taming the treble in t-wreck inspired amp

[krash]

Hi all. I'm a newbie here and generally new to trainwreck type amps.

Here's my question. I have a silverface Princeton Reverb with a fair amount of mods, most electrical mods are "trainwreckizing" the preamp in terms of cathode resistor/caps and the 0.002uF/150K between the second and third triodes. I didn't change the tone stack (already had the reverb knob converted to a midrange control). In a semi-open-back pine cabinet with a Weber Silver Bell (12"), the amp sounds Real Good but it's bright. Have to turn the treble all the way down and it is just on the edge of useful. BTW on '2' on the knob it crunches as much as my 18W does dimed.

So, can I tame the top end and maybe get a bit more range on the volume knob before it crunches that much by changing the .002/150K to something like .0047/68K? Will this really change the character of the amp (distortion character, that complex and "chewy" kind of tone)? I know this is not a strictly trainwreck question but this amp is really out of this world sounding other than being too bright. My other option would be to swap the speaker. R's and C's are a lot cheaper and I really like the Silver Bell.

Thanks!

[btw my next project is to gut my Classic 30 and turn it into a quasi Liverpool or Rocket with a twist ... but I'll get to that later!]

[slajeune]

Hi Krash,

I had the same thing as you. Basically, I built a derailment (single ended trainwreck inspired amp). I felt that there was too much treble. I simply changed the .002 coupling cap for a .0047 and voila, a lot less treblish and pretty much to my liking!

Try it, it's a simple mod that might produce the right tone for you. I wouldn't touch the 150k resistor as this would change the load of the previous stage. The 150k and 10k resistor on the cathode of the third stage is part of the trainwreck sound.

Cheers,
Stephane.

[krash]

I had another .0022uF and put it in parallel with the first one. Didn't get a chance to crank it this morning, will try it later today and see how it works.

Will the tonestack changes warm it up any?

[krash]

well I think adding the .0022uF along with the first one maybe didn't do much to tame the top end, but might have made the bottom more muddy. Hard to say because I didn't spend a lot of time with it. My strat still sounds very bright and glassy through the amp with the treble on 0 ... but everything is muddier with the bass on 10.

thoughts, ideas? It was real good before so maybe I'll just take it back.

[RidingTheBlinds]

Hello

I had the same problem with the muddy low end after changing the .002 coupling cap! You may want to try and adjust the caps related to your tone control, especially if you used the values from the Princeton! At least that will shore up your tone adjustment some. Amps can be a lot of fiddling around in order to get the sound you want! All of the variables can contribute! Personally I found that the Poly Prop caps sounded harsh in my TW. Remember every part contributes, Tubes, Caps, and Iron Mattered the most in my situation! Also try a lower gain tube like a 5751 to loose some of that push on the front end! Some Marshall guys like using 12AY7's in the phase inverter! 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!

[krash]

Thanks for the tips. This is obviously not a Trainwreck type amp anyway just borrowing a bit. I think I will go back to just the .002 by itself and find a way to get some range out of the treble control instead. Any specific advice?

The Princeton Reverb has 220pf/250K treble, .1uF/250K bass and .047uF mid (borrowed reverb pot + series/parallel to get it to 6.8K on 5). I have a handful of .022uf's here and might even be able to scare up a 470pf and a 1M pot to redo the tonestack. The question is, will this get brighter, or less bright, with tonestack change? I would think the 500pf/1M would have to get much darker with treble turned down compared to the 220pf/250K.

Thanks!

[HiGain]

From my experience, the result of altering the tone stack to 470pF/100k/.022/.022/1m pots with 25k mid pot, is a perceived fuller sound, with less overpowering highs. In short, I think this will go a step toward fixing your problem. You might try just changing the bass and mid caps first. The .1/.047 combo scoops out a lot of mids, and leaves a lot of lows and highs in the mix.

If that doesn't work, you could always try a conjunctive filter, as detailed in the Blues Express schematics in the express pdf file.

Good luck!

Jake

[krash]

Thanks again. I think I'll try the tone stack changes. I looked at them in Duncan's tonestack app and definitely there's a major low-mid scoop that you can't avoid with the Fender values, the Twreck changes a lot.

[krash]

Hey I plugged in the values for the Trainwreck tone stack (1M/500pf, 250K/.022uF, 25K/.022uF) and also those of my Fender with added mid (250K/250pf, 250K/.1uF, 25K/.047uF) into Duncan's Tone Stack Calculator. The Fender has more low-bottom end (below 100Hz) which is basically useless for guitar tone, and has a huge midrange "scoop" at about 600 Hz that's about -10dB compared with the rest of the response with all the controls on 5. Turning down the treble all the way gets this "scoop" to turn into a shelf at 600 Hz but cranking the midrange knob turns up the treble another 5-6dB whether you like it or not.

The Trainwreck values on the other hand have basically flat frequency response from about 40 Hz on up with the controls set to 5. This is a way better design. Turning down the treble has the effect of bumping up the bass and only shelving the >1K response. With the treble all the way down, the mid control functions basically like a treble knob. With the treble on 5+ the mid basically is a volume knob. It is not intuitive, but it's extremely functional.

So I redid the amp with these values and now it'll go from dark and wooly to strident and chop your head off with any of my guitars. The T-wreck tone controls are definitely the answer!

[Jackie Treehorn]

I recently switched the treble cap from a silver mica to a polystyrene and the top end definitely mellowed a bit; it's a little less clangy. I tried it at rehearsal yesterday and there's still a lot of cut, just that the top is a little less overpowering. The cap I took out measured 498 pf and the one I put in was 480 pf, so there's a little difference there.

High voltage polystyrene caps are available at Triode electronics. No 500 pf, just 470pf.

[hellhound]

Hi,

I was wondering if putting a relatively big resistor(68K-470K Try using a pot first) from the junction of the 2nF/150K to the grid of the third stage would help. The miller capacitance would cut some highs. ???

More about the issue miller at http://www.aikenamps.com/MillerCapacitance.html

[UR12]

Here is a table I posted in the Ginger Clone thead.

One thing to note, the higher the value of the resistor the more gain from the third stage. You should be able to find a combonation that will work for you using the chart. It seemed to my tired ears that if I increased the bass I didn't think the Highs were so trebley any more.

The resistor and cap combination for a 6db/octave hi pass filter. Here are some calculations on the frequency of the filter using various components.

56k / .001 = 2843.5hz
56k /.0022 = 1292.5hz
56k /.0033 = 861.7hz
56k /.0047 = 605.0hz

68k / .001 = 2341.7hz
68k /.0022 = 1064.4hz
68k /.0033 = 709.6hz
68k /.0047 = 498.2hz

100k / .001 = 1592.4hz
100k /.0022 = 723.8hz
100k /.0033 = 482.5hz
100k /.0047 = 338.8hz

150k / .001 = 1061.6hz
150k /.0022 = 482.5hz
150k /.0033 = 321.7hz
150k /.0047 = 225.9hz

It would appear to me that if you used a 150k resistor and a .001 cap you would up the gain to the third stage and keep the same hi pass freq on the filter (68k/.002 = 1064hz ..........150k/.001 = 1061hz)

[ODwan]

Also try out a Vox style Cut circuit. It lets you dial in just the right amount of bite!

Timo

[krash]

I did put in a Vox-like cut control and I dug it. It might even still be wired in. I didn't have a good spot to put it though, so I put it in the ext. speaker jack.

[Mark]

Another thing that has been popular in regards to taming the top end on these amps is shunting cap/s across the plate resistor/s. These may vary from 100pF to 500pF.

The one question does come to mind is, what speakers are you using?
I used an open back cab and hated the sound of the amp. I found that the 4 X 12" cab was the way to go, as it offered more bass and veiled the treble to my liking.

Let us know how you get on with this problem.