Well, I'm finally building my Express...

[PlinytheWelder]

I just started building my version of an Express. It's going to have a VVR3, some funny parts and a slightly different layout...

Here's the start...
[img:900:675]http://verosurfcam.com/TW1.jpg[/img]

[img:900:510]http://verosurfcam.com/TW2.jpg[/img]


Here's one days progress...
[img:900:462]http://verosurfcam.com/TW3.jpg[/img]

[img:900:675]http://verosurfcam.com/TW4.jpg[/img]

All comments are welcome and thanks to all on this board because it wouldn't be possible without you.
Back to work!

[JamesHealey]

I think those Vishay Metal Film resistors you've used through out the amplifier will turn out to sound a little too bright and brittle in the express circuit.

What coupling caps are those? oil paper?

Are those FRED diodes? Interesting choice.

[FYL]

I think those Vishay Metal Film resistors you've used through out the amplifier will turn out to sound a little too bright and brittle in the express circuit.

How can resistors make the amp "a little too bright and brittle"?

[mojotom]

The vishay resistors do sound good at least not bright, especially for the plates, at least for a Dumble kind of amp.

I've build an Express in 2006 with exotic parts (sozo and PIO, tantalum resistors, non solid wire, etc) and wasn't really pleased with the sound until
I used the 6PS caps, carbon film resistors and solid wire. The sound was nicer less brutal and harsh.

Everything seems to add up about the express. For exemple the Pacific OT
sound smoother than the modern Heyboer.

+1 for the pacific OT and VVR3.

[PlinytheWelder]

I think those Vishay Metal Film resistors you've used through out the amplifier will turn out to sound a little too bright and brittle in the express circuit.

What coupling caps are those? oil paper?

Are those FRED diodes? Interesting choice.

Those are Silicon Carbide Schottky diodes that supposedly have NO switching noise. PIO caps and Black Gate electrolytics for cathode bypass.

Here's the boards fitted...
[img:900:475]http://verosurfcam.com/TW5.jpg[/img]

[Structo]

Man, some of you guys have much better hearing than I do.

You can hear the difference between solid wire and stranded?

[mojotom]

Well Tom I do change wires from silver coated PTFE to solid PVC and I do notice a difference, mainly less harsh high end and somehow a more directive sound and it's not hard to hear at all.

The most dramatic change was Sozo to 6PS because the mids opened up a lot along with the bass and if I remember correctly it was a bit tighter and balanced with 0.1 6PS and 0.022 Sozo. A bit too much with all 6PS.

Really a huge difference in a good way. I think the Express is such a fast attack circuit you need to stay away from fast attack caps and resistors. It may sound silly but it seems good PIO and Hifi kind of caps and resistors do
"react" faster when you want some form of sag.

Well it's just a theory of mine.

[RJ Guitars]

Man, some of you guys have much better hearing than I do.

You can hear the difference between solid wire and stranded?

Tom I thought the wire thing was a bunch of bunk for a long time. And it turns out that I still think that the wire itself is still not going to make a difference. Electron behavior and skin affect at guitar amp frequencies is not really an issue. However, there was a pretty good thread running for a while that had a pointer to an old Ken Fischer's document on wire. In that document Ken tells us that it is the old PVC insulation on the wire that is at least one critical part of the Express circuit. The thread helped reveal that it is very likely that the wire with the PVC coating was acting like a capacitor coupling to ground or whatever, ultimately leaking off some portion of the signal and "taming" the circuit. In his document on wire Ken mentions that if you build an Express with "good" wire, then it will sound harsh. He goes on to talk about helping design the Komet's so that they could use good wire and how other aspects of the circuit had to be changed so that amps would not sound harsh.

Anyway it was an interesting read and it helps me understand that it is possible that the wire matters... or more specifically the insulation on the wire matters. Getting the wires lined up, bent in all the right places, and critical distances adhered to so you can make that capacitive coupling the same as an original wreck.

Ultimately this also would imply that if you understood where and how much capacitive coupling was happening, you could use "good" wire and put some capacitive components in the right places and duplicate that circuit. I can only guess that this would be a tough job to quantify and duplicate but if you ever got it down then you could potentially tame the Express and reproduce your circuit reliably. FWIW...

By the way, nice build going on here Gary! I see the can caps - love the way they clean up a Wreck power supply. What is the Output tranny you've got?

rj

[geetarpicker]

I've even noticed the difference tonally between different types of PCV solid core wire in these amps. It's all in the details with these!

[redshark]

Hi Glen, Could you please tell us...where did you get the non-irradiated PVC wire?

[FYL]

fast attack caps and resistors.

What is the highest fundamental frequency produced by a guitar?
What is the rise time of a 10 KHz trapezoidal wave?
What is the maximum slew rate of a quadripole passing a 10 KHz trapezoidal wave with 100 mV in and 20 V out?

Now, can you define fast and "fast attack caps and resistors"?

[Structo]

OK, I agree the cumulative sum of all parts go towards building a great sounding amp.

I will also agree that caps, resistors, wire and inductor selection and construction techniques all affect the overall tone of the amp.

Didn't Ken use the cheaper 300v PVC wire in his amps?
I think I stopped reading when he said something about the red dye in the PVC affecting tone.....
I know he had a very good grasp on tube amps and probably was able to test all manner of things and construction techniques.

I wish I had a high quality capacitance meter and a blank aluminum chassis.

It would be interesting to run some wire on the chassis floor and at various elevations above the floor and measure the capacitance to see how much the coupling effect of wire to chassis exists.

[Jackie Treehorn]

The silver plated is the type that sounds harsh. I did read an explanation for the sound somewhere that made some sense; basically copper and silver, having different conductivity, present different impedances to the higher frequencies so you get some smearing in the highs. Non plated stranded wire sounds warmer to me than solid core which sounds a bit etched. I don't think the insulation is a major factor. In terms of capacitance, it's the distance and area between conductors that are important. I don't think the insulation on the wire is going to do much there.

Like many others, I find the Express to be a pretty bright circuit when stock, and I would say solid core wire contributes to brightness more than tame it. While using dull, smooth sounding parts to alleviate the brightness is certainly a valid approach, changing the circuit and using modern parts is just as valid. I think it depends on your approach as a builder. I use mostly polypropylene caps and sometimes Riken Ohm resistors (although those are pretty fat sounding), but I change the circuit to get a lot more bass and get the response more even.

Brightness, though, is pretty easily dealt with in a number of ways. It's really midrange and transient response that are areas that can be degraded with polyester caps or cheap wire. I do think transient response is important in getting the best guitar/speaker couplingn hence a LOT of harmonic feedback. Ultimately, it depends on the player, though, whether they like the extra speed and clarity. I've also noticed that when you've got an amp loaded with polypropylene, you get cut and clarity throughout the whole amp's bandwidth. So, you can set it dark and still have slam and defintion. I had an amp loaded with Mallory 150's for awhile and it seemed like all the cut and defintion was contingent upon the top end, but when you turned up the top, it was this plasticy, bland type of tone rather than the sound of the guitar and tubes. I think a lot of older amps have a similar quality, if you turn the treble down you hear that there's no definition in the mids.

I think the parts in the amp in question, though, could certainly work really well. The vishay metal films- I had a shared cathode marshall with one vishay plate and one carbon comp and the carbon comp side sounded a lot better. I ended up switching them out. I had a Dumble build with all carbon comps on the plates but that amp got a lot better with the vishay's on the plates. I've also used the vishays in a phono preamp and they work pretty well there. I've got one in my Express as the feedback resistor; it sounded the best to me, there.

[FYL]

I did read an explanation for the sound somewhere that made some sense; basically copper and silver, having different conductivity, present different impedances to the higher frequencies so you get some smearing in the highs.

Silver shows a 1.59×10−8 ohm/m resistivity / 63.0 × 10E6 Sm-1 conductivity, Copper 1.68×10−8 / 59.6 × 10E6. Impedance is another story.

There's a whopping 0.0000000069 difference in resistivity and 0.00000034 diff in conductivity, which - for all audio related applications - amounts to nothing.

No wonder nobody has ever been able to demonstrate any kind of subjective difference between equivalent wires (eg. 22 ga 7-strand copper vs. 22 ga 7-strand silver plated copper) in proper double blind tests. By nobody I mean nobody, not even Superman or Billy Bo.

[Jackie Treehorn]

There's a whopping 0.0000000069 difference in resistivity and 0.00000034 diff in conductivity, which - for all audio related applications - amounts to nothing.

For my applications, it does amount to something. It may be good enough for others, though, depends what result you want.