Difference between Forte 4 and 4A amp ?

Does any one out there know the difference between the Forte (Threshold) 4 and 4A amps ? Also, does the face plate displays the 4A model ? I just bought the Forte and the owner told me that it is a 4A model. However, the face plate and the back says it is a model 4. I am not sure what I got. Appreciate any help on this. Regards.
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.

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
I have owned a forte 1a since 1991 and it sounds great for the money.. I would love to get a 100+ watt Threshold but wonder how much different or better it would sound for the thousands $ more.. I am not familier with the model 4 or 4a but would stay away from the 3. Only other amp I would consider for the price range is an Eagle.
Yes 4 is 'just RCA' and Forte' 4a has both RCA inputs and balanced inputs, and switches to go between also on the back. I agree about removing the balanced inputs and switchs on the 4a. (I've had a Forte' 4a since new and really like it. It runs hot and uses a lot of power idling, and sounds best if left on at least 8 hours. (the amp adds $10 a month to my electric bill when I leave it on all the time)
Xiekitchen, out of curiosity, what don't you like about the 3 or feel that it should be avoided ? You can lay it on the line with me... : )

As to Elizabeth's comments, all of the Forte' amps run hot and sound best after being left on all the time. I find this true of most amps that run Class A or rich Class A/B. You can't stuff these into enclosed racks since the heatsinks are on the sides and they do run so warm. Sean
All this glowing talk of the Forte amps leaves me a little perplexed as I purchased a Model 6 new in 11/91, replacing a Heath amp, and although it was better than the Heath, I struggled through the 90's with a system I didn't like. I was using a Forte Model 2 preamp and I used several different speakers trying to be pleased with my system (Mirage M3's, Linn Keildh's, Linn AV5140's). In 8/97 I replaced the Forte 6 with a Meridian 557 and found a huge improvement and was much happier with my system and felt I wasted a lot of years, and money, sticking with the Forte.
Brian :

I've had a couple of Forte 6's as well and can understand your experience. I found both of them pleasant but a bit bland and uninvolving compared to the 4. The 4 was considerably more open & punchy. They look identical except that the 4 ran MUCH warmer being more deeply class A biased. This correlates well my general experience of class A versus class A/B operated SS amps. Those deeply biased into class A just seem more involving and open, especially at lower listening levels.
My 3's, 4's and 6's all ran at about the same temp give or take. The 4's should have been "warmer" in theory. All of these amps idle at about 115* - 120* or so and climb slightly from there when "gettin' it". Maybe my bias is up a bit on the "A/B" models. Should probably check into that.

The 3's actually sound slightly sweeter and airier ( but a little leaner ) to me than the 4's. Then again, my 3's were modified by Jon Soderberg of Vintage Amp. The 6's retain most of the sonics of the 4's but offer greater headroom and "oomph" in my opinion. Since most of my speakers are both low impedance and low efficiency, the bigger amps are a little more suitable to my situation. The 4's are QUITE beefy for "50 watters" though.

I ended up selling the 4's and kept a pair of 3's and a pair of 6's for use in a pretty big system that i'm working on. All four of these amps will be getting "tweaked" even more too far down the road.

My 1A actually ran noticeably cooler than all of these amps. That is, even though it was supposed to be "Class A" like the 4's. While it was noticeably lean sounding ( moreso than the 3's ), it also lacked the air and "sweetness" that i hear in the other Forte' amps. That is not to say that it is a bad amp, only that it was not what "I" was looking for. Who knows, maybe that one was slightly out of whack in terms of bias, caps partially drying up, etc.... Either way, the guy that got it absolutely loves it. His speakers were somewhat warm and he lives in an apartment, so he did not need a lot of "oomph" and the lean sonics complimented the rest of the system. A match made in heaven as far as he's concerned.

As to Brian's amp, it might have simply been a "lemon" or didn't blend well with the rest of his gear and various cabling. You would think that a pre / power amp combo from the same company would blend well together, but not necessarily so. Like anything else, it is all about system synergy and personal preference. That is why so many of us stress "in-home auditions". What floats your boat with your other gear might not float mine and vice-versa. Glad that he did find something that was to his liking though.

I've used one of my Forte's as a "loaner" on several occassions. Everyone that has used it has commented on how "sweet" it sounded. This with SS, or tube pre's including one guy running a passive. Somehow, everyone keeps using the same description ("very sweet sounding") of these amps without any coaxing or previous knowledge of them. The fact that they picked that single phrase, out of all of the audiophile terminology to choose from, tells me that there must be something to it.

As a point of interest, one of the 6's that i picked up had been previously repaired. The owner was not aware of this when he bought it. As such, he was not that thrilled with the amp, etc... and sold it to me. Once i got it home, I found the repair work and inspected the rest of the amp. The labor was done pretty poorly and using substandard parts. The amp ran much better once it was straightened out.

As mentioned, these amps sound MUCH better in terms of air, detail, spaciousness, etc.. after they've been on for hours and hours. If someone is turning these off and on as needed, they will never hear what they are fully capable of. I leave them on ALL the time for best results. Turning them off for an extended period of time "flattens" them out quite noticeably in my opinion. 24 - 36 hours after turn on, they should be pretty solid. I think that they sound best after about 3 days of continuous power though. All "high bias" amps appear to operate similarly to me. Amps that typically run "cool" or use digital / switching supplies don't seem to benefit from "continual on" nearly as much. Sean
Sean, a couple notes of clarification and a small disclaimer. First the disclaimer, I am not being critcal of what all is being said here, I am just sharing my experiences.

Sean said, "As to Brian's amp, it might have simply been a "lemon" or didn't blend well with the rest of his gear and various cabling. You would think that a pre / power amp combo from the same company would blend well together, but not necessarily so. Like anything else, it is all about system synergy and personal preference."

I don't think it was a lemon for the fact that I had to send it in for repair at one time and I would think they would test it after the repair. As for not blending well with the rest of the system, I used many speakers, as stated, many CD players and two different speaker cable setups. When I installed the Meridian 557, changing nothing else, the system was MUCH better, it had much more low end, which was my biggest complaint for years, and the sound was improved in all areas.

"That is why so many of us stress "in-home auditions".

I did bring this home and try it before purchasing it. I had also brought home other amps before the Forte, this was the first to clearly outperform the amp I was using. Where I went wrong was, even though it outperformed the other, it still lacked the low end I would of liked. I bought it simply because it had more detail.
Your statements are completely valid and thanks for the clarification. I'm sorry if i came across as belittling.

While i would agree that none of the Forte's are "bass masters" and have previously stated so, i don't really consider the 6's to be "anemic" sounding. The 1's and 3's are leaner than the 4's and 6's in my experience. I have previously stated that these amps work best from a few hundred hertz and up. From your clarification, i guess you would probably agree.

My Classe' 70 was FAR leaner / brighter sounding than any of the Forte's that i've owned. As you probably know, Classe' amps are reputed to be "warm and smooth". We tried it in three different systems and had the same results each time. My Father found it so "painful" to listen to that he offered to hold the door for me so that i could take it out to the trash. Maybe that specific one was "funky". Who knows. Obviously components respond differently in various configurations and with different tastes.

As to the factory checking things out, i run into this all the time. Something measures fine but just doesn't perform "right". Kind of like when your car isn't running good yet everything checks out "okay" at the mechanic. So long as things are within spec, they probably won't dive in to find out what is "wrong". To them, there is nothing wrong because it is "up to spec". Tough to deal with sometimes, but part of life. Sean
Thank you everyone for the inputs. I really appreciate it. It looks like I bought a model 4 amp since it does not balanced input. Anyway, I like the sound of this amp very much. The only slight negative is the bottom end. Also, I have been turning it on/off. I usually turn it on for an hour before listening. Based on most of your inputs, it sounds like I should leave it on constantly. I will try that next. Again, thanks. Regards.

Thong, i had to laugh when i initially saw your name ( Sas quach ) tied to this thread. Given my email address ( bigfoot1 ) and my liking of these amps, i found it to be too much of a coincidence.

As to the bottom end of this amp, i don't think that it is bad at all. Then again, that is simply my opinion and worth no more or less than anyone else's. I would leave the amp on and see how that works for you. If it doesn't give you what you want out of it, you might want to investigate into various cabling. Sean
NEWSFLASH: A rehash of old info that pertains to this new thread about old gear : )

I was digging through some audio rags and ran across some information that might explain some of the variances regarding these amps. Moncrieff of IAR stated that the majority of the Nelson Pass designed Threshold amps were quite load sensitive. As such, changing speakers and / or cables could change tonal balance to a very noticeable degree. Depending on the impedance / type of load that the amp was seeing, the tonal balance could swing one way or the other. Since Nelson designed the Forte' amps, i would imagine that much of this syndrome carries over to that product line also.

According to what "J. Peter" had to say, these amps could sound bright and thin if used with speakers that were relatively resistive by nature ( non-reactive ) and / or had a relatively higher average impedance. Going to a speaker that was higher in reactance and / or lower in impedance would tend to bring the amp closer to a flat response or even towards the warm and rolled off side of neutral. I think that THIS explains a LOT of what we might be encountering with these amps.

Since most of my speakers are of lower impedance than average and generate a relatively high amount of reflected EMF due to large motor structures ( making them more reactive than resistive ), one could see how i might hear them as being relatively well balanced & smooth but still lacking in extreme bottom end. Hooking them up to speakers that were nominally 8 ohms or so and resistive might give me similar results to what others have already commented on.

So, in plain English, EVERYBODY is "right" on this one. Given the variables with all of our experiences and selection of speakers / cables / support components, these amps could end up creating quite a varied response from user to user and system to system. This goes to show just how important it is to check a component in YOUR system when striving for the ultimate in "system synergy".

With all of that in mind, it kind of confirms what cables i've found to work well with these amps. For the record, i've always liked Goertz the best with these amps. The fact that they are highly reactive ( capacitive ) by nature and offer a much lower nominal impedance ( about 2-4 ohms ) than most other cables somewhat confirms what Moncrieff stated. Chris VH's 27 pair Teflon CAT5 design actually gave me the most bass foundation, but i found the Goertz to be quite a bit more liquid in the mids with more air and detail up top. Since both of these cables are capacitive and could cause wide bandwidth amps to oscillate, i would recommend the use of Zobel Networks should someone else choose to use either in their system. Other speaker cables that i've tried in this system are Kimber's, XLO, Audioquest, Axon, Monster, YBA Diamond's, etc.. and various home-brew designs. While some sounded notably better than others, the Goertz are still hooked up in this specific system.

Hope this helps and explains some of the variables that we've encountered along the way in this thread. I would be curious as to find out if the other "fans of Forte" are using low impedance / reactive speakers and what type of speaker cables that they are coupled to. Sean
For the record, I stated this above, but in lieu of Sean's comments, here is the speakers I used with the Model 6.

* Mirage M3's
* Linn Keilidh's
* Linn AV5140's

Speaker cables:
* Audio Quest Midnight for lows and Cardas Quadlink 5 for mid/highs.
* Linn K400

If what Sean says is true, I have no reason to doubt, it would cause me to shy away from such a touching product. It sounds by the comments from others, that it can be a nice sounding amp under the right conditions. As with Sas_Quach, I too suffered from very little low end.