Difference between Forte 4 and 4A amp ?

I had a model 4 and it was my first step into the high end world. I didnt even know it was made by Threshhold and I have no idea of the difference between models. I can tell you that its a pretty sweet amp and regardless of the difference between models you will be very pleased with it.

I owned a Model 4a - both face plate and back sticker were marked "4a".

I am not sure if this is correct, but I believe that it is close to correct. Forte originally offered a model 1A and a model three amplifier. The model 1A was a fifty watt per channel class A amplifier and the model 3 was a 150 watt per channel class AB amplifier.

Threshold and Forte began using IGBT, insulated gate biploar transistors, and the model 4, as well as the model 6 if I am not mistaken, were born. The Model 4 being the 50 watt per channel class A amplifier and the Model 6 being the 150 watt class AB amplifier. I am familiar because I owned a Forte Model 4 amplifier sometime around 1993.

I am not sure if there is a difference between the Model 4 and 4A. I believe that one model was preceded by the other and that one model, the latter model, offered balanced and rca inputs and the other model offered rca inputs only. I could very well be wrong. I know that the amplifier changed very little, if any, after its initial product run.

What I remember most is that the Forte Model 4 drove a pair of Celestion SL600's in a wonderful way. It was a great amplifier, a little dark and a pleasure to listen to.

Enjoy,
Drew

I've owned at LEAST a dozen of these amps. I cycle them thru my system and sell'em to friends. A truly great little amp with the ability to drive low/complex impedance loads. You should hear a pair of them driving my electronicly bi-amped Apogee Stages & Duetta Signatures.

Anyway, the basic difference, besides minor face plate cosmetic differences, is that the 4a has a set of balanced inputs while the 4 does not. Pretty much end of story. There were some minor parts differences as the production line aged but I've found little if any sonic differences even between samples with large gaps in the serial numbers.

There is one tweak I can recommend though and that is to get the 4a and bypass the input selector switch & balanced inputs. Run it with just the single ended inputs. I have noticed a slightly more open sound (even over the 4) running it this way. The tweak is easy & reversible.

In general, avoid the balanced inputs as they have an input impedance that is just south of 1K ohm, which is a very difficult load for most pre-amps (certainly tubed ones).

Voltage gain is 26 DB and they actually work quite well into an Adcom Ace 515 line conditioner, most other conditioning flattens the amp dynamically (and this amp DOES boogie). A Wire World Aurora power cord is a nice upgrade as well.

Good Luck, you have a fine amp!!

Drew & 1953 both offered a good bit of info on these amps. As mentioned, the main differences between the 4 & 4A was that the 4A had balanced inputs. Personally, i consider the Forte' amps some of the best buys in audio. The fact that most of them sell so cheaply has made me both quite happy and quite perplexed. Like 1953, i have had quite a few Forte's. The fact that he's running these "budget" amps with speakers the calibre of Apogee's should tell you something. The fact that the Apogee's are VERY tough loads should also tell you something about the "intestinal fortitude" of the "little" 4's / 4A's also.

I've had everything from the 1A to the 3 to the 4A and the 6 and 6A. All of them sound very sweet, airy, etc... Some moreso than others but none of those that i've owned would disappoint. I'd assume that the others sound very similar. Hearing one of these "budget" or "baby" versions of the more costly Threshold amps can really open your eyes and ears as to how good SS can sound for reasonable money. Don't expect massive bottom end "slam" out of these amps though. They are not a Krell or Perreaux. The common word used for these amps, and you'll notice it in almost every description of them that you read, is "sweet". As such, "sweet" and "brute" rarely go hand in hand.

Power ratings have varied somewhat depending on what you are using as a reference. Even the factory was "confused" in some of their own literature. Out of all of the Forte' amps ( 1, 1A, 3, 4, 4A, 5, 55, 6, 6A, 7 ), the 4 / 4A is the one that offered the most consistent ratings. Everything that i have seen about these ALWAYS states 50 wpc @ 8 / 100 wpc @ 4. I would call this an extremely conservative rating as this amp can drive just about anything you throw at it (within reason). Keep in mind that i am typically a "more is better" kinda guy when it comes to wattage, so long as the "quality" of wattage does not suffer along the way. One reviewer stated that the Forte' 4 series played louder than ANY 50 wpc amp had the right to.

I hope you enjoy your purchase. So long as you're not expecting to play hip-hop at lease breaking levels, i think you'll find it to be one of the "best buys" that you'll make in your audio career. Sean
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