Classic Reverb Signature vs John Mayer Signature

[tallen11]

Hello,
I'm going to be attempting a Two Rock CLRS build at some point and am trying to piece together a schematic. I know the CLRS is very similar to the John Mayer Sig circuit, but I'm wondering how it differs. Let's start with the voicing:
I know the CLRS has a more vintage, blackface fender type voicing and the John Mayer amp is pretty dark sounding. How is this accomplished? Comparing the JM schematic to the AB763 super reverb schematic, the most obvious thing that sticks out to me is plate voltage: it appears that the JM amp has significantly lower B+ going to V1 than the super reverb due to the 22K resistor in its filtering section of the power supply. That seems significant as I believe a lot of the blackface tone comes from high B+.
The next thing I looked at was the coupling and cathode bypass caps. The JM circuit actually has smaller caps in most cases: 5uF vs 25uF for cathode caps and 0.02uF vs 0.047uF for the V1b coupling cap. I'm not entirely convinced these minor differences would contribute too greatly to tonal differences, but I don't really know. Perhaps the larger bass response and gain created by the larger caps in the super reverb lend to the chewy tone and feel that I'm going for. On the other hand, the coupling cap going into the phase inverter is actually larger on the JM circuit.
Finally, it looks like the phase inverters are biased differently.
As far as feel goes, I was wondering how important tube rectification is to the feel of the amp. Certain amps like blackface fenders are described as feeling chewy or bouncy. How much of this is due to the rectifier (tube vs solid state) and how much is due to the circuit design? I'm starting to think the circuit is much more important than the rectifier as two rock traditional clean is described as bouncy but has solid state rectification.
So ultimately my question would be what is worth focusing on to get the JM circuit closer to sounding and feeling like a CLRS/blackface fender? I'm pretty new to all this so any help is appreciated. Thanks.

[norburybrook]

the JM isn't dark sounding IMHO, it can have a deep bass if you want but it's anything but dark.



M

[fred.violleau]

Hey Tallen,

From my little understand (and I mean little..) Dumble amps are not spongy amps, usually punchy and mid focused. You are comparing the JM which if I remember well was modeled after a Dumble SSS to a blackface super reverb, mid scooped and a lot more spongy if I may say so... two really different beasts.

The bypass cap is a great way to tweak the tone of the amp as it allows to filter out or emphasize certain frequencies. Then there is the builders choice: all those stages of amplification, depending on how hard you want to push these, will add overtones that become real frequencies and fill the spectrum. So you may trim these out and shape the tone before the PI, or you may continue and keep tweaking on the PI. Subtle changes at the beginning may result in obvious changes in the sound after three stages of amplification and a tone stack... And there is a reason why on those high gain amp you see small cathode bypass caps on the preamp : it trims away some of the bass that would squash the signal too early in the chain before it gains complexity with the overdrive harmonics and overtones. It may seem simple, but it takes a lot of expertise to tweak to get the right result (even more so expected results).. but that for me is the fun of building!

Also you bring in another interesting topic with the use of rectifier tube. From what I understand, and tried, and again there are gurus here that will probably get into more details, the lower the note amplified, the higher need in current. So if you play ala SRV slamming the low e string with a pedal pushing the preamp and playing at 80% of you amp capabilities, yes the choice between a tube rectification or diodes will be heard. A tube will not provide as much current as fast than a diode bridge and may choke under a huge current demand, where a diode bridge will be more consistent. But if you play comfortably, don't push the amp, and have a light right hand, then you will not hear much difference. Usually bridge diodes makes tighter bass, but again there are nuances.

All these are subtle but again add salt, pepper, a bit of cayenne, paprika and you're getting more complexe flavors.

Build, test and learn

Have fun!

Fred.

[amplifiednation]

Don’t overthink it...just add the OD channel back. Everyone says the JM was modeled after the SSS...but if you go pull the low plate classic layout it’s literally the exact same amp.

Figuring out where to put the reverb back in is the tricky part.

[TheHammer]

@amplifiednation Does this mean that the JM Signature is the clean channel of an ODS then, considering the Classic Reverb should be that.

[WhopperPlate]

@amplifiednation Does this mean that the JM Signature is the clean channel of an ODS then, considering the Classic Reverb should be that.

w/ plate driven reverb mixer gain stage like Taylor implied