A Tube-Powered 2×12 FRFR Rig for Guitar & Bass Software?

Back in the 20th century, I used to plug my guitar into a preamp/multi effect processor, amplified by a Peavey Classic 50/50 tube power amp plugged into a stereo Marshall 1922 2×12 guitar cab.

…A nice setup that has been gathering dust since I have migrated to a full-software solution!

I have been thinking about transforming this rig into an FRFR (Full Range Flat Response) system for years, to amplify the simulations from my laptop.

Finding Full Range 12” Speakers

Indeed, while the limited frequency response of the Marshall cab was not a very big deal with the multi effects processor (as it was setup for this particular rig, with an adapted response), it would not work for quality of the recent software simulations that were designed on studio monitors and already have very detailed built-in speaker simulation. You can somehow compensate with EQ, but it’s not as good and definitely lacks clarity.

Also, the Celestion G12T-75 16 ohms speakers have a huge bump in the 1.5-4kHz range, which is very aggressive When pushing the volume and does not work well with simulations:

After a long search, I finally found some full range drivers that can do the job, for a very competitive price: the Fane SOVEREIGN 12-250TC speakers. These 12” coaxial speakers with three cones can be used to easily replace the original 12” drivers. No need for additional crossovers or extra tweeters, it’s all integrated!

The response is pretty flat in average, and like with speakers designed for guitar cabs, there is more treble in front of the speaker, while it gets attenuated when increasing the angle:

That’s perfect for what I was looking for: the sensation of playing thru a regular guitar amp, with the sound and the flexibility of the software. Also, it goes up to 17kHz (and more), which is definitely enough for guitar tones, even with special effects or backing tracks. These speakers are 8 Ohms (instead of 16 for the original ones), so I have changed the impedance setting on the power amp.

I definitely prefer this type of setup with coaxial speakers compared to regular 2 or 3-way speakers, as the response and diffusion are much closer to a regular guitar cab. That’s the type of driver that the Line6 Power Cab uses by the way, and it feels great too.

Alternatives?

Celestion also offers two speakers that could fit, the F12-X200 and the F12M-150 TC (however limited to 12 kHz). Their cutoff frequency response in the low-end is however a bit high (resp. 75 and 60 Hz) if you want to use them for a bass guitar rig. Also if you look at the graphs closely, the F12-X200 has a pretty large dip around 5kHz, probably due to its conception (it seems that is built with 2 speakers and a crossover, which may indeed produce interferences around the crossover frequency). I am afraid this might color the sound a bit too much.

As a side note, they are much more expensive too, and often not available!

Replacing the Noisy Fan

One big problem with the Peavey Classic 50/50 power amp though is the noise produced by the fan. While you don’t care much when playing with a drummer and a loud audience, it is unbearable at low volume in the studio!

So I have searched for a replacement, and thanks to this post, I found this fan that works and keeps the tubes cool (you want the fan to blow enough air, or the tubes my get too hot). It is much quieter than the original fan, but still a bit noisy.

But it seems that most of vibrations and noise is now coming from the transformers that vibrate and resonate with the chassis… Not much I can do about it, I guess!

The Result

And here you go! I now have a tube-powered “vintage” FRFR setup to amplify software amp simulations!

It sounds and feels great, and there is plenty of power available to play with a band, for both guitar and bass! My only concern is the noise of the tube power amp when playing at low volume, so I’ll probably try later the same cab with a fanless solid-state power amp (class D).

Anyway, the cab with the full range speakers is just great, the solution has been validated: yes, you can upgrade your guitar cabs to full range easily!

…I think I’ll work on a 4×12” version soon!