Looking for feedback on Express tweaks

[chrisq206]

The tweaks I'm curious about are

820r resistor on input on second pre amp tube input

Extra parallel cap with the .0022 pre amp cap

Different bypass caps on the pre amp cathodes

I've seen variations in different schematics, but they are not in the main Amp Garage schematic.

Let me know

[Colossal]

820r resistor on input on second pre amp tube input

A resistor on the input grid of the second stage helps to reduce blocking distortion and radio interference. The reference schematic Kelly '90 and the Francesca photos do not show this resistor but there is a handwritten letter by Ken Fischer in which he discusses adding 820R, if needed. I believe this value became stock on Liverpool amps, but don't quote me on that.

Extra parallel cap with the .0022 pre amp cap

The 0.0022uF/150k network on the entrance to the third stage sets the low frequency roll off. By paralleling a cap or just adding a single larger value (500p to 1000p, usually ceramic), there will be an increase in low end. Season to taste. I have found the Express to have plenty of low end with good transformers and tubes. It's fun to see what works for you however.

Different bypass caps on the pre amp cathodes

This will affect the gain of the respective stage. The stock values are 22uF on the first two stages. It's good to have the first stage fully bypassed because this will help reject B+ noise and with an Express, absolutely everything counts so what goes in, gets much louder. FWIW, I have experimented pretty extensively with lower cap values on both stages but always came back to fully bypassed, using caps at 22uF or greater (nominal values were 22uF but measured more like 23-25uF).

[pleasantbullet]

i Just did these tweaks this week.

I added the 820R on pin 2, and added 10k to the input at pin 7.

I also put the .0022uf mod, I didn't have ceramic, so i used an Orange drop. I took it a bit further, put it on a toggle switch, with another option of a .0056 mallory pvc cap.

So what i have is a Fat / normal / Fatter Switch. I like it.
The .0056 cap is more Obese than Fat, but its an interesting option for messing around.

I dont know how to technically say this. But as for the resistor mods: the first week that I was playing my express, I kinda of felt like the amp was a crazy beast, similar to my moustache after a hot shower, beautiful and robust, but a tad scraggly.
But after the mods, the amp felt like my moustache after I've waxed the tips, still beautiful and robust....but ready to face the outside world.

Hope that is helpful feedback.

[xtian]

similar to my moustache

Well, now we need to see photos.

[JPGraphX]

similar to my moustache

Well, now we need to see photos.

+1

[KellyBass]

This one that I built:

http://youtu.be/8Pj3RRDBI4Y

If I remember right, is running a 1k2 ohm and a 1uf vishay ero film cap at the first stage. Seems like at the 2nd stage, I ended up using a 10uf electrolytic. I remember taking a real close look at the rocket PI values for inspiration on this particular xpress's PI.

[chrisq206]

Here's are photos

[chrisq206]

Nice Vid. Very lear sounding amp. How does it sound with humbuckers? What speakers were you playing through?

[KellyBass]

Thanks! Dustin's a fine guitar player. He just returned home from some road gigs...one of which was Buddy Guy's in Chicago. Supposedly, the boss man complimented Dustin on his tone. I was stoked to hear that! The amp seems to behave pretty well with h'buckers. In fact, I think I might have labelled the brite cap as "humbuckers" on the faceplate! I can't recall offhand what value i ended up using for the brite cap. I do remember it was a low value, maybe 80pf, polystyrene cap and not a silver mica.

Clarity was a big priority on this particular amp and it took a little tweaking to get that bite to happen with Dustin's dynamics and pick attack alone...and not before. In this video, It looks like he's using his Zbest 2x12 cabinet. I really like the sound of that cab. It sure seems to be a great match for the amp.

Your build looks great! I love the way you've got those cap cans laid out. I gotta try that at some point...I may have to borrow your layout. One of many things I love about Ken's amp designs, is that they seem to be a great platform for experimenting with different values and component types. The xpress is SO sensitive to every change, I rarely ever switch something out and think to myself "i can't tell any difference". To me, they sound different when the air conditioning kicks on!

[chrisq206]

I'd like to have mine be a little tighter and Marshallesque for crunchier rhythm sounds any ideas?

Thanks for the nice words on the caps. It seemed easier and I didn't feel like spending money on Spragues.

I like mine much better through 25s, and I've tried a bunch of stuff. 25s seem to bring out tons of detail in mine. I will say it sounds good though most speaks though.

Those Z Best cabs do sound incredible with the right amp.

[KellyBass]

I'll bet ya that you'll have a lot of excellent ideas on how to achieve that!...and they'll all be tried and true. These guys really know their stuff. In the meantime, I'm gonna look at my notes before I give out wrong numbers.

[chrisq206]

Thank you.

I've tried tweaking other amps and ulitimately have trouble bettering original legendary designs. Go figure.

I'll have to try a few thing before I ask anymore questions though.

[KellyBass]

I know exactly what you're saying. I once took a couple of 10 position rotary switches and built this elaborate triode cathode bypass resistor and capacitor array. I had selectable values from 500 ohm to 2.5k, and 0 to 50 uf. I could try all these different combinations to see what sounded best. Then move it to the next stage and so on. I didn't label the positions...using only my ears. I ended up with 1.5k/25uf on the first two stages. Groundbreaking research, no doubt.

[Tillydog]

I'd like to have mine be a little tighter and Marshallesque for crunchier rhythm sounds any ideas?

For better or worse, I found that reducing the coupling cap between the 2nd & 3rd stages tightened the bass up no end - maybe try 1n5 or 1n8 instead of the 2n?

YMMV!

[M Fowler]

Good looking build but needs the TW Davies knobs