Majestic/Cal 45 2-in-1

[ntuncer]

It seems RC4558 is a unity gain stable which unused op-amp could be used as a voltage follower instead of terminating it.

 

[Chuck D. Bones]

Leaving the inputs of unused opamps or CMOS floating is an absolute no-no. Unpredictable & generally bad things can happen. I can understand why a builder might use only part of a dual (or quad), but leaving unused inputs floating is bush-league.

If you want to put the spare opamp to good use, wire it as a unity gain buffer and stick it between the TREBLE & VOLUME pots. you'll have to relocate C3 after the buffer.

The other thing J Rockett did that is problematic is connecting a capacitor from an opamp output to ground, which is what happens with C8 when TREBLE is dimed. A capacitor between the output & ground can cause instability if the capacitor is too large. How large is too large? Hard to say because it varies from mfgr to mfgr & lot-to-lot. It also depends on the feedback network. Sometimes the datasheet provides guidance. Better to avoid the problem altogether. A 100Ω resistor between the opamp's output and the load capacitor is sufficient to ensure stability, so J Rockett could have done that.

 

[HamishR]

For the simplicity (over-simplicity!) of this circuit it does sound remarkably good. Of course since I built the combo pedal I have moved on to other ODs, but none of them are all that different from this. I really like the Timmy platform because it's very malleable and you can easily tweak it to get a different sound. I have also learnt that using the second triode/gain stage (whatever you want to call it) you can bolster the sound, add body, add mids, add grunt - all good guitar friendly things. All of this I have learnt through trial and error and help from here, especially Mr Bones.

It seems a waste not to use the second half of the IC. I am a super-fan of minimalism but by using just a few extra caps and resistors you can improve the Rockett circuit significantly, both sonically and electronically.

 

[ntuncer]

Leaving the inputs of unused opamps or CMOS floating is an absolute no-no. Unpredictable & generally bad things can happen. I can understand why a builder might use only part of a dual (or quad), but leaving unused inputs floating is bush-league.

If you want to put the spare opamp to good use, wire it as a unity gain buffer and stick it between the TREBLE & VOLUME pots. you'll have to relocate C3 after the buffer.

The other thing J Rockett did that is problematic is connecting a capacitor from an opamp output to ground, which is what happens with C8 when TREBLE is dimed. A capacitor between the output & ground can cause instability if the capacitor is too large. How large is too large? Hard to say because it varies from mfgr to mfgr & lot-to-lot. It also depends on the feedback network. Sometimes the datasheet provides guidance. Better to avoid the problem altogether. A 100Ω resistor between the opamp's output and the load capacitor is sufficient to ensure stability, so J Rockett could have done that.

Thanks for detailed information! I will study and digest your message.

 

[ntuncer]

Leaving the inputs of unused opamps or CMOS floating is an absolute no-no. Unpredictable & generally bad things can happen. I can understand why a builder might use only part of a dual (or quad), but leaving unused inputs floating is bush-league.

If you want to put the spare opamp to good use, wire it as a unity gain buffer and stick it between the TREBLE & VOLUME pots. you'll have to relocate C3 after the buffer.

The other thing J Rockett did that is problematic is connecting a capacitor from an opamp output to ground, which is what happens with C8 when TREBLE is dimed. A capacitor between the output & ground can cause instability if the capacitor is too large. How large is too large? Hard to say because it varies from mfgr to mfgr & lot-to-lot. It also depends on the feedback network. Sometimes the datasheet provides guidance. Better to avoid the problem altogether. A 100Ω resistor between the opamp's output and the load capacitor is sufficient to ensure stability, so J Rockett could have done that.

Hello Chuck, if I understood correctly you mean the modifications like below. With these modifications, with the help of unity gain buffer we will have low impedance at the pin 7 and solve stability issue using 100R resistance. But tonewise, what do we expect to have? I guess less noise because no more unused op-amp and 100R resistor, but the sound of the pedal remains same?

 

[DSL74]

For anyone who wants to try a Majestic - and I would very much recommend it - here is the schematic. Apologies if the schematic layout is wrong - I never studied electronics so don't know exactly how to do these things. But everything is correct as far as I know.

The only mods I have done to this circuit is replace the Ge diodes with 1N4148s and the 100K gain pot for a 250K. The 1N4148s don't actually sound very different - maybe a hair brighter but it's not a big difference. I really like the combo of 1N4148s with 1N4001s. Could be just my perception but it sounds a tiny bit less shrill than all 4148s and clearer than using the Ges. As usual, I could be talking outa my bum but this circuit does it for me! FWIW I find this circuit to sound a lot like the Caliber 45 (strange, huh?) but it has a bit more low-mid content. It works incredibly well at the clean to dirt transition thing, and all with bugger-all parts. Fab.

View attachment 3322View attachment 3322

My first post. This is an amazing forum and I am very impressed by some of the builds and info I am seeing. So what components or design make the Majestic pedal a so-called Jimmy Page HTWWW (as advertised by JRAD, anyway) tone Marshall in a box vs other MIAB pedals? Thanks!

 

[Chuck D. Bones]

Hello Chuck, if I understood correctly you mean the modifications like below. With these modifications, with the help of unity gain buffer we will have low impedance at the pin 7 and solve stability issue using 100R resistance. But tonewise, what do we expect to have? I guess less noise because no more unused op-amp and 100R resistor, but the sound of the pedal remains same?

View attachment 75288

You could put the Rxx either where you have it or between SignalFromPin1 and TREBLE pin 3. I'd use C10K, not B10K. The buffer is not absolutely, but does isolate the next device from the Treble network. If you use the buffer, VOLUME could be as low as 10K. I'd use A-taper for VOLUME, but it's a personal preference.

 

[Chuck D. Bones]

My first post. This is amazing forum and very impressed by some of the builds and info I am seeing. So what components or design make the Majestic pedal a so-called Jimmy Page HTWWW tone Marshall in a box vs other MIAB pedals? Thanks!

Yeah, good question. It's amazing how many pedals claim to "nail the Jimmy Page tone" as if Jimmy only had one tone. He didn't always use Marshalls, he didn't always play a Les Paul. He had his gear modded and he knew how to get the most out of his gear, the studio and the mix.

Jimmy could walk into Guitar Center, pick up a random guitar, plug into a random amp, turn a few knobs and sound like Jimmy Page.

The bottom line is there is no magic in any of these pedals. The so-called MIAB pedals don't all work the same and don't all sound the same. You test-drive a few and go with the ones that sound good to you.

 

[HamishR]

And unfortunately I could walk into Guitar Centre, pick up a random guitar, plug into a random amp, turn a few knobs and sound like me.