Matchless spitfire clone?

[chuckb]

Hey guys , i just finished a Matchless Spitfire clone build and I have to say it's a very bright amp,kinda voxy. Is there a mod or mods that i can preform on this amp to cut back on some of that brightness and add a little more "hair" to the sound? Also Iwould like some more gain as well?

Chuck.

[Jazz P Bass]

What speaker are you using?
Looking at the schematic, the coupling caps look as if they are a tad small.
So the circuit, as designed, is reducing the bass frequencies throughout the amp.

[Chuck H]

Here's the beef: Changes in red.

[chuckb]

What size coupling cap would you suggest? I'm using a V30 but have also tried a G12m greenback.

Chuck.

[chuckb]

Thanks Chuck, I'll give these changes a try and see what the results are like? I appreciate it.

Chuck.

[darkbluemurder]

I would replace that Crossline Master Volume for a LarMar PPIMV. Sounds much better but still changes the tone a lot. This amp definitely lives on power tube overdrive - the preamp is not capable of driving the PI into heavy overdrive.

I would also toss that tone control and put a cut control in there - 500kA pot with a 2200 pf cap is a good starting point.

Cheers Stephan

[chuckb]

Hey Stephan, would you have a schematic of your suggested changes as it applies to the Spitfire? Would really like to give it a try?

Chuck.

[darkbluemurder]

Hi Chuck,

Here is an amp I built that has the LarMar PPIMV. It can be directly transferred to the Spitfire.

It consists of a dual 250k log pot which replaces the 220k grid leak resistors for the power tubes. The 2M2 resistors are there for safety purposes so that the grids stay connected to ground in case the pot wiper lifts.

Cheers Stephan

[Chuck H]

Thanks Stephen. Looks like a real grinder. The "Lar Mar" master has been discussed here many times. Including the additional 2.2M insurance resistors. I even have a variation that swaps the connections so it can be used with bias vary trem. But the Spitfire is pretty much all about power tube clipping. It's such a short signal path that there isn't likely to be enough useful clipping behind the power tubes to make it worth the implementation of even a post PI master. That doesn't mean someone won't do it.

BTW... I see your low post count. Welcome. And thanks for the addition.

[darkbluemurder]

But the Spitfire is pretty much all about power tube clipping. It's such a short signal path that there isn't likely to be enough useful clipping behind the power tubes to make it worth the implementation of even a post PI master. That doesn't mean someone won't do it.

I actually did it once with a Spitfire preamp and 6V6 tubes and found exactly what you described. Power scaling/VVR would probably be the solution that changes the tone least.

The PPIMV works very well if most of the overdrive happens in the PI - such as the HoSo amp of which I posted the schem. You can hear a little more of the EL84 colour at very high master volume settings but if I had built that amp with 6V6, EL34 or 6L6 the tonal variation would be even less.

That is also why I think the Spitfire design works best with EL84 tubes - the others will not provide enough overdrive. Maybe the 6BM8 would be a good alternative if you want a bit less volume.

Cheers Stephan

PS: Yeah, I just registered, even though I knew for quite a while the forum existed. Thanks for the warm welcome.