Two tips for taming 'shrillness' in Express clones

[badgerline]

Having a built a couple now, I thought I'd share a couple of ideas that might help peeps starting out:

- The 'AO' TW tonestack has a TONNE of high end when all controls are on 5 - lots more than a Marshall. Silly as it seems to point out, just turn down the treble and turn up the middle (not too much bass!)

- Depending on component choice, your amp might tend to being a bit bassy or a bit toppy. Instead of the simple HPF stage before the cold clipper, you might consider adding an Orange-style switchable HPF ('FAC' in Orange parlance). Essentially, this is is a 6-position rotary switch with caps in series across the throws. Assuming a 150k resistor to ground, I recommend (as a starting point) the following values: .0022 -> .001 -> .0022 -> .0022 -> .0047 -> .047. As you switch through, you 'recruit' more of the caps to the series, decreasing the knee frequency of the HPF, ranging from about 530Hz down to 16Hz. Use an Express for an extreme metal bass tone - why not (I have!)? Just like on an Orange Graphic, you then have a load more tonal options with various combinations of EQ and HPF settings.

Cheers,
Badgerline

[badgerline]

Hi, I'm going to add a third tip, unsolicited as it may be. You want to cut the ice-pick... how about cutting the hiss into the bargain?

The solution: connect a 33nF to 47nF cap in series with a 100k-330k resistor across the OT primaries. This cancels a load of high end at the latest possible stage of the amp, thereby eliminating built-up hiss. Even better, why not mount a 500k (or 1M if you want the option of tonnes of hiss) pot on the back of the amp to use in place of the resistor? If you do that, on no account ground the pot, as you will redplate a tube. Just use two lugs as a variable resistor.

I can get the hiss barely audible in a silent room and still have enough high end to cut with the best of them.

I just used this on my latest build (47nF and 500k) and I'm very happy with it. Credit to Rob Robinette's site for introducing me to the Fender Model 26 Deluxe power tube plate-to-plate High Cut Control.

Bonus tip: use shielded cable on the feedback connection from the OT secondary.

[Mark]

What speakers and cab are you guys using?

I've never had to knock off any treble. Another mods is to put a small value cap across a plate resistor. There are plenty examples of that on Blue Guitar site.

[Roe]

the right caps also helps. I like the bc vishay 450v electrolytics

[Mark]

Why do you like the Vishay BC electro's. I can't say I've heard a difference between different electro caps, mind you I haven't compared them either. I think the inductance would make the greatest difference.

Has anyone tried the mod where you bypass the electro with a large poly cap. I've tried it ages ago on Fender amp and only the treble frequencies were affected.

I thought I tried it on a Liverpool clone and didn't hear a difference.

[badgerline]

Hi Mark, I'm personally using a Budda 2x12 closed back. IMO, it's quite a 'hi-fi' cab, so as brutally honest as an Express-type amp. My experience of this and other Express-type builds has been that the standard high-pass filter stage results in an anaemic tone, except with an old WEM 2x15 cab (Dave Gilmour-style). That said, I have always used out-of-spec transformers salvaged from broken amps. So, a 'true' Express might/will not need these tweaks, I'm sure you're right! I'm just sharing them because I've seen that others have needed to address similar issues with their amps - I suspect that the trannies are probably the issue in our trebly cases.

That said, I think the variable HPF before the cold clipper is cool because it gets a much fuller clean tone when there's 0.1uF rather than the standard .002uF, especially with Leo-designed guitars. Also, the power tube cut control gets rid of HF crud that the the presence control will re-inject into the signal, so tweaking these controls together can get a super-hairy tone that's still smooth as Kojak's noggin. Admittedly, the variable HPF takes a bit of work to solder all the caps on to the rotary switch (and, IMO, is best with shielded coax to and from the board), but even including chassis drilling (use a deep shot glass pushed against the drill exit point to catch the shards) the cut control took me only 10 minutes to install and I'm slow.


Roe, I used those exact caps for this build! Great price-quality ratio. Signal caps are all Vishay 1813, which are also great value and are less prone to ice-pick than polyprops. I'm not at all aiming for Ken-accuracy - if anything, I'm aiming more for an Alessandro-kind of amp capable of early AC-DC barely overdriven stiff crunch (high plate voltage, cleans to die for)

[badgerline]

Hi again, Mark - I've tried such things and have only heard differences in hifi builds, not guitar amps. I think they could make a difference once a dozen other things were silenced, but probably at the expense of killing all coolness of tone

[M Fowler]

While not traditional Trainwreck, I like to get rid of the presence and replace it with a treble cut pot. Sold a few of thoses to weekend bandits getting lots of play time.
No more treble problems or presence circuit problems.

Mark

[Roe]

Yes, those BC caps do not only have a good price/quality ratio. They also got a warm, nice top-end. IMHO filter caps do matter, esp. at the screens. It is not only about capacitance but also about ESR and other parameters. Those who recap alot of amps will easily hear and feel the difference. It is all about finding the right caps for the amp, and the BC caps sound great in an Express. Probably much better than the Mallories

[badgerline]

I just installed a 100pF snubber at the PI plates, then a 100pF from plate to ground at V1b and V2a (cold clipper). Each reduced hiss - together, it's almost non-existent. The one at the cold clipper also drastically improved the smoothness of transition into overdrive, which had been bothering me a bit.

I'm now so happy with the tone, feel, and low noise of the amp that I think I'll stop tweaking and maybe start playing guitar through it like a regular guy.

[hitchcaster]

try a 4X12 with the right speakers.

[Mark]

A 4 X 12" is a great start in getting great top from an Express. I have tried Celestion 65's in a Dumble style open box which sounded good.

[badgerline]

Another thing is to just play the thing for 10 hours after the build: I swear that the tone has filled and smoothed out a lot just by 'breaking it in', controversial though that notion might be with some folk.

[Markusv]

While not traditional Trainwreck, I like to get rid of the presence and replace it with a treble cut pot. Sold a few of thoses to weekend bandits getting lots of play time.
No more treble problems or presence circuit problems.

Mark

Mark
Quick question please- Do you still apply set feedback (presence) to the circuit, and then add a hi-cut?

[Mark]

One would think the Presence would be set to "0" if there is a problem with excess treble response. It will be interesting to see what Mark says.