent state with most of this stuff!!
So Martin, are you saying that there's no easy way to make the PAB on my amp have more mid/bass?
I like what the mid switch does but obviously that's not on a footswitch, would be nice did the mid switch came in with the PAB.
Couldn't I just make it like the Bluesmaster boost? I noticed that there's no resistor on the bass pot at all in that, it is a 500k pot and a 50k mid pot. The PAB is fuller on the BM which got me wondering about the #102 PAB.
I tried it with the ported 1x 12 EVM cab which is very clean and then tried with the dumble oval cut out 1x 12 with a celestion g12 80 and that gave it a slight crunch when pushed, much like a fender combo.
