Express Question - Preamp vs. Poweramp distortion

[heisty]

Hi can u knock the bass on the head by changing the value of the 150k resistor to ground here? which way do u go in value to loose bass

[Fischerman]

That .002uF cap and 150K resistor form a HPF (high-pass filter). Lower the value of the cap or resistor and you reduce bass...increase either one and you increase bass. However, the resistor will also affect the gain...lower is less and higher is more. IME, 150k is right in the zone where slight adjustments either way can make a significant difference. If that resistor were, say, 470K, then you could probably increase/decrease it by 100K and wouldn't make that much difference in gain...but here a 100K swing either way would make a significant difference.

In short, if you want to adjust the bass it's probably best to do it elsewhere. But that's not to say that you won't have success adjusting that 150K resistor. If you look at all the clones...people use all sorts of values here.

[heisty]

Thanks , where is the best area to look at changing or lowering and tightening the bass?? My cieratone clone kit has to much bass
Cheers

[Fischerman]

There are several areas. The cathode bypass caps, the PI input cap, the PI output coupling caps, even the tone stack. I'm hesitant to suggest anything because I could just never get my Ceriatone Express where I thought it should be. It distorted and sounded 'good' and could be coaxed into feedback...but it didn't 'sing' the way I wanted and it didn't sound absolutely spectacular. Anything less than 'absolutely spectacular' was going to be a disappointment so...it had a tall order to fill from the get go.

From what reading I've done over the years...people have always struggled with either excessive brightness or muddy/flabby bass or maybe a mixture of both with the Express clones. I'm sure some people get it right, either by stroke of luck or through diligence but I never have. It's fairly easy IMO to get 'in the general ballpark' and make a good sounding amp with an Express clone...but getting that last 5% or 10% is really the whole point behind the thing (again, IMO) and I just haven't got there.

[heisty]

yeh thats right ,ive tryed lowering cathod caps a bit and bass is a little better , but seems to lack a tight punch to the sound and changed the .002 coupling cap also,what mods have you done
cheers