I have 2 Forte 4a's, both have the "Soderbug" modifications which is said to turn the already good Forte 4a into a "giant killer."

I have compared these amps in my system to many excellent solid-state amps and many tubed designs as well. The Forte 4a (Soderburg mods) sounded noticeably better than anything else I've heard driving my Quad ESL-57's, the midrange panels of my tri-amped Magnepan MG 3.6's, or the Red Rose Music 'Classic' speakers I own. In particular the modded 4a has the most 'liquid' midrange of any solid state amp I've ever heard, easily on par with a good EL-34 design; bass is extended, taut, and tuneful; the treble range is smoother and more glare- and grain-free than any other solid state amp I've ever heard, while being as detailed as any.

The IGBT output devices used in the Forte 4a are just about bulletproof- I've only ever heard of one 4a where the output devices failed. However, it is true that these IGBT's are no longer manufactured. Nonetheless, I understand that Jim Soderburg at Vintage Amp Repair has a large stock on hand in case anyone needs their Forte amp repaired. ( http://www.vintageamprepair.net/ )

I paid $800 and $700 for my two Soderburg-modded Forte 4a's, a fantastic bargain.

Power is 50 watts / channel at 8 ohms, and 100 w/ch at 4 ohms, the amp operates in Class A. It does get quite warm, but I would say that it does not actually become hot to the touch.

Reading the previous view is a reminder that one has to be selective about the information they read on the internet.

First, IGBT transistors ARE and have been currently available, one merely has to know where to obtain them. In this case Jon Soderberg, of Vintage Amp Threshold and Forte amp restoration is the go to technician for anything Threshold or Forte. He's had IGBT's in stock and should any Forte product require servicing or if you'd prefer a product upgrade. Additionally, it's common knowledge that the failure rate for IGBT's is very minimal if ever.

Having gotten that bit of misinformation out of the way...In these brands alone I've owned the following amplifiers:

Threshold T200
Threshold T100
Coda 11.5
Coda 10.5
Pass Aleph 3
Pass Aleph 5
Pass Aleph O's
Pass Aleph 2's

Each of these share a similar lineage, aside from being produced in the region of Sacramento, CA.

A recent acquisition of the Forte Model 4a by comparison to the above as follows:

The 4a has twice the drive, energy, dynamics as either the Pass Aleph 5 or 3. Sonically it bests the Aleph 2's, which as you may know sold for close to $6k new.

The Model 4a has all the drive of the T100, the sonic elegance and delivery of the T200, without the cosmetics. They do get warm, but not hot. Ventilation of ANY Class A amplifier is a given.

The 4a bests the Coda 10.5 in both sonics and power, and sonic equivalent of the 11.5.

This is simply one GEM of an amplifier, aka a SLEEPER of a find in the 2010 marketplace. Frankly, the term biggest bang for buck does it no justice. It's in a league of its own.


This 'lil gem of a vintage amp produces 100 watts true Class A @ 4 ohms. Currently it's driving electrostats, providing all the current and dynamics necessary, and comparable performance of an amplifier many times its power rating and price.

For anyone to suggest that this amplifier doesn't compete with todays offerings is beyond me, for that's entirely NOT been my experience, and quite the contrary. The Forte Model 4a, should you be fortunate enough to locate one, is a GIANT KILLER of an amp, especially so against over priced faceplate and chassis designs of today. At least that's been my experience, which goes back approaching some 20 years of die hard amplification both SS and Tube.

If you see one for sale, you better grab it, for below the $1k price they can be found they're a steal. And their performance could not be duplicated on average of today's offerings for less than $2500.

The Forte Model 4a is far and away the absolute best by in SS amplification.
That's my story and I'm sticking to it.

system:
BAT VK50SE pre
Forte Model 4a
Marantz TT51 turntable
Benz Ebony MC cartridge
Sony SCD1 redbood SACD player
Martin Logan CLS iiz loudspeakers
JPS Labs speaker and interconnect cables

Just a word of Caution:
Although this amplifier sounded good in its day, it DOES NOT compete well with todays offerings. It uses 200W at idle and requires lots of space to avoid overheating.

Furthermore, it uses IGBT transistors which were NOT designed for audio are no longer available!

Mine blew up and I couldn't get replacements. I sold it for a fraction of what I paid.

See Nelson Pass's comments in the following forum:

http://www.diyaudio.com/forums/showthread.php?postid=1153171#post1153171

Otherwise, when the work they sound pretty nice.

beauty,design,clean sound, high current, class A, just a jewel......

for the money ?- non what so ever !

It's a great hounor to be the first to review this wonderful amp.
i bought this amp 6 months ago on ebay, mint condition and i have listen to it as my amp , repalcing my old luxman m4000, a beauty in it's right.
let me start by saying this : this amp , 50 watts per channel in class a operation, is by far the best power unit you can buy for under $1000.
it has the cleanest most vivd sound i have ever heard for it's size and i am in deep the audio game for the last 20 years.
this baby, is so simple in design that it makes you wonder how the hell it can drive picks of up to 50 amperes !
my speakers, proac 125 are jumping from joy as this little power house drives them to places they never thought possible......
i use a "strange" set for an audiophile :
speakers- proac 125,preamp-meridian 561, cd/dvd- meridian 586 and dual bi-wired jps cables.
if you listen to jazz/classical music, this is the amp for you, regardless of price !

one last thing- this baby gets hot, i mean really hot, give it all the space in the world and it will fly........

50watts per cahnnel into 8 ohms
100watts per cahnnel into 4 ohms

Similar Products Used:

to years of hearing all that's out there....for luxman to mark levinson.