I posted a simulation long ago but graphs were lost during the transition to the new forum.
I ran two sims, one comparing a variable input cap and a tone pot, and the other showing the effect of input impedance on the middle peak.





mac

Quote from: mac on February 26, 2024, 12:41:36 PMI posted a simulation long ago but graphs were lost during the transition to the new forum.
I ran two sims, one comparing a variable input cap and a tone pot, and the other showing the effect of input impedance on the middle peak.





mac

Awesome! I knew the potentiometer solution was too good to be true  . Well it is true in a way, but it can't replace the cap selector 1:1. I wonder how audible is the small difference we see between these curves.

Quote from: mozz on February 26, 2024, 07:13:38 AMWasn't the OC44/45 a rf transistor? I would think the capacitance would be less than 47pf. Maybe they were buying rejected parts as you wouldn't pay more for a rf transistor if it wasn't needed.  I may have some here, will have to measure. 

It's a bit more of a fudge than just the collector-base capacitance.   The OC44 and OC45 have a low fT which makes the base-emitter capacitance quite high as well.   When you only add an external collector-base capacitance it needs to be large enough to compensate for both OC44/OC45 capacitances, so it ends up being a bit larger than expected.   (The base-emitter capacitance is a diffusion capacitance, as opposed to a depletion capacitance, so it can only be measured in circuit with a collector current.)

For 5V across the base and collector the OC44/OC45 should end up with a base-collector capacitance of around 11pF but I wouldn't be shocked to see double that.   As the base-collector voltage drops the base-collector capacitance will rise considerably.  An LCR meter will likely measure the larger value, and will only be a meaningful measurement with AC coupling since the BC diode will screw things up.  A pulse type capacitance meter will most likely show the lower value since there's an average DC bias.

The numbers I posted earlier weren't very precise.  It's possible adding a collector-base capacitance of 22pF might do.   If you want to emulate the the capacitances of a germanium transistor more accurately it's better to add a BC capacitor and a BE capacitor.

If you consider the OC71 as an option then the collector base capacitance is a lot higher than the OC44.   That puts a big window on what is acceptable.

Can I recommend the Omega by Runoffgroove?

It's my favourite treble booster and it's an easy build.

https://runoffgroove.com/omega.html

Quote from: akc1973 on February 26, 2024, 09:05:11 PMCan I recommend the Omega by Runoffgroove?

It's my favourite treble booster and it's an easy build.

https://runoffgroove.com/omega.html

I will build it and compare it to my BD139 driven RM. This looks neat.

Quote from: akc1973 on February 26, 2024, 09:05:11 PMCan I recommend the Omega by Runoffgroove?

It's my favourite treble booster and it's an easy build.

https://runoffgroove.com/omega.html

If I were to build this circuit, I would label the 1 megohm pot as "SUCKAGE" because it gives variable tone sucking from a minimum at high resistance to a maximum at low resistance.

If I were to build this circuit, I would put the high-pass after a buffer and maybe have an independent "SUCKAGE" control up front.
Though we are veering further away from the classic Rangemaster design.

Quote from: amptramp on February 27, 2024, 09:23:50 AM

Quote from: akc1973 on February 26, 2024, 09:05:11 PMCan I recommend the Omega by Runoffgroove?

It's my favourite treble booster and it's an easy build.

https://runoffgroove.com/omega.html

This doesn't sound good... Is it how the vintage treble boosters worked or is it a "feature" of the runoffgroove implementation? Does it matter if it is the first pedal after the guitar or not?
If I were to build this circuit, I would label the 1 megohm pot as "SUCKAGE" because it gives variable tone sucking from a minimum at high resistance to a maximum at low resistance.

Quote from: RaistMagus on February 27, 2024, 10:32:54 AMIs it how the vintage treble boosters worked

Yes. As I noted in reply #12. Also illustrated in mac's third sim.

QuoteDoes it matter if it is the first pedal after the guitar or not?

Yes. See above.

RoG mention it does have guitar loading implemented. It is meant to go first, so does RM.

This is a *treble* booster + soft distortion based on a BMP and Electra distortion.



EE say "if you want more gain pay with bandwidth"; in this case if you want distortion pay with volume 
A second transistor can be used to increase volume.

mac

A RM has (9v-7v)/10k = 0.2ma across the transistor so the reflected impedance at the base is,
hfe*0.026mV/ie =  hfe*130 ohm
Say hfe*150 ohm assuming some bypass cap internal resistance.
A germ having a gain around 80 is recommended, see RG article.
80*150 ohm = 12k
In // with 68K (ignoring the 470k) Zin = 10k

This is the value I used in my Fet treble booster. A Mosfet can also be used with a fixed bias network and a 1uf+10k at the gate.
I had posted both versions but again picts are gone.

A RM vs single Fet version.
Note the effect of the gate resistor.

Quote from: Lino22 on February 27, 2024, 05:58:14 AMI will build it and compare it to my BD139 driven RM. This looks neat.

RoG Omega needs a lower min *sucker*    resistor and a lower pot, 100k. I'd also remove the input 33k and use a 4n7 to 6n8.

I ran a simple simulation, a mic guitar model to a variable cap to a 10k to gnd.
Not a big boost 



mac

If you are only going to use a guitar as an input, I would remove the 1 megohm input resistor and the input capacitor and leave it DC-connected like a Tillman.  With the capacitor in place, you will get a tuned circuit with resonance set by the pickup inductance and the input capacitor and the suckage control may act like it is tuning a resonant response.

With the 3n3 capacitor gone, the noise performance at low frequencies will improve because the suckage pot will be in parallel with the guitar level pot and the pickup at high levels of the guitar level pot and with the value of the resistance to ground and the resistance of the level pot above the slider in series with the pickup resistance.  When you calculate noise and you have a 522 K resistance in parallel with the level control, the noise of the  resistance is in parallel with resistance of the level pot and the pickup in that sense and the 522 K resistance is not isolated from the guitar output resistance at low frequencies.

Quote from: amptramp on February 28, 2024, 07:21:02 AMIf you are only going to use a guitar as an input, I would remove the 1 megohm input resistor and the input capacitor and leave it DC-connected like a Tillman.

I'm not familiar with those      JFETs behaviour but I think input cap/Gate do need a path to GND, or else, leakage current will eventually cause the Gate to charge up..

Quote from: RaistMagus on February 25, 2024, 08:15:36 AMI want to get a treble booster, one with selectable range.

A MFB bandpass filter (f.e. Phuncgnosis) *behaves like* a RM with a *variable input cap*.
I'm thinking of a filter with unity gain doing the sweep, and a transistor doing the boost.

Quote from: Lino22 on February 25, 2024, 03:22:41 PMYeah, i've got it on all the time and use just the volume knob on my guitar. After 20 years of doing this, i may stick with it for the rest of my days. The best pedal out there. I just had to remove the Ge tranny, it was too hissy. BD139/140 does the job and they are quiet.

The only pedal I can't live without.
It pushes my tube amps and my 60s radio recorders nicely.

Mine has a quiet Matsushita 2SA102 hfe 70 leakage 200ua with 3 input caps, 6n8, 10n and 22n.
Jap germs are the best, IMHO.

mac

QuoteMine has a quiet Matsushita 2SA102 hfe 70 leakage 200ua with 3 input caps, 6n8, 10n and 22n.
Jap germs are the best, IMHO.

Mine had Matsushita 2SA102, but after 20 years some fellow in the audience asked me to turn it off, so he can hear other stuff, not just my hiss. So i did.

Quote from: Lino22 on February 28, 2024, 10:08:56 AMMine had Matsushita 2SA102, but after 20 years some fellow in the audience asked me to turn it off, so he can hear other stuff, not just my hiss. So i did.

 
Was it always hissy?

mac

Quote from: RaistMagus on February 25, 2024, 08:15:36 AMI want to get a treble booster, one with selectable range

I came up with this,



I didn't test it yet.
The sim shows that highs drop faster, and I ignore if the filter is noisy.

mac

600 to 700Hz shouldn't be considered "Treble", should they..??

make it secret weapon?