Bob S wrote:Speakers make a huge difference.
The 0.002uF/150k 3rd stage entrance is a good tweek zone too.
Good Luck - you'll get there.
Better speakers are just not in my budget now.
What do you suggest for that filter network?
I have also found that lowering my pickups slightly from their previous positions (set using lower gain amps for reference) has helped. I have one guitar with unpotted Alnico II humbuckers that I am considering changing out with potted ones as it tends to feed back too easily.
KellyBass wrote:I've had success by replacing the silver micas with polystyrenes of the same value.
Interesting.
I was pretty shocked by the difference. The silver mica's are great in some circuits. They really add some nice glassy shimmer. But in the express, they sounded a bit sterile to my ears...and I had a heck of a time trying to line out the treble. I popped a 510pf PS treble cap in and man, what a difference! The express is SO sensitive around v1a and the vol/treble area.
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KellyBass wrote:I've had success by replacing the silver micas with polystyrenes of the same value.
Interesting.
I was pretty shocked by the difference. The silver mica's are great in some circuits. They really add some nice glassy shimmer. But in the express, they sounded a bit sterile to my ears...and I had a heck of a time trying to line out the treble. I popped a 510pf PS treble cap in and man, what a difference! The express is SO sensitive around v1a and the vol/treble area.
I've ordered some Mallory 150 0.0022 mF caps to replace the silver mica caps I used for coupling and also found a source for 510 pF polystyrenes which I ordered. I'll give them a shot.
I installed the Mallory 0.0022 mF coupling cap and the 510 pF polystyrene treble cap. That did help. But I also decided to replace the Heybour power transformer with the Weber transformer that has the option of lower B+. This brought my bias set point down to 405 VDC plate voltage at a cathode current of 44 mA (plate current about 42 mA). I haven't had the chance to really crank it, but mildly loud levels sound really good. I also dropped the slope resistor to 56k and rewired the tone stack to a 5F6A/JTM45 configuration. This brought up the low mids a fair amount and really sounds smoother. Hope to crank her up tomorrow afternoon when I get home from work.
Finally got a chance to crank up my amp. I have to say that changing power transformers to drop the B+ from about 475 VDC at the bias set point to 405 VDC at the final set point has really made a difference. Plus changing the 0.0022 coupling cap from a silver mica to a Mallory 150, the silver mica 500 pF treble cap to 510 pF polystyrene and the 100K slope resistor to 56K have really made the overdrive highs much smoother and the overall sound thicker and more midrangy like I like. Very happy now.
I'm also intrigued by geetarpicker's use of two fairly high capacitance cables to help tame the beast. My bright switch only uses a SPST switch to select a 100 pF bright cap or none. I never liked the 500 pF cap. I'm thinking of putting back in a DPDT switch to select a 100 pF bright cap, no cap, and about a 1500 pF cap across the guitar input jack to tame bright pickups. I use two 10' Planet Wave American Stage cables (with a buffered Radial Bones Twin City A/B/Y switch to select between two amps in between). The cables are rated at only 28 pF/foot and this would make sort of a bright/flat/roll off switch. what do you think?
That's great to hear that you're getting her dialed in to your liking. Fun amp, isn't it? It's amazing how different the amp sounds with different component build types. Metal film vs. metallized film?...the difference is there.
I really didn't like the 500 cap either and settled on a 230pf or something.
Normally, I wouldn't put much stock in cable lengths, etc. But, with an express, anything is possible and everything matters...and geetarpicker is THE MAN when it comes to these amps.
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I decided to try the 1000pF cap in parallel with the 100K plate resistor on V2B. That was the magic fix! The overdrive highs are much thicker and smoother with no loss of highs when the guitar volume is turned down for a clean sound. Overall high frequency noise is noticeably reduced. Even better, I can actually use the Bright switch with a humbucker equipped guitar without the high frequency noise increasing. I was also able to drop the PI plate to plate cap from 250pF back to 100pF. The amp is stable with all controls dimed.
From an AC analysis point of view the B+ is at AC ground. That means that wiring that cap across the 100K anode load resistor OR wiring it from the anode pin to 0V will do exactly the same thing.
There is one important difference, wiring the cap across the anode load resistor will also cause any B+ power supply noise to be coupled into your signal by that cap.
It is ALWAYS better to wire the cap from the anode pin to 0V - although I have to confess that my Express Clone has a 300pF Silver Mica currently wired across the anode resistor as a mild bright tamer - must get in there and move it - one of these days.
gingertube wrote:There is one important difference, wiring the cap across the anode load resistor will also cause any B+ power supply noise to be coupled into your signal by that cap.
As I noted previously, the amp is quieter with the cap across the plate resistor than it is without it. Hiss is significantly reduced with no real loss in highs and there is no increase in any noise that could be attributed to the power supply. Turning on the bright switch (I only have a 100pF cap) results in less noise than before the plate cap was installed.
gingertube wrote:There is one important difference, wiring the cap across the anode load resistor will also cause any B+ power supply noise to be coupled into your signal by that cap.
As I noted previously, the amp is quieter with the cap across the plate resistor than it is without it. Hiss is significantly reduced with no real loss in highs and there is no increase in any noise that could be attributed to the power supply. Turning on the bright switch (I only have a 100pF cap) results in less noise than before the plate cap was installed.
With a well filtered power supply node you almost certainly won't notice any difference between the 2 ways of wiring the cap. Just saying that the cap wired from anode to 0V is theoretically the better option. If anyone wants to try this mod then I suggest anode to 0V should be the "default" choice.
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