taming the treble in t-wreck inspired amp

[krash]

OK, well the amp is *just* usable now, I mean it's bright but it sounds extremely good and it's highly addictive to play. Kind of like audio methamphetamine. Probably not very good for you but you just can't quit. I still run the treble down at about 1 or 2 almost all of the time and also turn the mid down quite a bit most of the time.

I have a Weber ceramic Silver Bell in the amp, and it is an open-back cabinet basically like a regular Princeton cabinet but made from solid pine and 1.75" deeper than a regular cab with a 12" cutout... 1/2" solid-pine baffle, and a 6" tall solid bottom-back in it. It has about 10x the bottom end of a regular Princeton but is still bright.

the story of the amp changes is here:

http://prophetsandpoets.com/josh/guitar ... jects.html

I ended up with a .003uF (actually .001uF + .0022uF in parallel) and I *think* 56K or 68K resistor before the clipping stage. I really can't recall whether I left the 100K or went down to 68K or 56K.

Bypassing the plate res sounds like a fair idea. I'll have to give that a shot. It's still really really bright but with the treble near zero it sounds pretty awesome.

[ODwan]

Please try a 1MegAudio as a bass pot. If you plug this in the TSC you'll see a huge increase in bass response which might scare you a bit, but this will subjectively lower the highs.

Timo

[jblues]

taming the treble in the express is done with the output transformer...the express uses like 6k impediance output transformer while most new amps are like 4k impediance the lower impediance means more volume and also more treble (more efficient) the old amps old marshals included have 6k impediance output trannies this tames the treble and a little volume so islver faced princeton has prob about 3.5k-5k output trannie looking in from the power tubes. the express is like a marshall topology in idea which was boost treble and cut bass on the input gain stages (in comparison to the fender bassman they coppied) along with boosting more treble right before the phase inverter that 3rd gain stage kicks upper harmonics up a notch giving the infinite sustain you get with the express then to compensate all the trebble overload ken puts in a huge dc blocking cap .1uF into the phase inverter grid(try that value with a fender design ed amp...hehe fart city)since there's a highpass filter there cap in series with signal in to the impediance of the actuall valve you get more signal with biller cap...so he's letting as much bandwidth trough into the phase inverter as possible here.
i hate snubbing caps ( caps across the plate resistors) just change the dc blocking caps a bit instead
the silver bell weber is a bit bright for this style of amp also...so try grid stopper resistors like marshal uses on the power tubes 5k is good start point but i used 8.2k into the plates or my 6v6 poer tubes to tame the treble a bit these need to be like 1 watt resistors they mount on the valve socket themselves.....also the express uses an 820 ohm resistor after the volume controll (which is mounted on the tube socet also)i have heard that some ppl have wrecks with up to 2.2k resistor values here this cuts treble a tiny bit.

[gearhead]

Which 880 (or 2.2k) resistor are you talking about? The only one's soldered directly to the tubes are the higher wattage 1.5k and 1K ones, but that's well after the volume control.

While I'm at it, which types of smaller value -pf- caps (polystyrene, polyster, or silver mica) did you all use and get a balanced trainwreck?

[skyboltone]

Hello

I had the same problem with the muddy low end after changing the .002 coupling cap! Im using octal 6SL7's in the pre amp and phase inverter. 70 amplification factor , as opposed to the 100 of a 12AX7

Good luck!

I haven't looked in years but good 6SL7's don't grow on trees. Have you found a reliable source of these guys?

[krash]

taming the treble in the express is done with the output transformer...the express uses like 6k impediance output transformer while most new amps are like 4k impediance the lower impediance means more volume and also more treble (more efficient) the old amps old marshals included have 6k impediance output trannies this tames the treble and a little volume so islver faced princeton has prob about 3.5k-5k output trannie looking in from the power tubes.

I bet it's more like 8K. I did notice that running the amp into a 16 ohm speaker, even in the old Fender stock circuit days, made it bright and shrill. So maybe I just need to tack an 8 ohm power resistor in parallel with the speaker output, or mount one of my cone-less speaker drivers in there in parallel to knock the load down to 3-4 ohms and get the transformer primary to look more like 3-4K...

i hate snubbing caps ( caps across the plate resistors) just change the dc blocking caps a bit instead

Uhh... you mean that .1uF PI cap? You can't get that any bigger. The amp has more than enough bottom end and changing that .002 (which I now have as a .001+.0022) in the "clipping stage" to a bigger cap doesn't fix the top end, just makes the bottom end flabby. I am actually thinking I need some kind of roll off cap somewhere... Really I dug the "cut" control. Maybe I just need to stick a 100K R in series with a .01uF across the grid leaks on the 6V6's... Well so many ideas...

the silver bell weber is a bit bright for this style of amp also...

Huh? Among all of my speakers, the SB is far and away the darkest. However, I must say, my Eminence Red Fang sounds pretty glorious with the Princeton Reverb. It's brighter clean but more compressed in the top end when it's driven really hard.

so try grid stopper resistors like marshal uses on the power tubes 5k is good start point but i used 8.2k into the plates or my 6v6 poer tubes to tame the treble a bit these need to be like 1 watt resistors they mount on the valve socket themselves.....

You mean grids, not plates...

That's a fair enough idea. Remember though that a lot is different with the PI & power stage in this amp. It has a split-load PI like a Tweed amp that sounds very different. It's not hitting the power tubes nearly as hard as a LTPI would.

[gearhead]

Krash,

Where did you wedge in the cut circuitry?

[krash]

You can see the details here:

http://prophetsandpoets.com/josh/guitar ... jects.html

A Princeton Reverb already has three gain stages before the PI. So I just used the third stage as a clipping stage by changing the coupling cap, adding the 100K resistor to ground and changing the cathode cap.