Really Bright!

[Gibsonman63]

I have been searching the forum, but I have not seen a concise post of the various tweaks to reduce the brightness in an Express. Mine sounds pretty good, but I have to run the treble pot on about 1/4 travel and max out the mids and bass to get a balanced tone. What are the tried and true tweaks for taming the brightness down?

I increased the capacitor in the PI to 100pF as suggested in the build guide, but it didn't seem to make a difference.

[M Fowler]

Well I have read many times in posts that real TW's are not brite so I won't go there.

Things that affect brightness are speakers, tubes, the cord, the guitar and naturally the tone circuit. How about the trannies used.

How about the type of wiring used in a TW, that surely has to affect brightness of an amp in my opinion.

4x12 closed back cabinet loaded with Celestian 25w green back or equivlent frequency speakers for an Express.

[Gibsonman63]

I appreciate the response, but at this point I am not looking to change any of the major components. I used Pacific Transformers, the 22 AWG solid core wiring from the BOM and I am running 40' of guitar cable.

I bought the recommended NOS Siemens and Sylvania tubes and at $400, I am hoping to stick with them for a while.

Basically, I went with all of the recommendations from the build guide and BOM.

I am looking for specific componant swapping recommendations to save some trial and error so I can get back to playing my guitar.

[Structo]

A simple thing to try is a long guitar cord, like 20 ft or more.
I believe Glen does this with his express.

Or maybe if you have a couple 15 ft cords you can make or buy a adapter to join the two male ends together for one long cord.

Or if you have a cheap cable around try that.

What this will do is dampen the high end at the input using the capacitance of the cable.

Or try a lower value on your treble cap (C2). Like a 250pf.
Or a larger valued coupling cap between V1 and V2 (C8), try a .005uF there.

[Cliff Schecht]

He already is using 40' of cable.

Something that you can play with is the wire clearances around the tonestack section. Moving wires around there makes a BIG difference in the sound, much more so than one would ususally think. Play with the clearance between the two wires coming off of the Bass pot and where they are positioned in relation to the chassis. Mine are (if I recall correctly) touching the bottom of the chassis, about a 1/4" apart and keep them parallel to each other as much as possible. Also, increasing the distance between the two parallel wires that go from the PI to the PA grid resistors makes a difference. I noticed that your wire feeding the treble pot (the yellow one) seems a bit short and direct, maybe try a longer wire here that runs along the ground buss and back of the pot entirely before connecting to the lug (as opposed to floating it completely). The wire placement in the tonestack is critical. Get out your chopsticks and move those wires around!

[KellyBass]

Switching out the silver mica 500pf coupling cap to a polystyrene cap of the same value worked wonders in taming the highs in both my express builds...absolute wonders.

[Cliff Schecht]

Oh yeah, I always forget that I used poly's almost everywhere in my amp for small values. Never tried mica though, perhaps I won't now.

[M Fowler]

Yeah one can change a bunch of the tone caps but that has been frowned upon when I previously mentioned all these changes to TWs in prior posts.

Therefore, I did not make any of those suggestions this time.

Sorry this has been discussed so many times on TAG and ruffles many feathers for some people. Some builders have changed the values of the tone caps, the slope resistor the bright caps themselves and even went so far as to change the value of the pots to get some bass into their wrecks.

Hope this helps, if not I can point you to past posts.

[Gibsonman63]

Thank guys. Here is what I ended up with:

Changed C2 from 500pF to 250pF (Silver Mica)
Changed C12 from 47pF to 100pF (Mica)

I also changed R5 from 2.7k to 1.5k to give it a bit more gain.

It is really starting to get the sound I am looking for. I can back off of the bass and mid now. I will order some Polysterene caps and give that a go next week when they arrive.

I have also been experimenting with my chopstick. My wires are fairly short and tight, so they don't have much play, but at least I have't found any loose solder connections.

[Gibsonman63]

Switching out the silver mica 500pf coupling cap to a polystyrene cap of the same value worked wonders in taming the highs in both my express builds...absolute wonders.

Do you guys have a US source for the polystyrene capacitors. I am not finding them from Mouser, Allied etc... Is it possible that they are called something else?

[M Fowler]

I also changed R5 from 2.7k to 1.5k to give it a bit more gain.

That would give it less gain.

[Cliff Schecht]

I have a big stash of small values that I stack together to make what I need. I'm not sure of a good place to buy them though, they haven't been in production in years (I think polyprop and Teflon types took over).

[KellyBass]

I've got some off of ebay before, but lately I've been getting them from Ken Watts at

www.turretboards.com

Swell guy.

From what I've been told they are very stable in high temp situations, as well. I just know that I LOVE them.

[Gibsonman63]

Very cool. Thanks again. I hope I can pay it forward one day.

[billyz]

Polystyrene caps are no longer made. Get em while you can, they are still cheap.