Marshall/Fender Combination?

[The Ballzz]

Hi Folks,
I am looking into creating an amp that has a classic marshall style sounding preamp AND a classic Fender style sounding preamp. I would like separate controls for each preamp channel and have the choices of:

A) Switching the channels back and forth.
B) Blending the channels together prior to the power amp section.
C) Possibility of cascading the two channels through each other.

I've already settled on the Marshall channel as a clone of the JMP 2203 prior to the changes made as they became the JCM800 series. This particular amp appears to be regarded as the quintessential epitome of all the best of the "CLASSIC" Marshall sound.

What to use for the power amp section and how many watts is still under consideration, but will likely be push/pull cathode biased. Low wattage and/or power scaling is a likely path.

I guess my main questions in this planning/design stage concern:

1) Which Fender preamp design to use to provide the most realistic "Holy Grail" Fender style rich, full, cleans while still providing that nice clear crunch that many Fenders can achieve. I'm kind of leaning towards a 6G6/6G6-A or possibly a variant of a Deluxe Reverb, but without the reverb or tremolo. I'm a card carrying, dyed in the wool, Marshall user, and am quite familiar with the operational nuances of one Marshall model to another. With that said, I've plugged into many Fender amps and found some to be glorious in their own rites, others horrendous for my use and yet others that were just marginally passable. I've not used them extensively enough to ascertain which model is the best of the best.
2) The best and most effective way to get the two separate preamp to work nicely together.

The amp will be much more complicated than this simple overview, but that is a work in progress and will mostly concern added features not really affecting the basic general layout. I realize there are likely several ways to skin this cat, however I do have a fairly clear vision of how I want the amp be, from an operational standpoint. Any help and/or suggestions would be truly appreciated.
Thanx In Advance,
Gene

[Smokebreak]

Hi Folks,
I am looking into creating an amp that has a classic marshall style sounding preamp AND a classic Fender style sounding preamp. I would like separate controls for each preamp channel and have the choices of:

A) Switching the channels back and forth.
B) Blending the channels together prior to the power amp section.
C) Possibility of cascading the two channels through each other.

I've already settled on the Marshall channel as a clone of the JMP 2203 prior to the changes made as they became the JCM800 series. This particular amp appears to be regarded as the quintessential epitome of all the best of the "CLASSIC" Marshall sound.

What to use for the power amp section and how many watts is still under consideration, but will likely be push/pull cathode biased. Low wattage and/or power scaling is a likely path.

I guess my main questions in this planning/design stage concern:

1) Which Fender preamp design to use to provide the most realistic "Holy Grail" Fender style rich, full, cleans while still providing that nice clear crunch that many Fenders can achieve. I'm kind of leaning towards a 6G6/6G6-A or possibly a variant of a Deluxe Reverb, but without the reverb or tremolo. I'm a card carrying, dyed in the wool, Marshall user, and am quite familiar with the operational nuances of one Marshall model to another. With that said, I've plugged into many Fender amps and found some to be glorious in their own rites, others horrendous for my use and yet others that were just marginally passable. I've not used them extensively enough to ascertain which model is the best of the best.
2) The best and most effective way to get the two separate preamp to work nicely together.

The amp will be much more complicated than this simple overview, but that is a work in progress and will mostly concern added features not really affecting the basic general layout. I realize there are likely several ways to skin this cat, however I do have a fairly clear vision of how I want the amp be, from an operational standpoint. Any help and/or suggestions would be truly appreciated.
Thanx In Advance,
Gene

Hey Gene, I'll take a stab at this as I just finished something similar.

Channel switching : totally doable and there are lots of different ways to split and join

Blending : doable as well, but it might not sound so great unless the channels are at least in the same ballpark, which is maybe why you are looking at tweeds for the Fender side? Nonetheless, you can do this with mixing resistors where the channels join, usually right before the inverter.

Cascading channels : This would mean 5-6 stages of gain. In itself this is possible, but that would mean looking at the entire system, and the attenuation that entails. Getting each individual channel to sound great, as well as the cascade, would be very very difficult(especially if you want "classic" on both sides, individually)

Cathode biased : I put a JCM800 type preamp in a cathode biased mule one time and was surprised at how good it sounded at lower volumes, but didn't care for it loud. That's just my experience.
I'm not sure what you mean regarding the changes to 2203 vs JCM800. I think the changes through these years were mostly in the power section, which you are abandoning for cathode biasing

Fender : Holy Grail Fender means a lot of different things to a lot of different people, but if I had to guess, especially for a "clean" channel, I'd say blackface topology. If you are looking for cranked fender "crunch" well yea maybe a tweed will do a better job there. But then your Marshall side should do that if you turn down the gain a bit Regardless, AB763 and 6G6 are different amps. Build them both both and see which one you like better. Don't skimp on the clean channel! For cleans I like gainstage>tonestack>gainstage>(maybe another little highly attenuated gainstage) phase inverter. That's classic Fender to me.

Speaking of the PI, you may have to have to compromise at bit. Regardless of values, have you considered ax7 vs at7? You'll also have to decide on output tube type, though I don't think that's a dealbreaker here. Maybe try some KT types. But the thing is, Marshall preamp distortion sounds pretty good, and Fender preamp distortion sounds pretty bad. They both can sound stellar when the power is cooking.

Don't forget about voltages and filtering, as well, depending on what you are going for. Side note : check out that Laney schematic that was recently posted. The "Crunch" channel(JCM800ish) is a really good example of a no-frills high gainer that has all the right stuff. The lead channel is fantastic, if you want to add another button to your footswitch;)

Hope that helps and good luck! - J

[pdf64]

Bear in mind the tonal contribution from the power amp, most particularly the effect of power amp - speaker interaction that a presence control in the global feedback provides, eg presence settings needed for the classic Marshall tone may work against a classic Fender tone.

[stretch2011]

A buddy made a jtm 45/bassman using the different channels. And if you wanted both you just bridged the channels.

[10thTx]

For consideration.

- Uses an A/B/Y box to switch between channels

- Uses simultaneous relay switching to switch between channels OR
blend channels

- Adds a 5879 OD stage instead of cascading Marshall into Fender stage
which I think would sound buzzy and probably have too much floor noise
and/or oscillation problems.

I included an editable SCH version for you to edit to whatever you want.

With respect, 10thtx

[gingertube]

Or take a shortcut:
I haven't used this kit but have built the circuit from scratch.
http://www.londonpower.com/tube-preamp- ... tar-preamp
Cheers,
Ian

[stephenl]

+1 on Gingertube's recommendation.
The "Standard" preamp is Fender clean + JCM800 lead. The channel switching scheme is flawless. You can get the complete schemo in TUT5 or use the London Power circuit boards.

I just built a complete amp using his boards and toroids and it's my favorite amp.

The prices are a little more attractive right now as the exchange rate with the US dollar is around .7

[The Ballzz]

Thanks 2 All Folks,
The replies and comments give me great food for thought. I really don't want any solid state components in the signal path, but the switching/blend layout is very helpful.

As to Smokebreak's thoughts, I've already built a duplicate of a JMP 2203 preamp, driving a pair of cathode biased 6AQ5/EL90's and it is glorious! The 6AQ5 when used properly seems to mimic the sound lost by lack of air movement by the the speakers in a low watt (10 or so LOUD watts in this case) situation. FWIW, the JTM 2203 (late 70's to early 80's) was just a tad different in the pre amp, but most of that seems to be voltage variances. Probably due to a different power supply/transformer choice! General consensus is that the JMP's have a certain magic that the JCM800's only come close to, but no ceegar!

I've pretty much decided on a 65-ish black face Super Reverb (no verb or tremolo) for the Fender preamp section. Man those Fender amps sure did change rapidly over the years! Getting those 6AQ5's "cookin'" shouldn't be too difficult!

Keep all those ideas coming as they are truly appreciated.
Thanx Again,
Gene

[10thTx]

I really don't want any solid state components in the signal path, but the switching/blend layout is very helpful

I certainly have no agenda for you & think you should build the amp however you wish to. I can appreciate your hesitancy to use solid state anything in a tube amp.

Having said that, as an FYI, I have found no difference in tone using a 12A_7 triode or a mosfet as a cathode follower. I have done it both ways and find a comparable tone whether it's a mosfet or a tube triode in the CF position.

http://www.geofex.com/Article_Folders/m ... tfolly.htm

With respect, 10thtx