Attempted Simplification of the Express - Non Traditional

[Colossal]

Here is my PCB Express build. Thanks again RJ! I added a PPIMV, Cut, and Presonance controls. The PPIMV is currently set to a max of 163k (250kA || 470k). Heaters are elevated to DC via the filament center tap. I also added switches on the back to select the secondary voltage or switch primary taps (5k2 or 6k6). I thought external bias test points and a trimmer might be useful so added them as well. As a nod to Paul Ruby (and a shortage of blue wire), I opted to go all black. Wire is 19ga. Kimber TCSS teflon over stranded copper (non-plated). I used 825R on the input grid of both V1a and V1b. I decided to go with faraday coils (Belden wire, not TCSS) to shield the V1a/b grid wires. They look like those cool coiled instrument cables. Metal film resistors for plates, grid leaks, and V1a/b grids, carbon film for cathodes, power amp grids and elsewhere. F&T electrolytics, PEC pots, Mercury Iron.

I am short one 0.1µF orange drop so had to draw it in on the photo Plate leads may get moved around, depending on how lucky I am on startup. I expect to be firing it up this week. Looking forward to it!

It was a fun project and easy with PCB construction.

[Zippy]

I also added switches on the back to select the secondary voltage...

Is that something you would do on an amp that you build for someone else? I've an amp (Mission 5F4 Super) with that feature too but I'm concerned with what might happen if someone were to flip the switch without rebiasing. Would you consider that a potential (no pun intended) issue?

[Colossal]

I also added switches on the back to select the secondary voltage...

Is that something you would do on an amp that you build for someone else? I've an amp (Mission 5F4 Super) with that feature too but I'm concerned with what might happen if someone were to flip the switch without rebiasing. Would you consider that a potential (no pun intended) issue?

Probably not something I'd add to an amp for sale. Purely for my own edification, just to see what I like. Nothing like hearing the differences first hand and it affords some future optionality. I built this to test out the viability of the Express board for RJ and to have something fun to try out ideas on.

[M Fowler]

Looks great Dave it will be interesting to hear how the amp sounds when fired up.

Mark

[Zippy]

I also added switches on the back to select the secondary voltage...

Is that something you would do on an amp that you build for someone else? I've an amp (Mission 5F4 Super) with that feature too but I'm concerned with what might happen if someone were to flip the switch without rebiasing. Would you consider that a potential (no pun intended) issue?

Probably not something I'd add to an amp for sale. Purely for my own edification, just to see what I like. Nothing like hearing the differences first hand and it affords some future optionality. I built this to test out the viability of the Express board for RJ and to have something fun to try out ideas on.

Thanks. That's an excellent looking build. I like your menu of features.

[martin manning]

That is very impressive indeed, Dave! A Swiss Army knife amp if there ever was one. I'll be very interested to hear how the PPIMV, the presonance, and the cut control play together.

[fishy]

Dave....That build looks cool......
I will be really interested to hear how this one sounds with a 7 string....

All these mods have me thinking back to RJ playing around with a few trimmers when working on the octal based Rocket. I was wondering if it would be worthy of including some provision for these in a later rev board since it did help dial that amp in. I also seem to recall several builders have found more favor with the Liverpool PI in their Express builds than with the Express PI.
Trimmers around the PI would provide the ability to do this.

[Colossal]

That is very impressive indeed, Dave! A Swiss Army knife amp if there ever was one. I'll be very interested to hear how the PPIMV, the presonance, and the cut control play together.

Hey Martin,

Thanks, it was a fun build and even though it's not "show" quality, it was fun to take the extra effort to make things tidy. I have a PPIMV, Presonance, and Cut on my Liver-mule and I think they are very useful tools and interact well for a wide variety of tones. The amp is so loud on its own that I decided to limit the grid leaks on the PPIMV to 163k (and I did it on this Express too). That will still peel the paint. The Liverpool does all of the trainwreck things really well but I have also modded it to push the gain up into modern territory. I will do the same to this Express.

I wanted the extra couple of switches to see how the amp reacts to lower voltages (maybe a little browner sounding?) and see how the different OT primaries sound. I like a bit more aggressive tone so want to hear the difference between 5k2 and 6k6 first hand.

[Colossal]

Thanks. That's an excellent looking build. I like your menu of features.

Thanks Zippy. Yeah, I had some unanswered questions so thought a couple of extras would be cool to try.

Dave....That build looks cool......
I will be really interested to hear how this one sounds with a 7 string....

All these mods have me thinking back to RJ playing around with a few trimmers when working on the octal based Rocket. I was wondering if it would be worthy of including some provision for these in a later rev board since it did help dial that amp in. I also seem to recall several builders have found more favor with the Liverpool PI in their Express builds than with the Express PI.
Trimmers around the PI would provide the ability to do this.

I'm really looking forward to powering up! I think the inclusion of pads for series trimmers in a few key places would be a good addition to a production PCB.

I have that 1k/39k mod on my list of things to try, depending how I like the Expresses voice. Have you tried it with your amps Pete?

[fishy]

I have that 1k/39k mod on my list of things to try, depending how I like the Expresses voice. Have you tried it with your amps Pete?

Of course not ...

I do recall some posts where someone prefered the Liverpool PI settings over the Express values. Can't find that now though..
Seems to be an area worth explorin. It might also prove useful if you wanted to run different tubes - 6v6s come to mind.

[Colossal]

I do recall some posts where someone prefered the Liverpool PI settings over the Express values. Can't find that now though..
Seems to be an area worth explorin. It might also prove useful if you wanted to run different tubes - 6v6s come to mind.

Pretty sure it was Jackie Treehorn that mentioned it. Good place for a trimmer!

[rooster]

Wow, Colossal, that is a very nice build, indeed!

One thing I see in your pic? The ground trace in the preamp area, does the circuit board screw by the input jack have a ground connection to the trace? It looks like it does. Just curious.

[Colossal]

Wow, Colossal, that is a very nice build, indeed!

One thing I see in your pic? The ground trace in the preamp area, does the circuit board screw by the input jack have a ground connection to the trace? It looks like it does. Just curious.

Thanks dude!

Yes, that little ground bus along the lower right hand corner of the board (where the tone stack and preamp cathodes ground) is connected to ground via a single screw. The screw is visible in the corner and goes into a spacer and on to the chassis.

[Reeltarded]

Excellent!

I like the way you think, Dave. Direction! Let's hear it soon? (!)

[Colossal]

Hey guys,

Just wanted to let you know that I fired up the amp. I only had to flip the plate leads and it was good to go. All the voltages checked out at startup and the bias voltage was -32.88V without even adjusting! Heaters are elevated to about 80VDC.

I started with a set of preamp tubes that are known to sound good (to me) and a new pair of Mullard Reissues. The Mullards sound good, if a little plain. I tried a set of GT EL34s (which Glen K. uses in his amp) but had one running at 52mV and the other at 33mV. Matched tubes (that is why I usually add TWO bias adjustments).

Anyway, the amp sounds really good. It's got the familiar Trainwreck grind and a lot of low end. Really huge compared with the Liverpool. I really like the Liverpool's grind (mine is modded for even more gain and sounds pretty killer) but the Express has really got a lot of punch. Very warm and woody sounding.

Cut Control seems to be quite useful. It takes some of the crispy fizz out without excessive damping. Resonance control seems a little more subtle than on my Liverpool. There's so much low end in the amp as is, I'm leaning more towards the presence side.

Ok, I do hear what some of you have mentioned -- a bit too much flab in the bass. It's just not as tight as it could (or should?) be. With my Liverpool, the 7 string is just amazing, super tight and defined. On the Express, it's a bit too loose and undefined. I plan to try:

1) reducing the 22µF to 0.68 - 2.2µF on the second stage
2) 1k/39k for the long-tailed pair
3) gain mod

As far as the amp and PCB go, I had no problems whatsoever. The build was straightforward, easy, and fun. The amp idles (even dimed) with no noise, just the usual hiss. Clean to mean is nice and the amp has a great clean sound. I think the grid resistors were a good idea (no RF!). I have not had to make any lead adjustments and it is feeding back easily. No oscillations or other nonsense either.

Thanks again RJ.