Unused triode -> Treble booster

[oh7hhi]

Hi!

I have an amp which has one unused triode. I'm going to use it as a treble booster.
What would be the best way to make it sound like rangemaster in front of amp?
At the moment it has 68k + 68k at plate (split load, output is taken between those resistors), 6,8k / 0.22uF at cathode and 1000pF plate bypass cap.
It's close, but it's still missing that "honk".

Any ideas?

[Firestorm]

You won't be able to replicate the distortion characteristics of the pedal, but if you just want the treble boost, the trick would be to add a first gain stage that has only unity gain at low frequencies, but boosts the upper range. Try a very large cathode resistor (47K) bypassed by a very small cap (.01-.02). A straight 100K plate load should be fine, but you can experiment with splitting it. To avoid boosting too much ultrasonic noise, bypass the plate load with something small: 47pF-100pF.

[oh7hhi]

Thanks for ideas!

I compared this boost-circuit and a rangemaster clone. Rangemaster sounds fatter.
Then I increased plate bypass cap to 2,2nF. That fattens up tone but it's still not enough "middy"...

[Paul Fawcett]

Hi!

I have an amp which has one unused triode. I'm going to use it as a treble booster.
What would be the best way to make it sound like rangemaster in front of amp?
At the moment it has 68k + 68k at plate (split load, output is taken between those resistors), 6,8k / 0.22uF at cathode and 1000pF plate bypass cap.
It's close, but it's still missing that "honk".

Any ideas?

Well, you're not going to get it sounding just like a Rangemaster. If my calculations are OK you can approximate the frequency response by doing something like the following:

Rk = 2K
Ck = 22uF (retained mostly for noise rejection, not gain)
Co = 220pF (yes, pF)
Split plate load = 82K (top) and 47K (bottom)
Rg(following stage) = 270K

[oh7hhi]

Yeah, I know it will never sound just like RM.
What I'm looking for is the midrange/upper midrange honk that good treble boosters produce.

Maybe I should have been more specific...

[Paul Fawcett]

Yeah, I know it will never sound just like RM.
What I'm looking for is the midrange/upper midrange honk that good treble boosters produce.

Maybe I should have been more specific...

Yes, well, the recipe I spelled out will come close to replicating the frequency response described by RG Keen in his treatise on the rangemaster. Naturally, the distortion characteristics will differ, and the output impedance from a tube driven stage will always be higher than from the transistor equivalent...

[oh7hhi]

Thanks!

I will give it a go !