Suggestion for a New FET Amp Simulation

[Paul Marossy]

Since everyone's been FET'n lately, I was wondering if anyone might be interested in trying an FET simulation of a Matchless Spitfire? I just heard a soundclip of someone's clone of that amp, and it sounds really nice! It's a clean, chimey sounding thing.
I guess that would end up being more of a clean boost kind of thing with a tone control...

[javacody]

How about a clone of one of those 18 watt marshalls? Dang, now I need to find a schem for one of these, anyone got any links?

[Paul Marossy]

you might be able to find one at www.18watt.com

[javacody]

Yeah, I found a lite version, can you guys suggest how I'd clone the power section with JFET's? I think the preamp section is pretty straightforward.

http://www.18watt.com/Storage/18w%20lite%20III.pdf

[Prive]

A really great amp to clone is the Steve Vai model from Carvin, itsn't the classic configuration, it use a baxandall tone control and some things very different to other amps and , of course the sound is incredible.
Doug, are you reading this?? :lol:

Saludos, Marcelo.

[Brian Marshall]

probably not exactly what you are looking for, but how about a jfet tube screamer with NO opamps, with the diodes and everything.

[spongebob]

JFET Tubescreamer, cool idea, but how do you model the feedback loop of an opamp?

A JFET Dist+ is something I could imagine more easily, gain stage + diodes to ground, but I don't know if a single JFET would have enough gain...

[Prive]

Take a look at the Boss Turbo Over drive, it uses differential amps with BJT, just a suggestion, a start point maybe.

Saludos, Marcelo.

[B Tremblay]

How about a clone of one of those 18 watt marshalls?

The runoffgroove.com R&D department worked out a nice emulation of it a couple weeks ago with good results.

We can share the schematic and perf layout, or we can provide advice while you puzzle it out.

[Bucksears]

How about a Mesa Mark I?

[Lucas Grijande]

A really great amp to clone is the Steve Vai model from Carvin, itsn't the classic configuration, it use a baxandall tone control and some things very different to other amps and , of course the sound is incredible.
Doug, are you reading this?? :lol:

Saludos, Marcelo.

Any schemo of this? :roll:  I'm thinking about to build some differents pre's using this technique (say marshall,fender,boogie,matchless....) and a common power stage to make them switchables.... it can be a good thing (maybe)

Regards

[Paul Marossy]

I'm not totally sure, but I think that the Spitfire is roughly based on the Marshall 18 watt circuit, but made to be cleaner sounding.

I would be interested to see what y'all came up with on runoffgroove.  

I just bought a Matchless Spitfire board kit off of ebay, so I think I'll build a real one. Well, a clone of one...

[petemoore]

I saw a schematic representation of the inside of an op amp.
 It looked like about a half day or better type build, if someone were to try the circuit with transistors.
 Nothin against the sound of OA's, but IIRC the author of the article that I was reading didn't like OA builds because an OA doesn't respond as well in some particular way [Memory] like recovery time...transistors do something opamps can't, was the gist of it. It did sound convincing, but I personally like OA's...?...
 OA's are really much too convenient, and I'm much too lazy to build one out with transistors and carefully matched parts to do the darn comparison...you're more than welcome to try it though...it does make sense that hand picking every active component and hand testing capacitors would result in a better than OA opamp build...[?]...I think.
 Has anyone ever tried this? What fits in one socket. could take a rather large piece of perf to build.
 Ahhhh...PCB layout of opamp... :idea: ...might be worth the effort.
 It would probably make for a rather large Tube Screamer  :lol:

[javacody]

Brian,
  Please do post the schem and layout. I would really appreciate it.

I'm starting to think that someone could work out a cool amp simulator with the pedals you guys have come up with and a 5 way switch.

[phillip]

How about a JFET emulation of the venerable Vox AC30, and even one with the Top Boost?  

Just a thought

Phillip

[Nasse]

I think Matchless Spitfire is Vox AC-15 clone, if I´m right? :?

And AC15 basic sound is quite similar to AC30...

Now if you could tailor a circuit that has vox clean and semiclean tones character (we have units that do the distortion thing quite well...)

I like normal channel sound much more than top boost "brilliant"

Top Boost was developed because The Shadows had used AC15´s and early AC30´s with Ef86 (?) input tube which had killer sounding treble but was microphonic and unreliable. When they later switched to ecc83 input stage it was darker sounding. So Dick Denney made Top Boost circuit for Hank and Bruce and rest is history.

[WGTP]

From Jay Doyle in Schematics 2 a discrete J201 op amp with clipping diodes (Jfets) to ground.  A discrete version of Aron's SB.  Jay knows what he is doing.

http://www.diystompboxes.com/pedals/schems/Shaka%20Discrete.pdf

[Paul Marossy]

Oh, it's based on the Vox AC15 circuit? I heard somewhere that it was a modified Marshall 18 watt. Anyhow, is the AC15 a "Class A" amplifier like the AC30 supposedly is?

Well, if that's the case, that Vox AC30 circuit at www.geofex.com would probably come very close to that sound, if you can get a clean sound out of it... I haven't looked at that one real close.

Anyway, I am going to build a clone of the real Spitfire amp, for a fraction of the cost of the real thing. This will be the second tube amp that I am going to build. I learned a lot from my first build!

[Transmogrifox]

From Jay Doyle in Schematics 2 a discrete J201 op amp with clipping diodes (Jfets) to ground.  A discrete version of Aron's SB.  Jay knows what he is doing.

http://www.diystompboxes.com/pedals/schems/Shaka%20Discrete.pdf

JFET Tubescreamer, cool idea, but how do you model the feedback loop of an opamp?

A JFET Dist+ is something I could imagine more easily, gain stage + diodes to ground, but I don't know if a single JFET would have enough gain...

WG has the idea.  Look at R3, C2 and the pot.  Change those to TS component values alonge with the 100 pF cap and use the standard TS tone stage from that point to the output.  It may be desirable to put a JFET buffer at the collector of Q4 and connect the feedback loop to the buffer instead of the collector.  Then you would have a class A output opamp.

[Paul Marossy]

"Look at R3, C2 and the pot. Change those to TS component values alonge with the 100 pF cap and use the standard TS tone stage from that point to the output. It may be desirable to put a JFET buffer at the collector of Q4 and connect the feedback loop to the buffer instead of the collector. Then you would have a class A output opamp."

That's an interesting idea, shapeshifter. :wink:  

I wonder how close it would sound to a real Class A amp. There is that other thread where people are saying that don't like the TS as a stand-alone pedal. Maybe in this case, it would be just what the doctor ordered?