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AUDIO FORUMS >> D.I.Y. >> Forte' model 3, Nelson Pass design
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Message started by 4krow on 12/19/17 at 02:22:22

Title: Forte' model 3, Nelson Pass design
Post by 4krow on 12/19/17 at 02:22:22

Started rebuilding an old Forte' Model 3 amp a few days ago. Since replacing the power capacitors with much larger ones, a bunch of stuff got moved around inside the amp. Also, the amp chassis had to be made wider. You guessed it, more work than I wanted to do. I ended up making brass extenders to set the heat sinks out about 1/2" . Of course, there is a lot more to do here, but this is where it stands at this time.

Title: Re: Forte' model 3, Nelson Pass design
Post by 4krow on 12/19/17 at 02:24:14

There is some alignment of the brass extenders to be done, and then making rear brass extenders to cover the gap. Then the faceplate will be dealt with.

Title: Re: Forte' model 3, Nelson Pass design
Post by 4krow on 03/16/19 at 06:05:07

Man, has it been so long? Well, here is an update on the project. I accidentally bumped into an amp designer that lives near me. He used to work for Sudgeon in Europe. I looked at their amps, and yah, classy stuff. Well, this started last December, and the parts were ordered. It will be a complete rebuild of both channels. John, the guy that I am involved with had a family emergency in Australia, and hasn't yet returned. In the meantime, I am building a smaller version of the amp design that he will be using here just to hear how it sounds. More later on that, since I am waiting on the power transformer to arrive. Just a few more days guys, just a few more days.

Title: Re: Forte' model 3, Nelson Pass design
Post by 4krow on 03/22/20 at 06:33:22

Hard to believe, but I just got this amp back on Friday!!! There are good reasons for it, so I won't even go into it. I will say this>>> if we had any idea how crazy the amp project would be along with life issues thrown in, it wouldn't have happened.
John Dee, the engineer who very graciously helped for most of the project, was able to clear hurdles that would have made me shoot the damned thing. If I am a patient man, I can't imagine what that makes him.
So, here we go. In the beginning, I replaced the power capacitors with new caps due to age. The only ones that I found were almost twice the capacity and only fit with chassis modifications that you see here. Once the amp was in Johns hands, we discussed what kind of expectations that I had. I told him that a class bias would be my preference. In the end every transistor was taken out because of faulty transistors all over the . Yes, thank me for that. John decreased the number of output transistors from I think 10 per channel to just 3? Dam, I should have paid more attention. He added faster/larger caps on the board to increase rise time I suspect. just about all of the parts were replaced or upgraded. His work is better than mine, so I am glad for that. Power caps were bypassed with film caps, as all other electrolytic looked to be bypassed as well. There was So much more that was done, so basically this is a new amp. It should be noted however that the original design was made so that the power supply could easily be changed by moving a few power leads in order for the original amp to run in class A at 50 watts. John asked what class A wattage would be in the ballpark for my speakers, and i stated that 20-30 watts would be a great start. The amp can be biased up to about 50 watts, but I want to try this level first.
it should also be said that I am using this amp with the DNA2 speakers that I recently made. This by a good margin the best SS design that I have used with these speakers. Since the damping factor is at 600, the bass is tight just the way I like. I do not know the rise time of this amp, but it works with the se Mark Audio drivers that I am using so well! This is one the few SS designs that gets the harmonics so much better than what I have heard from other SS designs. That means a bunch to me. Unfortunately, I cannot comment on the high frequency response of this amp, since, even though I still have fair hearing, the high frequencies are not what they used to be, period. I boost the treble by 3 db and that gives me the impression that this all sounds right. In the end I haven't heard a system this good in a very long time. Not since I sold Rachel, and was using the ZOB speakers.

Title: Re: Forte' model 3, Nelson Pass design
Post by 4krow on 03/24/20 at 04:26:17

This will close the subject of the remodeled Forte' 3. I have had only a few days with this amp speaker combination, but can say that I don't want to change a thing, um ok, I will be moving my speakers out from the wall a bit because bass is slightly more than I am used to. On the other end, I would give anything to go back 20 years and hear the treble that is actually there. I realize that I am missing more than I would like, and yes, I can increase the level of treble by about 3db and that does help. Just a fact of life. What impresses me is the control over the power region that this combination puts out. There is a fine line between this control and just making something too rich. Recordings are making more of a difference than they did before, and as many Decware owners know, this can be a matter of getting into research of finding the right recording or remix to suite your taste. It is good to take a breath and really enjoy piano, female solo, and some well recorded rock music. When it's right you can breath and just let the music be. Without the help of the DNA2 cabinets and the Mark Audio driver this would not be happening. BTW, it is important to note that the DNA2 cabinets are even completed yet! I still have the final layer of ply, and some trimming to do. The weather has finally cleared, and I must remove the cabinets back to the shop. ugh!